'mu_id'|'mu_desc'
1|'Lakes, Rivers, Ocean, etc..'
150|
151|
152|
153|'Including granite, rhyolite porphyry, dacite porphyry, and granodiorite'
154|
155|'Includes leucocratic granite border phase.

See Kiilsgaard and others (2001) for additional information.'
156|'Member 4 (Wolfcampian to Leonardian) of the Grand Prize Formation consists of more than 450 m of thin- to medium-bedded carbonaceous siltstone, sandy to silty micrite, and minor micritic sandstone (fig. 6). Carbonaceous siltstone of member 4 gradationally overlies banded sandstone and siltstone of member 3. Member 4 weathers to a dark-gray regolith and forms slopes in the southern part of the White Cloud Peaks area.'
157|'Member 3 (Wolfcampian to Leonardian) of the Grand Prize Formation consists of 650-1,700 m of fine-grained sandstone and siltstone arranged in rhythmically interbedded couplets 30 cm-3 m thick. The distinctive banded appearance of the member is produced by these couplets of light-gray fine-grained micritic sandstone gradationally overlain by dark-gray carbonaceous siltstone. Interbedded with the couplets is thick-bedded light-brown micritic sandstone and light-gray sandy micritic limestone (fig. 6). Member 3 gradationally overlies member 2. Member 3 has an irregular weathering pattern; the sandier intervals are exposed in bold relief against the more easily weathered finer grained intervals. The member forms distinctly banded light-gray cliffs throughout the White Cloud Peaks area.'
158|'Member 2 (Desmoinesian to Wolfcampian) of the Grand Prize Formation consists of 500-1,100 m of thick-bedded to massive light-brown micritic sandstone and subordinate light-gray sandy micritic limestone and gray carbonaceous siltstone. Member 2 gradationally overlies member I; the contact is placed above the bioclastic limestone of member I. Member 2 forms discontinuous cliffs and ledges in the northern Smoky Mountains and in the White Cloud Peaks.'
160|'The upper member of the Dollarhide Formation (Wolfcampian and Leonardian) is approximately 900 m thick and is composed of thin-bedded to laminated dark-gray carbonaceous siltstone and light-gray silty micritic limestone and minor light-brown micritic sandstone and conglomerate (fig. 6). The upper member gradationally overlies the middle member, and the upper boundary is not recognized due to erosion. The upper member weathers to a dark-gray regolith, is poorly exposed, and forms slopes throughout the Smoky Mountains, which, as a result, contain large areas of sparsely vegetated "black-shale" regolith (Wavra and Hall, 1989) (fig. 1, plate 1).'
161|'The middle member of the Dollarhide Formation (lower Wolfcampian) consists of about 300 m of fine-grained light-brown micritic sandstone and light-gray sandy micritic limestone and subordinate dark-gray to black carbonaceous siltstone and lenticular conglomerate (fig. 6). The middle member forms prominent light-colored cliffs throughout the central and southern Smoky Mountains. North of Deer Creek (plate 1) it is interpreted to grade into thick sandstone beds of the Eagle Creek Member of the Wood River Formation.'
162|'The lower member of the Dollarhide Formation (Desmoinesian to lower Wolfcampian) is at least 800 m thick and consists of rhythmically interbedded dark-gray carbonaceous silty micritic limestone and very fine grained light-gray to light-brown micritic sandstone and subordinate medium- to thick-bedded light-brown micritic sandstone and light- to dark-gray lenticular conglomerate containing mainly intrabasinal clasts of siltstone and bioclastic limestone. Extrabasinal clasts (vitreous quartzite and fine-grained sandstone) are rare. The lower member of the Dollarhide Formation includes at the base a minimum of 175 m of quartzite, phyllite, and calc-silicate hornfels formerly assigned to the "Carrietown sequence." The lower member is exposed in the southern Smoky Mountains, where it forms dark-colored slopes punctuated by thin ridges of resistant micritic sandstone. The base of the lower member either is a fault or is masked by the Idaho batholith, and the upper contact is placed above a mappable dark-gray carbonaceous limestone and below thick light-brown micritic sandstone of the middle member (O''Brien, 1991) (fig. 6).'
163|'The Wilson Creek Member (Wolfcampian to Leonardian) consists of more than 800 m of dark-gray carbonaceous siltstone and sandstone, thin-bedded light-brown graded silty micritic limestone, light-brown silty micritic limestone, light- to dark-gray sandy micritic limestone, and subordinate light-brown medium-bedded micritic sandstone (fig. 6). The member forms slopes and is sparsely exposed east of Bellevue and Hailey, although it is well exposed in alpine ridges of the Boulder Mountains northeast of Ketchum (figs. 1, 9, plate 1). The fine-grained, thin-bedded silty micritic limestone of the Wilson Creek Member weathers to a characteristic reddish-brown regolith. The upper part of the member is dolomitic in part and contains diagenetic chert. The Wilson Creek Member contains a diverse assemblage of bathyal trace fossils that has been interpreted to reflect oxygenation levels controlled by turbidite depositional facies (Burton and Link, 1991). The upper contact of the Wilson Creek Member is eroded below an unconformity with the Eocene Challis Volcanic Group or the present-day topographic surface (fig. 8).'
164|'The Eagle Creek Member of the Wood River Formation (upper Desmoinesian to Wolfcampian) is 880-1,300 m thick and consists of 260 m of light-purple silty micritic limestone overlain by 620-1,140 m of light-brown micritic sandstone, light-gray sandy micritic limestone, and subordinate quartzarenite (fig. 6). The Eagle Creek Member forms the bulk of the outcrop area of the Wood River Formation both east and west of the Wood River. It is best exposed on the high ridges of the Boulder Mountains (fig. 9).

About 250 m of anomalous carbonate-rich facies assigned to the Eagle Creek Member by Batatian (1991) crops out just east of the summit of Kent Peak. The rock is coarse-grained carbonaceous bioclastic limestone and resembles bioclastic beds in the Wilson Creek Member (David Seeland, U.S. Geological Survey, written commun., 1992). The unit yielded conodonts (collection 12, fig. 7) that indicate a Late Pennsylvanian to Early Permian age and macrofossils, including Chaetetes sp., that indicate a (Middle Pennsylvanian) Desmoinesian age (D.E. Fortsch, Idaho State University, oral commun., 1991). If the Desmoinesian age is correct, the beds may be the carbonaceous equivalent of limestone in the upper part of the Hailey Member. The facies resembles bioclastic parts of the Bloom Member of the Snaky Canyon Formation (Chesterian to Missourian) exposed 55 km to the east across several thrust faults in the Lost River Range (Skipp, Kuntz, and Morgan, 1979) (fig. 7).'
165|'The basal Hailey Member of the Wood River Formation, as defined by Mahoney and others (1991), consists of the Hailey Conglomerate Member and the bioclastic limestone of unit 2 of the Wood River Formation, as described by Hall and others (1974). Unit 2 is vertically and laterally gradational with the conglomerate (Burton, 1988; Mahoney and others, 1991). The Eagle Creek Member consists of units 3 through 6 of Hall and others (1974), and the Wilson Creek Member consists of units 7 and 8 of Hall and others (1974, 1978).

The Hailey Member is 0-200 m thick and consists of 0-180 m of light-brown to light-gray conglomerate gradationally overlain by 15-30 m of bluish-gray bioclastic limestone (fig. 6). The member is primarily exposed east of the Wood River in the Pioneer and Boulder Mountains, although it is exposed in a few areas west of the Wood River near Hailey (plate I). To the east, near Fish Creek Reservoir in the Idaho Falls lx2 quadrangle, the Hailey Member contains 180 m of calcareous sandstone and dispersed chert-pebble conglomerate and bioclastic beds (Link and others, 1988). The Hailey Member may have been deposited on an irregular topographic surface and is locally depositionally absent (Winsor, 1981).

The basal contact of the Hailey Member is a locally sheared unconformity with the underlying Devonian Milligen Formation (Burton, 1988; Burton and others, 1989; Ratchford, 1989. in press; Mahoney and others, 1991; Burton and Link. this volume). In many areas interstratal slip along the unconformity has produced a shear zone in which the Hailey Member is present as kilometer-scale boudins, or is attenuated. particularly in fold limbs, or is thickened in fold hinges. Silver-lead-zinc vein deposits are present locally along this sheared unconformity (Burton and Link, this volume). The upper contact of the Hailey Member is placed at the first appearance of the distinctive light-purple silty micrite of the Eagle Creek Member (table 2, fig. 6). The age of the Hailey Member is Desmoinesian, based on the biostratigraphy of coral. fusulinid, and phylloid green algae occurrences (Bostwick, 1955; Hall and others, 1974) (fig. 9).'
166|'Includes rocks west of the Pioneer thrust fault.

The Copper Basin Formation contains graded beds of cobble and pebble conglomerate, as well as sand- and silt-size siliciclastic turbidite and argillite. Clasts in conglomerate include dark-colored chert and argillite similar to rocks of the Devonian Milligen Formation, as well as a large proportion of light-colored quartzite clasts of uncertain provenance.'
167|'Includes the Scorpion Mountain Formation of Paull and others (1972) and rocks equivalent to the Green Lake Limestone Member.

An upper unit (unit Mcu) of pebble and cobble conglomerate, sandstone, and argillite (more than 1,150 m thick) is mapped on plate I. This upper unit includes the Scorpion Mountain Formation of Paull and Gruber (1977), the lower part of the Muldoon Canyon Formation of Paull and Gruber (1977), and the beds mapped as Green Lake Limestone Member of Copper Basin Formation north of Dry Canyon along the East Fork of the Big Lost River by Dover (1981).'
168|'Includes the Little Copper Member and Drummond Mine Limestone Member of Paull and others (1972) and Dover (1981).

The lower part of the Copper Basin Formation is of Early Mississippian age (Kinderhookian and Osagean) and is at least 3,000 m thick....the formation consists of a lower interval (unit Me!) that contains a basal of dark-gray argillite, siltite, and granule conglomerate turbidite (the Little Copper Member, from 0 to more than 660 m thick) overlain by a discontinuous, but generally eastward thickening wedge of fine-grained mixed carbonate-siliciclastic turbidite (Drummond Mine Limestone Member, 0-910 m thick).'
169|'The Lower to Upper Devonian Milligen Formation is the host for rich silver-lead-zinc ores in the historically productive Minnie Moore and Triumph mineralized areas near Hailey and Bellevue (fig. I). The Milligen Formation was named by Umpleby and others (1930) for carbonaceous and argillaceous rocks originally included in the lower part of the Wood River Formation by Lindgren (1900). As described by Sandberg and others (1975), Dover (1981), and Turner and Otto (1988, this volume), the Devonian Milligen Formation contains more than 1,200 m of unfossiliferous, fine-grained, locally carbonaceous strata that are poorly exposed on sagebrush- and grass-covered slopes in the Boulder and Pioneer Mountains east of the Wood River. The base of the Milligen Formation has not been observed in detailed mapping of the Triumph mine area or on the western side of the Boulder Mountains (Dover, 1983; Turner and Otto, this volume). The upper contact varies along strike and is locally an unconformity below the Middle Pennsylvanian Hailey Member of the Wood River Formation, a possibly conformable contact with strata mapped as Mississippian Copper Basin Formation, or a fault against Pennsylvanian and Permian strata of the Sun Valley Group.

A stratigraphic division of the Milligen Formation in the area near the Triumph mine (Turner and Otto, 1988, this volume) (fig. 3) includes, as informal members, (1) a lower argillite member (130+ m thick), which locally contains diamictite or is chert- or sandstone-rich, (2) the limestone member of Lucky Coin (50-250 m thick), which contains limestone turbidite, black argillite, and diamictite, (3) the quartzite member of Cait (lenses of variable thickness, usually less than 10m), which contains carbonaceous coarse grained sandstone, diamictite, and black argillite, (4) the argillite member of Triumph (0-150 m thick), which contains black argillite, locally cherty, and interbedded sandstone, and (5) the sandstone member of Independence (150+ m thick), which contains interbedded sandstone and limestone turbidite. Diamictite in the lower argillite member, coarse-grained sandstone in the quartzite of Cait, and calciclastic turbidite of the limestone of Lucky Coin represent distinctive markers that allow correlation of the Milligen Formation across structurally complex areas.'
170|'Includes the Trail Creek and Phi Kappa Formations and unnamed rocks'
171|'Carey Dolomite, Jefferson Formation, Picabo Formation in the Dry Canyon inlier; Hanson Creek Formation, unnamed Middle Silurian limestone unit, Roberts Mountain Formation, and unnamed carbonate, conglomerate, and breccia units of Devonian age in the Wildhorse Canyon inlier.'
173|'Exposed only below the Pioneer thrust fault and Wildhorse detachment fault in the core of the Pioneer Mountains'
174|'Calc-silicate, gneissose quartzite, pelitic schist, and marble'
175|'Layered quartzofeldspathic, quartzitic, and mafic gneiss, as well as calc-silicate marble'
300|'Bridger Range area:  Alluvium, colluvium, talus, landslide deposits, rock glaciers, and glacial and glaciofluvial deposits.  Only selected major areas, generally exposed for at least 1 mi in a single direction, are shown.

Crazy Mountains area:  Alluvium, talus, rock glaciers, and glacial deposits.  Only selected major areas, generally exposed for at least 1 mi in a single direction, are shown.'
301|'Sandy and conglomeratic tuffaceous siltstone with interbedded volcanic ash, freshwater gastropod limestone, and fossiliferous lenses of conglomerate and gravel.  Coarse fractions mostly derived from Proterozoic Belt Supergroup and Paleozoic limestone.  Shown only in extreme northeast corner of Bridger Range.  Exposures more than 100 ft thick; actual thickness not measured (McGrew, 1977).'
302|'Bridger Range area:  Dacite, diorite, diabase, and basalt dikes and sills.  Diorite dike in northern part of Bridger Range is olive-gray, coarsely crystalline, pyroxene phenocrysts (Skipp and Peterson, 1965); composite dike in southern part of range may be similar in composition (McMannis, 1955).  Sills differentiated into upper syenite layer and lower layer of biotite-augite diorite.  Thickness 80-200 ft (McMannis, 1955).

Crazy Mountains area:  Diorite, diabase, and fine-grained rocks ranging from basalt to rhyolite; includes dikes and sills.  Commonly porphyritic; phenocryst composition ranges from 5 to 50 percent.  Transitional between alkaline and calc-alkaline compositions.  Probably genetically related to quartz monzodiorite phase of Big Timber stock (Tqm) (du Bray and others, 1993).  Probably includes alkalic bodies (Ta) on west flank of Crazy Mountains and north of Shields River.'
303|'Bridger Range area:  Cliff-forming, massive, nonmarine conglomerate, sandstone, and siltstone; conglomerate clasts derived from pre-Cretaceous rocks.  Contains fossil spores, plants, wood, freshwater mollusks, and vertebrates.  About 6,600 ft thick (Roberts, 1964b, c; 1972).

Crazy Mountains area:  Siltstone, mudstone, sandstone, and pebble conglomerate.  Unit is mainly hornfels in a several-mile-wide aureole of contact metamorphism adjacent to Big Timber stock (du Bray and others, 1993).  Near Livingston, 6,615 ft thick (Roberts, 1972).'
304|'Bridger Range area:  In descending order, includes Hoppers, Billman Creek, and Sedan Formations.  Sedan Formation correlates with Miner Creek and Cokedale Formations, which are exposed in southernmost part of Bridger Range and in a narrow band extending to the east past Cokeville and Livingston (Skipp and McGrew, 1977).  Livingston Group is volcaniclastic conglomerate, sandstone, and mudstone; and volcanic flows, sills, tuff, and breccia (Roberts, 1972).  Hoppers Formation is purple-gray to gray-green, epiclastic volcanic sandstone, siltstone, mudstone, and conglomerate; 2,400 ft thick (Skipp, 1977).  Billman Creek Formation is grayish-red, grayish-green, and gray volcanic mudstone and siltstone interbedded with minor volcanic sandstone, conglomerate, and vitric tuff.  Includes freshwater gastropods and dinosaur bones (Skipp, 1977); 2,500 - 3,000 ft thick (Roberts, 1972; Skipp, 1977).  Sedan Formation is primarily greenish-gray, epiclastic volcanic sandstone, mudstone, and conglomerate interbedded with mudflow conglomerate, welded tuff, devitrified silicified vitric tuff, bentonite, and lignitic coal (Skipp and McGrew, 1977).  Freshwater mollusks, wood, and dinosaur bones present in upper part of Sedan Formation.  Lower part contains ironstone nodules, magnetite-rich beds, volcanic granule-and-pebble conglomerate, and carbonaceous plant material.  Lignite coal locally present at base.  Sedan Formation about 3,000-4,500 ft (Skipp and McGrew, 1977).

Crazy Mountains area:  Volcaniclastic conglomerate, sandstone, and mudstone; tuff and volcanic breccia.  Contains flows and sills (Roberts, 1972).  Thickness 6,455 ft (Roberts, 1972).'
305|'Upper part is gray, thin- to thick-bedded, very fine grained to conglomeratic, largely calcareous, cross-bedded sandstone; calcareous concretions and intercalated coal and shale.  Lower part is massive, indurated, ledge-forming, cross-bedded sandstone and greenish-gray and grayish-orange volcanic sandstone and conglomerate; intercalated coal, siltstone, and shale.  Thickness 150-300 ft (Roberts, 1964a; Skipp, 1977; Skipp and Hepp, 1968; Skipp and Peterson, 1965).'
306|'In descending order, includes Telegraph Creek Formation, Cody Shale, and Frontier Formation.  Telegraph Creek Formation is predominantly gray, biotitic, silty shale that contains thin interbeds of fine-grained sandstone, limestone, and altered crystal vitric tuff.  Upper part contains large calcareous cannonball concretions; lower part contains pelecypods and ammonites.  About 285-400 ft thick (Roberts, 1964a; Skipp, 1977; Skipp and Hepp, 1968; Skipp and Peterson, 1965).  Cody Shale is dark-gray shale and mudstone that contain thin interbeds of gray-green, glauconitic, calcareous to argillaceous, cross-laminated and rippled, fossiliferous (ammonites) sandstone and siltstone; ironstone nodules and cone-in-cone structures occur locally.  About 600-1,100 ft thick (McGrew, 1977; Skipp, 1977; Skipp and Hepp, 1968; Skipp and Peterson, 1965).  Frontier Formation is mostly gray, green, or brown, thin- to medium-bedded, fine- to coarse-grained, calcareous to argillaceous, locally cross-laminated, ridge-forming sandstone; light-gray quartz, feldspar, and rock fragments contrast with dark-gray chert grains and give the sandstone a characteristic "salt-and-pepper" appearance.  Contains interbeds of mudstone, siltstone, shale, quartzite, chert-pebble conglomerate, siliceous limestone, and fossil oyster banks; mudstone and siltstone intervals form valleys.  About 500-700 ft thick (McGrew, 1977; Skipp, 1977; Skipp and Peterson, 1965).'
307|'In descending order, includes Mowry Shale (Upper Cretaceous) and Thermopolis Shale and Kootenai Formation (Lower Cretaceous).  Mowry and Thermopolis Shales are dark-gray shaly mudstone and porcellanite interbedded with greenish-gray, medium-grained to very coarse grained, feldspathic, calcareous and argillaceous, thin-bedded sandstone; basal grayish-orange, ledge-forming quartzitic sandstone.  Shales total about 600 ft thick (McGrew, 1977; Roberts, 1964a; Skipp, 1977; Skipp and Hepp, 1968).  Kootenai Formation is red, gray, and purple hematitic mudstone interbedded with yellowish-gray and grayish-purple, quartzose, medium- to coarse-grained sandstone.  Gray, nodular, gastropod-bearing, freshwater limestone common in upper part (about 100 ft below top) and just above basal ledge- and talus-forming, salt-and-pepper sandstone.  Lenses of granule- to pebble-size chert conglomerate in basal sandstone.  About 200-400 ft thick (McGrew, 1977; Skipp, 1977).'
308|'Includes Morrison Formation (Upper Jurassic) and underlying Ellis Group (Upper and Middle Jurassic).  Ellis Group comprises Swift, Rierdon, and Sawtooth Formations; near Livingston the Sawtooths lithic equivalent is the Piper Formation.  Morrison Formation is red, gray, and purple mudstone and hackly shale intercalated with light-gray, yellowish-brown, and yellowish-orange siltstone and sandstone, some conglomeratic; calcareous, quartzose, commonly cross-bedded.  Black shale near top; gray freshwater limestone in beds and nodules; thick red mudstone at base.  About 200-400 ft thick (McGrew, 1977; Roberts, 1964a; Skipp and Hepp, 1968; Skipp and Peterson, 1965).  Ellis Group is light-gray to light-brown, quartzose, calcareous, commonly iron stained sandstone and siltstone, interbedded with gray, fossiliferous, ledge-forming oolitic or sandy limestone and chert-pebble conglomerate.  Basal bed grades from chert breccia or chert-pebble conglomerate on the west to thin gray mudstone to fossiliferous limestone on the east.  Thickness ranges from 2 to 213 ft (McGrew, 1977; Skipp and Hepp, 1968; Skipp and Peterson, 1965).'
309|'In descending order, includes Phosphoria (Permian), Quadrant (Pennsylvanian), and Amsden (Lower Pennsylvanian and Upper Mississippian) Formations.  Phosphoria Formation (McKelvey and others, 1959) (probably better correlated with Shedhorn Sandstone in this area) consists of a thin (no thicknesses given- presumably not more than several feet thick) section of phosphorite, phosphatic mudstone, carbonaceous mudstone, and chert (McKelvey and others, 1959); mapped with Quadrant Formation by Roberts (1964a, 1972).  Quadrant Formation is well-sorted calcareous quartzite to quartzose sandstone; light-gray dolomite in lower part; lower part forms ledges.  Thickness 0 to 150 ft (McGrew, 1977; Roberts, 1964a; Skipp and Hepp, 1968).  Amsden Formation is light-gray, weathering to white, thin- to thick-bedded dolomite.  Interbeds of pale-grayish-orange sandstone and siltstone in upper part.  Massive red sandstone, gray sandstone, siltstone and mudstone, and red claystone interbedded with gray argillaceous limestone in lower part; dolomite-limestone breccia at base.  About 250-600 ft thick (McGrew, 1977; Skipp and Hepp, 1968).'
310|'Includes Mission Canyon Limestone and underlying Lodgepole Limestone.  Mission Canyon Limestone is gray, aphanitic to medium-crystalline, cherty, massive, cliff-forming limestone and dolomite.  Red-siltstone-filled cavernous zones, limestone breccia beds, and gray dolomite locally in upper part.  About 700-1,200 ft thick (McGrew, 1977; Roberts, 1964a; Skipp, 1977; Skipp and Hepp, 1968; Skipp and Peterson, 1965).  Lodgepole Limestone is gray, thin- to medium-bedded, fossiliferous, locally cherty limestone and dolomite; weathers into platy blocks.  Red and yellow silty limestone interbeds; thin dark-gray shale at base.  Forms step-like ledges.  About 500-750 ft thick (McGrew, 1977; Roberts, 1964a; Skipp, 1977; Skipp and Hepp, 1968; Skipp and Peterson, 1965).'
311|'Three Forks Formation is yellow calcareous siltstone, impure gray fossiliferous limestone, and dark-gray and green mudstone and shale.  Thin beds of dolomite in upper part; olive-gray and reddish-brown, calcareous, fossiliferous shale in lower part.  Thickness 150-200 ft (McGrew, 1977; Roberts, 1964a; Skipp and Peterson, 1965).  Underlying Jefferson Formation is brownish- to olive-gray, thick-bedded to massive, sparsely fossiliferous, fetid dolomite and interbedded gray limestone; local stromatolites.  About 400-600 ft thick (McGrew, 1977; Roberts, 1964a; Skipp and Peterson, 1965).'
312|'In descending order, includes Snowy Range Formation (and laterally equivalent Red Lion Formation) and Pilgrim Limestone (Upper Cambrian); and Park Shale, Meagher Limestone, Wolsey Shale, and Flathead Sandstone (Middle Cambrian).  Locally may include Devonian Maywood Formation (McGrew, 1977), a red and yellow calcareous siltstone and gray dolomitic limestone (Skipp and Peterson, 1965).  Snowy Range Formation is mainly limestone and shale distinguished by rounded limestone pebbles in the Grove Creek Limestone Member; underlain by thick red, gray, and green shale, gray limestone, and siltstone-pebble conglomerate of undivided lower members; bed of columnar limestone locally in lower part of formation (Roberts, 1964a; Skipp and Peterson, 1965).  Combined thickness of Maywood and Snowy Range Formations 100-200 ft (Skipp and Peterson, 1965). Pilgrim Limestone is gray, thin-bedded to massive limestone and dolomite; forms cliffs.  Oolites, grayish-orange and yellow mottling, and flat-pebble conglomerates are common.  Interbeds of greenish-gray shale in lower part; glauconitic and fossiliferous at base.  Thickness 350-500 ft (McGrew, 1977; Roberts, 1964a; Skipp and Peterson, 1965).  Park Shale is grayish-green to multicolored clay shale; thin beds of argillaceous limestone, siltstone, and sandstone; sparse fossiliferous limestone and limestone-pebble conglomerate in upper part.  Nonresistant; forms valleys.  Thickness 100-200 ft (McGrew, 1977; Roberts, 1964a; Skipp and Peterson, 1965).  Meagher (pronounced "mar") Limestone is thin- to medium-bedded, mottled grayish-orange and medium-gray, fine-grained limestone and yellowish-gray dolomite; locally oolitic; crumpled bedding.  Thickness 300-600 ft (McGrew, 1977; Roberts, 1964a; Skipp and Peterson, 1965).  Wolsey Shale is olive- to brownish-gray micaceous clay shale; contains gray impure limestone in upper part and fine-grained, thin-bedded, glauconitic sandstone in lower part.  Abundant trace fossils ("worm cast" markings).  Forms valleys.  Thickness 100-500 ft (Roberts, 1964a; Skipp and Peterson, 1965).  Flathead Sandstone is yellowish-gray to reddish-gray, fine- to coarse-grained, thin- to thick-bedded, locally cross-bedded quartzite and quartz sandstone.  Locally conglomeratic in lower part.  Very resistant; forms ridges.  Thickness 0-300 ft (McGrew, 1977; Roberts, 1964a; Skipp and Peterson, 1965).'
313|'Includes the Spokane and underlying LaHood (formerly North Boulder Group) Formations of the Belt Supergroup.  Spokane Formation is light-grayish-green argillite, gray to yellowish-gray quartzite and sandstone, and minor thin-bedded grayish-red limestone; rippled beds are common.  Thickness 2,200-3,200 ft (McGrew, 1977).  LaHood Formation is dark-greenish-gray, medium-grained to very coarse grained to conglomeratic, micaceous, feldspathic sandstone that contains interbedded dark-gray limestone and impure aphanitic laminated calcareous argillite; sandstone forms about 30 percent of sequence and is most common in upper part; limestone, with cone-in-cone structures, and argillite dominate lower part.  More than 2,500 ft thick (Skipp and Peterson, 1965).'
314|'Primarily gneiss.  Includes schist, granite, quartzite, pegmatite, amphibolite, and mafic intrusive rocks (Roberts, 1964a).'
316|'Mafic alkalic rocks (including malignite, nepheline syenite, analcite syenite, and theralite), trachyte porphyry, and related intrusive rocks.  Typically these rocks are sodium rich, silica undersaturated, and strongly alkaline (Harlan, 1986).  No plagioclase feldspar and calcic amphibole (Dudas, 1990).  Includes dikes, sills, laccoliths, and small stocks.'
318|'Quartz monzonite to granodiorite.  Locally contains inclusions of diorite and gabbro (Tdg) along contact.  Forms an irregular-shaped mass at center of Big Timber stock (du Bray and others, 1993).  40Ar/39Ar ages on biotite:  49.230.1 and 49.330.12 Ma (S.S. Harlan, USGS, unpub. data, 1996).'
319|'Granular diorite and gabbro form main part of Big Timber stock.  Locally contains stoped blocks of pyroxene-rich gabbro.  Coarser grained and darker in color than quartz monzodiorite phase (Tqm) (du Bray and others, 1993).  40Ar/39Ar ages on biotite: 49.20.07 and 49.330.11 Ma (S.S. Harlan, USGS, unpub. data, 1996).'
320|'Quartz monzodiorite porphyry, compositionally similar to quartz monzodiorite phase of Big Timber stock (Tqm).  Separated from main body of Big Timber stock by sedimentary rocks of Fort Union Formation (TKf).  At southern end of area of outcrop, unit has a quenched appearance with plagioclase phenocrysts (2- to 5-mm long) in an aphanitic to glassy groundmass (du Bray and others, 1993).'
400|'Sedimentary and volcanic deposits, undivided.'
401|'All Miocene and Pliocene volcanic and sedimentary rocks including rocks of the Magic Mountain eruptive center, the Banbury Basalt and coeval rocks, the Idavada Volcanics, the tuff of Cannonball Mountain, and the Payette Formation.'
402|'Eocene extrusive volcanic rocks, volcaniclastic sedimentary rocks, and smaller hypabyssal bodies of the Challis Volcanic Group.'
403|'Mostly hypabyssal bodies, many of which are too small to show.'
404|'Pink to light-gray granite in the Sawtooth, Trinity, and Soldier batholiths and many smaller plutons.'
405|'Diorite, granodiorite, dacite porphyry, latite, quartz monzonite, and hornblende gabbro in the border areas of major batholiths and many smaller plutons.'
406|'Granite and leucogranite.'
407|'Major phases of the Idaho batholith.'
408|'Potassium-rich granodiorite and quartz diorite, mainly in the southwestern border areas of the Idaho batholith.'
409|'Includes the Eagle Creek and Hailey Members of the Wood River Formation and equivalent parts of the Dollarhide and Grand Prize Formations.'
410|'Includes the Wilson Creek Member of the Wood River Formation and equivalent parts of the Dollarhide and Grand Prize Formations, the Milligen Formation, unnamed Devonian and Silurian rocks, and the Trail Creek and Phi Kappa Formations.'
411|'Mainly carbonate and sandstone turbidite. Includes the McGowan Creek and Copper Basin Formations.'
414|'Includes the White Knob Limestone, the Surrett Canyon, South Creek, Scott Peak, Middle Canyon, and Jefferson Formations, and the Laketown and Fish Haven Dolostones.'
417|
425|'Unconsolidated silt, sand, and gravel along modern-day streams.'
426|'Unconsolidated deposits consisting mainly of slope wash and talus.'
427|'Unconsolidated mantle of alluvium, colluvium, and, near Lake Helena, wind-blown silt.'
428|'Unconsolidated earthflow deposits that contain a mixture of rock materials ranging from silt to boulders in size.'
429|'Glacial till, moraine, glaciofluvial deposits, and minor alluvium and colluvium.'
430|'Unconsolidated deposits of unsorted and unstratified clay, silt, sand, gravel, and boulders; in general lacks morainal form.'
431|'Unconsolidated clay, silt, sand, and gravel deposited from meltwater streams that flowed from glaciers; generally stratified.'
432|'Sand, silt, and clay that is sorted, stratified, and firmly compacted. Present in vicinity of Missouri River.'
433|'Unconsolidated gravel and fan deposits, and conglomerate in northern part of Big Belt Mountains.'
434|'Sandstone, siltstone, claystone, shale, marl, siliceous sinter, and minor poorly sorted conglomerate; locally carbonaceous and tuffaceous; rare coal and limestone. Volcaniclastic components common.'
435|'In southeastern most part of Big Belt Mountains, interbedded siltstone and tuff. Along central and southwestern most flank of Big Belt Mountains, composed of tuffaceous conglomerate and sandstone, subordinate stream-laid siltstone, freshwater limestone, and volcanic ash.'
436|'Sandstone and conglomerate that includes both volcaniclastic and non-volcaniclastic units; and lava flows and flow breccias. Present only in westernmost part of Forest.'
437|'Slim Sam Formation lies at top of sequence and is composed of interbedded volcaniclastic sandstone, tuff, and lapilli tuff; present only in Elkhorn Mountains. Eagle Sandstone consists of ledge-forming chert-rich sandstone; in Elkhorn Mountains locally contains fossil marine placers of magnetite. Telegraph Creek Formation consists of marine mudstone, siltstone, and sandstone.'
438|'In descending order, includes Vaughn (Upper part is dark siliceous sandstone and interbedded siliceous shale and siltstone; light gray porcellanite and lapilli tuff. Middle part is lenticular conglomerate of quartzite and chert clasts in matrix of sandstone. Lower part is sandstone interbedded with shale, bentonitic mudstone, and siltstone; some interbeds of limestone and limestone concretions.), Taft Hill (sandstone and dark shale, mudstone, and siltstone), and Flood Members (sandstone in upper part and dark gray fissile shale and minor interbedded siltstone in lower part).'
439|'Upper part is dark siliceous sandstone and interbedded siliceous shale and siltstone; light gray porcellanite and lapilli tuff. Middle part is lenticular conglomerate of quartzite and chert clasts in matrix of sandstone. Lower part is sandstone interbedded with shale, bentonitic mudstone, and siltstone; some interbeds of limestone and limestone concretions. Present in western part of Forest.'
440|'Taft Hill consists of sandstone and dark shale, mudstone, and siltstone. Flood consists of sandstone in upper part and dark gray fissile shale and minor interbedded siltstone in lower part. Present in western part of Forest.'
441|'In descending order, includes Cody Shale (Upper Cretaceous), Frontier Formation (Upper Cretaceous), Mowry Shale (Upper Cretaceous), and Thermopolis Formation (Lower Cretaceous). Cody consists of dark gray mudstone, and minor interbedded siltstone and sandstone. Frontier consists of light-gray sandstone, siltstone, and lesser interbedded mudstone. Mowry consists of sandstone, siltstone, tuffaceous siltstone, mudstone, and tuffaceous mudstone. Thermopolis consists of dark-gray fissile shale in upper part and rusty-brown quartz-rich sandstone and interbedded siltstone in lower part. Present in Elkhorn Mountains and southern part of Big Belt Mountains.'
442|'In Elkhorn Mountains and southern part of Big Belt Mountains. upper part is light-gray freshwater limestone, medial part is reddish orange mudstone and interbedded siltstone, and lower part is gray chert-rich sandstone and conglomeratic sandstone. In remainder of Forest, uppermost part is interbedded red to green shale, mudstone, siltstone, and light-gray sandstone; light-gray freshwater limestone and dolomite, and minor interbedded shale, siltstone, and sandstone; medial part is reddish orange mudstone, siltstone, shale, and light-gray sandstone; dark-gray shale and interbedded sandstone and siltstone; basal part is light-gray vitreous quartzite.'
443|'Includes the following map units: 
Blackleaf Formation; In descending order, includes Vaughn (Upper part is dark siliceous sandstone and interbedded siliceous shale and siltstone; light gray porcellanite and lapilli tuff. Middle part is lenticular conglomerate of quartzite and chert clasts in matrix of sandstone. Lower part is sandstone interbedded with shale, bentonitic mudstone, and siltstone; some interbeds of limestone and limestone concretions.), Taft Hill (sandstone and dark shale, mudstone, and siltstone), and Flood Members (sandstone in upper part and dark gray fissile shale and minor interbedded siltstone in lower part).

Kootenai Formation; In Elkhorn Mountains and southern part of Big Belt Mountains. upper part is light-gray freshwater limestone, medial part is reddish orange mudstone and interbedded siltstone, and lower part is gray chert-rich sandstone and conglomeratic sandstone. In remainder of Forest, uppermost part in interbedded red to green shale, mudstone, siltstone, and light-gray sandstone; light-gray freshwater limestone and dolomite, and minor interbedded shale, siltstone, and sandstone; medial part is reddish orange mudstone, siltstone, shale, and light-gray sandstone; dark-gray shale and interbedded sandstone and siltstone; basal part is light-gray vitreous quartzite.

Jurassic rocks, undivided (Upper and Middle Jurassic) In descending order, includes Morrison Formation (Upper Jurassic), Swift Formation (Upper and Middle Jurassic), Riordan Formation (Middle Jurassic), and Sawtooth Formation (Middle Jurassic). Morrison consists of gray to reddish purple and orange mudstone, shale, siltstone, and sandstone. Swift consists of gray calcareous sandstone and conglomeratic sandstone, and minor interbeds of siltstone and shale. Riordan consists of gray calcareous shale and siltstone and interbedded limestone. Sawtooth consists of gray calcareous sandstone and siltstone, and lesser amounts of shale and limestone.

Present only in northern part of Big Belt Mountains and directly west of Helena.'
444|'In descending order, includes Morrison Formation (Upper Jurassic), Swift Formation (Upper and Middle Jurassic), Rierdon Formation (Middle Jurassic), and Sawtooth Formation (Middle Jurassic). Morrison consists of gray to reddish purple and orange mudstone, shale, siltstone, and sandstone. Swift consists of gray calcareous sandstone and conglomeratic sandstone, and minor interbeds of siltstone and shale. Rierdon consists of gray calcareous shale and siltstone and interbedded limestone. Sawtooth consists of gray calcareous sandstone and siltstone, and lesser amounts of shale and limestone.'
445|'Includes the following map units, described below: Phosphoria Formation and Quadrant Formation, undivided; Amsden Formation and Big Snowy Group, undivided. Present only in northern part of Big Belt Mountains.

Phosphoria consists of gray phosphorite, phosphatic and calcareous sandstone, siltstone, shale, black phosphatic chert, and limestone.   In Big Belt and Elkhorn Mountains and near Helena, in southern part of Big Belt Mountains, consists of chert, phosphatic sandstone, limestone, and quartzose sandstone; in northern part of Big Belt Mountains, consists of chert and cherty sandstone; in Elkhorn Mountains and near Helena, consists mainly of chert and quartzitic sandstone, but locally contains one to two thin beds of phosphatic rock.

Quadrant consists of light-gray tightly cemented quartz-rich sandstone, locally with interbeds of siltstone and dolomite at base

Amsden consists of reddish orange mudstone, shale, sandstone, and gray limestone and dolomite; present only in Big Belt Mountains and Elkhorn Mountains. 

Big Snowy Group, in descending order, comprised of Heath, Otter, and Kibbey Formations. Heath consists of gray limestone, petroliferous limestone and shale, and calcareous sandstone. Otter consists of varicolored shale, limestone, and siltstone. Kibbey consists of gray shale, siltstone, limestone, and calcareous sandstone. Big Snowy Group present only in Big Belt Mountains.'
446|'Shedhorn consists of gray siliceous sandstone. Phosphoria consists of gray phosphorite, phosphatic and calcareous sandstone, siltstone, shale, black phosphatic chert, and limestone. Park City consists of gray limestone, cherty limestone, calcareous siltstone, and sandstone. Snowcrest Range Group, in descending order, consists of lateral equivalents of Conover Ranch Formation (Lower Pennsylvanian and Upper Mississippian), Lombard Limestone (Upper Mississippian), and Kibbey Sandstone (Upper Mississippian) Conover Ranch and its lateral equivalents consists of reddish brown to reddish purple calcareous shale and siltstone. Lombard consists of gray limestone and dolomite. Kibbey consists of gray to red calcareous shale, siltstone, and sandstone.

In Big Belt and Elkhorn Mountains and near Helena:

Phosphoria: in southern part of Big Belt Mountains, consists of chert, phosphatic sandstone, limestone, and quartzose sandstone; in northern part of Big Belt Mountains, consists of chert and cherty sandstone; in Elkhorn Mountains and near Helena, consists mainly of chert and quartzitic sandstone, but locally contains one to two thin beds of phosphatic rock.

Throughout Forest:

Quadrant consists of light-gray tightly cemented quartz-rich sandstone, locally with interbeds of siltstone and dolomite at base.'
447|'Amsden consists of reddish orange mudstone, shale, sandstone, and gray limestone and dolomite; present only in Big Belt Mountains and Elkhorn Mountains. Tyler Formation consists of pale brown sandstone; present only in Dry Range area, northeast of Big Belt Mountains. Big Snowy Group, in descending order, comprised of Heath, Otter, and Kibbey Formations. Heath consists of gray limestone, petroliferous limestone and shale, and calcareous sandstone. Otter consists of varicolored shale, limestone, and siltstone. Kibbey consists of gray shale, siltstone, limestone, and calcareous sandstone. Big Snowy Group present only in Big Belt Mountains.'
448|'Includes Mission Canyon Formation (Upper and Lower Mississippian) and Lodgepole Formation (Lower Mississippian); and in Choteau quadrangle, Castle Reef Dolomite (Upper and Lower Mississippian) and Allan Mountain Limestone (Lower Mississippian). All units are composed of limestone and (or) dolomite; local chert.'
449|'Includes the following map units. 

Madison Group; Includes Mission Canyon Formation (Upper and Lower Mississippian) and Lodgepole Formation (Lower Mississippian); and in Choteau quadrangle, Castle Reef Dolomite (Upper and Lower Mississippian) and Allan Mountain Limestone (Lower Mississippian). All units are composed of limestone and (or) dolomite; local chert

Three Forks Formation (varicolored shale. siltstone, limestone, and locally minor thin beds of sandstone) and Jefferson Formation (gray to brown dolomite, limestone, limestone breccia, and dark-gray fetid dolomite; minor siltstone and shale), undivided; 

Cambrian formations, undivided. Includes Upper snowy Range Formation (Upper Cambrian), Pilgrim Limestone (Upper Cambrian), Park Shale (Middle Cambrian), Meagher Limestone (Middle Cambrian), Wolsey Shale (middle Cambrian), and Flathead Sandstone (Middle Cambrian). Also includes Maywood Formation (Lower Devonian), described above, in southern part of Big Belt Mountains. Snowy Range consists of limestone and dolomite, including pebble conglomerate, and intervals of micaceous shale and siltstone. Pilgrim consists of yellowish gray to brown limestone and dolomite; green clay shale in lower part. Park consists of green fissile clay shale and minor interbeds of siltstone and limestone; local limestone pebble conglomerate. Meagher consists of light gray limestone and dolomite. Wolsey consists of greenish gray micaceous shale and glauconitic siltstone, and minor limestone and quartzite. Flathead consists of gray to maroon quartz sandstone, locally conglomeratic.

Present only in northern part of Big Belt Mountains.'
450|'Three Forks consists of varicolored shale. siltstone, limestone, and locally minor thin beds of sandstone. Jefferson consists of gray to brown dolomite, limestone, limestone breccia, and dark-gray fetid dolomite; minor siltstone and shale. Maywood consists of reddish and yellowish gray siltstone and interbedded limestone and dolomite; sandstone present locally. Maywood in southern part of Big Belt Mountains is included with Cambrian formations, undivided, below.'
451|'Includes Upper Snowy Range Formation (Upper Cambrian), Pilgrim Limestone (Upper Cambrian), Park Shale (Middle Cambrian), Meagher Limestone (Middle Cambrian), Wolsey Shale (middle Cambrian), and Flathead Sandstone (Middle Cambrian). Also includes Maywood Formation (Lower Devonian), described above, in southern part of Big Belt Mountains. Snowy Range consists of limestone and dolomite, including pebble conglomerate, and intervals of micaceous shale and siltstone. Pilgrim consists of yellowish gray to brown limestone and dolomite; green clay shale in lower part. Park consists of green fissile clay shale and minor interbeds of siltstone and limestone; local limestone pebble conglomerate. Meagher consists of light gray limestone and dolomite. Wolsey consists of greenish gray micaceous shale and glauconitic siltstone, and minor limestone and quartzite. Flathead consists of gray to maroon quartz sandstone, locally conglomeratic. Map unit present only east of 112 longitude.'
452|'Red Lion consists of gray limestone and discontinuous bands of siliceous dolomite, and interbedded gray limestone and varicolored shale. Hasmark consists of gray dolomite and limestone, minor local interbeds of green shale and siltstone. Map unit present only west of 112 longitude.'
453|'Park consists of green fissile clay shale and minor interbeds of siltstone and limestone; local limestone pebble conglomerate. Meagher consists of light gray limestone and dolomite. Wolsey consists of greenish gray micaceous shale and glauconitic siltstone, and minor limestone and quartzite. Flathead consists of gray to maroon quartz sandstone, locally conglomeratic. Map unit present only west of 112 longitude.'
454|'Silver Hill consists of green clay shale, medium-gray limestone, and, in lower part, minor interbedded siltstone, sandstone, and shale. Flathead consists of gray to maroon quartz sandstone, locally conglomeratic. Present only in vicinity of Elliston.'
455|'Varicolored argillite, siltite, and metasandstone that ranges from feldspathic to quartz-rich; locally contains glauconite and chert.'
456|'Pale pink to light brown fine- to coarse-grained feldspathic metasandstone; sparse dark-red argillite and siltite; commonly cross-laminated, local ripples.'
457|'North of St. Marys fault, western part of Forest: Brown, red, and gray-green interbedded feldspathic metasandstone, siltite, and argillite. Thin interbeds of pale-green to light-gray quartzite. Contains ripples, desiccation cracks, raindrop impressions, salt casts, and cross-laminated beds. Formation divided into three members, in descending order:
Yms3-Member 3-Gray siltite, argillite, and quartz-rich metasandstone and feldspar-quartz metasandstone.

Yms2-Member 2-Varicolored quartzite and feldspar-quartz metasandstone.

Yms1-Member 1-Varicolored argillite, siltite, feldspathic metasandstone.'
458|'Gray siltite, argillite, and quartz-rich metasandstone and feldspar-quartz metasandstone.'
459|'Varicolored quartzite and feldspar-quartz metasandstone.'
460|'Varicolored argillite, siltite, feldspathic metasandstone.'
461|'Green, white, and yellowish-gray calcareous and dolomitic argillite and siltite; argillaceous limestone and dolomite, locally stromatolitic; local beds of quartzite that contain rounded quartz grains. Ripples, fluid-escape structures, desiccation cracks, mud-chip rip-up clasts, and cross-lamination common.'
462|'North of St. Marys fault, in western part of Forest: On Hoadley thrust plate, interbedded red-brown siltite, gray-green siltite, and dark-red argillite. Red-purple feldspathic metasandstone at base.

South of St. Marys fault, in western part of forest:

Grayish red quartzite and feldspathic metasandstone, and interbedded zones of siltite and silty argillite. Zones of green beds of siltite, argillite, and fine-grained metasandstone, locally calcareous or dolomitic, distributed unevenly through formation. White to light-gray lenticular quartzite distributed throughout formation.

On Hoadley thrust plate, interbedded red-brown siltite, gray-green siltite, and dark-red argillite. Red-purple feldspathic metasandstone at base.

South of St. Marys fault, in western part of forest:

Grayish red quartzite and feldspathic metasandstone, and interbedded zones of siltite and silty argillite. Zones of green beds of siltite, argillite, and fine-grained metasandstone, locally calcareous or dolomitic, distributed unevenly through formation. White to light-gray lenticular quartzite distributed throughout formation.

On Eldorado thrust plate in Big Belt Mountains:

Interbedded gray-green sandy siltite, dark-green argillite, and in basal part coarse-grained metasandstone. Ripple and rip-up clasts common; local stromatolitic beds.'
463|'Dark-gray dolomitic limestone, calcareous siltite, and argillite, commonly cyclically interbedded; local light-gray fine-grained metasandstone. Stromatolite beds common in upper and lower parts of formation. Common sedimentary structures include ripples, syneresis cracks, scour-and-fill structures, and fluid-escape structures.'
464|'Interlaminated gray-green dolomitic siltite and pale-green argillite. Light-gray fine-grained quartzite beds present in lower part of formation. Sedimentary structures include syneresis cracks, water-expulsion structures, and ripple cross-lamination.'
465|'Interbedded grayish red purple argillite and siltite, and lesser gray-green siltite; middle part, and to lesser extent lower part contains light-gray feldspathic metasandstone. Local dolomitic limestone. Common sedimentary structures include load casts, rip-up clasts, fluid-escape structures, ball-and-pillow structures, syneresis cracks, and ripple cross-lamination.'
466|'Interlaminated gray-green dolomitic siltite and pale-green argillite. Light-gray fine-grained quartzite beds present in lower part of formation. Sedimentary structures include syneresis cracks, water-expulsion structures, and ripple cross-lamination.'
467|'Includes the Spokane, Greyson, and Newland Formations, described above and below. Present only in northern part of Big Belt Mountains.  Interbedded grayish red purple argillite and siltite, and lesser gray-green siltite; middle part, and to lesser extent lower part contains light-gray feldspathic metasandstone. Local dolomitic limestone. Common sedimentary structures include load casts, rip-up clasts, fluid-escape structures, ball-and-pillow structures, syneresis cracks, and ripple cross-lamination.

Spokane Fm:   Interbedded grayish red purple argillite and siltite, and lesser gray-green siltite; middle part, and to lesser extent lower part contains light-gray feldspathic metasandstone. Local dolomitic limestone. Common sedimentary structures include load casts, rip-up clasts, fluid-escape structures, ball-and-pillow structures, syneresis cracks, and ripple cross-lamination.

Greyson Fm:  In northwestern part of Forest:  Interbedded dark greenish gray siltite and argillite, a few beds of lenticular quartzose metasandstone, and dolomitic siltite that contains algal laminations.

In Big Belt Mountains:  Upper member consists chiefly of argillite in lower part that grades upward into siltite; local gray fine-grained feldspathic metasandstone. Minor limestone and calcareous siltite and metasandstone present in upper part. Lower member consists of interbedded gray fine- to coarse-grained feldspathic metasandstone and, locally, quartzite; some beds ripple cross-laminated; conglomeratic beds, locally graded from small boulders in lower part to pebbles in upper part; medium-gray feldspathic siltite; local yellowish brown finely laminated (porcellanitic?) siltite; and gray finely laminated argillite.

Newland Fm:  Upper member consists of interbedded units of medium-gray limestone, some beds mottled dark gray with algal-like structures; calcareous and noncalcareous finely laminated siltite, and locally ripple cross-laminated siltite; locally light-gray, yellowish-orange-weathering porcellanitic argillite; minor feldspathic metasandstone and, locally, quartzite. Lower member consists of medium-gray, light-brown-weathering argillite and dolomitic argillite that is finely laminated. Minor interbeds of gray fine-to medium-grained feldspathic metasandstone beds a few inches thick. Formation exposed only in Big Belt Mountains.'
468|'In northwestern part of Forest:  Interbedded dark greenish gray siltite and argillite, a few beds of lenticular quartzose metasandstone, and dolomitic siltite that contains algal laminations.

In Big Belt Mountains:  Upper member consists chiefly of argillite in lower part that grades upward into siltite; local gray fine-grained feldspathic metasandstone. Minor limestone and calcareous siltite and metasandstone present in upper part. Lower member consists of interbedded gray fine- to coarse-grained feldspathic metasandstone and, locally, quartzite; some beds ripple cross-laminated; conglomeratic beds, locally graded from small boulders in lower part to pebbles in upper part; medium-gray feldspathic siltite; local yellowish brown finely laminated (porcellanitic?) siltite; and gray finely laminated argillite.'
469|'Upper member consists of interbedded units of medium-gray limestone, some beds mottled dark gray with algal-like structures; calcareous and noncalcareous finely laminated siltite, and locally ripple cross-laminated siltite; locally light-gray, yellowish-orange-weathering porcellanitic argillite; minor feldspathic metasandstone and, locally, quartzite. Lower member consists of medium-gray, light-brown-weathering argillite and dolomitic argillite that is finely laminated. Minor interbeds of gray fine-to medium-grained feldspathic metasandstone beds a few inches thick. Formation exposed only in Big Belt Mountains.'
470|'Basalt flows, flow breccia, and plugs.'
471|'Andesite flows, flow breccia, and plugs.'
472|'Flows, porphyry plugs, breccia plugs, dikes, tuff, and welded tuff; includes minor andesite and latite flows and plugs.'
473|'Volcanic flows and dikes of basaltic, andesitic, and latitic composition; present only west of 112 longitude.'
474|'Volcanic rocks ranging from rhyolite to quartz latite to dacite in composition; includes plugs, dikes, stock, diatreme, flows, welded tuff, and air-fall tuff, locally volcaniclastic rocks. Present in Elkhorn Mountains and to west, south of U.S. Highway 12.'
475|'Lava flows, breccia, plugs, tuff, and volcaniclastic sedimentary rocks. Present only in southwesternmost part of Forest, south of Elliston.'
476|'Dark gray dike of highly altered igneous rock composed chiefly of mafic minerals; present along west flank of middle part of Big Belt Mountains.'
477|'Light gray intrusions of porphyritic latite to quartz latite. Present along west flank of central part of Big Belt Mountains.'
478|'Medium to dark gray lava flows, flow-breccia, air-fall tuff, and ash-flow tuff; composition ranges from rhyolitic to andesitic, and locally basaltic. Unit also includes related intrusive rocks (described below) where they are areally too small to show separately at this scale. Volcaniclastic sedimentary rocks, derived from debris of volcanic rocks, include conglomerate, sandstone, and mudstone. Present only in Elkhorn Mountains and area to west.'
479|'Dacite to andesite sills, dikes, and irregularly shaped intrusions. Shown only in Elkhorn Mountains.'
480|'Welded tuff and lava flows ranging from rhyolite to dacite in composition; dikes of andesitic composition; and volcaniclastic conglomerate, sandstone, siltstone, and mudstone. Unit present only in central and southern part of Big Belt Mountains.'
481|'Porphyritic dacite plug of Knopf (1963). Present northwest of Helena.'
482|'Dark-gray gabbro pluton. Present only east of Elliston.'
483|'Gray granitic intrusion of monzodiorite composition. Present only southeast of Lincoln.'
484|'Light-gray monzonite in stocks, dikes, and sills; present only in northwesternmost part Forest.'
485|'Light-gray aegirine-augite-bearing granitic intrusions of monzodiorite composition. Present only in Boulder Baldy-Boulder Mountains area of Big Belt Mountains.'
486|'Light-gray quartz monzodiorite intrusions. Present only in Big Belt Mountains.'
487|'Light- to medium-gray quartz monzonite intrusion. Present only in eastern part of Elkhorn Mountains.'
488|'Light-gray monzogranitic intrusion. Present only south of Lincoln..'
489|'Dark-gray dioritic rocks that form small stocks, dikes, and sills. Present in area between Helena and Elliston in western part of Forest.'
490|'Medium-gray granodiorite stocks and plugs.'
491|'Medium-gray granodiorite stock near Marysville, northwest of Helena.'
492|'Medium-gray granodiorite stock near Ogden Mountain, southwest of Lincoln.'
493|'Medium-gray intrusion granodiorite stock near Blackfoot City, northwest of Elliston.'
494|'Medium-gray granodiorite stock near Dalton Mountain, south of Lincoln.'
495|'Dark-gray granodiorite pluton along the northern margin of the Boulder batholith. Present south of Helena and in northwestern part of Elkhorn Mountains.'
496|'Light- to medium-gray granitic intrusions with many separate phases; composition ranges from monzogranite to granodiorite. Includes small areas of aplite (described below) too small to show separately. Forms the major rock type of the Boulder batholith in Elkhorn Mountains and in area south of U.S. Highway 12.'
497|'Light-gray, small leucomonzonite plutonic masses; present only west of Helena, north of U.S. Highway 12.'
498|'Dark-gray monzogabbro of plagioclase and clinopyroxene phenocrysts in groundmass of micropegmatite; present only south of Helena along northern margin of the Boulder batholith.'
499|'Light-gray to white rock of feldspar and quartz. Forms sheets, pods, dikes, and irregularly shaped masses within Butte quartz monzonite. Only larger bodies are shown. Present only in Elkhorn Mountains and in area south of U.S. Highway 12.'
500|'Dark-gray to gray-green sills and dikes.'
501|'Dark gray-green mafic sills; present only in northwestern part of Forest.'
575|'Gravel, sand, silt, and clay in flood plains and low terraces along present drainages.'
576|'Angular blocks of bedrock in finer grained matrix; mixed at places with glacial debris.'
577|'Includes till (ground and end moraines), outwash, and other fluvioglacial deposits. Dune sands are common in a few places. Locally includes lake sediments where not mapped separately as unit Ql.'
578|'Buff, laminated clay and silt containing a few lenses of gravel and scattered dropstones. Tends to form vertical cliffs along present stream courses; topographic surfaces are gently rolling. Sediments represent bottom deposits of various glacial lakes.'
579|'Conglomerate, sandstone, siltstone, marlstone, oil shale, and coal representing fill in Kishenehn basin; presently restricted to the valley along the North Fork of the Flathead River in northeastern part of map area. As much as 11,000 ft thick (Constenius, 1988).'
580|'Quartz latite porphyry, diorite, and lamprophyre intruded along faults. Only dikes thicker than 20 ft shown; one crosses Callahan Creek and one is at southeastern edge of map area.'
581|'Biotite or hornblende-biotite granite, quartz monzonite, and granodiorite. Occurs as stocks and also as small unmapped dikes in and near the Cabinet Mountains. The Dry Creek stock in the central Cabinet Mountains has a minimum Rb-Sr age of about 73 Ma (Wells and others, 1981).'
582|'Gray to buff, coarse-grained stocks and dikes. Composed largely of orthoclase, andesine, and small amounts of pyroxene and hornblende (Gibson, 1948). Largest exposures are in pyroxenite-syenite complex at Vermiculite Mountain about 6 mi east from Libby, Mont. Syenite interpreted to be essentially the same age as the pyroxenite (Kpy), which the syenite intrudes (Boettcher, 1967).'
583|'Found only in the Rainy Creek-Vermiculite Mountain area. A core of biotitite is surrounded by coarse-grained biotite pyroxenite, which in turn is ringed by magnetite pyroxenite (Boettcher, 1967). Biotitite yielded a Rb-Sr age of 1043 Ma (C.E. Hedge, U.S. Geological Survey, unpub. data, 1982). Biotite pyroxenite has been altered at places to rocks containing vermiculite; Rainy Creek stock is main source of vermiculite in United States.'
584|'An incomplete section of deformed Fernie is exposed on a thrust plate in northeast Whitefish Range adjacent to north boundary of map. Upper part is gray dolomitic sandstone and interbedded dark-gray siltstone and shale. Lower in the section are layers of black fissile shale and gray limestone that contain belemnite fossils. Base not exposed. Minimum thickness about 500 ft.'
586|'Found only on thrust plates in northeast Whitefish Range. Light-gray, well-sorted, laminated and cross-laminated quartzite. Commonly has carbonate cement. Ripple marks present locally. Upper part includes beds of sandy dolomite that contain chert nodules. Contact with underlying Mississippian strata may be disconformable. Minimum thickness about 600 ft.'
587|'Includes Etherington, Mount Head, Livingstone, and Banff Formations as identified and described by Barnes (1963), and as published by Johns (1970). These rocks, found only on faulted thrust plates in northeast Whitefish Range, are a series of limestone and dolomite units that include some shale and calcarenite. Some units are bituminous, and several are cherty. Fossils that help distinguish the formations include brachiopods, crinoids, bryozoans, and corals. Estimated minimum thickness about 3,000 ft.'
588|'Found only in fault blocks and thrust plates across north end of Whitefish Range. Primarily dolomite and minor dolomitic sandstone and siltstone (Barnes, 1963). Estimated thickness about 2,000 ft.'
589|'In descending order, carbonate-bearing rocks, shale, and sandstone found in a series of fault blocks in northern Whitefish Range, in a southerly trending zone of faults beginning about 14 mi south of Libby, Mont., and in an isolated exposure of carbonate-bearing strata about 6 mi south of Troy, Mont. In more complete exposures along Fishtrap Creek, about 12 mi south of southernmost exposures in Kalispell quadrangle, the carbonate-bearing rocks have been called informally the Fishtrap dolomite (Keim and Rector, 1964; Bush and Fischer, 1981) or the dolomite of Fishtrap Creek (Harrison and Cressman, in press). The carbonate-bearing rocks consist principally of gray crystalline to pelletoidal or oolitic dolomite and interbedded shale, limey mudstone, and minor laminated siltstone. Conformably beneath the carbonate-bearing strata is an olive, fissile shale unit, a few hundred feet thick, that is equivalent to the Wolsey (or Gordon) Shale. Conformably beneath the shale is a buff-colored sandstone unit, a few tens of feet thick, that is equivalent to the Flathead Quartzite. The Flathead rests unconformably on the underlying Libby Formation. Maximum thickness of the Middle Cambrian sequence is about 430 ft in northern Whitefish Range and about 2,400 ft in southern exposures at Fishtrap Creek.'
590|'Used locally in northern Whitefish Range where units are too thin to show individually at map scale.'
592|'Dioritic to gabbroic rocks that commonly show alteration of mafic minerals. Sills range in thickness from less than 3 to 500 ft. Thicker sills tend to have contact-metamorphosed zones around them. Sills commonly persist for many miles; some maintain approximately the same stratigraphic position, whereas others cut across the section at a low angle. Intrusion probably occurred three times (at about 1,430, 1,100, and 800 m.y. ago; Harrison, 1972). Unit ZYd used for younger two generations of sills above the Prichard Formation; unit Yd used for oldest generation of sills and confined to Prichard.'
593|'Upper half of unit is dark, olive-gray, silty-argillite that is very thinly laminated or apparently structureless; about 415 ft thick near Libby. Lower half of unit is dark greenish-gray, blocky-weathering hummocky cross-laminated, coarse siltite to very fine grained quartzite; siltite or quartzite beds commonly 3-15 ft thick and separated by partings of even-parallel-laminated silty argillite 1-3 in. thick; about 510 ft thick near Libby. Grades by interlayering into the lower part of the Libby. Minimum thickness of upper part is about 925 ft near Libby but increases to at least 3,200 ft in northern Whitefish Range where upper part overlies the McNamara Formation.'
594|'In addition to separately mapped upper part (Ylu), includes Kidders lower five informal members, which on Flagstaff Mountain are, in descending order: (1) about 1,850 ft of alternating beds of dark-gray argillite and wavy-laminated green siltite, (2) about 1,380 ft of wavy-laminated green argillite and siltite that contain scattered carbonate concretions, (3) about 950 ft of stromatolitic and oolitic parallel- to wavy-laminated green siltite, (4) about 280 ft of light- and dark-green parallel-laminated siltite containing abundant small-scale sedimentary structures and thin chert laminae and chips, and (5) about 180 ft of dark-gray argillite thinly interlaminated with dark-green siltite. Rests sharply on the Bonner Quartzite or its siltite facies. Lower five members are probably a distal black and green facies of the green and red McNamara Formation into which it grades laterally by interlayering and intertonguing.'
595|'Predominantly grayish-green, interbedded and interlaminated argillite and siltite that contain thin chert laminae and chips. Oolites, stromatolites, quartzarenite, and stratabound copper minerals present at places. Three relatively thin red-bed sequences of laminated argillite and siltite occur at top, middle, and bottom of section in Whitefish Range. Strata commonly exhibit ripple marks, shrinkage cracks, scours, and small-scale cross-bedding. Red-bed sequences drop out to west where green strata pass to dark-gray and green strata of lower five members of the Libby Formation. Sharply overlies the Bonner Quartzite. Maximum thickness of about 4,200 ft exposed in northern Whitefish Range.'
596|'Red to pink, micaceous, arkosic, cross-bedded, fine- to medium-grained quartzite containing red argillite intraclasts; tabular and trough cross-beds and climbing ripple marks common. Interbeds of red, laminated argillite and pink, planar-laminated siltite increase in abundance to north, and siltite facies (Ybos) mapped where quartzite beds decrease to minor component. Sharply overlies the Mount Shields Formation. Maximum thickness about 1,000 ft.'
597|'Interbedded fine- to medium-grained feldspathic siltite and red argillite seen as beds and tongues in all exposures of Bonner; siltite facies is a minor component in the southern Libby thrust belt and southernmost Purcell anticlinorium. Cross-bedding and ripple cross-lamination common. Contains a few 10- to 20-ft-thick beds of typical Bonner Quartzite. Also contains some beds of green, parallel-laminated argillite and siltite, particularly near base. Sharply overlies the Mount Shields Formation. Thins from about 900 ft in south to 600 ft in north.'
598|'West of the lead thrust in the Libby thrust belt, the upper two members (shown as members 6 and 5 on fig. 2) are mapped together as the upper part of the Mount Shields where exposure permits. Member 6 (uppermost member) is black and green or white, thinly laminated argillite and siltite commonly displaying small-scale slump folds and shrinkage cracks. Maximum thickness about 300 ft. Member 5 (conformably underlying member 6) is gray, silty, stromatolitic limestone and dolomite that has conspicuous boxwork structure formed by siliceous laminae intersected by thin quartz veinlets along vertical joints. Green, dolomitic, silty argillite beds as thick as 30 ft are interlayered with the boxwork limestone. Maximum thickness about 500 ft.'
599|'In western part of map area, includes members 6 and 5 (where not mapped as Ymsu) plus members 4 through 1 (from upper to lower, as shown on fig. 2). Member 4 is blocky, green, dolomitic, silty argillite that shows parallel-laminated graded couplets; 1-ft-thick carbonate beds are scattered through member, and stromatolites are common near base; rare salt casts; ranges in thickness from about 350 ft in south-central part of map area to 550 ft in north- and east-central parts. Member 3 is predominantly alternating red and green beds of interlaminated argillite and siltite; mud chips, mud cracks, ripple marks, and fluid-escape structures are common; salt casts are abundant, particularly in red beds; stratabound films of chalcopyrite or chalcocite occur in some green beds; thickness ranges from about 700 ft in south-central part of map area to about 1,200 ft in north-central part. Member 2 is pale-red or green, flat-laminated, coarse-grained siltite to fine-grained quartzite that is blocky, feldspathic, and dolomitic; dolomite in cement, streaks, and pods parallel to bedding; minor layers of red or green argillite; red or buff stromatolite and oolite zone at top; ranges in thickness from about 700 ft in south-central part of map area to a maximum of 1,700 ft in west-central part. Member 1 is red to maroon, feldspathic, medium- to coarse-grained quartzite interbedded with red siltite; red argillite partings common between beds; cross stratification, mud chips, and heavy mineral streaks common; stromatolites at a few places; thickness about 1,000 ft in southern Libby thrust belt but thins in all directions from there (fig. 2). Sharply overlies Shepard Formation.

In eastern part of map area in Whitefish Range, member 1 is missing, member 2 is thin in the south and missing in the north, member 3 is lowest member exposed in the north and is about 1,000 ft thick, and member 4 thickens to about 700 ft and includes at the top about 180 ft of thinly laminated, grayish-green argillite and siltite that contain a few beds of olive, fine-grained arenite (Whipple, 1984). Sharply overlies Shepard Formation.'
600|'Dark-gray, amygdaloidal basalt. Occurs only in lower part of Mount Shields Formation in Glacier National Park. About 30 ft thick.'
601|'Consists of a variety of rock types, most of which are carbonate bearing or carbonate rich. Exposures in northern and northeastern parts of map area are mostly gray, fine-grained quartzite and siltite, some of which is pyritic and calcareous; less abundant interbeds include limestone (some of which is stromatolitic and oolitic), dolomite, and green calcareous argillite. Exposures in western and southwestern parts of map area contain a few quartzite beds but are predominantly (1) green, platy, dolomitic argillite, (2) green, slightly dolomitic, interlaminated argillite and siltite, and (3) silty dolomite that at places is stromatolitic and oolitic and may also display molar-tooth structure or horizontal calcite pods. Pyrite is common in the more carbonate-rich rocks. Zones of red interlaminated argillite and siltite are limited to a few places in the green argillitic rocks of south-central part of map area and locally in Whitefish Range. Black laminated argillite first appears in the green argillitic beds in southwestern part of map area and thickens to the west. The Shepard is commonly sheared or folded into chevrons where found in tight to overturned major folds. Grades by interlayering into the Snowslip Formation or its green facies, but the contact is marked at places by shallow channels of quartzite or, in the northeastern part of map area, by an angular unconformity that separates the Shepard from the Purcell Lava. The Shepard is lithologically similar to and correlates with members 4 and 5 of the Wallace Formation as mapped by Harrison and Jobin (1963) in the Clark Fork 15-minute quadrangle, which is adjacent to southwest corner of map area. Thickness ranges from about 280 ft in northern Whitefish Range (Whipple, 1984) to about 2,800 ft in southwest corner of map area.'
602|'Black to blackish-green basalt of continental alkaline basalt affinity (McGimsey, 1985). Multiple flows, commonly 5-10 ft thick, in the upper part of the Snowslip Formation or at the Snowslip-Shepard contact. Generally can be divided into two or three groups of flows in most areas.

In northeastern part of map area, upper, middle, and lower flows are present. Upper flows are fine grained in their lower parts and amygdaloidal and vesicular in their upper parts (Whipple, 1984); ropy flow structures cap many flows. Middle flows have indistinct contacts and fine-grained porphyritic zones. Lower flows are porphyritic and contain long (1-2 in.) tabular plagioclase crystals in a fine-grained and highly altered groundmass. Flows are locally pillowed. Thickness ranges from 0 to about 700 ft.

In western and southwestern parts of map area, only upper and lower flows were observed. Upper flows are similar to those of northeastern part of map area except rope flow tops are absent. Lower porphyritic flows have vague pillow structures and vesicles or amygdaloids at their tops. At a few places, individual flows are separated by a few inches to a few feet of beds similar to those of the Snowslip. Southern end of exposed flows is found at two places in southern Whitefish Range and near the mouth of the Fisher River in western part of map area. Thickness ranges from 0 to about 160 ft.'
603|'Generally contains units from a hundred to several hundred feet thick of thinly laminated red to purple argillite and siltite interbedded with thinly laminated green argillite and siltite that alternate with similarly thick units of couplets of greenish-gray siltite and olive argillite. Some units contain beds of arenite, carbonate, and stromatolites. Whipple and Johnson (1988) recognized six informal members in northeast corner of map area; similar members were separated on the basis of amount of arenite or presence of carbonates and stromatolitic limestone. Mud cracks, ripple marks, and fluid-escape structures are common in argillite beds. Arenite beds display small-scale cross laminae at many places. In west-central part of map area, red beds become fewer and thinner, green laminated argillite and siltite predominates, and a marker bed of thinly laminated black argillite and green siltite is found in green strata about one-third of the distance below the top of this facies. Green beds commonly have chlorite on bedding surfaces and some contain small amounts of stratabound copper minerals. This facies of the Snowslip either grades by interlayering into the upper member of the Wallace Formation or rests sharply on the middle member. Thickens in all directions from about 600 ft in northern Whitefish Range to 3,000 ft or more in northern and central parts of map area (fig. 2).'
604|'Predominantly evenly laminated couplets of green argillite and siltite containing sparse or no red beds. Chlorite common on bedding surfaces. Laminated black argillite and green siltite increases in abundance to the west (fig. 2). The black argillite commonly displays small soft sediment folds, shrinkage cracks, small-scale cut-and-fill structures, and fluid-escape structures. Grades laterally by intertonguing into red and green facies of the Snowslip and grades vertically by interlayering into the underlying Wallace Formation. This informal member is lithologically similar to and correlates with member 3 of the Wallace Formation as mapped by Harrison and Jobin (1963) in the Clark Fork 15-minute quadrangle, which is adjacent to southwest corner of map area. Thickness ranges from about 2,000 to 3,000 ft.'
605|'Thinly to very thinly laminated dark-green or black argillite and light-green siltite. Beds locally show small-scale cut-and-fill structures and shrinkage cracks. Dark- to light-green beds are always very thinly laminated and have parallel bedding. Differs from overlying green beds of the Snowslip in displaying thinner laminae, being less silty, and having no chlorite on bedding surfaces. Thickness ranges from 0 to 1,200 ft.'
606|'Black argillite alternating with white slightly dolomitic siltite or very fine grained quartzite layers and lenses that range from 1 to 20 in. in thickness; characteristically uneven and wavy bedded. Thicker siltite layers and lenses commonly display load casts and flame structures. Zones a few hundred feet thick in upper and lower parts are at places carbonate rich and show irregular, vertical calcite ribbons (molar-tooth structure) or small (2 in.), vertical calcite pod structures that transect tens of feet of beds. Also includes some beds of black laminated argillite, green interlaminated argillite and siltite, and dolomitic argillite. Slump folds in zones a few feet thick are present in southern Libby thrust belt (fig. 2). Cycles of quartzite or black silty argillite overlain by dolomitic siltite or dolomite a few feet thick are sparsely present in southwest corner of map area; these cycles are similar to those that characterize the main body of the Helena Formation, Pyrite and chalcopyrite common in any of the carbonate-bearing lithologies. Thickness ranges from about 500 ft in Whitefish Range to about 6,000 ft at west edge of map area.'
607|'Predominantly blocky, green, parallel-laminated and interbedded dolomitic argillite and argillitic siltite, some of which contains molar-tooth structure and pods or irregular blobs of calcite. Includes a few beds a foot or two thick of white to buff, medium-grained quartzite. Resembles the Empire Formation but differs in containing molar-tooth structures and not exhibiting fluid-escape structures that characterize the Empire. Interfingers laterally with the lower member of the Helena in northwestern part of map area where the interfingered zone has been mapped as either lower Wallace or lower Helena depending on the predominant lithology. Where underlain by the St. Regis Formation, the contact is fairly sharp; where underlain by the Empire Formation, the contact grades by interlayering. Thickness ranges from 0 to about 900 ft.'
608|'Wallace Formation'
609|'Used only in southern part of Cabinet Mountains for unit mapped by Wells and others (1981).'
610|'Hundreds of distinct lithologic cycles in units a few feet to a few tens of feet thick form the main body of the Helena. Each complete cycle consists of three parts: an upper bed of dense conchoidal-fracturing dolomite that weathers orange brown, a middle bed of gray dolomite that commonly displays horizontal calcite pods or blobs that grade successively upward to vertical pods and blobs and then into molar-tooth structures, and a lower clastic bed rarely more than a foot thick of white quartzite or quartzite and black argillite resting on a cut surface. Complete cycles are seen in many exposures, but most commonly the lower bed is missing and less commonly one of the other beds is missing, Pyrite and some chalcopyrite common. Stromatolite beds present at some places, particularly east of the Rocky Mountain trench. A zone a few tens to a few hundred feet thick at top of map unit is black wavy-bedded argillite and tan-weathering white dolomitic siltite typical of the middle member of the Wallace Formation. At places includes the lower member of the Helena Formation where not mapped separately. Main body of Helena interfingers with middle member of Wallace in northern and central parts of map area (fig. 2). Thickness of main body of Helena ranges from about 9,000 ft in southeastern part of map area to 0 where it fingers out westward into the middle member of the Wallace.'
611|'Alternating beds a few feet to a few tens of feet thick of dense, orange-weathering dolomite and thinly laminated, apple-green to tan argillite. Half-inch-thick beds of brown-weathering quartzite scattered through unit. Dolomite commonly pyritic and displays irregular-shaped pods of calcite and molar-tooth structure. Tongues and layers of main body of Helena a few hundred feet thick are common in unit. Contact with main body of Helena placed on top of uppermost green and tan argillite bed. Grades by interlayering into the underlying Empire Formation, and grades by intertonguing laterally into lower member of the Wallace Formation. Maximum thickness about 3,000 ft.'
612|'Mapped in north-central part of map area where beds of the main body of the Helena and middle member of the Wallace are interlayered and intertongued on a scale of a few tens of feet to a few hundreds of feet. Minor interlayering at other places is mapped as either Helena or middle Wallace depending on the predominant lithology. Includes lower member of the Helena where not mapped separately.'
613|'Thinly laminated, dark-green and light-green dolomitic argillite and silty argillite or siltite. Laminae mostly wavy  and discontinuous although some are even parallel. Fluid-escape structures are characteristic, and horizontal pods of white or pink calcite are particularly abundant in upper part. Ripple marks, syneresis cracks, and mud chips common in places. Lower part contains white dolomitic quartzite beds as thick as 2 ft. White, rounded-grain quartzite beds and lenses a few inches thick occur in northeast quarter of map area; cross-bedding and mud chips common in these beds. Pyrite cubes common in more carbonate-rich strata, and a few exposures display stratabound copper minerals. A few purple interlaminated argillite and siltite beds commonly occur near base and at places near middle of unit. Intertongues with underlying St. Regis Formation and probably with overlying lower member of Wallace. Thickness ranges from 0 to about 2,000 ft.'
614|'Purple interlaminated argillite and siltite beds that alternate with green interlaminated argillite and siltite beds. Upper part has carbonate specks and some carbonate cement; lower part has scattered beds of pink, fine-grained quartzite or siltite. Sedimentary structures include abundant mud cracks, mud chips, ripple marks, and fluid-escape structures. Formation present only in western part of map area. Grades by interlayering over a few tens of feet into underlying Revett Formation. Maximum thickness is about 1,000 ft, but thins to about 600 ft in north and to a few feet in southwest (fig. 2) before thickening again to about 1,100 ft near Clark Fork, Idaho, a few miles west of map area (Harrison and Jobin, 1963).'
615|'Characterized by blocky cosets of white, green, or pale-purple- gray, cross-bedded quartzite beds. In most areas, the Revett can be divided into three informal members: upper and lower quartzite-rich members and a middle member that contains significantly more argillite and siltite. Some quartzite is purple striped and commonly shows Liesegang rings of purple hematite coloration both along and across bedding. Many beds display climbing ripple marks, ripple cross laminae, load casts, and 1- to 5-ft-deep channels. Heavy minerals are common on cross laminae. Argillite beds are purple or green, generally display even- to wavy-parallel laminae, and contain mud cracks, mud chips, ripple marks, and fluid-escape structures. Siltite beds are commonly pale purple and parallel laminated; siltite alternates with beds of argillite. In southwestern part of map area, parts of the upper and lower quartzite members are green or white, show conspicuous iron-carbonate cement, and contain major ore deposits of stratabound copper-silver. In northern and western parts of map area, the characteristic quartzite beds are purple gray, thinner and less abundant, and enclosed in argillite and some siltite. In some of the easternmost exposures, the characteristic quartzite beds are only a few tens of feet thick. Small flakes of secondary biotite and tiny euhedral magnetite crystals are displayed in the formation throughout map area. Grades by interlayering into underlying Burke Formation. Thickness ranges from about 2,000 to about 2,800 ft in exposures west of the Rocky Mountain trench; formation is not recognized east of the trench.'
616|'Three lithologic members are found in most areas. Upper member has beds a few feet to a few tens of feet thick of green laminated argillite and siltite that alternate with beds of purple laminated argillite and siltite. Dolomitic cement is common as are ripple marks, mud chips, desiccation cracks, fluid-escape structures, ball-and-pillow structures, and flute casts. Beds a few inches to a few feet thick of white, rounded-grain, medium-grained, cross-bedded quartzite that displays mud chips and balls on cross strata are abundant in eastern part of map area but decrease rapidly in both number and thickness west of the Rocky Mountain trench. A section of this member on Blacktail Mountain about 13 mi south of Kalispell was drilled extensively to evaluate stratabound copper mineralization in green beds. Detailed descriptions of the surface geology of that area are given by Harrison and Reynolds (1979) and of selected cores by Reynolds (1979). Middle member is predominantly pink to purple-gray, very fine-grained feldspathic quartzite or coarse siltite that has planar lamination or long tabular cross lamination. Interbeds of purple argillite are common. Lower member is similar to the upper member but has more purple argillitic beds, is more dolomitic, and has scattered iron-carbonate specks and cement.

The Spokane intertongues westward with the St. Regis and Revett Formations, but exact nature of intertonguing is uncertain owing to lack of critical exposures in and near the Rocky Mountain trench. Where the Spokane loses the distinctive white, rounded-grain quartzite beds westward and the underlying Revett loses the definitive cosets of cross-bedded quartzite eastward, the formations are difficult to distinguish, and some identifications of the mapped units were arbitrary. Thickness ranges from about 5,000 ft in eastern part of map area to 0 ft in western part.'
617|'Formation nomenclature as used by Whipple (in press). Lithologically the same as upper and lower members of the Spokane Formation, but the upper part of the Grinnell contains as much as 20 percent of white, rounded-grain quartzite beds (Whipple and others, 1984). Mapped only in Glacier National Park where it is about 2,600 ft thick.'
618|'Divisible into three informal members in most areas (fig. 2). Upper member consists predominantly of blocky beds of purple-gray interlaminated argillite and siltite interbedded with greenish-gray interlaminated argillite and siltite. Mud cracks and mud chips common in upper part of member. White to purple-gray parallel-laminated siltite and quartzite beds a few feet thick are interbedded in the upper part of the member and increase in abundance upward. Contact with the overlying Revett is placed where cosets of cross-bedded quartzite first appear. 

Middle member is predominantly gray to purple-gray parallel- and thinly-laminated siltite in blocky planar beds that have minor argillite partings or beds. Some siltite has zebra-striped markings of hematite coloration. Outcrops of middle member along northern part of Lake Koocanusa show wavy, wispy, discontinuous laminae.

 Lower member is predominantly green parallel-laminated interbedded argillite and siltite that generally are in beds about 2-20 in. thick and weather to give a blocky-flaggy outcrop. Upper part of lower member has some purple-gray interbeds of argillite and siltite.

Siltite and some argillite lithologies in all members are commonly speckled by tiny euhedral magnetite crystals and display small flakes of secondary biotite. Grades by interlayering into the transition member of the underlying Prichard Formation. In the southern Cabinet Mountains, the Burke as mapped by Wells and others (1981) includes the transition member of the underlying Prichard Formation. Thickness ranges from about 2,500 ft to 3,600 ft west of the Rocky Mountain trench.'
619|'Predominantly thin to thick beds of olive siltite and very fine grained quartzite speckled by brown spots of limonite after iron carbonate and perhaps magnetite. Lamination faint but generally even parallel; minor cross lamination. Contact placed above highest black argillite bed in underlying transition member of the Prichard. Unit unnamed because authors differ in interpretation of the rocks as a facies of either the Burke or the Appekunny Formation. Mapped only along west side of Whitefish Range and west of Blaine Mountain. Thickness about 600 ft.'
620|'Formation nomenclature as used by Whipple (in press). The Appekunny Formation of Glacier National Park has been divided by Earhart and others (1983) into an upper part and a lower informal "Wolfgun member." Regional mapping of the Kalispell quadrangle and regional synthesis of the Prichard Formation by Cressman (1989) indicates that the Wolfgun is actually a stratigraphic and lithologic equivalent of the transition member of the Prichard Formation, which has been mapped over thousands of square miles to the west and southwest of Glacier National Park. As a consequence, we do not use "Wolfgun member" and assign those beds to the transition member of the Prichard (Ypt). The Appekunny as shown in the park consists mostly of interlaminated green argillite and siltite and some beds an inch or two thick of light-gray quartzite. Thickness is about 140 ft where exposed but thickens eastward.'
621|'Identical in composition and habit to unit ZYd but confined to the Prichard Formation and inferred to be the oldest of three generations of similar sills. Maximum thickness of a single sill is about 1,800 ft in the No.1 Gibbs borehole (near Lincoln County-Flathead County line in T. 28 N., R. 26 W.). One sill in lower part of Prichard along the Kootenai river about 22 mi northwest of Troy, Mont., yielded an age of 1,43330 m.y. for igneous zircon in a granitic differentiate in the sill (Zartman and others, 1982). Sills are prominent seismic reflectors that decrease in abundance eastward from the crest of the Purcell anticlinorium to the Rocky Mountain trench (Harrison and others, 1985).'
622|'Generally consists of three units: (1) an upper unit of interlaminated light- and dark-gray siltite and argillite similar to the middle unit, but containing interbeds of light-olive-gray siltite and quartzite similar to those in the overlying Burke Formation, (2) a middle unit of interlaminated light- and dark-gray siltite and argillite, and (3) a basal unit of medium-gray blocky-weathering siltite and minor quartzite. All three units are present in nearly every outcrop area of member, but their relative proportions vary from place to place. Laminae are wavy to lenticular; scour-and-fill structures, fluid-escape structures, and syneresis cracks common. Iron sulfides weather to give rusty aspect to many outcrops. Randomly oriented biotite porphyroblasts common, particularly near top of upper unit, in all but easternmost exposures. Calcareous siltite and argillite beds make up a small part of the member (some in the middle unit but most in the upper unit) and gradually become more abundant eastward; in Glacier National Park contains some stromatolitic beds. Basal contact is sharp. Member is 2,000-2,500 ft thick throughout much of quadrangle but thins to about 1,050 ft in Whitefish Range and to about 860 ft in Glacier National Park. Some variation in the mapped thickness results from inconsistencies in placement of the gradational upper contact.'
623|'Medium-gray argillite that contains planar laminae and thin planar beds of light-gray and dark-gray silty argillite. Alternating light and dark layers, 1-3 mm thick, give lined or banded appearance. Dark-gray silty argillite contains discontinuous laminae of carbonaceous matter and iron sulfide (mostly pyrrhotite, but locally pyrite). Iron sulfide weathers to give rusty appearance to outcrops. Randomly oriented biotite porphyroblasts common except in Glacier National Park. In the park, upper part of member contains thin lenticular beds and pods of calcareous and dolomitic silty argillite. Near Lake Koocanusa, upper part of member contains some thin beds of white quartzite that at places contains metamorphic garnet, hornblende, and calcite; white quartzite beds become less abundant westward and are absent on west limb of Sylvanite anticline. Slump folds locally in lower part of member. Basal contact ranges from sharp to gradational through several hundred feet. Member is 1,600-2,000 ft thick in most of map area west of Rocky Mountain trench, and about 3,500 ft thick in Whitefish Range; about 3,500 ft is exposed east of map area near head of McDonald Lake in Glacier National Park.'
624|'Interbedded quartzite and argillite that enclose a distinctive tongue of argillite mapped separately as unit Ypa. Mostly (65 percent) medium-dark- to medium-light-gray, fine-grained and very fine grained, slightly feldspathic, argillitic quartzite in even beds 0.7-2 ft thick and in sets mostly 3-5 ft thick. Quartzite beds commonly grade to siltite and argillite in top few inches, and some beds exhibit sole marks. Quartzite sets alternate with argillite sets mostly about 10 ft thick. Argillite is silty, dark gray, and weathers brownish gray. Xenoblastic biotite present throughout member in amounts of as much as 20 percent; xenoblastic chlorite present locally. Member is a minimum of 12,000 ft thick in the Sylvanite anticline and west of the Moyie thrust system. Quartzite member thins and intertongues eastward with argillite in lower part of the Prichard (Ypl); is less than 4,000 ft thick and included in upper part of the lower Prichard (Ypl) immediately west of the Pinkham thrust; and probably pinches out near the Rocky Mountain trench.'
625|'Slabby-weathering, medium-gray, silty argillite in beds 0.5-1.5 ft thick. Parts of member display dark-gray laminae and thin beds of silty argillite that contain abundant pyrrhotite and carbonaceous matter; pyrrhotite weathers to impart rusty color to outcrops. Slump folds common near base. Xenoblastic biotite and chlorite common. Upper and lower contacts with enclosing quartzite member are sharp. About 800 ft thick in the Sylvanite anticline. Argillite member exposed in the Sylvanite anticline and west of the Moyie thrust system is a tongue of the argillite that makes up most of the Prichard Formation (Ypl) in central and eastern parts of quadrangle (see cross section B-B).'
626|'Where exposed on the Purcell anticlinorium, consists of quartzite interbedded with argillite and is similar in character to the quartzite member. About 1,000 ft exposed. In No. 1 Gibbs borehole, lower part consists of six lithologic units that correlate with the informal members A-G described by Cressman (1985, 1989). These are from top to bottom:

Quartzite interbedded with argillite and similar to quartzite member (member G). Total thickness of unit including core and surface exposures is about 4,000 ft.

Dolomitic siltite, 3,000 ft thick (facies of member F).

Interlaminated siltite and argillite interbedded with well-sorted quartzite, 2,800 ft thick (member E).

Argillite, 500 ft thick (member D).

Argillitic quartzite, 160 ft thick (member C).

Argillite and siltite, 2,500 ft thick (members A and B, undifferentiated).

Lowest beds in borehole are schistose and garnetiferous.

Inferred thickness of entire Prichard Formation as shown in cross sections is about 25,000 ft and is based on thickness at borehole plus interpretation of gravity, magnetotelluric, and seismic data of depth to basement (Harrison and Cressman, in press).'
650|'Silt, sand, and gravel in channels and flood plains of existing streams and rivers and in alluvial fans.'
651|'Angular fragments of bedrock mixed with soil or heterogeneous boulders and finer-grained material; characterized by irregular, hummocky topography.'
652|'Unsorted mixture of boulders, cobbles, pebbles, and sand deposited by glaciers and by glacial meltwater. Unit includes undivided till and outwash of at least two major glacial episodes.'
654|'Light gray to yellowish-brown partly tuffaceous sandstone, siltstone, and shale, and subordinate interbeds of limestone and marl and lenses of pebble and cobble conglomerate composed of locally derived rock fragments. Locally, unit includes thin beds of lignite and lignitic shale in the Medicine Lodge Creek basin. Commonly veneered with gravel and a thin layer of eolian silt.'
655|'Includes limonitic, calcareous tufa near Shenon Creek and in the upper part of Medicine Lodge Creek, and calcareous, siliceous tufa and massive chalcedonic silica near the North Fork and South Fork of Everson Creek. Locally, unit contains repeatedly fractured and rehealed siliceous breccias. The Shenon Creek deposit probably is the source of placer gold mined in the Chinatown diggings in Jeff Davis Creek.'
656|'Basaltic andesite, andesite, latite, rhyodacite, and rhyolite as flows, ash-flow tuffs, and tuff and flow breccias. Locally, unit contains thin interbeds of light olive-gray, biotitic, tuffaceous, fine- to coarse-grained sandstone and conglomerate composed of volcanic detritus. Age ranges from about 48 Ma to 40 Ma (Staatz 1979; Ruppel and Lopez 1988; M''Gonigle and Dalrymple 1996).'
660|'Unit includes rocks originally mapped as Quadrant Formation (Pennsylvanian) (Lucchitta 1966; Smith 1961; Ruppel 1968; and Ruppel and Lopez 1988) that are now included in the Bloom and Gallagher Peak Sandstone Members of the Snaky Canyon Formation (latest Mississippian to Late Pennsylvanian) and in the Bluebird Mountain Formation (latest Mississippian) (Skipp et al. 1979). Consists mainly of quartzitic sandstone, dolomite, and limestone, and includes three units: (1) an upper pale yellowish-brown, fine-grained, thickly bedded, prominently cross-bedded, calcareous quartzitic sandstone with thin interbeds of similarly colored cherty, sandy dolomite; probably equivalent to the Gallagher Peak Sandstone Member of the Snaky Canyon Formation; (2) a middle unit of medium gray to medium light gray, thin- to medium-bedded, partly cherty limestone and dolomite; probably equivalent to the Bloom Member of the Snaky Canyon Formation; and (3) a lower unit of interbedded medium-light gray to medium-dark gray quartzitic sandstone, dolomite, and limestone probably equivalent to the Bluebird Mountain Formation; the sandstone is fine-grained, thickly bedded to massive; dolomite and limestone are finely to coarsely crystalline, thinly bedded or thickly bedded to massive. The three units are roughly equal in thickness; total thickness of interval is 1,300 ft to 1,700 ft.'
661|'Unit includes the Upper Mississippian and Lower Pennsylvanian Snowcrest Range Group (Wardlaw and Pecora 1985) and the Lower to Upper Mississippian Tendoy Group (Sando et al. 1985), the Upper Mississippian Railroad Canyon Formation, and carbonate rocks originally mapped as the Mississippian Madison Group, Paine Limestone, and Milligen Formation that are now included in the Surrett Canyon, South Creek, Scott Peak, Middle Canyon, and McGowan Creek Formations (Huh 1967; Sandberg 1975). The Railroad Canyon Formation is the temporal and partly the lithologic equivalent of the Lombard Limestone in the Snowcrest Range Group, and includes rocks originally mapped as Big Snowy Formation in the Beaverhead Mountains. The upper two-thirds of the formation is medium-dark gray to pale red, thin- to thick-bedded, fine- to medium-grained limestone and interbedded brownish-gray to pale red siltstone and mudstone; the lower third of the formation is grayish-red to dark gray mudstone and papery shales. The formation is 850 ft thick (Ruppel and Lopez 1988).

The Railroad Canyon Formation is underlain by thickly bedded to massive, medium-light gray to medium-dark gray limestones of the Middle Canyon and Scott Peak Formations. The formations have a combined thickness of about 3,000 ft to 3,500 ft, but are greatly thinned by faulting in much of this region. The McGowan Creek Formation at the base of the Mississippian consists of medium gray to dark gray, fissile to chippy, carbonaceous siltstone, mudstone, and shale, and thin interbeds of dark gray fine-grained limestone. Thickness ranges from 100 ft to 200 ft.'
662|'Dolomite, medium-dark gray to dark gray, finely to medium crystalline, fetid, locally sandy near base of formation, and locally conglomeratic. The Three Forks Formation is known to be present only in the Hawley Creek area where it consists of dark gray siliceous mudstone and is less than 100 ft thick (Lucchitta 1966). The Jefferson Formation is about 800 ft thick.'
663|'Unit includes rocks of the Jefferson, Three Forks, and Summerhouse Formations.'
666|'Unit includes rocks of the Summerhouse Formation and Kinnikinic Quartzite and may locally include rocks of Devonian age. Units typically are too thin to be mapped separately or are so poorly exposed as to be inseparable. Regionally, the Summerhouse Formation (Lower Ordovician) is composed of sandstone that is quartzitic or feldspathic to arkosic, light gray to white, medium- to coarse-grained, locally feldspathic and micaceous, and locally conglomeratic; Scolithus burrows locally abundant; thickness ranges from 0 ft to about 230 ft (Ruppel et al. 1975).'
667|'Quartzite, white or light gray, vitreous, fine- to medium-grained; partly mottled, with irregular lenses and blebs a few cm long of reddish-brown sandstone cemented by ferrodolomite. Present only in thin, thrust-faulted slices and thins depositionally to 0 ft in the Beaverhead Mountains.'
668|'Quartzite, pale purple to grayish-pink, medium- to coarse-grained and grains well sorted and well rounded, beds 3 ft to 6 ft thick, partly prominently cross-laminated; contains abundant hematite grains. Thickness ranges from 0 ft to about 10,000 ft as a result of later Proterozoic and early Paleozoic erosion.'
669|'Quartzitic sandstone, pale red, medium- to coarse-grained, feldspathic to arkosic, locally conglomeratic. Present only near the north border of the map area east of Horse Prairie.'
670|'In this area the group includes (Ruppel 1975; Ruppel and Lopez 1988):  Gunsight Formation, Apple Creek Formation, and Big Creek Formation.'
671|'Light brownish-gray to grayish-reddish-purple, thin- to medium-bedded, fine- to medium-grained, feldspathic quartzite; many beds laminated or cross-laminated. Minimum thickness about 6,000 ft.'
672|'Grayish-green, thinly bedded siltite and very fine-grained quartzite; contains streaks and lenses of light-gray ferrodolomite-cemented sandstone. Thickness about 1,000 ft, but present only in thin, fault-bounded slices in the map area.'
673|'Pale greenish-gray to light gray, thickly bedded or massive, fine-grained feldspathic quartzite. Thickness about 10,000 ft.'
674|'Medium gray to medium-dark gray, mostly thin- to medium-bedded, very fine-grained to fine-grained, feldspathic, finely biotitic quartzite and subordinate, interbedded, similarly colored siltite and argillite. Probable thickness more than 20,000 ft.'
675|'Quartzofeldspathic gneiss and schist and related granitic crystalline metamorphic rocks of Late Archean age (MGonigle 1993); originally included in the Dillon granite gneiss of Heinrich (1960).'
676|'Basaltic andesite, andesite, latite, rhyodacite, and rhyolite as flows, ash-flow tuffs, and tuff and flow breccias. Locally, unit contains thin interbeds of light olive-gray, biotitic, tuffaceous, fine- to coarse-grained sandstone and conglomerate composed of volcanic detritus. Age ranges from about 48 Ma to 40 Ma (Staatz 1979; Ruppel and Lopez 1988; M''Gonigle and Dalrymple 1996).'
700|'Well-rounded gravel and sand with lesser amounts of silt and clay.'
701|'Includes alluvial terrace deposits, braided stream deposits, alluvial fan deposits, and glacial outwash deposits.'
702|'Well-rounded cobbles, gravel, and sand in deposits with flat-topped surfaces that are 10-30 ft (3-9 m) above the present flood plain.'
703|'Unconsolidated material, typically clay-rich, that has moved down slope. Common northwest of Missoula in Tgc unit, particularly where it is overlain by more permeable Taf unit (Harris, 1997).'
704|'Varved, light-brown clay and silt of Glacial Lake Missoula.'
705|'Poorly sorted deposits of boulders and finer material in high mountain valleys.'
706|'Unconsolidated material consisting of weathered cobbles and finer-grained sediment. Cobbles in the upper Petty Creek area are Belt Supergroup, primarily quartzite, suggesting either a local source or a northerly source. Exposure immediately north of Missoula is described as conglomerate by Harris (1997).'
707|'Locally derived, poorly sorted, angular to rounded boulders, cobbles, gravel, sand, and silt. Probably equivalent to the Sixmile Formation of southwest Montana (Jim Sears, pers. comm., 1997).'
708|'Channel and flood plain deposits of the ancestral Bitterroot and Clark Fork rivers. Includes well-sorted and well-rounded cobbles, gravel, sand, silt, clay, and volcanic ash deposits. Clasts are not locally derived. Marked angular unconformity at top of unit near Missoula is overlain by Taf unit. To the south in the Bitterroot Valley the underlying Tgc beds are not as steeply dipping and this contact is a disconformity. Coarser intervals are permeable, but clay-rich zones are not. Probably equivalent to the Renova Formation of southwest Montana (Jim Sears, pers. comm., 1997).'
709|'Buff to light gray with variable amounts of smoky quartz and potassium feldspar phenocrysts. Entirely glassy (gray vitrophyre) in exposures north of Montana Creek. Large dike west of the Lolo Hot Springs batholith is locally syenitic in composition and, like many of the dikes, follows preexisting faults (Simpson, 1985; Lewis 1992a).'
710|'Pink to buff crystal-rich tuff containing approximately 30% phenocrysts of smoky quartz and sanidine in an aphanitic matrix.'
711|'Gray, porphyritic rocks with plagioclase, biotite, and hornblende phenocrysts in an aphanitic matrix.'
712|'Gray, porphyritic, volcanic tuffs or lava flows northwest of the Lolo Hot Springs batholith (Simpson 1985). Unit includes poorly exposed rhyolite flows(?) or dikes(?) southwest of Florence.'
713|'Light-gray to pale-pink, nonfoliated biotite monzogranite. Largest mass is the Lolo Hot Springs batholith, which is mostly medium grained but which contains some fine-grained zones, particularly near the margins (Leischner 1959; Simpson 1985). Alkali feldspar is strongly perthitic, and miarolitic cavities contain smoky quartz and alkali feldspar crystals. Smaller body in extreme southwest part of map is poorly mapped but is distinguished from the Idaho batholith by K2O>Na2O, <400 ppm Sr, and well-developed perthite. It has been mapped only in the Ranger Peak area on the Idaho side of the state line (Lewis et al. 1992b) and is projected into Montana on the basis of geochemical analyses (samples IG32A, IG33A, and IG37A) of Shuster and Bickford (1985).'
714|'Well-foliated and well-lineated mylonite along the front of the Bitterroot Range. Rocks have a granitic protolith south of Bass Creek and a metasedimentary protolith to the north. Movement is down-to-the-east based on shear-sense indicators (Hyndman et al. 1975; Hyndman and Myers 1988).'
715|'Primarily medium-grained, nonfoliated biotite granodiorite but also includes fine-grained biotite granodiorite, hornblende-biotite granodiorite, tonalite, and quartz diorite, some of which is foliated. These rocks, previously mapped as the Skookum Butte stock (Nold 1968, 1974), almost certainly represent more than one period of intrusion. Granodiorite in the west in the Sally Basin area is characterized by euhedral biotite crystals, interstitial potassium feldspar and quartz, and a relatively narrow zone of contact metamorphism. These features suggest shallow emplacement levels and a probable Eocene age. More nearly equigranular rocks at Skookum Butte are similar in appearance to Cretaceous granodiorite of the Idaho batholith. Rocks in the central part of the unit weather to large boulders that, although they resemble glacial deposits, are probably in situ.'
716|'Fine-grained diorite and gabbro consisting of plagioclase, hornblende, and pyroxene. Typically occurs as thin dikes and sills, but also present as larger masses.'
717|'Foliated and nonfoliated fine- to medium-grained (muscovite-) biotite granodiorite. Includes rocks mapped as granitic sheets by Wehrenberg (1971). Largest mass in the southern part of the area is part of the Idaho batholith, and there it contains zones with megacrystic potassium feldspar (Chase 1973; Shuster and Bickford 1985). The batholith in general is characterized by Na2O>K2O, except where megacrystic, in which case K2O exceeds Na2O. The age of the batholith in this area is uncertain, in part due to inheritance of Precambrian zircon and the possible disturbance of the U-Pb system during Eocene mylonitic deformation (see discussions in Bickford et al. 1981; Shuster and Bickford 1985; and Foster and Fanning 1997). Three U-Pb zircon ages of 69 to 75 Ma (Shuster and Bickford 1985; Toth and Stacey 1992) from along the Lochsa River west of the map area are probably the best age estimate for the Kgd unit. Samples near and in the mylonite zone give Eocene U-Pb zircon ages (Chase et al. 1983; Foster and Fanning 1997).'
718|'Foliated, medium-grained, biotite- and hornblende-biotite tonalite and granodiorite. Sphene fission track ages of 81 and 85 Ma from similar rocks just west of the map area (Ferguson 1975) provide the best age estimates for this unit.'
719|'Described by Hall (1969) as interbedded silty dolomite, dolomitic siltstone, and green shale (Dry Creek Shale Member) overlain by interlaminated limestone and siltstone (Sage Member). The Sage Member is nodular and composed of distinctive gray micritic mottles that weather recessively within a groundmass of darker, more resistant silt and dolomite (Winston 1998). Thickness 300-373 ft (92-114 m).'
720|'Hall (1969) describes unit as cliff-forming, medium- to coarsely-crystalline, gray dolomite. Contains lenses, stringers, and irregular patches of chert. Thickness 1,860-2,000 ft (570-610 m).'
721|'Hall (1969) reports a limestone member, consisting of gray, orange-mottled limestone, local brown calcareous siltstone, and green shale, and a shale and glauconitic sandstone member consisting of interbedded green shale and greenish-gray glauconitic sandstone. Thickness 465 ft (142 m).'
722|'Vitreous quartzite. Not mapped by Hall (1969), who showed all quartzite below the Silver Hill as Pilcher Quartzite. Projected into area based on mapping to the north by Wells (1974), who estimated the thickness to be 40-100 ft (12-31 m). According to Winston (1998) the Flathead in the Missoula area is only 10-20 ft (3-6 m) thick and composed of green, glauconitic quartzose sandstone with tracks and trails.'
723|'Massive to foliated, light-gray, medium-grained anorthosite. Berg (1965) speculated that the anorthosite bodies were residual from a melting event rather than intrusive in origin, in which case a Cretaceous age would be more likely than Proterozoic.'
724|'Coarse- to medium-grained, reddish or buff quartzite containing thin beds of sandy argillite as well as detrital muscovite. Characterized by trough cross-beds with distinctive alternating purple and light gray cross laminae (Winston 1998). Thickness uncertain, but 350-400 ft (110-120 m). Probably remains below the unconformity with the overlying Flathead Quartzite.'
725|'Tan-weathering, grayish-green micaceous quartzite and impure argillite. Thickness was probably on the order of 3,000 ft (920 m) in the area based on estimates from adjoining areas (Hall 1969), but a complete section is no longer present.'
726|'Red and green interbedded argillite and siltite, and buff quartzite. Contains distinctive green and red chert beds and clasts. Mudcracked, rippled and even silt and fine sand to clay couplets are common; less common are horizontally laminated sand beds (Winston 1998). Thickness in the map area is uncertain but probably on the order of 2,000-3,000 ft (610-915 m).'
727|'Pink or buff, medium- and coarse-grained feldspathic quartzite. Matrix-supported granules and pebbles present locally. Abundant trough cross-beds. Contains 15 to 25% potassium feldspar, but only trace amounts of plagioclase. Thickness in the map area is uncertain, but probably on the order of 1,000-2,000 ft (300-610 m).'
728|'Quartzite and subordinate argillite and siltite in lower part of section. Upper part is predominantly argillite and siltite. Typical reddish color is bleached out to light gray in the Fish Creek drainage, probably as a result of metamorphism and (or) hydrothermal alteration. Exposures do not permit subdividing the unit in this area.'
729|'Reddish argillite and siltite with lesser amounts of green siltite and argillite and thin-bedded quartzite. Thin dolomitic zone in uppermost part of section. Contains salt casts that are otherwise rare in the Belt Supergroup. Thickness is uncertain but probably on the order of 2,000-2,500 ft (610-760 m).'
730|'Reddish very fine- to medium-grained quartzite and lesser amounts of argillite and siltite. Thin layers of dolomitic rock present locally. Abundant planar laminations and ripple cross laminations. Upper 200 ft (61 m) of section are the coarsest, and can be difficult to distinguish from the Bonner Quartzite. Sampling in the northern part of the area indicates subequal amounts of plagioclase and potassium feldspar (25-35% total) in contrast to the plagioclase-poor Bonner Quartzite. Hall (1969) measured a section of member 2 on Petty Mountain, which at the time was thought to be Bonner Quartzite. A total thickness of 900 ft (275 m) was determined. Mount Shields member 1 was not recognized in the Missoula West quadrangle, but is present to the east in the northern part of the Butte 1 x 2 degree quadrangle (Slover and Winston 1986).'
731|'Green microlaminated argillite, and thin lenticular beds of green dolomitic siltite and fine-grained quartzite. Dolomitic beds have characteristic orange-brown weathering rinds. Uppermost part is a distinctive pinkish-red, thinly bedded dolomitic quartzite and siltite. Abundant load casts and ripple marks. Poorly exposed and easily missed when mapping. Unit has formed calc-silicate rocks next to the Lolo Hot Springs batholith and contains scapolite in the Kid Lake area. Included in the uppermost part of the Miller Peak Formation by previous mappers in the Missoula area (Nelson and Dobell 1961). Section of the Miller Peak Formation measured by Hall (1969) on Petty Mountain included approximately 850 ft (260 m) of the Shepard Formation, but this part of section was poorly exposed. Unit appears thicker west of Petty Creek.'
732|'Green and red argillite and siltite in the lower and middle parts of the section. Uppermost 200 ft (61 m) of section is reddish quartzite that is difficult to distinguish from member 2 of the Mount Shields Formation. Abundant straight-sided mud cracks in lower part of section. Hall (1969) measured a section on Petty Mountain that was assigned at that time to the lower part of the Miller Peak Formation. The Snowslip in that section is 2,975 ft (910 m) thick.'
733|'Primarily carbonate-bearing rocks of the middle member of the Wallace Formation but may include green siltite and argillite of the lower member along the lower part of Lolo Creek.'
734|'Green, diopside- and hornblende-rich rocks that are interlayered with thin quartzitic beds forming a calc-silicate gneiss (Nold 1968). Unit results from metamorphism of the middle member of the Wallace Formation (Ywm). More resistant to weathering than Ywm.'
735|'Dolomitic and calcareous siltite and quartzite, and black argillite. Minor amounts of green siltite and argillite. Quartzite beds show evidence of scour, along with hummocky cross stratification. Some quartzite is carbonate free. Tan-weathering dolomitic siltite with black argillite caps ("black and tan" rock type) is common. Unit is scapolite-bearing in the extreme western part of the area. Presence of black argillite and abundant calcite distinguishes these rocks from the Shepard Formation. Vertical fractures in quartzite are common, as are "birdsfoot" cracks on argillite surfaces. Orange-weathering dolomite-rich sedimentary breccia is present within the middle member. Clasts are predominantly white quartzite and range in size from less than a centimeter to several meters. Thickness of middle member highly uncertain, but probably on the order of 2,500-4,500 ft (760-1,370 m). No upper member of the Wallace Formation was mapped in this area, unlike in the Coeur dAlene Mining District to the west. The upper member there is probably a lateral equivalent to the Snowslip and Shepard formations mapped in this study.'
736|'Green siltite and light green argillite predominate, typically with carbonate pods, but includes dolomitic siltite and quartzite. Bedding typically cyclical, with thin carbonate beds at the top of each cycle. Lower and middle parts are thinly bedded and the least quartzitic, and are probably lateral equivalents of the Empire Formation mapped just north of the area by Wells (1974). Thickness highly uncertain, but probably on the order of 3,000-5,000 ft (900-1500 m).'
737|'Highly recrystallized quartzite and lesser amounts of phyllite and schist. These rocks are along strike with rocks of the Mount Shields Formation and were considered metamorphosed equivalents of the Mount Shields by C. Wallace and Lidke (1991). Previous workers assigned them to the Ravalli Group (Wehrenberg 1971; Winston 1991). Because these rocks are at structurally low levels, they are probably Ravalli Group equivalent.'
738|'Gray-weathering, well-layered, quartz-rich feldspathic gneiss. Unit contains areas of unmapped granitic sills and dikes. Quartz content averages 51% and biotite 13% in the southwest part of the area (Chase 1973), where the rock clearly had a sedimentary protolith. Williams (1976) reports a lower quartz content (average 32%) for the Bass Lake area, and there the unit may include unmapped granitic rock. Includes the gray-weathering gneiss units of Anderson (1959) and Wehrenberg (1971). Chase (1977) correlates these rocks with the Ravalli Group of the Belt Supergroup, but previous assignments to the Prichard Formation (Anderson 1959; Wehrenberg 1971; Chase 1973) are more likely given the overall lack of quartzite in the unit.'
739|'Brown-weathering biotite- and muscovite-biotite schist, biotite-sillimanite gneiss, muscovite-biotite quartzite, and minor calc-silicate rocks. Quartz content averages 38%, biotite 24%, and sillimanite 12% in the southern part of the area (Anderson 1959; Chase 1973). Typically has feldspar augen, and contains an abundance of unmapped granitic sills and dikes, as well as minor amounts of garnet amphibolite (metamorphosed mafic sills). Increasing amounts of gneiss and igneous material southward. Calc-silicate rocks are present along Kootenai Creek one mile west of the range front. Includes rocks mapped as the brown-weathering gneiss of Wehrenberg (1971), pelitic schist of Williams (1976), and sillimanite gneiss of Anderson (1959) and Berg (1965). Previous workers have correlated these rocks to the Prichard Formation of the Belt Supergroup, at present considered the most likely protolith.'
925|'Gravel, sand, and silt deposited in modern channel or on present flood plain (tf).'
926|'Unsorted landslide debris (tf)'
927|'Gravel and sand, typically at or near present alluvial channel level (tf).'
929|'Quaternary-Tertiary sediments, undifferentiated.'
930|'Gravel and sand deposits, primarily above present alluvial channel levels (tf).'
931|'Upper greenstone facies; lower unit includes calcareous shale, siliceous limestone, argillite, and phyllite.'
932|'Light to medium gray and black massive and thin units of limestone, marble, phyllite, and sandstone.'
933|'Light gray to black, coarse marble and limestone, some quartzitic sandstone, argillite, phyllite, and chloritic schist, with basal conglomerate.'
934|
935|'Occasional phenocrysts of plagioclase and rare olivine.'
936|'Aphyric, dense, fine-grained basalt.'
937|'Phyric, coarse-grained basalt with large plagioclase and olivine phenocrysts.'
938|'Dark, fine-grained vesicular basalt.'
939|'Dikes of granitic composition (tf).'
940|'Light pink to gray rhyolite and dark purple to black volcanic breccia; contains xenoliths of older metamorphic and igneous rocks.'
941|'"Bovill" syenite (may be related to Potato Hill Volcanics or Gold Hill syenite).'
942|'Gray to reddish vesicular andesites.'
943|'Light gray quartz latite; contains widely spaced glassy bands.'
944|'Gray, medium- to coarse-grained rock with biotite and hornblende.'
945|'Gray to reddish, fine- to coarse-grained rock.'
946|'Coarse-grained rock with hornblende and biotite.'
947|'Medium-grained foliated rock containing biotite.'
948|'Coarse-grained plagioclase-hornblende rock.'
949|
950|'Moderately weathered hornblende syenite.'
951|'Biotite-hornblende-plagioclase quartz dioritic orthogneiss.'
952|'Coarse- to medium-grained hornblende-plagioclase-epidote rock.'
953|'Green to grayish green metamorphosed complex of lava flows, pyroclastics, and calcareous and noncalcareous sedimentary rocks.'
954|'Dark, well-foliated, medium-grained plagioclase-hornblende rocks.'
955|'Medium gray to olive-colored, thin-bedded siltite (which produces a soil similar to loess).'
956|'Vitreous quartzite which includes feldspathic quartzite with micaceous sheen.'
957|'Coarse-grained, garnet-mica schist.'
958|'Diopside gneiss, biotite gneiss, and biotite quartzite interbedded with schist.'
959|'Libby Formation through Prichard Formation, undifferentiated.'
960|'Medium- to coarse-grained garnet-mica schist.'
961|'Thick-bedded, coarse- to medium-grained pure quartzite with thin micaceous laminae.'
962|'Gray, coarse- to medium-grained garnet-mica schist.'
963|'Micaceous, medium-grained granular quartzite interbedded with schist.'
964|'Coarse-grained, garnet-mica schist; diopside gneiss; biotite gneiss; and biotite quartzite interbedded with schist..'
971|
975|'Stream deposits primarily of silt, sand, and gravel in floodplains, terraces, and valley bottoms.  Locally the unit includes lacustrine, paludal, and eolian deposits in depressions.'
976|'Brown to yellow-brown fibrous peat, sedimentary peat, and muck present in flatlands near lakes. Peat is locally mixed with sand and silt and mixed or interbedded with one or two medium to thin beds of volcanic ash.  The peat was mapped by Rigg (1958) at the southern end of Liberty Lake, the northwestern edge of Newman Lake, in Saltese Flat, the south end of Bailey Lake, and around Little Trout Lake.  Only larger deposits are shown on Plate 1.'
977|'Active and stabilized dunes of predominantly fine to medium sand; mostly composed of quartz and basalt grains reworked from older sedimentary rocks (Kiver and others, 1979).'
978|'Unstratified and poorly sorted clay, silt, sand, and gravel deposited by rotational and translational slides and flows (Kiver and others, 1979).  Slides are generally restricted to the sides of the "prairies and bluffs" and are as much as several kilometers in length, and some are more than 1.5 km across.  Some slides contain individual blocks of basalt that are nearly 8 m in diameter.  Well logs show that the Latah Formation generally underlies the slides.  Most slides are covered with or partially buried by Pleistocene flood deposits (Qfg) and appear to be late Pleistocene in age.  A few slides, such as along Deep Creek, have been active in historic time (Griggs, 1976). '
979|'Light- to medium-brown, unstratified, eolian silt, clay, sand, and ash.  The unit contains 5 percent sand, 60 percent silt, and 35 percent clay.  Clay is mostly montmorillonite and illite in a ratio of 3:1; it also contains minor kaolinite.  The sand and silt fraction is composed of angular quartz grains and lesser amounts of feldspar and muscovite.  Heavy minerals include limonite, monazite, tourmaline, hornblende, garnet, epidote, and apatite.  The loess mantles the Columbia River basalt and is most common on the tops of low hills and plateaus where erosion by water has been minimal.  The loess is as thick as 23 m in Spokane County; it averages 6 m thick south of the Spokane River and thins to the north where there is more topographic relief (Hosterman, 1969).

Evidence for several episodes of loess deposition comes from exposures in the Washtucna area in the Connell 1:100,000-scale quadrangle.  Near Washtucna, buried paleosols with negative magnetic polarity are interstratified with loess that is interbedded with flood gravel.  The polarity indicates the loess there was deposited prior to 790 ka (McDonald and Busacca, 1988).  Near Washtucna, the presence of younger loess is indicated by an interbed of set C tephra from Mount St. Helens dated at 36 ka (McDonald and Busacca, 1988) and loess blanketed by 7 ka Mount Mazama tephra (Foley, 1982).'
980|'Light-gray, friable, poorly bedded, fine sand, silt, and clay deposited in pre-late Wisconsin Lake Spokane (Kiver and others, 1989; Weissenborn and Weis, 1976; Weis, 1968).  This unit, as mapped, includes some Holocene deposits along Liberty Creek and Saltese Flat (Weis, 1968).'
981|'Till, outwash, and ice-contact stratified deposits in moraines, till plains, and meltwater channels and terraces deposited during the last glacial advance.  The unit is generally restricted to the Chamokane Creek valley (Kiver and others, 1979).'
982|'Poorly sorted, stratified mixture of boulders, cobbles, gravel, and sand resulting from multiple episodes of catastrophic outbursts from glacier-dammed lakes, such as glacial Lake Missoula.  The Spokane Valley was one of the main channelways for outburst flood waters from glacial Lake Missoula which inundated much of the present Clark Fork River drainage in Montana and Idaho.  Floods flowed from the Spokane Valley through the Cheney Palouse Scabland tract to the Columbia Basin.  Flood waters also traveled north of Mount Spokane through the Hillyard trough to the Little Spokane and Spokane Rivers (Molenaar, 1988).  The upper elevation of effective erosion by flood water in the Spokane Valley was more than 800 m near Dishman (Kiver and Stradling, 1989).

Radiocarbon dating and paleomagnetic measurements indicate that flood deposits are late Wisconsin and pre-late Wisconsin in age.  Examination of graded couplets in flood deposits in the Spokane quadrangle and elsewhere led Waitt (1985) to the interpretation that in excess of 40 flood episodes took place during the late Wisconsin.  Waitt (1985) has estimated that glacial Lake Missoula existed for 2,000 to 2,500 years, between 15,300 and 12,700 yr B.P.  A giant ripple field near Airway Heights contains Mount St. Helens ash in the troughs of dunes overlain by flood gravel, indicating that one or more floods occurred at about 13,000 ka (Kiver and others, 1989).  Tephra correlation and accelerated radiocarbon dating near Washtucna show that some of the pre-late Wisconsin floods occurred at 40 ka (McDonald and Busacca, 1988, 1989).  On the basis of paleomagnetic measurements on interbedded loess, McDonald and Busacca (1989) suggest that more than five episodes of flooding occurred prior to 790 ka in the Cheney Palouse Scabland tract.

In the Acme gravel pit in the Spokane Valley, flood deposits consist of cobble- to boulder-size (to 3 m long) clasts; large-scale, west-dipping foreset beds are 5 to 6 m thick and are overlain by a lag deposit of horizontally bedded sand and gravel (Kiver and Stradling, 1989).  In a pit near Barker Road in the Spokane Valley, rhythmic bedding from lower energy flood waters in a relatively protected site are exposed.  Each set of rhythmites consists of coarse, poorly bedded, pebbly sand disconformably overlain by well-bedded, fine sand.  Pebbles and rip-up clasts of Pleistocene lake deposits and Miocene Latah Formation are present near the base of each coarse sand unit (Kiver and Stradling, 1989).'
983|'Glaciolacustrine deposits containing silt and clay couplets interbedded with coarser clastic deposits of catastrophic floods.  The deposits are generally restricted to Latah Creek and the lower Spokane River.  Along Latah Creek, 1.5- to 5-m-thick units of cyclic, upward-fining and -thinning sequences containing coarse clastic sediments are interbedded with 2-cm- to 20-cm-thick beds of varve-like, fine-laminated clay and silt couplets. The sand- to granule-size fragments in the coarse-grained material are chiefly composed of metamorphic rocks and lesser amounts of basalt, plutonic rocks, and quartz grains; pebble- to boulder-size clasts (to 106 cm in diameter) are similar in composition to the sand- and granule-size fragments and include clasts of semiconsolidated material, some of which is recognizable as Latah Formation.  Unconformably overlying and incised into the cyclic sediments is a 7- to 9-m-thick, cut-and-fill channel filled with coarse gravel. Generally above the gravel are cyclic, upward-fining and -thinning, rhythmically bedded, buff-colored, sand and silt-rich units which are similar to the Touchet beds in southern Washington.  The sequence is overlain by Mazama ash that is radiocarbon dated at 6,700 ka (Rigby, 1982).

Rigby (1982) concluded that the sediments below the unconformity are turbidites generated by catastrophic floods from glacial Lake Missoula and deposited into a lake that was present in the Latah Creek area from 37 ka to 18 ka.  Sediments above the unconformityare thought by Rigby (1982) to be slackwater deposits derived from pulses of catastrophic floodwaters surging upstream from the Little Spokane River between approximately 17 ka and 13 ka.'
984|'Well-indurated, manganese- and iron-cemented conglomerate that is present 14 km north of Wellpinit.  The conglomerate overlies horizontal beds of arkosic sand that also contain manganese and iron cements.  The conglomerate contains as much as 0.023 percent U2O3 in the matrix (Ingersoll and others, 1980).  Directly to the north in the Chewelah 1:100,000-scale quadrangle, the unit overlies the rocks of the Columbia River Basalt Group (F. K. Miller, USGS, oral commun., 1988 in Waggoner, 1990).'
985|'Fine- to coarse-grained, aphyric basalt flows of reversed magnetic polarity (Swanson and others, 1979).  They generally contain fine phenocrysts of plagioclase and olivine.  The basalt is of the Rosalia chemical type and has higher titanium and lower magnesium and chromium contents than other flows of the Wanapum Basalt (Wright and others, 1989).  The unit overlies and is commonly invasive into the lakebed sediments of the Latah Formation or overlies the Grand Ronde Basalt N2 unit.  Flows of the Priest Rapids Member are thought to have been extruded between 15.3 and 14.5 Ma (Reidel and Fecht, 1987).  This unit includes the "Rim rock" flows of Pardee and Bryan (1926).'
986|'Upper flows of the Grande Ronde Basalt, of normal magnetic polarity.  The basalt is aphyric to sparsely phyric and contains minor amounts of small plagioclase laths.  The flows, which are commonly pillowed, are as much as 50 m thick, but are generally 15 to 25 m thick.  Flows of the Grande Ronde Basalt are thought to have been extruded between 15.6 and 16.5 Ma (Reidel and Fecht, 1987), and they overlie pre-Tertiary rock in the Spokane quadrangle.  The Grande Ronde Basalt makes up the "Valley flows" of Pardee and Bryan (1926).  The base of the basalt reportedly was penetrated at about 130 m below the valley floor in the well at the Davenport Hotel in downtown Spokane (Griggs, 1976).'
987|'Gray to tan to yellow-orange siltstone, claystone, and minor sandstone named by Pardee and Bryan (1926) for lacustrine and fluvial deposits along Latah Creek.  Kirkham and Johnson (1929) suggested extending the formation name west to Grand Coulee; however, Griggs (1976) has suggested that the name Latah be restricted to the drainage of the Spokane River, as originally intended by Pardee and Bryan (1926).

Pardee and Bryan (1926) included in the Latah Formation both the sediments interbedded with the Miocene Columbia River Basalt Group and the 305 meters of sediments below the base of the basalt in the Latah-Texas well near the mouth of Latah Creek.  They also include the 73 meters of sediment below the lowest basalt in the well at the Davenport Hotel (Pardee and Bryan, 1926).  A large part of the exposure of the Latah Formation is located between flows of the Grande Ronde Basalt and the Priest Rapids Member.

Floral assemblages in the Latah Formation indicate a Miocene age (Knowlton, 1926).  More than 95 forms make up the floras in the Spokane and Coeur d''Alene areas.  These include well-preserved species of Ginkgo, Sequoia, Taxodium, Populus, Castanea, Quercus, Ulmus, and Acer.'
988|'Medium- to thick-bedded, fine-grained, muscovite-bearing quartzite to silty quartzite that contains minor chlorite, and thin-bedded, light- to dark-gray, quartz-rich phyllite and muscovite schist that also includes minor biotite.  These rocks are contiguous with the unit of metasedimentary rocks of uncertain age mapped by Becraft and Weis (1963) to the west on the Turtle Lake 15'' quadrangle (Coulee Dam 1:100,000-scale quadrangle).  The rocks mapped by Becraft and Weis (1963) appear to be thicker than those generally exposed in the lower Paleozoic sequence in this part of northeastern Washington, suggesting a Precambrian age.  However, in the Coulee Dam 1:100,000-scale quadrangle, the unit contains a thick section of calcite-bearing marbles; carbonate rock in the Precambrian section is generally dolomitic.  Because of the uncertainty in the age of the rock and the lithologies present, this unit is probably Cambrian or Middle Proterozoic (Precambrian Y) in age.'
989|'Medium- to thick-bedded, white to light-gray, fine-grained, vitreous quartzite that contains authigenic feldspar.  The quartzite is interbedded with medium- to thin-bedded buff and light-green siltite.  This poorly exposed unit is most probably Precambrian Y in age; however, it could be part of the Cambrian-Precambrian Z Addy Quartzite.'
990|'White to light-gray, thick-bedded quartzite, pebbly quartzite, and medium- to dark-gray, thin-bedded siltite.  Pebble-bearing quartzite is present on Fancher Butte and Booth Hill. The pebbles are 3- to 6-mm-long, white and blue, opaque, rounded to subrounded quartz clasts that define bedding in the quartzite.  Larger pebbles, as much as 25 mm long, are composed of purplish and pinkish quartzite and constitute as much as 50 percent of the pebbly quartzite.  On the western hill of Fancher Butte medium- to dark-gray, thin-bedded, thin- to very thin laminated siltite and minor quartzite are present as float.  Quartzite on Fancher Butte and Booth Hill could be the Addy Quartzite, but it is most likely part of the Buffalo Hump Formation.  The thickness of this unit in the Spokane quadrangle can not be accurately estimated because of poor exposure and probable structural complexities.'
991|'White to light-gray, medium- to thick-bedded, medium- to coarse-grained, grain-supported quartzite interbedded with medium- to thin-bedded muscovite-biotite schist.  The unit is exposed as isolated outcrops on ridge tops and in small drainages in the northwest part of the map area.  This quartzite locally contains minor disseminated pyrite, muscovite, and chlorite.  The unit is most likely part of the Buffalo Hump or Togo Formations of the Deer Trail Group, but it could be part of the Cambrian-Precambrian Z Addy Quartzite.  Outcrops of the quartzite are too scattered to permit accurate thickness estimates.'
992|'Medium- to dark-gray argillite interlaminated with tan, light-gray and white siltite to quartzite laminae that crops out on Magnison Butte and Hanning Butte.  Bedding thickness ranges from laminations on the sub-millimeter scale to fining-upward couplets as thick as 30 mm.  Even parallel laminations and soft-sediment deformation are common.  The McHale Slate in the Spokane quadrangle appears to be similar to the lower 100 to 120 m of the formation as described by Miller and Whipple (1989) in the Chewelah 1:100,000-scale quadrangle.  The unit exhibits weak cleavage.'
993|'Calc-silicate, hornfels, calcite- and epidote-cemented quartzite, gray fissile argillite, phyllite, mica schist, and quartz-plagioclase-biotite gneiss that is present near Medical Lake.  Original lithologies were probably similar to those of rocks mapped as the lower Wallace Formation by Griggs (1973) in the Rosalia 1:100,000-scale quadrangle. There, the upper part of the unit consists of couplets of black argillite and light-gray to greenish-gray siltite, and medium- to thick-bedded carbonate-bearing quartzite.'
994|'Quartzite, silty quartzite, schist, and siltite present south and west of Spokane (Griggs, 1973).  The unit is dominantly vitreous, medium- to coarse-grained, white to light-gray, medium- to thick-bedded quartzite and interbeds of quartz-biotite-muscovite schist.  The quartzite contains as much as 10 percent authigenic feldspar.  The unit is generally thermally upgraded south of Spokane and near Cheney; greenschist-facies rocks are present immediately west of State Route 195.  The contact relation with older gneiss is undefined.  On Krell Hill, the contact of the heterogeneous metamorphic rocks (PChm) with the Ravalli Group is obliterated by the intrusion of a body of alaskite (TKiaa).  This contact, however, is likely a fault, as rocks of different metamorphic grade and probable age are in juxtaposition.  Outcrops of the quartzite abruptly terminate at the drainage south of Browns Mountain, suggesting a possible structural contact with the higher grade rocks there.  The maximum thickness of the unit south of Spokane is 1,200 m.'
995|'Light- to dark-gray hypabyssal, porphyritic dikes generally in the northern and western part of the map area.  The fine-grained matrix is composed of feldspar, quartz, hornblende, and biotite.  Phenocrysts include hornblende (as much as 0.5 cm long), subhedral biotite, plagioclase (as much as 1 cm long), and minor K-feldspar (Miller, 1974c).  A dike that has a similar mineralogy on the Chewelah 1:100,000-scale quadrangle northeast of Elk yielded a K-Ar age of 47.31.6 Ma on hornblende and 46.81.4 Ma on biotite (Miller, 1974c).'
996|'Lineated (nearly east-west lineation) and foliated, medium- to coarse-grained, biotite-hornblende monzodiorite to granodiorite.  The unit is present west of Tumtum and near Medical Lake.  West of Tumtum the unit is characterized by:  aligned, euhedral, black hornblende; pink and white poikilitic K-feldspar phenocrysts aligned subparallel to the hornblende; and abundant wispy mafic xenoliths.  The biotite to hornblende ratio is 1:2; hornblende commonly has pyroxene cores.  The rock contains 1 to 2 percent titanite.

Near Medical Lake the unit includes leucocratic, medium-grained, equigranular to porphyritic, foliated and lineated diorite to granodiorite that has macroscopic mineralogy and fabric similar to the rock near Tumtum.  The rock at Medical Lake contains subhedral quartz that is interstitial to feldspar, anhedral plagioclase, white euhedral to subhedral K-feldspar, subhedral black biotite which is associated with pyrite, and hornblende as euhedral phenocrysts and/or in clots with pyroxene cores.  The rock contains accessory magnetite and abundant titanite.  Schlieren is locally present.

The unit near Tumtum is thought by F. K. Miller (USGS, oral commun., 1989) to be similar to the border phase of the Silver Point Quartz Monzonite in the Chewelah 1:100,000-scale quadrangle.  North of the Spokane River, the unit is cut by brittlely deformed alaskite pegmatite dikes which cut across the fabric in the monzodiorite and cement a breccia that contains fragments of a deformed monzodiorite that is well exposed in NE1/4 sec. 16, T. 27 N., R. 40 E.  The contact of the intrusive rock near Tumtum with the Silver Point Quartz Monzonite is generally gradational.  South of the Spokane River, the unit is probably in fault contact with the biotite-bearing intrusive rock near Four Mound Prairie.'
997|'Leucocratic (color index 14-21), coarse-grained, porphyritic hornblende-biotite quartz monzonite that is present on Scoop Mountain.  The formation was named by Miller and Clark (1975) for exposures near Silver Point on Loon Lake in the Chewelah 1:100,000-scale quadrangle.  The groundmass has a characteristic bimodal texture and consists of K-feldspar, quartz, hornblende, biotite, and plagioclase; K-feldspar and quartz are coarser grained than the other constituents in the matrix.  Biotite is more common in the fine-grained phase of the groundmass than in the coarse-grained part.  Microperthitic orthoclase phenocrysts are 6 to 37 mm in length and make up 1 to 5 percent of the rock.  Quartz is interstitial to other minerals.  Hornblende is subhedral to euhedral, has a long dimension as much as 10 mm, and is associated with biotite.  The hornblende to biotite ratio is consistently .75:1.  Titanite is the most common accessory mineral, followed by magnetite, apatite, zircon, and rare allanite (Miller and Clark, 1975).  The pluton is generally massive, but it is foliated in Rail Canyon parallel to the contact with the biotite-bearing intrusive rock in Corkscrew Canyon (TKiac) and foliated near the contact with the biotite-hornblende-bearing intrusive rock near Tumtum.  The Silver Point unit is cut by north-northwest-trending, biotite-chlorite-silica-bearing zones that display cataclasis (Miller and Clark, 1975).  Two samples from the localities in the Chewelah 1:100,000-scale quadrangle returned whole-rock Rb-Sr ages of 394 Ma and 462 Ma (Armstrong and others, 1987).  Recalculated K-Ar ages on rocks from the Chewelah 1:100,000-scale quadrangle are 51 Ma on biotite and 62 Ma on hornblende (Miller and Clark, 1975).  The initial 87Sr/86Sr ratio of 0.70630.0002 from the pluton was the lowest found by Armstrong and others (1987) after studying several plutons in the area.  Armstrong and others (1987) suggest that the low initial isotope ratios confirm that the pluton has an Eocene age and not a reset Cretaceous age.'
998|'Massive to very weakly foliated, leucocratic, fine- to medium-grained, equigranular, muscovite-biotite quartz monzonite to granite that forms small plutons and dikes that sharply cut the foliation of the older mylonitic rocks.  The unit was named by Rhodes and Hyndman (1984) for exposures on Mount Rathdrum in Idaho and is present in the Spokane quadrangle near Hauser and Newman Lakes.  The granite contains quartz, K-feldspar, plagioclase containing myrmekitic intergrowths, biotite, and minor muscovite (Weissenborn and Weis, 1976).  The bodies are intruded along the axis of the south-plunging Spokane dome of the Priest River complex.  Larger bodies of this intrusive unit are generally massive, whereas dikes commonly have structural fabric.  Dikes of Mount Rathdrum granite commonly dip 10o to 15o more steeply to the west than mylonitic foliation of the enclosing metamorphic rock.  Partings in the dikes display moderate to strong slickenside-like lineation parallel to the N. 70o E. lineation in the mylonitic rocks of the Hauser Lake Gneiss (Rhodes and Hyndman, 1984).

Preliminary discordant U-Pb geochronology from undeformed samples suggest a minimum early Eocene (52 Ma) age for the pluton (Bickford and others, 1985).  Rhodes and Hyndman (1984) suggest that the granite is a late synkinematic rock intruded during mylonitic deformation associated with the Priest River complex, and thus it experienced only a small increment of the total strain.  Dikes and sills which cooled more rapidly exhibit more deformation and likely cooled before the last movement along the mylonite zone (Rhodes and others, 1989).'
999|'Discontinuous sill- and dike-like bodies of alaskite, pegmatite, aplite, and fine- to coarse-grained quartz monzonite.  This unit consists of quartz, K-feldspar, plagioclase, muscovite, and minor red subhedral garnet; it locally contains minor biotite.

Leucocratic, white to tan alaskite intrudes and is gradational with the biotite-muscovite-bearing Mount Spokane granite.  This alaskite consists of medium- to coarse-grained quartz, megacrystic K-feldspar, plagioclase, and muscovite; biotite is absent except near intrusive contacts.  Accessory minerals include garnet, apatite, zircon, and monazite.  Pegmatite and graphic intergrowths are common (Weissenborn and Weis, 1976; Weis, 1968).  As mapped, the alaskite unit locally includes outcrops of the Mount Spokane granite. Autunite and meta-autunite are present as fracture coatings and solid masses of crystals on alaskite on the west side of Mount Kit Carson.  A total of 90,000 lb of U3O8 were produced from nine properties; most of the ore came from the Daybreak mine (Weissenborn and Weis, 1976).

The unit includes alaskite, pegmatite, and quartz monzonite that intrudes the heterogeneous metamorphic rocks (PChm) and metasedimentary rocks of the Ravalli Group (Ymsr) on Krell Ridge.  Alaskite pegmatite with K-feldspar megacrysts (to 15 cm in length) generally has no fabric on Krell Hill; however, biotite, where present, is commonly clotted.  The alaskite is intruded parallel to subparallel to the foliation in quartzite and gneiss of the heterogeneous metamorphic rocks, with local stoping.  On Krell Ridge, the body forms small resistant knobs and is present along the contact, a probable fault, between the high-grade metamorphic rocks and the metasedimentary rocks of the Ravalli Group.

Brittlely deformed alaskite cements breccia and stopes intrusive rocks on the east side of Chamokane Creek from the north border of the map area to near the Spokane River.  In NE1/4 sec. 16, T. 27 N., R. 40 E., at the petroglyph site, the brittlely deformed alaskite is well exposed, cementing a breccia of and assimilating the foliated and lineated orthogneiss near Tumtum, which is of probable Eocene age.  Thin (0.1-1 m), light-colored bands of mylonite that cut the Newman Lake Gneiss near the contact with the Mount Spokane granite on Beacon Hill probably had an alaskite parent.

Rb-Sr ages of alaskite from the Mount Spokane area range from 40 to 159 Ma (Armstrong and others, 1987; Table 1).'
1000|'Scattered bodies of undeformed, leucocratic, coarse-grained, equigranular to porphyritic, biotite granite to granodiorite at several localities in the Spokane quadrangle.  Some of these bodies are proximal to deformed plutons but are not themselves deformed, suggesting that they may be Eocene in age or not in the zone affected by mylonitization.

Near Griffith Springs, south of the Little Spokane River, the unit includes equigranular biotite granite to granodiorite. This body contains 20 to 30 percent white to lavender, anhedral quartz; 10 to 15 percent subhedral, interstitial black biotite; white K-feldspar; and plagioclase.  The intrusive rock is cut by garnet-bearing alaskite dikes, which are, in turn, cut by near-vertical lamprophyre dikes.  Minor chlorite and epidote are present on fractures.

Near Milan, leucocratic, equigranular, coarse-grained, biotite quartz monzonite to granite is present and is cut by alaskite pegmatite dikes.  The unit also includes coarse-grained, highly weathered, biotite granite containing white K-feldspar phenocrysts that crops out in the valley bottoms near Hangman Valley.'
1001|'Coarse-grained, equigranular to porphyritic, biotite quartz monzonite to granite east of Chamokane Creek.  Biotite is anhedral to clotted; lavender-gray quartz is anhedral; and K-feldspar phenocrysts are poikilitic.  The weathered intrusive rock is cut by brittlely deformed alaskite, pegmatite, and aplite dikes, which also locally cement breccia made up of blocks of the unit.  The biotite-bearing intrusive rock is foliated along the contact with the Silver Point Quartz Monzonite and the orthogneiss near Tumtum.  These rocks are possibly part of the body of leucocratic intrusive rock exposed south of the Spokane River (TKiaf).'
1002|'Leucocratic, coarse-grained, equigranular, biotite quartz monzonite to granite with trace to 1 percent isolated flakes of muscovite.  Quartz is present as light-gray, rounded grains in coarse-grained aggregates and pods.  The intrusive rock contains coarse grains and phenocrysts of white, twinned K-feldspar, 3 to 8 percent subhedral black biotite, and 1 percent magnetite as isolated grains.  The unit is megascopically similar to the alaskite, pegmatite, and aplite unit, except that the intrusive rock near Mud Creek has relatively increased biotite and decreased muscovite contents.  It is possibly a late-stage phase of the muscovite-biotite-bearing intrusive rock near the Little Spokane River.'
1003|'Massive to weakly foliated, leucocratic, medium- to coarse-grained, equigranular, biotite granite to quartz monzonite present south of the Spokane River on Four Mound Prairie.  As mapped, the unit probably includes more than one body, and it is possibly part of the biotite-bearing intrusive rock in Corkscrew Canyon (TKiac) on the north side of the Spokane River.  Light-gray quartz is present in clots or aggregates of crystals and is intergrown with K-feldspar.  White K-feldspar forms some phenocrysts and clots of phenocrysts.  Anhedral to subhedral, black biotite comprises 2 to 7 percent of the rock and generally is interstitial to other minerals.  The unit is cut by alaskite pegmatite dikes.  Outcrops east of Davis Lake (secs. 5 and 6, T. 26 N., R. 40 E.) are foliated and lineated and contain clotted and stretched quartz grains.'
1004|'Leucocratic, medium- to coarse-grained, locally porphyritic quartz monzonite to granite that is present near Round Mountain.  Similar rock was named by Becraft and Weis (1963) for exposures in the Coulee Dam 1:100,000-scale quadrangle to the west.  The intrusive rock contains 26 to 32 percent K-feldspar, 20 to 42 percent quartz, 26 to 32 percent plagioclase, 1 to 4 percent muscovite, and 0 to 3 percent biotite that is partially replaced by chlorite and muscovite.  K-feldspar, followed by quartz and plagioclase, are the dominant phenocrysts.  Quartz is anhedral and has a smoky color; subhedral to euhedral plagioclase is twinned.  Muscovite is present as inclusions within K-feldspar or as an alteration product of biotite and is associated with chlorite (Kinart, 1980).  Accessory minerals include magnetite (to 1%), apatite, fluorite, garnet, zircon, and monazite.  Alaskite and quartz porphyry comprise more than 10 percent of the pluton (Castor and others, 1982).  The average U3O8 content of this intrusive body is 19 ppm; the range is from 1 to 46 ppm.  Strong argillic alteration is locally present (Castor and others, 1982).  A U-Pb age of 75 Ma from zircon is reported from the Coulee Dam 1:100,000-scale quadrangle by Ludwig and others (1981).  Asmerom and others (1988) reported a Rb-Sr age of 74.73 Ma from samples taken in the Coulee Dam 1:100,000-scale quadrangle.'
1005|'Leucocratic, equigranular to porphyritic, medium- to coarse-grained granodiorite to monzogranite that crops out west of the Little Spokane River.  The granodiorite was named by Miller (1974c) for exposures near Fan Lake in the Chewelah 1:100,000-scale quadrangle.  The granodiorite contains zoned plagioclase of an intermediate composition, quartz, K-feldspar, biotite, and hornblende.  Euhedral hornblende phenocrysts are locally as much as 1 cm in length.  Accessory minerals include titanite, allanite, zircon, apatite, and opaque minerals.  Quartz and K-feldspar are interstitial to plagioclase and mafic minerals.  K-Ar ages are 95.14 Ma on hornblende and 93.42.6 Ma on biotite from the Fan Lake granodiorite in the Chewelah 1:100,000-scale quadrangle (Miller, 1974c).'
1006|'Leucocratic, massive, medium-grained, biotite-hornblende granodiorite that crops out south of Wellpinit.  The granodiorite contains 25 to 30 percent quartz; 35 to 40 percent subhedral, zoned plagioclase (An40-55); 10 to 15 percent interstitial K-feldspar; 7 to 15 percent euhedral biotite in laths 2 to 5 mm long; and 7 to 12 percent subhedral to euhedral hornblende.  Mafic minerals are partially altered to chlorite.  Accessory minerals include titanite, apatite, magnetite, and zircon (Becraft and Weis, 1963).  The body is cut by hypabyssal hornblende-biotite dacite dikes and alaskite, pegmatite, and aplite dikes.  Three Pb-a ages ranging from 9510 Ma to 10510 Ma were obtained by Becraft and Weis (1963) from exposures on the Turtle Lake 15'' quadrangle in the northern part of the Coulee Dam 1:100,000-scale quadrangle.'
1007|'Leucocratic, coarse-grained, equigranular, foliated, muscovite-biotite quartz monzonite to granite that is present north of Milan.  The unit is probably part of the deformed muscovite-biotite quartz monzonite mapped by Miller (1974c) near Eloika Lake in the Newport Number 3 quadrangle in the Chewelah 1:100,000-scale quadrangle (Waggoner, 1990).  Biotite is chloritic; muscovite is present both as discrete crystals and intergrown with chlorite and biotite.  The micas are commonly wrapped around quartz and feldspar.  Sillimanite replacing biotite and cataclasis were observed by Miller (1974c) in thin sections of similar rocks from the Chewelah 1:100,000-scale quadrangle.  The two-mica granite is highly weathered and cut by alaskite pegmatite dikes.  This intrusive rock is most likely Cretaceous on the basis of its similarities to other muscovite-bearing plutons of probable Cretaceous age in the area.'
1008|'Leucocratic, foliated to massive, medium- to fine-grained biotite-muscovite granite to monzogranite that is present on Mount Spokane.  The granite contains quartz, K-feldspar, plagioclase, muscovite, biotite, and accessory apatite, zircon, garnet, and rutile.  Biotite and muscovite are shredded; muscovite replaces biotite and replaces feldspar along crystal boundaries.  The granite is intruded by and gradational over tens of meters with alaskite, pegmatite, and aplite dikes and sill-like bodies (TKiaa).  Muscovite-biotite-bearing granitic rocks on Mount Spokane were mapped as a biotite-muscovite quartz monzonite by Weissenborn and Weis (1976) and later informally called the Mount Spokane granite by Rhodes and others (1989).

The Mount Spokane granite structurally overlies the Newman Lake Gneiss (Rhodes and Hyndman, 1984; Bickford and others, 1985).  Various amounts of strain are exhibited at the contact of these two intrusive units.  A 2- to 5-m-thick zone containing 0.25- to 1-m-thick bands of light-colored mylonite is present on Beacon Hill in lineated (N. 70o E.) Newman Lake Gneiss near the contact with the Mount Spokane granite.  The granite on Beacon Hill is foliated and in places contains stretched quartz grains for approximately 15 to 40 m above the mylonite; it then grades upward into generally undeformed rock (DGER, unpublished mapping).  Elsewhere to the north, the contact with the Newman Lake Gneiss is represented by a zone of foliated and lineated rock (TKqf and TKqh units of Weissenborn and Weis, 1976).  The contact of the Mount Spokane granite with the orthogneiss near Mount Spokane (Kogs), which is thought by Rhodes and Hyndman (1984) to be deformed Mount Spokane granite in the mylonitic zone, is gradational over 500 to 1,000 m of structural thickness (Rhodes and Hyndman, 1984).  East of Mount Spokane, south-trending, west-dipping foliation is generally present in the granite within 3 to 5 km of the contact with the orthogneiss (Kogs); foliation in the Mount Spokane granite fades to the west (Weissenborn and Weis, 1976).

Two samples from the west side of Mount Kit Carson yielded concordant K-Ar muscovite and biotite ages of about 47 Ma and represent the age of emplacement or reset ages (Miller and Engels, 1975; Engels and others, 1976).  Bickford and others (1985) report lower U-Pb intercepts indicating ages of 925 Ma on muscovite and 755 Ma on biotite.  Additional dating of the pluton has been done by Armstrong and others (1987).  Two zircons yielded discordant U-Pb ages of 94 to 143 Ma.  Three granitic rocks and one pegmatite gave a maximum age of 844 Ma and an initial Rb/Sr ratio of 0.7108.  Two other samples analyzed by Armstrong and others (1987) contain more radiogenic Sr; calculated Rb-Sr ages are 1132 Ma and 1593  Ma.  Armstrong and others (1987) suggest that the U-Pb ages and the Rb-Sr isochrons indicate a middle to Late Cretaceous age for the pluton.'
1009|'Leucocratic, medium- to coarse-grained, foliated to massive, muscovite-biotite quartz monzonite to granite that is similar to the Mount Spokane granite.  Quartz is light gray and present as clusters of broken and annealed quartz grains; quartz commonly forms graphic intergrowths with feldspar.  White K-feldspar is present as phenocrysts as much as 2 cm in length.  Plagioclase is commonly slightly altered.  Subhedral biotite comprises as much as 10 percent of the rock and forms clots.  Muscovite ranges from 0 to 3 percent of the rock and is present as single euhedral crystals, in clots, or with biotite.  Foliation is strongest near the Little Spokane River and fades to the north, where the intrusive body is generally massive.  The body is intruded by dikes and small bodies of massive hornblende-biotite granodiorite and is cut by alaskite dikes that in places make up as much as 50 percent of the total volume.  This intrusive unit yielded discordant K-Ar ages of 48 Ma on biotite and 53 Ma on muscovite (Miller and Engels, 1975).  These ages are probably reset; the muscovite-biotite intrusive near the Little Spokane River is most likely of the same age as the Mount Spokane granite.'
1010|'Medium- to dark-gray, medium- to coarse-grained, mylonitic, hornblende-biotite granodiorite gneiss named by Weis (1968) for exposures on the northwest side of Newman Lake.  The unit is characterized by megacrysts of subhedral to euhedral crystalloblastic orthoclase as much as 2 cm in length and contains plagioclase, K-feldspar, quartz, biotite, hornblende, and accessory titanite, allanite, zircon, apatite, and opaque minerals (Miller, 1974c).

Obvious effects of cataclasis can be seen in most thin sections.  The rock was recrystallized during cataclasis, and development of a pervasive lineation is recorded by streaked-out clots of biotite (Miller, 1974c).  The trend of the weak to strong lineation is consistent with the N. 70o E. to S. 70o W. trend of lineation observed elsewhere in the PRC.  Crystalloblasts of K-feldspar are distinctively aligned parallel or subparallel to the foliation where the rock is strongly deformed.

The Newman Lake Gneiss is structurally overlain by the Mount Spokane granite (Rhodes and Hyndman, 1984; Bickford and others, 1985).  On Beacon Hill a 2- to 5-m-thick zone containing light-colored, 0.25- to 1-m-thick bands of mylonite is interlayered with deformed Newman Lake Gneiss at the contact with the Mount Spokane granite.  Elsewhere, the muscovite-megacryst-bearing granite (Kogsm) is generally present at the contact of the Newman Lake Gneiss and the Mount Spokane granite (Weissenborn and Weis, 1976); minor thin (<15 mm) mylonite zones are also present. Rhodes and Hyndman (1984) suggest that the Newman Lake Gneiss structurally overlies the Hauser Lake Gneiss.

Rb-Sr isotopic analyses of the Newman Lake Gneiss returned values similar to those for the Mount Spokane granite.  Zircons yielded U-Pb ages of 45 and 139 Ma; however the data produced poor isochrons (Armstrong and others, 1987).  The gneiss is thought by Armstrong and others (1987) to be Cretaceous in age.  Bickford and others (1985) report a lower U-Pb intercept on mylonitic rock of 55 Ma.'
1011|'Coarse-grained, quartz-feldspar-biotite-muscovite orthogneiss that has distinctive coarse banding of light minerals and dark biotite-rich layers (Weissenborn and Weis, 1976).  The structural fabric is dominated by a strong mylonitic foliation defined by mica and mylonitic lineation which lies in the plane of the foliation; lineation is defined by slickenside-like striae.  The orientation of the lineation is consistently N. 70o E. to S. 70o W. (Rhodes and others, 1989).

This unit is the banded gneiss of Weissenborn and Weis (1976), which they suggested was Precambrian in age.  However, Weissenborn and Weis noted that it is difficult to distinguish the orthogneiss on Mount Spokane from the Mount Spokane granite and that contacts with the Mount Spokane granite are gradational.  Rhodes and Hyndman (1984) suggest that the banded gneiss of Weissenborn and Weis (1976) is the Mount Spokane granite deformed in the mylonitic zone of the PRC.  The contact between the orthogneiss near Mount Spokane and the Mount Spokane granite is transitional through 500 to 1,000 m of structural thickness; the mylonitic zone is overlain by undeformed granite (Rhodes and Hyndman, 1984).  The unit structurally overlies the Newman Lake Gneiss (Weissenborn and Weis, 1976).'
1012|'Foliated and lineated biotite-muscovite quartz monzonite east of Mount Spokane.  This unit generally separates the Mount Spokane granite from the Newman Lake Gneiss.  The megacryst-bearing granite is similar in composition to the Mount Spokane granite, but it has books of muscovite as much as 2.5 cm in diameter; biotite is commonly interleaved with the muscovite.  At the contact with the Newman Lake Gneiss, the rock is highly sheared, and the muscovite books are obliterated (Weissenborn and Weis, 1976).  The unit contains thin to thick (<2 cm to 1 m) bands of mylonite which apparently developed from alaskite dikes.  The unit forms gradational contacts with the Mount Spokane granite (Kiats), the orthogneiss on Mount Spokane (Kogs), and the Newman Lake Gneiss (Kogn) (Weissenborn and Weis, 1976).'
1013|'Local pods and small bodies of amphibolite containing an assemblage of plagioclase  hornblende, titanite, garnet, diopside, ilmenite, and quartz (Rhodes, 1986).  Individual bodies are locally as thick as 28 m (Miller, 1974c).  Amphibolite is shown on Plate 1 only in the Hauser Lake Gneiss, but it is also present in gneiss south of the Spokane River (Weis, 1968) and in the heterogeneous metamorphic rocks (PChm) on Browns Mountain (P. L. Weis, retired USGS, oral commun., 1988).'
1014|'Rusty-weathering, medium-grained, well-banded, foliated and lineated mylonitic biotite-orthoclase-plagioclase-quartz gneiss, and schist that contains minor quartzite (Weis, 1968; Rhodes and Hyndman, 1984).  Muscovite-biotite schist layers are less than 1 m thick and quartz-feldspar layers are more than 1 m thick (Miller, 1974c).  The gneiss is locally intruded by abundant pods of garnet-bearing amphibolite (PCam) (Rhodes and Hyndman, 1984; Weis, 1968).  The unit was named by Weis (1968) for exposures on the east side of Hauser Lake, Idaho.  The unit extends in a continuous band to the north into the Chewelah 1:100,000-scale quadrangle; a structural thickness of more than 6,000 m was estimated by Weissenborn and Weis (1976).

A Precambrian age for the protolith was suggested by Weis (1968), Weissenborn and Weis (1976), Miller (1974c), and Griggs (1973).  The gneiss is thought by Miller (1974c), Griggs (1973), and Rhodes (1984) to have a protolith of the Prichard Formation (Belt Supergroup).  Weis (1968), Armstrong and others (1987), and Rhodes and others (1989) have suggested a pre-Beltian age for the protolith.   Armstrong and others (1987) suggest a pre-Belt protolith because samples are consistently more radiogenic (Rb-Sr) than Belt Supergroup rocks.  Whole-rock 87Sr/86Sr analyses of 13 samples suggest an age of 2,053 Ma for the Hauser Lake Gneiss, whereas euhedral zircons indicate a discordant age of 1,66832 Ma.  Augen gneiss that intrudes the Hauser Lake Gneiss near Priest River, Idaho, yielded a single whole-rock Rb-Sr age of 1,440 Ma (Clark, 1973).  Armstrong and others (1987) suggest that an old age is indicated for the metamorphic banding because of the large layer-to-layer variation in Sr isotopic composition (Armstrong and others, 1987).  According to Armstrong and others (1987), a major metamorphic event to create that banding might be dated at 1,670 Ma, on the basis of the upper intercept obtained from zircons.

Rhodes and others (1989) correlate the rusty-weathering sillimanite-bearing paragneiss and schist south of the Spokane Valley with the Hauser Lake Gneiss.  The gneiss south of the river has a gently dipping lineation and non-penetrative mylonitic foliation and is thought by Rhodes (1986) to be below the mylonitic zone on the south limb of a synform that has its axis parallel to the Spokane River valley.

The Hauser Lake Gneiss is structurally overlain by the Cretaceous Newman Lake Gneiss (Weissenborn and Weis, 1976; Rhodes and Hyndman, 1984; Rhodes and others, 1989).  The gneiss unit is intruded by the foliated and lineated dikes of the Mount Rathdrum granite (Eiatr), which cut the foliation in the gneiss.'
1015|'Light- to medium-gray, medium- to coarse-grained, prominently layered gneiss, schist, and quartzite present south of the Spokane River.  In the Dishman Hills and near Glenrose, the unit appears to be predominantly feldspathic orthogneiss that displays compositional banding and injected layers composed of biotite, muscovite, feldspar, and quartz.  On Browns Mountain and south of hill 881 (3 km northwest of Chester), the unit is predominantly biotite-bearing, medium- to coarse-grained, medium- to thick-layered quartzite and interbedded medium- to coarse-grained biotite-muscovite and muscovite-biotite schists.

Dark-colored graphitic schist and light- to dark-colored schist interlayered with quartzite are present on Silver Hill.  Dark-gray to black, fine-grained graphitic schist contains quartz, pink crystalline andalusite, biotite, muscovite, and locally abundant tourmaline.  Light- to dark-gray sillimanite-biotite schist to gneiss is interlayered with quartzite and also contains quartz, biotite, andalusite, tourmaline, and muscovite.  Dark-gray to black, fine-grained, massive quartzite is composed of quartz and minor muscovite, biotite, feldspar, andalusite, sillimanite, and graphite (McLeod, 1923).  McLeod (1923) suggests that the tourmaline content of the schist increases with proximity to the granitic rocks (TKia).

The unit is cut by alaskite pegmatite dikes; alaskite on Krell Hill and near Big Rock generally intrudes the quartzite of the heterogeneous metamorphic unit parallel to subparallel to foliation.  Schist and quartzite on Silver Hill are intruded by biotite-bearing intrusive rocks (TKia) (Page, 1942).  On Browns Mountain biotite schist and paragneiss are cut by biotite-hornblende diorite and amphibolite of probable Precambrian age'
1016|'Medium-grained, thin- to thick-bedded quartzite.  Five to 35 meters of massive, white quartzite are present at the base of the unit and grade upward into gray, thin- to medium-layered, arkosic quartzite and micaceous feldspathic quartzite containing 60 to 90 percent quartz.  The unit is intruded by pegmatitic bodies.  The contact with the underlying gneiss of Mica Peak (PCbgm) is sharp (Weis, 1968).  The quartzite is thought to be part of the Prichard Formation by Griggs (1973) and to be older than the Belt Supergroup by Weis (1968).'
1017|'Light-gray, coarse-grained muscovite-quartz-feldspar schist and segregation gneiss that consists of mica-rich layers separating quartz-feldspar layers.  The schist commonly contains more than 50 percent mica and is locally contorted.  Sillimanite and biotite are locally present.  Concordant and discordant granitic bodies make up as much as 50 percent of the unit.  Small scattered amphibolite bodies intrude the gneiss in the eastern part of the unit.  The contact with the underlying gneiss (PCscr) is gradational through 5 to 35 m (Weis, 1968).  The unit is thought to be part of the Prichard Formation by Griggs (1973) and to be older than the Belt Supergroup by Weis (1968).'
1018|'Light pinkish gray, medium- to fine-grained, quartz-feldspar-muscovite-sillimanite schist and gneiss.  The gneiss is poorly layered and contains abundant small folds.  It is intruded by sparse pegmatite and granitic dikes and minor small amphibolite bodies.  The contact with gneiss near Cable Peak (PCbgc) is poorly exposed (Weis, 1968).  The gneiss near Round Mountain is thought to be part of the Prichard Formation by Griggs (1973) and to be older than the Belt Supergroup by Weis (1968).'
1019|'Light- to dark-gray, chiefly medium-gray, prominently layered gneiss and schist.  Individual layers are generally less than 15 cm thick and include quartzite, feldspathic quartzite, and micaceous quartz-feldspar gneiss, granitic gneiss, amphibolite, and schist.  The gneiss characteristically has a wide range of composition in adjacent layers (Weis, 1968).  The gneiss is thought to be part of the Prichard Formation by Griggs (1973) and to be older than the Belt Supergroup by Weis (1968).'
1075|'Stream deposits in modern drainages.'
1076|'Poorly sorted and poorly stratified, unconsolidated deposits principally of glacial origin. Includes till in lateral and ground moraines as well as outwash and minor modern stream alluvium.'
1077|'Unconsolidated, poorly sorted, fluvial sediment 70 to 330 m above the present stream levels. Ranges in size from clay to boulders and is derived from local sources (Hosterman, 1956).'
1078|'Small stocks of hornblende monzonite, porphyritic hornblende monzonite, alkali-feldspar syenite, and pyroxene syenite (Schlack, 1989). Age determinations have yielded conflicting dates, but emplacement ages of about 100 Ma are likely (Marvin and others, 1984; Schlack, 1989).'
1079|'Interbedded quartzite and argillite with some arenaceous dolomitic beds; usually thinly bedded (Hobbs and others, 1965). Colors range from purplish-gray and very pale pink to gray and green. Mud cracks and ripple marks common.'
1080|'Predominantly thinly laminated medium- to dark-gray argillite; some interbedded light-gray quartzite and arenaceous dolomite (Hobbs and others, 1965).'
1081|'Light-gray dolomitic and calcareous quartzite interbedded with medium- to dark-gray argillite (Hobbs and others, 1965). Some impure dolomite beds near top. Ripple marks, small scale cross-bedding, and molar-tooth and ovoid structures in some layers. Mapped as YwI by Hobbs and others (1965).'
1082|'Thick-bedded impure to pure quartzite at base, grading upward to interbedded and interlaminated impure quartzite and argillite that comprise bulk of formation (Hobbs and others, 1965). Characteristically thin bedded and many layers laminated. Predominantly purplish red and grayish red; argillite is darker. Some carbonate-bearing beds, mostly in upper part. Ripple marks, mud cracks, and mud-chip breccia in some layers.'
1083|'Thick-bedded white to light-gray quartzite containing interbedded impure and nearly pure quartzite in upper and lower parts, and a few widely spaced argillite partings (Hobbs and others, 1965). Cross-bedded and laminated in part.'
1084|'Light- to greenish-gray fine-grained impure quartzite with lesser amounts of nearly white to light-gray nearly pure to pure quartzite (Hobbs and others, 1965). Beds predominantly 5 to 20 cm thick. Ripple marks and pseudoconglomerate are common.'
1085|'Light-gray to nearly white pure to impure quartzite interbedded with laminated argillite (Hobbs and others, 1965). Quartzite beds 5 to 45 cm thick. Ripple marks and graded bedding are common.'
1086|'Banded dark-gray argillite, laminated in part; weathers rusty red (Hosterman, 1956).'
1100|'Stream deposits in modern drainages.'
1101|'Unconsolidated deposits on terraces above the modern drainages. Some may be glacial outwash deposits.'
1102|'Poorly sorted and poorly stratified, unconsolidated deposits principally of glacial origin. Includes till in lateral and ground moraines as well as outwash and minor modern stream alluvium.'
1103|'Unconsolidated, poorly sorted, fluvial sediment preserved in erosional remnants 250 to 350 m (800 to 1150 ft) above the present river bottoms. Includes beds of cobble gravel, sand, and orange-weathering clay. Slumps are common.'
1104|'Small exposure of basalt in the extreme western part of the map area.'
1105|'Gray dikes that contain plagioclase, biotite, and hornblende phenocrysts in an aphanitic groundmass'
1106|'Light-gray, medium- to coarse-grained, equigranular to porphyritic granodiorite. The Roundtop pluton contains about 20 percent quartz, 50 percent zoned euhedral plagioclase, 15 to 25 percent orthoclase, and 5 to 15 percent hornblende and biotite combined (Hietanen, 1968). Fabric is weak to absent in most places, but gently-dipping igneous flow foliation is present in the central part of the pluton and strongly developed contact-parallel mylonitic foliation and lineation is present in the southern part (Steve Box, pers. comm., 1997). Age is 527 Ma by U-Pb methods on zircon (Marvin and others, 1984). The Herrick stock contains biotite, minor hornblende, and plagioclase that is in part strongly zoned (Holland, 1947). The Herrick stock is deeply weathered except along the St. Joe River canyon. Hornfels has formed adjacent to this intrusion and forms a resistant ridge along its northeast side.'
1107|'Medium- to fine-grained, equigranular hornblende-pyroxene gabbro and diorite. Hornblende is present as either rims on pyroxene or completely replacing pyroxene and olivine is present at a few localities (Hietanen, 1963; 1968). Plagioclase constitutes about 30 to 40 percent of the rock and has all anorthite content of 45 to 74 percent. Some exposures are highly altered, but others, particularly in the southwest part of the area , are unaltered. Typically intruded along or near fault zones. Includes the Wishard Sill of Pardee (1911) which is exposed along the state line from Wishard Peak northwest to beyond Dominion Peak. Age is highly uncertain, as no reliable radiometric dates are available. Hietanen (1968) assigned them a Tertiary age. Harrison and others (1986) assigned only the southern exposures this age, and thought the Wishard sill was Proterozoic. A whole-rock K-Ar age of 5754 Ma on the Wishard sill (Marvin and others, 1984) may represent a partially reset Proterozoic age, or an incorrect old age resulting from excess argon.'
1108|'Light-gray, medium- to coarse-grained, massive to foliated, (muscovite-) biotite granodiorite. Pegmatite dikes and biotite schlieren are common in the intrusion along the Little North Fork of the Clearwater River (Hietanen, 1963). None of these rocks have been reliably dated, but the presence of a foliation, muscovite, and an abundance of pegmatites suggest a Cretaceous age.'
1109|'Gray, medium-grained, strongly foliated (hornblende-) biotite tonalite, granodiorite, and quartz diorite. Contains euhedral epidote interpreted to be magmatic in origin. Foliation is mylonitic at several localities. No reliable dating of these rocks exists, but a Cretaceous age is likely given the degree of fabric development.'
1110|'White to light-gray, foliated to massive, medium- to coarse-grained anorthosite. Contains bimodal plagioclase populations (andesine and bytownite) and minor amounts of hornblende, biotite, and chlorite (Hietanen, 1963). Weathers more readily than surrounding metasedimentary rocks. Hietanen (1963) speculated that the anorthosite formed by metamorphic rather than igneous processes.'
1111|'Dark-gray, foliated or lineated hornblende-plagioclase rocks, typically garnet-bearing. May in part be metamorphosed carbonate-bearing rocks, but most are thought to be metamorphosed igneous sills and dikes (Hietanen, 1963).'
1112|'Quartzite-dominated interval in the northwestern part of the area where subdivision into members has not been attempted.'
1113|'Red to light-gray, decimeter- to meter-scale beds of fine- to medium-grained parallel-laminated quartzite. Informally termed member three in this report. Exposed at the type section on Striped Peak where approximately 305 m (1,000 ft) is exposed. The upper part is truncated by faulting, so this represents a minimum thickness. Laterally equivalent to the Bonner Quartzite, described to the cast (Harrison and others, 1986). Contains abundant K-feldspar (18-23 percent) and lesser amounts of plagioclase (6-7 percent) based on two samples stained for feldspar.'
1114|'Red and subordinate green siltite and argillite interbedded with minor amounts of quartzite and carbonate. Beds are typically centimeter to millimeter scale. Informally termed member two in this report. Exposed at the type section on Striped Peak where it is approximately 105 m (350 ft) thick. Laterally equivalent to member 3 of the Mt. Shields Formation, described to the east (Harrison and others, 1986).'
1115|'Red or gray fine- to very fine-grained quartzite and subordinate amounts of siltite, argillite, and carbonate. At Cedar Mountain, north of Avery, unit consists of fine-grained quartzite in tabular, decimeter- to meter-thick beds with green siltite and argillite along partings. Lower part of unit there grades upwards from Ywu3 with increasing 5 to 10 cm white quartzite beds and dark green siltite, increasing ripple-drift cross lamination and rippled tops and more common mud cracked surfaces. Some beds are graded and there seem to be thinning and fining-upward cycles, Rocks highest in section are 20 to 40 cm thick flat-laminated quartzites with rippled tops and rarer mud-cracked thin argillite caps. Carbonate is present in some thin (~5 cm) zones at or near bedding surfaces. Entire member exposed at the type section on Striped Peak where it is approximately 245 m (800 ft) thick. Informal unit designated here is laterally equivalent to Mt. Shields Formation, members 1 and 2, described to the east (Harrison and others, 1986). A single sample of quartzite from Striped Peak stained for feldspar contained about 20 percent plagioclase and no K-feldspar.'
1116|'Carbonate-free microlaminated and wavy couplets of siltite and argillite. Most argillite is light green but some is black. Mapped and described by Hobbs and others (1965) in part of the Coeur dAlene mining district, and by Vance (1981) south of the district. Vance (1981) estimated a thickness of about 400 m (1300 ft) on the northeast side of Foolhen Mountain. May be equivalent to Wallace 5 of Clark Fork section (Harrison and Jobin, 1963) or upper Shepard (Burmester, 1986; Lemoine and Winston, 1986).'
1117|'Rock is typically microlaminated dark-green siltite and light-green argillite, and dolomitic siltite beds 2 to 5 cm thick. Thin quartzite lenses and starved ripples produce a lenticular sediment type. More quartzitic in southeast part of area where unit contains an abundance of load casts on bed bottoms. Vance (1981) estimated a thickness of about 210 m (700 ft) on the northeast side of Foolhen Mountain. Likely correlates with Wallace 4 of Clark Fork section (Harrison and Jobin, 1963). May be equivalent to the middle or lower part of Shepard Formation (Lemoine and Winston, 1986).'
1118|'Dark-gray, thinly laminated argillite and siltite in the lower part grading upward to green thinly laminated argillite and siltite. Rare, thin (2-5 cm) coarse siltite or very fine-grained quartzite layers have ripple-drift cross lamination and ripple tops. Upwards, bedding becomes thinner and more planar with the highest gray rocks being microlaminated white-weathering siltite and black (biotitic?) argillite with characteristic planar partings. Above that, dark green siltite and light green argillite becomes more abundant and thickly and unevenly laminated, with more thin rippled quartzite beds and mud chips and mudcracked surfaces. Top is gradational into Ywu2 with siltite and argillite becoming more microlaminated. Equivalent to the Snowslip Formation in the Missoula area to the northeast (Winston, 1986). Unit lacks the red argillite and siltite of the Snowslip, and the gray thinly laminated lower part is missing from the Snowslip to the northeast. An estimated a thickness of about 460 in (1500 ft) on Foolhen Mountain, south of the Coeur dAlene district (Vance, 1981) is probably a minimum because the lower contact is not exposed there.'
1119|'Unit in the Coeur dAlene mining district (Ywl of Hobbs and others, 1965) where subdivision into separate members has not been attempted. Also includes structurally complex rocks in the southwest part of the map area.'
1120|'Characterized by pinch and swell couplets (Winston, 1986) of white quartzite that grade upward into black argillite caps. The quartzite is fine- to very fine-grained, commonly calcareous, with hummocky to low-angle cross-stratification and scoured or loaded basal contacts. Centimeter-scale beds of silty, molar-tooth limestone and dolostone are widespread. Zones of tan-weathering calcareous siltite to very fine-grained quartzite with black, non-calcareous argillite caps (black and tan rock type) are locally common. Microlaminated white siltite to black argillite is present, although not dominant. Minor zones with horizontal pods of non-resistant calcareous siltite are present low in the section. Amalgamated, decimeter beds of quartzite grading to cm-scale, tan, non-resistant, calcareous siltite and thin black argillite caps occur in some intervals, and commonly underlie or are interspersed with zones of sedimentary breccia. The breccia typically consists of rounded to angular, pebble- to boulder-sized calcareous quartzite clasts in orange-weathering calcitic siltite matrix with abundant soft-sediment deformation features. Outcrops of the breccia are commonly silicified and form prominent hoodoos. Several breccia zones mapped by Nord (1967) as fault breccias are interpreted here as sedimentary breccia.'
1121|'Characterized by wavy, even, thin laminations and less common couplets of green siltite with light green to white argillite caps. Lenticular couplets locally common. Intervals of "tri-color" white quartzite, dark green siltite, and pale green argillite alternate with the laminated green siltite-argillite lower in the unit. Carbonate is present in the lower part as punky-weathering, molar tooth silty limestone beds up to 1 m in thickness. Zones of horizontal pods of silty carbonate are common in the upper part of the unit; the carbonate is non-resistant and normally weathers out, leaving distinct voids. Pinch and swell couplets of white and quartzite and black argillite increase in abundance toward the top of the unit, as do thin intervals of the "black and tan" rock type, characteristic of Ywm.'
1122|'Gray to brown muscovite-biotite schist and phyllite that is coarsest in the southern part of the area and grades into argillite and siltite to the north and east. Micas grow to about 5 mm, but grain size in biotite quartzite (siltite part of protolith) remains small. Lowest rocks are scapolite-rich, graded dark-gray to black siltite and argillite in even to wavy couplets. Growth of scapolite may have destroyed microlaminae. Rocks commonly show metamorphic succession from tabular chloritoid, increasing size garnets, staurolite, then kyanite (Lang and Rice, 1985a). Compositional layering is typically parallel to foliation, but locally is folded isoclinally with centimeter- to outcrop-scale wavelengths. Mapped as schist within the Wallace Formation by Hietanen (1968). Unit is the metamorphic equivalent of Ywu1. Contact with Ywu1 drawn at the garnet isograd.'
1123|'Medium-grained, thin-bedded quartzite that contains minor amounts of calc-silicate minerals (primarily actinolite and diopside) and thin layers of phyllitic black argillite or schist that locally contain scapolite. The lower contact west of the Roundtop pluton appears to be gradational with downward decreasing quartzite content and bedding thickness and increasingly even bedding style. Equivalent to less-metamorphosed rocks of Ywm and Ywml units. Mapped by Hietanen (1968) as quartzite unit of Wallace Formation.'
1124|'Thick-bedded impure to pure quartzite at base, grading upward to interbedded and interlaminated impure quartzite and argillite that comprise bulk of formation (Hobbs and others, 1965). Characteristically thin bedded to laminated. Predominantly purplish red and grayish red; argillite is darker. Some carbonate-bearing beds, mostly in upper part. Ripple marks, mud cracks, and mud-chip breccia in some layers. Rocks at Ward Peak along the state line, tentatively assigned to Ysr, are green siltite and light green to white argillite with lesser amounts of wavy, decimeter-scale quartzite beds. Abundant white rounded argillite rip-up clasts are present, some with unusually equant dimensions. These rocks resemble Ywl, but are assigned to Ysr because of quartzite beds, scarcity of carbonate, and the presence of abundant rip-ups. Similar rocks arc described and mapped (where exposures permitted) as uppermost St. Regis in the Coeur d Alene mining district (Ysg unit of Hobbs and others, 1965). Along Gold Creek the St. Regis is characterized by rounded mud-chip rip-ups and evenly bedded, cm-scale white quartzite grading up into cm-scale black argillite caps.'
1125|'Thick-bedded white to light-gray quartzite containing interbedded impure and nearly pure quartzite in upper and lower parts, and a few widely spaced argillite partings (Hobbs and others, 1965). Cross-bedded and laminated in part.'
1126|'Light- to greenish-gray fine-grained impure quartzite with lesser amounts of nearly white to light-gray nearly pure to pure quartzite (Hobbs and others, 1965). Beds predominantly 5 to 20 cm thick. Ripple marks and pseudoconglomerate are common.'
1127|'Muscovite-rich schist, thin quartzite intervals, and minor calc-silicate rocks. Garnet present but neither abundant nor ubiquitous. Exposures west of Granite Peak show increasing amounts of quartzite down section, assuming the relict NE-dipping bedding is upright. Unit probably is equivalent to the St. Regis Formation of the Ravalli Group, but may include part of the Revett Formation. Tentatively assigned to the Ravalli Group on the basis of stratigraphic position.'
1128|'Mostly fine-grained, sugary and friable white feldspathic quartzite with muscovitic partings and rare, thin biotite quartzite tops. Minor fine- to medium-grained (1-2 mm) biotite-muscovite schist. Unit is probably equivalent to the Revett Formation of the Ravalli Group, but may include part of the Burke and St. Regis Formations. Tentatively assigned to the Ravalli Group on the basis of stratigraphic position. Thickness is about 800 m (2500 ft) west of Granite peak where this unit includes what Hietanen (1968) mapped as Wallace quartzite. It is not assigned here to the Wallace because features expected of metamorphosed Wallace were not found. Among these are relict pinch and swell bedding, evidence of carbonate such as scapolite or calc-silicate mineral assemblages, and schist and quartzite proportions and thicknesses similar to siltite-argillite and quartzite observed in the Wallace lithologies to the north.'
1129|'Light gray to nearly white impure to pure quartzite interbedded with laminated argillite (Hobbs and others, 1965). Quartzite beds 5 to 45 cm thick. Ripple marks, mud cracks, and graded bedding are common.'
1130|'Typically dark, rusty-weathering coarse-grained (5 mm micas) biotite-muscovite-feldspar-quartz schist. Commonly crenulated; locally garnetiferous or sillimanite-bearing [sic]. Also contains as discontinuous layers fine-grained (muscovite)-biotite-feldspar quartzite with moderately-developed foliation. This quartzite is similar to unit described below but generally represents less than 10 percent of the Ys unit. Includes rocks assigned by Hietanen (1968) to Prichard Formation. Some of the unit at Monumental Buttes originally assigned to the Prichard Formation (Hietanen, 1963) but later assigned to the Boehls Butte Formation and thought to be pre-Belt in age (Hietanen, 1984). Correlation with specific Belt Supergroup (or older) units is too speculative at the present time, but most are probably metamorphic equivalents of the Prichard Formation.'
1131|'Gray to white, coarse- to medium-grained quartzite. Includes rare garnetiferous and calc-silicate concentrations. Mapped by Hietanen (1968) as quartzite of the Prichard Formation and later subdivided to include quartzite of Boehls Butte Formation (Hietanen, 1984). Most is probably quartzite of the Prichard Formation, but present understanding of stratigraphy and structure in the area precludes assignment to a formation.'
1132|'Bluish gray-green, medium- to coarse-grained rocks rich in diopside, hornblende, or both (Hietanen, 1963). Quartz, plagioclase, tremolite, scapolite, and calcite are also present.'
1133|
1150|'Well rounded, well-sorted cobbles, gravel, and sand deposited in active stream channels and floodplains. Provenance appears to include much of west central Montana.'
1151|'Unsorted and unstratified mixtures of angular material that have been moved down slope by gravity. Landslides are uncommon in areas underlain by Belt rocks. The most dramatic example of a landslide in the Wallace quadrangle is the Little Joe Slide (T17N R29W sec 36) that formed catastrophically in 1968.'
1152|'Well sorted, well rounded boulders, cobbles, gravel, sand, and silt deposited by streams, later incised by modern streams and now stranded up to 15 m above the present watercourses. Includes both terrace deposits along rivers and outwash fan deposits emerging from the mountains.'
1153|'Light tan to light brown, varved silt and clay deposited in Glacial Lake Missoula. Supports vertical cuts along streams and in road cuts. On topographic maps, form flat surfaces that are usually dissected into a badlands topography.'
1154|'Unsorted, unstratified clay- through boulder-sized material deposited by glaciers; only occurring above 1250 m in elevation. Many small moraines in the mountain valleys are not shown on the map.'
1155|'Locally derived, poorly sorted, subangular to subrounded boulders, cobbles, gravel, sand, and silt deposited in fans along the mountain front just south of the Osburn Fault. Surfaces of these dissected fans generally stand 60 m above the present streams.'
1156|'Mostly fluvial channel deposits of well rounded, well sorted boulders, cobbles, pebbles, and sand. Clasts of Bonner Formation and some of granitic rocks and porphyritic volcanic rocks are from outside the area. Found up to 1500 m in elevation, and interpreted to have been deposited by the ancient Clark Fork River system. South of St. Regis, these rocks dip 30 into the Boyd Mountain fault indicating late Tertiary listric normal movement on the Boyd Mountain Fault.'
1157|'Medium- to fine-grained, equigranular hornblende-pyroxene gabbro and diorite. A Late Cretaceous-Early Tertiary age is inferred for dikes and sills from their common occurrence along faults, although Harrison et al. (1996) assigned a late Proterozoic age to some.'
1158|'Greenish-gray, micaceous, tabular and lensoidal, hummocky cross-stratified, fine-grained quartzite with argillite interbeds. Some chert chips and beds in the lower part. Entire thickness is not exposed, but at least 500 m.'
1159|'Dense, bright green and red interbedded siltite and argillite in microlaminae and couplets. Mudcracks and chips are common. Contains diagnostic thin chert beds and chips. The upper part contains some pink to gray cross-bedded quartzite in beds less than 0.5 m thick. Dominated by mudcracked even couplet and mudcracked lenticular couplet sediment types. Whole unit not exposed, but at least 600 m thick.'
1160|'Pink, medium-grained, feldspathic, cross-bedded quartzite. Lewis (1998) found 15-25% potassium feldspar but only a trace of plagioclase in the Bonner Formation. Mostly comprised of the cross-bedded sand sediment type. The sole exposure in the Wallace quadrangle is fault bounded, but it is probably 300 m thick.'
1161|'Red siltite to argillite couplets with abundant mudcracks, mud chips, and salt casts. Mostly mudcracked even couplet and mudcracked lenticular couplet sediment types. About 600 m thick.'
1162|'Pink to gray, flat-laminated, fine-grained quartzite, with tan weathering dolomitic blebs. Some cross bedding, which can make it difficult to distinguish from the Bonner Formation. However, in contrast to the Bonner, Lewis (1998) found subequal amounts of plagioclase and potassium feldspar and a total feldspar content of 25-35% in the Mount Shields. Characterized by the flat-laminated sand sediment type; about 900 m thick.'
1163|'Distinguished by dark green siltite and light green argillite in microlaminae and couplets that are dolomitic and have a characteristic orange-brown weathering rind. Poorly exposed but weathers into thin plates. Some 2-5 cm thick white quartzite beds are present in the upper part. Common sediment types are calcareous microlaminae and calcareous uncracked (non-mudcracked) even couplets. Estimated to be 250 m thick.'
1164|'Mostly silver-green siltite and argillite in planar parallel beds 2-5 cm thick that weather into small blocky pieces with a characteristic spotted, rusty-red-on-green appearance. Green siltite-argillite laminae are common near the base. Mudcracks are abundant. Some fine-grained feldspar-poor quartzite is present in beds less than 0.5 m thick, especially in the lower part. Dominant sediment types are mudcracked even couplet and mudcracked lenticular couplet. Faults must complicate thickness estimates, because apparent thicknesses range from 600 to 900 m in the quadrangle.'
1165|'Tan-weathering dolomitic siltite and quartzite is capped by black argillite in pinch and swell couplets and couples to form a distinctive lithology. The quartzite and siltite commonly have scoured bases or bases with load casts. Non-polygonal "birdsfoot" cracks common in black argillite. Carbonate-rich beds have molar-tooth structures. Sedimentary breccia, consisting mostly of white quartzite clasts in punky, orange weathering silty dolomite, is common, although we believe some sedimentary breccia zones shown by Campbell (1960) are actually tectonic in origin. The breccia weathers into spires and hoodoos. Euhedral scapolite crystals are present in breccia zones. Severe deformation within this unit makes thickness estimates problematic, but it is no more than 2000 m.'
1166|'Consists of cycles, from 1 to 10 m thick and usually incomplete, of a basal white quartzite or intraclast unit, overlain by uncracked (non-mudcracked) even and lenticular couplets of green siltite and argillite, and capped by dolomitic beds. However, these cycles are difficult to recognize in the typical small outcrop. The unit is more easily recognized by wavy but parallel, silver-green couplets of darker green siltite and lighter green argillite, by white quartzite, by beds of tan or brown weathering dolomite from 0.5 to 1 m thick, and by weathered-out pods of carbonate in the green siltite. Some couplets are mudcracked. About 150 m above the base of this unit is an interval of abundant thick black argillite beds and some pinch and swell couplets capped by black argillite like those of the middle member of the Wallace Formation. This is probably the severely deformed interval displayed in the footwall of the Camel''s Hump structure. Carbonate mud and uncracked (non-mudcracked) even couplets are the principal sediment types in this interval. The severity of deformation within the lower Wallace makes thickness unknown, but it is probably about 700 m (Don Winston, personal communication, 1999).'
1167|'Identified by gray-purple or, more commonly, bright green mud-cracked silt to clay couplets with abundant mud chips. Dolomitic silt beds in the upper part weather to a siderite-colored brown, darker than the carbonate in the Wallace Formation. Toward the base, gray-purple, flat-laminated quartzite beds 10 to 30 cm thick become common. Down section in the Revett Formation, the thickness of these quartzite beds increases to 0.5 to 1 m and mud cracks and chips become less common. Comprised mainly of mudcracked even couplet, mudcracked lenticular couplet, and even couple sediment types. Thickness is estimated to be 850 m.'
1168|'There are three informal members, here undivided. The uppermost member is white to purple or lavender, banded medium-grained quartzite in 1-2 m thick beds. Quartzite beds are capped by green argillite, 5-10 cm thick, that is not obvious in outcrop. Very thin mud skins and associated mud chips are common. Quartzite beds are flat-laminated to cross-bedded. Some cross-beds are overprinted and intersected by purple liesegang bands. The middle member consists mostly of gray-green siltite and argillite in indistinct wispy beds 5-20 cm thick. Load, pillow, and fluid escape structures are common. Some mud cracks and chips are present. This member is mostly of the discontinuous layer sediment type. The lowermost member is banded quartzite very similar to the upper unit. The contact with the Burke Formation is gradational and somewhat arbitrary and placed where the quartzite beds thin to less than 1 m. The Revett is 900 to 1250 m thick.'
1169|'Poorly exposed and relatively unknown. The uppermost part is purple-gray to white, flat-laminated and cross-bedded sericitic quartzite in beds 0.3-1 m thick interbedded with green siltite. Flat-laminated sand and even couples characterize the sediment types. The middle and lowermost parts contain purple, or alternating green and purple, mudcracked siltite-argillite couplets with abundant mud chips. In the siltite, abundant euhedral magnetite grains may be diagnostic. The middle and lowermost parts are mainly mudcracked even couplet and mudcracked lenticular couplet sediment types. Approximately 900 m thick.'
1170|'The upper part consists of pyritic, black and gray, evenly laminated argillite and siltite couplets and couples. Lower in the section, flat-laminated, gray, fine-grained, micaceous quartzite predominates. The whole formation weathers a rusty brown from the abundant pyrite and pyrrhotite. Principal sediment types are plane-laminated silt and clay, flat-laminated sand, and even couples. The entire formation, not exposed in the Wallace quadrangle, is probably more than 6000 m thick.'
1171|'Diorite and gabbro'
1200|'Gravel, sand, silt, and clay in flood plains and low terraces along present drainage. Includes alluvial fans.'
1201|'Angular blocks of bedrock in finer grained matrix; mixed, at places, with glacial debris.'
1202|'Buff to lavender varved clay and silt containing a few lenses of gravel and scattered dropstones. Tends to form vertical cliffs along present stream courses; old surfaces are gently rolling; eroded surfaces tend to show a badlands topography. Sediments represent bottom deposits of Glacial Lake Missoula, which was filled several times during the Pleistocene to a maximum altitude of 4,200 ft when ice dammed the mouth of the Clark Fork River (Pardee, 1910; Alden, 1953; Bretz and others, 1956).'
1203|'Includes till (ground and end moraines), outwash, and other glaciofluvial deposits and flood-related deposits. Particularly abundant and thick in drainages and basins connecting to or north of the Flathead-Clark Fork River system. Torrential gravel deposits related to catastrophic emptying of Glacial Lake Missoula are in perched valleys at places along the Clark Fork River, form large point bars as terraces, form giant ripples, and show coarse cross-bedding convex upstream at the mouths of many tributaries to the Clark Fork northwest of Thompson Falls, Mont.'
1205|'Semiconsolidated to consolidated conglomerate interlayered with shale, coal, and volcanic ash.'
1207|'In northeast: rhyodacite vent agglomerate, volcanic conglomerate and breccia containing thin interbeds of crystal tuff, andesitic to dacitic crystal tuff characterized by large hexagonal crystals of biotite, and minor basalt. In southeast: andesitic to dacitic welded crystal tuff and a few dikes; phenocrysts in tuff are commonly fragmented and consist of smoky quartz, sanidine, plagioclase, and minor biotite.'
1208|'Intrusive rocks ranging in composition from granodiorite to granite. Most are biotite or hornblende-biotite seriate porphyritic granodiorite; some plutonic phases contain muscovite; and a few have significant amounts of granite pegmatite. Also includes andesite porphyry in volcanic center in northeast. These rocks range in age from about 35 m.y. to about 50 m.y. (Marvin and others, 1984).'
1210|'Mostly porphyritic hornblende-biotite quartz monzonite and granodiorite. These rocks range in age from about 70 m.y. to 120 m.y. (Marvin and others, 1984). Some of these plutons have been offset by faulting.'
1211|'Mostly medium- to coarse-grained aegirine-hornblende-mica-bearing feldspathic rocks in a complex of plutons that include syenite, fenite, and quartz syenite. About 105 m.y. old (Marvin and others, 1984).'
1212|'Used in the southeast and in cross sections. Includes, in descending order, Red Lion Formation (shale, limestone, and dolomite), the Hasmark Dolomite, the Silver Hill Formation (shale and limestone), and the Flathead Quartzite. Rests unconformably on the Pilcher, Garnet Range, and McNamara Formations of Proterozoic age. Total thickness is about 2,700 ft.'
1213|'Unit mapped in north-central area. Unnamed gray to tan dolomite. Consists of a lower dolomudstone about 1,020 ft thick, a middle laminated shaly unit about 280 ft thick, and an upper dolomudstone about 1,200 ft thick that has an erosional top (Aadland, 1977). Total thickness exposed is about 2,500 ft.'
1214|'Unit mapped in north-central area. About 300 ft of olive fissile shale (Wolsey or Gordon Shale) that contains trilobites and brachiopods of early Middle Cambrian age (Keim and Rector, 1964). Underlain by red to maroon quartzite at base grading up into buff quartzite (Flathead Quartzite). Base of quartzite has sparse trace fossils. Quartzite thickness about 30 ft. Disconformably overlies Libby Formation of Proterozoic age; micaceous and hematitic weathered zone in upper few feet of Libby. Disconformity has thin secondary chert zone along it.'
1215|'Dioritic to gabbroic rocks that commonly show alteration of mafic minerals. Sills and dikes range in thickness from less than 3 ft to 1,500 ft. Thicker sills tend to have wide (600 ft) contact-metamorphosed zones around them. Sills commonly persist for many kilometers; some maintain approximately the same stratigraphic position, whereas others cut up through the section. Dikes are rare. Only the larger or more persistent sills and dikes are shown. Intrusion occurred at least twice (at about 1,400 m.y. and 800 m.y.; Harrison, 1972).'
1216|'Mostly red to light pink, cross-bedded, micaceous and feldspathic fine-grained quartzite containing thin, shaly, argillitic layers in the upper part. Pre-Flathead erosion has removed all the Pilcher in places, and a complete section is nowhere present. The maximum exposed thickness is about 1,770 ft.'
1217|'Predominantly gray-green micaceous siltite containing beds and zones of fine-grained quartzite and dark-green to black argillite; calcareous at places. Red argillite and siltite zones are rare and scattered through upper two-thirds of formation. Lower part is predominantly black or dark-green laminated argillite and siltite, calcareous at places, and contains a few stromatolite beds, oolite beds, and black or green chert in chips and layers. Most of the unit shows mud chips, mud cracks, ripple marks, small-scale cross-beds, and cut-and-fill structures. Red weathered zone a few feet thick is present beneath Flathead Quartzite where Flathead rests on Garnet Range. Anomalous amounts of chalcopyrite in places in lower black argillite; chalcocite and bornite in a few green strata. Thickness is about 8,200 ft.'
1218|'Consists mostly of interlaminated argillite and siltite and, in the upper part, quartzite. Contains three informal members. Upper member is mostly black interlaminated argillite and siltite and contains abundant mud-crack casts, ripple marks, and soft-sediment structures. Green fine- to medium-grained cross-bedded quartzite and siltite become common in upper half. A zone of red interlaminated argillite and siltite occurs in the north-central part of the quadrangle near the top of the section about 300 ft below the erosional unconformity that terminates the unit. Red weathered zone is present at top of Libby beneath the unconformity. Middle member is mostly evenly laminated dark-green argillite and light-green siltite and contains mud chips, chert chips and beds, cut-and-fill structures, and ripple marks. Anomalous amounts of chalcocite or bornite occur in a few beds. Lower member is black and white or green interlaminated argillite and siltite and contains scattered beds of dolomite and stromatolites. Maximum exposed thickness of Libby is about 5,500 ft.'
1219|'Interbedded, laminated and interlaminated red and green argillite and siltite; ripple marks, mud cracks, scours, and small-scale cross-bedding common; rare salt casts. Distinctive, very fine grained, dense, mostly pale-green but locally red siltites are common in beds generally less than 8 in. thick. A few chert beds are present, and rounded chert grains and chips are common. A few green strata contain anomalous amounts of chalcocite and bornite. Thickness is about 3,600 ft in the southeast. In the north-central area, the unit is mostly green laminated argillite containing only sparse red argillite, sparse chert, and rare stromatolites; thickness about 300 ft.'
1220|'Red to pink, micaceous, arkosic, cross-bedded, fine- to medium-grained quartzite containing red argillite interclasts: tabular and trough cross-beds and climbing ripples common. Interbeds of red laminated argillite increase in abundance to west and north. Northernmost exposures contain scattered beds of planar-laminated green fine-grained quartzite as much as 30 ft thick. Ranges in thickness from about 1,400 ft in the southeast to about 500 ft in the north-central area.'
1221|'Type locality for the Striped Peak Formation (Ransome and Calkins, 1908) is on Striped Peak, a few kilometers southwest of Wallace, Idaho. Here, and at more extensive exposures about 10 km southwest of the peak, the formation (Ysp) consists of four informal members. The upper member consists of interbedded red and green laminated argillite and siltite that contains mud chips, ripple marks, mud cracks, and salt casts. The erosional remnant of this member on Striped Peak is about 300 ft thick, but it is about 2,300 ft thick a few kilometers to the southwest. The member below is a buff-weathering stromatolitic dolomite about 200 ft thick. The third member down section is a red, medium-grained, planar-bedded, stromatolitic dolomite containing some dolomite cement and streaks and is about 650 ft thick. The basal member is interbedded argillite, siltite, and quartzite that are dominantly red in color but contain some green strata; mud cracks, ripple marks, and small-scale cross-beds are common; the member is about 1,000 ft thick. Anomalous amounts of copper sulfides occur at places in green beds of the lower part of the Striped Peak and in the carbonate members. The Striped Peak as originally defined is the red rock sequence above black argillites of the upper part of the Wallace Formation. Using this definition, Anderson (1930) called red strata above the Wallace and below the Libby Formation in the Clark Fork, Idaho, area the Striped Peak Formation (fig. 2). In the Clark Fork area, the sequence of members seen at Striped Peak is found in the lower 600 ft of section (fig. 2); above this, Harrison and Jobin (1963) mapped: a dolomite member about 400 ft thick characterized by boxwork structure, stromatolites, and oolites; a black interlaminated argillite and siltite member about 300 ft thick; and a red arkosic, planar-bedded, fine- to medium-grained quartzite member about 650 ft thick. All these units are included in the Striped Peak Formation (Ysp) mapped in the northwestern part of the area.'
1222|'In the north-central area, range from 0 ft to 400 ft in thickness and are mapped between the Mount Shields Formation, equivalent to the Striped Peak at Striped Peak, and the Bonner Quartzite, equivalent to the quartzite member of the Striped Peak at Clark Fork. These two members, along with some beds in the upper part of the Wallace Formation, commonly contain several hundred parts per million of boron (Harrison and Grimes, 1970)-a feature unique to the western facies in this part of the stratigraphic section.'
1223|'Consists of three informal members. The upper member is interbedded laminated argillite and siltite; dominantly red with minor green strata in the lower part, but dominantly green argillite and siltite containing dolomitic beds near the top. Red strata commonly contain salt casts, mud cracks, mud chips, and ripple marks. Some green strata contain anomalous amounts of chalcocite and bornite or, more rarely, chalcopyrite. Ranges in thickness from about 3,300 ft in the south, where upper green-bed zone is about 100 ft thick, to about 1,000 ft in the north where upper green-bed zone is about 330 ft thick: Middle member is red fine-grained arkosic planar-bedded quartzite containing at places tan dolomitic lenses, streaks, and cement; has a zone of red stromatolite beds near top. Ranges in thickness from about 3,300 ft in the southeast to about 650 ft in the north. Basal member is interbedded siltite, quartzite, and argillite; dominantly red in color but contains some green argillite and siltite; mud cracks, mud chips, ripple marks, and cut-and-fill structures abundant. Argillite is commonly in partings between planar beds of micaceous arkosic siltite and quartzite. Ranges in thickness from about 3,300 ft in the southeast to about 1,000 ft in the north.'
1224|'Predominantly thinly and evenly laminated, green and pale-green dolomitic argillite; weathers readily into tan platy rubble. Stromatolite heads or beds are scattered through the section but particularly in lower part. A few green strata have anomalous amounts of copper sulfides. Near middle of unit contains a zone about 300 ft thick that has two or more thin (10-ft-thick) beds of red interlaminated argillite and siltite. Ranges in thickness from about 1,200 ft in the southeast to about 2,200 ft in the north. Unit is missing in the west.'
1225|'Interbedded red and green interlaminated argillite and siltite contains mud cracks, mud chips, and ripple marks. Dolomitic beds scattered through section. Commonly has green-bed zone at base. Chlorite and muscovite on bedding planes. Green beds at places contain anomalous amounts of disseminated chalcocite and bornite. In northern area contains an interlaminated black and white argillite unit about 390 ft thick. Thickness of Snowslip ranges from about 1,600 to 1,800 ft. Unit is missing in southwest and west.'
1226|'The upper member of the Wallace, as exposed on the south side of Striped Peak and on Foolhen Mountain, was divided into three lithologic units by Shenon and McConnel (1939). The middle unit can be further subdivided, so that in those localities the upper member of the Wallace consists of, from youngest to oldest: (1) an upper zone of black, thinly laminated argillite similar to the lower zone but including beds showing intricate small folds from soft-sediment deformation; (2) a zone of dolomite, stromatolites, and oolites containing interbeds of green dolomitic argillite; (3) a zone of green planar-laminated argillite and siltite that is pyritic and dolomitic; and (4) a lower zone of thinly laminated black argillite containing some green laminated argillite, moderately abundant desiccation cracks, and cut-and-fill structures. The uppermost contact is fairly sharp and is marked by the appearance of green or red siltites and quartzites of the overlying Striped Peak Formation. The lowermost contact of the upper member grades into the alternating beds of black argillite and white siltite of the middle member of the Wallace. Lithologic units and their proportions vary in the upper member. To the north, the characteristic black laminated argillite is interbedded in various proportions with green laminated argillite and with minor amounts of red laminated argillite. In the type locality, the upper member is overlain by the basal unit of the Striped Peak (equals Mount Shields), but in other areas it is overlain by either the Snowslip or Shepard Formation. Ranges in thickness from 0 ft in the southeast to about 5,000 ft in the northwest.'
1227|'Middle member: Characteristic lithology is uneven and wavy bedded; black argillite alternates with slightly dolomitic white siltite or very fine grained quartzite layers that range from an inch to 20 in. in thickness; this is the unit exposed in the type locality of the Wallace in road cuts and valleys at the town of Wallace, Idaho. Also included are some beds of black laminated argillite, green interlaminated argillite and siltite, and dolomitic argillite. Zones of dolomitic argillite and siltite similar to rocks of the lower member, some of which show vertical ribbons of calcite ("molar tooth structure"), are commonly a few feet thick but may dominate in zones 1,300 ft thick. To the south and southeast, sedimentary breccias of high carbonate content are common and are associated with large slump folds in zones as thick as 60 ft. The breccias consist of angular fragments of quartzite and blocks of typical middle Wallace lithology suspended in a silty matrix and cemented by calcite, dolomite, iron-carbonate, and quartz; these breccias are commonly dotted by crystals or pseudomorphs of scapolite or shortite(?). Thicker breccias and slumped zones tend to be near the base, but occur throughout the middle member in the southwestern and south-central part of the area. The brecciated and slumped zones are well displayed in road cuts along Trout Creek south of Superior, Mont. Unit contains rare salt casts. Metamorphosed rocks in the south-central area have light-gray scapolite crystals speckled through black argillite. The contact with the lower member is gradational and is placed where the green laminated dolomitic argillites begin to dominate the section. Thickness ranges from about 7,000 ft in the south to about 4,400 ft in the north.

Lower member:  Dominantly green interlaminated dolomitic argillite and siltite, some of which contains irregular vertical ribbons ("molar tooth structure") and pods or irregular blobs of calcite. Most of the unit contains some carbonate, either as impure beds or cement. Beds containing stromatolites are scattered through the section. Unit also contains a few interbeds having lithologies similar to those characteristic of the middle and upper members. Lower contact is sharp where underlain by the quartzite member or by purple laminated argillites of the St. Regis, but is gradational where green laminated argillite occurs at the top of the St. Regis. Rocks typical of the unit are well exposed in cirques at the head of drainages on both sides of the Idaho-Montana line in the south-central area. Thickness ranges from about 8,200 ft in the south to about 500 ft in the north part of the map area.'
1228|'Characteristic lithology is uneven and wavy bedded; black argillite alternates with slightly dolomitic white siltite or very fine grained quartzite layers that range from an inch to 20 in. in thickness; this is the unit exposed in the type locality of the Wallace in road cuts and valleys at the town of Wallace, Idaho. Also included are some beds of black laminated argillite, green interlaminated argillite and siltite, and dolomitic argillite. Zones of dolomitic argillite and siltite similar to rocks of the lower member, some of which show vertical ribbons of calcite ("molar tooth structure"), are commonly a few feet thick but may dominate in zones 1,300 ft thick. To the south and southeast, sedimentary breccias of high carbonate content are common and are associated with large slump folds in zones as thick as 60 ft. The breccias consist of angular fragments of quartzite and blocks of typical middle Wallace lithology suspended in a silty matrix and cemented by calcite, dolomite, iron-carbonate, and quartz; these breccias are commonly dotted by crystals or pseudomorphs of scapolite or shortite(?). Thicker breccias and slumped zones tend to be near the base, but occur throughout the middle member in the southwestern and south-central part of the area. The brecciated and slumped zones are well displayed in road cuts along Trout Creek south of Superior, Mont. Unit contains rare salt casts. Metamorphosed rocks in the south-central area have light-gray scapolite crystals speckled through black argillite. The contact with the lower member is gradational and is placed where the green laminated dolomitic argillites begin to dominate the section. Thickness ranges from about 7,000 ft in the south to about 4,400 ft in the north.'
1229|'Dominantly green interlaminated dolomitic argillite and siltite, some of which contains irregular vertical ribbons ("molar tooth structure") and pods or irregular blobs of calcite. Most of the unit contains some carbonate, either as impure beds or cement. Beds containing stromatolites are scattered through the section. Unit also contains a few interbeds having lithologies similar to those characteristic of the middle and upper members. Lower contact is sharp where underlain by the quartzite member or by purple laminated argillites of the St. Regis, but is gradational where green laminated argillite occurs at the top of the St. Regis. Rocks typical of the unit are well exposed in cirques at the head of drainages on both sides of the Idaho-Montana line in the south-central area. Thickness ranges from about 8,200 ft in the south to about 500 ft in the north part of the map area.'
1231|'This formation is the eastern and more carbonate-rich facies of the "middle Belt carbonate." Predominantly dolomite, dolomitic siltite, and dolomitic argillite. Characterized by 3- to 10-foot-thick cycles that begin on a cut surface and consist of gray or green dolomitic argillite, fine-grained quartzite, and siltite that grade upward into impure dolomite, which is overlain by dense orange-weathering dolomite. Irregular calcite ovoids and ribbons commonly change from horizontal pods to vertical pods and, at some places, to vertical ribbons in the impure dolomitic beds. Stromatolites and oolites are present. Upper part has zones as much as 150 ft thick that are similar to the middle member of the Wallace Formation and consist of abundant black argillite irregularly interlayered with dolomitic siltite; these zones commonly display soft-sediment deformation structures. Pyrite and minor chalcopyrite scattered throughout unit. Thickness about 8,800 ft.'
1232|'Mostly thinly and evenly laminated light and dark-green dolomitic argillite or argillite and siltite. Flattened ovoids of pink or white calcite commonly weather out and leave distinctive zones of subhorizontal voids in the exposures. Mud chips and pebbles, mud cracks, and ripple marks are common. A few shallow channels are filled by subrounded plates of limestone (rip-up clasts). Contains red argillite zones near middle of unit. Pyrite common; anomalous amounts of chalcopyrite, chalcocite, and bornite in a few strata, particularly near base. Thickness from 0 ft in the west to about 1,200 ft in the east.'
1233|'Alternating beds of dark-purple and dark-green interlaminated argillite and siltite. Lower part has beds of light-purple siltite and very fine grained quartzite; upper part is dolomitic. Abundant deformed mud-crack casts, mud chips, and ripple marks. Some green strata contain anomalous amounts of copper sulfides. Type locality is at the headwaters of the Saint Regis River. Thickness ranges from about 1,000 to 3,000 ft.'
1234|'Three lithologic units can be found in most areas. The upper unit is about 400 ft thick and is similar to lower unit, but has more green beds and contains medium-grained white quartzite beds as much as 4 in. thick. In many areas, one or more of the green beds contains anomalous amounts of chalcocite and bornite. Middle unit is about 900 ft thick and consists of alternating beds of purple argillite and pink to purple-gray, very fine grained feldspathic quartzite or coarse siltite; quartzite beds show planar cross-bedding and are as much as 50 ft thick. The lower unit is about 1,700 ft thick and is dominantly purple to purple-gray, thinly laminated argillite or argillite and siltite; mud cracks, ripple marks, fluid-escape structures, mud-chip breccias, small ball-and-pillow structures, and flute casts are common. Some dolomite cement and scattered siderite specks. A few beds of pale-purple siltite and quartzite. Green dolomitic argillite layers a few feet thick occur near base and top; some contain anomalous amounts of copper sulfides.'
1235|'Characterized in its type locality (Coeur dAlene district) by white medium-grained cross-bedded quartzite interbedded with white siltite and green laminated argillite. Quartzite shows horizontal lamination, planar cross-bedding, festoon cross-bedding, and climbing ripples; channels, load casts, and soft-sediment structures are common; heavy mineral laminations are present on cross-beds at many places. Argillitic rocks contain mud cracks, mud chips, and ripple marks. Northeast and east from type locality, unit contains progressively less quartzite and more siltite and argillite, much of which is purple or purple gray. Consists in most areas of three lithologic units: upper and lower units dominated by quartzite, and a middle unit containing quartzite interbedded with abundant argillite and siltite. Hematitic banding in quartzite and siltite commonly forms pseudocross-bedding that transects true bedding. Zone of abundant white quartzite trends north from type locality and contains, at places, anomalous amounts of silver and copper sulfide that reach ore grade in a few localities. Thickness of Revett ranges from about 500 ft to 2,500 ft.'
1236|'Several lithologic units can be identified at many places and commonly include the following four: 

(1) an upper zone similar to the one underlying it, except it contains white to purple-gray fine- to medium-grained quartzite beds 3-6 ft thick that increase in abundance upward; 

(2) a zone of green-gray to purple-gray interbedded blocky argillite and siltite that contain mud cracks and mud chips; 

(3) a zone dominated by parallel- and thinly laminated gray to purple-gray siltite in blocky planar beds that have minor argillite partings or beds; and

(4) a lower zone of green parallel-laminated interbedded argillite and siltite that are generally in beds about 2 in. to 20 in. thick and give a blocky-flaggy outcrop (upper part of this zone has purple-gray interbeds of argillite and siltite). 

Siltites are commonly speckled by tiny euhedral magnetite crystals. Anomalous amounts of chalcocite occur near the top of the lower zone and in zone (2). Thickness ranges from about 2,500 ft in the type locality near Burke, Idaho, to about 3,450 ft in the north and northeast to the thickest known section of about 7,500 ft in the southeast.'
1237|'The upper part, as used here, includes a transition zone, as originally used by Hobbs and others (1965), consisting of pyritic black and gray laminated, wavy and lenticularly bedded argillite and siltite that contain thin blocky beds of pyritic green argillite and siltite, cut-and-fill structures, and ripple marks, plus a lower zone of pyritic, evenly laminated, black and gray argillite and siltite in planar couplets that range from 0.5 in. to 1 in. in thickness; the basal 650 ft contains some beds of planar-laminated quartzite. Base of this part is the top of the gray micaceous quartzite sequence that is present throughout the area and marks the top of the lower part of the Prichard Formation. Some mappers have limited the upper part to the transition zone only, whereas others have placed the transition zone in the Burke Formation; we have not changed their contacts in this compilation. Thickness of the unit ranges from about 1,970 ft to 5,250 ft, depending in large part on whether only the transition zone was mapped as the upper part of the Prichard.'
1238|'Consists of seven lithologic units. The informal members identified by Cressman (1981, 1982) in the area of Plains, Mont., include from top to bottom:

(1)Planar-laminated medium-gray fine-grained micaceous quartzite interbedded with olive-gray siltite and medium-light-gray argillite; quartzite beds grade to argillite in top 0.5-1 in. Thickness 1,640 ft.

(2)Interlaminated and very thinly interbedded dark-gray and light-gray argillite and siltite; pyrite or pyrrhotite laminae are present locally. Black tourmaline-bearing chert bed as much as 12 in. thick is present locally. Argillite pebble conglomerate that contains scattered clasts of galena-sphalerite is present locally in lower part. Thickness from 3,200 ft to 3,600 ft.

(3)Interlaminated siltite and argillite interbedded with some quartzite, particularly in lower part; cross-bedding, scour-and-fill structures, mud cracks, and mud-chip breccias common. Thickness 2,710 ft.

(4)Platy-weathering olive-gray silty argillite that contains abundant chlorite porphyroblasts and sparse garnet; some interbedded quartzite in lower part and interbedded siltite in upper part. Thickness about 950 ft.

(5)Medium-gray fine-grained quartzite in beds 1-2 ft thick; planar laminated in part; cross-lamination in upper part of some beds; beds grade to argillite in top 0.5-1 in. Thickness 250 ft to 360 ft.

(6)Graded siltite-argillite couplets several tenths of an inch to an inch thick; siltite is dark gray; argillite is light gray. Some black argillite laminations contain felted masses of tourmaline. About 15 percent of the member consists of slump folds in composite slump sheets that average 2.5 ft thick. Thickness about 3,280 ft.

 (7)A member similar in lithology to member above but without slump folds. About 1,970 ft exposed.'
1250|'Silt- to boulder-size, moderately sorted to well-sorted sediments in modern floodplains, including overbank deposits. Larger clasts are moderately rounded to well-rounded. Maximum thickness greater than 5 m.'
1251|'Black to dark-brown organic-rich clay, silt and sand in grassy or willow-covered flat outcrops. Mostly represents eutrophication of shallow lakes.'
1252|'Unconsolidated to slightly indurated, mostly massive, dark-brown to light-gray-brown deposits that mantle gently to moderately sloping surfaces; sediment types are intermixed by downslope movement. Colluvium contains cobbles and pebbles derived from weathering of bedrock; loess is very fine grained sand, silt, and minor clay. Commonly contains poorly to moderately developed soil profile in upper part. Includes alluvium in small channels and sheetwash on steeper hillsides. Some small areas (as in Tobacco Root Mountains) underlain by till in valleys above about 2,000 m. Unmapped in many areas, particularly where deposit is thin and forms discontinuous veneer. Maximum thickness probably less than 10 m.'
1253|'Angular and subangular cobbles and boulders at base of steep valley walls or cliffs. Boulders generally as large as 2 m, although in places as large as 10 m. Locally includes minor alluvial deposits and rock-glacier deposits. Maximum thickness greater than 20 m.'
1254|'Ranges from chaotically oriented debris to almost intact slump blocks of bedrock. About 10 m to greater than 50 m thick.'
1255|'Hummocky, lobate deposits of angular boulders having a frontal slope near the angle of repose; locally active. In places, grade into and include some talus (unit Qt). About 20 m thick.'
1256|'Moderately well sorted pebble- to boulder-size gravel in fan-shaped deposits at base of mountain fronts. Includes piedmont-slope deposits and debris-flow deposits.'
1257|'Moderately well-sorted cobble and boulder gravel that forms a prominent alluvial fan at mouth of Cedar Creek in Madison Valley. Clasts rounded to subrounded. Surface characterized by braided stream pattern. Locally mantled by loess less than 1 m thick. Fan formed mainly during Pinedale (about 20-14 ka) and Bull Lake (about 140-100 ka) glaciations; deposits of both ages exposed at surface (Ritter and others, 1990); minor proximal fan development during Holocene. Modern channel of Cedar Creek incised about 10 m into fan deposits near mouth of creek, indicating proximal fan deposits presently eroding. As much as 150 m thick. Unit shown separately from other fan deposits due to its prominent size and detailed studies (Ritter and others, 1990).'
1258|'Unsorted, unstratified, unconsolidated, subangular to subrounded boulders in an unsorted matrix as fine as silt. Most till deposited during Pinedale (about 20-14 ka) and Bull Lake (about 140-100 ka) glaciations. Pinedale-age till preserved in hummocky deposits that contain numerous closed depressions and have a thin or non-existent soil profile; deposits of Bull Lake-age till have more rounded topography, are more dissected, and generally exhibit a well-developed soil profile. As much as about 50 m thick.'
1259|'Unsorted, unstratified, nonconsolidated deposit composed of angular to subangular clasts of Archean gneiss as large as 2 m. Believed to be mostly debris-flow deposits, but may include some till and landslide deposits. Mapped only in Jack Creek area. Maximum thickness greater than 20 m.'
1260|'Moderately sorted, moderately rounded to well-rounded sand and gravel. Underlies about 12 recognized terrace surfaces in Madison Valley. Bearzi (1987) recognized 11 geomorphic surfaces along Jack Creek. In Madison Valley, east of Madison River, includes all but the highest (and oldest) terrace-gravel deposit, which is shown separately (unit Qgc). West of Madison River in Madison Valley, highest terrace-gravel deposits may correlate with terrace-gravel deposits of the Cameron bench (unit Qgc). Mantled by less than 2 m of loess at most places, although loess on many higher surfaces is thick enough to support cultivation. Mostly less than 10 m thick.'
1261|'Moderately sorted, moderately rounded to well-rounded sand and gravel underlying topographically highest (and oldest) terrace deposits in Madison Valley. Formed during Bull Lake glaciation (about 140-100 ka) (Schneider and Ritter, 1987). Mantled by less than 2 m of loess in most places.'
1262|'Interbedded, moderately sorted, poorly consolidated to unconsolidated, well-bedded to massive silt, sand, and well rounded cobbles that are exposed in slopes adjacent to, and below, terraces in Madison Valley. Exposed basin-fill deposits are interpreted to be no older than Pliocene, although they overlie deeply buried basin-fill deposits, as thick as 4,500 m, that may be as old as Eocene in the Madison Valley (Rasmussen and Fields, 1983).'
1263|'Light brown to gray, massive welded tuff that contains sparse phenocrysts of sanidine, quartz and plagioclase. Matrix is mostly devitrified glass shards, opaque minerals, and aphanitic minerals. Contains sparse pumice fragments. Lithophysae and vesicles not observed in quadrangle. Forms prominent cap to many ridges and buttes. Age of unit is 2.0 Ma and source is from Yellowstone caldera (Christiansen and Blank, 1972), the northern edge of which is about 30 km south of quadrangles southeastern corner. Thickness increases to south and maximum thickness in quadrangle about 50 m.'
1264|'White, light gray, and light-brownish-gray, moderately to well indurated, locally vuggy limestone, limy sandstone, ash-bearing sandstone, pebbly sandstone, and pebble conglomerate. Interlayered ash deposits common, especially is association with limestone. Limestone may be either lacustrine deposits or carbonate paleosols (Hanneman and others, 1991). Mapped along Madison River, east of Ennis Lake, and in Spanish Creek basin. One maximum 40Ar/39Ar age on sanidine from just east of Ennis Lake in Madison Valley (NE 1/4, Sec. 6, R. 1 E., T. 5 S.), is 16.20.19 Ma (K.K. Kellogg and S.S. Harlan, unpublished data, 1990). Deposits in Spanish Creek basin undated, but probably Miocene. Maximum thickness greater than 1,000 m.'
1265|'Light brownish-gray to yellowish-gray, locally vuggy, well-bedded, fine-grained limestone. Similar to thin limestones associated with ash-bearing sediments in unit Ts, although much thicker, so is considered to be Miocene in age; maximum thickness greater than 20 m. Mapped along west side of Madison Valley (Hadley, 1969a, b).'
1266|'Probably basaltic, contains fragments of clay and basalt (Wier, 1982). Intrudes both volcanic rocks and Archean gneiss. One oval outcrop mapped, about 200 m in diameter, just south of Virginia City.'
1267|'Mostly dense to scoriaceous basalt and andesite flows, volcanic agglomerates, sandy tuff, and interbedded basaltic cinder deposits. Flows are black and dark brown and contain small phenocrysts of calcic plagioclase, olivine, augite, opaque minerals, and, in places, potassium feldspar and biotite (Hadley, 1980). At least one silicic (latitic?) plagioclase-phyric flow occurs near base of unit, 4 km southeast of Virginia City. Three localities gave the following potassium-argon (K-Ar) dates: 1) 49.32.5 and 51.11.9 Ma (biotite) and 51.03.8 Ma (plagioclase); this flow is just north of Virginia City and overlies Archean basement, 2) 34.43.0 Ma (whole rock), and 3) 32.71.4 Ma (whole rock) (Marvin and others, 1974). Unit greater than 200 m thick.'
1268|'Dark-gray to black aphanitic rhyolite flows north and northwest of Ennis Lake (Kellogg, 1993b; Vitaliano and Cordua, 1979). Cut by many faults; local steep dips. Correlated with volcanic rocks of Virginia City volcanic field.'
1269|'Pale gray to white rhyolitic air-fall ash, tuffaceous sandstone, and sparse gravel lenses. Poorly exposed in most places and occurs locally at base of sequence of volcanic rocks of Virginia City volcanic field. Large areas mapped by Hadley (1969b) as felsic tuff are underlain mostly by chaotic, locally tuffaceous landslide deposits. Thickness as great as about 40 m.'
1270|'Coarse-grained, well bedded, cross-bedded volcaniclastic sandstone, pebbly sandstone, and pebble and cobble conglomerate that in places underlie the rocks of the Virginia City volcanic field (Hadley, 1969b, 1980).'
1272|'Mapped in Madison Valley in southern part of quadrangle (Hadley, 1969b); may be outlier of volcanic rocks of Virginia City volcanic field.'
1273|'Light- to medium-gray, and brownish-gray, dense, porphyritic dacite. Phenocrysts are euhedral plagioclase, hornblende, and biotite. Petrographically very similar to dacite porphyry of Fan and Lone Mountains, but at least some stocks intrudes Eocene volcanic rocks; other nearby rocks of similar composition intrude Cambrian strata and Archean gneiss. One potassium-argon biotite date of 49.51.5 Ma (Chadwick, 1969, p. 160).'
1274|'Dark gray, very fine-grained basalt or andesite intrusive breccia containing sparse, small phenocrysts of plagioclase. Forms two small necks in upper Porcupine Creek, east of Gallatin Valley. Intrudes Eocene volcanic rocks and Archean gneiss. Not included in Absaroka Volcanic Supergroup by Simons and others (1985), but unit probably formed feeder vents for younger rocks of Supergroup.'
1275|'Mapped where proportion of mostly andesitic and basaltic flows predominate over volcaniclastic rocks, as mapped by the U.S. Geological Survey (1972). Compositions similar to those in Sepulcher Formation, described below. Conformably overlies rocks of Sepulcher Formation.'
1276|'Mafic and intermediate-composition volcaniclastic rocks, flow breccias, and lava flows. Contains sparse beds of light-reddish-brown welded tuffs. Includes the Fortress Mountain and Daly Creek Members (Smedes and Prostka, 1972), and Hyalite Peak Volcanics (Chadwick, 1969; Hiza, 1994). Most of unit composed of dark grayish-brown laharic breccias, volcaniclastic conglomerate, and light- to medium-gray volcaniclastic sandstone. Both laharic deposits (vent facies) and conglomeratic deposits (alluvial facies) are greater than 100 m thick in places, crudely stratified, and well indurated. Laharic deposits composed of unsorted, angular to subrounded volcanic debris containing clasts as large as 3 m across. Both lahars and conglomerates contain much silicified wood, commonly as large trunks as thick as 3 m, in growth positions.

Lavas are mostly medium-gray to dark-gray, fine-grained to sparsely porphyritic pyroxene or olivine-pyroxene andesite and basalt. Flows with compositions as silicic as latite or trachyandesite occur in upper part of section (as on Steamboat Mountain). Proportion of flows appears to increase upward in section.

Basal Daly Creek Member of Sepulcher Formation commonly mapped on basis of lighter color and preponderance of alluvial-facies material. However, except for a gradual increase upward in percentage of flows, no distinct difference was noted between lower and upper parts of Sepulcher Formation.'
1277|'Cobbles and boulders predominantly of Archean rocks, with subordinate clasts of Paleozoic carbonate and Tertiary volcanic rocks, mapped near Garnet Mountain in the northeastern part of quadrangle (McMannis and Chadwick, 1964). Conglomerate is locally overlain by a thin, discontinuous siltstone of late early Eocene age. Not overlain by volcanic rocks in quadrangle, but similar rocks in adjacent areas occur at the base of volcanic sequences of the Absaroka Supergroup.'
1278|'Greenish-gray to pinkish-gray, sparsely porphyritic, massive, siliceous dacite or rhyolite. Most phenocrysts consist of as much as 15 percent white, strongly saussuritized plagioclase crystals as long as 3 mm. Rock commonly stained black by manganese oxide. Mainly forms thin sills, dikes, and irregular pods intruding exclusively Archean rocks. Described by Kellogg (1993b). Unit undated, but shares compositional and textural similarities with both Upper Cretaceous dacite porphyry of Fan and Lone Mountains and Eocene rhyolite and rhyodacite plugs near Norris (Kellogg, 1994, 1995), about 10-15 km north of quadrangle.'
1279|'Black, medium-grained plagioclase-clinopyroxene gabbro that typically weathers into spheroidal blocks. In places completely weathered into grussy orange-brown soil. Several larger sills contain irregular dikes, as wide as 2 m, of fine-grained pinkish-gray inequigranular clinopyroxene-biotite syenite, in which the clinopyroxene forms conspicuous rods as long as 1 cm. Syenite, in turn, intruded by thin aplitic dikes. Unit crops out near Meadow Village at Big Sky and intrudes Upper and Lower Cretaceous rocks.'
1280|'Gray to greenish-gray porphyritic dacite that weathers to a very light gray or tan. Euhedral to subhedral phenocrysts compose 30-50 percent of the rock; phenocrysts, 70-90 percent zoned plagioclase (An25-35) as long as 1 cm, trace to 15 percent green hornblende as long as 6 mm, 0-15 percent biotite as long as 3 mm, and 0-10 percent equant quartz as long as 5 mm. Mafic minerals commonly altered to chlorite and epidote; plagioclase sericitized. Matrix is very fine grained and dense, and contains about 5 percent opaque minerals. Fine-grained chill zone extends inward several centimeters from contacts. Commonly contains mafic autoliths as large as about 0.5 m. Forms sills, some greater than 80 m thick, in two intrusive centers underlying Fan Mountain and Lone Mountain. The sills are thought to form a "Christmas-tree laccolith" complex underlying both mountains (Swanson,1950), although Kellogg (1992) found no evidence for a central "trunk." Late Cretaceous beds dip away from the central peaks at both Fan and Lone Mountains. Intrudes rocks that range in age from Middle Cambrian to Late Cretaceous. Where less than about 20 m thick, unit is indicated on map by a single line. Potassium-argon (K-Ar) and 40Ar/39Ar ages from hornblende are about 68-69 Ma (Tysdal and others, 1986; K.S. Kellogg and S.S. Harlan, unpublished data).'
1281|'Gray, coarse-grained, inequigranular to porphyritic, massive hornblende-biotite granodiorite, monzogranite, and monzodiorite (classification of Streckeisen, 1976). Typically contains 50 percent normally zoned oligoclase (An25-An28), 15-25 percent green hornblende, 10-20 percent microcline (slight development of braid perthite) commonly as phenocrysts as long as 3 cm, 0-20 percent quartz, 5 percent biotite, 0-1 percent clinopyroxene cores in some hornblende, trace to 3 percent magnetite, and traces of apatite and conspicuous sphene and zircon; hypidiomorphic texture. Includes minor dark-gray hornblende diorite and granodiorite along border and in satellitic stocks east of main batholith. Weathers light gray, in rounded tors or flat grussy outcrops. K-Ar age of batholith is 71-74 Ma (Vitaliano and Cordua, 1979).'
1282|'Reddish-orange conglomerate with sandstone matrix cemented by calcite and hematite. Contains well-rounded cobbles and boulders derived from Paleozoic and Mesozoic strata shed from thrust plates to west; represents an unroofing sequence, with clasts generally increasing in age upwards (DeCelles and others, 1987). Lower contact is conformable with underlying Livingston Formation. Well exposed only on Sphinx Mountain and The Helmet. Minimum thickness about 610 m.'
1283|'Conglomerate and interbedded limestone containing well-rounded clasts of Archean gneiss and Belt Supergroup quartzite.  Mapped by Hadley (1969b) as two separate units (Sphinx Conglomerate and Tertiary gravel) but both units reinterpreted on fossil and stratigraphic evidence as Beaverhead Group rocks of Cretaceous age (J.M. ONeill, personal commun., 1997).'
1284|'Livingston Formation exposed on west side of Madison Range, near Sphinx Mountain, and east of Gallatin River, south of the Spanish Peaks fault. Does not crop out west of Madison Valley. Undivided unit shown only in southeastern part of quadrangle. Description after Tysdal (1990).'
1285|'Cobble and boulder conglomerate of well-rounded volcanic clasts in matrix of coarse-grained volcaniclastic sandstone; upper part predominantly sandstone. Lower contact is conformable. Thickness as much as 180 m.'
1286|'Brown, maroon, and gray dacite to basalt flows, autoclastic breccia, tuff breccia, and welded tuff; minor interlayered volcaniclastic sandstone. Lower contact is conformable. Thickness estimated 300-450 m.'
1287|'Complexly intertonguing units of dark-green to dark-brown, medium- to coarse-grained, locally pebbly volcaniclastic sandstone, olivine basalt, mudflow breccia, volcaniclastic conglomerate, and mudstone. Conformable with underlying Everts(?) Formation. Thickness ranges from about 60 to 210 m).'
1288|'May locally include Muddy Sandstone and Thermopolis Shale.  Mapped in area of Cretaceous outcrops east of Gallatin River.'
1289|'Everts Formation - Thin- to medium-bedded light-gray to dark-gray, poorly to moderately sorted quartz-rich sandstone; intercalated with thin-bedded, greenish-gray to dark gray mudstone and siltstone. Contains a few thin beds of dense limestone, porcellanite, and coal. About equal quantities of sandstone and finer-grained sedimentary rocks. Does not crop out west of Madison Valley. Conformably overlies Virgelle Sandstone. About 425 m thick.

Virgelle Sandstone - Thin- to thick-bedded, medium- to coarse-grained, light-brown to yellowish-brown, trough-cross-bedded quartz sandstone that forms prominent white-weathering ledges. Conformably overlies Telegraph Creek Formation. Does not crop out west of Madison Valley. About 25-50 m thick.'
1290|'Light-gray to dark-brown, thin- to medium-bedded, feldspathic, calcite-cemented sandstone and interbedded dark-gray siltstone and mudstone. Middle marker sequence is a 20-m thick white tuffaceous siltstone and sandstone. Contains thin flaggy sandstones in lower part. Conformably overlies Cody Shale. Does not crop out west of Madison Valley. Thickness about 200 m.'
1291|'Upper part consists of thin-bedded black fissile shale that is interbedded with minor amounts of thin-bedded, brown, commonly bioturbated calcareous, fine-grained sandstone. Lower part consists of black, fissile shale and minor siltstone that weathers dark gray. Does not crop out west of Madison Valley. Conformably overlies Frontier Formation. Thickness about 300 m.'
1292|'Mostly a sequence of alternating black shale and light-gray to yellowish-tan, thin- to very thick bedded, cross-bedded sandstone. In the Madison Range, sandstone ledges as thick as 3 m; ratio of sandstone to shale about 1:3. Shale is locally carbonaceous or coaly. Shale sequences are as thick as about 20 m and commonly contain equally spaced 5- to 10-cm-thick sandstone beds, spaced 15-20 cm apart. Contains several white porcellanite beds; one prominent porcellanite bed in the Madison Range, about 6 m thick, is about 15 m above base of sequence and displays well-developed ball-and-pillow structures. Conformable with underlying Mowry Shale. Formation thickens greatly to the west; thickness in Madison Range about 140-180 m while that in Gravelly Range is greater than 1,500 m.'
1293|'Mostly brownish-gray and greenish-gray tuffaceous mudstone and shale and, in upper part, contains abundant thin sandstone beds. Lower Vaughn Member consists of conspicuous gray, green, yellow, brown, orange, pink, and cream-colored bentonitic mudstone, porcellanite, siltstone, and minor interbedded quartz sandstone, although strikingly varicolored units missing in northern Madison Range. Poorly exposed in most places. Unconformable with underlying Muddy Formation. Thickness 90-180 m.'
1294|'Muddy Sandstone:  Thin- to medium-bedded, medium- to coarse-grained, brown to brownish-gray, poorly to moderately indurated, clayey, ledge-forming, salt-and-pepper sandstone; locally contains mud chips as long as 1 cm. In northern Madison Range, formation typically exposed as upper and lower sandstone sequence with central, poorly exposed shaly sequence. Thickness varies widely; in the northern Madison Range is about 20-45 m thick; further south in the Madison Range it is as great as 107 m (Tysdal, 1990); in the Gravelly Range it is about 15 m thick (Hadley, 1969b, 1980).

Thermopolis Shale:  Composed of an upper sequence (three-quarters of the total thickness) that is black to dark-gray, locally carbonaceous fissile shale and poorly indurated, thin-bedded, silty brown sandstone. Lower one-quarter of unit is thin- to medium-bedded, fine-grained white to tan quartzite that contains black shale interbeds; Ripple marks and Liesegang bands are common in sandstone beds. Unconformable contact with underlying Kootenai Formation. Thickness throughout quadrangle about 70-80 m.'
1295|'Upper 10-15 m is medium-bedded light-gray, micritic, oolitic limestone that contains abundant gastropod fossils in uppermost part. Middle part is variegated red, purple, yellow, and gray shale, mudstone, siltstone, sandstone, and locally nodular freshwater limestone. Formation typically weathers to a reddish soil. Lower 10-40 m is medium- to coarse-grained gray, well-indurated, ledge-forming salt-and-pepper sandstone that contains a basal chert-pebble conglomerate as thick as 1 m. Lower contact is unconformable. Total thickness in the northern Madison Range is about 90 m (Kellogg, 1992, 1993a); in the Gravelly Range it is as thick as 170 m (Hadley, 1980), and in the southeastern part of the map area it as much as about 130 m thick.'
1296|'Morrison Formation:  Upper 20-30 m is mostly black and locally purple shale that contains minor intercalated thin- to medium-bedded, rusty-brown and gray quartz sandstone that is lensoidal in places. The lower, thicker part of the Morrison is composed of thin-bedded, gray, yellow, orange, red, and green shale and siltstone interbedded with lesser amounts of gray quartzite and thin-bedded, brown limestone. Unconformable with underlying unit. About 75-100 m thick.

Ellis Group includes:  Swift Sandstone--brown, medium- to coarse-grained glauconitic sandstone, locally containing abundant chert pebbles, and minor olive-green shale; glauconite commonly weathered to orange limonitic clots. More calcareous in eastern part of map area (Tysdal, 1990). Unconformably overlies Rierdon Limestone. Less than 12 m thick.

Rierdon Limestone - Thin- to thick-bedded, yellowish-gray to brownish-gray, fine-grained, oolitic limestone; contains a few limy siltstone interbeds. Bivalves Camptonectes sp. and Gryphaea sp. locally abundant. Forms prominent cliffs near Shell Creek in western Madison Range. Thickness about 8-30 m.

Sawtooth Formation - Interbedded limestone and shale, weathers yellowish-brown, and is very poorly exposed. Sawtooth unconformably overlies Dinwoody Formation. Thickness 25-55 m.

Woodside Siltstone - Brick-red to orange-red, thin-bedded siltstone and mudstone, interbedded with gypsum and scattered thin beds of gray limestone. Mostly poorly exposed, although forms prominent red soil. Thickness increases markedly to southeast; nonexistent north of Porcupine Creek in the Gallatin Range (Simons and others, 1985) and only a "feather edge" may exist in the northernmost Gravelly Range (Hadley, 1980). Unit previously mapped as Chugwater Formation in the southeastern part of the quadrangle (Simons and others, 1985). Thickness 0 to about 220 m (Tysdal, 1990).

Dinwoody Formation - Brown, silty sandstone, siltstone, and thin-bedded brown limestone. Small brachiopods locally abundant. Weathers light yellowish-brown and is poorly exposed. Dinwoody unconformably overlies Shedhorn Sandstone. Thickness ranges between about 20 and 80 m.'
1297|'Upper 20-30 m is mostly black and locally purple shale that contains minor intercalated thin- to medium-bedded, rusty-brown and gray quartz sandstone that is lensoidal in places. The lower, thicker part of the Morrison is composed of thin-bedded, gray, yellow, orange, red, and green shale and siltstone interbedded with lesser amounts of gray quartzite and thin-bedded, brown limestone. Unconformable with underlying unit. About 75-100 m thick.'
1298|'In most places this combined unit is poorly exposed. Total thickness about 185 m.

Swift Sandstone - Brown, medium- to coarse-grained glauconitic sandstone, locally containing abundant chert pebbles, and minor olive-green shale; glauconite commonly weathered to orange limonitic clots. More calcareous in eastern part of map area (Tysdal, 1990). Unconformably overlies Rierdon Limestone. Less than 12 m thick.

Rierdon Limestone - Thin- to thick-bedded, yellowish-gray to brownish-gray, fine-grained, oolitic limestone; contains a few limy siltstone interbeds. Bivalves Camptonectes sp. and Gryphaea sp. locally abundant. Forms prominent cliffs near Shell Creek in western Madison Range. Thickness about 8-30 m.

Sawtooth Formation - interbedded limestone and shale, weathers yellowish-brown, and is very poorly exposed. Sawtooth unconformably overlies Dinwoody Formation. Thickness 25-55 m.

Woodside Siltstone - Brick-red to orange-red, thin-bedded siltstone and mudstone, interbedded with gypsum and scattered thin beds of gray limestone. Mostly poorly exposed, although forms prominent red soil. Thickness increases markedly to southeast; nonexistent north of Porcupine Creek in the Gallatin Range (Simons and others, 1985) and only a "feather edge" may exist in the northernmost Gravelly Range (Hadley, 1980). Unit previously mapped as Chugwater Formation in the southeastern part of the quadrangle (Simons and others, 1985). Thickness 0 to about 220 m (Tysdal, 1990).

Dinwoody Formation - Brown, silty sandstone, siltstone, and thin-bedded brown limestone. Small brachiopods locally abundant. Weathers light yellowish-brown and is poorly exposed. Dinwoody unconformably overlies Shedhorn Sandstone. Thickness ranges between about 20 and 80 m.'
1299|'Mapped in Garnet Mountain quadrangle by McMannis and Chadwick (1964), who used the term Phosphoria Formation instead of Shedhorn Sandstone.

Shedhorn Sandstone - Mostly medium- to massive-bedded, gray, fine- to coarse-grained, very well indurated quartz-rich sandstone that contain white cherty stringers and nodules. Thin, shaly phosphorite beds in middle of formation are rarely exposed. Dolomitic near base. In Gravelly Range, chert is locally massive and filled with voids, so that chert outcrops commonly have a rubbly appearance. Conformably overlies Quadrant Sandstone. Formation about 35-70 m thick, though is about 50 m thick in northern Madison Range.

Quadrant Sandstone - Medium- to thick-bedded, white to yellowish-tan, well-sorted, fine- to medium-grained, dolomite-cemented quartzite; cross-beds common. Lower half and at least upper 15 m of formation contain a few medium-bedded, light-yellowish-tan dolostone beds. Crops out prominently.

Conformable contact with underlying Amsden Group. Thickness about 75 m.

Amsden Group - Varies widely, both in stratigraphy and thickness. In central and southern Madison Range, and in the Gravelly Range east of the Greenhorn Thrust, the unit consists of about 12 to 50 m of brick-red, reddish-brown, and pink calcareous siltstone, silty shale, shale, sandstone, and light-gray limestone and yellowish-gray dolomite. Along western Madison Range, upper part contains medium- to thin-bedded gray to grayish-tan dolostone, locally quartzitic, that grades downward into gray limestone beds (correlated by Kellogg, 1992, with the Middle and Lower Pennsylvanian Devils Pocket Formation and Alaska Bench Limestone of Wardlaw and Pecora, (1985); this sequence overlies maroon siltstone and shale that contain a few thin beds of gray limestone and dolostone (correlated with Lower Pennsylvanian Tyler Formation of Wardlaw and Pecora, 1985). Total thickness of Amsden Group rocks in the western Madison Range is 88 m.'
1300|'Mostly medium- to massive-bedded, gray, fine- to coarse-grained, very well indurated quartz-rich sandstone that contain white cherty stringers and nodules. Thin, shaly phosphorite beds in middle of formation are rarely exposed. Dolomitic near base. In Gravelly Range, chert is locally massive and filled with voids, so that chert outcrops commonly have a rubbly appearance. Conformably overlies Quadrant Sandstone. Formation about 35-70 m thick, though is about 50 m thick in northern Madison Range.'
1301|'Quadrant Sandstone - Medium- to thick-bedded, white to yellowish-tan, well-sorted, fine- to medium-grained, dolomite-cemented quartzite; cross-beds common. Lower half and at least upper 15 m of formation contain a few medium-bedded, light-yellowish-tan dolostone beds. Crops out prominently.

Conformable contact with underlying Amsden Group. Thickness about 75 m.

Amsden Group - Varies widely, both in stratigraphy and thickness. In central and southern Madison Range, and in the Gravelly Range east of the Greenhorn Thrust, the unit consists of about 12 to 50 m of brick-red, reddish-brown, and pink calcareous siltstone, silty shale, shale, sandstone, and light-gray limestone and yellowish-gray dolomite. Along western Madison Range, upper part contains medium- to thin-bedded gray to grayish-tan dolostone, locally quartzitic, that grades downward into gray limestone beds (correlated by Kellogg, 1992, with the Middle and Lower Pennsylvanian Devils Pocket Formation and Alaska Bench Limestone of Wardlaw and Pecora, (1985); this sequence overlies maroon siltstone and shale that contain a few thin beds of gray limestone and dolostone (correlated with Lower Pennsylvanian Tyler Formation of Wardlaw and Pecora, 1985). Total thickness of Amsden Group rocks in the western Madison Range is 88 m.

Snowcrest Range Group - Mapped only in western Madison Range (Kellogg, 1992), although rocks of the group may have been either unrecognized elsewhere or placed in the Amsden Group. The upper 57 m of the Snowcrest Range Group (Upper Mississippian Lombard Limestone) is mostly thin- to medium-bedded gray limestone that becomes more dolomitic and shaly toward base. The Lombard overlies the Kibbey Sandstone, which consists of about 75 m of thin- to medium-bedded yellowish-gray to maroon friable dolomitic sandstone, sandy dolostone, and siltstone.'
1302|'Mapped only west of Greenhorn thrust in Gravelly Range (Hadley, 1969b, 1980); upper, thicker part consists of thin- to thick-bedded, pale olive gray, locally very fossiliferous limestone and minor dark-greenish or olive-gray mudstone and shale. Lower 60 m or so consists of red and greenish-gray shale and calcareous sandstone and minor greenish-gray cherty limestone; sandstone and red color increase downward in sequence. Detailed description of the Big Snowy Group is given by Hadley (1980). Total thickness 135-275 m.'
1303|'Includes:  Mission Canyon Limestone - Medium- to massive-bedded, light-gray, gray, and brownish-gray, medium-crystalline limestone and minor dolostone. Weathers light gray. Chert stringers and nodules common; locally fossiliferous; solution breccias in uppermost part. Prominent ridge-forming unit. Conformable with underlying Lodgepole Limestone. Thickness about 240 m.

Lodgepole Limestone - Thin- to medium-bedded, gray to brownish-gray, finely crystalline limestone that commonly grades into silty limestone interbeds several centimeters thick. Locally cherty; upper half is profusely fossiliferous. Conformable with underlying Three Forks Formation (erroneously described as unconformable above the Three Forks in Kellogg, 1992, 1993a). Thickness about 180 m.'
1304|'Medium- to massive-bedded, light-gray, gray, and brownish-gray, medium-crystalline limestone and minor dolostone. Weathers light gray. Chert stringers and nodules common; locally fossiliferous; solution breccias in uppermost part. Prominent ridge-forming unit. Conformable with underlying Lodgepole Limestone. Thickness about 240 m.'
1305|'Thin- to medium-bedded, gray to brownish-gray, finely crystalline limestone that commonly grades into silty limestone interbeds several centimeters thick. Locally cherty; upper half is profusely fossiliferous. Conformable with underlying Three Forks Formation (erroneously described as unconformable above the Three Forks in Kellogg, 1992, 1993a). Thickness about 180 m.'
1306|'Three Forks formation - Mostly thin-bedded, yellowish-orange to yellowish-tan siltstone and silty limestone containing a few thin interbeds of brick-red-weathering siltstone. Weathers light yellowish tan. Contains a medium-gray, irregularly bedded, approximately 12-m-thick, rough-weathering limestone about 25 m above base of unit (Logan Gulch Member). Formation poorly exposed; forms slopes and swales. Unconformably overlies Jefferson Dolostone. Thickness 40-60 m.

Jefferson Formation - Thin- to thick-bedded, black, brown, dark-gray, and light-gray, petroliferous, medium-crystalline to coarsely crystalline dolostone; colors vary considerably over short stratigraphic intervals. Weathers mostly brown and outcrops are typically knobby and irregular; forms conspicuous brown hoodoos. At least upper 15 m is thick- to massive-bedded, gray dolostone solution breccia (Birdbear Member). Unconformably overlies Bighorn Dolomite(?) in northern Madison Range. Thickness about 110 m.'
1307|'Bighorn Dolomite(?) - Medium-gray, sugary dolostone in 0.2- to 1.0-m-thick beds; weathers very light gray. Tentatively placed in Bighorn Dolomite by Hanson (1952) along ridge in NE 1/4, sec. 22 and NW 1/4, sec. 23, T. 5 S., R. 1 E in northwestern Madison Range; not recognized south of this location. Unconformably overlies Red Lion Formation. Thickness about 3 m at location noted above.

Red Lion Formation - Thin-bedded, medium-gray to tan, siliceous dolostone containing conspicuous orange-tan to reddish-tan, cherty stringers as thick as 2 cm;  lower 7 m contains intraformational clasts as large as 5 mm. Along west side of Gallatin Range, contains a lower greenish-gray, locally quartzitic shale sequence as thick as 10 m (Dry Creek Shale Member) (McMannis and Chadwick, 1964). Unconformably overlies Pilgrim Formation. Thickness about 40-60 m.

Pilgrim Dolomite - Gray, light-gray, and brownish-gray, medium- to massive-bedded, locally oolitic, medium-crystalline dolostone. Weathers light gray and contains irregularly shaped darker gray mottles. Conformably overlies Park Shale. Forms conspicuous crags. Thicknesses about 30 m in northern Madison Range (Kellogg, 1992), about 60 m in the south-central part of the quadrangle (Tysdal, 1990); as much as 120 m in the Gravelly Range, although is missing along east side of range (Hadley, 1969b), and as much as 75 m in the northern Gallatin Range (McMannis and Chadwick, 1964).

Park Shale - Greenish-gray to tan, fissile shale. Poorly exposed, slope-forming unit conformably overlies Meagher Limestone. Thickness about 30-50 m in the Madison Range and Gravelly Range, although is missing along eastern side of Gravelly Range (Hadley, 1969b); thickness 50-75 m in northern Gallatin Range (McMannis and Chadwick, 1964).'
1308|'Mapped east of Gallatin River and north of Spanish Peaks fault (McMannis and Chadwick, 1964)

Red Lion Formation - Thin-bedded, medium-gray to tan, siliceous dolostone containing conspicuous orange-tan to reddish-tan, cherty stringers as thick as 2 cm;  lower 7 m contains intraformational clasts as large as 5 mm. Along west side of Gallatin Range, contains a lower greenish-gray, locally quartzitic shale sequence as thick as 10 m (Dry Creek Shale Member) (McMannis and Chadwick, 1964). Unconformably overlies Pilgrim Formation. Thickness about 40-60 m.

Pilgrim Dolomite - Gray, light-gray, and brownish-gray, medium- to massive-bedded, locally oolitic, medium-crystalline dolostone. Weathers light gray and contains irregularly shaped darker gray mottles. Conformably overlies Park Shale. Forms conspicuous crags. Thicknesses about 30 m in northern Madison Range (Kellogg, 1992), about 60 m in the south-central part of the quadrangle (Tysdal, 1990); as much as 120 m in the Gravelly Range, although is missing along east side of range (Hadley, 1969b), and as much as 75 m in the northern Gallatin Range (McMannis and Chadwick, 1964).'
1309|'Mapped south of Cedar Creek and east of Madison Valley (Tysdal, 1990; Kellogg, 1992).

Red Lion Formation - Thin-bedded, medium-gray to tan, siliceous dolostone containing conspicuous orange-tan to reddish-tan, cherty stringers as thick as 2 cm;  lower 7 m contains intraformational clasts as large as 5 mm. Along west side of Gallatin Range, contains a lower greenish-gray, locally quartzitic shale sequence as thick as 10 m (Dry Creek Shale Member) (McMannis and Chadwick, 1964). Unconformably overlies Pilgrim Formation. Thickness about 40-60 m.

Pilgrim Dolomite - Gray, light-gray, and brownish-gray, medium- to massive-bedded, locally oolitic, medium-crystalline dolostone. Weathers light gray and contains irregularly shaped darker gray mottles. Conformably overlies Park Shale. Forms conspicuous crags. Thicknesses about 30 m in northern Madison Range (Kellogg, 1992), about 60 m in the south-central part of the quadrangle (Tysdal, 1990); as much as 120 m in the Gravelly Range, although is missing along east side of range (Hadley, 1969b), and as much as 75 m in the northern Gallatin Range (McMannis and Chadwick, 1964).

Park Shale - Greenish-gray to tan, fissile shale. Poorly exposed, slope-forming unit conformably overlies Meagher Limestone. Thickness about 30-50 m in the Madison Range and Gravelly Range, although is missing along eastern side of Gravelly Range (Hadley, 1969b); thickness 50-75 m in northern Gallatin Range (McMannis and Chadwick, 1964).'
1310|'Mapped east of Gallatin River and north of Spanish Peaks fault (McMannis and Chadwick, 1964)

Park Shale - Greenish-gray to tan, fissile shale. Poorly exposed, slope-forming unit conformably overlies Meagher Limestone. Thickness about 30-50 m in the Madison Range and Gravelly Range, although is missing along eastern side of Gravelly Range (Hadley, 1969b); thickness 50-75 m in northern Gallatin Range (McMannis and Chadwick, 1964).

Wolsey Shale - Mostly thin-bedded, greenish-gray, olive-drab, gray, and grayish-brown micaceous sandstone, siltstone, and shale. Sandstone beds are wavy and bioturbated, contain green and gray- and green-mottled shale interbeds, and generally weather brown; animal trails common; locally glauconitic. Near middle of unit is a 10- to 15-m-thick section of thin-bedded, dark-gray, brown-weathering argillaceous limestone interbedded with lesser amount of sandstone and shale. Upper 5 m is interbedded wavy-laminated, thin-bedded, gray limestone and gray, micaceous siltstone. Conformable with underlying Flathead Sandstone. Forms slopes and swales. Thickness 30-65 m.

Flathead Sandstone - Thin- to medium-bedded, medium- to coarse-grained, reddish-brown, tan, and purplish-tan, quartz-rich, feldspathic sandstone; locally weathers to rusty red. Two thin zones of fine-grained, micaceous, greenish-gray argillaceous sandstone near top of formation. Basal part of formation contains rounded pebbles of metamorphic rock. Unconformably overlies Archean crystalline rock. Thickness variable, from 15 to 75 m.'
1311|'Thin- to massive-bedded, light-gray to brownish-gray, finely crystalline limestone. Locally oolitic, especially in upper part. Upper 30 m is thin-bedded, gray limestone that contains conspicuous orange mottles; upper few meters contain fissile gray-green shale. Middle 50 m is medium- to massive-bedded limestone, locally mottled tan, and containing small silicic limestone stringers. Lower 30 m is thin- to medium-bedded, tan-mottled, gray limestone that contains a few intercalated micaceous shale beds in lower part. Forms cliffs. Conformably overlies Wolsey Shale. About 100-150 m thick in the Madison Range (Tysdal, 1990; Kellogg, 1992), 100-110 m thick in the Gravelly Range (Hadley, 1980), but only about 50 m thick in northern Gallatin Range (McMannis and Chadwick, 1964).'
1312|'Wolsey Shale-Mostly thin-bedded, greenish-gray, olive-drab, gray, and grayish-brown micaceous sandstone, siltstone, and shale. Sandstone beds are wavy and bioturbated, contain green and gray- and green-mottled shale interbeds, and generally weather brown; animal trails common; locally glauconitic. Near middle of unit is a 10- to 15-m-thick section of thin-bedded, dark-gray, brown-weathering argillaceous limestone interbedded with lesser amount of sandstone and shale. Upper 5 m is interbedded wavy-laminated, thin-bedded, gray limestone and gray, micaceous siltstone. Conformable with underlying Flathead Sandstone. Forms slopes and swales. Thickness 30-65 m.

Flathead Sandstone-Thin- to medium-bedded, medium- to coarse-grained, reddish-brown, tan, and purplish-tan, quartz-rich, feldspathic sandstone; locally weathers to rusty red. Two thin zones of fine-grained, micaceous, greenish-gray argillaceous sandstone near top of formation. Basal part of formation contains rounded pebbles of metamorphic rock. Unconformably overlies Archean crystalline rock. Thickness variable, from 15 to 75 m.'
1313|'Black to dark-greenish-gray, fine- to medium-grained, equigranular, well-indurated diabase in steep, northwest-striking dikes as wide as 30 m (most are considerably thinner). Contains about 30-50 percent euhedral labradorite, 30-60 percent augite, 0-30 percent hornblende (inverted from augite), 0-10 percent potassium feldspar, 5-8 percent opaque minerals, 1-3 percent apatite, 0-5 percent biotite, 0-3 percent quartz, and from trace to 1 percent epidote. Emplaced during two periods: 1455 Ma and 750-780 Ma (Harlan and others, 1990).

Low-grade metamorphic rocks of the Ruby Creek area, eastern Gravelly Range (Proterozoic or Archean):
Metamorphic grade of rocks in this area is as low as chlorite facies (quartz-albite-epidote-biotite subfacies of Turner and Verhoogen, 1960), but increases in grade southward to almandine-amphibolite facies. The Ruby Creek assemblage is bounded on the north by a north-dipping thrust, which places marble in the hanging wall above the lower grade rocks of the Ruby Creek area. The age of the assemblage is unknown, but may be as young as Proterozoic (J.M. ONeill, personal commun., 1995). The geology for this area is modified from Vargo (1990) and Hadley (1969a,b).'
1314|'Mapped by Hadley (1969a, b) but not described in detail.'
1315|'Green metamorphosed fine-grained clastic sedimentary rocks, locally showing good cross-bedding and graded beds. Contains quartz, plagioclase, actinolite, and epidote. Weathers to blocky outcrops.'
1316|'Dark brown-gray to black, well-foliated schist containing quartz, plagioclase, biotite, chlorite, magnetite, and muscovite; porphyroblasts of plagioclase abundant.'
1317|'Greenish-gray, greenish-red, gray-red, and dark gray phyllite containing quartz, biotite, chlorite, muscovite, hematite, magnetite, and rare garnet.  Contains thin layers of micaceous and actinolite-bearing quartzite and lenticular amphibolite bodies (not shown).'
1318|'Well foliated chlorite-actinolite schist that contains abundant shear-bounded bodies of metagabbro, metadiorite, and amphibolite.  Interpreted as sheared amphibolite (J.M. ONeill, personal commun., 1995) and may be approximately equivalent to biotite chlorite schist (unit P_Abs). Includes a thin staurolite-sillimanite mylonite that bounds southern contact of unit.'
1319|'Approximately as mapped by Hadley (1969b); part of quartz-feldspar gneiss and pegmatite unit of Vargo (1990).'
1320|'Approximately as mapped by Hadley (1969b), who did not describe unit in detail. Not known if unit is intrusive into adjacent units or forms older basement.'
1321|'Alternating layers, typically 2-10 cm thick, of reddish-brown to black magnetite-quartz and quartzite. Contains minor hydrobiotite and magnetite locally oxidized to hematite and goethite. Layers commonly tightly folded.'
1322|'Pink, coarse-grained, massive to slightly foliated biotite monzogranite porphyry. Contains about 20 percent conspicuous euhedral to subhedral potassium-feldspar phenocrysts as long as 1.5 cm; matrix contains about 30 percent quartz, 35 percent plagioclase, 15 percent potassium feldspar, and about 20 percent biotite. Locally sheared, forming well-developed pinkish-gray augen gneiss, as on Indian Ridge in Spanish Peaks.'
1323|'Light-gray to light pinkish gray, generally tan-weathering, medium-grained, hypidiomorphic, weakly to moderately foliated orthogneiss generally ranging in composition from tonalite to monzogranite. Mafic mineral almost exclusively biotite (trace to 15 percent); may contain as much as 5 percent almandine and, rarely, 5 percent hornblende, 2 percent augite, and 2 percent muscovite; also contains traces of zircon, epidote, allanite, and opaque minerals. One unusual occurrence is a pluton near Summit Lake in the Spanish Peaks, the pluton is a discordant body composed of massive to weakly foliated, very-light-gray biotite tonalite.'
1324|'Black (commonly speckled with white feldspar and pink garnet), fine-grained, equigranular, granoblastic, weakly foliated to massive hornblende-augite-almandine metabasite. Composition variable; contains 15-45 percent plagioclase (mostly andesine), 10-60 percent yellowish-green to brown hornblende, 2-20 percent augite, 0-20 percent almandine, 0-5 percent reddish-brown biotite, 1-3 percent opaque minerals, and trace of apatite. In some places relict porphyritic texture is preserved as white clusters of fine-grained plagioclase as long as 1 cm. Mostly occurs as sills as wide as about 40 m concordant to foliation; in some places sills show pinch-and-swell structure and boudinage. Commonly enveloped in medium-grained amphibolite margin as wide as 10 m, indicating post-emplacement metasomatism at amphibolite grade. Equivalent to orthoamphibolite of Vitaliano and Cordua (1979) in Tobacco Root Mountains.'
1326|'Light- to medium-gray, medium-grained, hypidiomorphic, poorly to well foliated hornblende-biotite granodiorite orthogneiss. Contains 30-40 percent plagioclase, 10-20 percent potassium-feldspar, 15-25 percent quartz, 10-20 percent hornblende, and about 10 percent biotite. Most rock is highly strained, forming well-developed foliation; in such places, mafic minerals are concentrated in ribbony layers 2-5 mm thick. Contains numerous, thin (3-10 mm) K-feldspar-quartz migmatitic layers. Cut by at least three periods of sill and dike intrusion; sills and dikes locally so closely spaced that they form an agmatite. Cut by granitic orthogneiss of Summit Lake pluton.'
1327|'Black to dark-greenish-gray, fine- to medium-grained, well foliated to massive, variably serpentinized ultramafic rocks of wide-ranging composition; includes olivine websterite, lherzolite, and olivine clinopyroxenite. Accessory minerals include olive-green spinel, magnetite, and apatite. Commonly contains secondary amphibole (anthophyllite or actinolite) serpentine, talc, dolomite, magnesite, and (or) mica. Occurs in lenses, pods, and small irregularly shaped masses, rarely more than 10 m in diameter. Probably tectonically incorporated into country rock.'
1328|'Mapped where rocks are heterogeneous, generally layered, light- to medium-gray microcline-plagioclase-quartz-biotite gneiss. Commonly migmatitic and blastomylonitic. Some areas not mapped in detail, such as south of Sphinx Mountain in the Madison Range and east of the Gallatin River in the Gallatin Range, which may contain many of the other gneissic rock units.'
1329|'Includes biotite-garnet schist, sillimanite-garnet schist, garnetiferous quartzite, quartzite, highly garnetiferous quartzofeldspathic gneiss, corundum gneiss, gedrite schist, cummingtonite schist, and garnetiferous amphibolite (Vitaliano and Cordua, 1979). May represent refractory component ("restite") after removal of partial melts.'
1330|'Most is gray to black, medium-grained, hypidiomorphic equigranular, moderately-foliated to well-foliated hornblende-plagioclase gneiss and amphibolite; contains as much as 5 percent quartz and traces of zircon, opaque minerals, and apatite; locally garnetiferous. Plagioclase typically An30 and weathers white. Commonly contains white, migmatitic leucosomes of anorthosite as thick as 10 cm. Similar unit in Tobacco Root Mountains interpreted to be either metamorphosed clay-rich dolomite or mafic-extrusive origin (Vitaliano and Cordua, 1979). Amphibolite envelopes around some metabasite intrusive bodies indicate at least some amphibolite was derived from intrusive rocks. Unit may include minor amounts of other Archean units.'
1331|'Black, dark gray, and gray, fine to medium grained biotite-plagioclase-quartz-hornblende-microcline schist. Interpreted to be sheared mafic rock that equilibrated at lower amphibolite facies; not studied in detail. Crops out in the Gallatin Canyon-Hellroaring Lake (Spanish Peaks) area.'
1332|'Cummingtonite gneiss is light gray, medium grained, strongly lineated, and vitreous. Contains as much as 90 percent cummingtonite, and variable amounts of quartz, almandine, muscovite, rutile, and opaque minerals. Grades into metaquartzite. Gedrite gneiss is brown to grayish brown, moderately well foliated gneiss that contains as much as 70 percent clove-brown gedrite, in addition to quartz, plagioclase, sillimanite, biotite, cordierite, and traces of magnetite and rutile. Both rock types occur as small lenses and concordant layers in other Archean rocks.'
1333|'White, light-gray, dark-gray, and black, medium-grained, well-foliated and well-layered gneiss. Leucosomes contain plagioclase, quartz, biotite, potassium feldspar, garnet, and a trace of opaque minerals. Melasomes contain biotite, hornblende, plagioclase, quartz, garnet, and trace of opaque minerals. Contains rare quartzite layers and sillimanite-bearing gneiss. Commonly migmatitic. Layers typically 1-20 cm thick. Injected by numerous sills of metabasite. Crops out extensively in Bear Trap Canyon of the Madison River. Similar rocks, also mapped as unit Abh, occur at several other less extensive localities.'
1334|'Light- to medium-gray mottled mylonite with a well-developed L-S tectonite fabric and a fine-grained recrystallized (granoblastic) texture. Composition variable, and ranges from that of quartzofeldspathic gneiss to amphibolite. The mylonite equilibrated at near-peak (lower granulite) metamorphic conditions and forms anastomosing, concordant zones in the northern Madison Range (Kellogg and Mogk, 1991). The margins of the unit are concordant with and grade into relatively unmylonitized gneiss.'
1335|'Gray to dark-brownish-gray, medium-grained, inequigranular, generally well-foliated, commonly micaceous gneiss and schist containing aluminosilicate (mostly sillimanite and rarer kyanite). Unit contains 5-90 percent anhedral quartz having undulatory extinction, 0-30 percent microcline, 0-35 percent plagioclase, 0-30 percent almandine, 0-20 percent muscovite, trace to 15 percent sillimanite or kyanite, 0-10 percent reddish-brown biotite, 0-2 percent opaque minerals, including graphite, and trace of zircon. Commonly rich in quartz and locally grades into quartzite. Several kyanite prospects are on east side of Gravelly Range, in Sec. 6, T. 8 S., R. 1 W. (Nordstrom, 1947).'
1336|'Light- to medium-gray, medium-grained, poorly to well foliated quartz-feldspar gneiss that contains abundant thin schistose layers with both biotite and muscovite. Aluminosilicate-bearing lenses are common and one prominent 20-50-m-thick schistose horizon contains as much as 50 percent coarse-grained biotite, about 20 percent quartz, 0-10 percent gedrite, 5 percent plagioclase, 5 percent sillimanite, 3 percent kyanite (as large blue blades), 3 percent garnet, and 3 percent muscovite. Mapped on north side of Hellroaring Creek valley in Spanish Peaks.'
1337|'White, medium- to coarse-grained, inequigranular, moderately foliated to massive quartzite; locally bright green where trace amounts of chromium-bearing mica (fuchsite) present. In most places, unit is composed entirely of anhedral quartz grains having undulatory extinction, but locally contains as much as 30 percent microcline, 20 percent muscovite, 15 percent sillimanite, 10 percent cummingtonite, 8 percent almandine, 2 percent actinolite, and trace of zircon and opaque minerals. Commonly forms prominent ridges, especially in northwestern Madison Range, where the core of a plunging, nearly isoclinal antiform is composed almost entirely of quartzite. Unit is interlayered in most places with mafic amphibolite.'
1338|'White, coarse-grained, massive to moderately well foliated dolomitic marble that contains as much as 3 percent quartz grains. Weathers orange- brown. Locally hydrothermally altered to commercial deposits of talc on east side of Gravelly Range. A few thin layers of calcitic marble, containing as much as 30 percent serpentine, mapped in northern Madison Range. Extensive, commercially exploited talc deposits occur in hydrothermally altered zones in large marble body on eastern side of the Gravelly Range.'
1339|'Alternating layers of reddish-brown to black magnetite-quartz and quartzite, typically 2-10 cm thick.  Contains minor hydrobiotite and magnetite locally oxidized to hematite and goethite.  Layers commonly tightly folded.  Mapped on eastern side of Gravelly Range by Vargo (1990).'
1340|
1400|'Man-made deposits, typically within Quaternary surficial deposits.'
1401|'Alluvium, fan and terrace gravel, gravel deposits on pediment surfaces, and landslide and travertine deposits (Pleistocene and Holocene); till, glacial lake, and outwash deposits (Pleistocene).'
1402|'Fan and gravel deposits on pediment surfaces (Pliocene); conglomerate, sandstone, mudstone, and volcanic ash beds (Eocene, Oligocene, or Miocene).'
1403|'Rhyolite, quartz latite, latite, and dacite interbedded with lesser amounts of basalt and andesite.'
1404|'Andesite, basalt, and latite flows.'
1405|'Quartz monzodiorite and granodiorite.'
1406|'Rhyolite and dacite flows and tuffs.'
1407|'Basalt and andesite flows, flow breccia, and air-fall tuff.'
1408|'Foliated and non-foliated biotite-muscovite monzogranite, leucomonzogranite, and granodiorite. Includes muscovite-bearing granitic rocks with Tertiary K-Ar ages (Wallace and others, 1992) assigned to Tmg unit of Wallace (1987). Because these age determinations may date cooling and not crystallization, a Cretaceous age is also possible.'
1409|'Foliated and nonfoliated biotite granodiorite, hornblende-biotite granodiorite, tonalite, and quartz diorite.'
1410|'Gabbro, microgabbro, diorite, and lamprophyre.'
1411|'Pyroxenite, leucosyenite, and hornblende syenite.'
1412|'Aplite, alaskite, and pegmatite dikes, sills, and pods.'
1413|'Granite and monzogranite porphyry, biotite monzogranite, biotite-muscovite monzogranite and granodiorite, and quartz monzonite.'
1414|'Foliated and non-foliated biotite-hornblende granodiorite, biotite-hornblende monzogranite, and tonalite.'
1415|'Hornblende quartz diorite, granodiorite, tonalite, quartz monzodiorite, diorite, quartz diorite, leucogranodiorite, and augite-hornblende monzonite.'
1416|'Diorite, gabbro, microgabbro, and diabase.'
1417|'Latite sill in northeastern corner of map.'
1418|'Andesitic, quartz latitic, and basaltic tuff, breccia, and flows.'
1419|'Unit includes, in descending order: Cretaceous Two Medicine Formation, Virgelle Sandstone, Telegraph Creek Formation, Marias River Shale, and Blackleaf Formation in northeast corner of quadrangle. Northwest of Deer Lodge unit consists of Cretaceous Golden Spike Formation, Carter Creek, Jens, and Coberly Formations of Gwinn (1961), Blackleaf Formation, and Kootenai Formation, as well as Jurassic Morrison Formation and Ellis Group.'
1420|'Unit includes, in descending order: Permian Shedhorn Sandstone, Phosphoria Formation, and Park City Formation, Pennsylvanian Quadrant Quartzite, Snowcrest Range Group (Pennsylvanian and Mississippian), Madison Group and related rocks (Mississippian), Three Forks Formation (Mississippian and Devonian) and Jefferson and Maywood Formations (Devonian).'
1421|'Red Lion Formation, Hasmark Formation, Silver Hill Formation, and Flathead Quartzite. Park Shale, Meagher Limestone, and Wolsey Shale are lateral equivalents to the Silver Hill Formation and are present in northeast part of quadrangle.'
1422|'Gabbro, microgabbro, and diorite dikes and sills.'
1423|'Coarse- to medium-grained, reddish or buff quartzite containing thin beds of sandy argillite.'
1424|'Grayish-green micaceous quartzite and impure argillite.'
1425|'Red and green interbedded argillite and siltite, and buff quartzite. Contains distinctive green and red chert beds and clasts. Amount of quartzite increases to the south and southwest.'
1426|'Pink or buff, medium- and coarse-grained feldspathic quartzite.  Matrix-supported granules and pebbles present locally.  Abundant trough cross-beds.'
1427|'Reddish quartzite and subordinate argillite and siltite in lower and middle parts of section. Upper part is predominantly reddish argillite. Matrix-supported granules and pebbles present in southern part of area, but medium to fine grain size is most common. Abundant planar laminations and ripple cross-laminations. Previously subdivided into three informal members, the middle one being the most quartzitic (Wallace and others, 1986). However, significant quartzite may be present in the lowermost part of the section as well, particularly in the western part of the map area.'
1428|'Shown as a single unit in the southwest part of area where the Shepard Formation is thin, poorly exposed, and only recognized at a few localities. Includes rocks previously mapped as carbonate facies of the lower part of the Mount Shields Formation (Wallace and others, 1986). In western part of area near Burnt Fork Lake both Snowslip and Shepard Formations are present but have yet to be mapped separately. Here they are more quartzitic than to the east in the Philipsburg area.'
1429|'Green microlaminated argillite at base overlain by thin lenticular beds of green dolomitic siltite and fine-grained quartzite. Upper part is red, thinly bedded dolomitic quartzite and siltite. Abundant load casts and ripple marks. Poorly exposed and easily missed when mapping.'
1430|'Green and red argillite near base and increasing amounts of siltite and quartzite up section. Some quartzite beds contain coarse, well-rounded quartz grains and less feldspar than is typical for quartzite in the Belt Supergroup. Upper quartzitic part of section is difficult to distinguish from Mount Shields Formation. Abundant straight-sided mud cracks in lower part of section.'
1431|'Limestone, dolomite, dolomitic and calcareous siltite, and argillite of the Helena Formation in the eastern part of the area and dolomitic siltite, quartzite, argillite, and sedimentary breccia of the Wallace Formation in the western part of the area.'
1432|'Mostly greenish-gray argillite and siltite with interbeds of quartzite and dolomite; red to purple argillite near base. Carbonate content increases up section.'
1433|'Reddish siltite, argillite, and thin beds of quartzite.'
1434|'Dark gray thinly laminated argillite and siltite grading up into light-gray to greenish-gray, thinly bedded siltite and quartzite.'
1435|'Highly recrystallized quartzite and lesser amounts of phyllite and schist. Although assigned to Mount Shields Formation by Wallace and others (1986), these rocks appear to underlie the Middle Belt carbonate and are probably Ravalli Group equivalent. Exposures of Yq in the Anaconda range were assigned to Ravalli Group by Calkins and Emmons (1915).'
1436|'Quartzofeldspathic gneiss, migmatite, schist, quartzite, and calc-silicate rocks. Includes rocks assigned to the Prichard Formation and Neihart Quartzite (lowermost Belt) by Calkins and Emmons (1915) and later assigned to the Mount Shields Formation by Wallace and others (1986). The older assignment is more likely, given their structural position in the uplifted block of the Anaconda Range. Also includes rocks in the southwest part of the map area which may be metamorphic equivalents of the Prichard Formation(?), Ravalli Group, and Middle Belt carbonate.'
1437|'Unit includes, in descending order: Permian Shedhorn Sandstone, Phosphoria Formation, and Park City Formation, Pennsylvanian Quadrant Quartzite, Snowcrest Range Group (Pennsylvanian and Mississippian), Madison Group and related rocks (Mississippian), Three Forks Formation (Mississippian and Devonian) and Jefferson and Maywood Formations (Devonian).

These rocks have been silicified and sheared.'
1450|'Silt, sand, and gravel in channels and flood plains of major rivers and streams and in related alluvial fans. May be partly of Pleistocene age. Maximum thickness unknown.'
1451|'Angular fragments of bedrock mixed with soil or heterogeneous boulders and finer grained material derived from glacial deposits on steep valley walls; characterized by irregular, hummocky topography; boggy in places. Many landslides are marked by torn sod, tilted trees, and steep unvegetated slopes that indicate continuing movement.'
1452|'Poorly sorted silty sand and gravel deposited in broad alluvial fans along valley margins. Includes gravel veneer on pediments.'
1453|'Silt and sand in thin-bedded, well-sorted deposits in the Big Hole basin in western part of map area.'
1454|'Unsorted mixture of boulders, cobbles, pebbles, and sand deposited by glaciers. Includes deposits of at least two, and in some places three, episodes of glaciation. Boulder fields in south-central part of map area are characterized by frost riving and frost-heaved boulders in locally boggy and commonly terraced terrane that formed by creep and solifluction on flanking hills. These boulder fields probably formed as a result of weathering in severe cold climate adjacent to Pleistocene glaciers. Rocks in the boulder fields are essentially in place, but structural information is incomplete or lacking.'
1455|'Poorly sorted bouldery gravel and sand deposited by glacial meltwater.'
1456|'Unconsolidated, deeply weathered angular to rounded pebbles, cobbles, and small boulders of quartzite, arkosic sandstone, and granitic rocks in sand matrix; commonly covered by a thin layer of eolian silt; most deposits are located along southeast flank of Highland Mountains. Elsewhere, consists of poorly sorted silt, sand, and bouldery gravel of uncertain age. Present on ridge crests in the vicinity of Fish Creek in northeastern part of map area, near Wise River in north-central part, and in Lemhi Valley. Overlies tuffaceous rocks of late Tertiary age at Fish Creek and in Lemhi Valley and Paleozoic and Mesozoic rocks at Wise River. Present locally overlying Bozeman Group and related valley-fill deposits (Tbz) but not mapped separately. Thickness 0-50 m.'
1457|'Light-gray to yellowish-brown, moderately indurated to well-indurated tuffaceous sandstone and siltstone containing subordinate interbeds of limestone and marl and lenses of pebble and cobble conglomerate composed of locally derived rock fragments. Exposures of related valley fill in Horse Prairie basin and in Salmon River valley include lignitic rocks of Oligocene age (Cavender, 1977; Harrison, 1982, 1985; Ruppel and Lopez, 1984, 1988). Commonly veneered with residual gravel or a thin layer of eolian silt. Thickness ranges from less than 300 m to about 3,000 m in the valley of Grasshopper Creek near the confluence of Grasshopper and Swamp Creeks and as much as 4,600 m in the Bighole basin. Deposits also include Tertiary landslide deposits derived from flanking mountains. Bozeman Group has been divided into Sixmile Creek and Renova Formations (Kuenzi and Fields, 1971), mainly on the basis of mammalian fossil data ; however, formation names are not used here because in most places in Dillon quadrangle the two formations cannot be separated lithologically (Hanneman, 1989). Maximum thickness, in Big Hole basin, exceeds 4,000 m.'
1458|'Grayish-black vesicular basalt or basaltic andesite flows near Sweetwater Creek in south-central part of map area are about 4 Ma (Daniel and Berg, 1981, p. 110); similar basaltic rocks are present in the central part of Ruby Range (James, 1990).'
1459|'Basaltic andesite, andesite, latite, rhyodacite, and rhyolite as flows, ash-flow tuffs, and tuff and flow breccias. Mainly dark-gray or very dark red to medium-gray and pale-reddish brown, partly vesicular to scoriaceous, porphyritic hornblende or pyroxene basaltic andesite and andesite, and pale-red or light-brownish-gray to light-gray and pale-brown, porphyritic, partly welded quartz latite, latite, and rhyodacite. Locally contains thin interbeds of light-olive-gray, biotitic, tuffaceous, coarse-grained sandstone and conglomerate composed of volcanic detritus. Present only in southwestern and west-central parts of map area. Includes rocks in Withington Creek caldera, about 10 km in diameter, at north end of Lemhi Range; caldera contains massive ash-flow tuffs at least 600 m thick that pass laterally across caldera margin into 50-100 m of thinly layered ash-flow tuffs and andesitic flows. Age probably about 40-45 Ma (Staatz, 1979, p. 12-23; Ruppel and Lopez, 1984). Preserved thickness in most places probably less than 200 m. Volcanic rocks east of Idaho-Montana State line are not clearly related to Challis volcanic field of east-central Idaho and are mapped as Tvu.'
1460|'Basaltic andesite, andesite, dacite, and rhyodacite. Light-brownish-gray to brownish-gray (tinted purple in places), fine-grained, locally porphyritic volcanic and associated intrusive rocks. Phenocrysts include sodic plagioclase, sanidine, quartz, and biotite. Partly equivalent to Eocene Lowland Creek Volcanics directly north of map area. Present mainly along east flank of Pioneer Mountains. Age 50-46 Ma (Zen, 1988). Individual flows as much as 50 m in thickness.'
1461|'Includes mainly dikes of dark-gray aphanitic basalt containing sparse phenocrysts of olivine(?) near North Fork of Salmon River in west-central part of map area (Lopez, 1982b) and a finely crystalline diorite dike that intrudes Beaverhead Divide-Miner Lake fault zone directly south of Center Mountain in the Beaverhead Mountains east of Salmon.'
1462|'Dikes, dike swarms, and associated extrusive volcanic rocks. Dark-green to pale-yellowish-brown, gray or yellowish-gray to pale-red, fine-grained, porphyritic volcanic and related intrusive rocks containing phenocrysts of sanidine, plagioclase, alkali feldspar, and quartz, or of plagioclase, biotite, and hornblende in more mafic rocks. Mainly rhyodacite and dacite. Extrusive rocks principally rhyodacite and dacite tuffs and breccias and rhyolite flows, tuffs, and welded tuffs. Present in northwestern and north-central parts of map area. Age about 43 Ma (Desmarais, 1983, p.49-50, 106).'
1463|'Greenish-black basaltic plug intruded along Grasshopper Creek in south-central part of map area. May be related to Tvu.'
1464|'Intrusive rocks in Carmen and Napoleon Ridge stocks and small plutons south of Gibbonsville in Beaverhead Mountains, in western part of map area; rocks intrude Yellowjacket Formation (Middle Proterozoic) and lower part of Medicine Lodge thrust plate. Age about 55-48 Ma; eastern part of Carmen stock contains small areas of more mafic rocks that are about 83-80 Ma (Kilroy, 1981; Ruppel and Lopez, 1988).'
1465|'Complex mixture of porphyritic, fine- to medium-grained, gray to dark-gray granodiorite stocks and dikes. Phenocrysts consist of orthoclase, plagioclase, and rounded glassy quartz. K-Ar age determined on biotite is 51 Ma (Desmarais, 1983).'
1466|'Light gray, medium to coarse grained, equigranular to porphyritic, and nonfoliated. Phenocrysts, where present, consist of orthoclase, microcline, and locally plagioclase. K-Ar ages determined on biotite and muscovite range from 58 to 50 Ma (Desmarais, 1983).'
1467|'Fine- to medium-grained, nonporphyritic granodiorite.'
1468|'Granitic batholithic rocks in the Anaconda Range:  Porphyritic and equigranular, medium-grained rocks in stocks and minor dikes.

Granitic rocks in the Boulder and Tobacco Root batholith:  Light-gray, equigranular to strongly porphyritic, medium-grained to very coarse grained granitic rocks that compose the Moose Creek stock, Hell Canyon pluton, and most of the Butte Quartz Monzonite in central part of Boulder batholith. Slight textural and compositional variants are present. Includes small bodies of dark-gray diorite and gabbro.'
1469|'Gray, medium to coarse grained, equigranular; characterized by distinctive foliation. K-Ar ages determined on biotite and hornblende range from 74 to 60 Ma (Desmarais, 1983).'
1470|'Light-gray rhyolitic dike, in southern Pioneer Mountains, composed of quartz and sanidine phenocrysts in a finely granular groundmass of quartz and potassium feldspar. Age about 46 Ma (Snee, 1982; Pearson and Zen, 1985).'
1471|'Light gray, medium to coarse grained, locally porphyritic. Age about 65-61 Ma (Snee 1982, p. 153-154; Marvin and others, 1983). Includes Clifford Creek Granite of Paleocene and Late Cretaceous age in north-central Pioneer Mountains (Zen, 1988).'
1472|'Pinkish gray, medium to coarse grained; contains euhedral potassium feldspar phenocrysts about 1 cm long. Includes associated tonalite, rhyodacite porphyry, rhyolite porphyry, intrusive breccia, pegmatite, and Grayling Lake Granite in north-central Pioneer Mountains (Zen, 1988). Age about 68-73 Ma (Snee, 1982, p. 134-152).'
1473|'Light-gray, medium-grained hornblende-biotite granodiorite of Uphill Creek Granodiorite (Zen, 1988), the predominant rock exposed in Pioneer batholith; includes plutons, mainly in northwestern part of batholith, of dark-gray to bluish-gray, medium-grained biotite and biotite-hornblende tonalite and quartz diorite. Ages of various plutons range from 68 to 77 Ma, age of granodiorite about 75 Ma (Snee, 1982, p. 104-134; Pearson and Zen, 1985; Pearson and others, 1987, 1988). Includes granitic rocks in McCartney Mountain stock, directly east of Pioneer Mountains, and in stocks north of Pioneer Mountains, in north-central part of map area.'
1474|'Dark greenish gray, medium to coarse grained. Contains as much as 50 percent hornblende in most places, but as much as 80 percent hornblende in northeastern part of Pioneer Mountains. Age about 80 Ma (Snee, 1982, p. 93-104).'
1475|'Bluish-gray, weakly to moderately foliated, fine-grained, porphyritic metadacite and meta-andesite; phenocrysts commonly fractured parallel to foliation; hornblende locally present as elongate crystals parallel to foliation. Exposed in northwestern Pioneer Mountains; interpreted by Berger and others (1983) as Precambrian cratonic rock.'
1476|'Bluish gray, strongly foliated, medium to coarse grained; contains porphyroblasts as much as 2 cm long of plagioclase, smoky quartz, and sparse microcline aligned parallel to foliation. Accessory minerals include sphene, magnetite, zircon, and apatite. Original rock may have been coarse-grained granodiorite or porphyritic dacite or andesite. Exposed only in northwestern part of Pioneer Mountains and interpreted by Berger and others (1983) as Precambrian cratonic rock.'
1477|'Dark bluish gray to bluish gray, medium to fine grained, strongly foliated; contains porphyroblasts of plagioclase and smoky quartz. Accessory minerals include epidote, sphene, magnetite, and zircon. Exposed in northwestern Pioneer Mountains; interpreted by Berger and others (1983) as Precambrian cratonic rock.'
1478|'Leucocratic, fine- to coarse-grained granite; occurs as small, irregular pods and stocks in Butte Quartz Monzonite. Only largest bodies are shown, many being too small to be shown.'
1480|'Medium- to dark-gray, equigranular, fine- to medium-grained rocks of Rader Creek and Donald plutons intruded along southeast margin of Boulder batholith. Also includes Tobacco Root batholith, a zoned pluton that is mostly a medium-gray, coarse-grained, porphyritic granodiorite in map area (O Neill, 1983), and related stocks in the Tobacco Root Mountains.'
1481|'Principally monzogranite, granodiorite, and related granitic intrusive rocks in small stocks and plugs in east-central and southern parts of map area. Includes porphyritic, high-potassium dacite in a 16-km-long intrusive sheet and as a 1-km-diameter plug that is hydrothermally altered and mineralized 15 km west of Dillon.'
1482|'Comprises an upper lava-flow and breccia unit of intermediate composition and a lower silicic pyroclastic unit. The upper unit is high-potassium dacite and minor andesite and dacite as volcanic breccia, lava flows, a volcanic dome, and minor volcanic-pebble conglomerate, volcaniclastic sandstone, tuff, and dikes. The lower unit comprises pale-colored pyroclastic flow deposits and tuff that are nonporphyritic to slightly porphyritic and, in most places, zeolitic.'
1483|'Light-gray to dark-gray and grayish-red to greenish-gray dominantly andesitic to latitic welded tuff and tuff breccia, tuff, lapilli tuff, lava flows, flow breccia, and poorly sorted volcanic sandstone and conglomerate in northeastern part of map area.'
1484|'Moderately indurated massive boulder, cobble, and pebble conglomerate having a quartz-sand matrix and cemented with calcite, and some interbedded sandstone and fresh-water limestone; in most places these rocks consist of rounded to subangular fragments of Proterozoic quartzite and Paleozoic carbonate rocks; however, near Bannock the sequence can be divided into an upper unit composed mainly of quartzite clasts that is separated from underlying carbonate-rich unit by volcanic rocks (Kvu) not assigned to the Beaverhead; as much as 350 m thick. Exposed only in south-central part of map area.'
1485|'Thick succession of poorly known, partly metamorphosed sandstone and shale that underlie McCartney Mountain in east-central part of quadrangle.'
1486|'Includes poorly known rocks of Blackleaf Formation and overlying strata. Blackleaf Formation of this report formerly was designated as part of Colorado Group, undivided, or as Aspen Formation.

Upper part (Upper Cretaceous) - Greenish-gray or light yellowish-gray to grayish-white, tuffaceous subgraywacke, tuffaceous sandstone, quartz sandstone, and tuff, locally interlayered with conglomerate lenses. Interbedded with grayish-green, greenish-blue, and dark-gray silty mudstone, shale, and siltstone. Beds near top of section locally contain plant fragments and pollen indicating mid-Campanian to Maastrichtian age (Zen, 1988). Thickness uncertain, but possibly as thick as 1,200 m. Exposed only along east flank of Pioneer Mountains northward to area of Granulated Mountain north of Wise River.

Lower part (Upper Cretaceous) - Sandstone, conglomerate, shale, mudstone, and porcelaneous mudstone, siltstone, limestone, and bentonite. Sandstone is yellowish gray, light olive gray, light to medium bluish gray to pale yellowish brown, brownish gray and medium to dark gray; mostly medium to coarse, rounded to angular grains, but finer grained in places; medium to thick bedded; prominent trough cross-stratification in many beds; commonly calcareous and stained with limonite, and contains disseminated carbonaceous material. Conglomerate commonly grades laterally into coarse-grained sandstone and contains rounded fragments as much as 30 cm in diameter predominantly of quartzite, chert, porcelaneous mudstone, and, less commonly, limestone, in a sandstone matrix. Mudstone, shale, and siltstone are light olive green and bluish gray to dark gray, calcareous, bentonitic, and commonly porcellanitic; commonly burrowed and bioturbated, and locally contains abundant carbonaceous material and leaf and wood impressions. Limestone, in rare, scattered, discontinuous beds 1 m or less thick, is medium gray to greenish gray, fine grained, silty, commonly bioturbated, and grades laterally into calcareous mudstone. In part lithologically equivalent to Frontier Formation near Lima Peaks in southern Beaverhead County (Dyman and others, 1989). Measured thickness as much as 420 m, but top of formation not present in this region (Dyman, 1985a, 1985b, 1985c; Dyman and Tysdal, 1989; Tysdal and others, 1989).

Blackleaf Formation (Upper and Lower Cretaceous)-Separable into two members. Flood Member separable into three informal lithofacies units as described by Dyman (1985a, 1985b, 1985c), Dyman and Nichols (1988), and Dyman and Tysdal (1989). Total thickness is 940 m at Rock Creek in Pioneer Mountains and about 460 m in Snowcrest Range.

Vaughn Member - Mudstone, porcelaneous mudstone, siltstone, volcanic-rich sandstone, conglomerate, and limestone. Predominantly mudstone and siltstone, which are light olive gray, light greenish gray, dusky red, greenish gray, and medium gray, partly thinly laminated, commonly porcelaneous in middle and upper parts of unit, partly calcareous, hard and dense, locally bentonitic, and locally pyritic; contains locally abundant lithophysae in tuffaceous beds. Sandstone and conglomerate occur in thin, laterally discontinuous channel fills. Sandstone and conglomerate are light olive gray and greenish or bluish gray to dark gray, mostly fine to medium grained, consisting of subrounded to angular grains; partly calcareous, partly pyritic, thin to medium bedded; conglomerate zones contain rounded to angular fragments as much as 3 cm in diameter of mudstone, shale, siltstone, quartzite, and chert. Silty, micritic limestone is rare and typically occurs in thin argillaceous lenses and grades into highly calcareous mudstone. Thickness 340-356 m in eastern Pioneer Mountains; thins eastward to 80 m in Snowcrest Range.

Flood Member - Clastic lithofacies-Interbedded with subordinate siltstone, mudstone, shale, and conglomerate. Sandstone is light olive gray and light greenish gray to dark yellowish brown and pale red, fine to coarse grained and locally conglomeratic; grains are rounded to angular; medium to thick bedded, ripple or horizontally laminated or trough cross stratified; commonly calcareous, micaceous, and contains abundant carbonaceous material and wood fragments. Siltstone, mudstone, and shale are yellowish-gray and light olive gray to yellowish brown and dark gray, partly calcareous, commonly bioturbated, and contain carbonaceous material and wood fragments. Thickness about 75 m in eastern Pioneer Mountains, thinning eastward to 4-15 m in and near Snowcrest Range.

Mudstone-shale lithofacies - Mudstone, shale, siltstone, and greatly subordinate sandstone. Mudstone, shale, and siltstone are medium gray to dark gray, partly thinly laminated, calcareous, and contain abundant calcareous nodules as much as 5 cm in diameter in discrete zones; commonly bioturbated, limonite stained, and commonly contain carbonaceous material, wood fragments, and coal. Sandstone is pale blue to medium light gray, very fine to fine grained, thin bedded and parallel laminated, and calcareous. Grains are rounded to subangular. Thickness about 20-50 m in eastern Pioneer Mountains, thickens eastward to about 75 m in and near Snowcrest Range.

Transitional clastic lithofacies - Sandstone, siltstone, mudstone, and subordinate limestone, shale, and conglomerate. Sandstone is medium light gray, light olive-gray, pale yellowish brown, and medium gray, and generally very fine to medium grained. Grains are rounded to subangular grains. Is in part horizontally laminated, ripple laminated, or trough cross-stratified, and in places coarse grained and conglomeratic, containing fragments of limestone and mudstone as much as 2.5 cm in diameter; calcareous, partly bioturbated, and contains carbonaceous material. Mudstone, shale, and siltstone are medium light gray and light olive gray to medium bluish gray, medium dark gray, and greenish black; calcareous, and locally contains calcareous nodules as much as 1 cm in diameter; partly thinly laminated, thin bedded, commonly bioturbated, and contains carbonaceous material. Limestone is medium light gray, light bluish gray, yellowish gray to medium gray, and medium bluish gray, micritic, thin bedded, typically nodular with nodules as much as 10 cm in diameter, carbonaceous, partly silty to sandy, and grades laterally into siltstone or sandstone. Thickness about 80-85 m near Pioneer Mountains, thinning eastward to about 15 m near Snowcrest Range.'
1487|'Mudstone, siltstone, limestone, and sandstone. Upper part of formation is principally limestone with subordinate interbedded mudstone, siltstone, and sandstone; limestone beds also occur in middle part of formation (Myers, 1952; Schwartz, 1983; Pearson and Zen, 1985). Limestone is medium light gray to medium dark gray, finely to coarsely crystalline, thin to medium bedded, and fossiliferous; abundant fragments of gastropods in some beds. Mudstone and siltstone, principally in middle and lower parts of formation, are light olive gray, grayish green, and medium light gray to pale red, grayish red, and medium dark gray, partly thinly laminated, partly fissile, calcareous, and contain carbonaceous material and fragments of fossil wood. Sandstone occurs in subordinate interbeds throughout formation but is predominant in lower part; typically it is light olive gray and medium light gray to medium dark gray, fine to coarse grained, thin to thick bedded, and calcareous; rounded to subangular quartz grains and grains of dark chert are abundant; basal sandstone commonly is conglomeratic and contains abundant pebbles and cobbles of chert. Thickness 200-400 m.'
1488|'Includes Jurassic Morrison Formation and the Triassic Thaynes Limestone, Woodside Formation, and Dinwoody Formation, undivided.'
1489|'Grayish-red, yellowish-gray, and greenish-gray shale and siltstone, and minor interbedded fine- to medium-grained sandstone. Maximum thickness about 60-65 m in Argenta and Wise River areas and about 10 m in Blacktail Mountains and Snowcrest Range, where these rocks are mapped with Kootenai Formation; absent elsewhere in Dillon region.'
1490|'Thaynes Limestone (Lower Triassic) - Light-gray limestone, sandstone, and siltstone. Maximum thickness about 120 m in south-central and southeastern parts of map area; absent elsewhere in Dillon region.

Woodside Formation (Lower Triassic) - Reddish-brown, reddish-purple, and medium-gray calcareous mudstone, siltstone, and limestone. Maximum thickness about 30 m in south-central part of map area and in Snowcrest Range; absent elsewhere in Dillon region.

Dinwoody Formation (Lower Triassic) - Grayish-green, yellowish-gray, and grayish-brown, calcareous, thinly laminated siltstone; fine-grained sandstone; shale; gray, pale-red and light-brownish-gray-weathering, thin-bedded limestone. Maximum thickness, in south-central part of map area, is about 250 m but most commonly 100-160 m.'
1491|'Includes the Phosphoria Formation (Permian) and Quadrant Formation (Pennsylvanian and Upper Mississippian).

Phosphoria Formation: Divisible into upper and lower units. Upper unit is yellowish-brown to brownish-gray and dark-gray, partly glauconitic chert, cherty fine-grained sandstone, and quartzitic sandstone. About 40-45 m thick. Lower unit, in most places, includes, from top to bottom, (1) dark-gray, carbonaceous, phosphatic mudstone and shale and phosphate rock, and oil shale on Retort Mountain and Dalys Spur; (2) a unit of light-gray to grayish-brown, cherty, fine-grained quartzitic sandstone and cherty or sandy dolomite; (3) a yellowish-brown and medium-bluish-gray chert, yellowish-brown to dark-gray, cherty, carbonaceous and phosphatic mudstone and phosphate rock; and (4) a basal unit of light-gray to yellowish-gray, pale-reddish-brown, fine-grained dolomitic sandstone, siltstone, chert, and cherty limestone containing minor interbeds of vitreous quartzite. Total thickness of formation ranges from 50 to 180 m; it thins northward mainly by disappearance of lower part of lower unit.

Quadrant Formation: Light-gray to pale-yellowish-brown, fine- to medium-grained, quartzitic sandstone and vitreous quartzite; contains well-sorted, subrounded to well-rounded quartz grains; commonly cross-stratified, locally hematitic. Locally includes thin interbeds of light-gray to medium-gray, micritic, silty or sandy dolomite or limestone; in some places lower 15-55 m of formation is mainly dolomite or limestone containing thin interbeds of dolomitic or calcareous, fine-grained sandstone. Thickness ranges from 210 m in Blacktail Mountains to 115 m near Wise River, thickness is 200-400 m in Pioneer Mountains, about 90 m in the Ruby Range, and 150 m in Snowcrest Range (Saperstone and Ethridge, 1984).'
1492|'Divisible into upper and lower units. Upper unit is yellowish-brown to brownish-gray and dark-gray, partly glauconitic chert, cherty fine-grained sandstone, and quartzitic sandstone. About 40-45 m thick. Lower unit, in most places, includes, from top to bottom, (1) dark-gray, carbonaceous, phosphatic mudstone and shale and phosphate rock, and oil shale on Retort Mountain and Dalys Spur; (2) a unit of light-gray to grayish-brown, cherty, fine-grained quartzitic sandstone and cherty or sandy dolomite; (3) a yellowish-brown and medium-bluish-gray chert, yellowish-brown to dark-gray, cherty, carbonaceous and phosphatic mudstone and phosphate rock; and (4) a basal unit of light-gray to yellowish-gray, pale-reddish-brown, fine-grained dolomitic sandstone, siltstone, chert, and cherty limestone containing minor interbeds of vitreous quartzite. Total thickness of formation ranges from 50 to 180 m; it thins northward mainly by disappearance of lower part of lower unit.'
1493|'Light-gray to pale-yellowish-brown, fine- to medium-grained, quartzitic sandstone and vitreous quartzite; contains well-sorted, subrounded to well-rounded quartz grains; commonly cross-stratified, locally hematitic. Locally includes thin interbeds of light-gray to medium-gray, micritic, silty or sandy dolomite or limestone; in some places lower 15-55 m of formation is mainly dolomite or limestone containing thin interbeds of dolomitic or calcareous, fine-grained sandstone. Thickness ranges from 210 m in Blacktail Mountains to 115 m near Wise River, thickness is 200-400 m in Pioneer Mountains, about 90 m in the Ruby Range, and 150 m in Snowcrest Range (Saperstone and Ethridge, 1984).'
1494|'Snowcrest Range Group - Formerly mapped as Amsden Formation and (or) Big Snowy Group in this region, but now defined as Snowcrest Range Group, which contains Conover Ranch Formation, Lombard Limestone, and Kibbey Sandstone (Wardlaw and Pecora, 1985; Tysdal and others, 1987).

Conover Ranch Formation (Lower Pennsylvanian and Upper Mississippian) - Pale-reddish-brown to pale-reddish-purple, thin-bedded, calcareous mudstone and minor interbeds of limestone, calcareous sandstone and siltstone, limestone-pebble conglomerate, and phosphatic claystone. About 13-33 m thick. Mainly of late Chesterian age but includes a few thin beds of Pennsylvanian age at top of formation.

Lombard Limestone (Upper Mississippian) - Light-olive-gray, thin- to thick-bedded fossiliferous limestone and thin interbeds of silty limestone, siltstone, and shale, about 85-125 m thick, underlain by olive-gray and medium-red to pale-reddish-purple calcareous mudstone about 40 m thick. Chesterian to late Meramecian age.

Kibbey Sandstone (Upper Mississippian) - Pale-red to pale-yellow, thin- to medium-bedded siltstone, sandstone, and claystone, and interbedded limestone solution breccia and evaporite solution breccia in middle part of formation. About 5-45 m thick. Late Meramecian age.

Madison Group - Limestone, dolomitic limestone, and shale included in Mission Canyon Limestone and Lodgepole Limestone.

Mission Canyon Limestone (Upper and Lower Mississippian) - Olive-gray to yellowish-gray and dark-yellowish-brown, light-gray-weathering, medium- and thick-bedded to massive, generally fine- to medium-grained (but ranges from very fine grained to coarse-grained) limestone. Locally  cherty. Includes a few beds of dolomitic limestone in places. Upper part of formation includes pale-red to grayish-orange limestone solution breccia. Thickness ranges from 240 m in Blacktail Mountains to as much as 420 m in Ruby Range and Pioneer Mountains.

Lodgepole Limestone (Lower Mississippian) - Medium- to dark-gray, fine- to medium-grained, thin- to thick-bedded limestone, overlying medium- to dark-gray and brownish-gray, thin-bedded, laminated, argillaceous limestone, containing thin interbeds and bedding partings of dark-gray shaly limestone and calcareous shale. In Blacktail Mountains, Ruby Range, and Highland Mountains the formation is composed of Woodhurst Member (upper) and Paine Member (lower). Thickness is 180-230 m in Ruby Range and Blacktail Mountains, and 100-200 m in Pioneer Mountains region.'
1495|'Three Forks Shale (Mississippian? and Upper Devonian) - Composed of, at top, Sappington Member of yellowish-orange calcareous or argillaceous siltstone and fine-grained sandstone; underlain by Trident Member of dark-gray shale and interbedded fossiliferous dark-gray limestone and yellowish-gray to yellowish-orange argillaceous limestone; and at base the Logan Gulch Member of brownish- to purplish-gray, finely crystalline limestone, yellowish- and brownish-gray to purplish-gray, thin- to thick-bedded limestone and dolomite solution breccia interbedded with greenish-gray shale near base. Thickness about 20-50 m in Ruby Range and Blacktail Mountains, 0-50 m in Pioneer Mountains region.

Jefferson Formation (Upper and Middle Devonian) - Moderate- to dark-yellowish-brown to dark-gray, medium- to thick-bedded, locally thinly laminated, fine- to medium-grained, fetid dolomite and interbedded yellowish-brown to yellowish-orange, thin-bedded, fine-grained dolomite and silty, shaly dolomite; locally includes minor beds of shale and solution breccia. Thickness ranges from about 30-35 m in Blacktail Mountains and 80 m in Ruby Range to 150-200 m in Pioneer Mountains region.'
1496|'White to grayish-white, vitreous quartzite, locally containing dark, heavy minerals in planar layers and cross-beds; interlayered near base with greenish-black, silty, locally sandy argillite (Lewis, 1990). Argillite contains numerous trace fossils that are definitely of Paleozoic age, most probably Ordovician (M.W. Reynolds, written commun., 1987).'
1497|'Contains Snowy Range Formation, Pilgrim Formation, Park Shale, Meagher Limestone, Wolsey Shale, and Flathead Sandstone (Ruppel and Lopez, 1984; Ruppel, 1985). In northern part of Pioneer Mountains, unit made up of Hasmark and Silver Hill Formations (Zen, 1988).

Snowy Range Formation (Upper Cambrian) - The name "Red Lion Formation" used in some areas. Both formations divided into Sage Dolomite Member and underlying Dry Creek Shale Member. Sage Member is yellowish-brown to light-gray, very fine grained to fine-grained, thin- to thick-bedded dolomite, mottled and ribboned grayish red in lower part; locally contains thinly laminated algal beds and dome-shaped to columnar stromatolites in upper part. Dry Creek Member is olive-gray to reddish-gray, fissile, finely micaceous shale. Thickness about 20-50 m; absent in Blacktail Mountains, southern Tobacco Root Mountains, and locally absent in Pioneer Mountains.

Pilgrim Formation (Upper Cambrian) - Pale-yellowish-brown to light-gray, fine- to medium- to thick-bedded dolomite; upper part is sandy and includes interbeds of fine- to medium-grained sandstone. About 90-120 m thick in eastern and central parts of Dillon region; thins to 12-13 m in western part, near Jackson.

Park Shale (Middle Cambrian) - Pale-olive or grayish-green, finely micaceous, fissile shale and minor thin interbeds of yellowish-brown, medium-grained dolomite and yellowish-gray, thinly platy, calcareous, fine-grained sandstone, siltstone, and mudstone. About 45-60 m thick, pinches out to the west.

Meagher Limestone (Middle Cambrian) - Medium-gray, medium-light-gray and yellowish-brown, fine- to medium-grained limestone, dolomitic limestone, and dolomite that partly is irregularly mottled yellowish gray, light gray, or pale red. Mainly limestone and dolomitic limestone in Tobacco Root Mountains and mainly dolomitic limestone and dolomite farther south and west, in Dillon region. Thickness about 75-150 m in Tobacco Root Mountains, 170-230 m in Ruby Range and Highland Mountains, and 166 m in Blacktail Mountains; thins westward to 12-13 m near Jackson.

Wolsey Shale (Middle Cambrian) - Olive-green, grayish-red and reddish-brown, micaceous, glauconitic siltstone and olive-green, fissile, micaceous shale interbedded with grayish-red and yellowish-gray, glauconitic, argillaceous, fine-grained, platy sandstone and medium-gray, fine-grained limestone. Thickness about 15-75 m in Tobacco Root Mountains, 80 m in Highland Mountains, 18-30 m in Ruby Range, 20 m in Blacktail Mountains, and 85-120 m near Jackson.

Flathead Sandstone (Middle Cambrian) - Pale-orange, light-yellowish-gray, and yellowish-brown, thin- to medium-bedded, mostly fine- to medium-grained, but locally coarse-grained, quartzitic sandstone and arkosic sandstone, locally conglomeratic. Upper part of formation commonly includes interbeds of glauconitic, fine-grained sandstone, and olive-green and pale-red mudstone and shale. Basal part of formation locally includes interbeds of yellowish-gray to pale-brown siltstone, mudstone, and shale. Thickness 0-43 m in Tobacco Root Mountains, 9-16 m in Ruby Range and Blacktail Mountains, and 20-30 m in Pioneer and Highland Mountains.

Hasmark Formation (Upper and Middle Cambrian) - Light-gray, thin- to thick-bedded dolomite; locally contains oolites, pisolites, pellets, and algal structures. About 235-300 m thick. Correlative of Pilgrim Formation, Park Shale, and Meagher Limestone.

Silver Hill Formation (Middle Cambrian) - Light-yellowish-brown calcareous shale, limestone, and dolomite and olive-green shale and mudstone; includes minor interbeds of thin-bedded sandstone. Thickness 0-100 m. Correlative of Park Shale, Meagher Limestone, Wolsey Shale, and Flathead Sandstone. Locally, also includes fine-grained clastic rocks of probable Middle Proterozoic Belt Supergroup age.'
1499|'Includes Gunsight Formation, Apple Creek Formation, and Big Creek Formation in Dillon quadrangle.

Gunsight Formation - Light-brownish-gray, medium-light-gray to grayish-red-purple, thin- to medium-bedded, fine- to medium-grained feldspathic quartzite; many beds laminated or cross-laminated. Minimum thickness about 1,800 m, but no unfaulted sections known.

Apple Creek Formation - Grayish-green, thin-bedded siltite and very fine grained feldspathic quartzite that contains irregular streaks and lenses of light-gray, ferrodolomite-cemented fine-grained sandstone; laminated or cross-laminated, commonly displaying mud cracks and ripple marks; locally pyritic. Lower part of formation includes subordinate beds of grayish-red-purple and dark-gray siltite and argillite. Thickness about 760-900 m.

Big Creek Formation - Pale-greenish-gray too light-gray, mostly thick-bedded or massive, fine-grained feldspathic quartzite. Many beds laminated or cross-laminated. Thickness about 3,100 m.'
1500|'Medium-gray to medium-dark-gray, mostly thin- to medium-bedded, very fine grained to fine-grained, feldspathic, finely biotitic quartzite and subordinate interbedded dark-greenish-gray to medium-dark-gray, thin- to medium-bedded siltite and argillite. Probable thickness more than 8,000 m, but the base of the formation has not been found and the upper part is everywhere bounded by Late Cretaceous Medicine Lodge thrust plate in east-central Idaho and adjacent southwestern Montana (Lopez, 1981,1982a).'
1502|'Pioneer Mountains and the east flank of the Beaverhead Mountains:  Unit includes Garnet Range Formation, McNamara Formation, Bonner Quartzite, and Mount Shields Formation and probable metamorphosed equivalents.

Garnet Range Formation-Grayish-red, medium-red to pale-red, and light-brown, fine- to coarse-grained feldspathic, limonitic sandstone in thin and platy beds separated by thin beds and bedding partings of grayish-red to dusky-red siltite and fissile argillite. Bedding surfaces commonly spangled with white mica. In part thinly laminated or cross-laminated. Thickness 0-800 m. Known to occur in vicinity of Warm Spring Creek near Jackson, on Big Hole Divide, and in Argenta mining district in south-central part of map area.

McNamara Formation-Grayish-red to pale-red, thin-bedded, platy, medium-grained, partly thinly laminated or cross-laminated feldspathic quartzite and quartzitic sandstone; thin interbeds and bedding partings of grayish-red argillite and interbedded greenish-gray, fine-grained quartzite and light-greenish-gray siliceous argillite; muscovite common on bedding surfaces; locally mud cracked and ripple marked. Thickness uncertain, possibly as much as 2,300 m. Known to occur in Warm Spring Creek area, as isolated outcrops near Jackson, and in northern part of Pioneer Mountains.

Bonner Quartzite and Mount Shields Formation-Grayish-pink, grayish-red, and pale-red to light-gray and medium-light-gray, medium- to coarse-grained, but locally fine grained, thin- to thick-bedded, commonly cross-laminated, micaceous feldspathic quartzite and subordinate grayish-green to grayish-red siltite and argillite, most commonly as thin bedding partings and chips in quartzite. Includes conglomerate beds and lenses as much as 3 m thick, mainly in northern part of Wise River valley and east of French Creek. Thickness unknown. Occurs in central part of map area from Horse Prairie Creek northward through Pioneer Mountains to French Creek and Little Granulated Mountain. In most places unit is probably the middle and upper parts of Mount Shields Formation, but probably mostly the overlying Bonner Quartzite in area between French Creek and Little Granulated Mountain.

In Beaverhead Mountains, quartzitic rocks included in Mount Shields Formation differ from those farther east, and probably are mostly lower part of Mount Shields Formation. Upper part of sequence is mainly light- brownish-gray, greenish-gray to light-gray, pale-red, or less commonly grayish-red-purple or dark-reddish-gray, fine- to medium-grained, thin-bedded to massive, locally ripple-marked, laminated and cross-laminated feldspathic quartzite; contains well-sorted, well-rounded glassy quartz grains and pink quartz and reddish chert grains in some places, and abundant dark-gray heavy minerals disseminated throughout the rock or concentrated on laminae and cross-laminae. Muscovite common on bedding surfaces; bedding partings and thin interbeds of dark-gray to greenish-gray and grayish-red argillite and siltite are present locally. Thickness unknown but probably more than 1,500 m.

Lower part of the Mount Shields in Beaverhead Mountains consists of three zones: (1) Upper zone of 10 to 50-m-thick units of interlayered thin- and thick-bedded to massive, light-brownish-gray to light-gray, fine- to medium-grained, laminated and cross-laminated feldspathic quartzite and quartzitic sandstone interlayered with thin beds of dark-gray argillite; bedding surfaces and partings are commonly calcareous or dolomitic; probably about 150-200 m thick. (2) Middle zone, as much as 500-700 m thick, of light-brownish-gray to pale-purple, fine- to medium-grained, thick-bedded to massive, in part coarsely laminated and cross-laminated, feldspathic, partly calcareous or dolomitic quartzite and quartzitic sandstone containing bedding partings and sparse thin beds of dark-gray argillite; sparse floating pebbles and pebbly zones are common on bedding surfaces, and dark-gray heavy minerals are disseminated throughout rock and concentrated on laminae and cross laminae. (3) Lower zone, about 150-200 m thick, of light-brownish- or greenish-gray to light-gray, pebbly and conglomeratic, fine-grained to very coarse grained, cross-laminated calcareous or dolomitic quartzite, quartzitic sandstone, and sparse lenticular beds of sandy dolomite and sparse bedding partings and thin interbeds of dark-gray argillite; includes conglomerate lenses, as much as 2 m thick, of subangular to subrounded pebbles 1-4 cm in diameter of white quartz and less common quartzite, granite, and feldspar pebbles in sand matrix and on bedding surfaces.

Lower part of Mount Shields Formation in Beaverhead Mountains exposed from vicinity of Ajax Lake and Lena Lake south to Hamby Lake; best exposed in vicinity of Ajax and Rock Island Lakes. Estimated thickness of lower part about 1,000 m; base not exposed.

Anaconda Range and in the northern Beaverhead Mountains:  Mount Shields Formation-Grayish-white to pink, fine- to coarse-grained, feldspathic quartzite locally interlayered with quartz-pebble conglomerate. Quartzite beds, generally less than 1 m thick, commonly become fine upward and are locally capped by siltite and argillite. The distinctive feldspathic quartzite beds of this formation grade downward into interlayered dark-gray argillite and feldspathic quartzite; argillite becomes predominant in lower part of formation, Upper contact of formation is not exposed. Thickness about 500 m.

Shepard Formation-Tan, calcareous and dolomitic siltite, fine-grained quartzite, and minor conglomerate. Thickness about 200 m.

Snowslip Formation-Tan to pinkish-white, fine- to medium-grained quartzite interbedded with dark-gray, thin-bedded, irregularly laminated siltite, silty argillite, and argillite. Contains sparse, thin (less than 20 cm thick) interbeds of clean, white, medium-grained quartzite. Thickness exceeds 450 m.

Highland Mountains and in the northern Tobacco Root Mountains:  Interlayered quartzite and siltite that pinches out to the east and west within Highland Mountains. Upper part consists of white to pinkish-white, fine- to medium-grained quartzite interlayered with minor tan siltite. Middle part consists of interlayered white to tan, thick-bedded, locally platy and cross-bedded quartzite interlayered with laminated, very fine grained, argillaceous quartzite. Quartzite grades laterally into subangular, pebble to cobble intraformational conglomerate in central part of Highland Mountains. Lower part consists of medium-gray, laminated, very fine-grained sandstone and siltstone showing even parallel lamination. Maximum thickness about 300 m.'
1503|'Metasediments in the Pioneer Mountains and the east flank of the Beaverhead Mountains:  Interlayered gray to greenish-gray and brownish-gray, fine-grained biotite-muscovite metaquartzite; locally contains garnet and sillimanite. Previously interpreted by L.W. Snee in Berger and others (1983) to be pre-Belt in age.

Metamorphosed Belt rocks in the Anaconda Range and in the northern the Beaverhead Mountains:  Quartz-feldspar-biotite gneiss and minor schist. Gneiss is medium gray to tan, micaceous, and well foliated, and contains thin interlayers of dark-gray to black schist. Locally, schist is predominant rock type and consists of dark-gray to black mica schist enclosing thin stringers of quartz and feldspar. These rocks can be traced laterally into unmetamorphosed sedimentary rocks.'
1504|'Light-gray, tan, and white, slightly feldspathic, medium- to coarse-grained, thick- to thin-bedded quartzite. Contains a distinctive quartz-pebble to quartz-cobble conglomerate, as much as 5 m thick, in middle part. Unconformably overlies conglomerate (Ycg). Maximum thickness 300 m. Quartzite is best exposed at Grace Lake, located 1.5 km south of Black Lion Mountain.'
1505|'Light- to medium-gray, matrix-supported pebble conglomerate, pebbly quartzite, and poorly sorted, argillaceous quartzite and sandstone grit. Most of unit is very similar to parts of LaHood Formation of Belt Supergroup in Highland Mountains to the east. Zen (1988) named this unit Black Lion Conglomerate and inferred a Cambrian age.'
1506|'White, yellowish-white, and pinkish-white, medium- to coarse-grained, weakly feldspathic, evenly parallel-laminated to cross-bedded quartzite common in the upper 20 m of the section. Quartzite is underlain by, and locally interbedded with, yellow-tan to greenish-tan, parallel to cross-laminated argillaceous sandstone and siltstone, minor laminated argillite, and rare brownish-gray limestone. Base not exposed. Equivalent to the sequence of Swamp Creek of Zen (1988) and to Belt Supergroup rocks of Frazer and Waldrop (1972) exposed 3-5 km directly south of Wise River. Upper quartzite is similar to quartzite of Grace Lake, and underlying argillaceous rocks are similar to the laminated Greyson Shale in Highland Mountains to the east. Maximum exposed thickness near 50 m.'
1510|'Greyson Shale rocks in the Anaconda Range and in the northern Beaverhead Mountains:  Quartzite is equivalent to Spokane Formation in Highland Mountains to the east.

Quartzite of Queener Mountain-Light-gray to white, fine- to medium-grained quartzite interlayered with minor dark-gray argillite and siltite. Quartzite grades upward into dark-gray argillite interlayered with minor dark-gray, fine-grained quartzite, and local, thin beds of clean, white, medium- to coarse-grained quartzite. Thickness is nearly 600 m. Quartzite is best exposed at Queener Mountain at the head of Seymour Creek, directly north of the quadrangle boundary. Unit is stratigraphically equivalent to Spokane Formation of Ravalli Group in Helena embayment of Belt Basin. It was mapped as Ravalli Formation by Emmons and Calkins (1913); however, Elliot and others (1985) included this unit in Missoula Group rocks.

Greyson Shale-Dark-gray to dark-greenish-gray, well-laminated argillite and silty argillite. Beds, generally less than 5 cm thick, commonly contain uneven, parallel lamellae of white to tan, very fine grained sandstone and siltstone. Contains thin, dark-gray quartzite lenses in the upper part. Thickness in excess of 1,000 m. Unit is stratigraphically equivalent and lithologically similar to Greyson Shale of the Helena embayment of the Belt basin. Unit was mapped as the Prichard Formation by Emmons and Calkins (1913) and included with Missoula Group rocks by Elliot and others (1985).

Spokane and Greyson Formation rocks in the Highland Mountains and in the northern Tobacco Root Mountains:  (Unit named "Spokane and Greyson Formations (Middle Proterozoic)", but has same map label.)  Spokane Formation consists of grayish-tan to tan, structureless to laminated and commonly cross-bedded, argillaceous siltite and minor dark-grayish-green silty argillite interlayered with 0.2- to 1-cm-thick, discontinuous, very fine grained sandy lenses. Conspicuous white to pinkish-white, fine- to coarse-grained, grain-supported quartzite beds 1-2 m thick are common in upper part of formation and are thickest and most abundant in central part of Highland Mountains.

Greyson Formation, underlying the Spokane, is thickest in central part of Highland Mountains, and consists of an upper dark-gray to black, laminated and platy to massive argillite and silty argillite that contains numerous soft-sediment slump structures. Basal part consists of light- to dark-gray silty argillite and argillaceous siltite having uneven to even parallel laminations and locally interlayered with tan, discontinuous silty lenses, commonly less than 1 cm thick; these basal siltite beds locally are interlayered with 0.2- to 0.5-m-thick, laterally discontinuous beds of matrixsupported quartzite composed of well-rounded grains, and locally dense, tan to white, cross-bedded quartzite. Thickness of combined formations ranges from less than 400 m in the west to more than 900 m in central part of Highland Mountains.'
1512|'Helena and Empire Formation rocks in the Highland Mountains and in the northern Tobacco Root Mountains:  Helena and Empire Formations are thickest in central part of Highland Mountains, pinch out to the west, and thin to the east. The Empire generally underlies the Helena, but the formations are locally complexly interlayered and grade laterally into one another. Helena Formation typically consists of tan, pinkish-gray to grayish-green, laminated to thin-bedded, calcareous, and commonly vuggy siltite; locally shows water-expulsion features, mud cracks, and very finely laminated, upwardly convex pods that may be algal mounds. In central part of range, upper part of the Helena consists of calcareous siltite and argillite that locally show well-developed water-expulsion structures and rip-up conglomerate lenses; lower part consists of upward-fining cycles of very fine grained sandstone showing wavy parallel lamination overlain by argillaceous siltite interlayered with very fine grained sandstone lenses. Empire Formation consists of dark-gray to black, very fine grained, argillaceous siltite containing elongate pods of tan, silty limestone that is locally interlayered with thick-bedded, purplish-gray siltstone. Maximum thickness of unit about 350 m.

Helena and Empire Formation rocks in the Anaconda Range and in the northern Beaverhead Mountains:  Helena Formation consists of dark- to medium-gray, laminated, locally silty, calcareous argillite, argillaceous limestone, and dolomite. Bedding is uneven, wavy, and laterally discontinuous. In eastern part of range, basal part of the Helena locally contains abundant interbeds of fine- to medium-grained, gray to tan quartzite. Underlying Empire Formation consists of dark-gray to black, calcareous siltite containing irregular pods of white to light-gray limestone. Combined thickness of these formations exceeds 1,000 m.

Middle Belt carbonate rocks appear to be present beneath rocks of Medicine Lodge thrust plate in Beaverhead Mountains north of Salmon, Idaho. Exposures directly north of North Fork consist of alternating sequences of calc-silicate rock, characterized by a basal upward-fining, fine-grained and laminated sandstone, 0.1 to about 2 m or more in thickness, capped by 0.1- to 1-m thick units of calcareous mud, silt, and sand in beds about 1 cm thick. The calcareous deposits are metamorphosed, are medium to dark green, and contain abundant porphyroblasts of actinolite-tremolite. In a few places the calcareous units become very thinly laminated. These calc-silicate units are interlayered with laminated to cross-bedded tan quartzites. Pinch-and-swell, centimeter-thick couplets of tan sand and brown to dark-gray argillite are common in upper part of sequence. These rocks, originally mapped as Yellowjacket Formation by Lopez (1982b), resemble the lower Yellowjacket Formation at its type locality at Yellowjacket Creek as well as similar exposures at Hayden Creek, where the unit exceeds 1,600 m (Lopez, 1981, p. 16-24). The cyclical clastic to carbonate cycles present in these rocks are also similar to sedimentary cycles of Wallace Formation of middle Belt carbonate to the north in Montana (D. Winston, personal commun., 1990) and are here tentatively correlated with these rocks rather than with the Yellowjacket. Rocks exposed directly south of Lost Trail Pass consist of at least three south-southwest-dipping rock units. Upper part of upright section consists mainly of cyclical deposits of clastic to calc-silicate rocks similar to those rocks to the south. These rocks are underlain by laminated, light-colored quartzite, very poorly exposed only on the east along Continental Divide, which in turn overlie thinly laminated siltite-argillite. The calc-silicate rocks are correlated with rocks directly to the south; these rocks were originally mapped as the Wallace Formation by Desmarais (1983). The underlying quartzite and laminated siltite-argillite are similar in sequence and lithology to the lower Belt quartzite and underlying siltite-argillite beneath the Helena Formation in the Anaconda Range (Ysg). Thickness of these units is not known.'
1514|'The Newland Formation consists of dark-gray to pinkish-gray argillite, silty argillite, and minor marl. Thin, discontinuous lenses of finely crystalline to medium-crystalline, medium-gray limestone are present in the upper part. The argillaceous rocks show a distinctive blocky bedding character: nonlaminated, structureless beds, 1-3 cm thick, of argillite are separated by ruler-straight, single to multiple lamellae of tan silt and very fine grained sandstone. Outcrops and float from the Newland are characterized by tabular, centimeter-thick beds having extremely planar parting surfaces. The Newland is everywhere underlain by a mappable sequence of argillite, siltite, and minor sandstone that lacks both the tabular, blocky beds of the Newland and the argillaceous grit found only in underlying LaHood Formation. 

The LaHood Formation consists of coarse sedimentary conglomerate and breccia; in Highland Mountains, cobble to boulder conglomerate grades laterally into quartz-pebble conglomerate, into coarse, argillaceous, lithic grit, and into arkose. The arkose grades into interlayered shale, siltstone, sandstone, and subordinate pebble conglomerate and argillaceous grit. Newland and LaHood Formations, like the overlying units, are thinnest on the west-less than about 700 m-and thickest in central part of Highland Mountains, more than 1,500 m.'
1515|'Quartzite, siltite, and argillite present only in Highland Mountains. Upper part of unit consists of massive white quartzite beds separated by 1- to 5-m-thick, upward-fining sequences of intraformational conglomerate, sandstone, siltstone, and argillite. Lower part consists of about 250 m of quartzite that is overlain by interbedded clean to argillaceous quartzite, siltite, and argillite. Basal contact is gradational into LaHood pebble and cobble conglomerate and sandstone; unit thins and pinches out to the west and is locally interlayered with Newland Formation on the east. Maximum thickness is more than 500 m.'
1516|'Dark-greenish-gray to black, fine- to medium-grained diabase dikes. Most dikes were intruded along pre-existing, northwest-trending faults in pre-Belt crystalline rocks between 1.4 and 1.1 Ga (Wooden and others, 1978).'
1517|'Light-colored, medium- to coarse-grained, generally equigranular microcline-plagioclase gneiss interlayered with dark-gray to black, fine-grained amphibolite, minor migmatitic and augen gneiss, and rare garnet-bearing calc-silicate schist and fine-grained calc-silicate gneiss. Exposed on north flank of Sheep Mountain. Age about 1.8-1.6 Ga (Arth and others, 1986; Zen, 1988).'
1518|'Dark-gray, medium- to coarse-grained, biotite-rich gneiss. Contains wispy lenses, seams, and augen of quartz and feldspar. In part, rock is very similar in composition and texture to mylonitic biotite gneiss (X(A)m) in Highland Mountains. Locally cut by numerous quartz-rich pegmatite dikes and large quartz veins. Exposed east of Bloody Dick Creek. Age about 1.8 Ga (R.E. Zartman, oral commun., 1987).'
1519|'Dense swarm of leucocratic, granitic aplite and pegmatite sills and minor dikes, and augen-bearing orthogneiss; interlayered mainly with mylonitic biotite gneiss and quartz-feldspar-biotite gneiss.'
1520|'Interlayered granitic to granodioritic, mylonitic orthogneiss and nonfoliated, leucocratic, medium- to coarse-grained granite sills.'
1521|'Dark-gray to black, medium-grained to very coarse grained, strongly folded, garnet-rich biotite gneiss; locally contains abundant thin ptygmatic quartz-feldspar veins.'
1522|'Dark-gray to black, medium- to coarse-grained, biotite-rich gneiss and minor schist. Contains conspicuous porphyroclasts of quartz and plagioclase that are commonly anhedral and broken, are sheared and drawn out in plane of foliation, or are augen; locally interlayered with granitic, augen-bearing orthogneiss.'
1523|'A diverse sequence chiefly composed of garnet-rich gneiss and schist; also contains discontinuous lenses of marble, quartzite, iron-formation, and amphibolite, Ranges in thickness from 0 to 100 m.'
1524|'Gray to tan, fine- to medium-grained quartz-feldspar-biotite gneiss in which compositional banding defines a distinct, platy foliation; locally interlayered with seams of finely layered mylonitic leucogneiss or sills of fine- to coarse-grained granite.'
1525|'Leucocratic, massive, medium- to coarse-grained, strongly deformed and lineated quartz-feldspar gneiss that contains sparse biotite or muscovite. Locally contains well-developed quartz-feldspar augen ranging in diameter from less than 1 cm to more than 6 cm.'
1526|'Black to dark-greenish-brown, coarse-grained rocks present as small lenses and irregularly shaped pods commonly less than 30 m in length or width but locally more than 1.5 km long. Consists of orthopyroxene, olivine, spinel, hornblende, and magnetite; locally partly altered to serpentine and talc (Desmarais, 1981).'
1527|'Complexly interlayered granitic, tonalitic, quartz-feldspar-biotite and hornblende-plagioclase gneiss (Vitaliano and Cordua, 1979). In Ruby Range the gneiss appears to underlie main metasedimentary succession (James, 1990); in Tobacco Root Mountains the gneiss is complexly interlayered with, and overlies, these metasedimentary rocks. In core of Armstead anticline, unit includes minor metasedimentary rocks (Lowell, 1965). Rb-Sr age determined from these rocks is 2.76 Ga (James and Hedge, 1980).'
1528|'Dark-gray to greenish-black, medium- to coarse-grained, hornblende-rich gneiss; forms lenses ranging from less than 1 m to more than 500 m in thickness. Rock composed mainly of hornblende and plagioclase.'
1529|'Light-colored, coarse-grained quartz-muscovite schist. Subordinate minerals include sillimanite or, locally, kyanite and minor garnet, anthophyllite, and biotite. Aluminous schist is closely associated with quartzite and marble.'
1530|'Composed mainly of quartz-feldspar-biotite gneiss, granitic gneiss, and amphibolite.'
1531|'Medium-gray to dark-brown, coarsely crystalline, carbonate-rich rocks present as layers that range from less than 1 m to more than 500 m thick. Rock composed mainly of calcite and dolomite, and contains subordinate amounts of quartz, diopside, tremolite, and forsterite.'
1532|'White to pinkish-gray, coarse-grained quartzite in lenses less than 2 cm thick to persistent beds 30-100 m thick. Commonly associated with marble and iron-formation. Thickest beds are present in southern Tobacco Root Mountains.'
1533|'Dark-gray rock consisting of alternate quartz-rich and magnetite-rich layers and lenses. All layers consist of essential magnetite, quartz, orthopyroxene and clinopyroxene, and garnet; individual layers typically 1-2 cm thick, but mappable units are as much as 30 m thick (James, 1981). Commonly associated with quartzite and aluminous schist. Present in southern Tobacco Root Mountains and Ruby Range.'
1534|'Well-foliated medium- to dark-gray biotite-hornblende-garnet gneiss, migmatite, augen gneiss, and aluminous schist. Structurally lowest sequence in Ruby Range (Karasevich and others, 1981).'
1550|'Gravel, sand, silt, and clay in flood plains and low terraces along present drainages. Includes alluvial fans.'
1551|'Includes large rock slumps, flow, and slides. Generally consists of angular blocks of bedrock in a finer grained matrix; mixed at places with glacial debris. Most abundant on slopes topographically below trace of Lewis thrust fault on east and south sides of Glacier National Park (Carrara, 1990).'
1552|'Includes till (in ground, end, and ablation moraines), outwash, and other fluvioglacial deposits from both continental and mountain glaciers. Includes eskers at a few places in Glacier National Park (Carrara, 1990).'
1553|'Conglomerate, sandstone, siltstone, marlstone, oil shale, and coal deposited in the Kishenehn basin. About 3,800 ft thick in the valley of the Middle Fork of the Flathead River in central part of map area (Whipple, 1992).'
1554|'Mainly dark-gray mudstone of the Marias River Shale as described by Mudge and Earhart (1983). May include the Horsethief Sandstone and St. Mary River Formation at northeast edge of Glacier National Park. At least 1,500 ft thick.

Mudge and Earhart (1983) description of Marias River Shale:  Mainly dark-gray, marine mudstone, ranges from 365 to 395 m thick. Divided into four members by Cobban, Erdmann, Lemke, and Maughan (1959b, 1976), in descending order: Kevin, Ferdig, Cone, and Floweree.

The Kevin is dark-gray, calcareous mudstone with some thin, very fine grained sandstone in upper part. Characteristically contains many thin, micaceous bentonite beds and zones of calcareous and ferruginous limestone concretions. Bentonite beds thicker and far more numerous in southern outcrops. Pelecypods and ammonites common. The Kevin Member ranges from about 226 m thick in the east to as much as 326 m in the west (Mudge, 1972).

The eastern facies of the Ferdig Member contains gray, noncalcareous mudstone with many very thin, iron-stained sandstone beds, concretions of yellow-weathering limestone and red-weathering ferruginous dolostone, and some very thin bentonite beds, about 50 m thick. The western facies of the Ferdig, exposed in the North and South Forks of the Sun River, is about 150 m thick, and resembles the Cardium Formation of southern Alberta, Canada (Mudge, 1972). Contains nodular sandstone, sandy shale, and even-bedded sandstone in the middle and upper parts of the western facies; thick-bedded, light-gray sandstone in upper part. Organic burrows and trails common. The lower part is like that exposed in the eastern facies.

The Cone Member contains abundant, very thin, medium-gray, calcareous siltstone and crystalline limestone beds in the upper part and dark-gray noncalcareous fissile shale with some limestone concretions in the lower part (Cobban, Erdmann, Lemke, and Maughan, 1976); contains several bentonite beds throughout. The upper beds commonly have petroliferous odor on a freshly broken surface. Contains a characteristic fauna which includes Mytiloides labiatus (Cobban, Erdmann, Lemke, and Maughan, 1976). Ranges from 15 to 30 m thick.

The Floweree Member is noncalcareous, dark-gray, nonfossiliferous shale (Cobban, Erdmann, Lemke, Maughan, 1976; Mudge, 1972). Locally contains basal siltstone with chert-pebble conglomerate. The shale has metallic luster and yellowish-brown stains on bedding and fracture planes (Mudge, 1972). Ranges from 9 to 12 m thick.'
1555|'Predominantly gray to olive mudstone and gray sandstone interbedded with some limestone. Includes the Blackleaf, Kootenai, and Mount Pablo Formations as mapped and described by Mudge and Earhart (1983). Thickness about 2,200 ft.

Mudge and Earhart (1983) description of Blackleaf, Kootenai, and Mount Pablo Formations:  BLACKLEAF FORMATION:  Gray, marine mudstone and interbedded sandstone. Divided into three members by Cobban, Erdmann, Lemke, and Maughan (1959b, 1976), in descending order: Vaughan, Taft Hill, and Flood. The formation ranges from about 200 m thick in southern outcrop to about 490 m in the west and about 260 m in the north.

The nonmarine Vaughan Member consists of alternating gray to olive-drab mudstones and bentonitic mudstone with many thin interbeds of light-gray, locally cross-bedded sandstone. Contains less sandstone to the north and lower beds are laterally equivalent to upper part of the marine Taft Hill strata to the south. Locally, beds of conglomerate fill small channels at base of some sandstone units (Mudge, 1972). In the Sun River area, the upper part of member contains tuffaceous debris, one bed contains accretionary lapilli (Mudge, 1972). Member locally contains wood and leaf fragments and, in the vicinity of Teton Pass, contains beds of coal and carbonaceous shale. Ranges from 90 m thick in the eastern outcrops to possibly 213 m in the north.

In the south, the marine Taft Hill Member consists of thinly bedded, gray, fossiliferous sandstone, locally cross-bedded and ripple marked (Mudge, 1972), interbedded with dark-gray mudstone containing some very thin bentonite beds. These units grade northward into nonmarine lithologies of the Vaughan. The Taft Hill is as much as 183 m thick in west-central part of the area, thins to 0 m to the north and 58 m in the southeast outcrop.

The marine Flood Member in the south consists of two sandstone units with a distinctive intervening shale unit. Lower sandstone absent to the north where upper sandstone unit is thicker and shale unit thinner, as compared to southern exposures. Gray, thinly cross-bedded, very fine grained, finely micaceous and moderately well sorted sandstones (Mudge, 1972); commonly weather grayish brown. Locally large sandstone nodules in lower part. The shale unit, transitional with upper sandstone unit, is distinct, very dark gray fissile shale with a metallic luster on bedding surfaces. Thin sandstone lentils and nodules of limestone and claystone common, locally phosphatic nodules present. Organic trails and burrows abundant in transition zone. The Flood ranges from 45 m thick in eastern outcrops to 165 m in western. About 40 m thick in the north part of mapped area (Rice and Cobban, 1977).

KOOTENAI FORMATION:  Nonmarine, gray-green and maroon mudstone with numerous lenticular, poorly sorted, greenish-gray sandstone beds, locally cross-bedded and contain lenticular basal conglomerates (Mudge and Sheppard, 1968; Mudge, 1972). Brown to brownish-gray limestone with thin to thick lenses of coquina with pelecypods and gastropods is near top of formation. Brown, iron-stained limestone nodules common in mudstone beds. The Sunburst Sandstone Member of Rice and Cobban (1977) is at base of formation in the southern outcrops and absent to the north. The Sunburst consists of many thin beds of hard, noncalcareous, poorly sorted quartz sandstone with few scattered grains of chert and feldspar. The Kootenai ranges from 198 to more than 305 m thick.

MOUNT PABLO FORMATION:  Nonmarine, formerly referred to as the western facies of the Morrison Formation in the Sun River Canyon area (Mudge, 1972). Consists of limestone, mudstone, and sandstone in upper part, variegated mudstone interbedded with sandstone in middle part, and sandstone and conglomerate in lower part (Mudge and Rice, 1980). Everywhere overlain unconformably by the Kootenai Formation (Kk). The lower sandstone and conglomeratic sandstone is the Cut Bank Sandstone Member, an important hydrocarbon reservoir rock near Cut Bank, Mont. The upper and middle parts of the formation are mostly gray to gray-green mudstone with some maroon and orange-red mudstone and thin beds of fine-grained sandstone. Mostly reddish-brown mudstone with some sandstone in southwestern area (Mudge, 1972). Widespread, light-gray, lacustrine limestone, as much as 10 m thick, near top of the formation. The Cut Bank Sandstone Member in places contains coarse-grained, cross-bedded sandstone in the upper part, composed of nearly equal amounts of quartz and black chert. Grades upward into very fine grained sandstone as much as 10 m thick in the north. The lower conglomeratic sandstone unit is prominent, cross-bedded, poorly sorted, very coarse  grained sandstone that grades upward into very fine sandstone. In many places has dominantly chert-pebble conglomerate at its base, to the south conglomeratic lenses common at various horizons. Commonly about 8 m thick, the lower sandstone unit is as much as 30 m thick. The Mount Pablo Formation (KJm) ranges from 0 to about 90 m thick, unconformably overlies the Morrison Formation except in northeastern outcrops where overlies the Swift Formation.'
1556|'Includes siltstone, sandstone, and shale accompanied by minor limestone and thin conglomerate at base of some members as mapped and described by Mudge and Earhart (1983). About 1,500 ft thick.

Mudge and Earhart (1983) description of Mount Pablo Formation (Lower Cretaceous), Morrison Formation (Upper Jurassic), and Ellis Group (Upper and Middle Jurassic), undivided unit:  The Morrison Formation is not mapped separately and therefore is described below.

The most complete sections of the Morrison are in east-central and southern outcrop areas. Mainly grayish-green, tuffaceous siltstone with interbedded sandstone, limestone, and some cherty siderite in the eastern part of the Sun River Canyon area (Mudge, 1972). Maroon and tints of pinkish-gray beds common in the upper part. Cherty siderite occurs as lenses in the middle part, limestone occurs as beds or nodules in the lower part. The Morrison is about 61 m thick in the Sun River area (Mudge, 1972), about 82 m thick in the Wolf Creek area (Schmidt, 1972a). Mostly eroded prior to deposition of the Mount Pablo Formation north of the Sun River area. In most places, the Morrison is less than 30 m thick.

Mudge and Earhart (1983) description of ELLIS GROUP:  Divided into three formations by Cobban (1945), in descending order: Swift, Rierdon, and Sawtooth. In the Wolf Creek area the Rierdon Formation is absent, the combined thickness of the Swift and Sawtooth Formations is about 65 m. The three formations have an aggregate thickness of about 87 m in the Sun River area, about 205 m thick west of that area, and more than 188 m in the northern part of mapped area (Mudge and Earhart, 1978).

The Upper and Middle Jurassic Swift Formation was divided into upper and lower unnamed members by Cobban (1945). Ranges from 30 to 36 m thick in the southeast to more than 60 m in the northwest. In the northeast, part of the upper member was eroded prior to sedimentation of the Cretaceous Mount Pablo Formation. The upper member is thin-bedded, gray to gray-brown, very fine to fine-grained sandstone. As much as 30 m thick in the Sun River area (Mudge, 1972), less than 3 m thick in the northeast outcrop. The lower member is dark-gray shale with some interbeds of sandstone. A thin bed of poorly indurated glauconitic sandstone with water-worn belemnites and locally chert pebbles, at base of the member except in the northern outcrops. The lower member averages about 15 m thick in the south and about 21 m thick in the north. The Swift unconformably overlies the Rierdon Formation.

The Middle Jurassic Rierdon Formation contains calcareous gray-brown siltstone and claystone in the upper part and calcareous, dark-gray, laminated shale and claystone in the lower part. Many thin beds of argillaceous limestone scattered throughout formation. Barite nodules, numerous pelecypods and some ammonites common. Phosphatic nodules common in the lower part of northern exposures. About 44 m thick in the Sun River area, as much as 56 m thick to the north.

The Middle Jurassic Sawtooth Formation is divided into three unnamed members by Cobban (1945), the lower member is absent in the northern outcrop area. Ranges in thickness from 15 to 69 m, thickening to the north. The upper siltstone member is a prominent unit, many thin beds of grayish-brown to yellowish-gray siltstone with a few thin beds of shale, increasingly sandy northward. Lenses of phosphatic pellets common in the western and northern outcrops. Pelecypods common and ammonites rare. Member 6-13 m thick in the south (Mudge, 1972), thickens northward to about 18 m (Imlay, 1962). The shale member is dark-gray shale with some siltstone, sandstone, and a few beds of limestone. Thickens northward from 5 m in the Sun River area to about 77 m near Mount Patrick Pass. Some beds locally pyritic. North of the Teton River contains black, phosphatic pellets and lies unconformably on Mississippian carbonate rocks. The lower sandstone member in the southern part of the area rests unconformably on Mississippian rocks. In most places, hard, fine-grained, and light-gray sandstone beds, conglomeratic in the basal part. Locally consists of two beds of sandstone separated by dark-gray shale. The conglomerate consists of pebbles and cobbles and locally boulders of Mississippian carbonate and chert (Mudge, 1972). The sandstone member ranges from 0-6 m thick, in most places 0.6-2 m thick (Mudge, 1972).

Mudge and Earhart (1983) description of MOUNT PABLO FORMATION:  Nonmarine, formerly referred to as the western facies of the Morrison Formation in the Sun River Canyon area (Mudge, 1972). Consists of limestone, mudstone, and sandstone in upper part, variegated mudstone interbedded with sandstone in middle part, and sandstone and conglomerate in lower part (Mudge and Rice, 1980). Everywhere overlain unconformably by the Kootenai Formation (Kk). The lower sandstone and conglomeratic sandstone is the Cut Bank Sandstone Member, an important hydrocarbon reservoir rock near Cut Bank, Mont. The upper and middle parts of the formation are mostly gray to gray-green mudstone with some maroon and orange-red mudstone and thin beds of fine-grained sandstone. Mostly reddish-brown mudstone with some sandstone in southwestern area (Mudge, 1972). Widespread, light-gray, lacustrine limestone, as much as 10 m thick, near top of the formation. The Cut Bank Sandstone Member in places contains coarse-grained, cross-bedded sandstone in the upper part, composed of nearly equal amounts of quartz and black chert. Grades upward into very fine grained sandstone as much as 10 m thick in the north. The lower conglomeratic sandstone unit is prominent, cross-bedded, poorly sorted, very coarse  grained sandstone that grades upward into very fine sandstone. In many places has dominantly chert-pebble conglomerate at its base, to the south conglomeratic lenses common at various horizons. Commonly about 8 m thick, the lower sandstone unit is as much as 30 m thick. The Mount Pablo Formation (KJm) ranges from 0 to about 90 m thick, unconformably overlies the Morrison Formation except in northeastern outcrops where overlies the Swift Formation.'
1558|'Upper part is the Castle Reef Dolomite and lower part is the Allan Mountain Limestone as mapped and described by Mudge and Earhart (1983). About 1,200 ft thick

Mudge and Earhart (1983) description of MADISON GROUP:  Divided into the Castle Reef Dolomite and the underlying Allan Mountain Limestone (Mudge, Sando, and Dutro, 1962), equivalent in age to the Mission Canyon and Lodgepole Limestones in Central Montana. The Madison ranges from about 275 m to 550 m thick, much of the variation in thickness is a result of pre-Jurassic erosion (Mudge, 1972).

The Upper and Lower Mississippian Castle Reef Dolomite, ranges from about 230 m thick in the eastern outcrops to about 305 m in the west, is divided into an upper member, the Sun River Member, and a lower unnamed member (Mudge, Sando, and Dutro, 1962). The Sun River Member, 76-137 m thick, consists mostly of thick beds of fine- to medium-crystalline dolomite (Mudge, 1972), and is main hydrocarbon reservoir rock on the Sweetgrass Arch (Chamberlain, 1955). In many places oil residues common in cavities, pores, fractures, and on bedding planes in the upper part of the member. The lower member of the Castle Reef consists of thin to thick beds of fine to coarsely crystalline, light-gray dolomite, calcitic dolomite, and dolomitic limestone, dolomite content increases westward. Beds of coarsely crystalline encrinites at various horizons in the Castle Reef, increasingly abundant to the north and west. Lenses and nodules of dark-gray chert common in lower and middle parts, light-gray chert nodules common in upper part. In places, sand-filled joints and bedding planes in upper part (Mudge, 1972). Corals and brachiopods common in the formation.

The Lower Mississippian Allan Mountain Limestone, ranges from about 165 to 200 m thick, contains three widespread unnamed members. The upper member is mainly gray, medium- to thick-bedded, fossiliferous limestone with some beds of dolomitic and magnesium limestone (Mudge, Sando, and Dutro, 1962). In places encrinite beds occur in middle and upper parts of member. Member ranges from 42 to 106 m thick. The middle member contains abundant, irregular-shaped lenses and nodules of very dark chert in sparsely fossiliferous, medium-bedded, dark-gray limestone and dolomitic limestone, ranges from 45 to 58 m thick. Chert is dispersed throughout member at 15-25 cm intervals. The lower member consists of very thinly bedded, dark-gray, argillaceous limestone and dolomitic limestone with dark-gray shale partings (Mudge, Sando, and Dutro, 1962). The lower part of lower member contains alternating beds of dark-gray to gray-brown limestone and very calcareous shale, locally potential hydrocarbon source rocks (Mudge, Rice, Earhart, and Claypool, 1978); ranges from 50 m to 67 m thick.'
1559|'Mainly limestone and dolomite in upper part; in lower part mudstone increases downward. Units mapped and described by Mudge and Earhart (1983). About 1,700 ft thick.

Mudge and Earhart (1983) description of THREE FORKS, JEFFERSON, AND MAYWOOD FORMATIONS, UNDIVIDED:  Widespread in the Lewis, Hoadley, and Eldorado thrust plates in western part of mapped area and in numerous thrust plates in the Sawtooth Range. Range from 290 m thick in the southeast exposures to 457 m northwestward at Slategoat Mountain (Mudge, 1972) and northward to about 519 m southwest of Swift Reservoir. Natural gas produced from Birdbear Member of the Jefferson on the Sweetgrass Arch, and from equivalent rocks and the Three Forks Formation in southern foothills of Alberta.

In most places the Upper Devonian Three Forks almost entirely an evaporite-solution breccia, consists of angular fragments (mostly less than 1 m across) of pale-yellowish-brown dolomite and dolomitic limestone (Mudge, 1972). Grayish-green mudstone and massive gray limestone bed, as much as 30 m thick, overlie breccia in the southern outcrop (Mudge, 1972). Elsewhere beds above the breccia are thinly bedded, yellowish-gray, silty limestone and siltstone and black shale. Black shale mostly about 30 cm thick, locally as much as 1 m thick, observed at north end of Sawtooth Ridge, in Deep Creek (Mudge, 1972), on north side of Crown Mountain, in tributary of the Dearborn River, south of Steamboat Mountain, on South Fork Teton River across from Rierdon Gulch, on a mountain on south side of the upper reaches of that fork, on northeast side of Family Peak, on southeast side of Mount Drewyer, and at head of the north fork of Whitetail Creek. The presence of black shale at these widely scattered localities indicates that it is widespread, but in places is absent as a result of tectonic deformation and in places is covered by thick talus deposits. Fossils recorded in black shale by Gutschick, Suttner, and Switek (1962) and Sandberg (1965). The Three Forks Formation as much as 60 m thick, locally about 15 m thick in eastern outcrops (Mudge, 1972). Thickens westward to 180 m at Slategoat Mountain.

The Upper Devonian Jefferson Formation contains the Birdbear Member at the top (Sandberg,1965) and a lower unnamed member. Ranges from 225 to 245 m thick in the eastern outcrop, thins westward to about 190 m at Slategoat Mountain. The Birdbear Member consists mostly of pale-yellowish-brown, very fine to finely crystalline, thin dolomite beds, characteristically pinches and swells, weathers light yellowish gray. Brachiopods most common fossil (Mudge, 1972). The Birdbear ranges from about 16 m thick in the north to 45 m in the southeast, about 72 m in the southwest. The lower member is mostly limestone in northern and southwestern exposures, mostly dolomite in southeastern exposures. Commonly gray-brown and locally light-gray fetid beds, about 30 cm thick. One or more thin, evaporite-solution breccias in lower part in southern outcrops; thicker and more numerous throughout member in northern outcrops. Biostromes of Amphipora widespread in upper part and locally in lower part, corals and brachiopods occur at several horizons. The lower member ranges from 200 to 210 m thick in the central part of the Sawtooth Range, thinning to about 120 m to the west at Slategoat Mountain and to 130 m to the southeast near Gibson Dam (Mudge, 1972).

The Upper and Middle Devonian Maywood Formation is divisible into two unnamed members (Mudge, 1972). Ranges from 16 to 85 m thick. The upper member is mostly thinly bedded, finely crystalline, somewhat fossiliferous limestone and dolomitic limestone, forms resistant ledges. Mostly grayish-brown, mottled to pale yellowish orange to yellowish gray on the weathered beds (Mudge, 1972). Locally thin, evaporite-solution breccia in lower part. The upper member thickens westward from about 8 m in the southeastern outcrops, 16 m in the northeastern, to about 50 m in the western outcrops. The lower member is mostly greenish-gray mudstone with thin beds of dolomite, dolomitic limestone, and breccia in the lower part. Maroon mudstone common in the upper part of member in the western outcrops. In places, coarse-grained sandstone at base. North of the Sun River, the lower part of member contains channel fills as much as 6 m deep; the Cambrian- Devonian unconformity is at the base of channel fill deposits, The lower member thickens westward from about 8 m in the Sun River area (Mudge, 1972), about 4 m west of Swift Reservoir, to about 63 m at Slategoat Mountain.'
1560|'Alternating units of carbonate and shale above a basal sandstone. In Montana disturbed belt, includes (in descending order): Devils Glen Dolomite (Upper Cambrian), Switchback Shale (Upper and Middle Cambrian), and Steamboat Limestone, Pentagon Shale, Pagoda Limestone, Dearborn Limestone, Damnation Limestone, Gordon Shale, and Flathead Sandstone (Middle Cambrian) (Mudge and Earhart. 1983). Only lower three or four formations exposed unconformably above Belt rocks in southern part of map area. Maximum exposed thickness about 1,000 ft.

Mudge and Earhart (1983) description of CAMBRIAN ROCKS:  Includes, in descending order: Devils Glen Dolomite, Switchback Shale, Steamboat Limestone, Pentagon Shale, Pagoda Limestone, Dearborn Limestone, Damnation Limestone, Gordon Shale, and Flathead Sandstone. Limestone formations contain considerable mudstone in the east, mostly limestone in the west. All formations well exposed in the western part of mapped area. Only upper three formations exposed in some thrust blocks in the Sawtooth Range. In the western part of the mapped area, Cambrian rocks thin northward from about 535 m in the southwest to about 440 m at Pagoda Mountain, and to 495 m at Pentagon Mountain (Deiss, 1939). In the southern part of the mapped area, the Dearborn River area, they are 680 m thick.

The Upper Cambrian Devils Glen Dolomite is thick-bedded, light-gray dolomite, in most places forms prominent, light-gray cliff. Trilobites recorded in the upper part in the Sun River Canyon area (Mudge, 1972). Ranges from about 32 m thick at Pagoda Mountain (Deiss, 1939) in the west to as much as 167 m at Nineteen Mountain (Mudge, 1972) in the southeast, and about 60 m thick to the north; variation in thickness very likely a result of pre-Devonian erosion.

The Upper and Middle Cambrian Switchback Shale is mostly noncalcareous, greenish-gray, thinly laminated, clayey shale with thin local interbeds of dolomite, limestone, sandstone, and conglomerate. Conglomerates locally contain brachiopods (Mudge, 1972). The Switchback varies considerably in thickness from about 35 m at Pentagon Mountain to 23 m at Pagoda Mountain (Deiss, 1939) to 77 m at Nineteen Mountain, and to 82 m at Arsenic Mountain (Mudge, 1972).

The Middle Cambrian Steamboat Limestone consists of two parts in the western outcrop, a lower shaly interval and a much thicker upper limestone and dolomite interval (Deiss, 1939; Mudge, 1972), whereas in the eastern outcrop, in the Sawtooth Range, is about equal parts of alternating sequences of limestone and dolomite, and calcareous shales. Carbonates in both areas consist of hard, nodular, dark-gray to yellowish-brown, thinly bedded, finely crystalline beds of limestone and dolomite with nodules and lentils of dark-yellowish-orange, limey siltstone. Thin beds of intraformational conglomerate present locally. Mudstone units mainly grayish-green, noncalcareous, clayey shale with interbedded calcareous siltstone and claystone. Trilobites and some brachiopods locally in both limestone and shale beds. The Steamboat Limestone is about 92 m thick at its type locality in Dearborn Canyon, 66 m at Pentagon Mountain, 81 m at Pagoda Mountain (Deiss, 1939), and 67 m at Nineteen Mountain (Mudge, 1972).

The Middle Cambrian Pentagon Shale is present only in the northern part of mapped area, occurs as clastic wedge that extends south from Pentagon Mountain about 22 km (Deiss, 1939), and north about 7 km. The Pentagon consists of calcareous, gray to tan-gray, thick-bedded, platy, fossiliferous shale, contains some platy, blue-gray, argillaceous limestone in upper part (Deiss, 1939). Ranges from 0 to 88 m thick.

The Middle Cambrian Pagoda Limestone consists of an upper limestone member and a lower shale member. Upper member is finely crystalline, pale-yellowish-brown, very thin bedded limestone and thin- to thick-bedded dolomitic limestone and dolomite, the most prominent cliff-forming unit in the Cambrian sequence. Intraformational conglomerate locally in the middle part of the Pagoda. The lower member consists of beds of grayish-green, thinly laminated to nodular, clay shale with some gray-brown limestone and minor sandstone. Fossils locally present in limestone beds. The Pagoda, in general, thickens to the south and west; varies from about 53 m thick along the Continental Divide in the central part of mapped area to about 107 m at Pagoda Mountain, and 111 m near Prairie Reef Lookout Station (Deiss, 1939).

The Middle Cambrian Dearborn Limestone consists of an upper, finely crystalline, pale-yellowish-brown to gray, very thinly and irregularly bedded limestone unit and a lower mudstone unit of gray to gray-green, clayey shale with some sandy shale that contains trilobites. Ranges from about 67 to 106 m thick, averages about 90 m (Deiss, 1939).

The Middle Cambrian Damnation Limestone consists of thinly bedded, finely crystalline, medium- to dark-gray dolomitic limestone and limestone with laminae of grayish-orange to yellowish-gray siltstone. Mottled, grayish-orange limestone beds. Trilobites present in lower part of formation (Deiss, 1939). The Damnation is 31 m thick on the Continental Divide near Cliff Mountain, thickens northward to 58 m at Pentagon Mountain, southward to 45 m at Prairie Reef (Deiss, 1939), and about 51 m thick in the Dearborn Canyon area (Deiss, 1939).

The Middle Cambrian Gordon Shale is mainly a dark-gray to gray-brown, very thinly laminated shale with greenish tint. Contains many thin beds of sandstone and some beds of limestone. In places, limestone contains glauconite, algal structures, fossil fragments, limestone chips, and quartz grains (Mudge, 1972). Organic burrows and trails common in lower sandstone beds. Trilobites numerous in upper part (Deiss, 1939). Thickens southward from about 43 m at Pentagon Mountain to about 90 m along the Continental Divide near Cliff Mountain (Deiss, 1939), from that area it thins southward to 60 m at Prairie Reef (Deiss, 1939).

The Middle Cambrian Flathead Sandstone consists of thin- to thick-bedded, noncalcareous, yellowish-gray, poorly sorted, poorly indurated, fine- to coarse-grained, cross-bedded quartzose sandstone with scattered quartz pebbles. Commonly contains organic trails and burrows, speckled with brown hematite. Ranges from about 13 to 35 m thick, rests unconformably on rocks of the Belt Supergroup.'
1562|'Dioritic to gabbroic rocks that commonly show alteration of mafic minerals to calcite, epidote, clinozoisite, and hematite or limonite. Sills range in thickness from a few tens to a few hundreds of feet. Thicker sills tend to have contact-metamorphic zones around them. Sills commonly persist for many miles and in most places maintain approximately the same stratigraphic position. Locally, they cut across the section at a low angle or, rarely, cut steeply across section to form dikes. Intruded in map area probably at about 1,000 Ma, or 800 Ma, or both (Harrison, 1972).'
1563|'Gray to olive, micaceous siltite to quartzarenite interlaminated or interbedded with gray-green, micaceous, argillitic siltite. Occurs only in small exposures at south edge of map area beneath Cambrian unconformity. Maximum thickness of remnant about 500 ft.'
1564|'Predominantly grayish-green, interbedded and interlaminated argillite and siltite that contain thin chert laminae and chips. Oolites, stromatolites, quartzarenite, and stratabound cooper [sic] minerals present at places. Relatively thin red-bed sequences locally interbedded in the green strata. Small-scale sedimentary features include ripple marks, shrinkage cracks, scours, and cross-beds. Rests sharply on Bonner Quartzite. About 4,000 ft thick.'
1565|'Red to pink, micaceous, arkosic, cross-bedded, fine- to medium-grained quartzite containing red argillite interclasts. Tabular and trough cross-beds and climbing ripple marks common. Interbeds of red, laminated argillite and pink, planar-laminated siltite scattered throughout unit. Rests in sharp contact on Mount Shields Formation. Thickness ranges from about 800 to 1,200 ft.'
1566|'Consists of a series of informal members similar to those seen to the west in the Kalispell 1x2 quadrangle (Harrison and others, 1992) where six informal members are described; sequence in the Cut Bank quadrangle is similar, but member 5 is missing. Type section (Childers, 1963), about 2,550 ft thick, is between the Blacktail and Roosevelt faults in southeast corner of Glacier National Park on Mount Shields. Childers did not use the informal members subsequently found to be widespread in the formation. Maximum thickness in map area about 2,900 ft.

Uppermost unit in map area (member 6) is a thinly laminated, black argillite and white or green siltite that commonly displays small-scale slump folds and shrinkage cracks. Thickness about 200 ft. Conformably below is member 4, which consists of blocky, green, dolomitic, silty argillite that shows parallel-laminated graded couplets. Foot-thick carbonate beds are scattered throughout unit, as are rare salt casts. Thickness about 900 ft. Grades downward into member 3, which is predominantly alternating red and green beds of interlaminated argillite and siltite. Mud chips, mud cracks, ripple marks, and fluid-escape structures are common. Salt casts are abundant, particularly in red beds. Thickness about 500 ft. Grades by interlayering, through a few tens of feet, to member 2 below. Member 2 is pale-red, flat-laminated, coarse-grained siltite to fine-grained quartzarenite that is blocky, feldspathic, and dolomitic. Dolomite is in cement or in streaks and pods parallel to bedding. Minor layers of red or green argillite. Red or buff stromatolites and oolites in a zone of one or more beds at top. Thickness about 700 ft. Grades downward into member 1. Member 1 is red to maroon, feldspathic quartzarenite interbedded with red siltite. Siltite increases in abundance to east and north. Red argillite beds and partings common between coarser-grained beds. Cross stratification, mud chips, and heavy-mineral streaks common. Rare stromatolites. Thickness about 600 ft in southern part of map area.'
1567|'Consists of a variety of rock types, most of which are carbonate bearing or carbonate rich. The most characteristic lithology is green to gray, dolomitic argillite and siltite in even-parallel to wavy laminae that show graded couplets. This rock weathers into distinctive orange-brown platy slabs. Common interbeds a few to a few tens of feet thick include gray dolomitic limestone, stromatolites and oolites, laminated green argillite, gray argillitic siltite, and white quartzarenite. All rock types may contain pyrite cubes, small-scale wiggly calcite segregations (molar tooth structure), horizontal carbonate pods, ripple marks, or mud cracks. Base of unit is marked at places by shallow channels of quartzarenite, or in northwestern part of map area by an unconformity that separates the Shepard from the underlying Purcell Lava. Shepard thickness ranges from about 700 ft in Glacier National Park to about 2,700 ft in the Swan Range in southwestern part of map area (fig. 2).'
1569|'Type section of the Snowslip Formation (Childers, 1963) is on the south spur of Mount Shields in the southern part of Glacier National Park. Detailed study of the Snowslip by Whipple and Johnson (1988) in the park has led to recognition of six informal members that can be correlated over at least the 1,000 mi2 of the park. The Snowslip generally consists of two alternating intervals that are each one hundred to several hundred feet thick. One interval consists of thinly laminated, red to purple argillite and siltite interbedded with thinly laminated green argillite and siltite. The other interval consists of couplets of greenish-gray siltite and olive argillite. Within both intervals are beds of stromatolites, arenite, and carbonate as layers or cement; certain characteristics of these carbonate and arenite interbeds help to distinguish the various members of the Snowslip (Whipple and Johnson, 1988). Small-scale sedimentary structures include mud cracks, ripple marks, mud-chip breccias, fluid-escape structures, cross lamination (particularly in the arenite beds), and flat-pebble conglomerate. Sharply overlies Helena Formation. The Snowslip and its members generally thin to the north and thicken to the west across depositional strike. Ranges in thickness from about 1,200 ft in the north to about 4,000 ft in the Swan Range to the south (fig 2).'
1570|'The most carbonate-rich formation in the Belt Supergroup. Contains abundant beds of dolomite, stromatolitic or oolitic limestone, and molar-tooth limestone and dolomite, and lesser amounts of quartzarenite and black argillite. In Glacier National Park contains an interval of stromatolitic limestone about 100 ft thick (the conophyton zone of Rezak, 1957) that separates the upper and middle parts of the Helena. Commonly displays sedimentary cycles, 6-50 ft thick, that in eastern exposures have a clastic bed at the base, stromatolitic and oolitic beds in the middle, and dolomite at the top (Eby, 1977). Abundance of stromatolites and oolites decreases rapidly to the west and south where cycles are still well defined but change to a clastic bed at the base, a middle unit of silty dolomite containing pods and ribbons of calcite, and an Lipper unit of dense, conchoidal-fracturing dolomite. Rests on laminated green argillite beds of the Empire Formation. Formation changes thickness rapidly across the various structural blocks in the map area (fig. 2), ranging from about 1,200 ft in southeastern Glacier National Park to about 7,000 ft in the Swan Range.'
1571|'Thinly laminated, dark-green and light-green dolomitic argillite and silty argillite or siltite. Laminae mostly wavy and discontinuous although some are even parallel. Fluid-escape structures are characteristic, and horizontal pods of white or pink calcite are particularly abundant in upper part. Ripple marks, syneresis cracks, and mud chips common in places. Lower part contains white dolomitic quartzarenite beds as thick as 10 ft. Pyrite cubes common in more carbonate-rich strata, and a few exposures display stratabound copper minerals. A few purple interlaminated argillite and siltite beds commonly occur near base and at places near middle of unit. Thickness about 500 ft.'
1572|'Three lithologic units are found in most areas. The upper member has beds a few feet to a few tens of feet thick of laminated, green argillite and siltite that alternate with much thicker beds of purple, laminated argillite and siltite. Dolomitic cement is common as are ripple marks, mud chips, desiccation cracks, fluid-escape structures, ball-and-pillow structures, and flute casts. Beds a few inches to a few feet thick of white, rounded grains forming medium-grained, crossbedded quartzite that displays mud chips and balls on cross strata are abundant in northern part of map area but decrease rapidly in both number and thickness in southern and western parts. The middle member is predominantly pink to purple-gray, very fine grained, feldspathic quartzite or coarse siltite that has planar lamination or long tabular cross lamination. Interbeds of purple argillite are common. The lower member is similar to the upper member but has more purple argillitic beds, is more dolomitic, and has scattered iron-carbonate specks and cement. The Spokane changes facies eastward and northward where abundance of distinctive white, rounded-grain quartzite has been used arbitrarily to define the laterally equivalent Grinnell Formation. Maximum thickness of the Spokane is about 4,500 ft in the Swan Range, but the unit thins to about 1,700 ft in northern exposures (fig. 2).'
1573|'Term used in Glacier National Park for the quartzarenite-rich lithofacies equivalent to the Spokane Formation. White, rounded-grain, crossbedded quartzarenite containing red argillite chips and pellets forms about 60 percent of the formation and almost 100 percent of the upper part. Amount of quartzarenite decreases rapidly westward and southward (fig. 2). Red to purple laminated siltite, silty argillite, and argillite form interbeds that make up most of the remainder of the unit. Argillitic beds generally have even-parallel lamination, and couplets of argillite and siltite display ripple marks, mud cracks, and fluid-escape structures. Grades by interlayering into the Appekunny Formation. Thickness ranges from about 1,700 to 2,600 ft.'
1574|'Predominantly bright-green to olive argillite interbedded and interlaminated with laminated olive siltite and gray pyritic quartzarenite that weathers brown. Lower part contains maroon argillite and siltite. Can be divided into five informal members in Glacier National Park (Whipple, 1992). Various members display mud cracks, mud-chip breccia, load structures, fluid-escape structures, and a few scour-and-fill structures. Rests unconformably on Altyn Formation in Glacier National Park but apparently intertongues with Prichard Formation transition member to southwest where unit mapped as Appekunny along west side of Flathead Range has beds characteristic of both Appekunny and Prichard. Maximum thickness about 2,000 ft.'
1577|'Generally consists of three units: a basal unit of medium-gray blocky-weathering siltite and minor quartzite, a middle unit of interlaminated light- and dark-gray siltite and argillite, and an upper unit similar to the middle but containing interbeds of light-olive-gray siltite and quartzite similar to those in the overlying Appekunny Formation. These three units are present nearly everywhere, but their relative proportions vary from place to place. Laminae are wavy to lenticular; scour-and-fill structures, fluid-escape structures, and syneresis cracks are common. Iron sulfide weathers to give rusty aspect to many outcrops. Randomly oriented biotite porphyroblasts common, particularly near top, in all but easternmost exposures. Calcareous siltite and argillite beds, some in the middle but most in the upper unit, make up a small part of the member. Contains some stromatolitic beds in Glacier National Park. Probably intertongues with Altyn Formation to east. Basal contact is sharp. Thickness about 2,000 ft.'
1600|'Unconsolidated stream-laid sand, gravel, and silt, bouldery, poorly to moderately well sorted. Includes alluvial fan, slope wash, colluvial and glacial outwash deposits of Bull Lake and younger in age. Thickness of deposits as much as 10 m.'
1601|'Mostly rock debris, locally coarse angular rock fragments in silt or clay matrix. Forms hummocky topography. Produced by rockfall- and rockslide-avalanches, slump, and earthflow. Thickness possibly as much as 300 m.'
1602|'Drift, heterogeneous mixture of rock fragments in silty clay matrix. Forms hummocky topography. Includes deposits from alpine and continental glaciations; as much as 100 m thick except in Swan River valley where thickness of mostly sand and gravel deposits exceed 300 m.'
1603|'Light-gray to dark-gray and gray-brown, thin- to thick-bedded silty clay, clay, and some sand; deposited in glacial lakes. Thickness of deposits as much as 30 m.'
1604|'Coarse stream-laid gravel on remnants of at least four bench surfaces as much as 250 m above modern stream alluvium. Maximum thickness is about 10 m.'
1605|'Gray, yellowish-gray, gray-brown, sandy silt, silt, clay, shale, marl, and some poorly sorted conglomerate; locally thin coal and carbonates. Locally includes wood and leaf fragments, insects, fish, gastropods, pelecypods, and ostracods. In Landers Fork, Blackfoot River includes tuff. Thickness possibly as much as 125 m.'
1606|'Map unit includes the Paleocene and Upper Cretaceous Willow Creek Formation (Viele, 1960; Schmidt, 1972b) in southeast corner of map where only the lower part of the Willow Creek is present and where it consists of grayish-green, olive-drab, and light-gray mudstone and sandstone. Some coarse to very coarse grained beds of volcanic sandstone. The upper part of the St. Mary River consists of light- to dark-red, purplish-red, brown, gray, greenish-gray mudstone and sandstone, and some beds of volcanic sandstone and conglomerate. A thin bed of white ash-fall tuff occurs near middle part. The formation is as much as 790 m thick.

The upper part of the St. Mary River Formation, west of Augusta, is mostly grayish-green, sandy mudstone with moderate-light-red and purple interbeds. It contains numerous zones of dark-brown limestone nodules. Near Augusta, strata equivalent to the lower part of the St. Mary River are present and consist of grayish-green, olive-drab, and light-gray mudstone, sandy mudstone, and sandstone with some gray argillaceous limestone and carbonaceous shale. Sandstones are fine to medium grained and crossbedded. They are as much as 12 m thick. Thin argillaceous limestone beds as much as 0.3 m thick are locally present. A carbonaceous shale bed as much as 1.0 m thick is beneath a 1.0 m oyster bed near the base of the formation. Some reptile bone fragments and pelecypods are near the base. In the Augusta area the formation thickness is as much as 430 m.'
1607|'Horsethief Sandstone is mostly gray to gray-brown, fine- to medium-grained crossbedded sandstone. The upper 6-12 m of the formation commonly contain lentils of titaniferous magnetite sandstone. Southeast of Augusta the Horsethief contains volcanic-rich sandstone and conglomerates (Viele and Harris, 1965). The Horsethief is absent in the southeast part of the quadrangle where its position is marked by an Ostrea glabra bed (Viele, 1960); locally the sandstone contains pelecypods. The Horsethief is as much as 50 m thick.

The Bearpaw-Horsethief transition unit of Cobban (1955) beneath the Horsethief, consists of dark-gray mudstone interbedded with light- to medium-gray mudstone and fine- to medium-grained sandstone that is thin bedded in the lower part becoming thicker bedded in the upper part. Near Sun River a 0.3 m coal bed occurs about 6 m below the top. Thickness of the transition unit as much as 60 m.'
1608|'Two Medicine Formation: Gray-green and gray mudstone with minor sandstone in upper and middle parts with gray-green, olive-drab, and gray sandstone and mudstone in lower part. Upper and middle parts locally contain reddish-gray, red-brown, and purple interbeds of mudstone. The sandstones are fine to coarse grained and locally conglomeratic. Carbonaceous shale and locally a coal bed are present in the lower part. Petrified wood common about 30 m above base; vertebrate bones common in the upper 150 m. Pelecypods locally present at various horizons. Thickness about 670 m.

Virgelle Sandstone: consists of moderately thick, light-gray, fine-grained sandstone beds of which some are locally iron impregnated and crossbedded. At the top of the Virgelle, a titaniferous magnetite sandstone bed, as much as 6 m thick, forms a prominent rimrock south, west, and northwest of Choteau, as well as numerous other localities in the outcrop area. The Virgelle rarely contains pelecypods; wood fragments are locally in upper part. Thickness ranges from about 40 m to 60 m.

Telegraph Creek Formation: A transitional unit between the underlying Marias River Shale and the overlying Virgelle Sandstone. Consists mainly of beds of gray mudstone and fine-grained sandstone. The sandstone beds are thinly bedded in the lower part becoming thicker bedded in the upper part. Pelecypods and ammonites are common. Thickness ranges from about 90 m in the eastern outcrop to about 165 m in the western outcrop.

Marias River Shale: Mostly a dark-gray mudstone that is divided into four members (listed in descending order), the Kevin, Ferdig, Cone, and Floweree, by Cobban, Erdmann, Lemke, and Maughan (1959, 1976). Total thickness ranges from 365 m to 395 m.

Kevin Member Dark-gray mudstone with some very thin sandstone beds, numerous bentonite beds, and many light-gray calcareous concretions. Pelecypods and ammonites common. Ranges in thickness from 245 m to 305 m.

Ferdig Member Gray, noncalcareous siltstone and shale with many thin, iron-stained sandstone lenses, concretions of yellow-weathering limestone, red-weathering ferruginous dolostone, and some very thin bentonite beds. Contains abundant organic trails and burrows, but pelecypods and ammonites are rare. In the western outcrop, along the tributaries of the Sun River, the Ferdig is mostly sandstone (Mudge, 1972). Ranges in thickness from 50 m to 105 m.

Cone Member Abundant, very thin, medium-gray calcareous siltstone and crystalline limestone beds in the upper part and dark-gray, noncalcareous shale in the lower part. Contains several bentonite beds throughout. Pelecypods and ammonites are common, especially in the upper part. The member ranges in thickness from 18 m to 30 m.

Floweree Member Dark-gray, noncalcareous fissile to thin-bedded shale with medium-gray siltstone in lower part that locally contains lenses of chert-pebble conglomerate. Pelecypods and ammonites are rare. Thickness about 10 m.

Blackleaf Formation: Blackleaf Formation mostly sandstone and mudstone, and includes some fissile shale.  Formation divided into three members (listed in descending order), Vaughn, Taft Hill, and Flood. The total thickness about 200 m in the eastern outcrop and 490 m in the western outcrop.

Vaughn Member:  Nonmarine, light-gray, gray-green, and green tuffaceous and bentonitic mudstone and sandstone. Dark-gray carbonaceous mudstone locally in the upper part in the southeastern outcrop. The sandstone units are fine to coarse grained, locally crossbedded, and in places contain pebble and cobble conglomerate channel-fill deposits as much as 6 m thick (Mudge and Sheppard, 1968). The member contains wood and leaf fragments, and in the vicinity of Teton Pass contains coal and carbonaceous shale. Thickness from about 90 m in the eastern outcrop to about 150 m in the western outcrop.

Taft Hill Member:  Marine, gray, thinly bedded, fine-grained sandstone units interbedded with dark-gray mudstone; the sandstone is locally crossbedded and ripple marked. In the northwest part of the quadrangle the upper part of the member is replaced by nonmarine strata of Vaughn lithologies. Locally the Taft Hill contains numerous pelecypods. Thickness ranges from about 58 m in the southeast to about 183 m in the west.

Flood Member:  Two marine, gray, sandstone units separated by as much as 150 m of dark-gray fissile shale. The sandstones are very fine grained, thin to moderately thick bedded, and locally crossbedded and ripple marked. Organic burrows and trails common. Thickness from about 45 m in the eastern outcrop to about 165 m thick in the western outcrop.

Kootenai Formation: Consists of nonmarine, gray-green, and dark-reddish-brown mudstone interbedded with lenticular thin to thick sandstone units. Numerous heavily iron-stained, spheroidal nodules of dark-grayish-red sandy limestone are in the mudstone. The sandstone is fine to coarse grained, grayish-green, with chert and quartz grains and locally magnetite. Pebble and cobble conglomerate, as much as 15 m thick, fill narrow channels locally at the base of some sandstone units. In most places a distinctive hard, dense, brown coquinoid limestone containing abundant pelecypods and some vertebrate fragments at or near the top. Thickness ranges from 198 m to 245 m.

Mount Pablo Formation:  Nonmarine. Exposures widespread in the eastern mountains but locally absent in the adjacent foothills. Rests unconformably on the Morrison Formation. In the western drainages of the Sun River area was included as part of the western facies of the Morrison Formation by Mudge (1972). Ranges from a dominantly sandstone sequence with interbedded bright-reddish-brown mudstone to a dominantly reddish brown mudstone sequence with some sandstone. Dense, dark-gray to light-gray limestone beds as much as 9 m thick are present in the upper part of the formation. In many places, coarse sandstone and thin beds of conglomerate occur as channel-fill deposits. The sandstones are medium to very coarse grained, crossbedded, and contain wood fragments. Thickness about 60 m.

Morrison Formation (Upper Jurassic) Nonmarine. A nearly complete section is present in the eastern and southern outcrop, but much of the formation was eroded prior to deposition of the Mount Pablo Formation in the western outcrop. Consists of tuffaceous, grayish-green, olive-green, and olive-gray claystone to siltstone with pink, maroon, purple, and yellowish-gray mudstones in the upper part. A thin, dark-gray carbonaceous shale present near the top in southeastern outcrop. Fine-grained clayey sandstone locally present. Abundant polished quartzite pebbles and limestone nodules characteristic of the Morrison locally. Cherty siderite lenses and nodules locally common about 35 m above the base of the formation. A thin, dark-gray-brown to gray limestone present in the lower part of the formation and locally in the middle part. Gastropods, pelecypods, plant fragments, ostracods, and vertebrate bones are sparse in the middle and lower parts of the formation. Thickness from 60 m to 82 m.

Swift Formation (Upper and Middle Jurassic) Marine. Consists of thinly bedded gray to gray-brown fine-grained sandstone in the upper part and dark-gray to olive-drab mudstone with many thin beds of sandstone in the lower part. The upper beds are locally ripple marked and contain minute cross laminations and wood fragments. A thin glauconitic sandstone, with water-worn belemnites, present at the base of the formation. Formation rests unconformably on the Rierdon Formation everywhere except in the southeast corner of the map where it rests on the Sawtooth Formation. Thickness about 35 m.

Rierdon Formation: Marine. Widely distributed except in the southeast corner of the map area. Consists mostly of gray, calcareous mudstone with thin interbedded argillaceous limestone. Barite nodules common in the upper and middle parts. Pelecypods and ammonites common throughout. Thickness from 33 m to 60 m.

Sawtooth Formation: Marine. The upper member is gray-brown to yellowish-brown, calcareous, thin-bedded siltstone that contains pelecypods and ammonites. About 8 m thick. The middle member is dark-gray, silty to clayey fissile shale with local thin beds of fine-grained sandstone and conglomerate. Locally rests unconformably on Mississippian rocks. From 5 m to 77 m thick. The lower member is mostly thin bedded, fine-grained gray to yellowish-brown sandstone with a basal conglomerate of Mississippian rock fragments. Dark-gray, silty, thinly laminated shale locally interbedded in the sandstone. Pelecypods are locally abundant. Thickness of the lower member as much as 16 m.'
1609|'Gray-green and gray mudstone with minor sandstone in upper and middle parts with gray-green, olive-drab, and gray sandstone and mudstone in lower part. Upper and middle parts locally contain reddish-gray, red-brown, and purple interbeds of mudstone. The sandstones are fine to coarse grained and locally conglomeratic. Carbonaceous shale and locally a coal bed are present in the lower part. Petrified wood common about 30 m above base; vertebrate bones common in the upper 150 m. Pelecypods locally present at various horizons. Thickness about 670 m.'
1610|'South of Augusta. The upper and middle parts are green, grayish-green, gray, brownish-gray, and maroon volcanic sandstone, mudstone, and conglomerate; brown, pink, and white ash-fall and ash-flow tuffs; and interbedded trachyte and latite flows (Viele, 1960; Viele and Harris, 1965; Schmidt and Strong, 1972; and Schmidt, 1972a, b, c). Lower 150 m is gray-green, olive-drab, and gray sandstone and mudstone. Thickness ranges from 640 m too possibly as much as 1,500 m.'
1611|'Virgelle Sandstone: consists of moderately thick, light-gray, fine-grained sandstone beds of which some are locally iron impregnated and crossbedded. At the top of the Virgelle, a titaniferous magnetite sandstone bed, as much as 6 m thick, forms a prominent rimrock south, west, and northwest of Choteau, as well as numerous other localities in the outcrop area. The Virgelle rarely contains pelecypods; wood fragments are locally in upper part. Thickness ranges from about 40 m to 60 m.

Telegraph Creek Formation: A transitional unit between the underlying Marias River Shale and the overlying Virgelle Sandstone. Consists mainly of beds of gray mudstone and fine-grained sandstone. The sandstone beds are thinly bedded in the lower part becoming thicker bedded in the upper part. Pelecypods and ammonites are common. Thickness ranges from about 90 m in the eastern outcrop to about 165 m in the western outcrop.'
1612|'Mostly a dark-gray mudstone that is divided into four members (listed in descending order), the Kevin, Ferdig, Cone, and Floweree, by Cobban, Erdmann, Lemke, and Maughan (1959, 1976). Total thickness ranges from 365 m to 395 m.

Kevin Member Dark-gray mudstone with some very thin sandstone beds, numerous bentonite beds, and many light-gray calcareous concretions. Pelecypods and ammonites common. Ranges in thickness from 245 m to 305 m.

Ferdig Member Gray, noncalcareous siltstone and shale with many thin, iron-stained sandstone lenses, concretions of yellow-weathering limestone, red-weathering ferruginous dolostone, and some very thin bentonite beds. Contains abundant organic trails and burrows, but pelecypods and ammonites are rare. In the western outcrop, along the tributaries of the Sun River, the Ferdig is mostly sandstone (Mudge, 1972). Ranges in thickness from 50 m to 105 m.

Cone Member Abundant, very thin, medium-gray calcareous siltstone and crystalline limestone beds in the upper part and dark-gray, noncalcareous shale in the lower part. Contains several bentonite beds throughout. Pelecypods and ammonites are common, especially in the upper part. The member ranges in thickness from 18 m to 30 m.

Floweree Member Dark-gray, noncalcareous fissile to thin-bedded shale with medium-gray siltstone in lower part that locally contains lenses of chert-pebble conglomerate. Pelecypods and ammonites are rare. Thickness about 10 m.'
1613|'Blackleaf Formation: Mostly sandstone and mudstone, and includes some fissile shale.  Formation divided into three members (listed in descending order), Vaughn, Taft Hill, and Flood. The total thickness about 200 m in the eastern outcrop and 490 m in the western outcrop.

Vaughn Member: Nonmarine, light-gray, gray-green, and green tuffaceous and bentonitic mudstone and sandstone. Dark-gray carbonaceous mudstone locally in the upper part in the southeastern outcrop. The sandstone units are fine to coarse grained, locally crossbedded, and in places contain pebble and cobble conglomerate channel-fill deposits as much as 6 m thick (Mudge and Sheppard, 1968). The member contains wood and leaf fragments, and in the vicinity of Teton Pass contains coal and carbonaceous shale. Thickness from about 90 m in the eastern outcrop to about 150 m in the western outcrop.

Taft Hill Member: Marine, gray, thinly bedded, fine-grained sandstone units interbedded with dark-gray mudstone; the sandstone is locally crossbedded and ripple marked. In the northwest part of the quadrangle the upper part of the member is replaced by nonmarine strata of Vaughn lithologies. Locally the Taft Hill contains numerous pelecypods. Thickness ranges from about 58 m in the southeast to about 183 m in the west.

Flood Member: Two marine, gray, sandstone units separated by as much as 150 m of dark-gray fissile shale. The sandstones are very fine grained, thin to moderately thick bedded, and locally crossbedded and ripple marked. Organic burrows and trails common. Thickness from about 45 m in the eastern outcrop to about 165 m thick in the western outcrop.'
1614|'All or part of the following formations are present in this unit.

Castle Reef Dolomite (Upper and Lower Mississippian) Divided into two members. Sun River Member at the top, which consists of thin to thick beds of medium to finely crystalline light-gray dolomite and locally some interbedded calcitic dolomite. Many beds contain thick lenses of encrinite and scattered brachiopods and corals. The Sun River is from less than 1 m to 137 m thick. The lower member is thick-bedded, fine to coarsely crystalline, light- to medium-gray dolomite, calcitic dolomite, dolomitic limestone, and limestone. The coarsely crystalline beds are encrinite and are more numerous in the northern and western outcrop. The lower member contains brachiopods and corals, locally abundant in the lower part. The lower member is 114 m to 145 m thick. Both members thin eastward, mainly as a result of pre-Jurassic erosion.

Allan Mountain Limestone (Lower Mississippian) Ranges in thickness from 163 m to 200 m, and contains three unnamed members. The upper member consists of gray, fine-grained, thin to thick beds of limestone, magnesian limestone, and dolomitic limestone. Nodules and lentils of gray- to gray-brown chert are common (Mudge, 1972). It has a large and varied fauna, mostly brachiopods and corals, and locally, lenses and beds of encrinite. Upper member 60 to 90 m thick. The middle member consists of dark-gray, fine-grained, thin to medium beds of limestone with some dolomitic limestone. Characteristically contains nodules and irregular-shaped to even-bedded lenses of dark-gray chert, of which some have a fibrous appearance (Mudge, 1972). Contains sparse brachiopods and corals (Mudge, Sando, and Dutro, 1962). The middle member about 45 m thick. The lower member mostly dark-gray, very thin bedded, argillaceous dolomitic limestone with many calcareous shale partings. Contains dense, gray, moderately thick limestone interbedded with dark-gray mudstone. The mudstone has abundant brachiopods and corals. Thickness of lower member 60 m to 89 m.

Three Forks Formation (Upper Devonian) The uppermost unit is a black shale bed of Early Mississippian age unnamed in this quadrangle but called the Sappington Member of the Three Forks elsewhere in Montana and is correlative to the Exshaw Shale in Alberta (Mudge, 1972). In most places it overlies thinly bedded, gray-brown to yellowish-gray limestone. The limestone commonly overlies an evaporite-solution breccia, but locally, in the Sun River area, overlies a thick bed of limestone and in one place a gray-green mudstone (Mudge, 1972). Fossils abound in the dark-gray shale and limestone beds. The rest of the Three Forks consists mostly of a pale-yellowish-brown to yellowish-gray evaporite-solution breccia consisting of angular fragments of dolomite and dolomitic limestone. Thickness from 15 m to 180 m.

Jefferson Formation (Upper Devonian) Consists of two members: the Birdbear and a lower member. The Jefferson thickens eastward from about 190 m in the western outcrop to 247 m in the east. The Birdbear Member consists mostly of pale-yellowish-brown to brownish-gray, finely crystalline dolomite beds that pinch and swell. Brachiopods are commonly present. Ranges in thickness from 45 m to about 72 m. The lower member is mostly dolomite in the eastern outcrop, whereas it is mostly limestone in the western outcrop (Mudge, 1972). Consists of distinctive gray-brown beds (mostly less than 1/2 m thick) that characteristically have a fetid odor on the broken surface. Many beds have a sucrosic texture. The lower part commonly contains one or more thin beds of evaporite-solution breccia. Dark-gray chert lenses common in the lower part in the eastern outcrop. Corals, brachiopods, and stromatoporoids common throughout and Amphipora biostromes are widespread in the upper part. Thickness from 128 m to 198 m.

Maywood Formation (Upper and Middle Devonian) Contains an upper limestone member and a lower mudstone member. The upper member is mainly dark grayish-brown and yellowish-gray, thinly bedded, finely crystalline limestone and dolomitic limestone that thickens eastward from about 21 m in the west to 48 m in the east. Contains brachiopods and corals. The lower member is mostly greenish gray dolomitic mudstone that in the western outcrops is interbedded with maroon mudstone. Contains thin beds of crystalline yellowish-gray to olive-gray dolomite and dolomitic limestone. A widespread dolomite with some breccia present in the middle part of the member. Charophytes and conodonts are locally present in one of the dolomite beds. The lower member ranges in thickness from about 8 m in the eastern outcrop to 63 m in the western outcrop.

Devils Glen Dolomite (Upper Cambrian) A distinctive, thick-bedded, light-gray, finely to very finely crystalline dolomite. Thickness from 54 m to 172 m (Deiss, 1939).

Switchback Shale (Upper and Middle Cambrian) Mostly noncalcareous, greenish-gray, thinly laminated clay shale with local thin interbeds of dolomite, limestone, sandstone, and conglomerate. Thickness from 21 m to 92 m.

Steamboat Limestone (Middle Cambrian) Differs in lithology between western and eastern outcrops. In the west consists of a lower shaly mudstone interval and a much thicker upper limestone interval (Deiss, 1939). In the eastern exposures is about equal parts of alternating sequences of limestone and calcareous shale. The carbonate units in both areas consist mostly of nodular, hard, dark-yellowish-brown, thinly bedded limestone and dolomite with nodules and lentils of dark-yellowish-orange siltstone. The mudstone units are mainly grayish-green noncalcareous shale with interbeds of calcareous siltstone and claystone. Trilobites, locally abundant, and some brachiopods occur in limestone lenses in the shales and locally near the top of the limestone units. Thickness from 65 m to 80 m.

Pentagon Shale (Middle Cambrian) A clastic wedge that consists of very fossiliferous, calcareous, gray to tan-gray, thick-bedded platy shale that contains some platy, blue-gray argillaceous limestone in the upper part (Deiss, 1939). Thickness ranges from less than 1 m to 88 m (Deiss, 1939).

Pagoda Limestone (Middle Cambrian) Forms prominent light-gray cliffs in the Cambrian sequence. The upper part consists of yellowish-gray to light-yellowish-brown, thin- to thick-bedded dolomitic limestone and some dolomite overlying very thin bedded limestone. The lower part consists of grayish-green, thinly laminated to nodular clay shale with some gray-brown limestone and minor sandstone. An intraformational conglomerate locally present in the middle and lower parts. Trilobites and brachiopods locally numerous in the shale (Deiss, 1939). Formation thickens to the south and west, and ranges in thickness from 28 m to about 120 m.

Dearborn Limestone (Middle Cambrian) Composed of an upper thick limestone unit and a lower thin shale unit. The limestone unit is finely crystalline, yellowish-brown to gray, thin to thick bedded and irregularly bedded. The lower unit consists of gray to gray-green clayey shale with some sandy shale and thin interbedded limestone. Trilobites present in the lower part of the shale unit. Thickness from 67 m to 106 m.

Damnation Limestone (Middle Cambrian) Consists of medium- to dark-gray, thin- to thick-bedded, finely crystalline dolomitic limestone and limestone with laminae of grayish-orange to yellowish-gray siltstone that thicken and thin. Locally they are oolitic and contain trilobites, brachiopods, and organic trails and burrows. Thickness from 30 m to 68 m.

Gordon Shale (Middle Cambrian) Mainly a dark-gray to gray-brown, very thinly laminated shale with a greenish tint and locally maroonish-gray beds. Contains many thin beds of sandstone and some beds of limestone, especially in the middle and upper parts. In places the limestones contain glauconite, algal structures, limestone chips, grains of quartz, and fossil fragments. The upper part contains numerous fossils (Deiss, 1939), whereas the lower beds locally contain organic trails and burrows, some by trilobites. Thickness from 42 m to 90 m.

Flathead Sandstone (Middle Cambrian) Consists of thin- to thick-bedded and crossbedded, noncalcareous yellowish-gray, poorly sorted, poorly indurated, fine- to coarse-grained quartzose sandstone with scattered quartz pebbles. Beds are characteristically speckled by disseminated hematite. Interbeds of gray, purple, or maroon mudstone locally present. Thickness from 13 m to 35 m.'
1615|'Mississippian rocks are the main cliff former in the eastern part of the mountains and are assigned to the Madison Group. The total thickness of the Mississippian rocks ranges from 275 m to 520 m. The Madison is divided into two formations, the Castle Reef Dolomite and the Allan Mountain Limestone, by Mudge, Sando, and Dutro (1962).

Castle Reef Dolomite (Upper and Lower Mississippian) Divided into two members. Sun River Member at the top, which consists of thin to thick beds of medium to finely crystalline light-gray dolomite and locally some interbedded calcitic dolomite. Many beds contain thick lenses of encrinite and scattered brachiopods and corals. The Sun River is from less than 1 m to 137 m thick. The lower member is thick-bedded, fine to coarsely crystalline, light- to medium-gray dolomite, calcitic dolomite, dolomitic limestone, and limestone. The coarsely crystalline beds are encrinite and are more numerous in the northern and western outcrop. The lower member contains brachiopods and corals, locally abundant in the lower part. The lower member is 114 m to 145 m thick. Both members thin eastward, mainly as a result of pre-Jurassic erosion.

Allan Mountain Limestone (Lower Mississippian) Ranges in thickness from 163 m to 200 m, and contains three unnamed members. The upper member consists of gray, fine-grained, thin to thick beds of limestone, magnesian limestone, and dolomitic limestone. Nodules and lentils of gray- to gray-brown chert are common (Mudge, 1972). It has a large and varied fauna, mostly brachiopods and corals, and locally, lenses and beds of encrinite. Upper member 60 to 90 m thick. The middle member consists of dark-gray, fine-grained, thin to medium beds of limestone with some dolomitic limestone. Characteristically contains nodules and irregular-shaped to even-bedded lenses of dark-gray chert, of which some have a fibrous appearance (Mudge, 1972). Contains sparse brachiopods and corals (Mudge, Sando, and Dutro, 1962). The middle member about 45 m thick. The lower member mostly dark-gray, very thin bedded, argillaceous dolomitic limestone with many calcareous shale partings. Contains dense, gray, moderately thick limestone interbedded with dark-gray mudstone. The mudstone has abundant brachiopods and corals. Thickness of lower member 60 m to 89 m.'
1616|'Consists of limestone, dolomite, and some shale and mudstone; they range in thickness from about 300 m in the eastern outcrop to about 458 m in the western outcrop, and are divided into the Three Forks, Jefferson, and Maywood Formations.

Three Forks Formation (Upper Devonian) The uppermost unit is a black shale bed of Early Mississippian age unnamed in this quadrangle but called the Sappington Member of the Three Forks elsewhere in Montana and is correlative to the Exshaw Shale in Alberta (Mudge, 1972). In most places it overlies thinly bedded, gray-brown to yellowish-gray limestone. The limestone commonly overlies an evaporite-solution breccia, but locally, in the Sun River area, overlies a thick bed of limestone and in one place a gray-green mudstone (Mudge, 1972). Fossils abound in the dark-gray shale and limestone beds. The rest of the Three Forks consists mostly of a pale-yellowish-brown to yellowish-gray evaporite-solution breccia consisting of angular fragments of dolomite and dolomitic limestone. Thickness from 15 m to 180 m.

Jefferson Formation (Upper Devonian) Consists of two members: the Birdbear and a lower member. The Jefferson thickens eastward from about 190 m in the western outcrop to 247 m in the east. The Birdbear Member consists mostly of pale-yellowish-brown to brownish-gray, finely crystalline dolomite beds that pinch and swell. Brachiopods are commonly present. Ranges in thickness from 45 m to about 72 m. The lower member is mostly dolomite in the eastern outcrop, whereas it is mostly limestone in the western outcrop (Mudge, 1972). Consists of distinctive gray-brown beds (mostly less than 1/2 m thick) that characteristically have a fetid odor on the broken surface. Many beds have a sucrosic texture. The lower part commonly contains one or more thin beds of evaporite-solution breccia. Dark-gray chert lenses common in the lower part in the eastern outcrop. Corals, brachiopods, and stromatoporoids common throughout and Amphipora biostromes are widespread in the upper part. Thickness from 128 m to 198 m.

Maywood Formation (Upper and Middle Devonian) Contains an upper limestone member and a lower mudstone member. The upper member is mainly dark grayish-brown and yellowish-gray, thinly bedded, finely crystalline limestone and dolomitic limestone that thickens eastward from about 21 m in the west to 48 m in the east. Contains brachiopods and corals. The lower member is mostly greenish gray dolomitic mudstone that in the western outcrops is interbedded with maroon mudstone. Contains thin beds of crystalline yellowish-gray to olive-gray dolomite and dolomitic limestone. A widespread dolomite with some breccia present in the middle part of the member. Charophytes and conodonts are locally present in one of the dolomite beds. The lower member ranges in thickness from about 8 m in the eastern outcrop to 63 m in the western outcrop.'
1617|'Complete sections of these rocks are only in the western outcrop. Deiss (1939) divided these rocks into nine formations: Devils Glen Dolomite (top), Switchback Shale, Steamboat Limestone, Pentagon Shale, Pagoda Limestone, Dearborn Limestone, Damnation Limestone, Gordon Shale, and Flathead Sandstone (bottom). The Pentagon Shale occurs only in the vicinity of Pentagon Mountain where Deiss (1939) noted it to extend about 25 km to the south and about 7 km north of the mountain. The Devils Glen, Switchback, and Steamboat are in thrust blocks in the eastern outcrops. The limestone formations contain considerable mudstone in the east, but they are mostly limestone in the west. All formations locally contain trilobites and some brachiopods. The Cambrian rocks thin northwestward from 681 m near the Dearborn River to 439 m at Pagoda Mountain (Deiss, 1939).

Devils Glen Dolomite (Upper Cambrian) A distinctive, thick-bedded, light-gray, finely to very finely crystalline dolomite. Thickness from 54 m to 172 m (Deiss, 1939).

Switchback Shale (Upper and Middle Cambrian) Mostly noncalcareous, greenish-gray, thinly laminated clay shale with local thin interbeds of dolomite, limestone, sandstone, and conglomerate. Thickness from 21 m to 92 m.

Steamboat Limestone (Middle Cambrian) Differs in lithology between western and eastern outcrops. In the west consists of a lower shaly mudstone interval and a much thicker upper limestone interval (Deiss, 1939). In the eastern exposures is about equal parts of alternating sequences of limestone and calcareous shale. The carbonate units in both areas consist mostly of nodular, hard, dark-yellowish-brown, thinly bedded limestone and dolomite with nodules and lentils of dark-yellowish-orange siltstone. The mudstone units are mainly grayish-green noncalcareous shale with interbeds of calcareous siltstone and claystone. Trilobites, locally abundant, and some brachiopods occur in limestone lenses in the shales and locally near the top of the limestone units. Thickness from 65 m to 80 m.

Pentagon Shale (Middle Cambrian) A clastic wedge that consists of very fossiliferous, calcareous, gray to tan-gray, thick-bedded platy shale that contains some platy, blue-gray argillaceous limestone in the upper part (Deiss, 1939). Thickness ranges from less than 1 m to 88 m (Deiss, 1939).

Pagoda Limestone (Middle Cambrian) Forms prominent light-gray cliffs in the Cambrian sequence. The upper part consists of yellowish-gray to light-yellowish-brown, thin- to thick-bedded dolomitic limestone and some dolomite overlying very thin bedded limestone. The lower part consists of grayish-green, thinly laminated to nodular clay shale with some gray-brown limestone and minor sandstone. An intraformational conglomerate locally present in the middle and lower parts. Trilobites and brachiopods locally numerous in the shale (Deiss, 1939). Formation thickens to the south and west, and ranges in thickness from 28 m to about 120 m.

Dearborn Limestone (Middle Cambrian) Composed of an upper thick limestone unit and a lower thin shale unit. The limestone unit is finely crystalline, yellowish-brown to gray, thin to thick bedded and irregularly bedded. The lower unit consists of gray to gray-green clayey shale with some sandy shale and thin interbedded limestone. Trilobites present in the lower part of the shale unit. Thickness from 67 m to 106 m.

Damnation Limestone (Middle Cambrian) Consists of medium- to dark-gray, thin- to thick-bedded, finely crystalline dolomitic limestone and limestone with laminae of grayish-orange to yellowish-gray siltstone that thicken and thin. Locally they are oolitic and contain trilobites, brachiopods, and organic trails and burrows. Thickness from 30 m to 68 m.

Gordon Shale (Middle Cambrian) Mainly a dark-gray to gray-brown, very thinly laminated shale with a greenish tint and locally maroonish-gray beds. Contains many thin beds of sandstone and some beds of limestone, especially in the middle and upper parts. In places the limestones contain glauconite, algal structures, limestone chips, grains of quartz, and fossil fragments. The upper part contains numerous fossils (Deiss, 1939), whereas the lower beds locally contain organic trails and burrows, some by trilobites. Thickness from 42 m to 90 m.

Flathead Sandstone (Middle Cambrian) Consists of thin- to thick-bedded and crossbedded, noncalcareous yellowish-gray, poorly sorted, poorly indurated, fine- to coarse-grained quartzose sandstone with scattered quartz pebbles. Beds are characteristically speckled by disseminated hematite. Interbeds of gray, purple, or maroon mudstone locally present. Thickness from 13 m to 35 m.'
1618|'PROTEROZOIC Y STRATIFIED ROCKS The Proterozoic stratified rocks in the quadrangle are assigned to the Belt Supergroup and consist of quartzite, siltite, argillite, limestone, and dolomite that are metamorphosed to the chlorite subfacies. The Belt Supergroup is divided upper, middle, and lower parts. The upper part is the Missoula Group which consists mostly of fine-grained clastic rocks and minor limestone and dolomite above the Helena Formation. The middle part is the Helena Formation which consists mostly of limestone and dolomite. The lower part, the Ravalli Group, contains mostly siltite and argillite with minor quartzite, limestone, and dolomite. Thickness of the Belt Supergroup in the quadrangle ranges from 2,000 m in the eastern part to more than 10,000 m in the western part.

Consists of pale-olive to medium-gray and moderate brown, poorly sorted, very fine to fine-grained, micaceous, thin even beds of sandstone and siltstone. Locally they are speckled by hematite, crossbedded and ripple marked. The formation varies in thickness due to pre-Middle Cambrian erosion and ranges from less than 1 m to 490 m, attaining its greatest thickness in the southern outcrops.'
1619|
1620|'In the central and southern parts of the area the McNamara is divisible into two unnamed members, an upper dominantly reddish-brown quartzite and a lower dominantly grayish-green siltite (Somers, 1966; Mudge and Earhart, 1978).

Quartzite in the upper member is interbedded with siltite and minor argillite. Most of the unit is thin-bedded, fine-grained, micaceous, minutely crossbedded, and locally ripple marked. The lower member contains thin beds of argillite and fine- to medium-grained quartzite and locally some reddish-gray siltite. Ripple marks, minute cross-bedding, and load casts are common. The upper part of the lower member contains thin beds of glauconitic sandstone, some barite nodules, and vuggy reddish chalcedony, particularly in the eastern outcrop area (Mudge, 1972; Mudge and Earhart, 1978). In the northern part of the area, the formation thickens and is dominantly grayish-green siltite. The formation varies in thickness, due in part to pre-Middle Cambrian erosion, and ranges from 47 m to 1,650 m.  Where overlain by the Garnet Range Formation its minimum thickness is 640 m; it thickens northward.'
1621|'Mapped only in the upper reaches of Smith and Elk Creeks.'
1622|'Consists mostly of pink, pale-red, and pinkish-gray, fine- to medium-grained, poorly sorted beds of quartzite that range in thickness from 31 cm to 76 cm. The quartzite is mostly feldspathic and locally includes fragments of red argillite. Many beds are crossbedded and ripple marked. Thickness ranges from 213 m to 580 m.'
1623|'Mostly bright reddish brown, thinly laminated, micaceous siltite, argillite, and thin- to thick-bedded quartzite. Sedimentary features include minute cross-laminations, ripple marks, mud-crack fillings, and mud chips. A grayish-green siltite unit with local interbedded dark-gray fissile shale widespread in the upper part of the formation. Salt-crystal casts widespread in the upper part of the formation, beneath the grayish-green unit. The quartzite beds are mostly fine to medium grained and more common in the middle and lower parts of the formation. A thick (155 m to 305 m) quartzite unit is present in the upper-middle part of the formation in the southern outcrop. It contains poorly sorted, fine- to coarse-grained, pinkish-gray to reddish-brown quartzite beds less than 1 m thick that are separated by thin beds of reddish-brown siltite and argillite. The color, grain size, and sedimentary features of the quartzite beds are similar to those in the Bonner Quartzite. The lower part of the formation in the eastern outcrop commonly contains thin beds of glauconitic quartzite. In the central and northern parts of the area the formation is more argillitic and contains beds of stromatolitic and oolitic limestone. The formation thickens south and west, from 555 m in the eastern outcrop to 2,180 m in the west at Swan Range and to 1,860 m in the south.'
1624|'Consists mostly of greenish-gray to grayish-yellow micaceous siltite and some silty limestone and argillite. Beds of maroon siltite and argillite widespread in the middle part and locally in the upper part. Thin glauconitic quartzite lentils widespread in the upper part of the formation in the eastern outcrop, but sparse elsewhere. Ripple marks, minute cross lamination, load casts, and mud cracks also common in the eastern outcrop. An edgewise conglomerate present near the base of the formation in the east, but elsewhere a stromatolitic limestone bed occurs at the same horizon. Other beds of stromatolitic limestone also present in the lower part of the formation in the Mission Range (Harrison and others, 1969). The formation thickens westward and southward, from 249 m in the eastern outcrop to about 900 m in the west in the Swan Range and about 715 m in the south.'
1625|'Consists of pale-red to reddish-brown beds and interbedded greenish-gray beds of argillite and siltite with some thin beds of very fine to fine-grained quartzite. Thin beds of stromatolitic and oolitic limestone and flat pebble conglomerate locally occur at various horizons. Crossbedded, minute laminae, ripple marks, and mud cracks common features; raindrop impressions mud-chip conglomerates less common. Thin beds of poorly sorted, fine- to coarse-grained quartzite and gritstone common near the lower contact. The formation thickens west and south, from about 215 m in the eastern outcrop to 1, 660 m in the Swan Range and 1,100 m in the southern part of the area.'
1626|'In most places the Helena is divisible into three units. The upper unit consists of beds of limestone interbedded with dolomite, siltite, and argillite. Beds of stromatolites, oolites, and edgewise conglomerates widespread. The middle unit, comprising most of the formation, consists of light- to medium-gray, thin to thick-bedded silty limestone, dolomite, and calcitic dolomite that weathers to a yellowish gray to grayish orange. Commonly, vertical ribbons, blobs, horizontal mats, lenses, and pods differentially weather to form crenulating patterns ("molar tooth structure," O Connor, 1967). Stromatolites, oolites, and edgewise conglomerates locally present at various horizons, especially in the eastern outcrop. The lower unit consists mostly of calcareous or dolomitic siltite with some beds of dolomite and quartzite. The siltite is gray, greenish-gray, and locally dark red near the lower contact. The quartzite that occurs at the base is light gray, thinly bedded, calcareous, medium grained, and poorly sorted. The Helena thickens westward and southward, from about 205 m in the central part of the eastern outcrop to about 3,000 m in the Mission Range (Harrison and others, 1969) to 1,662 m in the south (Mudge and others, 1974).'
1627|'Undivided only in the eastern and part of the southern outcrop area. In those areas the unit is pale-red, maroon, green, and gray siliceous argillite and siltite, with minor thin beds of poorly sorted, fine-grained quartzite. Locally in the eastern outcrop also contains some thin beds of dolomite, edgewise conglomerate, and stromatolite beds.'
1628|'A transitional unit between the Helena and Spokane Formations. Mostly greenish gray argillite and siltite with interbeds of quartzite, dolomite, and locally stromatolitic and oolitic carbonate rock. The quartzites are poorly sorted, ranging from very fine to medium grained, and locally carbonate cemented. The amount of carbonate appears to increase upward. Red to purple beds of predominantly argillite occur in the lower part of the formation. The formation varies in thickness from less than 1 m too as much as 610 m (Mudge and others, 1974, 1978).'
1629|'Mostly pale-purplish-red and grayish-red siltite and argillite interbedded with lithologically similar greenish-gray beds. The southeastern and northwestern outcrops contain light-gray, very fine to medium-grained, thin beds of quartzite that locally contain minute cross-beds and ripple marks. The formation as much as 1,500 m thick in the Swan Range (Johns, 1970) and as much as 915 m thick in the southeast (Schmidt and Strong, 1972).'
1630|'The oldest unit exposed in and near the map area; therefore, its base is not exposed. Consists of light-gray to greenish-gray, thinly bedded siltite with some quartzite, grading down into dark-gray, greenish-gray, very thinly laminated argillite and siltite in the lower part. Its sedimentary features include ripple marks, mudcracks, and locally salt crystal casts (Schmidt and Strong, 1972). Thickness of the formation is as much as 762 m (Schmidt and Strong, 1972).'
1632|'Volcanic neck or plug and sills, gray to light-gray, aphanitic groundmass of greenish-gray feldspar with phenocrysts of light-gray feldspar, hornblende, and biotite. Present only at and near Haystack Butte in southeastern part of map area.'
1633|'Light-gray, fine-grained, equigranular dikes and sills composed of andesine, sanidine, hornblende, augite, biotite, magnetite, and apatite. Hornblende needles, 3-4 mm long, characterize the rock (Schmidt, 1972b, c; Schmidt and Strong, 1972). Dated as 46.3 m.y. by the K-Ar method (R. G. Schmidt, 1978). Widespread in southeast corner of map area.'
1634|'Stocks, dikes, and sills, of light-gray, abundant, 1-cm and larger phenocrysts of orthoclase that weather out as euhedral crystals. Dated at 58.3 m.y. by the K-Ar method (U.S. Geological Survey, 1971; Schmidt, 1978). Present only in southeast corner of map area.'
1635|'Dikes, sills, and irregular-shaped bodies. Includes trachybasalt and biotite trachybasalt of Schmidt (1972b, c, 1978). Dark-gray, aphanitic groundmass with hornblende and some biotite phenocrysts, weathers brown. Present only in the southeast corner of map area.'
1636|'Volcanic and volcanic-sedimentary rocks. Trachyandesite and trachybasalt flows (Schmidt, 1972a), volcanic conglomerate, breccia, and lacustrine deposits of volcanic sandstone, siltstone, and mudstone (Schmidt, 1972a, 1978). Present only in southeast corner of map area.'
1637|'Sills, dark grayish brown, aphanitic groundmass of feldspar with phenocrysts of plagioclase, potassium feldspar, pyroxene, and quartz (Mudge, 1972). Widespread near the North Fork Sun River.'
1638|'Dikes and sills, light-gray to white; finely porphyritic with abundant 2-3 mm phenocrysts of quartz and oligoclase (Schmidt, 1972c, 1978). Present only in southeast corner of the map area.'
1639|'Sills, light-grayish-orange; coarsely porphyritic with abundant 1 cm and larger phenocrysts of potassium feldspar and oligoclase-andesine in a fine-grained groundmass (Schmidt, 1972c, 1978).'
1640|'Sill, gray, grayish-purple; massive and porphyritic with abundant phenocrysts of labradorite in an aphanitic groundmass (Schmidt, 1972c, 1978). Present only in southeast corner of map area.'
1641|'Includes rhyodacite porphyry and diorite as mapped by Schmidt and Strong (1972) and Schmidt (1978). The rhyodacite is greenish gray with phenocrysts of oligoclase and hornblende mainly in a groundmass of quartz and feldspar. The diorite is greenish gray, fine grained, and equigranular (Schmidt and Strong, 1972). Present only in southeast corner of map area.'
1642|'Mostly diorite and quartz diorite, locally minor diorite-gabbro and monzonite. Dark gray, weathers grayish brown. Dated at 75025 m.y. by K-Ar method (J. D. Obradovich, oral commun., 1966). Widespread throughout map area.'
1650|'Gravel, sand, silt, and clay along active channels of rivers, creeks, and tributaries.'
1651|'Locally derived slope-wash deposits mainly of sand, silt, and clay. Commonly grades into Qal. Locally contains well-rounded cobbles reworked from alluvial terrace gravel. Typically thin veneer concealing bedrock, but locally as thick as 30 ft.'
1652|'Colluvium and alluvium are combined where mapping is insufficient to differentiate between those deposits that grade into one another.'
1653|'Gravel, sand, silt, and clay deposited in fans being formed by tributary streams along major valley margins. Display characteristic fan-shaped map pattern and convex upward profile. Typically grade into Qal. Thickness ranges from very thin at toe to as much as 50 ft at head of fans.'
1654|'Gravel near shore, grading into clay and marl in center. Thickness 1-3 ft (Skipp and others, 1999).'
1655|'Accumulations of locally derived boulder- to pebble-size angular detritus at heads of drainages on both sides of the crest of the Bridger Range.'
1656|'Unconsolidated mixture of soil and blocks of bedrock transported down steep slopes by mass wasting. Characteristic hummocky surface with concentric swales and ridges near down-slope limits. Common along steep slopes beneath resistant rocks but may have developed wherever steep slope and high moisture content produce unstable conditions.'
1657|'Angular and subangular cobble and smaller gravel, sand, and silt derived from local bedrock. Surfaces of deposits are smooth pediments sloping away from the Crazy Mountains and Beartooth Mountains. About 10 to 30 ft thick.'
1658|'Unsorted mixture of clay to boulder size sediment transported and deposited by alpine glaciers. Has characteristic hummocky surface form. Occur in valleys near the Beartooth Mountains in the southwest corner of the map area. Clasts are predominantly Archean metamorphic rocks with lesser amounts of quartzite, dolomite, and limestone. Thickness unknown.'
1659|'Gravel, sand, silt, and clay underlying terraces about 20 to 600 ft above present altitude of modern streams and rivers. Equivalent to one or more of Qat1 through Qat5. Thickness 10 to 40 ft.'
1660|'Gravel underlying terraces about 10 to 20 ft above present altitude of rivers. Mostly cobbles and pebbles with minor amounts of sand and silt. Clasts are mainly granitic igneous rocks, granitic gneiss, schist, and quartzite, with much less limestone and sandstone. 10 to 40 ft thick.'
1661|'Gravel underlying terraces about 20 to 40 ft above Qal. Mostly cobbles and pebbles with minor amounts of sand and silt. Clasts are mainly granitic igneous rocks, granitic gneiss, schist, and quartzite, with much less limestone and sandstone. 10 to 40 ft thick.'
1662|'Gravel underlying terraces about 50 to 90 ft above present altitude of rivers. Mostly cobbles and pebbles with minor amounts of sand and silt. Clasts are mainly granitic igneous rocks, granitic gneiss, schist, and quartzite, with much less limestone and sandstone. 10 to 30 ft thick.'
1663|'Gravel underlying terraces about 200 to 300 ft above present altitude of rivers. These terraces locally exhibit a relatively steep gradient toward the Yellowstone River Valley and may actually include several levels of terraces that are difficult to distinguish. Cobble- and pebble-size clasts are mainly granite, granitic gneiss, schist, and quartzite. Thickness up to about 20 ft.'
1664|'Gravel underlying terraces about 400 to 600 ft above present altitude of rivers. Occur mainly as small discontinuous erosional remnants. Cobble- and pebble-size clasts are mainly granite, granitic gneiss, schist, and quartzite. Local calcite cement, especially at base. Thickness ranges from a very thin remnant to about 20 ft'
1665|'Poorly stratified variously consolidated tuffaceous siltstone, claystone, sandstone, and conglomerate (Roberts, 1964g).'
1666|'Applies to areas within the Absaroka-Beartooth Study Area and the southwestern corner of the Livingston quadrangle where formations within the volcanic sequences were not mapped. Largely composed of units in the Absaroka Volcanic Supergroup. Total thickness unknown.'
1667|'A small intrusive body in Archean metamorphic rocks near the southwestern corner of the quadrangle.'
1668|'Described by Harlan (1986) as typically sodium rich, silica undersaturated, and strongly alkaline (Wilson and Elliott, 1997).'
1669|'An olivine-augite-biotite diorite dike; and a composite sill that consists of upper and lower layers of biotite-augite diorite and a middle layer of syenodiorite (Skipp and others, 1999).'
1670|'Sills intruded into the Fort Union Formation that consist mainly of potassium feldspar with abundant biotite, and locally minor pyroxene. The most prominent of these is the sill that forms Sheep Mountain. Both the syenite intrusive and associated resistant hornfels cap this ridge.'
1671|'Gray to grayish-yellow, fine- to medium-grained, cross bedded sandstone. Interbedded with brownish-gray carbonaceous shale and siltstone and minor thin coal beds. Sandstone beds are ledge forming and commonly support growths of pine trees. About 400 ft of this member is present in the northeastern part of the map area, but thickens dramatically westward. The top of this member was not observed in the map area.'
1672|'Predominantly dark-gray to olive shale, locally yellowish-gray claystone, thin interbedded sandstones and siltstone, yellowish gray. Typically forms smooth grassy slopes below the Tongue River Member. Pinches out in the northeastern part of map area; thickness 0 to 250 ft.'
1673|'Yellowish-gray, fine- to medium-grained, ledge-forming sandstone, cross-bedded in part. Interbedded with gray to greenish-gray claystone, siltstone, and minor carbonaceous shale. Supports growths of pine trees. About 400-600 ft thick in the eastern part of the map area but thickens westward where it could not be mapped separately.'
1674|'Cliff-forming massive sandstone, siltstone, mudstone, and lesser amounts of conglomerate. Conglomerate contains clasts of reworked Cretaceous and older rocks; contains fossil spores, plants, wood, freshwater mollusks, and vertebrates (Roberts, 1964d). Thickness increases toward axis of Crazy Mountain Basin and is probably at least 10,000 ft. Skipp and others (1999) show the Fort Union about 8,000 ft thick in a cross-section on the west side of the Crazy Mountains.'
1675|'Interbedded light-brownish gray, cliff and ledge-forming, fine-grained, thin- to thick-bedded sandstone, and gray, pale greenish gray and pale purple gray mudstones. Sandstone beds support growths of pine trees. Includes basal beds commonly mapped as Lennep Formation that are typical of basal Hell Creek to the east (personal communication, Susan Vuke and Edie Wilde). The Hell Creek and the upper part of the Livingston Group are laterally equivalent and are eastern and western facies respectively. Hell Creek is recognized east of the Shields River north of the Yellowstone River, and east of Springdale south of the Yellowstone River. Total thickness of the formation is about 900 to 1,100 ft.'
1676|'Dark-gray to medium-gray fine-grained diorite and diorite porphyry with phenocrysts of plagioclase, hornblende, pyroxene, and locally biotite. Occurs as stocks, sills, and dikes in the southeastern corner of the quadrangle. Radiometric age is 74-77 Ma (du Bray and Harlan, 1993 and du Bray and others, 1994).'
1677|'This unit includes all the volcanic rocks erupted from the Sliderock stratovolcano (du Bray and others, 1994). Mostly andesite breccia (lahars) gray, pale-purple gray, pale-greenish gray. Andesite in clasts is porphyritic with phenocrysts of chalky plagioclase, hornblende and pyroxene; matrix is similar but lighter in color and slightly finer grained. Very resistant, forming cliffs and very rugged topography especially near the vent zone in the Sliderock Mountain area (on Big Timber quadrangle, Lopez, 2000). In distal areas, as near town of Springdale, clasts are less angular but otherwise similar to breccias elsewhere. The unit contains minor flows of porphyritic andesite and basaltic andesite, with phenocrysts of plagioclase, hornblende and pyroxene. Thickness is at least 1000 ft (du Bray and others, 1994).'
1678|'Descriptions of formations below are from Roberts, 1964c.  Includes the Hoppers Formation, Billman Creek Formation, Miner Creek Formation, and the Cokedale Formation.'
1679|'Andesitic sandstone with interbedded claystone and siltstone; massive crossbedded yellowish-gray sandstone member at the base.'
1680|'Olive-gray, brownish-gray, and grayish-red claystone with interbedded sandstone, siltstone, and conglomerate; contains fresh-water mollusks and dinosaur bones.'
1681|'Andesitic siltstone and sandstone with beds of tuff and bentonite in lower part; contains fossil spores, plants, wood, and dinosaur bones.'
1682|'Andesitic siltstone and sandstone with claystone, tuff, bentonite and coal; lower part carbonaceous with some thin coal beds; sandstone locally conglomeratic; contains fossil spores, plants, wood, dinosaur bones, and fresh-water mollusks.

Sedan Formation (Upper Cretaceous)-Shown only for the Sedan 15'' quadrangle. The Sedan Formation is equivalent to the Miner Creek and Cokedale formations of the Livingston Group. Descriptions for the members of the Sedan Formation from Skipp and others, 1999.'
1683|'Ridge-forming, olive-gray, greenish-gray, volcaniclastic sandstone, conglomerate, and minor mudstone and devitrified tuff. Unit contains rare dinosaur bone fragments, freshwater and brackish-water mollusks, and, in northern part of quadrangle, trace fossils of Ophiomorpha. Thickness about 350-500 ft.'
1684|'Greenish-gray and brownish-gray, volcaniclastic, mudstone, siltstone, sandstone, and minor interbedded conglomerate and altered vitric tuff. Member forms valleys and low barren hills and has a gradational contact with the middle sandstone member. Unit contains freshwater mollusks, wood, and dinosaur bones. Thickness ranges from 900-1000 ft.'
1685|'Olive-green, olive-gray, and dark-greenish-gray, volcaniclastic sandstone, conglomerate, mudflow conglomerate, and minor siltstone and mudstone. Unit forms series of ridges and disconformably overlies ash-flow tuff member; basal contact is placed at top of highest ash-flow tuff or ash-flow tuff conglomerate. Thickness is about 1000-1430 ft.'
1686|'Pale-yellowish-green, light-greenish-gray, grayish-red, and pale-yellowish-brown, welded to nonwelded tuff and ash-flow tuff conglomerate, interbedded with volcaniclastic conglomerate, sandstone, mudstone, and porcellanite. Unit forms resistant knobs and ridges and disconformably overlies lower sandstone member. Thickness about 200-500 ft.'
1687|'Dark-olive-gray, greenish-gray, and yellowish-gray, volcaniclastic sandstone, siltstone, mudstone, altered crystal lithic tuff, minor volcaniclastic granule and pebble conglomerate, minor grayish-red-purple hornblende dacite, and minor lignitic coal. Unit forms a low ridge and has an abrupt contact with underlying Eagle Sandstone throughout most of the Sedan quadrangle. Thickness 500-1000 ft.'
1688|'Interbedded gray sandstone, mudstone, and shale. Sandstone is feldspathic and lithic. Used in southeast part of map area where this thick interval lies between the Telegraph Creek Formation and Hell Creek formations. Not divided because the intervening Claggett Shale was not observed, although Richards (1957) believed rocks equivalent to the Claggett Shale are present in this area. Thickness is about 1000 to 1400 ft.'
1689|'Light-brownish-gray to very-pale orange, very-fine to fine-grained, cross-bedded sandstone, burrowed to bioturbated in part; interbedded with shale. Thickness about 150 ft.'
1690|'Eagle Sandstone:  Light-brownish-gray to very-pale orange, very-fine to fine-grained, cross-bedded sandstone, burrowed to bioturbated in part; interbedded with shale. Thickness about 150 ft.

Telegraph Creek Formation:  Shale and sandy shale, brownish-gray to medium-dark-gray with thin interbedded sandstone. Dusky-red concretions common near base. Sandstone beds thicker and more abundant upward, grading into Eagle Sandstone. Contact with Eagle is placed at the base of the first cliff-forming sandstone. Maximum thickness about 250 ft.'
1691|'Shale and sandy shale, brownish-gray to medium-dark-gray with thin interbedded sandstone. Dusky-red concretions common near base. Sandstone beds thicker and more abundant upward, grading into Eagle Sandstone. Contact with Eagle is placed at the base of the first cliff-forming sandstone. Maximum thickness about 250 ft.'
1692|'Shale, olive-gray and dark-brownish gray, fissile, and contains abundant thin bentonite beds. Upper half calcareous, containing few very thin bentonite beds, and near top contains thin beds of very calcareous laminated sandstone, siltstone, and sandy limestone. Concretions medium-light-gray to pale-yellowish-brown and from a few inches to one or two ft in diameter are commonly present. Inoceramus prisms common. Upper contact placed at change from calcareous shales to non-calcareous shales of Telegraph Creek. Zone of dusky-red concretions in the Telegraph Creek, just above contact also helps establish its position. Basal contact not exposed, thickness unknown.'
1693|'Gray shale and mudstone interbedded with grayish-green and olive-gray sandstone and siltstone and minor brown-weathering nodular limestone and yellowish-gray bentonite. Entire formation is locally fossiliferous and contains fish scales, starfish, ammonites and other mollusks. Thickness is about 1000 ft (Skipp and others, 1999). Division of Cody Shale into members as listed below for the southwestern part of the Livingston quadrangle from Roberts, 1965.'
1694|'Dark-gray to brown marine shale and siltstone with interbedded very fine-grained sandstone. Thickness 500 to 845 ft (Roberts, 1965, p. B59).'
1695|'Persistent thin-bedded, marine, glauconitic, greenish-gray, fine-grained sandstone. Thickness 90 to 120 ft (Roberts, 1965, p. B59).'
1696|'The lower shale member of the Cody is consists of dark-gray to dark-brown marine shale with interbedded siltstone. The Frontier Formation is as described below. Thickness 400 to 590 ft (Roberts, 1965, p. B59).

Frontier Formation:  Light brownish gray, fine-grained thick-bedded to massive, salt and pepper sandstone. Contains three sandstone intervals interbedded with dark-gray, fissile shale.'
1697|' (Roberts, 1965, p. B59).  Cody Shale:  Gray shale and mudstone interbedded with grayish-green and olive-gray sandstone and siltstone and minor brown-weathering nodular limestone and yellowish-gray bentonite. Entire formation is locally fossiliferous and contains fish scales, starfish, ammonites and other mollusks. Thickness is about 1000 ft (Skipp and others, 1999). Division of Cody Shale into members as listed below for the southwestern part of the Livingston quadrangle from Roberts, 1965.

Frontier Formation:  Light brownish gray, fine-grained thick-bedded to massive, salt and pepper sandstone. Contains three sandstone intervals interbedded with dark-gray, fissile shale. Maximum mapped thickness about 550 ft.'
1698|'Light brownish gray, fine-grained thick-bedded to massive, salt and pepper sandstone. Contains three sandstone intervals interbedded with dark-gray, fissile shale. Maximum mapped thickness about 550 ft.'
1699|'This unit is equivalent to Mowry Shale and Thermopolis Shale undivided as mapped by Roberts (1964c). Top of unit (Mowry) is interbedded, siliceous, very fine- to fine-grained sandstone, siltstone, and shale. Contains several prominent bentonite beds. Sandstones and siltstones mostly light gray to medium gray, with a silvery sheen. Fish scales on bedding planes of sandstones and siltstones are characteristic of this formation. Thermopolis Shale is predominantly dark-gray fissile shale, bentonitic shale, and several beds of bentonite. Has hematitic concretionary zone near base. Fall River Sandstone is brownish-gray, thin-bedded, argillaceous, fine-grained, quartz sandstone. Generally poorly exposed in map area, mostly covered by glacial deposits. Total thickness is approximately 1300 ft.'
1700|'Mostly reddish-brown, olive-gray, and dusky-purple mudstone with interbedded, lenticular, fine- to coarse-grained sandstones. Locally thick, lenticular, fluvial, fine-grained sandstone, the Greybull Sandstone, is present at the top. The basal Pryor Conglomerate Member is brown conglomerate and pebbly coarse-grained sandstone and is 20 to 60 ft thick. The total thickness of the Kootenai Formation is about 500 ft.'
1701|'Total thickness about 900 ft.

Morrison Formation:  Mainly variegated greenish-gray and pale-reddish-brown mudstone. Very fine- to fine-grained, quartzose, calcareous, cross-bedded sandstones are commonly present at about mid-section, 5 to 10 ft thick but locally can be as much as 30 ft thick. Fossil dinosaur remains common. Upper contact placed at the base of the Pryor Conglomerate. The basal contact is placed at the top of fossiliferous limy sandstone and coquina of the underlying Swift Formation. Thickness about 300 ft.

Ellis Group:  Includes the Swift, Rierdon, and Piper Formations. The Swift is interbedded medium-gray shale, limestone and limy sandstone, fossiliferous. Brownish-gray, fossiliferous, very sandy limestone occurs at the top of the formation, which generally includes brownish-gray coquina at the top. The Rierdon Formation is mostly pale greenish-gray very fossiliferous shale with minor interbedded brownish gray limestone. Typically poorly exposed, forming smooth slopes littered with fossils, including oysters (Gryphaea and Ostrea), belemnites (Pachyteuthis), and crinoid fragments (Pentacrinus). The Piper is interbedded medium-gray, and pale reddish-gray, thin-bedded limestone and medium-gray shale. Includes thin interbedded gypsum. Forms ledge below smooth slopes of the Rierdon shale. Thickness of the Ellis Group is about 600 ft.'
1702|'Mainly variegated greenish-gray and pale-reddish-brown mudstone. Very fine- to fine-grained, quartzose, calcareous, cross-bedded sandstones are commonly present at about mid-section, 5 to 10 ft thick but locally can be as much as 30 ft thick. Fossil dinosaur remains common. Upper contact placed at the base of the Pryor Conglomerate. The basal contact is placed at the top of fossiliferous limy sandstone and coquina of the underlying Swift Formation. Thickness about 300 ft.'
1703|'Includes the Swift, Rierdon, and Piper Formations. The Swift is interbedded medium-gray shale, limestone and limy sandstone, fossiliferous. Brownish-gray, fossiliferous, very sandy limestone occurs at the top of the formation, which generally includes brownish-gray coquina at the top. The Rierdon Formation is mostly pale greenish-gray very fossiliferous shale with minor interbedded brownish gray limestone. Typically poorly exposed, forming smooth slopes littered with fossils, including oysters (Gryphaea and Ostrea), belemnites (Pachyteuthis), and crinoid fragments (Pentacrinus). The Piper is interbedded medium-gray, and pale reddish-gray, thin-bedded limestone and medium-gray shale. Includes thin interbedded gypsum. Forms ledge below smooth slopes of the Rierdon shale. Thickness of the Ellis Group is about 600 ft.'
1704|'Formations not mapped separately because of narrow outcrop width. Phosphoria is poorly exposed and includes, yellowish-gray shale, light gray limestone, sandstone and quartzite, commonly grayish pink, cherty; thickness is 50 to 75 ft. The Phosphoria interval is present in the southeast part of the map area. It thins westward and was not recognized by Richards (1957) or Roberts (1964). The Tensleep Sandstone is light-brown to very-pale-orange sandstone, fine grained, well sorted, well rounded, cross-bedded. Locally contains thin limestone beds, locally cherty near the top, and is locally silicified to form quartzite; about 250 ft thick. The Amsden Formation is interbedded grayish-pink to light-red mudstone, limestone, and siltstone. Limestones are commonly cherty. Unconformably overlies karst surface developed on limestone of the Madison Group. Characteristically produces pink stain on underlying cliffs of Madison Group; thickness about 200 ft but locally tectonically thinned to only a few feet along the mountain front. Total thickness about 500 to 600 ft.'
1705|'Used in areas where Phosphoria is absent and Quadrant and Amsden outcrop bands are too narrow to map separately.

Quadrant Formation:  Quartzite, well sorted quartzose sandstone, and dolomite (Roberts, 1964f).

Amsden Formation:  Dolomite, calcareous sandstone, and siltstone in upper part; argillaceous limestone in middle part; massive sandstone and red calcareous siltstone and limestone in lower part; mostly concealed (Roberts, 1964b).'
1706|'Quartzite, well sorted quartzose sandstone, and dolomite (Roberts, 1964f).'
1707|'Dolomite, calcareous sandstone, and siltstone in upper part; argillaceous limestone in middle part; massive sandstone and red calcareous siltstone and limestone in lower part; mostly concealed (Roberts, 1964b).'
1708|'Gray and gray-brown limestone and dolostone; red, pink and yellow-orange sandstone; red and pink siltstone; red to purple shale; and red-stained breccia (Skipp and others, 1999).'
1709|'Limestone and dolomitic limestone, light gray to light brownish gray. Thick bedded to massive in the upper part (Mission Canyon Limestone) and thin-bedded to thick bedded in the lower part (Lodgepole Limestone). Also contains thin interbedded gray shales. Fossiliferous and cherty beds are present throughout. Thickness of the Madison Group is about 1000 ft in the southeastern part of the map area.'
1710|'Pale yellow-brown, massive, poorly bedded limestone and dolostone that weather light gray and form cliffs and castellated ridges. Unit has a gradational lower contact with Lodgepole Limestone. Thickness is about 720 to 950 ft (Skipp and others, 1999).'
1711|'Gray and brown limestone and minor dark-brown to black silty shale. Formation unconformably overlies Sappington Member of the Three Forks Formation. Total thickness is 750 to 800 ft (Skipp and others, 1999).'
1712|'Light- and dark-brown dolostone; gray and gray-green, nodular limestone; yellowish-brown sandstone; pink and gray siltstone; black and green shale; and minor dolostone breccia. Unit disconformably overlies upper Cambrian beds. This entire interval is 740 to 940 ft thick. (Skipp and others, 1999).'
1713|'The Three Forks is mainly yellowish-weathering argillaceous limestone and medium-gray shale, very poorly exposed. The Jefferson Formation is dolomitic limestone, light brownish gray, fetid, poorly exposed, typically occurs as float. The Big Horn Dolomite is cliff-forming dolomite and dolomitic limestone, very light gray to very pale orange, lower part massive, thin to thick bedded in upper part. Has characteristic pock-marked surface because of differential weathering. Interval thickness about 600 ft.'
1714|'Dark- and light-gray mottled and grayish-brown limestone, limestone-pebble conglomerate, and grayish-green shale. Entire interval about 530 to 700 ft thick (Skipp and others, 1999).'
1715|'Light red sandstone and quartzite, greenish-gray shale and sandy shale, gray thin-bedded limestone and greenish-gray flat-pebble limestone conglomerate. Includes the Flathead, Wolsey, Meagher, Park, and Pilgrim formations. Thickness is 600 to 800 ft.'
1716|'Grove Creek Formation is limestone, intraformational conglomerate, and shale; Snowy Range Formation is green shale and gray limestone that is partly a flat-pebble conglomerate; bed of columnar fractured limestone locally present in lower part of Snowy Range Formation; mostly concealed. (Roberts, 1964b). Note: Skipp and others, 1999 assigned a Lower Ordovician age to the Snowy Range Formation in the Sedan 15'' quadrangle.'
1717|'Massive, cliff-forming oolitic, mottled, magnesian and dolomitic limestone with edgewise intraformational limestone-pebble conglomerates, interbedded shale and siltstone, and glauconitic limestone. Thickness is 360-430 ft (Skipp and others, 1999 and Roberts, 1964b).'
1718|'Park Shale:  Multicolored shale with thin beds of argillaceous limestone, siltstone, and sandstone; mostly concealed. (Roberts, 1964b).

Meagher Limestone:  Thin-bedded, silty, medium-gray limestone and yellowish-gray dolomite; locally oolitic (Roberts, 1964b).

Wolsey Shale:  Greenish gray calcareous shale and mudstone with thin beds of limestone; mostly concealed (Roberts, 1964b).

Flathead Quartzite:  Gray to red quartzose sandstone and quartzite; conglomeratic in lower part locally. (Roberts, 1964b).'
1719|'Multicolored shale with thin beds of argillaceous limestone, siltstone, and sandstone; mostly concealed. (Roberts, 1964b).'
1720|'Thin-bedded, silty, medium-gray limestone and yellowish-gray dolomite; locally oolitic (Roberts, 1964b).'
1721|'Greenish gray calcareous shale and mudstone with thin beds of limestone; mostly concealed (Roberts, 1964b).'
1722|'Gray to red quartzose sandstone and quartzite; conglomeratic in lower part locally. (Roberts, 1964b).'
1723|'Dark-grayish green, reddish-weathering, coarse-grained, massive, poorly bedded arkose and conglomeratic arkose. Thickness ranges from 7,000 to 10,000 ft (Skipp and others, 1999).'
1725|'Upper anorthosite zone - Plagioclase cumulate with 0-50 percent pyroxene, much of which is post-cumulus. A convoluted relationship between coarse-grained and fine-grained rock characterizes the uppermost part of the zone on the ridge southwest of Burnt Gulch (northwest of Picket Pin Mountain) and on a knoll at the west side of the Boulder River. Plagioclase cumulate with post-cumulus magnetite (including magnetite oikocrysts) constitute some of the coarse-grained phase. Euhedral (cumulus) plagioclase laths in a groundmass of anhedral pyroxene and plagioclase grains (probably post-cumulus) constitute the fine-grained phase: in places the rock is porphyritic, with plagioclase crystals as much as 1-2 cm long in a fine-grained groundmass. Plagioclase-magnetite cumulate also occurs in two thin layers near the top of the section west of Wright Gulch (north side of Contact Mountain). Plagioclase cumulate in the rest of the zone contains increasing amounts of clinopyroxene (10 to 50 percent) down-section, and near the bottom of the zone some of the pyroxene is orthopyroxene. Megascopically and in thin sections, practically all pyroxene in the unit appears to be anhedral, and hence interstitial. However, McCallum and others (1980), who made a detailed petrographic study of a section across the east end of Contact Mountain, found much cumulus clinopyroxene and inverted pigeonite in the zone. Their "Gabbronorite III unit" contains the Upper anorthosite and Upper gabbro zones of this map. The Upper anorthosite zone has a maximum exposed thickness of 800 m, but east of Picket Mountain and west of the Boulder River the unit is truncated completely by the unconformity at the base of the Paleozoic sedimentary rocks.

Upper gabbro zone - Principally plagioclase-two pyroxene cumulate. Ratios of orthopyroxene to clinopyroxene and of plagioclase to pyroxene vary, but plagioclase is generally dominant and the rock tends to be leucocratic. Plagioclase-clinopyroxene cumulate is rare or absent throughout the zone. The upper contact is the highest limit where abundant cumulus clinopyroxene is seen in hand specimen. A lens of pegmatoid orthopyroxene cumulate 1 m thick is exposed at the top of the zone north of Picket Pin Mountain. Turbulent flow structure is exhibited near the middle of the zone on a low ridge south of a cirque northeast of Picket Pin Mountain. There, wispy xenoliths, chiefly of plagioclase cumulate, are enclosed in the two pyroxene rock. A prominent lens of plagioclase extends from about 100 m to 200 m above the base of the zone; it is well exposed in cuts along the cirque road east of Picket Pin Mountain. This lens thins westward and disappears near the east end of Contact Mountain. Plagioclase-orthopyroxene cumulate and plagioclase cumulate form several minor layers along and near the base. The zone attains a maximum thickness of 600 m on the north side of Contact Mountain, but is truncated out by the unconformity at the base of the Paleozoic sequence east of Picket Pin Mountain and west of the Boulder River.

Upper mixed zone - Plagioclase-olivine cumulate dominant, but there are interlayers and lenses of plagioclase cumulate and, rarely, of olivine cumulate. Immediately down-section from the upper contact, nonparallel lenses of plagioclase-olivine cumulate are enclosed in plagioclase cumulate. Lens endings are generally pointed, but some are blunt and squared off. These features possibly are evidence of tilting of the magma chamber during deposition of compositional layering. A lens of olivine cumulate 3-5 m thick crops out near the bottom of the map unit on the southeast side of Picket Pin Mountain, but pinches out completely in 100-200 m between there and the summit. Plagioclase-orthopyroxene cumulate and orthopyroxene-plagioclase cumulate form a layer 2-3 m thick at the base of the zone 1 3/4 km ESE of Picket Pin Mountain. In the Upper mixed zone and in underlying units of the Stillwater Complex the exposed grains of olivine tend to weather out, so that typical exposures of plagioclase-olivine cumulate have pitted surfaces. Magnetite is a characteristic alteration product of the olivine. Despite chemical decomposition of the olivine, the Upper mixed zone is locally erosion-resistant, and holds up Picket Pin Mountain and the ridge between there and the East Boulder River. Because the lithology is so distinct from that of the overlying units and next underlying unit, the zone is a reliable stratigraphic marker. Thickness is 60 to 110 m, except where this unit is truncated by the unconformity on Mount Rae, to the west, and in the drainage of Picket Pin Creek, to the east.'
1726|'Almost 100 percent plagioclase cumulate: an exceptionally monolithologic rock unit. A zone of sulfides, generally less than a few centimeters thick, is exposed near the top of the zone a little south of the summit of Picket Pin Mountain. In 1979 this zone was claimed, drilled, and extensively sampled by the Anaconda Mining Co. on both sides of Picket Pin Mountain and on the north side of Contact Mountain to the west, but the project was subsequently dropped for lack of exploitable concentrations of nickel, copper, and platinum-group metals. Pods of gossan as much as 30 cm thick are also exposed near the top of the zone at and near a pinnacle on top of the northeast edge of the faceted west end of Contact Mountain. Centers of the pods are replete with pyrrhotite. Oikocrysts of clinopyroxene appear locally throughout the unit. Thickness is 0-690 m; the zone is thickest on Contact Mountain, less than half as thick near Picket Pin Mountain, and it is truncated both east and west by the unconformity at the base of the Paleozoic sequence.'
1727|'Middle mixed zone - Contains three cycles. Sequence from top to bottom in each cycle is plagioclase-olivine and (or) plagioclase-orthopyroxene cumulate, and plagioclase cumulate. Though it is dominant throughout, the cumulus plagioclase component decreases and the cumulus olivine component increases from one cycle to the next lower one. Only the lowermost cycle seems to be present west of the Boulder River. The zone is cut out by unconformity on Mount Rae, to the west, and by the Horseman Thrust, on the ridge between Picket Pin Creek and West Fork Stillwater River to the east. However, part of the unit reappears from under the unconformity near the east end of the complex. About 90 m of plagioclase cumulate with a little postcumulus clinopyroxene is exposed along the road to Benbow Mine. Plagioclase-olivine cumulate occurs on a ridge northwest of the road. Thickness of the Middle mixed zone is 0-400 m.

Middle gabbro zone - Chiefly plagioclase-orthopyroxene-clinopyroxene cumulate and plagioclase-clinopyroxene cumulate on Contact Mountain, where the zone was first described and defined by Segerstrom and Carlson (1977). West of the Boulder River the lower third of the zone is plagioclase cumulate. A sharp change of lithofacies eastward across the East Boulder River brings in more plagioclase cumulate and cumulus olivine. A distinctive feature of the zone near Picket Pin Mountain is augen-like segregations of plagioclase parallel to regional foliation. Four-phase rock, plagioclase-orthopyroxene-clinopyroxene-olivine cumulate is identified in some outcrops, especially on the eastern part of the ridge between Picket Pin Creek and Iron Creek. To the west the zone is truncated by the un-conformity on Mount Rae. Near West Fork Stillwater River the unit is cut out along the Horseman Thrust, but farther east it reappears south of Horseman Flats. It is cut out again in the Stillwater River valley and farther east until it finally reappears near the road to Benbow Mine. There, the zone is chiefly plagioclase cumulate with post-cumulus orthopyroxene. Some plagioclase-clinopyroxene cumulate present. Thickness 0-280 m.

Lower mixed zone - Principally plagioclase-olivine cumulate with 5-40 percent cumulus olivine and smaller amounts of post-cumulus clinopyroxene. Plagioclase cumulate and plagioclase-clinopyroxene cumulate with scattered grains of cumulus olivine (<5 percent) make up some beds. The middle third of the zone is almost all plagioclase cumulate on the west side of the Boulder River. Alternating bands of plagioclase cumulate and plagioclase-olivine cumulate characterize outcrops at the bottom of the zone on the first spur ridge east of the Stillwater River. The exposure is discontinuous, as it is cut out by faulting and unconformity at five different places. The westernmost exposure of the unit is just south of Mount Rae. Thickness of the zone is 0-300 m.'
1728|'Mostly plagioclase cumulate with oikocrysts of clinopyroxene. The upper contact is defined at the top of a relatively thick plagioclase cumulate layer: sulfides were noted in this rock near the east end of Contact Mountain and on the first spur ridge east of the Stillwater River. Along the road to Benbow Mine cumulus olivine occurs in varying amounts throughout the zone, mostly <5 percent; some of the olivine is poikilitic in oikocrysts of clinopyroxene. Poikilitic olivine in plagioclase cumulate is also noted at the bottom of the zone on the first spur ridge east of the Stillwater River. The zone is exposed continuously along the entire outcrop of the Stillwater Complex, except where it is concealed by Quaternary deposits and except for one short stretch at West Fork Stillwater River and another a little west of the main Stillwater River that are cut out along the Horseman Thrust. Thickness 0-480 m.'
1729|'Lower gabbro zone - Largely plagioclase-two pyroxene cumulate. Layers of plagioclase cumulate, plagioclase-clinopyroxene cumulate, and plagioclase-orthopyroxene cumulate are interspersed throughout the sequence. "Pillow troctolite" (Hess, 1960, p. 82-83), a pegmatoid plagioclase-olivine cumulate, occurs as a crosscutting injection or replacement in fine-grained plagioclase cumulate and plagioclase-clinopyroxene cumulate at the top of the zone about 750 m west of the 10,056-ft summit of Contact Mountain. Lenses of plagioclase-olivine cumulate and olivine cumulate occur at the top of the zone southeast of Contact Mountain and southwest of Picket Pin Mountain. "Inch-scale" layered rock is exposed a few tens of meters below the top of the zone at various localities along the strike of layering. The classic exposure of this unusual rock is in a landslide along the road to the Mountain View mine on west side of valley of Stillwater River, where disc-shaped oikocrysts of clinopyroxene are alined edgewise to form vertical dark layers a few millimeters to 2 or 3 cm thick. The repeating dark layers are generally separated by 2-3 cm of light-colored plagioclase cumulate. Alternation of layers is fairly uniform for 10-20 m across strike, but deviations occur in which the layers are paired or even more complexly grouped. Other exposures of inch-scale layering, at the same stratigraphic position, are: (1) on both sides of the gorge of lower Brownlee Creek, about 1 km west of the East Boulder River, (2) on the spur ridge about 1.8 km east of the Stillwater River (a little olivine is present in the upper part of the layered zone here), and (3) on the spur ridge immediately west of Prairie Creek. A thick sequence of plagioclase cumulate is sandwiched in plagioclase-two pyroxene cumulate of the Lower gabbro zone between Brownlee Creek and Iron Creek. The middle of the Lower gabbro zone is interrupted by a few meters of plagioclase-olivine cumulate and olivine cumulate overlain by plagioclase cumulate well exposed as vertical beds in a cut on the road to Mountain View Mine in SW corner sec. 16, T. 5 S., R. 15 E. Plagioclase-olivine cumulate is interbedded with plagioclase cumulate through much of the sequence on the spur ridge about 1.8 km east of the Stillwater River, so that the Lower gabbro zone there bears little resemblance to a typical section on the south side of the 10,065-ft summit of Contact Mountain. Olivine gradually diminishes toward the eastern end of the complex, and it is not seen in exposures of the Lower gabbro zone along the road to Benbow Mine.  Repeating cycles of plagioclase cumulate, plagioclase-orthopyroxene cumulate, and plagioclase-two pyroxene cumulate can be recognized in the middle of the Lower gabbro zone for a short distance westward from Brownlee Creek.  There are at least two showings of inch-scale layering in plagioclase cumulate a little over 100m above the bottom of the zone.  One of these is on the spur ridge east of the Stillwater River. The other is about 75 m north of down-faulted limestone on the spur ridge west of Prairie Creek. Contact of the zone with the underlying Norite zone tends to be transitional, particularly from the East Boulder River westward to the divide between the East Boulder and main Boulder River. The transition is between plagioclase-two pyroxene cumulate above and plagioclase-orthopyroxene cumulate below. All gradations between these two rocks are exhibited within a stratigraphic range of about 200 m, where interstitial clinopyroxene and fine-grained cumulus clinopyroxene occur in varying proportions with coarser-grained cumulus orthopyroxene. Except where the unit is covered with fill deposits in the main river valleys, the Lower gabbro zone is continuously exposed from southwest of Mt. Rae to the east side of Black Butte, a distance of 40 km. Thickness 0-590 m. Near where it is cut off at either end by unconformity, the zone is only 100-200 m thick.

Norite zone - The upper contact is where rock containing cumulus orthopyroxene readily seen in hand specimen underlies rock devoid of easily recognizable cumulus orthopyroxene. The upper part of the zone is mainly plagioclase-orthopyroxene cumulate. Oikocrysts of clinopyroxene are common in this rock and also in interlayers of plagioclase cumulate. A group of mixed layers provides a major break in continuity about halfway down the sequence. There, through a stratigraphic interval of about 100 m, 28 distinguishable layers a meter or so thick have been counted in one section. This section includes eight olivine-bearing layers interspersed between layers of plagioclase cumulate and plagioclase-orthopyroxene cumulate. Among these strata lies a zone, centered approximately at the divide between Brownlee Creek and Graham Creek that for a distance of 5.5 km and through a thickness of 2.1 m, has an average grade of 0.65 troy oz of Pt and Pd per short ton. This is one of the richest known deposits of platinum-group metals (PGM) in the world. The PGM zone there occurs where a layer of olivine cumulate and a layer of plagioclase cumulate together first became dominant upsection from the base of the Norite zone (Todd and others, 1979, p. 461-462, 464). The Pt and Pd are contained in sulfides, native alloys, arsenides, antimonides, bismuthinites (Cabri and La Flamme, 1974). The principal PGM-bearing minerals are pyrrhotite and pentlandite. Geochemical sampling and the driving of two adits by Johns-Manville in 1976-1980 have shown that the package of mixed layers containing one or more zones of PGM anomalies extends through the entire 40 km of strike length of the Norite zone. Drilling and the driving of an adit by Anaconda in 1979-1980 confirmed the existence of ore-grade PGM near the main Stillwater River. Facies changes within the zone result locally in fewer olivine-rich layers, lensing of pegmatite, and changes in stratigraphic position and grade of PGM anomalies. Two ore zones with a stratigraphic separation of 6-8 m have been locally encountered by Johns-Manville (E. L. Mann, oral commun., August 1980). Ore-grade PGM is encountered through a stratigraphic interval of 20-26 m by Anaconda in the Minneapolis adit (R. N. Miller, oral commun., August 1980). Below the group of mixed layers there is an interval of plagioclase-two pyroxene cumulate, then a much wider interval of principally plagioclase-orthopyroxene cumulate to the bottom of the section. Off-lap and slump structures indicating floor tilt, as well as graded bedding are seen in the lower interval of plagioclase-orthopyroxene cumulate on the west side of the Stillwater River. Scattered injections of pegmatoid orthopyroxene cumulate (bronzite), irregular in shape, crosscutting the layering, and locally rich in sulfides occur at the base of the Norite zone in two areas: (1) for about 1 km northwest of the East Boulder River, and (2) between Iron Mountain and Iron Creek. These sulfides also contain anomalous concentrations of platinum-group metals and were intensively drilled and trenched by Johns-Manville before the more persistent zone of interest was discovered higher in the Norite zone. At the maximum thickness of the zone, across the east end of Contact Mountain, the generalized sequence from top to bottom is: plagioclase-orthopyroxene cumulate, 250 m; mixed group (distinctively plagioclase cumulate and plagioclase-olivine cumulate), 100 m; plagioclase-two pyroxene cumulate, 75 m; and plagioclase-ortho-pyroxene cumulate 275 m making a total thickness of 700 m. The plagioclase-two pyroxene interval thins considerably west of the Brownlee Creek-Graham Creek divide and east of the West Fork of the Stillwater. To the west, the entire Norite zone is faulted out by the Lost Creek fault, near the Boulder River, and to the east the outcropping zone disappears in the moraine of West Fishtail Creek.'
1731|'Includes trondhjemitic gneiss-amphibolite, paragneiss, and heterogeneous gneiss sequences of trondhjemitic gneiss, tonalitic gneiss and amphibolite. Also includes minor schist, quartzite, and iron formation (Van Gosen and others, 2000).'
1732|'Predominantly granitic gneiss and migmatite; commonly consists of alternating bands of more felsic and more mafic gneiss; contains inclusions of metasedimentary rocks (granitic gneiss of Van Gosen and others, 2000).'
1733|'Interlayered quartzite and amphibolite. Amphibolite typically contains 60 percent hornblende, 30 percent feldspar, 5 percent garnet, and 5 percent quartz. The abundance of garnet distinguishes this amphibolite from the hornblende-rich gneiss in the quartzofeldspathic gneiss. Quartzite is coarse-grained and locally contains minor garnet, feldspar, anthophyllite, biotite, fuchsite, and sillimanite. A few layers of chlorite schist occur in this unit.'
1734|'Gneiss that consists mainly of feldspars and quartz with variable amounts of hornblende and biotite. Ranges from gray to pink gneiss because of abundant orthoclase. Layers and small concordant bodies of amphibolite occur scattered throughout this gneiss.'
1735|'Biotite schist that includes minor quartzite, iron formation and amphibolite (Van Gosen and others, 1993).'
1736|'Gneiss composed of sillimanite, garnet, quartz, feldspar, and biotite. Contains distinctive twinned, white plagioclase porphyroblasts. Coarse-grained marble that contains both calcite and dolomite with minor biotite and magnetite(?) forms layers up to 100 ft thick.'
1737|'Includes Barney Creek amphibolite, George Lake marble, and Jewel quartzite of Van Gosen and others (2000). Includes amphibolite, dolomitic marble and marble, quartzite, minor schist, and iron formation (Van Gosen, and others, 1993). Exposed south of Livingston in the northwestern part of the Beartooth Mountains.'
1738|'Sills are usually associated with hornfels.'
1740|
1741|
1750|'Includes modern stream alluvium, terrace gravel, talus and related slope material, landslide debris, and unconsolidated glacial moraines and outwash gravel.'
1751|'Floodplain, terrace, and alluvial-fan deposits that include stream-deposited gravel, sand, and silt. Gravel and peat are in filled ponds and lakes.'
1752|'Shown separately only in area near Challis and Antelope Flat (4418 N., 11404 W.), 30 km north of southeast corner of quadrangle.'
1753|
1754|'Unsorted boulders, cobbles, pebbles, sand, silt, and clay in moraines and in glaciofluvial outwash. Belt of coalescent moraines along eastern front of Sawtooth Range has been attributed to two major late Pleistocene glaciations, the Bull Lake and the Pinedale (Williams, 1961).'
1755|'Yellowish-white to cream-colored, irregularly thin- to medium-bedded, locally finely banded deposits of travertine showing varying degrees of irregular cellular and concentric texture with local cavities and encrustations. Layering in most of the deposit is nearly horizontal. Many exposures at eastern margin have steeply inclined layering; some of these clearly are of slumped blocks; others could be of undisturbed travertine deposited on steep slopes. Thought to once have covered about 2.5 km2 on southwest side of Bradbury Flat (4426 N., 11410 W.). Probably related to presently extinct hot springs that issued from faults in underlying Paleozoic carbonate strata. Estimated thickness 100 m.'
1756|'Dark-gray to black, fine-grained ophitic basalt; consists chiefly of plagioclase laths embedded in augite, and scattered crystals of magnetite. Exposures include small cap on ridge immediately west of Grimes Pass (4401 N., 11549.8 W.) and small outcrops west of Paddy Flat (4445 N., 11559 W.), near northwest corner of quadrangle.'
1757|'Stratified, tan to gray, loosely consolidated arkosic sandstone and siltstone and interstratified conglomerate and thin-bedded, dark-gray to black shale in which are abundant impressions of upper middle to lower upper Miocene leaves (W. C. Rember, written commun., 1983). Formation also contains seams of low-rank coal as much as 30 cm thick, bedded intervals several meters thick of light-gray to white diatomaceous earth, and beds of gray volcanic ash as much as 30 cm thick. Formation crops out along west side of Middle Fork of Payette River northwest of Crouch (4407 N., 11558 W.). It was deposited in an intermontane basin and is now part of a west-tilted, down-faulted block. Minimum thickness 1,680 m; base not exposed.'
1758|'Thunder Mountain cauldron complex and environs:
These small rhyolite intrusions have potassium-argon ages of 39.80.9, 41.1-0.9, 42.41.5, and 45.21.5 m.y. (see table 1). Additional description see below.

Western and south-central parts of quadrangle:
Rocks are light colored and generally porphyritic, containing rounded and embayed quartz phenocrysts. Potassium feldspar phenocrysts are more plentiful than plagioclase. Matrices are pinkish gray and aphanitic. Modal compositions include rhyolite, quartz-latite, and rhyodacite. The rocks are altered: sericite is developed from feldspars and iron oxides from pyrite. Dikes range from a few meters to more than 30 m wide and are as much as several hundred meters long. Rhyolite dikes are more numerous near bodies of granite (Tg), to which they probably are related, and, like that rock, are more radioactive than other plutonic rocks or dikes. Granophyric matrices common in dikes cutting Idaho batholith rocks north of Stanley. Some dikes in that area also are composite, having marginal zones more mafic than rhyolite.'
1760|'Thunder Mountain cauldron complex and environs:
Sanidine from a sample taken from Monumental Creek (4456 N., 11512 W.) was dated by potassium-argon methods at 44.61.5. For additional description, see below.

Northern part of Van Horn Peak cauldron complex and Panther Creek graben:
Dikes and plugs of mostly light-gray, dense, phenocryst-poor rhyolite; locally contains conspicuous phenocrysts of sanidine as long as 8 mm and sparse phenocrysts of quartz, as at Red Rock Peak, along northern border of Challis quadrangle at long 1142530" W. Rock at Red Rock Peak grades into, and forms composite bodies with, quartz porphyry intrusions (Tqp). Sanidine from Red Rock Peak yielded potassium-argon age of 44.61.5 m.y. (see table 1).

Custer graben area:
Gray, white, and pink dikes, plugs, and domes that contain phenocrysts of alkali feldspar and quartz, and minor amounts of biotite and plagioclase.'
1764|'Thunder Mountain cauldron complex and environs:
Gray dacite porphyry and minor diorite porphyry. Consists of both extrusive and intrusive rock. These rocks mostly have a dense or cryptocrystalline groundmass but, locally, have a holocrystalline, fine-grained groundmass (diorite porphyry). Phenocrysts of plagioclase generally are conspicuous and, in Indian Creek area (4448 N., 11513 W.), commonly are 2-3 mm long. Quartz is sparse. Mafic minerals consist of varying proportions of biotite, hornblende, and pyroxene. Phenocryst content varies from about 20 to 50 percent. In places, dacitic rocks clearly intrude lapilli tuff (Tdq) and possibly younger tuff units as well. In other places, rocks appear to be stratiform, having flow layering that defines gentle dips and containing interlayered zones of flow breccia characteristic of contact zones between lava flows. As mapped, therefore, this unit in some places includes dacite lava that is correlative with the lower latite lava (Tll) and in other places includes dikes and irregularly shaped intrusives that probably are younger than lapilli tuff (Tdq). Also correlates in part with dacite and diorite porphyry (Tdc) mapped in western part of quadrangle (see p. 20).

Northern part of Van Horn Peak cauldron complex and Panther Creek graben:
A mixed sequence of gray and green-gray extrusive and intrusive rocks of intermediate composition; most are dacite porphyry that locally displays flow layering, flow brecciation, and dense to glassy groundmass indicating they are lavas. In places, porphyry is massive, has crystalline groundmass, and locally exhibits intrusive contacts with country rock as young as basal part of tuffs of Camas Creek-Black Mountain (Tc, see p. 7). Therefore, this unit, as mapped, probably includes intermediate lava as old as 51 m.y. and younger dikes and irregularly shaped intrusive masses 48 m.y. old or younger. Phenocrysts (30-45): q, 0 (in most rocks) to 5; af, 0; pf, 60-75; b, 1-12; hb, trace-25; px (mostly altered but in places includes both fresh opx and cpx), trace-20. Contacts are gradational over short distances from hornblende- and biotite-rich varieties to pyroxene-rich varieties. Thickness 0 to more than 500 m.

Twin Peaks caldera and southern part of Van Horn Peak cauldron complex:
Biotite from sample collected near Casto (4434 N., 11450 W.) gave potassium-argon age of 48.61.4 m.y. (see table 1). Sample collected from probable extrusive rock 8 km north of Casto yielded hornblende age of 46.92.8 m.y. and biotite age of 49.51.4 m.y. (see table 1).'
1778|'Thunder Mountain cauldron complex and environ:
Thickness 0 to more than 50 m.

Western and south-central parts of quadrangle:
Includes three small ridge caps of rhyolite and discordant rhyolitic tuff near headwaters of North Fork of Boise River (4405 N., 11511 W.) and, in northern part of area, exposures on headwaters of Rapid River (4440 N., 11502 W.) and on headwaters of Riordan Creek (4449 N., 11524 W.).'
1779|'Dikes and plugs of pink porphyry that varies greatly in size of phenocrysts and texture of groundmass; typically contains smoky quartz phenocrysts as much as 3-4 mm long, tabular alkali feldspar and sparse plagioclase phenocrysts as much as 6-8 mm long, and sparse flakes and books of biotite as much as 3 mm long, in dense micrographic groundmass of quartz and alkali feldspar; commonly, however, has microgranular or cryptocrystalline groundmass. Locally contains extremely large phenocrysts of resorbed quartz in bipyramids as much as 1 cm long and alkali feldspar and plagioclase phenocrysts as much as 3 cm. long in graphic groundmass. Single large sanidine crystal 3 cm long from dike east of Yellowjacket Creek (4459 N., 11424 W.) yielded a potassium-argon age of 44.41.0 m.y. (see table 1). The quartz porphyry is described as pink granophyre by Ross (1934). Some dikes contain rhyolite without quartz phenocrysts; in places these quartz-poor dikes were included with lapilli tuff (Tdq), in other places with rhyolite intrusions Tr, see below). Phenocrysts (19-35): q, 15-58; af, 37-83; pf, 0-12; b, trace-4.'
1781|'Dikes and plugs of basaltic composition similar to or same as basaltic lava (Tb, see below). Includes mafic to intermediate rocks, near Van Horn Peak and elsewhere, that are conspicuously porphyritic, containing phenocrysts of pyroxene (hypersthene, pigeonite, or both) and plagioclase as long as 5 mm; locally contains sparse biotite and hornblende.'
1783|'Thunder Mountain cauldron complex and environs, Northern part of Van Horn Peak cauldron complex and Panther Creek graben:
Corresponds to "Casto pluton" of Ross (1934) and of Cater and others (1973). Mostly equigranular pink granite: q, 22-34 (0.2-5 mm long); af (perthitic cloudy orthoclase and microcline), 31-57 (0.5-10.0 mm. long); pf, 18-33; b, 20-37; hb, 0-3.5; trace amounts of sphene and allanite. These rocks plot in granite field of both Johannsen (1948) and Streckeisen (1973). Also includes light-gray rocks that are distinctly richer in plagioclase and fall in quartz monzonite field of Johannsen (1948). Armstrong (1975) reports potassium-argon age on biotite of 43.91.3; Leonard and Marvin (1982) report potassium-argon age from the same locality, also on biotite, of 47.81.9 m.y. (see table 1). On Loon Creek (4443 N., 11448 W.), biotite from the granite has a potassium-argon age of 45.11.6 m.y. (see table 1). Biotite from fine-grained, light-gray rock exposed near Grouse Lake (4450 N., 11441 W.) has a potassium-argon age of 46.61.6 m.y.

Western and south-central part of quadrangle:
Pink to gray, medium- to coarse-grained granite characterized by pink perthitic feldspar. Relative proportion of salic minerals (calculated from the CIPW norm): q, 39; af, 34; pf, 27. Rock contains miarolitic cavities, locally lined with smoky quartz crystals, and is more radioactive than granodiorite of Idaho batholith. Hornblende from one sample was dated by potassium-argon methods at 44.31.3 m.y. (see table 1). Granite includes part of Sawtooth batholith (Reid, 1963).'
1788|'Varicolored, nonwelded to partly welded ash-flow and ash-fall rhyolite tuff. Sequence overlies and underlies a single genetically related, densely welded cooling unit of tuff of Castle Rock (Tck) having identical phenocryst mineralogy. Lower part of monolith-forming tuff locally includes unrelated soft, bedded tuff containing abundant biotite; includes several zones rich in small, variegated volcanic lithic fragments. Rock above and below tuff of Castle Rock (Tck) weathers to tepee-shaped hoodoos and other variously shaped monoliths. Unit typically contains vitric, silky pumice lapilli and fresh black glass shards, but zeolitized and otherwise altered in many places. Phenocrysts, (15-25): q, 33-50; af, 50-60; pf, 0-3. b, 0-1; hb, 0-trace; px (mostly pseudomorphs), 0-3; commonly contains smoky quartz and chatoyant alkali feldspar. Thickness 0-300 m.'
1789|'Within cauldron includes five cooling units of reddish ash-flow tuff and thin interbeds of ash-fall tuff. Upper cooling unit is densely welded and about 228 m thick. Beneath upper unit are, successively, two thin, partly welded, lithic-rich cooling units, each about 30 m thick; a cliff-forming, moderately welded cooling unit about 150 m thick; and a lowermost slope-forming, partly welded cooling unit rich in lithic fragments, about 190 m thick. Densely welded upper unit is inferred to correlate with densely welded part of outflow unit (Tmt). If this is the case, soft tuff preserved above densely welded unit in Panther Creek graben has been stripped away at Castle Rock (4449 N., 11425 W.). Phenocrysts, upper cliff-former (28): q, 47; af, 50; pf, 0.7; b, 0.3-0.7; altered cpx, 0.7; (base) to 2.9 (top). Phenocrysts in lower cliff former show considerable variation from base to top: q, 15 (base) to 45 (top); af, 78 (base) to 49 (top); pf, 3.8 (base) to 4.1 (top); b, trace (base) to 1.0 (top); hb, trace; cpx, 3.1 (base) to 1.4 (top). Same minerals are present in thin cooling units between cliff-formers and in thick, moderately welded lower unit. Quartz is slightly smoky throughout sequence, and all units contain zones of chatoyant alkali feldspar. Total thickness 620 m.'
1791|'Black and brownish-gray lava that probably ranges in composition from potassium-rich basalt to trachyandesite or latite; vesicular to dense; contains scattered small (0.5-2 mm long) phenocrysts of pyroxene and plagioclase in pilotaxitic groundmass composed of plagioclase laths, pyroxene, and glass; locally contains small altered olivine phenocrysts and commonly contains xenocrysts of quartz that have reaction rims composed of tiny pyroxene prisms and glass. Unit is intercalated with rocks as young as basal tuff of Castle Rock (Tck) and with rocks as old as tuff of Ellis Creek (Te, see p. 8). Thickness 0-50 m.'
1792|'Light-green-gray and reddish-gray, locally flow-layered, densely welded ash-flow tuff erupted during collapse of Castle Rock cauldron segment (see table 4). Consists of at least two cooling units. Locally, unit in Panther Creek graben is flow laminated and layered from base to top; these characteristics indicate that hot ash flows there coalesced to liquids before coming to rest. Elsewhere, especially on slopes south of West Fork of Camas Creek (4447 N., 11435 W.), rock is only locally flow layered and displays zones containing abundant brown-green pumice lapilli that are darker than light-gray or light-greenish-gray enclosing matrix. Abundance and relative proportions of phenocrysts vary greatly. Phenocrysts (20-35): q, 19-50; af, 25-45; pf, 15-40; b, 2-20; hb, trace-5; px, trace. Some quartz phenocrysts in this unit show a peculiar tendency to be biaxial, even where they are not obviously strained. They tend to be smoky and nearly everywhere are incipiently to strongly resorbed. Allanite is a common accessory mineral. Thickness 0-300 m.'
1793|'Light-greenish gray and reddish-gray tuff, commonly altered to yellow and various pastel shades; flow-layered and laminated, densely welded, locally containing recognizable well-flattened pumice lapilli. Ash flows in this unit coalesced to liquids before they stopped flowing. Named for sparse, but conspicuous, euhedral phenocrysts of water-clear, "plate glass" tabular alkali feldspar crystals as long as 5-6 mm and altered and inconspicuous euhedral plagioclase crystals as long as 5-6 mm. Spherulitic in several localities; unit has an altered perlitic basal vitrophyre. Phenocrysts (6-10): af, 30-40 (locally as much as 50); pf, 45-66; altered mafic mineral (probably pyroxene), 2-8. Unit is intruded by dense rhyolite at Singheiser (4451 N., 11424 W.) and Rabbit Foot (4453 N., 11420 W.) mines and is weakly mineralized. Thickness 0-300 m.'
1795|'A cauldron-filling sequence of mostly very densely welded ash-flow tuff consisting of 10 or more separate cooling units that all are characterized by small phenocrysts (about 2 mm long) that in upper part of sequence consist of plagioclase and fairly abundant mafic minerals, in middle part consist of plagioclase and sparse to moderate amounts of alkali feldspar, and in lower part consist of plagioclase and sparse alkali feldspar and quartz. Entire sequence contains abundant mafic minerals consisting mostly of altered pyroxene, and includes variable amounts of biotite and sparse hornblende. Lower part of sequence has more biotite and hornblende than pyroxene. Assemblage is similar to tuff of Eightmile Creek (Tem, see below) although phenocrysts make up a greater proportion of tuff of Eightmile Creek. Phenocrysts in upper cooling unit (11-40): q, 0-trace; af, 0-trace; pf, 67-75; b, trace-13; altered hb, 0-trace; altered pyroxene, 10-20. Phenocrysts in middle cooling unit (5-25): q, 0-trace; af, trace-20; pf, 65-77; altered b, trace-9; altered hb, trace-3; altered px, 3-10. Phenocrysts in lower cooling unit (3-15): q, 2-12; af, 2-8; pf, 60-75; altered b, 2-10; altered hb, trace-3; altered px, trace-10. Sequence appears to have been almost entirely confined to cauldron complex formed principally as result of eruption of tuff of Ellis Creek (Te, see below). Only thin, partly welded ash-flow tuff and minor ash-fall tuff appear outside the complex. Outflow units are mapped with tuff of Pennal Gulch (Tp, see below). Thickness 0-3,000 m.'
1796|'Northern part of Van Horn Peak cauldron complex and Panther Creek graben:
Outflow equivalent of tuff of Van Horn Peak. See below for additional description.

Corral Creek cauldron segment and area north and east of Challis:
Pale-grayish-red to yellowish-brown, densely welded rhyolite or quartz latite ash-flow tuff, probably a simple cooling unit. Phenocrysts (10-13): pf, 82-90; b, 7-13; altered px, 2-5. Black basal vitrophyre a few meters thick contains abundant small volcanic lithic fragments a few millimeters to a few centimeters in diameter. Biotite from vitrophyre has a potassium-argon age of 47.81.7 m.y. (see table 1). Unit has reversed magnetic polarity. Source for this unit is a vent at Van Horn Peak (4446.5 N., 11419.5 W.)-(Ekren, 1981). Thickness 0 to more than 100 m.'
1797|'Thin ash-flow tuff cooling unit of Camas Creek-Black Mountain lithology interbedded with thin-bedded ash-fall tuff of similar lithology and lacustrine tuffaceous siltstone, sandstone, and conglomerate. Thickness 0-100 m.'
1800|'Pink and orange-gray, flow-laminated, hydrated rhyolite glass that has retained its perlitic texture despite deep weathering and alteration; mapped in all localities to include subjacent and superjacent horizontal beds of tuff and tuffaceous sandstone. Quartz is amethystine to smoky and as much as 4 mm long. Phenocrysts (21-33): q, 27-35; af, 9-31; pf, 19-47; b, 6-12; hb, 4-6.5; altered px, 2. Thickness 0-35 m.'
1801|'Northern part of Van Horn Peak cauldron complex and Panther Creek graben:
Two or more cooling units of green-gray quartz latitic and rhyodacitic ash-flow tuff that together are more than 300 m thick near Sleeping Deer Mountain (4446 N., 11441 W.) within cauldron complex, but rarely exceed a few tens of meters each outside cauldron complex or Custer graben. Unit overlies tuff of Ellis Creek (Te), underlies the tuffs of Camas Creek-Black Mountain (Tc), and locally shares some characteristics of each unit. Included in tuff of Pennal Gulch (Tp) south of Table Mountain. Where densely welded and rich in phenocrysts, it is not easily distinguished from tuff of Ellis Creek; it differs only in containing significant amounts of alkali feldspar and fewer mafic minerals. Phenocrysts (14 (weakly welded) to 46 (densely welded within the cauldron complex)): q, 10-22; af, 6-16; pf, 44-63; b, 6-16; hb, 1-5; px, trace-2. Unit contains abundant apatite, modest amounts of zircon, and sparse allanite as accessories. Most quartz phenocrysts are slightly embayed. Large grains that are extensively embayed are common. Biotite from exposures of this unit near West Fork of Morgan Creek (4443 N., 11415 W.) has potassium-argon age of 48.41.7 m.y. (see table 1), which agrees with stratigraphic position of this tuff, below 47.8-m.y.-old tuff of Table Mountain (Ttm). Thickness 0 to more than 300 m.

Corral Creek cauldron segment and area north and east of Challis:
Light-gray and green-gray, massive-weathering, partly welded and densely welded quartz latite or rhyodacite ash-flow tuff; appears to be simple cooling unit in Corral Creek area (4445 N., 11414 W.), where it is poorly exposed and, in most areas, was not mapped separately at base of tuff of Pennal Gulch (Tp). Phenocrysts (25-35): q, 13-19; af, 12-18; pf, 47-57; b, 9-14; hb, trace-2; cpx, trace. Thickness 0-50 m.

Twin Peaks caldera and southern part of Van Horn Peak cauldron complex:
Erosional remnant of this tuff on lower Mill Creek (4432 N., 11417 W.) overlies thin-bedded tuffaceous sandstone, siltstone, and reworked pumice beds that in turn overlie aphanitic intermediate lava (TI, see p. 12). Tuff is light greenish gray to brownish gray, nonwelded, and only slightly devitrified; it contains pale-green to white pumice lapilli. Phenocrysts (approximately 26): af, 15; q, 22; pf (strong oscillatory zoning), 33; b, 23; hb (green), 7. On southwest side of Corkscrew Mountain (4432 N., 11423 W.), erosional remnants of tuff of Eightmile Creek are light gray to greenish gray, nonwelded, and pumiceous, containing medium-brownish-gray pumice lapilli that are darker than matrix. Crystals, as much as 2 mm long, commonly are broken. Phenocrysts (42): af, 15; q, 8; pf (strong oscillatory zoning), 64; b, 12; hb, 1. At Red Butte (4439 N., 11420.5 W.) about 60 m of this tuff underlies rhyolite of Red Butte (Trb). Tuff is nonwelded to partly welded, very pale gray, and rich in pumice. Phenocrysts (as much as 2.5 mm long) (27-33): af, 11-12; q, 17-22; pf (strong oscillatory zoning), 52-55; b, 13-15; hb, 0-2. From upper Spider Creek to upper Parker Creek (44 38 N., 114 33 W.), unit is greenish-gray, densely welded, and pumiceous; contains whitish-green pumice lapilli that generally are lighter than matrix. The tuff is altered to calcite and chlorite; sericite, clay minerals, and epidote locally are present. Biotite from sample from West Fork of Morgan Creek (44 42 N., 114 18 W.) has potassium-argon age of 48.41.7 (see table 1). Phenocrysts (25-35): af, 12-17; q, 9-27; pf, 43-66; b, 7-18; hb, 2-4.

Custer graben area:
Gray, greenish-gray, pale-brown, and grayish-pink, bluff-forming, pumice-rich, crystal-rich, densely welded, quartz latitic ash-flow tuff characterized by phenocrysts, as much as 4 mm long, of plagioclase, quartz, sanidine, biotite, amphibole, clinopyroxene, orthopyroxene, zircon, apatite, and allanite. Biotite from vitrophyre exposed west of mouth of Tenmile Creek (4428 N., 11435 W.) has potassium-argon age of 47.51.3 m.y. (see table 1); this age supersedes previously published age of 46.91.6 m.y. (McIntyre and others, 1982). Unit has reversed magnetic polarity. On west side of Eightmile Creek about 4 km above its mouth (4427 N., 11439 W.), four cooling units having total thickness of more than 215 m are exposed.'
1803|'Northern part of Van Horn Peak cauldron complex and Panther Creek graben:
Rhyodacitic, crystal-rich ash-flow tuff characterized by phenocrysts of plagioclase, strongly resorbed quartz, and abundant biotite and hornblende, all of which are present in subequal amounts. Rocks exposed within cauldron complex commonly are partly altered to chlorite, epidote, and associated minerals. Locally, as along West Fork of Camas Creek (4449 N., 11418 W.), abundant very fine-grained magnetite darkens rock. Sample from northeast of Duck Peak (4455 N., 11429 W.), in Panther Creek graben, has potassium-argon age on biotite of 48.41.6 m.y. (see table 1). Thickness 0 to more than 2,000 m.

Corral Creek cauldron segment and area north and east of Challis:
Light-green-gray, massive-weathering, densely welded rhyodacite ash-flow tuff that is outflow from Van Horn Peak cauldron complex. A multiple-flow compound cooling unit or, possibly, two cooling units; everywhere contains conspicuous pumice; contains zones within which pumice lapilli are lighter than matrix and zones within which lapilli are darker than matrix. Phenocrysts (36-50): q, 4-15 (commonly "worm-eaten" and as long as 4 mm); pf, 60-75 (as long as 6 mm); b, 12-20; hb, 8-16; cpx, trace. Thickness 0-300 m.

Twin Peaks caldera and southern part of Van Horn Peak cauldron complex:
Along lower Eddy Creek this unit consists of two outflow cooling units, each about 60 m thick, separated by 1-2 m of thin-bedded tuff and reworked, cross-bedded, fluvial tuffaceous sandstone containing abundant biotite. Ash-flow tuff in both cooling units is gray green and moderately welded; contains pale-green pumice lapilli as much as 3 cm long. Phenocrysts (28-34): q, 3-6; pf, 66-67; b, 22-24; hb, 5-6.'
1804|'Northern part of Van Horn Peak cauldron complex and Panther Creek graben:
Principally cliff forming, dark-gray, conspicuously porphyritic lava of dacitic composition; blocky weathering; inconspicuous flow layering; unit locally includes phenocryst-poor, dark purplish-gray latite or andesite. Phenocrysts, dacitic lava (25-40): q, 0-trace; pf, 60-70 (as long as 6 mm); b, 0-4; hb, 15-23; cpx, trace-15; opx, trace. In some areas mafic minerals are oxidized to black opaque iron oxides or replaced by chlorite and iron oxide. Latite or andesite lava contains 5-15 percent phenocrysts (0.5-2 mm long) of plagioclase and clinopyroxene, and traces of orthopyroxene and oxidized hornblende; locally, pyroxene and hornblende phenocrysts are as long as 1 cm. Biotite from sample collected near Red Rock Peak (4500 N., 11425 W.), in Panther Creek graben, gave potassium-argon age of 48.61.7 m.y. (see table 1). Sample from Little West Fork of Morgan Creek (4442 N., 11419 W.) has potassium-argon age on biotite of 51.11.8 m.y. (see table 1). Thickness 0 to more than 1,000 m.

Corral Creek cauldron segment and area north and east of Challis:
Thickness 0-900 m.

Twin Peaks caldera and southern part of Van Horn Peak cauldron complex::
Rhyodacite lava and agglomerate exposed southeast of Challis Creek near Corkscrew Mountain (4432 N., 11423 W.) and north of Challis Creek (4436 N., 11420 W.) between Pats Creek and Eddy Creek. Dark-brown-weathering, brown to gray, porphyritic, locally vitrophyric, massive rhyodacite lava and coarse agglomeratic breccias containing 0.2-3 m blocks of monolithologic rhyodacite porphyry in matrix of glassy to devitrified rhyodacite. Phenocrysts (28-44): pf (as much as 5 mm long), 60-75; b, 1-14; px (both opx and cpx), 7-35; hb, 0-13. Contacts between massive and agglomeratic phases of unit are irregular and commonly steep. Cavities filled with chalcedonic silica locally abundant. Biotite from sample collected from southwest side of Corkscrew Mountain (4432 N., 11423 W.) has potassium-argon age of 50.41.8 m.y. (see table 1).

Custer graben area:
In Custer graben consists chiefly of crystal-poor, potassium-rich andesite that contains phenocrysts, generally smaller than 2 mm long, of plagioclase and clinopyroxene. Characterized by propylitic alteration in Sunbeam mine-Estes Mountain area (4427 N., 11444 W.) and in area surrounding Custer (4423.5 N., 11441 W.).

Southeastern part of quadrangle:
Contains heterogeneous group of rocks erupted from numerous vents scattered over area from Challis to south edge of quadrangle. Individual, local units generally can be consistently distinguished during mapping at large scales (see, for example, Hobbs and others, 1975). Compositions mainly dacite and rhyodacite; contain as phenocrysts various combinations of the minerals plagioclase, biotite, amphibole, clinopyroxene, orthopyroxene, and, uncommonly, olivine or quartz. Includes minor amounts of potassium-rich andesite characterized by phenocrysts of pyroxene and(or) olivine. Has normal and reversed magnetic polarity. Ranges in age from about 49 m.y. to about 51 m.y. Potassium-argon ages on biotite are 49.21.2 m.y. and 51.11.7 m.y.; plagioclase is dated at 49.31.4 m.y. (see table 1).'
1809|'Corral Creek cauldron segment and area north and east of Challis:
Similar to intermediate and mafic lavas (TI), listed on p. 17. 

Twin Peaks caldera and southern part of Van Horn Peak cauldron complex:
Includes dark-gray to bluish-black, dark-brown-weathering, aphanitic, porphyritic, intermediate intrusive rocks containing 3-5 percent euhedral plagioclase phenocrysts as much as 6 mm long and 1-2 percent altered euhedral pyroxene phenocrysts. Exposed on Challis Creek at mouth of Eddy Creek (4435 N. 11419 W.) and on Moose Creek (4548.5 N., 11410 W.).'
1814|'Northern part of Van Horn Peak cauldron complex and Panther Creek graben, southeastern part of quadrangle, and Twin Peaks caldera and southern part of Van Horn Peak cauldron complex:
Predominantly aphyric, reddish-brown-weathering, gray, purple, and greenish-gray, blocky to platy lava, locally containing interbedded oxidized breccia. Olivine and pyroxene occur as phenocrysts in some samples. Plagioclase not commonly found as phenocrysts. Microphenocrysts include olivine, clinopyroxene, orthopyroxene, and sieve-textured plagioclase. Quartz xenocrysts commonly present. Plagioclase-rich groundmass commonly is trachytic or pilotaxitic and may contain apatite and reddish-brown, strongly pleochroic mica. In region surrounding Challis, rock compositions range from potassium-rich andesite to potassium-rich basalt, andesite probably predominating. Farther south, in area between East Fork of Salmon River and Jerry Peak (4403.5 N., 11406.5 W.), compositions range from potassium-rich andesite to latite. Latite is more common toward top of section. Magnetic polarity indeterminate in area near Challis; lava toward south has reversed magnetic polarity. Near Challis, the lava overlies tuff of Ellis Creek (Te, 48.41.6 m.y.) and is overlain by tuff of Eightmile Creek (Tem, 48.41.6 m.y. and 47.51.3 m.y.) and tuff of Table Mountain (Ttm, 47.81.7 m.y.). Toward south, lava overlies tuff dated at 49.02.9 m.y. (Tvs) and is overlain by tuff of Herd Lake (Th, 48.11.7 m.y.).

Corral Creek cauldron segment and area north and east of Challis:
In Corral Creek area (4445 N., 11414 W.), thickness is 0-700 m.'
1821|'Light-gray, tan, and pinkish-red, generally crystal-poor or only moderately crystal-rich, porphyritic intrusive rocks and minor flows. Rock typically contains phenocrysts of quartz and sanidine in variable amounts; plagioclase locally present in minor amounts. Locally contains minor biotite and, rarely, trace amounts of pyroxene. These rocks display fabrics ranging from massive to flow laminated to autobrecciated. In thin section, textures vary from glassy to devitrified to fine grained, allotriomorphic, and granular. In ridges between East Fork of Mayfield Creek and Yankee Fork (4430 N., 11440 W.) at least two generations of rhyolite are present. Older rhyolite is glassy to devitrified and is intruded by dikes and pluglike masses of more massive rhyolite. Narrow rhyolite dikes and irregularly shaped intrusive masses pervade west and north margins of Twin Peaks caldera and crosscut lower part of tuff of Challis Creek (Tcrl, see p. 12) and the caldera-wall slump debris (Tsd, see p. 11). Potassium-argon age of sanidine is 46.51.7 (see table 1).'
1822|'Light-gray to brown-gray, light-brown-weathering dikes of porphyritic trachyte and(or) rhyolite that contain phenocrysts of sanidine, as long as 5 mm, and locally contain minor amounts of pyroxene and biotite. Plagioclase crystals, where present, generally are small, resorbed, and mantled by alkali feldspar. These dike rocks occur principally within Twin Peaks caldera, where they intrude tuff of Challis Creek (Tcrl, see p. 12) and caldera-wall slump debris (Tsd, see p. 11).'
1824|'Light-gray to pinkish-red or lavender, red- to lavender-weathering, fissile to flaggy, flow-laminated, and locally autobrecciated intrusive rock along north and east margins of Twin Peaks caldera. Phenocrysts (9-21): af, 0-25; pf (strong oscillatory zoning), 53-69; b, 17-34; hb, 0-5. Locally, near contacts, rock is black and vitrophyric or perlitic, devitrified, and gray-green weathering. Rock has steep to vertical flow foliation and locally has isoclinal flow folds with steep to vertical axial planes of variable strike. Locally, this rock contains cavities lined with chalcedonic quartz. In hand specimen, rock resembles rhyolite of Red Butte (Trb, see p. 13), except that, unlike rhyolite of Red Butte, it generally contains scattered sanidine phenocrysts. Unit is in intrusive contact with tuff of Challis Creek (Tcr) in upper Pats Creek area (4436 N., 11421 W.) and in upper Eddy Creek above Eddy Basin (4440 N., 11427.5 W.). A pluglike mass (not shown on map) containing plagioclase, biotite, sanidine, and hornblende phenocrysts is on Spider Creek (4440.5 N., 11426.5 W.). This rock is light greenish-gray, medium-brown weathering, and steeply flow foliated; it contains abundant gas cavities lined with rosettes of gypsum and minor calcite.'
1827|'Dark-brown to purple-brown, dark-brown-weathering, porphyritic dikes or flows containing abundant phenocrysts as much as 3 mm in length of plagioclase and pyroxene, less abundant hornblende, and minor biotite. On lower Bear Creek (4434.5 N., 11424 W.) a probable dike of this unit, which appears to occupy ring-fracture fault of Twin Peaks caldera, contains phenocrysts of sanidine in addition to above minerals. Contacts of this unit near Mosquito Flat Reservoir (44 31 N., 11426 W.) are not exposed, and relations with tuff of Challis Creek (Tcr) are uncertain.'
1828|'Northern part of Van Horn Peak cauldron complex and Panther Creek graben:
Not shown separately in this area.  Massive to faintly flow-laminated and locally vitrophyric at intrusive margins. Present in area of East Fork of Mayfield Creek (4429 N., 11437 W.) and in Custer graben. In upper Tenmile Creek area (4428 N., 11437 W.), reddish-brown to lavender, porphyritic rhyodacite intrudes tuff of Eightmile Creek (Tem) and is intruded by porphyritic rhyolite (Trf). Phenocrysts (22-25): pf, 54-58; b, 10-15; hb, 23-26; op, 5-7. Potassium?argon age of intrusive mass on upper Tenmile Creek is 46.01.7 m.y. (biotite); 48.92.9 m.y. (hornblende).

Twin Peaks caldera and southern part of Van Horn Peak cauldron complex:
Massive to faintly flow-laminated and locally vitrophyric at intrusive margins. Present in area of East Fork of Mayfield Creek (4429 N., 11437 W.) and in Custer graben. In upper Tenmile Creek area (4428 N., 11437 W.), reddish-brown to lavender, porphyritic rhyodacite intrudes tuff of Eightmile Creek (Tem) and is intruded by porphyritic rhyolite (Trf). Phenocrysts (22-25): pf, 54-58; b, 10-15; hb, 23-26; op, 5-7. Potassium-argon age of intrusive mass on upper Tenmile Creek is 46.01.7 m.y. (biotite); 48.92.9 m.y. (hornblende) (see table 1).

Custer graben area:
Brown- and reddish-brown-weathering, crystal-poor rocks that contain phenocrysts less than 2 mm in length of plagioclase, amphibole or pyroxene, and minor biotite.'
1829|'Medium- to dark-gray, brownish-gray, gray- to brown-weathering, porphyritic intrusive rock containing abundant phenocrysts of plagioclase as long as 7 mm and less abundant hornblende, pyroxene, and minor biotite in pilotaxitic microcrystalline to devitrified, blotchy matrix. Where fine-grained, rock has steep flow foliation of variable strike and in places flow folds have steep axial planes. This rock intrudes tuffs of Camas Creek-Black Mountain (Tc) at head of Parker Creek (4437 N., 11432 W.). Unit is intruded by rhyolite (Trf).'
1831|'Heterogeneous deposit of coarse talus and megabreccia (following usage of Lipman, 1976) interfingering and admixed with ash-flow tuff. Deposits of this material are localized along ring-fracture system on southeast margin of Twin Peaks caldera (4434 N., 11423 W.) and in northern part of caldera, where they extend into caldera from its north and west margins. In lower part of unit are bedded, indurated, coarse conglomeratic sandstone and angular talus deposits, resembling concrete on fresh fracture; these deposits also form thin, lens-like layers and pods throughout the map unit. Megabreccia consists of tuffaceous matrix-supported to block-supported deposits of angular, unsorted pebble- to boulder-size clasts and house-size blocks of ash-flow tuff, intermediate and siliceous lava, epiclastic rock, and abundant fragments of tuff of Challis Creek. Ash-flow tuff matrix of megabreccia  is nonwelded and crystal poor; it resembles tuff of Challis Creek except for higher plagioclase content. Phenocrysts (4-20): af, 40-47; q, 37-57; pf, 3-17; b, trace. Thickness more than 400 m.'
1832|'Multiple flow, compound cooling unit of crystal-rich rhyolite ash-flow tuff. Phenocrysts (22-26 in basal nonwelded tuff, 36-44 in remainder of unit): af, 54-69; q, 25-45; pf, 0-3; b, trace; hb, rare; px, 0-4.5. Accessory minerals are zircon, allanite, and trace amounts of apatite. Sanidine phenocrysts, as long as 5 mm, are chatoyant. Quartz phenocrysts commonly are slightly resorbed, bipyramidal, and smoky. Phenocrysts are somewhat smaller and less abundant in basal part of unit than in densely welded tuff. This unit, like middle and lower cooling units (Tcrm and Tcrl), has little or no plagioclase or ferromagnesian minerals. Plagioclase does not generally exceed 0.5 percent of total phenocrysts, biotite is uncommon, and minor pyroxene grains are preserved only in most densely welded tuff. Except locally near base, this unit is medium-gray to brownish-gray, brown-weathering, densely welded, devitrified ash-flow tuff containing pumice lapilli as much as 12 cm long and 3 cm thick (uncommonly as much as 26 cm long and 2 cm thick) and scattered pebble- to cobble-size fragments of gray to lavender, aphyric intermediate to rhyolitic lava. Pumice lapilli are in places medium to rusty brown and darker than matrix or light gray and lighter than matrix. Sanidine has been dated by 40Ar-39Ar methods at 45.50.3 m.y. (see table 3). At base, this tuff is light gray to light brown, nonwelded to moderately welded, and glassy and contains more abundant lithic fragments than do rocks exposed above; lithic fragments less than about 8 cm in diameter constitute 4-6 percent of rock and include porphyritic intermediate lava, light-gray, flow-banded rhyolite (in places as much as 1 m long at base of unit), and fragments of ash-flow tuff that has mineralogy of tuff of Challis Creek. The most pumiceous nonwelded to moderately welded basal part of tuff is as much as 60 m thick and is overlain by densely welded tuff at the base of which is a laterally discontinuous vitrophyre as much as 6 m thick. Original top of unit is not exposed. Thickness is more than 700 m.'
1833|'Two, or possibly three, cooling units of light-gray to greenish-gray or brownish-gray, partly to densely welded, pumiceous rhyolite ash-flow tuff that weathers gray, light brown, or lavender. Phenocrysts (as much as 2 mm long) (15-26): af, 43-59; q, 38-57; pf, 0-trace; b, 0-1.5; px, 0-2. Pumice lapilli in upper cooling unit are greenish brown, darker than matrix, and as much as 6 cm, but generally less than 1 cm, long. In lower cooling unit, pumice lapilli are pale greenish gray and lighter than matrix. Sanidine from zeolitized middle unit gives an 40Ar-39Ar age of 45.90.2 m.y. (see table 3). Middle unit (Tcrm) typically is in sharp contact with overlying upper unit (Tcru). There are concentrations of lithic fragments near contact. Middle unit locally overlies thin tuffaceous sediments at contact with underlying lower unit (Tcrl). Thickness 22-48 m.'
1834|'Light- to dark-brownish-gray, brownish-gray-weathering, moderately to densely welded, crystal-rich, pumiceous rhyolite ash-flow tuff. Phenocrysts (2-4 mm long) (15-48): af, 50-71; q, 26-47; pf, 0-3 (generally less than 0.5); b, rare; px (preserved only in vitrophyre), 0-2. Variable amounts of pumice and vertical variation in compaction (welding zonation) within this unit, especially in upper part, suggest compound cooling. Unit shows similar alternating variations in crystal and lithic fragment content. Lithic fragments generally are small and scattered but locally are as much as 0.3 m in diameter and constitute as much as 10 percent of rock. They consist principally of flow-banded, aphyric, felsic lava and moderately crystal-rich, quartz- and sanidine-bearing ash-flow tuff that resembles tuff of Challis Creek. Pumice is lighter or darker than matrix depending on degree of welding, and lapilli commonly range from 1 to 6 cm in diameter but can be as much as 15 cm. Vitrophyric zones of this unit locally are as much as 22 m thick. Tuff forms distinct buff to pale-green, treeless or sparsely tree-covered outcrops where altered to zeolites north and west of Twin Peaks (4436 N., 11428 W.). Sanidine crystals from this unit were dated at 45.80.2 m.y. and 46.50.1 m.y. (see table 3). Thickness more than 610 m (base not exposed).'
1835|'Corral Creek cauldron segment and area north and east of Challis:  See both descriptions below.

Twin Peaks caldera and southern part of Van Horn Peak cauldron complex:
Reddish- to gray-brown, partly to densely welded rhyolite ash-flow tuff containing 13-45 percent phenocrysts (as much as 4 mm long): af, 38-70; q, 27-60; pf, 0-3; b, trace; px, 0-3. Comprises rocks outside Twin Peaks caldera that cannot be correlated with certainty with units within caldera. Outflow tuff of Challis Creek, where it caps high mountain peaks north and west of Twin Peaks caldera, consists of single cooling unit at least 200 m thick. Locally, as exposed on uppermost Tenmile Creek (4429 N., 11439 W.), outflow tuff of Challis Creek grades upward from crystal-rich, moderately welded tuff to very fine grained, crystal-poor ash-fall tuff. Tuff there and in nearby exposures on upper East Fork of Mayfield Creek (4430 N., 11439 W.) is interpreted to be associated with an early collapse segment of Twin Peaks caldera that is west of west margin of Twin Peaks caldera proper. This early collapse segment is obscured by a mass of intrusive rhyolite (Trf). Sanidine from this unit was dated by 40Ar-39Ar methods at 46.30.2 m.y,

Southeastern part of quadrangle:
Red, reddish-purple, yellowish-brown, or gray, densely welded, devitrified ash-flow tuff containing 5-20 percent crystals as long as 3 mm of chatoyant alkali feldspar and smoky quartz in matrix of fine shards. Locally contains abundant pumice. Also contains sparse zircon, allanite, biotite, and a few crystals of plagioclase. Near Challis, single cooling unit overlies an irregular erosion surface carved on underlying tuff of Pennal Gulch (Tp). Two, or possibly three, densely welded cooling units present in Spar Canyon-Sand Hollow area. One of these units may be younger than tuff of Red Ridge (Trr). Unit has normal magnetic polarity. Potassium-argon age of sanidine is 45.01.3 m.y.'
1838|'Heterogeneous deposit of cobble- to house-size blocks of volcanic rock. Blocks include highly fractured pyroclastic rocks that resemble tuffs of Camas Creek-Black Mountain (Tc), rocks that may be tuff of Ellis Creek (Te) and tuff of Eightmile Creek (Tem), intermediate porphyritic lava, and blocks of coarse-grained volcaniclastic rock. Indurated matrix consists of smaller fragments of same materials that make up the blocks. Exposed in slope west of lower Ibex Creek (4434.5 N., 11443.5 W.). Megabreccia is intruded on all sides by rhyolite (Trf) and gray porphyry (Tgp). Megabreccia is interpreted to represent caldera-wall slump debris shed from west margin of Van Horn Peak cauldron complex after eruption of tuffs of Camas Creek-Black Mountain (Tc). Thickness more than 150 m.'
1839|'Northern part of Van Horn Peak cauldron complex and Panther Creek graben, Corral Creek cauldron segment and area north and east of Challis - both descriptions below apply to these two areas:

Twin Peaks caldera and southern part of Van Horn Peak cauldron complex:
In Darling Creek area (4438 N., 11417 W.), unit consists of gray-brown to buff to pale-green or red bedded tuff, tuffaceous sediment, nonwelded ash-flow tuff, and pumice flows. Typical pumice-rich ash-flow tuff or pumice flows contain phenocrysts (2 mm in length) (9-14): af, 0-15; q, 0-7; pf, 62-83; b, 12-26; hb, trace. Ash-flow tuff ranges in thickness from 1 to 52 m and is rich in pumice. Noncollapsed pumice fragments in these tuff beds generally are 1-2 cm. in maximum diameter and constitute 30-70 percent of rock, so many of these units are pumice flows. Lithic fragments in these tuff beds typically are pebble-size clasts of aphyric felsic lava and intermediate porphyritic lava containing feldspar and biotite phenocrysts. Interbedded with pumice-flow tuff beds are buff to green and lavender, thin-bedded, fine- to medium-grained fluvial tuffaceous sandstone, siltstone, reworked pumice beds, and coarse conglomerate beds that contain debris-flow lenses and siltstone and range from 1 to 35 m thick. Map unit is at least 355 m thick and is unconformably overlain by tuff of Challis Creek (Tcr).

Southeastern part of quadrangle: 
Gray, pale pink, or pale green, silicic, crystal-poor pyroclastic flows and air-fall, both subaqueous and subaerial. Chiefly massive to crudely bedded, pumice-rich, coarse tuff and pumice-lapilli tuff, but also includes beds of sorted, thin-bedded volcanic sandstone and mudstone. Commonly contains crystals as much as 2 mm long of plagioclase, sanidine, and biotite, and subordinate or very minor quartz, amphibole, allanite, zircon, and apatite. Sparse carbonized or silicified plant fragments are present in some pyroclastic flows. Locally in exposures east and north of Round Valley (4430 N., 11411 W.) and northwest of Ellis (4441.5 N., 11403 W.), a ledge-forming vitrophyre as much as 15 m thick consists of black, crystal-poor, perlitic, rhyodacitic glass containing crystals of plagioclase, sanidine, clinopyroxene, and zircon. Some samples contain abundant lithic inclusions. Unit has reversed magnetic polarity. Tuff of Eightmile Creek (Tem) included within basal part of map unit south of Table Mountain (4444 N., 11412 W.). Thickness 0 to more than 370 m.'
1840|'Red, reddish-gray, lavender, pale-brown, or buff, pinkish-tan to reddish-brown-weathering, flow-laminated and layered rhyolite that forms a cap rock on Red Butte (4439 N., 11420.5 W.), east of Twin Peaks caldera. On ridge between mouth of Pats Creek and Eddy Creek, just north of Challis Creek (4435 N., 11420 W.), this unit contains basal flow-banded vitrophyre 10 m thick that grades upward into flow-banded rock that displays crude columnar jointing and contains abundant flattened gas cavities (as much as 8 cm long). Vitrophyre locally flow brecciated with blocks up to 0.3 m. To north, in Morgan Creek area (4440 N., 11417 W.), rhyolite locally displays pyroclastic characteristics and may represent a pyroclastic deposit that flowed after coalescing to liquid. Phenocrysts (2-5 mm in length) (5-16): pf, 76-81; b, 15-17; hb, 0-11; af (with reaction rims of pf), rare. Abundant accessory apatite and zircon. Allanite uncommon. Biotite from a sample collected on east side of Red Butte (4437 N., 11418 W.) has a potassium-argon age of 46.91.6 m.y. (see table 1). Thickness 0-250 m.'
1845|'A heterogeneous unit consisting primarily of poorly sorted, poorly bedded, coarse sedimentary breccia that contains angular to rounded, pebble- to boulder-size clasts of aphyric and porphyritic intermediate lava and fragments of siltstone and claystone in a matrix of coarse sand to clay. Also contains discontinuous beds of tan-gray to light-brown, light-brown-weathering, coarse conglomerate and thin interbeds of coarse-grained tuffaceous sandstone containing abundant grains of feldspar, altered ferromagnesian minerals, and minor quartz. Locally present are mudflow breccia deposits containing intermediate lava clasts in biotite-bearing epiclastic matrix and log-size and smaller fragments of petrified wood. Unit underlies potassium-rich andesite, latite, and basalt lava (Tl) exposed along lower Challis Creek (44 34.5 N., 114 18 W.). May be correlative with intermediate lava and breccia of mixed zone (Tmz) exposed in Corral Creek cauldron segment. Thickness 0-130 m.'
1850|'Custer Graben area:
Gray, brownish-gray and greenish-gray, holocrystalline, medium- to fine-grained dike rocks, primarily gabbro and diabase, made up chiefly of plagioclase and clinopyroxene; pyroxene commonly partly or wholly altered to chlorite. Have reversed magnetic polarity.

Western and southcentral part of quadrangle:
Rocks are dark green to gray and commonly porphyritic, containing phenocrysts of zoned plagioclase as long as 2 cm; compositions are primarily andesite, dacite, and latite. Phenocrysts of hornblende, somewhat altered to chlorite, and euhedral biotite also commonly present. Quartz phenocrysts are sparse. Phenocrysts are set in groundmass of andesine-oligoclase, minor potassium feldspar, hornblende, and magnetite. Sphene and allanite are common accessories. Dikes range from a few meters to more than 30 m wide and are as much as several hundred meters long. They are more numerous near exposures of Tertiary diorite complex (Tdc), to which they probably are related.'
1852|'Porphyritic to equigranular rocks that range in composition from granodiorite to quartz monzonite. Major element analysis of quartz monzonite resembles analysis of tuff of Eightmile Creek (Tem). Rocks exposed are in roof zone of pluton intruding intermediate lava (Tdf, see below); blocks of lava are common as inclusions, and in some exposures intrusion more closely resembles swarm of closely spaced dikes cutting lava, as first described by Anderson (1949). Aeromagnetic data and distribution of thin dikes indicate buried extension of intrusion for at least 3 km west of principal outcrop area. Intrusion and country rock both are propylitized; minor hydrothermal biotite locally developed in intrusion.'
1853|'Gray and grayish-red, chiefly crystal-poor rhyolite containing phenocrysts of alkali feldspar and quartz. On ridgecrest east of upper Basin Creek (4422 N., 11453 W.) it is unaffected by faults that offset underlying volcaniclastic rocks (Tps) and intermediate lava (Tdf).'
1854|'Nonwelded tuff sequence that overlies tuff of Eightmile Creek (Tem, see below) in Custer graben, chiefly east of Jordan Creek. Locally includes tuff of Ninemile Creek (McIntyre and others, 1982), a densely welded unit not shown separately on this map, and debris possibly derived from rhyolite domes in upper Jordan Creek area (4426 N., 114 44 W.) (Foster, 1982). Thickness more than 600 m.'
1855|'Custer Graben area:
Ash-flow and ash-fall tuff that overlies tuff of Eightmile Creek west of Bonanza (4423 N., 11443.5 W.). Coarser grained rocks in this unit are characterized by crystals of plagioclase, sanidine, and quartz (quartz more abundant than sanidine in most places); biotite is only mafic mineral present. On ridge west of Lightning Creek (4425.5 N., 11449 W.), thin flow of intermediate lava occurs within the unit.

Southeastern part of quadrangle:
Ash-flow tuff, thin-bedded volcanic sandstone, siltstone, and mudstone, containing local zones of impure lignite; unit exposed from Little Antelope Flat (4423 N., 11404 W.) southwestward to Spar Canyon area (4414 N., 11413 W.). Coarsest grained rocks in this unit are characterized by crystals of plagioclase, sanidine, and quartz (quartz commonly more abundant than sanidine); biotite is only mafic mineral present. West of mouth of Spar Canyon nonwelded and densely welded ash-flow tuff related to the tuff of Challis Creek are locally present but have not been mapped separately. Subaqueous pyroclastic flow that is probable equivalent of tuff of Eightmile Creek (Tem) crops out in Spar Canyon and in Sand Hollow. Conglomerate containing clasts of quartzite, slate, and granitic rock, in addition to volcanic clasts, caps sequence south of Spar Canyon and is exposed in hills east of Tub Spring (4415.5 N., 11411 W.).'
1859|'Twin Peaks caldera and southern part of Van Horn Peak cauldron complex: See both descriptions below.

Custer graben area:
Volcanic sandstone, conglomerate, siltstone, and mudstone exposed northeast of Basin Creek. The coarsest grained rocks in lower part of unit, which include volcanic sandstone, conglomerate, and massive, pumice-rich pyroclastic flow more than 15 m thick, contain crystals of plagioclase, sanidine, quartz, and biotite. Rocks higher in unit lack sanidine and contain plagioclase, quartz, biotite, and hornblende. Beds of nonvolcaniclastic arkosic sandstone locally present in upper part of unit.

Southeastern part of quadrangle:
Includes subaqueously deposited pyroclastic flows, mudflow breccia and conglomerate, volcanic sandstone, and mudstone exposed along the Salmon River west and south of Challis, near Centennial Flat, along East Fork Salmon River, along Road Creek, and along Herd Creek. Also includes subaerial ash-fall and ash-flow deposits intercalated with and overlying intermediate lava in and north of Squaw Creek drainage basin (4422 N., 11428 W.). Volcanic components of all these rocks contain plagioclase, biotite, and amphibole. Quartz is minor and variable in amount. Some samples contain a few grains of pyroxene. Coeval with parts of intermediate lava sequence (Tdf); ranges in age from about 50 m.y. to about 48 m.y. Potassium-argon dating on sample from southeast of Jerry Peak yielded ages of 49.01.8 m.y. on biotite and 49.02.9 m.y. on hornblende (see table 1). A subaqueous pyroclastic flow, about 12 m thick, that is probable equivalent of tuff of Ellis Creek (Te, 48.41.6 m.y.) occurs within this unit in area south of Centennial Flat. Arbitrarily included in this unit are outcrops of pyroclastic flow exposed south of mouth of Squaw Creek that contains significant alkali feldspar, in addition to plagioclase and quartz, and biotite as sole mafic mineral.'
1860|'Gray arkosic sandstone and local beds of conglomerate that contains pebbles and cobbles of gray quartzite. Occurs as discontinuous lenses at base of sequence east of Basin Creek (4418 N., 11451 W.). Many occurrences too small to be shown at this map scale.'
1861|'Rhyodacite plugs at Bradbury Flat-Black, columnar-jointed, glassy rhyodacite and gray, grayish-brown, or red-purple devitrified rhyodacite containing as much as 30 percent phenocrysts as much as 4 mm long of plagioclase, orthopyroxene, clinopyroxene, biotite, apatite, and opaque oxides.

Cross-cutting plugs of rhyodacite in bluff exposures along Salmon River west of Bradbury Flat (4426 N., 11410 W.) and in hills north and east of Bradbury Flat. Have normal magnetic polarity. Northeast-dipping slab of similar rock at southwest margin of Bradbury Flat has reversed magnetic polarity.'
1862|'Rhyodacite domes at Bradbury Flat-Black, columnar-jointed, glassy rhyodacite and gray, grayish-brown, or red-purple devitrified rhyodacite containing as much as 30 percent phenocrysts as much as 4 mm long of plagioclase, orthopyroxene, clinopyroxene, biotite, apatite, and opaque oxides.

Irregularly shaped domelike masses of rhyodacite in hills northwest of Bradbury Flat. Potassium-argon age for columnar-jointed rhyodacite exposed at northwest margin of Bradbury Flat is 39.71.2 m.y. (see table 1).'
1863|'Olivine-bearing intrusive rocks that have been mapped separately only along Road Creek (4410 N., 11410.5 W.), and Horse Basin Creek.'
1864|'Southeastern part of quadrangle:
Trends are primarily northeast.

Western and south-central parts of quadrangle:
Diabase dikes are the more common. Rock is dark and fine- to medium-grained; consists chiefly of lath-like crystals of plagioclase enclosed in matrix of pyroxene crystals. Diabase dikes are youngest dikes and crosscut all others. They are the most continuous and commonly trend northwest. Lamprophyric dikes are dark gray to black, fine grained, and somewhat porphyritic; commonly range from a few centimeters to a meter or so in width and are only a few meters in strike length. Augite, brown hornblende, biotite, and plagioclase are principal minerals of this rock, which is a young rock but its relation to the diabase is unknown.'
1865|'Dikes, sills, and plugs that commonly consist of brown- or reddish-brown-weathering, dark-gray, greenish-gray, or black, crystal-poor rocks containing variable proportions of phenocryst minerals clinopyroxene, orthopyroxene, olivine, and plagioclase. Exposed as dikes, sills, and plugs along Salmon River near Centennial Flat (4422 N., 11416.5 W.), in region between Summit Rock and Bald Mountain, and as altered, irregularly shaped intrusive masses north of Little Antelope Flat. Near Centennial Flat, intrusive rocks were altered by reaction with wet, semiconsolidated sediments they intruded to produce chlorite-, clay-, and carbonate-rich, light-greenish-gray rocks. Whole-rock potassium-argon age for the unaltered part of one intrusive mass is 48.21.4 m.y. (see table 1). Magnetic polarities are normal and reversed.'
1866|'Irregularly shaped, sill-like mass of medium- to coarse-grained syenite that crops out east of Tub Spring, in upper Spar Canyon (4415.5 N., 11411 W.). Rock contains potassium feldspar, clinopyroxene, biotite, apatite, and magnetite. Clinopyroxene commonly altered to carbonate; both clinopyroxene and biotite commonly altered to chlorite. Carbonate also occurs as veins. Some, if not most, carbonate may be primary. Marginal facies of intrusion are dark, basalt-like rocks containing altered olivine phenocrysts; thin sections show that these rocks have holocrystalline matrices made up chiefly of alkali feldspar and biotite. Emplacement of intrusion probably penecontemporaneous with eruption of nearby latite lava (Tl, see p. 17).'
1868|'Olivine-bearing basaltic lava and associated volcaniclastic rocks that crop out south of Road Creek (4410 N., 11410.5 W.).'
1869|'Red- and reddish-brown weathering, grayish-purple or reddish-purple, blocky to platy, crystal-poor ash-flow tuff containing phenocrysts less than 1 mm long of alkali feldspar (chiefly anorthoclase). Vitrophyre at east end of Red Ridge (44 06 N., 11429.5 W.) contains a few crystals of green pyroxene and amphibole. This unit found only along east flank of White Cloud Peaks (4411 N., 11427 W.) and in Spar Canyon-Sand Hollow (4413 N., 11412.5 W.) area. Thickness 0 to more than 140 m.'
1873|'Red-purple or red-brown, devitrified, flow-laminated, locally lithophysal, crystal-poor rhyolitic rock that contains phenocrysts of plagioclase, biotite, and clinopyroxene 1 mm long. Two cooling units, separated by breccia zone, present north of Herd Lake (4405 N., 11410 W.). In most places these rocks resemble rhyolite lavas; however, exposure on ridge about 3 km south of Jerry Peak reveals marginal vitrophyre rich in shards. This exposure and sheetlike aspect of deposit indicate that unit was emplaced as very hot ash flow that coalesced and moved like lava prior to final chilling. Biotite from vitrophyre has potassium-argon age of 48.11.7 m.y. (see table 1). Map unit has reversed magnetic polarity. Overlies unit Tl. Thickness 0-150 m.'
1875|'Black, gray, and greenish-gray vitrophyric rhyolite lava and gray to pink, banded, devitrified rhyolite lava containing 1-5 percent phenocrysts, as much as 2 mm in length, of plagioclase and biotite. Also contains hornblende, allanite, zircon, apatite, and opaque oxides. Some flows also contain alkali feldspar and quartz. Four flows that have aggregate thickness of about 235 m are present in butte east of Mill Creek Summit (4428 N., 11429 W.). Potassium-argon age on biotite is 48.51.2 m.y. (see table 1). All flows have reversed magnetic polarity.'
1876|'Dark, sparsely porphyritic basaltic and andesitic lava, exposed along Salmon River near Centennial Flat (4422 N., 11417 W.) that contains variable proportions of olivine, pyroxene, or plagioclase phenocrysts. Probably related to mafic intrusive rocks (Til) that crop out nearby.'
1879|'Dark, sparsely porphyritic basaltic and andesitic lava that crops out below, and is interbedded with, flows of intermediate composition lava (Tdf) in hills southwest of Challis. Mafic lava contains variable proportions of olivine, pyroxene, and plagioclase phenocrysts. Sample from Garden Creek (4429.5 N., 11419 W.), west of Challis, has whole-rock potassium-argon age of 50.31.5 m.y. (see table 1).'
1880|'Densely welded, vitrophyric ash-flow tuff and associated volcanic sediments exposed in ridges northwest and southeast of Germania Creek (4401 N., 11432 W.). Includes "ignimbrite of Germania Creek" of Motzer (1978). Ash-flow tuff contains as much as 40 percent phenocrysts, as long as 1 mm, of plagioclase, amphibole, clinopyroxene, orthopyroxene, and biotite. Mafic phenocrysts make up more than 40 percent of total phenocrysts. Ash-flow tuff resembles tuff of Burnt Creek (Tbc, below) except for preponderance of amphibole. More thorough sampling may show that this characteristic is not consistent. Has reversed magnetic polarity.'
1881|'Dacitic lava and ash-flow tuff, locally vitrophyric, but commonly rusty brown and devitrified, containing phenocrysts of plagioclase, orthopyroxene, clinopyroxene, amphibole, and biotite. More than 40 percent of total phenocrysts in ash-flow tuff commonly are mafic minerals. Presence of one thin ash-flow tuff cooling unit that has these mineralogic features within tuff of Sage Creek (Tsc) in Sage Creek drainage basin (4405 N., 11405 W.) shows that the two units are contemporaneous, despite large contrast in composition. Probably has normal magnetic polarity.'
1882|'Ash-flow and ash-fall tuff and associated sedimentary rocks characterized by phenocrysts of plagioclase and sanidine, together with minor biotite, amphibole, and rare pyroxene. Quartz not present. Exposed chiefly near southeast corner of quadrangle in the drainage basin of Sage Creek, and on ridge south of Sheep Mountain. There are isolated outcrops of this rock type, too small to show on map, opposite mouth of Spar Canyon, east of lower Herd Creek, and along East Fork of Salmon River northwest of mouth of McDonald Creek (4408.5 N., 11419 W.). At all these localities, these rocks crop out beneath volcaniclastic rocks mapped as Tvs. Near Sheep Mountain, tuff of Sage Creek is mixed with breccia and intermediate lava (Tdf); contact between the two units is arbitrary. In some samples of breccia containing blocks with phenocrysts of plagioclase, quartz, biotite, and amphibole, dominance of matrix by crystals of plagioclase and sanidine demonstrates intermingling of material from two sources. Has normal magnetic polarity.'
1883|'Chiefly cobble and boulder (as large as 2 m in diameter) conglomerate; black, pink, gray, or white quartzite clasts predominate near base, and volcanic clasts predominate near top. Matrix of conglomerate contains volcanic component throughout. Locally includes pyroclastic flow that contains lava blocks containing plagioclase, biotite, amphibole, and quartz phenocrysts. Present only near southeast corner of quadrangle. Also included in this unit is prevolcanic fanglomerate exposed southeast of Lone Pine Peak (4421 N., 11410 W.). Clasts in fanglomerate were derived from nearby exposures of Paleozoic rocks, which formed topographically high ridges prior to volcanism.'
1886|'Red-weathering, yellowish-gray, aphanitic rhyolite that contains sparse phenocrysts of quartz as long as 1mm and pyrite or pyrite casts. Forms massive outcrops. Rhyolite is well exposed on ridge southeast of Cape Horn Creek (4421.5 N., 11511.5 W.), where stock contains roof pendants of granodiorite (Kgd, see p. 21) and metasedimentary rocks (rp, see p. 26).'
1888|'Rhyolite to diabase dikes.'
1890|'Complex suite of rocks ranging from nonporphyritic diorite to porphyritic granodiorite, which is prevalent. Rock is characterized by abundance of hornblende, euhedral biotite, and magnetite, which together make up as much as 35 percent of it. Phenocrysts in porphyritic rocks are chiefly zoned plagioclase and pale-red perthitic microcline, which may be as long as 1 cm; phenocrysts are set in fine-grained, pale-red matrix. Quartz phenocrysts are rare. Relative proportion of salic minerals (calculated from CIPW norm): q, 19; af (microcline), 21; pf, 60. Rocks weather to chocolate-brown soil, darker than soil formed from granitic rocks of area. Diorite and dark-greenish-gray aphanitic andesitic phases are generally peripheral to porphyritic rock. Biotite, hornblende, and whole-rock potassium-argon ages for three samples collected in Jackson Peak (4405 N., 11525 W.) and Monumental Peak areas are 46.20.9 m.y., 46.60.5 m.y., 47.71.1 m.y., 48.23.0 m.y., and 46.01.7 m.y. (see table 1). In some areas this unit is mapped to include large numbers of andesite, dacite, and latite dikes (Td).'
1892|'Light-gray welded lithic tuff exposed north of Obsidian, near south edge of quadrangle. Weathers reddish-purple, brownish gray, and brown. Rock is light-gray ash-flow tuff that contains phenocrysts of sanidine and quartz in a fine, light-gray matrix.'
1893|'Dark-gray to black, thinly layered, flow-banded, aphanitic lava that has pilotaxitic texture. Contains olivine phenocrysts, rimmed by iddingsite, set in groundmass of andesine microlites and interstitial pyroxene and magnetite. Overlies rhyolitic flows where exposed on ridge top between Knapp and Beaver Creeks (4425 N., 11505 W.).'
1894|'Yellowish-gray to pale-red to purple, aphanitic lava that commonly shows flow-banding and flattened quartz-lined vugs along flow laminae. Contains phenocrysts of platy sanidine and rounded, embayed quartz. Rock erodes to conspicuous massive knobs on ridge line and to reddish, slabby scree. Includes minor amounts of rhyolitic tuff. Sanidine has a potassium-argon age of 37.62.1 m.y. (see table 1). Geologic relations suggest that this age is too young. Preserved in a graben between Knapp and Beaver Creeks (4423 N.,11508 W.).'
1896|'Rocks in the northern part of the Sawtooth Range, west of Stanley, were mapped in 1967-68 and not restudied and are shown on the geologic map (Fisher and others, 1992, in pocket) as Idaho Batholith (Ki), but probably are chiefly biotite granodiorite.'
1897|'Light-gray to white, fine to medium-grained granite having distinctive anhedral texture. Principal minerals are quartz (33 percent), potassium feldspar (29 percent), and plagioclase (An26-30, 33 percent). Biotite may constitute as much as 2 percent of rock, garnet is common, and feldspars are altered to sericite and small irregular flakes of muscovite. This rock, described as leucocratic quartz monzonite by Reid (1963) and by Kiilsgaard and others (1970), as aplite by Cater and others (1973), and as aplitic quartz monzonite by Anderson (1947), occurs as dikes and irregularly shaped stocks that are resistant to erosion and tend to form high points on ridges. Rubbly, weathered scree from these high points may be extensive on lower hillsides and may give the impression of being eroded from larger masses than actually exist. Intrudes biotite granodiorite (Kgd, see below) and is itself intruded by Tertiary granite (Tg) and stocks of Tertiary diorite complex (Tdc). It also occurs as small dikes and plugs intrusive into biotite granodiorite and granite (Kgd, see below) in exposures along east side of Stanley Basin. Potassium-argon ages of biotite from five samples range from 63.61.4 to 72.62.5 m.y. (see table 2).'
1898|'Gray to light-gray, medium- to coarse-grained, equigranular to porphyritic granodiorite; contains books of muscovite that are visible in hand specimen and make up as much as 5 percent of rock. Except for visible muscovite, rock is similar to biotite granodiorite (Kgd), with which it is transitional through zone about 2 km or more wide. It is exposed in western part of quadrangle and comprises what is considered to be core of Atlanta lobe of Idaho batholith. Includes quartz monzonite of Warm Lake of Schmidt (1964). Potassium-argon ages of nine samples range from 65.3 to 73.92.7 m.y. for biotite and from 68.80.2 to 74.72.7 for muscovite (see table 2).'
1899|'Gray to light-gray, medium- to coarse-grained, and equigranular to porphyritic rock. Plagioclase (An22-30) is chief component of rock, which has lesser quantities of quartz and potassium feldspar. Biotite is principal mafic mineral, constituting as much as 5 percent of rock in most places; however, east of Stanley Basin it makes up 25 percent of rock. Hornblende is rare. Biotite granodiorite is most common granitic rock of Idaho batholith and is exposed over vast areas. In western part of quadrangle rock was identified by Schmidt (1964) as granodiorite of Gold Fork. Biotite granodiorite is intruded into older tonalite (Kt, see below) and in the 60- to 90-m-wide contact zone it exhibits intensive primary foliation as well as xenoliths of tonalite. Includes foliated diorite in Loon Creek (4435 N., 11451 W.) and at mouth of Camas Creek (4453 N., 11444 W.). Potassium-argon ages of biotite range from 61.5 to 98.13.3 m.y. (see table 2).'
1900|'Mapped by Schmidt (1964) as leucocratic quartz diorite of Little Valley.'
1901|'Coarsely porphyritic granitoid rock containing metacrysts of pink potassium feldspar (microcline) from 3 to 10 cm long in medium- to coarse-grained matrix that contains roughly equal amounts of microcline, plagioclase, and quartz; generally 5-15 percent biotite and variable amounts of hornblende. Foliation commonly present and locally strongly developed in area west and north of Stanley Basin. Also included in this unit are rocks that form cores of stock at White Cloud Peaks and large pluton east of Stanley Basin. In those areas rocks are unfoliated porphyritic biotite granite and biotite granodiorite that contain metacrysts of microcline 1-3 cm long in medium-grained granitoid matrix containing predominantly 5-10 percent, and rarely as much as 20-25 percent, biotite and approximately equal amounts of quartz, potassium feldspar, and plagioclase. Equigranular margins of two bodies are separated from porphyritic granite cores by potassic metasomatized transition zone as much as 1.5 km wide that contains abundant veins and pods of potassium feldspar and locally abundant secondary muscovite that coats joints. Potassium-argon ages of biotite from four samples range from 62.6 to 842 m.y. (see table 2).'
1902|'Gray, medium- to coarse-grained, equigranular to porphyritic, commonly foliated granodiorite; biotite and hornblende are aligned in plane of foliation. Rock commonly is associated with xenoliths and pendants on high ridges in western part of quadrangle. It is intermixed with tonalite (Kt); the two rock types form border zone of Atlanta lobe of Idaho batholith.

For additional information see Kiilsgaard and Lewis (1985).'
1903|'Gray to dark-gray, medium- to coarse-grained, equigranular to porphyritic rock. Plagioclase (andesine) is dominant mineral of rock, some of which contains biotite or hornblende and which ranges from massive to highly foliated. It is exposed in western part of quadrangle, where it includes quartz dioritic gneiss of Donnelly (Schmidt, 1964), and in west-central part of quadrangle in Loon Creek drainage basin (4432 N., 11451 W.). East of Stanley and southwest of mouth of Warm Spring Creek (4408 N., 11558 W.) this unit is equigranular, medium-grained, granitoid rock containing 30-35 percent amphibole laths, 40-50 percent plagioclase, and about 20 percent quartz. Amphibole is partly altered to brown, highly pleochroic biotite and to epidote. Sphene is principal accessory mineral. Potassium-argon ages of biotite from three samples range from 71.92.5 to 81.62.9 m.y. (see table 2).'
1905|'Dark-grayish-green, medium- to coarse-grained rock containing primary mineral assemblage of calcic plagioclase, clinopyroxene, and magnetite, whose texture is overprinted by alteration assemblage of chlorite, pale-green acicular amphibole, albite, sphene, and small amounts of apatite, prehnite(?), pumpellyite(?), carbonate and(or) secondary quartz. Occurs as numerous small, irregular dikes, small plugs, and sill-like tabular masses scattered over area east and northeast of Clayton. Most commonly found intruded along or near thrust fault at base of Clayton Mine Quartzite (OCq). Fission-track age of 140.117.4 m.y. was obtained from zircon in quartzite immediately adjacent to contact with gabbro at mouth of Bayhorse Creek (4422.5 N., 11415 W.) (R. A. Zimmermann, written commun., 1983). This age for the zircon indicates time of track annealing caused by heat from gabbro intrusion. It also serves as limiting age for thrust fault beneath Clayton Mine Quartzite, already in existence prior to intrusion of gabbro.'
1906|'Well-exposed sequence of fine-grained, dark-gray, carbonaceous argillite, siltite, limy siltite, and silty limestone. Weathers dark brown, reddish-brown, or dark gray. Much of sequence is graded and has abundant cross-bedding, convolute structures, and prominent banded appearance. Measured section on north side of Pole Creek at confluence with Grand Prize Creek (4356 N., 11441 W.) at type locality in Hailey 1x2 quadrangle is about 2,000 m thick, but neither top nor bottom is exposed. Conodonts collected by C. M. Tschanz from low in section at Pole Creek are reported to be Leonardian-Roadian (upper Lower Permian) by Bruce Wardlaw (written commun., 1979). On Pungo Mountain a sequence about 100 m thick of thin-bedded limestone and calcareous argillite that have been extensively metamorphosed to tremolite-actinolite is questionably assigned to this unit. Sequence forms black soil. Mapped to include clean, well-sorted quartzite on east side of Pungo Mountain.'
1907|'Includes units 5 and 6 of Hall and others (1974). Thick sequence of gray and light-brown, fine-grained, calcareous sandstone that weathers dark brown and dark reddish brown. Interbedded in calcareous sandstone are fine-grained sandy limestone, fine- to medium-grained bioclastic limestone, and brown, thick-bedded, fine-grained quartzite. Cross-bedding and convolute structures are common. Unit is dated on basis of abundant fusulinids. Minimum thickness 3,400 m at type locality (Hall and others, 1974).'
1908|'Includes units 1, 2, 3, and 4 of Hall and others (1974). Lower part of Wood River Formation is present only from Railroad Ridge (4408.5 N., 11435.5 W.) at Little Livingston and Hermit mines south to Livingston mine. Unit 1 is chert and quartzite conglomerate present as thin fault slivers at Little Livingston and Hermit mines. It is overlain by succession about 150 m thick of fine-grained limy sandstone, silty limestone, and limy siltstone that includes units 2, 3, and 4.'
1909|'Medium- to dark-gray, thin- to thick-bedded, well-laminated argillite, siltstone, calcareous siltstone, and fine-grained calcareous sandstone; some local grit and nearly pure, medium-gray limestone. Weathers tan, medium brown to dark brown, and, locally, light gray, blue gray, and pink. Sandstone is predominantly very fine to fine grained; some medium sand and grit layers; localized thin beds of chert-like, very siliceous argillite. Rock composed of variable proportions of quartz (predominant), clay minerals, carbonaceous material, sericite, mica, feldspar (usually only few percent), lithic fragments (argillite, shale, chert, fine-grained quartzite), various accessory minerals, and carbonate. Faint to prominent lamination in most places; cross lamination, current bedding, and sole structures in many fine-grained, thin sandstone beds and laminae. Dark colors related to amount of carbonaceous material, which ranges from nil to nearly 100 percent in few impure, coaly seams. Age of this assemblage is poorly known. Megafossils recovered from blocks of float found near mouth of Mill Creek (4415 N., 11433 W.) were assigned a Mississippian age (Hobbs and others, 1975). Conodonts collected from lower Thompson Creek (4416.5 N., 11431 W.) and from Slate Creek (4412 N., 11436 W.) have Late Cambrian and Devonian ages (J. Repetski, written commun., 1984). Base of sequence as exposed in quadrangle is thrust fault; overthrust by Grand Prize Formation (Pg) between Warm Springs and Slate Creeks (4413 N., 11438 W.) and by Wood River Formation (P[Pw and [Pwl) near Washington Peak (4401 N., 11400 W.). Thickness and sequence of units indeterminate in most places because of isoclinal folding and thrust faulting. About 1,400 m is present along Last Chance Creek (4411.5 N., 11437 W.), but neither base nor top is exposed.'
1910|'Gray, fossiliferous, pure, thick-bedded, cliff-forming limestone and grayish-red-purple, impure, thin-bedded, slope-forming limestone. Top not exposed in quadrangle. Thickness about 400 m in area to east (Mapel and others, 1965).'
1911|'Medium-dark-gray, chert-bearing bioclastic limestone; weathers medium dark to medium light gray; chert medium dark to medium gray, weathers brownish-tan, forms discontinuous thin layers and nodules scattered along bedding. Medium to thick bedded. Forms ledges. Contains much crinoidal debris, many corals, and brachiopods. Locally contains jasperoid (black silica as replacement of carbonate rocks). Evidence obtained elsewhere in region indicates that this material was formed during or after Eocene volcanism (B. A. Skipp, oral commun., 1983). Fragments of what appears to be this material within conglomerate at base of volcanic sequence (Tcg) suggest that jasperoid in this area may be both older than and penecontemporaneous with the volcanic rocks. Present only in southeast corner of quadrangle. Thickness about 750 m.'
1912|'Succession of medium-bedded cherty limestone and impure limestone exposed as smooth, float-covered slopes in southeast corner of quadrangle. Upper half is impure, medium-dark-gray to medium-gray, cherty, microgranular limestone. Black chert abundant in layers and nodules. Weathers to medium- or light-gray, small, irregularly shaped blocks that have slight yellow or pink mottling. Lower half is very fine-grained sandy limestone, silicified in part. Float in lower half is more brightly colored and more angular than that of upper part. Locally, limestone is replaced by jasperoid; see discussion under Scott Peak Formation (Msp), above. Thickness about 200 m.'
1913|'Chiefly gray, ledge-forming, thick- to thin-bedded fossiliferous limestone; locally sandy, variably cherty, but in middle part also includes gray to yellowish-brown chert and quartzite granule to cobble conglomerate, sandstone, siltstone, and mudstone. Locally, limestone is replaced by jasperoid; see discussion under Scott Peak Formation (Msp), above. Thickness about 1,150 m.'
1914|'Poorly exposed unit of mudstone (or argillite), subordinate siltstone, partly calcareous claystone, sandstone, and minor pebble conglomerate. Extensively sheared; formation sustains steep slopes covered by slabby or platy, locally finely blocky or pencil-like fragments; weathers medium light gray, yellowish-gray, or light olive gray. Measured thickness 1,100 m in Lost River Range, east of quadrangle (Mapel and others, 1965; Sandberg, 1975).'
1915|'Light-gray to black, medium- to thick-bedded conglomerate, sandstone, siltstone, and mudstone. Conglomerate contains clasts as much as 20 cm in diameter of chert, quartzite, quartz, and argillite in sandstone matrix. Unit is series of proximal to distal turbidites (Nilsen, 1977). Crops out chiefly near southeast corner of quadrangle. An isolated outcrop at confluence of Herd Creek and Lake Creek (4407 N., 11414.5 W.) is questionably assigned to this formation. Thickness more than 3000 m.'
1916|'Grand View Dolomite - Includes microgranular, medium-dark- to medium-light-gray dolomite that weathers medium light gray and lighter and much recrystallized medium-light-gray to very light gray, fine- to coarse-grained dolomite that weathers grayish-orange or pale yellowish-brown. Scattered sandy intervals; a few shaly beds. Beds thick, commonly laminated. Formation moderately to highly resistant; forms blocky ledges and, locally, cliffs. At south end of, and southwest of, Grand View Canyon (4421.5 N., 1143.5 W.) map unit includes small patches of calcareous shale and dolomite elsewhere assigned to overlying Three Forks Formation (Hays and others, 1978). Thickness about 365 m.

Jefferson Dolomite - Resistant, well-exposed unit of medium-dark-gray to medium-gray and subordinate dark-gray dolomite, Weathers to similar dark colors, partly mottled, commonly having brown cast; a few beds weather medium light gray. Grain size ranges from microgranular to fine; little silt or sand; commonly fetid. Beds thick to very thick (0.3-1.5 m); some thin, regular lamination. Highly resistant, forms ledges and cliffs. Thickness about 300 m.'
1917|'Includes microgranular, medium-dark- to medium-light-gray dolomite that weathers medium light gray and lighter and much recrystallized medium-light-gray to very light gray, fine- to coarse-grained dolomite that weathers grayish-orange or pale yellowish-brown. Scattered sandy intervals; a few shaly beds. Beds thick, commonly laminated. Formation moderately to highly resistant; forms blocky ledges and, locally, cliffs. At south end of, and southwest of, Grand View Canyon (4421.5 N., 1143.5 W.) map unit includes small patches of calcareous shale and dolomite elsewhere assigned to overlying Three Forks Formation (Hays and others, 1978). Thickness about 365 m.'
1918|'Resistant, well-exposed unit of medium-dark-gray to medium-gray and subordinate dark-gray dolomite, Weathers to similar dark colors, partly mottled, commonly having brown cast; a few beds weather medium light gray. Grain size ranges from microgranular to fine; little silt or sand; commonly fetid. Beds thick to very thick (0.3-1.5 m); some thin, regular lamination. Highly resistant, forms ledges and cliffs. Thickness about 300 m.'
1919|'Unit B contains dark-gray to olive-gray, medium-bedded to very thick-bedded dolomite and minor dolomitic sandstone; unit A contains dark- to light-gray, medium- to thick-bedded, moderately silty dolomite; Beartooth Butte Formation contains gray and brownish-gray, medium- to thick-bedded, very fine grained quartzite, sandstone, and siltstone.'
1920|'Strikingly light colored dolomite that commonly forms ridges and peaks. Dolomite is predominantly medium light to light gray, mostly very fine to fine grained, and almost pure. Few scattered sandy intervals. Beds medium to very thick, mainly 0.3-1 m; locally, rock is massive and bedding is obscure. Joints common. Resistance to erosion high; forms rounded, light-gray to very light gray ledges and cliffs. Thickness 215-395 m.'
1921|'Medium-dark- to medium-gray, carbonate-bearing, fine-grained detrital rocks and impure carbonate rocks. Most are mudstone, siltstone, and very fine silty sandstone, mainly dolomitic, partly calcareous; less abundant and irregularly distributed are muddy, silty, or finely sandy microgranular to very fine grained limestone and dolomite; small amount of siltite and quartzite. Beds medium to very thick. Regular lamination, 3 mm or less thick, and cleavage that may be parallel or oblique to bedding common. Resistance to erosion moderate to weak. Upper part contains fossils of late Wenlock and probable Ludlow age. Thickness about 800 m in Lone Pine Peak quadrangle (Hays and others, 1978).'
1922|'Black, fissile, carbonaceous shale; bedding obscured by cleavage. Exposures totaling less than 1 km2 along lower reaches of Big Lake Creek and Pine Creek (4409 N., 11423 W.), tributaries to East Fork of Salmon River. Generally deformed, especially in highest exposures beneath thrust contact with Salmon River assemblage (Pzsr). Tentatively correlated with Ordovician Phi Kappa Formation to south, as suggested by Dover and others (1980). Maximum of 35 m of unit exposed, total thickness unknown.'
1923|'Upper and Middle Ordovician Saturday Mountain Formation is predominantly medium-dark- to medium-gray, microgranular to very fine grained, fairly pure dolomite that contains abundant (as much as 50 percent), irregular layers of medium-dark-gray chert in uppermost part of exposed section; some chert color laminated. Weathered surfaces medium light gray with yellowish cast. Forms blocky outcrops strongly ribbed by brownish-weathering chert. Contains considerable limestone, siltstone, and black shale in Squaw Creek area (4418 N., 11429 W.). Uppermost part of Saturday Mountain Formation may be Silurian. Middle Ordovician Kinnikinic Quartzite is fine-grained quartzite that is mainly light to very light gray with yellowish or brownish cast; locally as dark as medium gray or mottled medium dark and lighter gray; very fine to fine grained, contains some medium-size rounded grains; clean. Medium to thick bedded (maximum 1 m), bedding commonly obscured by shearing and partial recrystallization; local faint lamination. Middle Ordovician Ella Dolomite is medium- to dark-gray or brownish-gray, medium- to thick-bedded dolomite that contains thin laminae of silt and sand. Sequence in extreme northeastern part of quadrangle at Rattlesnake Creek (4458 N., 1140.5 W.) includes quartzite that possibly is older than Ella Dolomite. Upper 30 m or so consists of medium-gray, fine-grained, mostly foliated dolomite, locally massive. Lower 10 m includes foliated dolomitic quartzite, which grades downward to massive, cliff-forming, white to light-gray quartzite about 200 m thick consisting of virtually pure quartz in two size fractions, a framework fraction 0.4-0.6 mm in diameter and a matrix fraction 0.1-0.2 mm in diameter. Landreth (1964) noted a few pale-red-purple beds near lower part of unit and considered entire sequence to be Kinnikinic Quartzite. Dolomite sampled by P. J. Modreski from upper 30 m contains conodonts of Middle or Late Ordovician age (J. Repetski, written commun., 1983) and an orthoid brachiopod identified by J. T. Dutro, Jr., (written commun., 1983) as probably genus Valcourea. Dutro further suggests that the collection might well represent Ella Dolomite. This allows possibility that quartzite is older than Kinnikinic and equivalent to Lower Ordovician Summerhouse Formation (Ruppel and others, 1975; McCandless, 1982). Total thickness about 1,450 m.'
1924|'Heterogeneous sequence of dolomite, silty dolomite, and dolomitic sandstone that crops out in Squaw Creek drainage basin, northwest of Clayton. Estimated thickness about 150 m.'
1925|'Thickness of at least 600 m exposed only near Kinnikinic Creek north of Clayton. Top eroded; thrust fault at base.'
1926|'Divided into five map units by Hobbs and others (1975). Over most of its outcrop area, consists mostly of Clayton Mine Quartzite (Middle Ordovician or older), which is poorly sorted, coarse- to medium-grained, feldspathic quartzite that, in upper two-thirds of section, includes conglomerate layers, pebbly quartzite, and scattered pebbles. Very thin shale partings throughout. More than 1,000 m thick.'
1927|'Gray, greenish-gray, purple, thin-bedded, well-laminated slate, locally phyllitic. Commonly shows well-developed cleavage at angle to bedding. Includes thin beds of sandstone toward top. Thick lens of conglomerate at base in outcrops west of Challis. Thickness about 800 m.'
1928|'Light-gray to yellowish-gray, medium-bedded to very thick bedded dolomite in upper part and medium- to dark-gray, thin-bedded, fine-grained limestone in lower part. Dolomite contains dark-gray, silicified oval structures resembling pisolites in several layers as much as 9 m thick. Both upper and lower parts locally contain thin interbeds of siltstone, argillite, or fine-grained sandstone. Top of unit is erosional disconformity characterized by zone of probable paleokarst topography. Minimum thickness about 400 m.'
1929|'Dark-gray to black, slightly calcareous phyllite. As shown, includes small area of dolomite beneath phyllite, which is exposed in bed of Bayhorse Creek west of Bayhorse. Estimated thickness is 150-300 m.'
1930|'Includes fossiliferous upper Middle Cambrian shale and underlying sequence of quartzite and carbonate rocks of Cambrian or older age.'
1931|'Sequence of predominantly quartzitic strata containing subordinate dolomite interbeds and some thin argillitic interbeds and locally thicker argillite intervals. Quartzite generally deep red to dark purplish gray to medium gray; some thick zones of light pinkish or tannish gray and very light gray to white; medium grays and purplish grays predominate. Thin to medium bedded, platy, laminated; some massive units are thick bedded and structureless; mostly medium to fine grained, locally coarse grained and pebbly; lamination prominent in some thick layers; includes several zones of very coarse conglomerate or intraformational breccia. Much of thin-bedded platy quartzite shows ripple marks, flute casts, worm trails; abundant magnetite in parts of section. Dolomite very fine grained to dense, light to medium tan on fresh surface, weathers rich reddish tan to brown; beds dispersed in quartzite and range from 0.2 m to several meters in thickness; restricted to area within 1 km east from Beardsley Hot Springs (4431 N., 11410 W.). Argillite occurs as laminae or thin interbeds in much of quartzite sequence and locally forms continuous sequence as much as 100 m thick; generally thin bedded, fissile; dark gray or purplish gray, in places altered to deep gray green. Many argillaceous layers metamorphosed to phyllite close to thrust faults. Sequence of rock types is indeterminate because of complex structure and discontinuity of exposures. General characteristics of strata and structural relations to Swauger Formation suggest possible correlation with Late Proterozoic Wilbert and (or) Lower Ordovician Summerhouse Formations (Ruppel, 1975) or with formation of Tyler Peak of Early Cambrian age (McCandless, 1982).'
1932|'Includes schist, quartzite, and calc-silicate rocks. At some places graphite is common constituent of rocks. Includes Thompson Peak Formation of Reid (1963).'
1933|'Exposures of these rocks east of Big Baldy Lookout (4447 N., 11413 W.) are principally staurolite-muscovite-biotite-quartz schist and locally, according to B. F. Leonard (written commun., 1983), contain garnet and andalusite.'
1934|
1935|
1936|'Thin- to medium-bedded and interbedded fine-grained, platy, pink to greenish-gray quartzite and dark purplish-gray quartzitic phyllite containing some zones of laminated purple, sandy argillite. Quartzite is feldspathic, locally containing much coarser mica on bedding planes, and has conspicuous ripple marks and other sedimentary structures. Some thicker quartzite beds similar to Swauger Formation in general characteristics. Base of sequence is gradational through distance of a few meters with the Swauger Formation on which it lies; top not known; minimum thickness about 1,300 m (Hobbs, 1980).'
1937|'Light-pink, pinkish-tan, purplish-gray to locally red, medium- to coarse-grained, fairly pure, well-sorted quartzite; commonly contains several percent feldspar; medium to thick bedded, locally prominent cross-lamination; few very thin shaly partings. Base not exposed; top seems to grade over several meters into Lawson Creek Formation (Yl). Minimum thickness about 3,000 m.'
1939|'Mainly siltstone and fine-grained sandstone; medium-greenish-gray to grayish-red-purple to dark-gray, thin-bedded, laminated siltstone containing irregular streaks and lenses of light-gray, pinkish to pale-brown sandstone cemented by ferrodolomite. Sandstone lenticles are typically a few millimeters to several centimeters thick and 1 m, more or less, long, although much longer lenses are known. Medium-gray to brownish-gray to light-gray or pale-red, feldspathic, fine-grained quartzite beds several centimeters in thickness occur in what appear to be stratigraphically higher parts of unit. Ripple marks and other sedimentary structures are abundant, and many bedding surfaces are coated with detrital mica; lamination and cross-lamination in fine-grained sandstone common. Disconnected exposures and complex structure prevent accurate correlation of beds and determination of thickness. No base or top exposed in quadrangle. It is possible that upper part of section mapped as Yellowjacket Formation (Yy) east and north of Iron Lake (4454.5 N., 11411.5 W.) and north of Iron Creek (4456 N., 11404 W.) actually is Apple Creek Formation.'
1942|'White, off-white, and light-brownish-gray, massive-weathering, thin- and thick-bedded, clean quartzite. Except for outcrops at top and base, bedding is obscure; crossbedded in beds 0.5-1.0 m thick; contact at base and top transitional with subjacent and superjacent Yellowjacket. Intensely fractured and sheared in most places. Quartz averages about 85 percent; feldspar averages 5-15 percent and consists of microcline, non-perthitic orthoclase, and sparse albite. Rocks near base and top contain as much as 10 percent biotite, sericite, and iron oxide formed from original clay-rich cement. Thickness 0-1,100 m.'
1943|'In Yellowjacket area corresponds to "hornblende quartz diorite" of Ross (1934), who considered rock to be Tertiary in age. This unit is mixed sequence of mostly gray, melanocratic rock ranging in composition from reconstituted gabbro to mafic-rich quartz monzonite. Composition of gabbro from near Middle Fork Peak (4458 N., 11439 W.): pf (1-10 mm long), 34.4; b, 2.8; hb (mostly after px), 18.4; fibrous actinolite-tremolite, 5.2; nonfibrous actinolite-tremolite, 15.1; chlorite, 7.6; black opaque oxides, 10.8; apatite, 5.7. According to Ross (1934, p. 58), typical hornblende quartz diorite is nearly white and contains the following minerals: q, trace-5 (locally as much as 20); af, trace-10; pf, 60; hb and b (mostly intergrown), 20-40 (locally hb, 43; b, 38). Rock commonly is altered to epidote, chlorite, sericite, and calcite. Cater and others (1973) considered these rocks to be Precambrian in age, and Peale (1982, p. 58) considered them to be Cambrian(?)-to Ordovician(?). Diorite and quartz diorite are part of composite mass that includes syenite (sr, see below). Gabbro and diabase may be as old as Precambrian, but ages of other rocks of this unit clearly are uncertain. Karl Evans (written commun., 1984) obtained an Ordovician age on zircons from syenite in this map unit from a locality a few kilometers east of Middle Fork Peak (4458 N., 11439 W.).'
2050|'Landslides are typically developed at the unconformity between Tertiary volcanic units and the Precambrian basement, possibly in bentonite beds situated at the base of the Tertiary volcaniclastic sequence.'
2051|'Younger alluvium generally confined to the present flood plain developed along active rivers and streams.'
2052|'Includes gravel deposits at elevations above present active flood plains and some deposits that contain a significant glaciofluvial component.'
2053|'Deposits of travertine on the east side of the Yellowstone Valley above Gardiner have been quarried for many years for decorative stone. Two distinct U-Th ages have been reported for this travertine deposit - 19.570.12 ka and 22.640.17 ka (Pierce et al., 1991). Modern travertine at La Duke hot springs and at Chico hot springs are too small to show at the scale of this map.'
2054|'Glacial lake deposits shown only in the Tom Miner and Cinnabar basins and along the Yellowstone Valley where they consist of varved silt and clay.'
2055|'Unsorted and unstratified material in glacial moraines.'
2056|'Welded ash flows. Shown in Yellowstone National Park (after U.S.Geological Survey, 1972).'
2057|'Basalt flows in the Gardiner area (after Van Gosen, et al., 1993).'
2058|'Welded ash flows. Shown for Yellowstone National Park (after U.S. Geological Survey, 1972).'
2059|'Alluvium, colluvium, talus, landslide deposits, rock glaciers, glacial and glaciofluvial deposits, and boulder fields (after Wilson and Elliott, 1977, also shown for those area [sic] mapped by Van Gosen, et al., 1993 and U.S. Geological Survey, 1972).'
2060|'Includes the middle Miocene Hepburns Mesa Formation (exposed at the mesa of the same name) that consists of sediments deposited in and adjacent to a perennial saline lake (Barnosky, 1989). Also included are tan-weathering silty claystones that contain unaltered volcanic glass that are poorly exposed west Yellowstone Valley in the northwestern part of the Gardiner quadrangle.'
2061|'Two basalt flows are exposed on Hepburns Mesa. A K-Ar date on the upper flow yields a date of 8.4 Ma (Bush, 1967). However Locke, et al (1995) suggest that the basalt on Hepburns Mesa is correlative with basalt west of Emigrant that has a 2.2 Ma date. The upper flow exposed on Hepburns Mesa is black to dark gray and generally contains scattered plagioclase and olivine phenocrysts whereas the lower flow contains labradorite, augite, and olivine phenocrysts (Bush, 1967).'
2062|'Dikes, sills, and irregular-shaped bodies; andesite, quartz latite, dacite, and rhyolite; commonly porphyritic (After Van Gosen et al., 1993).'
2063|'Volcanic and volcaniclastic rocks including basaltic, andesitic, and dacitic flows and flow breccias, rhyolitic ash-flow tuff and vitrophyre, tuff breccias, lahars, agglomerates, agglutinates, conglomerate, and minor andesitic and dacitic intrusive bodies (After Van Gosen et al., 1993).'
2064|'Stock near head of Emigrant Creek (After Van Gosen et al., 1993).'
2065|'Generally massive and porphyritic with large quartz and feldspar phenocrysts in a chocolate brown, glassy matrix. At some localities appears altered with green alteration product. May be associated with welded tuff included within Tfpy.'
2066|'Dominantly light-colored andesitic volcaniclastic rocks and andesite lava flows.'
2067|'Includes thin planar pumiceous beds that are interpreted to represent air fall deposition. These beds also contain a few andesite pebbles. Also included in Tfpy is welded tuff with large phenocrysts of quartz and feldspar. These tuffaceous beds are altered to mottled purple and gray bentonitic clay that contains sand-size material consisting of quartz, biotite, and lithic fragments.'
2068|'Stock composed of multiple phases of andesitic intrusive breccia, monzodiorite, quartz monzodiorite, and quartz monzonite; cut by minor granite dikes (After Van Gosen et al., 1993).'
2069|'Reddish to gray, altered, hornblende porphyry with sparse feldspar laths. In hand specimen the rock appears massive, but when viewed from a distance flow geometry is obvious. Some flow breccia. Shown in area west of the Yellowstone River.'
2070|'Stock, laccoliths, sills, dikes, plugs, and irregular-shaped bodies; includes some andesitic and rhyolitic rocks (After Van Gosen et al., 1993).'
2071|'Pink to light gray, fine-grained, feldspar-hornblende porphyry. Small hornblende phenocrysts much more abundant than feldspar phenocrysts. Shown in area west of the Yellowstone River.'
2072|'Also exposed west of the Absaroka Beartooth Study Area (After Van Gosen et al., 1993).'
2073|'Andesitic volcaniclastic rocks.'
2074|'plugs, laccoliths, dikes, sills, and irregular bodies.'
2075|'Light-colored ash flow tuff.'
2076|'Dominantly light-colored andesitic rocks.'
2077|'Light-colored rhyodacite ash flow tuff.'
2078|
2079|'Well too poorly stratified. This unit is thought to be correlative with the Sepulcher Formation of the Washburn Group as mapped by the U.S. Geological Survey near the northern boundary of Yellowstone National Park (1972).'
2080|'Commonly autobrecciated; includes some epiclastic lenses. This unit is thought to be correlative with the Mount Wallace Formation of the Sunlight Group as mapped by the U.S. Geological Survey near the northern boundary of Yellowstone National Park (1972).'
2081|'(after Chadwick, 1982)

At the Point of Rocks volcanic center, epiclastic breccias and vesicular vent breccias and agglomerates are intercalated with autobrecciated lava lenses and sheets.  Major breccia sheets dip outward quaquaversally from the Point of Rocks area and become more stratified.  The Point of Rocks breccias, which are treated as one unit on the map, are intruded by numerous andesite and dacite dikes and dacite plugs.'
2082|'(after Chadwick, 1982)  Massive hornblende andesite

At the Point of Rocks volcanic center, epiclastic breccias and vesicular vent breccias and agglomerates are intercalated with autobrecciated lava lenses and sheets.  Major breccia sheets dip outward quaquaversally from the Point of Rocks area and become more stratified.  The Point of Rocks breccias, which are treated as one unit on the map, are intruded by numerous andesite and dacite dikes and dacite plugs.'
2083|'Description of individual breccia units from Chadwick (1982).

Unit B, 130 ft thick, Brown, tan, gray-green; altered clasts of pyroxene and hornblende andesite and some dacite.

Unit D, 130+ ft thick, Similar to Unit E, but green to tan; strongly chloritized.

Unit E, 250+ ft thick, Gray to greenish-gray; probably epiclastic; contains clast fo altered pyroxene and hornblende andesite, some dacite; crudely stratified with one well-stratified sandy unit.

Unit H, 40 ft thick, Clasts of white, pink and gray argillized, hematized biotite dacite and andesite in fragmental matrix; grades downward into unit G.'
2084|'Includes minor intrusions.

Description of individual flow units from Chadwick (1982).

Unit A,  270+ ft thick., Black augite andesite, sparse hypersthene; base not exposed.

Unit C, 140 ft thick, Black, microcrystalline andesite with augite, subordinate hypersthene, minor chloritized hornblende (?).

Unit F, 400+- ft thick, Blue-black to gray hornblende-augite andesite, considerable propylitized and hematized.  Along Dry Creek, locally coarsens near intrusive masses and veinlets of granodiorite and dacite, where it may contain sparse biotite.

Unit G, 650+- ft thick, Dark-gray to greenish-gray augite-hypersthene-hornblende andesite; contains red hematite specks.'
2085|'Unit added during present mapping.

Hornblende-augite andesite porphyry;  pilotaxitic to swirly pattern of microlites; irregularly intrudes units F and G. (thickness up to 600 ft / 185 m).'
2086|'Dikes and sills of andesite and basalt (After Van Gosen et al., 1993).'
2087|'Laccoliths, plugs, dikes, sills, and irregular-shaped bodies of fine-grained and porphyritic rhyolite, dacite, quartz latite, andesite, and diorite (After Van Gosen et al., 1993).'
2088|'Exposure near Cinnabar Creek added by MBMG, no older reference found.  Exposure near Hyalite Reservoir described by Wilson and Elliott (1997).'
2089|'(After Wilson and Elliott,1997) In descending order, includes Mowry Shale (Upper Cretaceous) and Muddy Sandstone, Thermopolis Shale, and Kootenai Formation (Lower Cretaceous).  Includes Mowry Shale except along Gallatin River in central part of map area where Mowry is included with undivided Upper Cretaceous sedimentary rocks unit (Ku); see unit Ku for description of Mowry Shale.  Upper part of Muddy Sandstone is gray to tan sandstone and arkosic sandstone; middle part is dark-gray siltstone, fine-grained sandstone, and shale; lower part is poorly sorted, ledge-forming, crossbedded sandstone; total thickness about 125-350 ft (Tysdal and Simons, 1985).  Upper part of Thermopolis Shale is dark-gray, locally carbonaceous, fissile shale; lower part is brown, rusty-weathering sandstone with cross-beds and ripple marks; total thickness 200-250 ft (Tysdal and Simons, 1985).  Upper part of Kootenai Formation is nonmarine gastropod limestone; middle part is variegated red-yellow-gray mudstone, siltstone, and minor sandstone and limestone; lower part is ledge-forming, cherty, quartzose sandstone and conglomeratic sandstone; total thickness about 350-500 ft (Tysdal and Simons, 1985).'
2090|'(After Wilson and Elliott, 1997) In descending order, includes Eagle Sandstone, Telegraph Creek Formation, Cody Shale, Frontier Formation, and Mowry Shale.  Includes Eagle Sandstone (Ke) along northwest corner of Yellowstone National Park; see description of unit Ke.  Telegraph Creek Formation is predominantly siltstone and thin-bedded, moderately well sorted sandstone cemented with calcite and containing calcareous concretions; weathers distinctive yellowish-gray (Roberts, 1972).  In Madison Range, upper part of Telegraph Creek Formation is light-brown-weathering mudstone and siltstone, with minor sandstone and glauconite in some beds; middle part has white-weathering tuffaceous siltstone marker; lower part is siltstone and mudstone overlying ledge-forming, gray, "salt-and-pepper" sandstone (Tysdal and Simons, 1985).  About 675 ft thick in Madison Range (Tysdal and Simons, 1985).  Cody Shale is mudstone and thin interbeds of gray-green siltstone and minor fine-grained sandstone; about 1,000 ft thick (Tysdal and Simons, 1985).  Frontier Formation is gray sandstone interlayered with darker gray siltstone and mudstone in northern part of map area; gray-green glauconitic sandstone, siltstone, and mudstone with zones of coaly shale, pale-green tuff and porcellanite in southern part; total thickness about 400 ft thick (Tysdal and Simons, 1985).  Mowry Shale is included only along Gallatin River in central part of map area; elsewhere, Mowry Shale is included with undivided Upper and Lower Cretaceous sedimentary rocks (Kul).  Upper part of Mowry Shale is slope-forming, gray mudstone; lower part is pastel-colored mudstone, porcellanite, welded tuff, siltstone, and sandstone; total thickness about 700-900 ft (Tysdal and Simons, 1985).'
2091|'In the northernmost part of the Gardiner quadrangle this designation includes the Cody and Frontier formations; in the area southwest of Corwin Springs it includes the Eagle Sandstone, Virgelle Sandstone, and Everts Formation; east of the Yellowstone River it includes the Landslide Creek Formation, Everts Formation, Eagle Sandstone, Telegraph Creek Formation, Cody Shale, and Frontier Formation.'
2092|'(After U.S.G.S., 1972)  Sandstone and shale.'
2093|'Red and green sandstone, mudstone, limestone, and fresh-water fossiliferous limestone; massive chert pebble conglomerate at base (After Roberts, 1964).'
2094|'(After Wilson and Elliott, 1997) In descending order, includes Morrison Formation (Upper Jurassic), Ellis Group (Upper and Middle Jurassic); Chugwater Formation (Triassic); and Thaynes(?) Formation, Woodside Siltstone, and Dinwoody Formation (Lower Triassic).  Morrison Formation is varicolored nonmarine claystone and mudstone; about 225-400 ft thick (Simons and others, 1985; Tysdal and Simons, 1985).  Ellis Group comprises Swift, Rierdon, and Sawtooth Formations.  Swift Formation is cream-colored to brown to gray, oolitic, shelly, cherty, calcareous and glauconitic sandstone, sandy limestone, and chert-pebble conglomerate; Rierdon Formation is gray-brown oolitic limestone, fossiliferous gray shale, and argillaceous limestone; Sawtooth Formation (lithic equivalent to Piper Formation of central Montana) is gray, fine-grained, fossiliferous limestone, argillaceous limestone, shale, and varicolored siltstone.  Ellis Group is about 80-300 ft thick (Simons and others, 1985; Tysdal, 1985).  Chugwater Formation is poorly exposed red siltstone, shale, and fine-grained sandstone; few thin gypsum beds; about 500 ft thick (Simons and others, 1985).  Thaynes(?) Formation is gray-orange, thin-bedded, calcareous siltstone and gray-green clay shale; local ledge former; only 0-10 ft thick (Tysdal and Simons, 1985).  Woodside Siltstone is red, thin-bedded siltstone and mudstone interbedded with gypsum and thin gray limestone beds; thickness varies from 0 to 725 ft (Tysdal and Simons, 1985).  Dinwoody Formation is brown to yellow-gray, chocolate-brown-weathering, thin-bedded limestone, silty limestone, and calcareous siltstone; about 70-265 ft thick (Simons and others, 1985; Tysdal and Simons, 1985).'
2095|'(After USGS, 1972) Sandstone and shale.'
2096|'Phosphoria Formation not described in source report.

Quadrant Formation, Amsden Formation:  (after Wilson and Elliott, 1997)  Quadrant Sandstone is white to tan, bedded, clean, well-sorted quartz sandstone with silica or calcite cement.  Interbeds of yellow-brown dolomite and gray limestone in lower part.  Thickness about 200-315 ft (Tysdal, 1990).  Underlying Amsden Formation is red to pink, calcareous siltstone to shale.  Upper part of formation contains calcareous sandstone cemented with iron oxides; middle and lower parts contain limestone, limestone-pebble conglomerate, and dolomite.  Thickness 40-160 ft (Tysdal, 1990).

Madison Group:  (after USGS, 1972) Limestone and dolomite.'
2097|'(after U.S. Geological Survey, 1972) Sandstone, dolomite, and chert.'
2098|'(after Wilson and Elliott, 1997)  Quadrant Sandstone is white to tan, bedded, clean, well-sorted quartz sandstone with silica or calcite cement.  Interbeds of yellow-brown dolomite and gray limestone in lower part.  Thickness about 200-315 ft (Tysdal, 1990).  Underlying Amsden Formation is red to pink, calcareous siltstone to shale.  Upper part of formation contains calcareous sandstone cemented with iron oxides; middle and lower parts contain limestone, limestone-pebble conglomerate, and dolomite.  Thickness 40-160 ft (Tysdal, 1990).'
2099|'(after USGS, 1972) Limestone and dolomite.'
2100|'Includes Three Forks Shale, Jefferson Formation, and Bighorn Dolomite; shale, limestone, and dolomite (after Van Gosen et al. 1993).'
2101|'(after USGS, 1972) dolomite, limestone, and shale.'
2102|'Includes Grove Creek Formation, Snowy Range Formation, Pilgrim Limestone, Park Shale, Meagher Limestone, Wolsey Shale, and Flathead Sandstone; limestone, sandstone, siltstone, and shale (after Van Gosen et al 1993).'
2103|'(after USGS, 1972) limestone and shale.'
2104|'(after USGS, 1972) Shale, limestone, and sandstone.'
2105|
2106|'Includes sills, dikes, stock, and irregular-shaped bodies of alkali olivine dolerite, metadolerite, metanorite, metagabbro, and quartz dolerite and dikes of uncertain or unknown affinities (After Van Gosen et al. 1993).'
2107|'The Snowy shear zone separates high-grade gneisses to the southeast from andalusite-bearing biotite-staurolite schists to the northwest (Erslev, 1992).

Note: Berg and others (1999) inadvertently included some of the Archean gneissic rocks in this unit.  See Erslev, 1992 and Van Gosen and others, 2000.'
2108|'Peridotite zone - The lower of the two zones that comprise the Ultramafic series. It consists of cyclic units of bronzite cumulates, olivine-bronzite cumulates, olivine cumulates, and chromite cumulates. At least 15 cyclic units have been recognized in the Peridotite zone. Cyclic units are of two types: (1) normal, complete units, and (2) beheaded units, (Jackson 1970, p. 390-401) that lack an olivine plus bronzite layer or bronzite layer or both. "Cumulus chromite and cumulus chromite plus olivine occur in at least 13 of the cyclic units near the base or in the lower part of the olivine cumulates" (Jackson, 1963). Chromite has been produced at three principal mines in the Stillwater Complex: Benbow, to the east; Mountain View, near the center; and Gish, in the western part. The Peridotite zone has an average thickness of about 1,000 m. It is probably not over 100 m thick where it is the only Stillwater rock exposed at the east end of the complex. There it is directly overlain by Paleozoic strata and in fault contact with older granite and metamorphic rocks. Near the Boulder River, to the west, the Peridotite zone is cut out by the Lost Creek fault.
Basal series - Shown as two separate zones on the Page and Nokleberg map (1974). Has spotty outcrop distribution along the southern edge of the Stillwater Complex. Locally as much as several hundred meters thick.

From Zientek and others (2002): The Basal series is a laterally persistent, but locally heterogeneous unit made up of bronzite-rich cumulates containing minor segregations of noncumulate mafic rock and inclusions of Archean metamorphosed sedimentary rocks (Page, 1979; Zientek, 1983; Zientek and others, 1985). It is approximately 150-m thick. The Basal series can be divided into two zones, an upper Basal bronzite cumulate zone and a lower Basal norite zone (Page, 1979). The Basal norite zone is characterized by locally-variable textures and proportions of minerals; orthopyroxene is the predominant cumulus mineral, but cumulus plagioclase, olivine, augite, inverted pigeonite, and chromite occur locally. The Basal bronzite cumulate zone consists predominantly of bronzite cumulates. Sulfide mineral accumulations are typical of the lower part of the Basal series; generally, the proportion of sulfide minerals increases toward the base of the complex (Page, 1979).
The Basal norite zone as mapped by Page and Nokleberg (1974) includes a suite of sills and dikes that intrude metasedimentary rocks near the base of the complex (Zientek, 1983; Helz, 1985). Zientek and others (1985) and Helz (1985) refer to the sill and dike rocks as Stillwater-associated sills and dikes because they are spatially and compositionally distinct from the layered cumulates that make up the bulk of the complex. At least five distinct compositional types of sills and dikes were recognized by Helz (1985), who referred to them as groups 1 through 5. Diabasic-textured rocks are slightly older than the Stillwater Complex (Premo and others, 1990) and include group 1-gabbro norites (2,7111 Ma) and group 4 high Ti-norite (2,7123 Ma). Sulfide-bearing ultramafic sills and dikes (groups 2 and 3) are comprised of lithologies that range from cumulates to more liquid-like compositions that resemble siliceous high-magnesium basalts (Sun and others, 1989); the age of these rocks is indistinguishable from the age of the Stillwater Complex (2,70310 Ma). The group 2 and 3 sills may be petrologically related to cumulates in the overlying Basal series (Zientek, 1983). Group 3 sills and dikes contain disseminated (less than 10 volume percent), matrix (10 to 60 volume percent), and massive (greater than 60 volume percent) accumulations of sulfide minerals. However, accumulations of matrix and massive sulfide minerals are largely restricted to the group 3 mafic norite sills and dikes near mineralized Basal series cumulates (Zientek, 1983).'
2109|'Upper orthopyroxene (bronzite) cumulate of the Ultramafic series. At the contact between the Banded upper series and the underlying Ultramafic series plagioclase abruptly ceases to occur as a cumulus mineral, and immediately below the contact the only cumulus mineral present is orthopyroxene. "The units are fine to coarse grained. Units in which grain size changes from fine to coarse upward appear to form repeated cycles throughout the sequence. From 3-6 m below the top of the Bronzitite zone in the Benbow area, a concentration of cumulus chromite can be traced for several meters along strike" (Page, 1977, p. 28). This chromite zone is also exposed on the north slope of the 9,587-ft hill 1.5 km east of Chrome Mountain, where it manifests itself in several layers a few millimeters thick and in local disseminations of very fine-grained cumulus chromite. Interstitial plagioclase and oikocrysts of clinopyroxene are common throughout the zone. Through most of the exposed length of the Stillwater Complex the Bronzitite zone is 350-1,000 m thick. West of the Boulder River it is cut out by the Lost Creek Fault and to the east the zone disappears in the moraine of West Fishtail Creek.'
2110|'Lower gabbro zone - Largely plagioclase-two pyroxene cumulate. Layers of plagioclase cumulate, plagioclase-clinopyroxene cumulate, and plagioclase-orthopyroxene cumulate are interspersed throughout the sequence. "Pillow troctolite" (Hess, 1960, p. 82-83), a pegmatoid plagioclase-olivine cumulate, occurs as a crosscutting injection or replacement in fine-grained plagioclase cumulate and plagioclase-clinopyroxene cumulate at the top of the zone about 750 m west of the 10,056-ft summit of Contact Mountain. Lenses of plagioclase-olivine cumulate and olivine cumulate occur at the top of the zone southeast of Contact Mountain and southwest of Picket Pin Mountain. "Inch-scale" layered rock is exposed a few tens of meters below the top of the zone at various localities along the strike of layering. The classic exposure of this unusual rock is in a landslide along the road to the Mountain View mine on west side of valley of Stillwater River, where disc-shaped oikocrysts of clinopyroxene are alined edgewise to form vertical dark layers a few millimeters to 2 or 3 cm thick. The repeating dark layers are generally separated by 2-3 cm of light-colored plagioclase cumulate. Alternation of layers is fairly uniform for 10-20 m across strike, but deviations occur in which the layers are paired or even more complexly grouped. Other exposures of inch-scale layering, at the same stratigraphic position, are: (1) on both sides of the gorge of lower Brownlee Creek, about 1 km west of the East Boulder River, (2) on the spur ridge about 1.8 km east of the Stillwater River (a little olivine is present in the upper part of the layered zone here), and (3) on the spur ridge immediately west of Prairie Creek. A thick sequence of plagioclase cumulate is sandwiched in plagioclase-two pyroxene cumulate of the Lower gabbro zone between Brownlee Creek and Iron Creek. The middle of the Lower gabbro zone is interrupted by a few meters of plagioclase-olivine cumulate and olivine cumulate overlain by plagioclase cumulate well exposed as vertical beds in a cut on the road to Mountain View Mine in SW corner sec. 16, T. 5 S., R. 15 E. Plagioclase-olivine cumulate is interbedded with plagioclase cumulate through much of the sequence on the spur ridge about 1.8 km east of the Stillwater River, so that the Lower gabbro zone there bears little resemblance to a typical section on the south side of the 10,065-ft summit of Contact Mountain. Olivine gradually diminishes toward the eastern end of the complex, and it is not seen in exposures of the Lower gabbro zone along the road to Benbow Mine.  Repeating cycles of plagioclase cumulate, plagioclase-orthopyroxene cumulate, and plagioclase-two pyroxene cumulate can be recognized in the middle of the Lower gabbro zone for a short distance westward from Brownlee Creek.  There are at least two showings of inch-scale layering in plagioclase cumulate a little over 100m above the bottom of the zone.  One of these is on the spur ridge east of the Stillwater River. The other is about 75 m north of down-faulted limestone on the spur ridge west of Prairie Creek. Contact of the zone with the underlying Norite zone tends to be transitional, particularly from the East Boulder River westward to the divide between the East Boulder and main Boulder River. The transition is between plagioclase-two pyroxene cumulate above and plagioclase-orthopyroxene cumulate below. All gradations between these two rocks are exhibited within a stratigraphic range of about 200 m, where interstitial clinopyroxene and fine-grained cumulus clinopyroxene occur in varying proportions with coarser-grained cumulus orthopyroxene. Except where the unit is covered with fill deposits in the main river valleys, the Lower gabbro zone is continuously exposed from southwest of Mt. Rae to the east side of Black Butte, a distance of 40 km. Thickness 0-590 m. Near where it is cut off at either end by unconformity, the zone is only 100-200 m thick.

Norite zone - The upper contact is where rock containing cumulus orthopyroxene readily seen in hand specimen underlies rock devoid of easily recognizable cumulus orthopyroxene. The upper part of the zone is mainly plagioclase-orthopyroxene cumulate. Oikocrysts of clinopyroxene are common in this rock and also in interlayers of plagioclase cumulate. A group of mixed layers provides a major break in continuity about halfway down the sequence. There, through a stratigraphic interval of about 100 m, 28 distinguishable layers a meter or so thick have been counted in one section. This section includes eight olivine-bearing layers interspersed between layers of plagioclase cumulate and plagioclase-orthopyroxene cumulate. Among these strata lies a zone, centered approximately at the divide between Brownlee Creek and Graham Creek that for a distance of 5.5 km and through a thickness of 2.1 m, has an average grade of 0.65 troy oz of Pt and Pd per short ton. This is one of the richest known deposits of platinum-group metals (PGM) in the world. The PGM zone there occurs where a layer of olivine cumulate and a layer of plagioclase cumulate together first became dominant upsection from the base of the Norite zone (Todd and others, 1979, p. 461-462, 464). The Pt and Pd are contained in sulfides, native alloys, arsenides, antimonides, bismuthinites (Cabri and La Flamme, 1974). The principal PGM-bearing minerals are pyrrhotite and pentlandite. Geochemical sampling and the driving of two adits by Johns-Manville in 1976-1980 have shown that the package of mixed layers containing one or more zones of PGM anomalies extends through the entire 40 km of strike length of the Norite zone. Drilling and the driving of an adit by Anaconda in 1979-1980 confirmed the existence of ore-grade PGM near the main Stillwater River. Facies changes within the zone result locally in fewer olivine-rich layers, lensing of pegmatite, and changes in stratigraphic position and grade of PGM anomalies. Two ore zones with a stratigraphic separation of 6-8 m have been locally encountered by Johns-Manville (E. L. Mann, oral commun., August 1980). Ore-grade PGM is encountered through a stratigraphic interval of 20-26 m by Anaconda in the Minneapolis adit (R. N. Miller, oral commun., August 1980). Below the group of mixed layers there is an interval of plagioclase-two pyroxene cumulate, then a much wider interval of principally plagioclase-orthopyroxene cumulate to the bottom of the section. Off-lap and slump structures indicating floor tilt, as well as graded bedding are seen in the lower interval of plagioclase-orthopyroxene cumulate on the west side of the Stillwater River. Scattered injections of pegmatoid orthopyroxene cumulate (bronzite), irregular in shape, crosscutting the layering, and locally rich in sulfides occur at the base of the Norite zone in two areas: (1) for about 1 km northwest of the East Boulder River, and (2) between Iron Mountain and Iron Creek. These sulfides also contain anomalous concentrations of platinum-group metals and were intensively drilled and trenched by Johns-Manville before the more persistent zone of interest was discovered higher in the Norite zone. At the maximum thickness of the zone, across the east end of Contact Mountain, the generalized sequence from top to bottom is: plagioclase-orthopyroxene cumulate, 250 m; mixed group (distinctively plagioclase cumulate and plagioclase-olivine cumulate), 100 m; plagioclase-two pyroxene cumulate, 75 m; and plagioclase-ortho-pyroxene cumulate 275 m making a total thickness of 700 m. The plagioclase-two pyroxene interval thins considerably west of the Brownlee Creek-Graham Creek divide and east of the West Fork of the Stillwater. To the west, the entire Norite zone is faulted out by the Lost Creek fault, near the Boulder River, and to the east the outcropping zone disappears in the moraine of West Fishtail Creek.'
2111|'Mostly plagioclase cumulate with oikocrysts of clinopyroxene. The upper contact is defined at the top of a relatively thick plagioclase cumulate layer: sulfides were noted in this rock near the east end of Contact Mountain and on the first spur ridge east of the Stillwater River. Along the road to Benbow Mine cumulus olivine occurs in varying amounts throughout the zone, mostly <5 percent; some of the olivine is poikilitic in oikocrysts of clinopyroxene. Poikilitic olivine in plagioclase cumulate is also noted at the bottom of the zone on the first spur ridge east of the Stillwater River. The zone is exposed continuously along the entire outcrop of the Stillwater Complex, except where it is concealed by Quaternary deposits and except for one short stretch at West Fork Stillwater River and another a little west of the main Stillwater River that are cut out along the Horseman Thrust. Thickness 0-480 m.'
2112|'Middle mixed zone - Contains three cycles. Sequence from top to bottom in each cycle is plagioclase-olivine and (or) plagioclase-orthopyroxene cumulate, and plagioclase cumulate. Though it is dominant throughout, the cumulus plagioclase component decreases and the cumulus olivine component increases from one cycle to the next lower one. Only the lowermost cycle seems to be present west of the Boulder River. The zone is cut out by unconformity on Mount Rae, to the west, and by the Horseman Thrust, on the ridge between Picket Pin Creek and West Fork Stillwater River to the east. However, part of the unit reappears from under the unconformity near the east end of the complex. About 90 m of plagioclase cumulate with a little postcumulus clinopyroxene is exposed along the road to Benbow Mine. Plagioclase-olivine cumulate occurs on a ridge northwest of the road. Thickness of the Middle mixed zone is 0-400 m.

Middle gabbro zone - Chiefly plagioclase-orthopyroxene-clinopyroxene cumulate and plagioclase-clinopyroxene cumulate on Contact Mountain, where the zone was first described and defined by Segerstrom and Carlson (1977). West of the Boulder River the lower third of the zone is plagioclase cumulate. A sharp change of lithofacies eastward across the East Boulder River brings in more plagioclase cumulate and cumulus olivine. A distinctive feature of the zone near Picket Pin Mountain is augen-like segregations of plagioclase parallel to regional foliation. Four-phase rock, plagioclase-orthopyroxene-clinopyroxene-olivine cumulate is identified in some outcrops, especially on the eastern part of the ridge between Picket Pin Creek and Iron Creek. To the west the zone is truncated by the un-conformity on Mount Rae. Near West Fork Stillwater River the unit is cut out along the Horseman Thrust, but farther east it reappears south of Horseman Flats. It is cut out again in the Stillwater River valley and farther east until it finally reappears near the road to Benbow Mine. There, the zone is chiefly plagioclase cumulate with post-cumulus orthopyroxene. Some plagioclase-clinopyroxene cumulate present. Thickness 0-280 m.

Lower mixed zone - Principally plagioclase-olivine cumulate with 5-40 percent cumulus olivine and smaller amounts of post-cumulus clinopyroxene. Plagioclase cumulate and plagioclase-clinopyroxene cumulate with scattered grains of cumulus olivine (<5 percent) make up some beds. The middle third of the zone is almost all plagioclase cumulate on the west side of the Boulder River. Alternating bands of plagioclase cumulate and plagioclase-olivine cumulate characterize outcrops at the bottom of the zone on the first spur ridge east of the Stillwater River. The exposure is discontinuous, as it is cut out by faulting and unconformity at five different places. The westernmost exposure of the unit is just south of Mount Rae. Thickness of the zone is 0-300 m.'
2113|'Almost 100 percent plagioclase cumulate: an exceptionally monolithologic rock unit. A zone of sulfides, generally less than a few centimeters thick, is exposed near the top of the zone a little south of the summit of Picket Pin Mountain. In 1979 this zone was claimed, drilled, and extensively sampled by the Anaconda Mining Co. on both sides of Picket Pin Mountain and on the north side of Contact Mountain to the west, but the project was subsequently dropped for lack of exploitable concentrations of nickel, copper, and platinum-group metals. Pods of gossan as much as 30 cm thick are also exposed near the top of the zone at and near a pinnacle on top of the northeast edge of the faceted west end of Contact Mountain. Centers of the pods are replete with pyrrhotite. Oikocrysts of clinopyroxene appear locally throughout the unit. Thickness is 0-690 m; the zone is thickest on Contact Mountain, less than half as thick near Picket Pin Mountain, and it is truncated both east and west by the unconformity at the base of the Paleozoic sequence.'
2114|'Upper anorthosite zone - Plagioclase cumulate with 0-50 percent pyroxene, much of which is post-cumulus. A convoluted relationship between coarse-grained and fine-grained rock characterizes the uppermost part of the zone on the ridge southwest of Burnt Gulch (northwest of Picket Pin Mountain) and on a knoll at the west side of the Boulder River. Plagioclase cumulate with post-cumulus magnetite (including magnetite oikocrysts) constitute some of the coarse-grained phase. Euhedral (cumulus) plagioclase laths in a groundmass of anhedral pyroxene and plagioclase grains (probably post-cumulus) constitute the fine-grained phase: in places the rock is porphyritic, with plagioclase crystals as much as 1-2 cm long in a fine-grained groundmass. Plagioclase-magnetite cumulate also occurs in two thin layers near the top of the section west of Wright Gulch (north side of Contact Mountain). Plagioclase cumulate in the rest of the zone contains increasing amounts of clinopyroxene (10 to 50 percent) down-section, and near the bottom of the zone some of the pyroxene is orthopyroxene. Megascopically and in thin sections, practically all pyroxene in the unit appears to be anhedral, and hence interstitial. However, McCallum and others (1980), who made a detailed petrographic study of a section across the east end of Contact Mountain, found much cumulus clinopyroxene and inverted pigeonite in the zone. Their "Gabbronorite III unit" contains the Upper anorthosite and Upper gabbro zones of this map. The Upper anorthosite zone has a maximum exposed thickness of 800 m, but east of Picket Mountain and west of the Boulder River the unit is truncated completely by the unconformity at the base of the Paleozoic sedimentary rocks.

Upper gabbro zone - Principally plagioclase-two pyroxene cumulate. Ratios of orthopyroxene to clinopyroxene and of plagioclase to pyroxene vary, but plagioclase is generally dominant and the rock tends to be leucocratic. Plagioclase-clinopyroxene cumulate is rare or absent throughout the zone. The upper contact is the highest limit where abundant cumulus clinopyroxene is seen in hand specimen. A lens of pegmatoid orthopyroxene cumulate 1 m thick is exposed at the top of the zone north of Picket Pin Mountain. Turbulent flow structure is exhibited near the middle of the zone on a low ridge south of a cirque northeast of Picket Pin Mountain. There, wispy xenoliths, chiefly of plagioclase cumulate, are enclosed in the two pyroxene rock. A prominent lens of plagioclase extends from about 100 m to 200 m above the base of the zone; it is well exposed in cuts along the cirque road east of Picket Pin Mountain. This lens thins westward and disappears near the east end of Contact Mountain. Plagioclase-orthopyroxene cumulate and plagioclase cumulate form several minor layers along and near the base. The zone attains a maximum thickness of 600 m on the north side of Contact Mountain, but is truncated out by the unconformity at the base of the Paleozoic sequence east of Picket Pin Mountain and west of the Boulder River.

Upper mixed zone - Plagioclase-olivine cumulate dominant, but there are interlayers and lenses of plagioclase cumulate and, rarely, of olivine cumulate. Immediately down-section from the upper contact, nonparallel lenses of plagioclase-olivine cumulate are enclosed in plagioclase cumulate. Lens endings are generally pointed, but some are blunt and squared off. These features possibly are evidence of tilting of the magma chamber during deposition of compositional layering. A lens of olivine cumulate 3-5 m thick crops out near the bottom of the map unit on the southeast side of Picket Pin Mountain, but pinches out completely in 100-200 m between there and the summit. Plagioclase-orthopyroxene cumulate and orthopyroxene-plagioclase cumulate form a layer 2-3 m thick at the base of the zone 1 3/4 km ESE of Picket Pin Mountain. In the Upper mixed zone and in underlying units of the Stillwater Complex the exposed grains of olivine tend to weather out, so that typical exposures of plagioclase-olivine cumulate have pitted surfaces. Magnetite is a characteristic alteration product of the olivine. Despite chemical decomposition of the olivine, the Upper mixed zone is locally erosion-resistant, and holds up Picket Pin Mountain and the ridge between there and the East Boulder River. Because the lithology is so distinct from that of the overlying units and next underlying unit, the zone is a reliable stratigraphic marker. Thickness is 60 to 110 m, except where this unit is truncated by the unconformity on Mount Rae, to the west, and in the drainage of Picket Pin Creek, to the east.'
2115|'Mostly tabular and lensoid bodies enclosed in granitic gneiss and migmatite (after Van Gosen et al. 1993).'
2116|'Includes trondhjemitic gneiss-amphibolite paragneiss, and heterogeneous: gneiss sequences; trondhjemitic gneiss, tonalitic gneiss, amphibolite; minor schist, quartzite, and iron formation (after Van Gosen et al. 1993).'
2117|'Predominately granitic gneiss and migmatite; commonly consists of alternating bands of more felsic and more mafic gneiss; contains inclusions of metasedimentary and metaigneous rocks (after Van Gosen et al. 1993).'
2118|'Includes stocks and irregular-shaped bodies of fine-, medium-, and coarse-grained quartz monzonite and aplite of the Stillwater area and of granite in the Gardiner area (after Van Gosen et al. 1993).'
2119|'Includes Barney Creek amphibolite, George Lake marble, and Jewel quartzite; amphibolite, dolomitic marble and marble and quartzite; minor schist and iron formation (after Van Gosen et al. 1993).'
2120|'Interlayered quartzite and orthoamphibolite; minor schist (after Van Gosen et al. 1993).'
2121|'Includes minor quartzite, iron formation, and amphibolite (after Van Gosen et al. 1993).'
2122|'Metasedimentary rocks consisting predominantly of schist and hornfels with minor quartzite, amphibolite, and iron formation; contact metamorphosed to hornblende hornfels and pyroxene hornfels facies at and near the base of the Stillwater Igneous Complex; host for Homestake-type gold deposits near Jardine (after Van Gosen et al, 1993).'
2150|'Unsorted and unstratified mixtures of locally derived material transported down adjacent slopes and characterized by irregular hummocky topography. Developed most often on slopes underlain by Tertiary sedimentary (Tgc) and volcanic (Tv) rocks with high clay content.'
2151|'Well sorted, well rounded gravel and sand with a minor amount of silt and clay. Well logs show an average thickness of 40 feet (McMurtrey and others, 1972).'
2152|'The surfaces of these deposits stand 15-25 feet above the present floodplain and consist of well rounded, mostly granitic cobbles. At least two terraces have been recognized (Uthman, 1998), but they cannot be distinguished everywhere. Well logs indicate a thickness of 60-70 feet of sand, gravel, and cobbles.'
2153|'Well to poorly sorted, well-rounded to sub-angular cobbles and boulders in a matrix of silt, sand, gravel deposited in alluvial fan and outwash fan environments. Includes deposits of several ages and topographic levels.'
2154|'Unconsolidated, unsorted, locally derived accumulations of angular boulders, cobbles, pebbles, sand, and silt on steep slopes.'
2155|'Unsorted, mostly unstratified clay, silt sand, gravel, and boulders up to 15 feet in diameter deposited in glacial moraines. Moraines record at least 3 glaciations beginning in early Pleistocene (Weber, 1972).'
2156|'Brown, unconsolidated to weakly lithified, poorly sorted, moderately stratified subangular to rounded boulders , cobbles, and sandy silt deposited in alluvial fan environments. Includes abundant brown, massive, micaceous silt beds. Found as interfluvial remnants perched 200 feet or more above the present Bitterroot floodplain, and capping pediments or strath terraces formed on older units. Clasts are locally derived, and are often coated with brown iron oxide or caliche. Bedding typically dips more steeply than the surface of this unit, indicating an erosional surface. Lag deposits of small, subangular boulders are common on these pediment surfaces. This unit is characterized by a gentle surface profile, weathered granitic clasts, oxide- or caliche-coated sedimentary clasts, extensive dissection, lack of braided channel patterns on air photos, and a lower contact at least 200 feet higher than the present Bitterroot River. It is a poor aquifer due to both its drained nature and its low permeability.'
2157|'Fluvial Gravel of the Ancestral Bitterroot River Channel, "ABR Facies".  Predominantly light gray to white, unconsolidated, well-sorted, well-rounded, well-stratified, sand, pebbles, and cobbles.  Clast lithologies are representative of rocks from the entire drainage basin and include granitic rocks, Bitterroot mylonite, Belt quartzite, Belt carbonate, high-grade metamorphic rocks, extrusive volcanic rocks, and black and red chert. Informally called the "ancestral Bitterroot River (ABR) facies."  Contains interbedded light tan clay and silt that predominate in the adjacent blue clay facies with which the ABR facies interfingers.  Fossil assemblages collected by Konizeski (1958) in the blue clay facies indicate an age of Oligocene to late Miocene.  The ABR facies hosts most of the developed sand and gravel deposits in the Bitterroot Valley: It is also a productive aquifer, with wells often yielding more than 50 gallons per minute. Deep drill holes show that unconsolidated sedimentary rocks similar to Tgc are up to 2400 feet thick in places (Norbeck, 1980).

Clay, Silt, and Tephra of the Ancestral Bitterroot River Channel, "Blue Clay Facies".  Informally called the "blue clay facies" after drill log descriptions. Mostly light gray clay and silt in beds 6 inches to 5 feet thick, with abundant interbedded tephra. Contains lenses of well-sorted, cross-stratified, fluvial gravel like that described for the ABR facies. Interfingers with the ABR facies. Some brown, ledge-forming massive silty layers with root casts and burrows are present and interpreted to be paleosols. Fossil assemblages indicate an Oligocene to late Miocene age (Konizeski, 1958). Landslides commonly develop where this unit underlies steep slopes, especially where irrigated. Swelling clays are also common.'
2158|'Includes flows, volcaniclastic rocks, tuff, and welded tuff. Mostly gray to yellow-gray porphyritic latite tuff, red to pink rhyodacite vitrophyre, and volcanic breccia containing fragments of porphyritic basalt, rhyodacite, obsidian, and quartz latite (Clark, 1979). Includes some intrusive dikes in the southeastern part of the map area.'
2159|'Dikes, sills, and other shallow porphyritic intrusive bodies of mainly rhyolite. These are mostly thin (less than 100 feet thick) dikes that are reddish, topographically resistant features containing phenocrysts of quartz, sanidine, plagioclase, biotite, and hornblende in an aphanitic groundmass. Flow banding is common.'
2160|'Undivided, small, epizonal plutons of medium- to coarse-grained nonfoliated rock.'
2161|'Pink to white, fine- to medium-grained, nonfoliated granodiorite. Contains 1-2% potassium feldspar megacrysts up to several centimeters long and 10% biotite and muscovite (Presley, 1971).'
2162|'White, fine-grained, equigranular, nonfoliated granodiorite containing 5% biotite and a trace of muscovite. Mineralogically, it is similar to the nearby Willow Creek stock and may be related (LaTour, 1974).'
2163|'A 500-1500 foot-thick zone mainly of deformed TKg exposed along the eastern flank of the Bitterroot Mountains, and gently dipping eastward (Toth, 1993). A pronounced foliation is defined by planes of recrystallized biotite and alignment of feldspar tails. Lineations are formed by quartz rods, kinked and streaked micas, and slickenside striae. Some glassy, black ultramylonite horizons are present. In the northern portion of the Hamilton quadrangle, metamorphosed Proterozoic sedimentary rocks (Ybm) have been deformed to create the mylonite.'
2164|'Medium-grained equigranular to porphyritic (with pink K-spar phenocrysts six millimeters long) monzogranite and granodiorite (Toth, 1983). Contains 5%-20% hornblende and biotite.'
2165|'A granitic complex of muscovite-biotite granodiorite and monzogranite, and local related quartz diorite, quartz monzodiorite, and syenogranite that makes up much of the Idaho batholith (Toth, 1983). Mostly light gray, slightly porphyritic (feldspar phenocrysts) biotite granodiorite with 2-5% biotite that defines a weak, but obvious, foliation.'
2166|'In the southeast corner of the map, foliated biotite granodiorite of the Idaho batholith (TKg) has been deformed into an augen gneiss. The contact is gradational.'
2167|'Dominated by gray, planar bedded fine- to medium-grained quartzite. Some is pink and feldspar rich. Sequences from one foot to several hundred feet thick of finer grained sediment types are present. These include red and green argillite, red to purple siltite, and some carbonate-rich facies. This unit overlies the middle Belt carbonate unit, but poor stratigraphic knowledge in this area and lack of exposure make assignment of formation names difficult. Some areas display up to amphibolite grade metamorphism.'
2168|'Much of this unit consists of gray limestone, calcareous siltstone, and black argillite interceded with white quartzite, and resembles the Helena Formation to the east rather than its more proximal western equivalent, the Wallace Formation. Textures vary from thinly-laminated to massive to porphyroblastic. Some degree of recrystallization has occurred everywhere, but some primary sedimentary features are preserved. The layering is defined by original sedimentary beds, and minerals display only weak preferred orientation. The more highly metamorphosed areas contain green layers mainly of diopside and actinolite, and scapolite forms large white porphyroblasts LaTour (1974) distinguished greenschist facies and amphibolite facies metamorphism within this unit on the basis of the presence or absence of diopside, but because the diopside is fine-grained, this is not possible in hand specimen. Within this unit, there are also some thick sequences of gray, medium-grained, planar bedded quartzite in beds 1-2 feet thick.'
2169|'Gray, medium-grained, biotite-rich planar-bedded quartzite. Thin, interbedded, fine-grained clastic layers have been metamorphosed into biotite-muscovite-quartz-feldspar schist, with foliation parallel to original bedding. This unit appears to conformably underlie the middle Belt carbonate unit but may be a thick quartzite sequence within the carbonate unit.'
2170|'Mostly migmatitic quartzofeldspathic gneiss with lesser amounts of calc-silicate gneiss, pelitic schist, and amphibolite. These are probably higher grade metamorphic equivalents of the Belt Supergroup rocks described above (Ymi, Yc, and Yq). Age of amphibolite grade metamorphism is uncertain.'
2171|'Banded gray to green gneiss consisting of light green layers of diopside, quartz, and actinolite alternating with light-gray layers of quartz feldspar, and biotite. Scapolite is common as large (up to 0.5 cm) white porphyroblasts. This unit is a higher grade metamorphic equivalent of Yc and may be gradational with Yc. It is also present but unmapped within Yc, where Yc has been metamorphosed and highly injected near contacts with Tertiary igneous intrusive rocks.'
2172|'Banded reddish-brown weathering rock composed of quartz-feldspar-biotite-rich layers, quartz-rich layers, and migmatite. Platy minerals are not always aligned, but they are concentrated in distinct layers. Primary sedimentary features have been obliterated. Layers of biotite-muscovite-rich pelitic schist with rare sillimanite are present but uncommon. This unit is assumed to be a higher grade metamorphic equivalent of the Belt Supergroup rocks described above (Ymi and Yq). Age of amphibolite grade metamorphism is unknown.'
2173|'Elongate bodies of medium-grained amphibolite and hornblende gneiss containing green to black hornblende and varying amounts of white plagioclase. Some biotite is visible.'
2174|'Reddish-brown gneissic rock consisting of medium- to coarse-grained plagioclase, potassium feldspar, quartz, and biotite. Elongate quartz pods and weakly aligned biotite define schistosity (Clark, 1979).'
2175|'Massive, hypidiomorphic-granular anorthosite containing small flakes of biotite (some altered to chlorite), muscovite, and minor clinozoisite (Chase, 1973).'
2200|'Unsorted and unstratified mixtures of locally derived material transported down adjacent slopes and characterized by irregular hummocky surfaces. Develops most often on slopes underlain by Tertiary sedimentary (Tgc) and volcanic rocks (Tv) with high clay content.'
2201|'Fresh, well-sorted, well-rounded gravel and sand with a minor amount of silt and clay. Occurs beneath modern flood plains and streams. Well logs show an average thickness of 40 ft (McMurtrey and others, 1972).'
2202|'Not exposed in outcrop, but the surfaces consist of unweathered, well-rounded, mostly granitic cobbles. These surfaces stand 15-25 ft above the present flood plain. Well logs indicate a thickness of 60-70 ft of sand, gravel, and cobbles. At least two terraces have been recognized (Uthman, 1988), but they cannot be distinguished everywhere.'
2203|'Well-rounded to subangular, well- to poorly sorted, locally derived cobbles and boulders in a matrix of sand, silt, and gravel deposited in alluvial fan and outwash fan environments. Includes deposits of several ages and topographic levels.'
2204|'Unsorted, mostly unstratified clay, silt, sand, cobbles, and boulders up to 20 feet in diameter deposited in moraines by glaciers. Moraines record at least 3 different glaciations beginning in the early Pleistocene (Weber, 1972).'
2205|'Fluvial Gravel of the Ancestral Bitterroot River Channel, "ABR Facies".  Predominantly light gray to white, unconsolidated, well-sorted, well-rounded, well-stratified, sand, pebbles, and cobbles.  Clast lithologies are representative of rocks from the entire drainage basin and include granitic rocks, Bitterroot mylonite, Belt quartzite, Belt carbonate, high-grade metamorphic rocks, extrusive volcanic rocks, and black and red chert. Informally called the "ancestral Bitterroot River (ABR) facies."  Contains interbedded light tan clay and silt that predominate in the adjacent blue clay facies with which the ABR facies interfingers.  Fossil assemblages collected by Konizeski (1958) in the blue clay facies indicate an age of Oligocene to late Miocene.  The ABR facies hosts most of the developed sand and gravel deposits in the Bitterroot Valley: It is also a productive aquifer, with wells often yielding more than 50 gallons per minute. Deep drill holes show that unconsolidated sedimentary rocks similar to Tgc are up to 2400 feet thick in places (Norbeck, 1980).

Clay, Silt, and Tephra of the Ancestral Bitterroot River Channel, "Blue Clay Facies"  Informally called the "blue clay facies" after drill log descriptions. Mostly light gray clay and silt in beds 6 inches to 5 feet thick, with abundant interbedded tephra. Contains lenses of well-sorted, cross-stratified, fluvial gravel like that described for the ABR facies. Interfingers with the ABR facies. Some brown, ledge-forming massive silty layers with root casts and burrows are present and interpreted to be paleosols. Fossil assemblages indicate an Oligocene to late Miocene age (Konizeski, 1958). Landslides commonly develop where this unit underlies steep slopes, especially where irrigated. Swelling clays are also common.'
2206|'Includes flows, welded tuff, and various volcaniclastic rocks. Composition is generally rhyolitic to quartz latitic.'
2207|'Dikes, sills, and other shallow porphyritic intrusive bodies of mainly rhyolite. These are mostly thin (less than 100 feet thick) dikes that are reddish, topographically resistant features containing phenocrysts of quartz, sanidine, plagioclase, biotite, and hornblende in an aphanitic groundmass. Flow banding is common.'
2208|'A 600 to 1,500 ft thick, east-dipping zone in which Precambrian metasedimentary rocks, and Cretaceous and Tertiary plutons have been intensely deformed to produce a well-foliated rock that is locally ultramylonitic (Toth, 1983).'
2209|'This pluton consist of four phases (Lund and others, 1983). Pink coarse-grained syenogranite shows evidence of nearly ubiquitous deuteric alteration. Monzogranite is gray and medium grained. Coarsely porphyritic monzogranite contains euhedral, 3- to 6-mm-long, microperthitic gray orthoclase phenocrysts. Gray, salmon, or white granophyric granite occurs near the roof of the Painted Rocks pluton.'
2210|'Medium-grained, light gray equigranular muscovite-biotite granodiorite (Toth, 1983).'
2211|'Pink, strongly porphyritic biotite monzogranite with potassium feldspar phenocrysts 5-6 cm long (Toth, 1983).'
2212|'Undivided, small epizonal plutons of medium- to coarse-grained nonfoliated rock.'
2213|'Medium-grained equigranular to porphyritic monzogranite and granodiorite (Toth, 1983).'
2214|'A granitic complex of muscovite-biotite granodiorite and monzogranite, and local but related quartz diorite, quartz monzodiorite, and syenogranite that makes up much of the Idaho batholith. Mainly light gray, slightly porphyritic (feldspar phenocrysts) biotite granodiorite with 2%-5% biotite that defines a weak but obvious primary flow foliation (Toth, 1983).'
2215|'Biotite granodiorite, monzogranite, syenogranite, quartz diorite, and quartz monzodiorite. In a few outcrops it can be seen that as many as 12 texturally and mineralogically distinct varieties were emplaced comagmatically (Toth, 1983).'
2216|'Quartz latite porphyry is the dominant rock type with lesser dacite and rhyodacite. Prominent phenocrysts of potassium feldspar, plagioclase and quartz are typical of these rocks (Fisk, 1969).'
2217|'Occurrences are limited to dikes and sills within the quartzite and quartzitic schist. Xenoblastic hornblende and plagioclase are the principal minerals.'
2218|'Microcline metacrysts up to 5 cm long and less commonly plagioclase metacrysts are surrounded by a matrix composed of quartz, muscovite, biotite, and feldspars.'
2219|'Amphibolite weathers dark green to brown and consists mainly of hornblende and plagioclase with lesser biotite. Concordant layers of augen gneiss occur within the amphibolite.'
2220|'Ranges from massive white to pink quartzite composed almost entirely of quartz to greenish gray feldspathic quartzite that contains beds of siltite and argillite. The quartzite is of green schist grade of metamorphism (Berg, 1977).'
2221|'Quartzitic schist weathers tan to reddish-brown and consists of micaceous layers that alternate with quartzose layers. Flexural slip folds are abundant in this unit.'
2222|'Quartz ranges from 35% to 50% in this gneiss, and feldspar, mainly plagioclase, ranges from 32% to 60%.'
2223|'Mostly migmatitic quartzofeldspathic gneiss with lesser amounts of calc-silicate gneiss, pelitic schist, and amphibolite.'
2400|'Till from continental glaciation, glacial flood deposits, and all alluvial material in modern drainages. Also includes some lacustrine deposits in Colville and Pend Oreille River valleys.'
2401|'Unconsolidated rubble resulting from slides and land slips. Found mainly around cliffs formed in the Columbia River Basalt Group in the southwestern part of the quadrangle. Identified chiefly by geomorphic forms observed on aerial photographs.'
2402|'Silt, sand, gravel, and probably clay; deposited in glacial and possibly post-glacial lakes occupying Kootenay River valley. Most of unit is poorly indurated, finely to massively bedded, fine-grained silt. Locally, unit contains gravel, sand, and boulders, some presumably ice-rafted.'
2403|'Conglomerate, sedimentary breccia, minor arkosic and lithic sandstone, iron oxide-cemented sandstone and conglomerate, and mudstone; poorly indurated. Restricted to southwestern 15-minute block of quadrangle.'
2404|'Fine-grained tholeiitic basalt flows. Considered to be N2 flows of Grande Ronde Basalt in Colville River drainage, and Priest Rapids Member of Wanapum Basalt elsewhere (Swanson and others, 1979). Maximum thickness estimated to be about 180 m; thins northward.'
2405|'Unit consists of Tiger Formation (Park and Cannon, 1943) in Pend Oreille River valley west of Newport, Sandpoint Conglomerate (originally considered to be Cretaceous in age by Harrison and Schmidt, 1971, and Harrison and others, 1972) north of Sandpoint, and unnamed conglomerate (Miller and Clark, 1975) north of Chewelah. Poorly to moderately-well indurated conglomerate, lithic arkose, and siltstone. Composition and sedimentary characteristics highly variable laterally and vertically. Unconformably overlies a variety of rock units. Tiger Formation considered to be syntectonic basin-fill deposits related to Eocene extensional tectonics (Gager, 1984; Harms and Price, 1992); Sandpoint Conglomerate and unnamed conglomerate probably of similar origin.'
2406|'Green to gray brittlely comminuted cataclastic rocks and highly fractured and chloritized rocks formed in footwall of Newport Fault zone. Breccia in upper part of zone is nearly aphanitic; grades downward through decreasing brecciation into unbrecciated, but commonly mylonitized rocks of footwall. Thickness ranges from a few meters along northern parts of both limbs of U-shaped trace to 150 to 250 m along southernmost part.'
2407|'Breccia and gouge derived from bounding rock units; materials range in size from powder to house-size blocks. Exposed only on west side of mountain between Jared and Ruby (fig. 2), but may typify unexposed hanging wall rocks immediately adjacent to Newport Fault along much of its trace.'
2408|'Volcanic flow rocks, breccia, conglomerate, and lithic arkose. All volcanic rocks fall within compositional range from dacite to andesite; average composition is dacite (Joseph, 1990; Waggoner, 1990). Includes rocks comprising Pend Oreille Andesite of Schroeder (1952), unnamed volcanic flows and sedimentary rocks south of Waitts Lake, flow or intrusive andesite northeast of Waitts Lake, isolated outcrops of flow rocks and sedimentary rocks east of Dunn Mountain, and flows and sedimentary rocks west and north of Colville (Pearson and Obradovich, 1977). Unconformably overlies a variety of rock units.'
2409|'Unit of Dings and Whitebread (1965). Olivine, clinopyroxene, and plagioclase in matrix of glass, palagonite, and orthoclase. Dark-gray to black, very fine-grained. Restricted to small area 7 km north of Metaline Falls. Considered to be part of Sanpoil Volcanics on basis of mineralogy and composition by Joseph (1990).'
2410|'Conglomerate and minor well-bedded tuff. Distinguished from other Eocene conglomerate units by absence of volcanic clasts. Tuff restricted to upper part of formation; both conglomerate and tuff vary greatly in thickness. Biotite from tuff gives potassium-argon age of 53 Ma (Pearson and Obradovich, 1977). Forms discontinuous exposures northwest of Colville and in northwestern part of quadrangle.'
2411|'Mafic dikes of widely varied mineralogic composition and moderately varied chemical and modal composition. Fine-grained, light- to dark-gray; contain phenocrysts of one or more of following: clinopyroxene, hornblende, biotite, plagioclase, potassium feldspar, quartz, and rarely orthopyroxene and olivine. Found throughout quadrangle, but rare to absent within inner parts of Priest River Complex; most too small to show on map. Hornblende and biotite give potassium-argon ages ranging from 48 Ma (Miller, 1974c) to 53 Ma (Yates and Engels, 1968) (both ages recalculated using current IUGS constants, Steiger and Jaeger, 1977).'
2412|'Hornblende-biotite monzogranite, granodiorite, quartz monzonite, and quartz monzodiorite; porphyritic with groundmass having distinctive bi-modal grain size. Occurs as two non-contiguous plutons. Extremely homogeneous with respect to composition and texture, except for foliate, mafic zone along north side of largest pluton near Davis Lake. Zircon gives slightly discordant uranium-lead age of 52 Ma (Whitehouse and others, 1992); biotite and hornblende give potassium-argon ages of 49 and 48 Ma, respectively, on one sample, and 52 and 48 Ma, respectively, on another (Miller, 1974c, recalculated using current IUGS constants, Steiger and Jaeger, 1977).'
2413|'Hornblende-biotite quartz monzodiorite to quartz monzonite; on basis of spatial association and mineralogic similarities, probably genetically related to Silver Point Quartz Monzonite (Tsp). Forms single pluton 8 km west of Loon Lake. Distinguished from other plutons by some hornblende having pyroxene cores, average color index of 28, and extremely abundant sphene. Biotite gives potassium-argon age of 50 Ma (Engels, in Miller and Clark, 1975).'
2414|'Hornblende-biotite quartz monzonite; on basis of spatial association and mineralogic similarities, probably genetically related to Silver Point Quartz Monzonite and quartz monzonite of Ahern Meadows. Forms single pluton northwest of Loon Lake. Distinguished from other plutons by nearly all hornblende having pyroxene cores. Fine-grained, with average color index of 18. Biotite gives potassium-argon age of 51 Ma (Engels, in Miller and Clark, 1975).'
2415|'Medium- to coarse-grained, highly porphyritic hornblende-biotite granodiorite; hornblende distinctly subordinate to biotite. Sphene and xenoliths abundant. Typically has 1- to 8-cm-long orthoclase phenocrysts. Homogeneous composition in southern half of unit except for felsic phase near margin; heterogeneous mixture of magmatically mixed mafic and felsic rocks in northern part. Texture variable; much of pluton has variably developed foliation, and rocks along northwestern margin have fine-grained matrix. Color index averages about 16. Zircon gives uranium-lead age of 51 Ma (Whitehouse and others, 1992); biotite gives potassium-argon age of 46 Ma (Miller and Engels, 1975, recalculated using current IUGS constants, Steiger and Jaeger, 1977).'
2416|'Quartz monzonite to monzonite. Chilled, fine-grained margin contains olivine, hypersthene, clinopyroxene, hornblende, and biotite phenocrysts; interior is medium-grained and contains clinopyroxene, hornblende, and biotite, but only sparse hypersthene and no olivine. Age assignment based on mineralogical similarities to other Eocene intrusive rocks, as well as absence of fabric found in surrounding Priest River Complex. Forms single pluton 18 km north of Priest Lake.'
2417|'Fine- to coarse-grained alkalic plutonic rocks that include locally porphyritic syenite, granite, monzonite, monzodiorite, and shonkinite. Form numerous, noncontiguous bodies on both sides of Columbia River in northwest part of quadrangle. Underlies much larger area in Canada. Color index widely variable from 1 to 15. Most of Coryell plutonic rocks fall in compositional range between syenite and monzonite. Sheppard Granite is leucocratic, equigranular granite and syenite containing abundant myrmekite; almost everywhere altered. Sheppard considered by Little (1982) to be a part of Coryell plutonic rocks. Zircon uranium-lead age of Coryell plutonic rocks is 51 Ma (Carr and Parkinson, 1989). Biotite potassium-argon age is 52 Ma (Yates and Engels, 1968, recalculated using current IUGS constants, Steiger and Jaeger, 1977).'
2418|'Conglomerate with minor sandstone. Clasts from 2 cm to 1 m across include quartzite, greenstone, and fine-grained granitic rock. Thickness unknown, but at least 100 m (Little, 1982). Unconformably overlies rocks of the Rossland Group. Restricted to northwest side of Columbia River in Sandpoint quadrangle. Cretaceous age assignment inferred on basis of platanoid leaves (Little, 1960).'
2419|'Medium- and coarse-grained, leucocratic, quartz-rich, muscovite-biotite monzogranite. Forms large body in southwestern part of quadrangle. Color index averages about 5; muscovite:biotite ratio averages about 1:2. Texture is seriate to hypidiomorphic-granular; much of pluton contains sparse, centimeter-long, microcline phenocrysts. Ludwig and others (1981) reported very slightly discordant U-Pb age of 75 Ma on zircon from lithologically similar pluton at Midnight mine 10 km to southwest.'
2420|'Medium- and coarse-grained, locally garnet-bearing muscovite monzogranite. Highly evolved petrologically; contains no mafic minerals, plagioclase composition is an3. Forms four small, noncontiguous, east-west-aligned plutons east of Deer Lake. Nonporphyritic, hypidiomorphic-granular. Largest pluton partly surrounded by well-developed greisen zone and associated huebnerite-bearing quartz veins. Muscovite gives potassium-argon age of 80 Ma (Engels, in Miller and Clark, 1975, recalculated using current IUGS constants, Steiger and Jaeger, 1977).'
2421|'Biotite monzogranite; characterized by very coarse grain size. Average color index of 7. Relatively uniform with respect to composition. Subtlety porphyritic, because 2- to 3-cm-long phenocrysts are only slightly larger than other minerals in rock. Texture variable, caused by ubiquitous, localized concentrations of potassium feldspar phenocrysts. Forms two large plutons east and west of Deer Lake in southwestern part of quadrangle. Rocks indistinguishable from very coarse-grained monzogranite 8 km southwest of quadrangle that gives slightly discordant 206Pb/238U age of 91 Ma on zircon (Ludwig and others, 1981).'
2422|'Medium- to coarse-grained leucocratic muscovite monzogranite. Averages 6 percent muscovite. Forms single pluton 3 km west of Upper Priest Lake. Locally garnet-bearing; contains minor biotite at a few places near margins. Color index 0 to 3. Texture ranges from seriate too hypidiomorphic-granular; locally has fine-grained, chilled border. Muscovite gives potassium-argon age of 98 Ma (Miller and Engels, 1975, recalculated using current IUGS constants, Steiger and Jaeger, 1977).'
2423|'Leucocratic biotite monzogranite; some parts muscovite-bearing. Forms several tabular bodies 6 km east of Ruby in central part of quadrangle. Characterized by extreme textural variation ranging from fine-grained to pegmatitic. Color index averages 5. Deeply weathered, poorly exposed; could actually be series of dikes related to monzogranite of Gleason Mountain (Kgm) or Galena Point Granodiorite (Kgp) rather than coherent pluton. Age considered Cretaceous based on compositional similarity to nearby leucocratic granitic rocks.'
2424|'Medium- to fine-grained monzogranite in small bodies and isolated discontinuous dikes and sills. Mapped 8 km southwest of Colville, but most too small to show on map. Probably includes leucocratic dike rocks associated with numerous Cretaceous plutons. Texture, grain size, and composition variable; most rocks contain muscovite, some are garnet-bearing, none have more than three percent biotite. Considered Cretaceous in age based on spatial association with, and mineralogical similarity to, dated Cretaceous rocks in map region.'
2425|'Medium- to coarse-grained muscovite-biotite monzogranite and granodiorite; more mafic in sparsely exposed eastern part of unit. Forms large two-lobed body 3 km south of Priest Lake (fig. 2). Average color index 10. As mapped, unit could include more than one pluton. Mafic-rich eastern part of northern lobe and muscovite deficient southern lobe could be discrete plutons. Most of unit is even-grained, but locally contains 2- to 4-cm-long microcline phenocrysts. Muscovite and biotite give potassium-argon ages of 102 Ma and 95 Ma respectively, (Miller and Engels, 1975, recalculated using current IUGS constants, Steiger and Jaeger, 1977).'
2426|'Very coarse-grained muscovite-biotite monzogranite and granodiorite; locally porphyritic. Forms single pluton 24 km northwest of Newport. Average color index of 5. Muscovite:biotite ratio noticeably higher than most two-mica rocks in region. Hypidiomorphic-granular; where porphyritic, 2- to 3-cm-long phenocrysts are microcline. Very uniform texture and composition, except along fine-grained southern border. Muscovite and biotite give potassium-argon ages of 102 Ma and 100 Ma, respectively (Miller and Engels, 1975, recalculated using current IUGS constants, Steiger and Jaeger, 1977).'
2427|'Muscovite-biotite granodiorite. Forms single pluton 5 km east of Ione, in central part of quadrangle. Coarse-grained but locally variable grain size. Some muscovite to 1 cm across. Average color index of 7. Hypidiomorphic-granular, nonporphyritic. Lithologically resembles, and may be genetically related to, Blickensderfer Quartz Monzonite. Muscovite and biotite both give potassium-argon ages of 103 Ma (Miller and Engels, 1975, recalculated using current IUGS constants, Steiger and Jaeger, 1977).'
2428|'Medium-grained, seriate, two-mica monzogranite and granodiorite. Forms a single pluton 25 km north of Lake Pend Oreille. Rocks in much of pluton characterized by 5- to 8-mm-wide muscovite grains, distinctly larger than other minerals. Color index about 10. Appears to have distinctly chilled margin against granodiorite of Kelly Pass (Kkp). Age considered Cretaceous based on textural and compositional similarities to nearby Cretaceous two-mica rocks.'
2429|'Medium- to coarse-grained, seriate, non-porphyritic muscovite-biotite monzogranite or granodiorite. Forms sparse, deeply weathered exposures 8 km southwest of Colville; most of pluton lies west of quadrangle. Color index averages about 12. Assigned Cretaceous age based on textural and compositional similarities to nearby Cretaceous two-mica plutons.'
2430|'Muscovite-biotite monzogranite and granodiorite. Forms small body 6 km southwest of Priest Lake. Medium-grained; contains sparse, irregularly distributed, potassium feldspar phenocrysts. Internally heterogeneous with respect to texture and composition. Average color index of 7, but ranges from at least 5 to 15. Irregularly foliate. Age considered Cretaceous based on textural and compositional similarities to nearby Cretaceous plutonic rocks.'
2431|'Medium- to coarse-grained muscovite-biotite granodiorite. Color index averages 13, higher than many muscovite-bearing plutons. Characterized by abundant epidote; possibly primary. Has subtle foliation in places. Small, but wide-spread exposures suggest pluton underlies much of valley southwest of Bonners Ferry, extending nearly to Moravia. Cretaceous age based on textural and compositional similarities to nearby Cretaceous two-mica plutons.'
2432|'Very porphyritic, medium- to coarse-grained biotite monzogranite with ubiquitous trace amounts of muscovite. Forms a single pluton at the north end of Priest Lake. Texture and phenocryst concentration variable; pluton may be texturally zoned. Distinguished by pink potassium feldspar phenocrysts up to 10 cm long. Contains trace amounts of sphene. Biotite gives potassium-argon age of 90 Ma (Miller and Engels, 1975, recalculated using current IUGS constants, Steiger and Jaeger, 1977), which is considered minimum age.'
2433|'Medium- to coarse-grained, porphyritic muscovite-biotite monzogranite. Forms a single, large pluton 8 km west of Priest Lake. Three to 7 cm-long white microcline phenocrysts very irregularly distributed throughout pluton; concentrations of phenocrysts make up 50 percent of rock locally. Color index averages 7. Muscovite and biotite give potassium-argon ages of 97 Ma and 93 Ma, respectively (Miller and Engels, 1975, recalculated using current IUGS constants, Steiger and Jaeger, 1977).'
2434|'Muscovite-biotite monzogranite. Forms two bodies, one intruding the eastern part of the Hungry Mountain pluton 3 km west of Priest Lake, and another flanking the west side of the Hungry Mountain pluton. Characterized by extreme variations in grain size, even in small exposures. Typical rock is medium grained, but contains pods of aplite or pegmatite from 1 cm to several hundred meters across that have diffuse, gradational borders. Color index averages 7. Grades outward through increasing grain-size and concentration of potassium feldspar phenocrysts into monzogranite of Hungry Mountain (Kh). Age considered Cretaceous based on spatial and probable genetic relationship with monzogranite of Hungry Mountain.'
2435|'Porphyritic medium- to coarse-grained biotite monzogranite. Forms single pluton 3 km west of Sullivan Lake in northwestern part of quadrangle. Pink orthoclase phenocrysts average 3 cm long, but range to 6 cm. Color index averages 8. Biotite gives potassium-argon age of 99 Ma (Miller and Engels, 1975, recalculated using current IUGS constants, Steiger and Jaeger, 1977).'
2436|'Medium- to coarse-grained biotite granodiorite; contains sparse hornblende. Forms small pluton 6 km east of Lake Pend Oreille. Color index about 15. Even-grained, non-foliate; uniform texture and composition. Contains sparse, but ubiquitous sphene and epidote. Biotite gives potassium-argon age of 72 Ma (Miller and Engels, 1975, recalculated using current IUGS constants, Steiger and Jaeger, 1977), which is considered minimum age.'
2437|'Medium- to coarse-grained biotite granodiorite. Even-grained, non-porphyritic. Color index about 12. Exposed only on eastern shore of Lake Pend Oreille, but aeromagnetic anomaly (Harrison and others, 1972) suggests that it probably underlies much of lake itself. Biotite gives potassium-argon age of 88 Ma (Miller and Engels, 1975, recalculated using current IUGS constants, Steiger and Jaeger, 1977), which is considered minimum age.'
2438|'Porphyritic medium- to coarse-grained hornblende-biotite and biotite granodiorite. Color index 12 to 16. May consist of more than one pluton, especially in westernmost rocks of unit. Biotite gives potassium-argon age of 75 Ma in western part of unit, and 98 Ma in eastern part (Miller and Engels, 1975, recalculated using current IUGS constants, Steiger and Jaeger, 1977).'
2439|'Medium- to coarse-grained biotite monzogranite, but includes lesser mixed mafic and leucocratic granitic rocks. Forms irregular shaped body 10 km east of Colville. Average color index of 10, but more variable than most Cretaceous plutons. Locally has slight foliation. As mapped, may include more than one pluton in northeastern part of unit. Biotite from rocks 2.5 km east of Black Lake gives potassium-argon age of 100 Ma. (Miller and Engels, 1975, recalculated using current IUGS constants, Steiger and Jaeger, 1977).'
2440|'Porphyritic, medium- to coarse-grained biotite monzogranite and granodiorite. Forms single pluton 8 km east of Colville. Orthoclase phenocrysts range from 2 to 6 cm, highly concentrated in places. Color index averages 13; contains variable amounts of sphene. May grade into, and be petrogenetically related to, Starvation Flat Quartz Monzonite. Age considered Cretaceous based on compositional similarity to Starvation Flat Quartz Monzonite and other nearby granitic rocks of Cretaceous age.'
2441|'Porphyritic medium- to coarse-grained biotite granodiorite and monzogranite. Average color index of 12. Forms large, irregular-shaped mass between Priest Lake and north-south leg of Pend Oreille River. Feldspar phenocrysts range from 2 to 8 cm in length; average 3 cm. Except for phenocryst size, texture and composition very uniform throughout most of pluton. Compositionally similar to, and may grade into, granodiorite of Yocum Lake (Ky), but contact relations poorly exposed and ambiguous. Biotite gives potassium-argon age of 101 Ma (Miller and Engels, 1975, recalculated using current IUGS constants, Steiger and Jaeger, 1977).'
2442|'Fine-grained, irregularly porphyritic biotite granodiorite. Forms single, small, elongate body 21 km west of Priest Lake in Le Clerc Creek drainage (fig. 2). Grain size variable, including very fine-grained chilled-margin phase. Feldspar phenocrysts small and irregularly distributed. Color index about 10. Trace amount of muscovite; possibly secondary. Age considered Cretaceous based on lithologic similarity to nearby granitic rocks of that age.'
2443|'Fine- to medium-grained, irregularly porphyritic, leucocratic biotite monzogranite. Phenocrysts are potassium feldspar and quartz, some of latter are bipyramidal. Forms small pluton 2 km north of town of Priest River (fig. 2). Grain size, texture, and concentration of phenocrysts highly variable, even at outcrop scale. Deeply weathered and cut by numerous Eocene hypabyssal dikes (Thd). Age considered Cretaceous based on lithologic similarity to nearby granitic rocks of that age.'
2444|'Fine- to coarse-grained muscovite-bearing biotite granodiorite. Characterized by abundant epidote and allanite. Forms six non-contiguous plutons between north end of Priest Lake and Ione, Washington (fig. 2). Texture and mafic content locally variable; slightly foliate at margins of some plutons. Average color index of 10, but ranges up to 17. Based on petrologic similarities, probably genetically related to granodiorite of Reeder Creek (Krc). Several plutons have tungsten, molybdenum, or gold geochemical anomalies associated with them (Miller and Theodore, 1982; Miller and Frisken, 1984). Biotite and muscovite give potassium-argon ages of 99 Ma and 96 Ma, respectively (Miller and Frisken, 1984).'
2445|'Medium- and coarse-grained muscovite-bearing biotite granodiorite; generally contains less than 1 percent muscovite. Forms large irregular-shaped pluton around Priest Lake. Characterized by fairly abundant epidote and allanite and irregularly shaped, poikilitic microcline enclosing randomly distributed euhedral plagioclase. Chemical and petrologic similarities and coarser grain size suggest granodiorite of Reeder Creek could be deep-seated equivalent of granodiorite of Hall Mountain. Biotite gives potassium-argon age of 94 Ma (Miller and Engels, 1975, recalculated using current IUGS constants Steiger and Jaeger, 1977), which is considered minimum age.'
2446|'Biotite granodiorite and hornblende-biotite granodiorite. Chief rock-type is medium- to coarse-grained; strongly inequigranular, slightly porphyritic biotite granodiorite. Forms large body west of Lake Pend Oreille in southernmost part of quadrangle. Locally contains sparse muscovite or acicular hornblende. Color index 8 to 12. Sphene and epidote very abundant. In north and west parts of body, rocks grade into medium- to coarse-grained slightly to moderately foliated hornblende-biotite granodiorite having stubby prismatic hornblende coequal to biotite. In east part, rocks grade into fine-grained hornblende-biotite granodiorite. Hornblende-bearing rocks also carry abundant sphene and epidote and have color index between 15 and 20. Zircon gives uranium-lead age of 889 Ma, sphene gives 880.5 Ma (J.L. Wooden, written commun., 1994).'
2447|'Medium- to coarse-grained, non-porphyritic monzogranite to granodiorite. Average color index of 15, contains abundant sphene. Very homogeneous with respect to texture and composition, except for local mafic-rich parts near contacts on northeast flank of Addy Mountain, and 6 km north of town of Addy. Hornblende and biotite give potassium-argon ages of 99 Ma and 100 Ma, respectively (Engels in Miller and Clark, 1975, recalculated using current IUGS constants, Steiger and Jaeger, 1977).  Includes Arden Pluton.'
2448|'Leucocratic biotite monzogranite and muscovite-biotite monzogranite genetically related to unit Ksh, but has slightly coarser grain size, lower color index, no hornblende, and it contains muscovite. Presumably evolved from same magma as Starvation Flat Quartz Monzonite. Average color index of 9. Incompletely exposed contact with hornblende-bearing phase (Ksh) suggests that these two rock types are gradational over a few meters.'
2449|'Coarse- to fine-grained hornblende-biotite and biotite granodiorite, monzogranite, and quartz monzonite. Forms large, composite pluton 7 km northwest of Ione (fig. 2). Pluton consists primarily of two concentrically zoned phases: (1) feldspar-porphyritic biotite monzogranite in central part, grading outward through seriate porphyritic monzogranite into (2) non-porphyritic biotite monzogranite and quartz monzonite. Subordinate phases include (3) mafic-rich rocks around eastern part of pluton margin and (4) scattered various-sized bodies of leucocratic rocks, especially in central part of pluton. Biotite gives potassium-argon age of 99 Ma (Yates and Engels, 1968, recalculated using current IUGS constants, Steiger and Jaeger, 1977).'
2450|'Medium- to coarse-grained hornblende-biotite and biotite granodiorite. Forms large pluton east of Copeland (fig. 2). Sphene-bearing. Color index ranges from 13 to 17. Porphyritic in part, containing feldspar phenocrysts 2.5 cm long. Fairly uniform with respect to texture and composition, except in southwestern part of unit. Scattered southwestern exposures devoid of hornblende and may be separate pluton. Hornblende and biotite from northern part of unit give potassium-argon ages of 95 Ma and 90 Ma, respectively (Miller and Engels, 1975; recalculated using current IUGS constants, Steiger and Jaeger, 1977); emplacement age inferred to be about 100 Ma.'
2451|'Medium- to coarse-grained hornblende-biotite granodiorite and monzogranite (fig. 3). Forms large pluton northeast of Ruby (fig. 2). Even-grained to seriate, non-porphyritic; uniform with respect to texture and composition. Average color index about 14. Strongly resembles hornblende-biotite monzogranite and granodiorite phase of Starvation Flat Quartz Monzonite. Hornblende and biotite both give potassium-argon ages of 100 Ma (Miller and Engels, 1975, recalculated using current IUGS constants, Steiger and Jaeger, 1977).'
2452|'Coarse-grained, porphyritic biotite granodiorite. Forms small pluton 8 km north of Upper Priest Lake. Nearly all potassium feldspar is in 2- to 5-cm-long phenocrysts, almost none in groundmass. Contains abundant sphene. Color index averages 20. Biotite gives potassium-argon age of 68 Ma (Miller and Engels, 1975, recalculated using current IUGS constants, Steiger and Jaeger, 1977), which is considered to be cooling age. Rock type is texturally and compositionally similar to nearby 100-Ma plutons.'
2453|'Medium- to coarse-grained hornblende-biotite and biotite granodiorite and monzogranite. Form numerous, small, non-contiguous, incompletely mapped bodies in the Cabinet Mountains (fig. 2) that may or may not be genetically related to one another. Age considered Cretaceous based on lithologic similarities to nearby granitic rocks of that age, but could include some Jurassic rocks.'
2454|'Hornblende-biotite granodiorite porphyry. Found only on Packsaddle Mountain east of Lake Pend Oreille. Fine-grained matrix enclosing 1-cm-long phenocrysts of plagioclase, quartz, and locally hornblende. One or both mafic minerals partially altered in most rocks. Biotite potassium-argon age is 98 Ma (J. K. Nakata, U.S. Geological Survey, written commun., 1993).'
2455|'Hornblende-biotite granodiorite; some parts of unit contain no hornblende. Forms small, isolated exposures from Bonners Ferry to Naples; also flanks southeast margin of granodiorite of Kelly Pass (Kkp). Contains sparse microcline phenocrysts averaging 2 cm in length. Contains abundant sphene and epidote. Color index averages about 16. Medium- to coarse-grained. Rock type has well-developed lineation and irregularly developed foliation. Biotite gives potassium-argon age of 89 Ma (Miller and Engels, 1975, recalculated using current IUGS constants, Steiger and Jaeger, 1977), which is considered cooling age, not emplacement age.'
2456|'Hornblende-biotite granodiorite ranging to monzogranite; medium- to coarse-grained. Forms large, sparsely exposed pluton around and east of Eloika Lake (fig. 2); extent south of quadrangle unknown. Characterized by large stubby hornblende crystals, abundant sphene, and color index averaging 19. Hornblende and biotite give potassium-argon ages of 97 Ma and 95 Ma respectively, (Miller and Engels, 1975, recalculated using current IUGS constants, Steiger and Jaeger, 1977); emplacement age inferred to be about 100 Ma.'
2457|'Medium-grained biotite monzogranite and granodiorite. Even-grained, non-porphyritic. Forms single, poorly exposed pluton 5 km northeast of Eloika Lake (fig. 2). Biotite is only mafic mineral; average color index of 12. Sphene-bearing, but difficult to see because rocks everywhere deeply weathered. Spatial association and textural similarities suggest genetic relation to Fan Lake Granodiorite (Kfl). Age considered Cretaceous based on relation to Fan Lake Granodiorite.'
2458|'Porphyritic hornblende-biotite granodiorite. Forms sparsely exposed pluton 22 km east of Ione. Contains 2.5-cm-long potassium feldspar phenocrysts. Average color index of 18. Medium- to coarse-grained, non-foliated. Contains abundant inclusions. Age considered Cretaceous based on lithologic similarities to nearby granitic rocks of that age, especially granodiorite of Priest Lake (Kgpl).'
2459|'Hornblende-biotite granodiorite. Forms sparsely exposed pluton 17 km east-southeast of Ione. Non-porphyritic, but in all other lithologic aspects similar to, and probably genetically related to, granodiorite of Sema Meadows (Kse). Also lithologically resembles Cretaceous granodiorite of Priest Lake (Kgpl). Age considered Cretaceous based on lithic similarity to nearby granitic rocks of that age, especially granodiorite of Priest Lake.'
2460|'Highly mafic biotite-hornblende tonalite. Forms single pluton just east of Clagstone (fig. 2). Color index about 30. Coarse-grained, moderately too weakly foliate. Contains abundant sphene and epidote, and minor microcline. Compositionally gradational into hornblende-bearing phase of granodiorite of Kelso Lake, but because of age difference, the two bodies are considered distinctly different plutons. Zircon gives uranium-lead age of 90 to 100 Ma; sphene gives age of 940.5 Ma (J.L. Wooden, written commun., 1994).'
2461|'Medium- to coarse-grained hornblende-biotite granodiorite. Forms sparsely exposed pluton in and west of Priest Lake. Hornblende almost as abundant as biotite. Average color index of 17. Very abundant sphene. Even-grained, non-porphyritic, non-foliate. Very uniform with respect to texture and composition. Zircon gives uranium-lead age of 96 to 103 Ma; sphene gives age of 1010.5 Ma (J.L. Wooden, written commun., 1994).'
2462|'Non-porphyritic medium-grained biotite-hornblende granodiorite. Forms small pluton exposed on both sides of Pend Oreille River 19 km north of town of Cusick. Distinguished from most other granitic units by average color index of 23 and by hornblende more abundant than biotite. Mafic content and grain-size highly variable in some parts of pluton. Abundant mafic inclusions. Hornblende and biotite gives potassium-argon ages of 104 Ma and 100 Ma respectively, (R.J. Fleck, written commun., 1989).'
2463|'Highly porphyritic, very coarse-grained biotite-hornblende and hornblende monzogranite and granodiorite. Forms single pluton concentrically enclosing two-mica monzogranite of Twentymile Creek (Ktmc) 1 km east of Naples (fig. 2). Blocky microcline phenocrysts from 3 to 10 cm long make up 25 percent of rock volume in much of body. Color index about 16. Very abundant sphene. Hornblende potassium-argon age is 99 Ma (J. K. Nakata, U.S. Geological Survey, written commun., 1993).'
2464|'Biotite-hornblende granodiorite. Forms two bodies divided by granodiorite of Kelso Lake (Kk) on west side of Lake Pend Oreille. Medium- to coarse-grained; non-foliated to well-foliated. Color index 15 to 20. Characterized by hornblende-biotite ratio greater than one. Contains abundant sphene, epidote, and allanite. Feldspars are commonly gray. Zircon gives U-Pb age of 945 Ma (J.L. Wooden, written commun., 1994). Biotite and hornblende give potassium-argon ages of 83 Ma and 137 Ma, respectively (R. Fleck, written commun., 1993); biotite age considered a cooling age; hornblende age probably reflects excess argon.'
2466|'Muscovite-biotite granodiorite that forms a large mass west of Pend Oreille River in west-central part of quadrangle. Ranges in composition from tonalite to monzogranite, more potassic in western part. Medium- to coarse-grained, irregularly porphyritic, with poorly formed, small, white phenocrysts of microcline and orthoclase. Color index averages 11. Includes abundant metamorphic rocks; some screens several hundred meters in length. Unit contains very abundant dikes, pods, and small bodies of pegmatite, alaskite, and fine-grained leucocratic two-mica monzogranite. Phillips Lake Granodiorite makes up western part of Priest River Complex. Biotite gives potassium-argon age of 94 Ma, and muscovite from related pegmatite gives age of 101 Ma (Yates and Engels, 1968, recalculated using current IUGS constants, Steiger and Jaeger, 1977).'
2467|'Medium-grained muscovite-biotite granodiorite. Forms single body north of Upper Priest Lake. Even-grained, non-porphyritic, except for poorly formed 2-cm-long phenocrysts locally. Color index averages 9. Abundant pegmatite and leucocratic dike rocks, but otherwise slightly more uniform than most other units of Priest River Complex.'
2468|'Two-mica granitic rocks with about 5 percent gneiss and amphibolite. Widespread north of Priest Lake. Some granitic rocks contain no muscovite. Highly irregular distribution of metamorphic rocks in unit. Granitic rocks extremely variable with respect to texture, composition, and grain-size. Most rocks in unit are leucocratic, but some are highly mafic; latter probably represent incompletely mixed residue of partial anatectic melt derived from mafic sills in Middle Proterozoic Prichard Formation. Very abundant pegmatite and leucocratic dike rocks.'
2469|'Medium-grained two-mica granodiorite, ranging to tonalite. Forms small pluton 10 km north of Upper Priest Lake. Foliate near margins. Characterized by pale tan garnet and abundant epidote. Unlike most other units of Priest River Complex, contains anhedral, embayed sphene. Mineralogy could result from incompletely mixed partial anatectic melt derived from Middle Proterozoic Prichard Formation and mafic sills in that unit.'
2470|'Medium- to coarse-grained muscovite-biotite granodiorite, but ranges from tonalite to monzogranite. Forms single pluton in Caribou Creek drainage 1 km northeast of Upper Priest Lake (fig. 2). Locally contains sparse potassium feldspar phenocrysts. Color index ranges from 4 to 10. Overall, much more uniform in appearance than most other units of Priest River Complex, but contains discrete areas of pronounced textural and compositional inhomogeneity.'
2471|'Medium- and fine-grained biotite granodiorite; ranges to tonalite. Forms small pluton 10 km northeast of Upper Priest Lake (fig. 2). Slightly foliated. Characterized by euhedral allanite with epidote overgrowths. Average color index of 15.'
2472|'Medium- and locally coarse-grained muscovite-biotite granodiorite. Forms moderate-size pluton 11 km northeast of Upper Priest Lake (fig. 2). Average color index 11. Slightly foliate in northeast part. More uniform in composition and contains lower proportion of leucocratic dike rocks than most other units of Priest River Complex.'
2473|'Biotite granodiorite, but ranges from tonalite to monzogranite. Forms moderate-size pluton at north end of Upper Priest Lake. Distinguished by relatively high color index for unit of Priest River Complex; ranges from 5 to 20, averages 13. Contains large, irregularly shaped mafic inclusions. Texture, composition, and concentration of inclusions extremely variable throughout body.'
2474|'Medium- to coarse-grained two-mica monzogranite and granodiorite. Forms large pluton east of Priest Lake. Characterized by relatively well-formed, 2.5- to 4-cm-long potassium feldspar phenocrysts that have well-defined crystal shapes. Composition and texture very uniform compared to other units of Priest River Complex. Locally foliate, and shows ductile grain-size reduction within 2 km of Newport Fault. Color index averages about 6.'
2475|'Heterogeneous, mostly leucocratic, two-mica monzogranite and granodiorite; includes abundant pegmatite, alaskite, and leucocratic dike rocks. Forms moderate-size pluton on east side of Priest Lake (fig. 2). Average color index of 6. Very similar to rock types found in mixed granitic rocks of Camels Prairie (Kpcp) unit. Lineate, foliate, and shows ductile grain-size reduction in western part.'
2476|'Biotite granodiorite. Forms moderate-size body east of the southern part of Priest Lake. Fine- to coarse-grained; moderately heterogeneous with respect to texture, very heterogeneous with respect to composition. Color index averages about 14, but ranges to over 20. Lineate, foliate, and shows ductile grain-size reduction in western part.'
2477|'Mixed leucocratic two-mica granitoid rocks, amphibolite, gneiss, and schist. Forms large, irregularly shaped body between Naples and Priest Lake (fig. 2). About 90 percent of unit is heterogeneous granitic rocks; most abundant rock type is even-grained, leucocratic two-mica monzogranite. Large proportion of granitic rocks are dikes, pods and irregular masses of pegmatite and alaskite.'
2478|'Leucocratic two-mica granitic rocks, schist, amphibolite, and minor gneiss. Forms two large masses, one between Sandpoint and south end of Priest Lake, other 6 km southwest of Sandpoint (fig. 2). About 55 to 75 percent of unit consists of extremely heterogeneous granitic rocks ranging in composition from tonalite to monzogranite; color index between 5 and 10. Differs from unit Kpcp chiefly in proportion of metamorphic rocks. Ratio of metamorphic to granitic rock varies greatly over short distances, but generally is greater south of granodiorite of Wrenco (Tw). Most metamorphic rocks appear to be derived from Middle Proterozoic Prichard Formation and mafic sills in that unit.'
2479|'Even-grained leucocratic two-mica granitic rocks, abundant dikes of pegmatite and alaskite, and minor metamorphic rocks. Forms two small bodies, 3 and 11 km southeast of Priest Lake. Granitic rocks similar in composition to those in surrounding mixed granitic and metamorphic rocks of Soldier Creek (Kpms) unit, but consistently contains less than 10 percent metamorphic rocks. Extreme textural and compositional variety in granitic rocks.'
2480|'Slightly foliate, porphyritic biotite-granodiorite; minor muscovite and garnet. Forms two small bodies 12 km northwest of Sandpoint (fig. 2). Color index about 8. Composition and texture noticeably more uniform than granitic rocks of bounding mixed granitic and metamorphic rocks of Soldier Creek (Kpms) unit, and concentration of pegmatite and alaskite dikes noticeably less.'
2481|'Slightly porphyritic, two-mica, monzogranite and granodiorite. Forms large irregularly shaped body 19 km west of Copeland (fig. 2). Characterized by equant 1- to 2-cm-square potassium feldspar phenocrysts. Color index variable, averaging 10. Mostly medium-grained, but ranges from fine- to coarse-grained. Texture and composition uniform over large areas, and variable over large areas.'
2482|'Mostly muscovite-biotite granodiorite, but includes some tonalite and monzogranite. Forms large north-south-elongated body 15 km west of Bonners Ferry (fig. 2). Unlike some two-mica units, muscovite easily visible in almost all parts of unit, locally megacrystic. Medium- to coarse-grained. Average color index of 7. Composition and texture generally more variable than bounding units, but not nearly as variable as mixed rocks units.'
2483|'Chiefly granodiorite, but includes some monzogranite and minor tonalite. Forms large north-south-elongated body 5 km west of Naples (fig. 2). Medium- to coarse-grained, but contains very abundant fine- to coarse-grained leucocratic dikes and pods. Biotite only mafic mineral; minor muscovite in western part of unit. Contains sparse to moderately abundant epidote. Composition, texture, and concentration of included leucocratic rocks variable in much of unit.'
2484|'Tonalite to granodiorite; average composition tonalite. Forms large north-south-elongated body 9 km west of Bonners Ferry (fig. 2). Medium- and coarse-grained; seriate in much of unit. Biotite only mafic mineral; color index higher than most other units in Priest River Complex, ranges from 11 to 17. Muscovite absent, except very locally. Unit characterized by very abundant pale-green epidote with allanite cores and abundant irregularly shaped mafic inclusions ranging from 1 cm to tens of meters across. Composition and texture uniform in much of unit, but variable in places.'
2485|'Heterogeneous, mafic to leucocratic granitic rocks with screens and inclusions of metamorphic rocks, chiefly schist. Mapped as two small bodies, one 5 km north of Moravia, other 8 km south of Moravia (fig. 2). Unlike most other units of Priest River Complex, some granitic rocks in unit contain hornblende and sphene, and are highly porphyritic locally. As mapped, may include some rocks belonging to granodiorite of Kelly Pass and granodiorite of Bonners Ferry.'
2486|'Sillimanite-bearing muscovite-biotite monzogranite. Forms small body 2 km northeast of Eloika Lake (fig. 2). Medium-grained with weakly developed foliation. Color index variable from 5 to 15, but overall texture and composition fairly uniform. Sillimanite forms acicular crystals in biotite and may be restricted to numerous sub-centimeter-size inclusions distributed throughout unit. Some distributed zones of ductile grain-size reduction. Considered to be Cretaceous in age based on compositional similarity to Cretaceous plutonic rocks in quadrangle.'
2487|'Heterogeneous mixture of alaskite, pegmatite, aplite, and two-mica monzogranite; includes metamorphic rocks derived from Middle Proterozoic Prichard Formation and mafic sills in that unit. Forms scattered bodies east and southwest of Scotia (fig. 2). Foliation, lineation, and ductile deformation common in eastern part of unit. Considered Cretaceous in age, based on compositional similarity to Cretaceous leucocratic two-mica rocks associated with Phillips Lake Granodiorite.'
2488|'Biotite granodiorite; contains sparse muscovite that may not be primary. Forms a small elongate pluton 3 km southeast of Scotia (fig. 2). Medium- to coarse-grained; nonfoliate to slightly foliate. Relatively uniform with respect to texture and composition; contains fewer leucocratic dike rocks than surrounding units. Considered Cretaceous in age based on compositional similarity to Cretaceous plutonic rocks in quadrangle.'
2489|'Medium- to coarse-grained megacrystic muscovite-biotite monzogranite. Forms large body 8 km northwest of Blanchard (fig. 2). Distinguished by muscovite megacrysts 2 to 3 cm across. Average color index of 8. Southeastern part has well-developed mylonitic foliation and lineation caused by ductile deformation related to early stage of development of Eocene core complex(es) in region. Relatively uniform with respect to texture and composition; composition and texture strongly resembles those of monzogranite of Long Mountain (Klm). Age considered Cretaceous based on lithologic similarity to nearby Cretaceous two-mica rocks.'
2490|'Biotite-muscovite monzogranite bearing megacrysts of muscovite and potassium feldspar. Forms large body west of Cocolalla Lake and small body 7 km north of Cocolalla Lake (fig. 2). Megacrysts range from 0 to 20 percent of rock volume; muscovite averages 2 cm across, potassium feldspar 3 cm long. Strongly foliated on northwest, moderately foliated to unfoliated on southeast; variably mylonitic. Pegmatite and aplite dikes abundant. Grades into and intrudes muscovite-biotite monzogranite (Kmg). Relatively uniform with respect to texture and composition; strongly resembles monzogranite of Blanchard Road. Age considered Cretaceous based on lithologic similarity to nearby Cretaceous two-mica rocks.'
2491|'Foliate and lineate muscovite-biotite monzogranite containing sparse microcline porphyroblasts up to 1 cm long. Forms moderate-size body 3 km north of Cocolalla Lake (fig. 2). Color index about 8; rocks contain about 3 percent muscovite. Includes abundant pegmatitic rocks.'
2492|'Biotite granodiorite. Forms small body near Sawyer (fig. 2). Medium-grained; slightly to moderately foliate. Color index ranges from 15 to 25; hornblende locally abundant in mafic parts; muscovite in rocks with lower color index. Contains sphene, epidote, and allanite. Hornblende paleobarometry indicates crystallization at 6.7 Kb (T.D. Hoisch, written commun., 1993). U-Pb isotopic data on zircon inconclusive, but suggests that 90-100 Ma is most probable age. Sphene gives U-Pb age of 650.5 Ma (J.L. Wooden, written commun., 1994); considered cooling age because of depth of crystallization.'
2493|'Fine- to medium-grained, leucocratic, gneissic granite. Forms small mass east of Sawyer (fig. 2). Unit comprises several small bodies, all with biotite, most with muscovite, one with megacrystic microcline. Highly foliated throughout. Age considered Cretaceous based on lithologic similarity to nearby Cretaceous two-mica rocks.'
2494|'Medium-grained, subequigranular to equigranular muscovite-biotite monzogranite. Forms small body 3 km east of Edgmere (fig. 2). Micas about equal in amount. Locally has anhedral cm-long potassium feldspar phenocrysts. Slightly to moderately foliated. Gradational into and cut by dikes of monzogranite of Long Mountain (Klm). Age considered Cretaceous based on lithologic similarity to nearby Cretaceous two-mica rocks.'
2495|'Porphyritic, medium- to coarse-grained, sphene-bearing biotite monzogranite and granodiorite. Forms an elongated series of noncontiguous bodies from 20 km northwest of Copeland (fig. 2) to within 3 km of the southern part of Priest Lake. Color index as high as 20 in northern part of body; progressively more leucocratic and sphene-deficient southward. In southern part of unit, rock has color index between 8 and 14, and contains no sphene. Almost everywhere rock is slightly gneissic, and displays incipient to strong ductile grain-size reduction in thin section. Appears to be older than most other granitoid bodies of Priest River Complex, caught up within, and strung out between, various units of the complex. Discordant zircon indicates age between 90 and 100 Ma (J.L. Wooden, written commun., 1994); Archibald and others (1984) report 94-Ma uranium-lead age on zircon from equivalent(?) unit in Canada.'
2496|'Medium- to coarse-grained biotite tonalite, granodiorite, and trondhjemite. Trondhjemite contains a few percent muscovite and forms small appendage along eastern edge of much larger tonalite and granodiorite pluton. Rocks of larger tonalite and granodiorite body contain trace muscovite. Biotite and some muscovite is interstitial to felsic minerals. Average color index of tonalite 17, of trondhjemite 9. Both rock types have abundant epidote and trace amounts of garnet and hornblende. Most muscovite and epidote is contained within water-clear plagioclase. Texture and mineralogy indicate pluton has been metamorphosed. Zircon gives U-Pb age of 120 Ma; sphene gives 1601.0 Ma (J.L. Wooden, written commun., 1994). Biotite from tonalite gives K-Ar age of 107 Ma; biotite and muscovite from trondhjemite give ages of 101 Ma and 96 Ma, respectively (Miller and Engels, 1975, recalculated using current IUGS constants, Steiger and Jaeger, 1977).'
2497|'Medium- to coarse-grained highly porphyritic biotite-hornblende quartz monzodiorite and granodiorite. Forms moderate-size pluton south of Waitts Lake (fig. 2). Potassium feldspar phenocrysts to 9 cm long; concentration variable. Groundmass has bi-modal grain size. Average color index 18. Characterized by hornblende-biotite ratio greater than one, very abundant sphene, large phenocrysts, and bi-modal grain size. Hornblende and biotite give potassium-argon ages of 161 Ma and 162 Ma respectively, (R. Fleck, U.S. Geological Survey, written comm., 1988).'
2498|'Highly sheared phyllite, carbonate-bearing phyllite, and brecciated carbonate rocks. Found only on Eagle Mountain 6 km northeast of town of Chewelah (fig. 2). All probably derived from Middle Proterozoic Togo, Chamokane Creek, and Wabash Detroit Formations. Abundant brecciated quartz veins found in this unit, some gold-bearing.'
2499|'Metamorphosed basalt, basaltic andesite, trachyandesite, flow breccia, and tuff. Mineralogy characteristic of greenschist-facies metamorphism. Lesser amounts of interlayered siltite and conglomerate; highly schistose locally (Beddoe-Stephens, 1982; Little, 1982; Hy and Andrew, 1988; Joseph, 1990). Unit depositionally overlies metasedimentary and metavolcanic rocks (Jrs) unit.'
2500|'Conglomerate, greenschist, argillite, chert, quartzite, wacke, limestone, and minor flow rock and flow breccia (Joseph, 1990); conglomerate and conglomeratic wacke most abundant. Metamorphosed to greenschist facies. West of quadrangle, unconformably overlies Permian Mount Roberts Formation (Roback, 1989). Thickness probably exceeds 400 m.'
2501|'Pyroxene-hornblende monzonite to quartz monzonite. Forms north-south-elongated pluton 12 km west of Copeland (fig. 2). Extremely heterogeneous with respect to composition, color index, and texture. Pyroxene is hedenbergite; hornblende is ferrohastingsite. Color index ranges from 6 to 20, averaging 8. Very abundant sphene, allanite, and inclusions. Fine- to coarse-grained. Appears to be pre-existing pluton caught-up within younger rocks of Priest River Complex, but is here considered to be part of Priest River Complex. Triassic or Jurassic age based on compositional similarity of pluton to other alkalic bodies of this age, and to compositional dissimilarity with Cretaceous and to Tertiary rocks in region.'
2502|'Hornblende quartz syenite. Forms small pluton 10 km east-southeast of Copeland (fig. 2). Fine- to coarse-grained; equigranular to porphyritic. Color index averages 18. Abundant epidote and sphene. Hornblende gives potassium argon age of 131 Ma (R. Fleck, U.S. Geological Survey, written commun., 1988), which is considered to be cooling age because pluton located in area where potassium-argon ages of mineral pairs from other plutons are discordant (Miller and Engels, 1975). Emplacement age inferred to be Triassic or Jurassic based on compositional similarities to other alkalic rocks of this age in region.'
2503|'Fine- to coarse-grained hornblende-biotite quartz monzodiorite and quartz monzonite, but ranges to granodiorite. Forms elongate pluton east of Chewelah (fig. 2). Composition and texture highly variable throughout body. Average color index greater than 20. Hornblende and biotite give potassium-argon ages of 198 Ma and 100 Ma, respectively (Engels in Miller and Clark, 1975; recalculated using current IUGS constants, Steiger and Jaeger, 1977). Amount of discordance suggests emplacement age older than 205 Ma; thus age of Flowery Trail is considered to be Triassic in this report.'
2504|'Metamorphosed interbedded siliciclastic and carbonate rocks. Found only in few fault-bounded exposures near Huckleberry Range Fault on northwest side of Columbia River. Thin-bedded to massively bedded limestone and dolomite, argillaceous limestone, phyllite, and minor quartzite. These rocks were originally mapped as part of Flagstaff Mountain sequence of Carboniferous(?) age (Yates, 1971). Triassic age based on conodonts (Joseph, 1990).'
2505|'Lithic sandstone and wacke with lesser siltstone and chert-bearing fossiliferous limestone, conglomerate, and metavolcanic rocks. Restricted to northwestern part of quadrangle, west of Huckleberry Range Fault. Includes Mount Roberts Formation as defined by Yates (1971). West of Echo, include siliceous and calcareous argillite interbedded with fine- to medium-grained wacke and pods of fossiliferous limestone which are of uncertain affinities, and may or may not be Mount Roberts Formation. Unconformably overlain by Early Jurassic greenstone (Jrv) and Early Jurassic metasedimentary and metavolcanic rocks (Jrs) units. Age based on macrofossils (Roback, 1989) and conodonts (Joseph, 1990).'
2506|'Limestone, dolomite, and carbonaceous shale. Probably includes parts of Metaline Formation, Ledbetter Formation, and unnamed Devonian and Mississippian units. Mapped 4 km northeast of Springdale, and 7 km west-southwest of Arden (fig. 2). Most rocks assigned to this unit are fault-bounded and brecciated; bedding features obliterated.'
2507|'Limestone with lesser dolomitic limestone and dolomite. Found in limited areas north and southwest of town of Springdale. Medium- to pale-gray; thick- to thin-bedded with irregularly discontinuous chert bands. Thickness about 200 m, but upper and lower contacts not exposed and section could be internally faulted. Mississippian age assignment based on conodonts Bactrognathus sp., Hindeodus aff. H. cristulus (Youngquist and Miller), Hindeodus aff. H. crassidentatus (Branson and Mehl), Kladognathus sp. indet., Ozarkodina sp. indet. (Waggoner, 1990) contained in unit.'
2508|'Upper 170 m of unit is light-gray dolomite interbedded with maroon and pale-green argillite, which conformably overlies 175 m of pale-gray, coarse-grained, bedded dolomite. Lower 200 m is medium-grained, mottled dark-gray, sparsely sandy dolomite. Found in limited areas on east side of Colville Valley south of town of Chewelah. Age assignment inferred on presumed stratigraphic position below fossiliferous Mississippian limestone (Ml) unit and above fossiliferous Devonian dolomite and limestone (Ddl) unit.'
2509|'Light-gray and cream-colored dolomite interbedded with medium-gray argillaceous or carbonaceous limestone. Stratigraphic relationships and thickness uncertain. Found only in limited outcrops northwest of town of Metaline and on single hill 3 km east of town of Valley. Near Valley, unit contains Late Devonian brachiopods Cytrospirifer sp., and Tenticospirifer (Miller and Clark, 1975) and Late Devonian conodonts Plamatolepsis quadrantinodosa inflexa Muller, Pelekysgnathus ? sp. indet., Polygnathus semicostatus Branson and Mehl, Polygnathus sp. Indet. (Waggoner, 1990).'
2510|'Argillite, phyllite, and slate, much of it carbonaceous, calcareous, and siliceous; interbedded with minor greenstone, metawacke, and quartzite; grades southwestward into metawacke, quartzite, metaconglomerate, and lesser phyllite, argillite, and slate. Forms 10-km-wide belt straddling Columbia River and continuing southward to near Colville. Both fine- and coarse-grained facies contain numerous pods and beds of limestone, some barite-bearing and some fossiliferous (Yates, 1964; Yates, 1971; Joseph, 1990). Interbedded metavolcanic rocks include metaflow rocks and metatuff. Interlayered metavolcanic rocks, which are locally shown as separate unit (Dv), are more abundant southwestward. Unit assigned Devonian(?) and Carboniferous(?) ages by Yates (1964; 1971), and Devonian(?) and Carboniferous(?) and Ordovician(?) to Carboniferous ages by Joseph (1990). Considered Devonian in age here because all contained fossils, chiefly conodonts, indicate Devonian age for both facies of unit, but may possibly include some Ordovician rocks.'
2511|'Greenstone and chloritic phyllite of probable volcanic origin. Mapped chiefly north and south of Echo (fig. 2) and northwest of Columbia River. Composed of albite, chlorite, actinolite, epidote, and carbonate minerals (Yates, 1971; Joseph, 1990). Part of unit may be pyroclastic. Assigned to Devonian because unit bounded by fossiliferous Devonian metasedimentary rocks (Ds) unit, but may possibly include some Ordovician rocks.'
2512|'Conglomerate and minor slate. Found only in a restricted area 6 km north of Metaline Falls (fig. 2). Angular to well-rounded quartz- and chert-bearing conglomerate; contains clasts of mudstone in fine-grained matrix. Interbedded slate contains graptolites (Joseph, 1990)'
2513|'Thin-bedded sandy, calcareous siltstone, argillite, limestone, and fossiliferous packstone. Found only in a restricted area 6 km north of Metaline Falls (fig. 2). Argillite contains monograptids and limestone conodonts. Sharply overlain by quartz-granule conglomerate (Sc) unit (Joseph, 1990).'
2514|'Dark-gray carbonaceous shale, slate, and limestone; minor quartzite and chert interbeds. Massively bedded to thinly laminated; most lamination inconspicuous. At most places, highly deformed internally, including single and multiple cleavage(s), small-scale folds, and faults with unknown sense and amount of offset. Thickness estimated to be between 670 m and 760 m (Dings and Whitebread, 1965). Ordovician age based on abundant graptolites contained in unit (Park and Cannon, 1943; Carter, 1989a, 1989b), conodonts (Hogge, 1982), and trilobites, (Schuster, 1976).'
2515|'Medium- to dark-gray phyllite, white to brown vitreous quartzite, and minor interbeds of sandy, dark-brown dolomite. Mapped only in a small area 4 km northwest of Jared (fig. 2). Unit is about 60 percent phyllite and 40 percent quartzite. Correlation with other units in quadrangle questionable, Lithologically, unit most closely resembles Cambrian upper part of Late Proterozoic and Cambrian Addy Quartzite, but it may, in fact, overlie Metaline Formation(OFm), and be Ordovician in age.'
2516|'Limestone, dolomite, shaly limestone, limestone conglomerate, and carbonate-bearing quartzite. Internal stratigraphy of formation in Metaline area differs markedly from that of unit in area west of Addy. In Metaline area, upper part of formation consists of 0 to 600 m of massively bedded, fine-grained, gray limestone; middle 1200 to 1400 m is dominantly light gray and white, fine to medium grained, bedded dolomite; and lower 300 to 900 m is thin bedded, dark-gray limestone interbedded with lesser black shale (Joseph, 1990). In Addy area, upper 600 m of unit is similar to lower thin-bedded part in Metaline area; middle part of formation is dolomite similar to middle part in Metaline area, but is only about 800 m thick; lower part of formation is about 830 m of alternating zones of thin-bedded, fine-grained limestone, and thick-bedded, coarse-grained limestone and limestone conglomerate. Included in lower part of unit is 210-m-thick zone of dark-gray, coarse-grained dolomite and dolomite breccia and 150 m of sandy limestone, carbonate-bearing quartzite, pebble conglomerate, and argillite making up the lower part of formation. Age assignment based on contained trilobites (Park and Cannon, 1942), conodonts (Repetski and others, 1989), and graptolites (Carter, 1989a).'
2517|'Limestone, dolomite, quartzite, and shale. Probably includes parts of (Middle Cambrian) undivided, Rennie Shale and Lakeview Limestone (Flr) and (Middle? Cambrian) Gold Creek Quartzite (Fgc). Mapped only in southernmost part of quadrangle west of Lake Pend Oreille.'
2518|'Fossiliferous greenish-gray fissile shale and light- to dark-gray well-bedded to massive limestone and dolomite. Shale and limestone contain Middle Cambrian trilobites and brachiopods. Shale about 30 m thick; limestone at least 610 m thick (Harrison and Jobin, 1963). Found only in Packsaddle Mountain area on east side of Lake Pend Oreille and in thin fault slice 7 km north-northeast of Moyie Springs (fig. 2).'
2519|'White, pink, tan, and purple, slightly feldspathic, medium- to coarse-grained quartzite; locally conglomeratic. Bedding ranges from massive to thin bedded; most is thick bedded. Thickness of unit about 120 m (Harrison and Jobin, 1963). Found only in Packsaddle Mountain area on east side of Lake Pend Oreille.'
2520|'Gray phyllite;  in lower part, calcareous in upper part. Thin bedded to laminated, but bedding poorly preserved in most of unit except where quartzite beds or lenses are present.'
2521|'Early Cambrian archaeocyathid-bearing limestone at base (Reeves Limestone Member; Yates, 1964) at base of Maitlen Phyllite and zones of probably discontinuous limestone beds distributed irregularly throughout formation.'
2522|'White, purple, pink, gray, and tan, vitreous quartzite with interbedded siltite and argillite. Includes Gypsy Quartzite in northern part of quadrangle, and Addy Quartzite everywhere else (Lindsey and others, 1990). Addy averages about 1,400 m thick west of Jumpoff Joe Fault, but probably less east of fault. Gypsy ranges from 1,350 to 1,855 m in thickness east of Newport-Flume Creek Fault; is about 30 percent thinner west of fault. Upper part of Addy contains Early Cambrian trilobite Nevadella addyensis and brachiopod Kutorgina sp (Okulitch, 1951). Lindsey and others (1990) note abundant body and trace fossils in roughly same part of formation.'
2523|'Quartzite, conglomeratic quartzite, conglomerate, and phyllite. Lower part consists of phyllite with scattered quartzite and grit beds; upper part is quartzite, conglomeratic quartzite, and conglomerate. Clast types include quartzite, argillite, chert, vein quartz, and rare volcanic rock. Most appear to be derived from formations of Deer Trail Group, but there is a conspicuous absence of carbonate clasts. Thickness about 2,000 m east of Newport-Flume Creek Fault, about 1,000 m west of fault. Not found south of Ione either because of non-deposition or removal by Late Proterozoic erosion.'
2524|'Conglomerate, megabreccia, diamictite, limestone, feldspathic and lithic quartzite, siltite, argillite, carbonaceous argillite, and locally, greenstone. Clast types in conglomerate, megabreccia, and diamictite include quartzite, dolomite, argillite, chert, vein quartz, and volcanic rock; most clast lithologies recognizable from formations of Deer Trail Group. Extremely variable lithostratigraphy and thickness over short distances, probably due to highly varied depositional conditions caused by syndepositional faulting.'
2525|'Greenstone, derived from lava flows, tuff, volcanic breccia, and volcaniclastic rocks; much is phyllitic. Composition is tholeiitic basalt (Miller, 1983a). Thickness of flows range from a few meters to several tens of meters. Pillow structure present, but subtle and difficult to recognize. Maximum thickness 1,850 m.'
2526|'Greenstone, derived from lava flows, tuff, volcanic breccia, and volcaniclastic rocks; much is phyllitic. Composition is tholeiitic basalt (Miller and Clark, 1975). Thickness of flows range from a few meters to several tens of meters; separated by flow breccia consisting of light-green angular clasts averaging 5 mm to 5 cm across in dark-green matrix. Pillow structure fairly abundant, especially in lower part of member, but pillows subtle and difficult to recognize. Thickness averages 975 m. Includes intrusive rocks that are similar to massive flow rocks but coarser grained; some is gabbroic.'
2527|'Diamictite, conglomerate, sandy siltite and argillite, and lithic quartzite. Clasts in diamictite and conglomerate appear to be derived almost totally from formations of Deer Trail Group. Pale-green and pale-gray matrix-supported diamictite and conglomerate are most common lithologies. Maximum thickness in Huckleberry Mountain area (fig. 2), 480 m; thins and pinches out eastward and northeastward.'
2528|'Phyllitic, matrix-supported diamictite and conglomerate and minor lithic quartzite; most of lower part is pale-tan and most of upper part is pale-green. Concentration of clasts ranges from only a few percent of rock volume to about 70 percent. Clast size ranges from centimeters to meters across; shape ranges from angular to moderately well-rounded. Bedding in member is readily apparent only where lithic quartzite is interbedded.'
2529|'Pale-gray, pale-green, and pale-tan phyllite. Contains very sparse lithic clasts to 1 cm in length and nearly ubiquitous, mm-size, round quartz grains. Bedding indistinct or unrecognizable in most of member. Northeast of Sullivan Lake, forms thick, northeastward-thinning sedimentary wedge bounded by conglomerate.'
2530|'Brownish-gray to pale-gray, slightly dolomitic limestone containing numerous, round, millimeter-size quartz grains and a moderate, but variable, amount of argillaceous material. Medium to thick bedded. Thickness estimated to be about 150 m.'
2531|'Massive and phyllitic greenstone; numerous 1- to 10-m-thick bodies too small to show at scale of map. No diagnostic primary features preserved; greenstone bodies could represent intrusive sills, flow rocks, or pyroclastic rocks.'
2532|'Medium- to fine-grained mafic-rich sills; intrude Wallace Formation and along Wallace Formation-Snowslip Formation contact. Lithologically indistinguishable from 1,433-Ma mafic intrusive rocks (Ymi) that are restricted to Prichard Formation, but considered by Harrison and others (1992) to be 1,100 or 800 Ma in age. Sills found only two places in quadrangle, 6 km north-northeast of Leonia and 6 km east-northeast of Moyie Springs; at both places they intrude Wallace Formation of Middle Proterozoic Belt Supergroup.'
2533|'Argillite, phyllite, and quartzite. Rocks of Deer Trail Group lacking distinguishing characteristics needed to assign them to individual formations because of poor exposure, metamorphism, or deformation.'
2534|'Interbedded vitreous quartzite and dark-gray to greenish-gray, massively bedded to faintly laminated argillite. Much of quartzite is coarse grained and cross bedded; some contains thin quartzite-pebble beds. East of Sullivan Creek, thickness and proportion of quartzite in unit may be greater than it is southwest of Chewelah. Unit southwest of Chewelah contains maroon, argillaceous, fine-grained quartzite in lower part that strongly resembles quartzite of Bonner Formation of Belt Supergroup. Maximum thickness of unit about 550 m.'
2535|'Southwest of Chewelah, formation consists of tan, pink, gray, and maroon dolomite with minor interbedded maroon and gray argillite. About ninety percent of formation is dolomite that contains relatively little non-carbonate material; relative purity is basis to distinguish unit from Wabash Detroit Formation. Near Idaho-Washington border, formation is white, tan, and gray dolomite containing much higher proportion of silt and argillaceous material and much higher proportion of interbedded gray phyllite. Fault-bounded Stensgar Dolomite in this area difficult to distinguish from undivided Wabash Detroit Formation and Chamokane Creek Formation (Ywcu). Formation is host to large deposits of magnesite, probably of remobilized syngenetic origin (Campbell and Loofbourow, 1962; Miller and Whipple, 1989). Thickness of Stensgar southwest of Chewelah averages 250 m; near Idaho-Washington border, appears to be about 300 m.'
2536|'Formation is almost entirely argillite. West of Chewelah, lower third of unit is medium- to dark-gray argillite; upper two-thirds is pale-greenish-gray and lavender-gray argillite or phyllitic argillite. Thickness averages 370 m. Near Idaho-Washington border, unit is entirely dark-gray phyllite. Thickness appears to be about 300 m, but unit here is everywhere faulted or internally deformed by intense cleavage.'
2537|'Thin- to thick-bedded, gray and white, impure dolomite with abundant thin interbeds of pale-green and gray argillite and carbonate-bearing siltite; locally, unit contains altered greenstone in upper part that may be volcanic flow rocks. Near Idaho-Washington border, rocks of unit are included with Chamokane Creek Formation because deformation and homogenization by faulting and multiple cleavages have destroyed sedimentary features used to distinguish the two units. Thickness southwest of Chewelah averages 240 m.'
2538|'Highly sheared and faulted dolomite, dolomitic quartzite, argillite, and quartzite. Close-spaced faults and multiple cleavages, especially in Idaho-Washington border area, have destroyed sedimentary and lithologic features used to distinguish Wabash Detroit Formation from Chamokane Creek Formation. Thickness unknown.'
2539|'Carbonate-bearing quartzite and siltite, interbedded with dolomite, and argillite. West of Chewelah, contains a 150-m-thick zone of interbedded vitreous quartzite and argillite. Vitreous quartzite zone present in section near Idaho-Washington border, but thickness uncertain. Very poorly exposed. Thickness of composite sections in both areas about 600 m.'
2540|'Medium- and dark-gray argillite with subordinate green argillite and green and gray siltite. Also contains rare, thin, beds of quartzite and dolomite in lower part of unit. West of Chewelah, minimum thickness about 800 m, but unit highly deformed internally and base of formation everywhere faulted. In section near Idaho-Washington border, Togo Formation is found mostly in extremely deformed fault-bounded blocks.'
2541|'Laminated black argillite and white siltite in lower part of unit, green cherty argillite, siltite, and silty limestone and dolomite in upper part. About 550 m thick, but unknown thickness removed by erosion (Harrison and Jobin, 1963). Found only in Clark Fork-Eastport sequence.'
2542|'Altered and bleached argillite, siltite, and lesser quartzite. Mapped as undivided unit only on one ridge east of Pend Oreille River in Newport sequence, where alteration and poor preservation of sedimentary features preclude assignment of rocks to specific formations.'
2543|'Maroon, pale-purple, and pale-green siltite, argillite, and quartzite. As mapped, unit in southern part of Clark Fork-Eastport sequence includes quartzite member of Striped Peak Formation (Harrison and Jobin, 1963). Unit mostly quartzite there; about 80 percent thin-bedded, coarse siltite in Newport sequence. In Clark Fork area, about 210 m thick; in Newport sequence, about 190 m thick; not present in Chewelah sequence.'
2544|'Argillite, siltite, quartzite, dolomite, and dolomitic siltite. As mapped, unit in southern part of Clark Fork-Eastport sequence includes lower three members of Striped Peak Formation (Harrison and Jobin, 1963); thickness about 400 m. In northern part of sequence, thickness is about 620 m. In Newport sequence, thickness about 420 m; not present in Chewelah sequence.'
2545|'Dark- to medium-gray, laminated argillite, thin-bedded siltite, and thick- to thin-bedded quartzite. As mapped, unit includes laminated argillite and siltite member of Wallace Formation at Clark Fork, Idaho (Harrison and Jobin, 1963); about 120 m thick there. About 155 m thick northeast of Bonners Ferry; about 350 m thick north of Newport; and about 650 m thick at Chewelah.'
2546|'Schist, calc-silicate rock, dolomitic marble, argillite, siltite, and dolomite. Sequence may contain unrecognized faults. Thickness unknown. Found only on mountain 16 km due north of town of Cusick.'
2547|'Pale green, white, tan, pale-gray, and maroon, stromatolitic and oolitic dolomite, dolomitic siltite, and siltite. North of Newport, contains some dark, chlorite-green siltite beds. As mapped, unit in Clark Fork area includes upper calcareous member of Wallace Formation (Harrison and Jobin,1963). Thickness in Clark Fork area, about 300 m; northeast of Bonners Ferry, about 380 m; north of Newport, about 360 m; east of Chewelah, about 430 m.'
2548|'Argillite, siltite, and porous quartzite. West of Fan Lake, all rocks hydrothermally altered, bleached, and deeply weathered. Sedimentary features used to distinguish formations are destroyed. East of Packsaddle Mountain, poor exposure and complex structure preclude specific formational assignment (Harrison and Jobin 1965). Thickness unknown.'
2549|'Green, and medium- and dark-gray, argillite and siltite, and minor quartzite; locally, all rock-types may contain carbonate minerals. In Clark Fork area, lower part of formation contains limestone and calcareous argillite and siltite. As mapped, formation there is most of argillite member and all of argillite, siltite, and limestone member of Wallace Formation as defined by Harrison and Jobin (1963). Thickness at Clark Fork, about 1,920 m; northeast of Bonners Ferry, about 880 m; north of Newport, about 380 m; east of Chewelah, about 1,400 m thick. Clark Fork and Chewelah sections may be thickened by faults.'
2550|'Quartz-feldspar-muscovite-biotite schist and calc-silicate rock. No primary sedimentary features preserved; thickness unknown. Mapped only in area south of Calispell Peak, 24 km northeast of Chewelah.'
2551|'Dolomite, dolomitic limestone, and carbonate-bearing siltite and quartzite with abundant thin interbeds of dark-gray argillite. In Clark Fork area, includes lower calcareous member and lower part of argillite member of Wallace Formation as defined by Harrison and Jobin (1963). Thickness in Clark Fork area, about 760 m; northeast of Bonners Ferry, about 1400 m; north of Newport, about 730 m; and east of Chewelah, about 800 m.'
2552|'Pale-green siltite, quartzite, argillite, dolomite, and carbonate-bearing siltite. Thickness northeast of Bonners Ferry, between 200 m and 580 m; north of Newport, 320 m. Included with St. Regis Formation east of Chewelah, and with Wallace Formation at Clark Fork.'
2553|'Siltite, quartzite, and argillite. Mapped as undivided only between Lake Pend Oreille and Cocolalla Lake (fig. 2). Probably includes part or all of each formation of Ravalli Group (St. Regis, Revett, and Burke Formations). Moderately metamorphosed close to plutons. Thickness unknown, but probably cut by more faults than shown on map.'
2554|'Maroon to purple siltite, argillite, and lesser quartzite. Unit characterized by ripple marks, mud cracks, mud-chip breccia, cross lamination, and fluid-escape structures. Thickness in Clark Fork area, from 180 to 335 m; northeast of Bonners Ferry, from 250 to 470 m; north of Newport, about 275 m; east of Chewelah, about 450 m as mapped (including Empire Formation).'
2555|'Quartzite and minor siltite; white, tan, light-gray, pink, and maroon. Formation northeast of Bonners Ferry and east of Chewelah contains larger proportion of finer grained rocks than formation in Clark Fork area. At Newport, much of formation is fine grained, maroon quartzite Thickness in Clark Fork area, about 610 m; northeast of Bonners Ferry, from 570 m to 750 m; north of Newport, about 750 m; and east of Chewelah, 950.'
2556|'Siltite with minor argillite and quartzite. Most of formation is uniform, medium- to pale-gray siltite in even beds ranging in thickness from a few centimeters to about 20 cm. Upper part of formation contains zone, up to 150 m thick, of lavender siltite and argillite containing abundant ripple marks and mud-chip breccia; strongly resembles strata of typical St. Regis Formation (Ysr). Thickness in Clark Fork area, about 975 m; northeast of Bonners Ferry, about 1360 m; north of Newport, about 850m, and east of Chewelah, about 1,100 m.'
2557|'Medium- to fine-grained sills and dikes of diabase composition intruding Prichard Formation. Composed of hornblende, biotite, plagioclase, quartz, and opaque minerals. Most bodies are sills, but discordance of intrusions appears to increase progressively with depth in Prichard Formation. Zircon from sill near Bonners Ferry, Idaho gives uranium-lead age of 1,433 Ma (Zartman and others, 1982). Sills and dikes are lithologically indistinguishable from sills and dikes (ZYmi) in Wallace Formation, which represent younger periods of intrusion at 1,100 and 800 Ma (Harrison and others, 1992). Some sills in Prichard Formation could belong to the two younger sill groups.'
2558|'Interbedded quartzite, siltite, and argillite; color ranges from white and pale-gray for quartzite, pale- to medium-gray for siltite, and medium- to dark-gray for argillite. Entire formation contains pyrite, highest concentration in argillites; oxidation of pyrite causes almost all rock surfaces in Prichard Formation to be iron-stained. Thickness in Clark Fork area, about 6,000 m (Cressman, 1989); northeast of Bonners Ferry, about 5,500 m; north of Newport, about 5,200 m; and east of Chewelah, about 4,100 m; all thicknesses include mafic sills. Undetected faults are probably present in all sections.'
2559|'Medium- to coarse-grained feldspar-quartz-muscovite-biotite schist and hornfels, locally containing aluminosilicates, intruded by two-mica granitic rocks of Priest River Complex. Contains bodies of medium- to coarse-grained amphibolite and garnet amphibolite derived from mafic intrusive rocks in Prichard Formation. East of Chewelah, contact with relatively unmetamorphosed Prichard Formation is gradational zone several hundred meters wide; generally placed where bedding in Prichard cannot be distinguished from metamorphic foliation. Much of unit within 4 km of Newport Fault shows incipient to strong mylonitization.'
2560|'Biotite-quartz-plagioclase-potassium feldspar orthogneiss. Contains traces of muscovite. Fine- to coarse-grained; much of unit is megacrystic. Foliation, lineation, grain-size-reduction, and tectonic rounding of megacrysts present in most of unit; caused by intense ductile deformation. Numerous pods composed of metamorphosed Prichard Formation and associated amphibolite are distributed throughout easternmost 300 to 500 m of unit. Possible age for Newman Lake Gneiss ranges from Proterozoic to Eocene; older age is preferred because of regional association of gneiss with metamorphosed Prichard Formation, and lithologically similar orthogneiss (gneiss of Leclede, Ylg) of known Middle Proterozoic age to north.'
2561|'Medium- to coarse-grained, megacrystic biotite orthogneiss. Composition ranges from monzogranite to granodiorite. Color index ranges from 8 to 13. Highly foliate and lineate throughout. Includes small areas of extremely heterogeneous gneiss, possibly paragneiss, on south side of Pend Oreille River and 5 km east of Priest River (fig. 2). Zircon from typical orthogneiss gives uranium-lead age of 1,578 Ma (Evans and Fischer, 1986).'
2562|'Coarse-grained quartz-feldspar-muscovite-biotite schist and gneissic rocks that include minor amphibolite bands and pods. Mapped only around Davis Lake (fig. 2). Intruded by texturally and compositionally heterogeneous leucocratic granitic rocks. Schist and gneiss could be metamorphosed Middle Proterozoic Belt Supergroup, but appear to be more thoroughly recrystallized, contain a higher proportion of granitic material, and are uniformly, strongly deformed; unit could be pre-Belt crystalline rocks.'
2575|'Alluvial silt, sand, and gravel along stream valleys; silt and peat in filled ponds and lakes.'
2576|'Glaciofluvial deposits of sand and gravel. Includes morainal till around the southwest end of Pend Oreille Lake.'
2577|'Areas of slump along valley walls.'
2578|'Glaciofluvial and glaciolacustrine deposits of silt, sand, and gravel, usually stratified and well sorted; includes some kame deposits and morainal material along margins of Spokane Valley and Rathdrum Prairie and in their tributary valleys.'
2579|'Loess deposits of tan to brown silt and fine sand, includes a number of overlapping soil zones of differing ages, some of which have well-developed clay and caliche layers; mantles the basalt plateau and the lower, gentler slopes of hills and ridges of pre-Tertiary rock that protrude above the top surface of the basalt flows and border the flows on the eastern side.'
2580|'Poorly consolidated gravel, sand, and silt capping terraces and some flat ridge crests or other gently sloping surfaces. Accumulation of some deposits began after outpouring of basalt flows of the Columbia River Group, which dammed stream drainages; some result from blocking of drainage to west by glacial material in Pleistocene time. Deposits all of local origin.'
2581|'Flows of dense, dark, tholeiitic basalt, usually from 50 to 150 feet thick, and all essentially flat lying. Pillow-palagonite tuff complexes are present. The interlayered or underlying lacustrine beds of the Latah Formation are included with the basalt and not shown separately are. The Latah Formation consists of poorly-indurated siltstone, claystone, sandstone, and minor conglomerate that are tan to gray in color, thin bedded, and in part laminated.'
2582|'Plutons to batholithic complexes that predominantly consist of felsic igneous rocks of quartz monzonitic to granodioritic composition, but including differentiates ranging in composition from diorite to alaskite. Most of rocks are medium- to coarse grained and in large part porphyritic, but also include some sill-like bodies of fine-grained quartz monzonite intruded into the high-grade metamorphic rocks. Some, such as the small pluton south of Wolf Lodge Bay on Coeur dAlene Lake, have apophyses and dikes of porphyries associated with them.'
2583|'Light- to dark-gray, thin- to thick-bedded, blocky limestone; includes blocky gray dolomite unit in upper part; contains some silty to sandy layers and zones. Metamorphosed to marble or hornfels adjacent to granitic intrusives.'
2584|'Rennie Shale - a fissile olive colored fossiliferous shale, about 100 feet thick; exposed only infrequently and generally poorly so. This units lies conformably between the Gold Creek Quartzite and the overlying Lakeview Limestone and is here mapped with the Gold Creek Quartzite.  

Gold Creek Quartzite - white- to pinkish- vitreous, coarse-grained quartzite. Some pebble conglomerate is always present at base. The quartzites are usually thick-bedded and commonly crossbedded; the unit is about 500 feet thick.'
2585|'Dominantly medium-gray to olive-colored siltite or laminated siltite and argillite. Very thinly laminated dark argillite makes up the lowest part of section. The unit also contains rare chert laminae. Mud-chip breccia and ripple marks are common structural features; mud cracks are rare. It characteristically weathers in a blocky habit. Maximum thickness of eroded remnants is approximately 2,000 feet.'
2586|'This formation consists of four distinct sub-units: 1) a basal mixed siltite, argillite, and quartzite member of red and green color overlain successively by 2) a tan dolomitic member, 3) a very thinly laminated dark-gray argillite-siltite member, and capped by 4) a dark-red arkosic quartzite unit (Harrison and Jobin, 1963). The combined thickness of the unit is nearly 2,000 feet and is about equally divided among the four sub-units. Basal unit thickens and overlying units wedge out southward. Mud cracks, ripple marks, and mud-chip breccia are found in red to green-colored rocks; salt casts and channeling are much less common structures. Several stromatolite layers occur in this unit. Micaceous sheen on bedding surfaces is characteristic at most outcrops. The transition into the overlying Libby Formation, and into the underlying upper part of Wallace Formation occurs through fairly narrow zones.'
2587|'Very thinly bedded dark-gray argillite or thinly laminated dark-gray argillite and light-gray siltite; a few beds or thin zones of lighter colored siltite are scattered through unit. A carbonate-bearing zone several hundred feet thick occurs near the center or toward the top of the map unit and appears to persist throughout area. It consists of greenish-gray to gray to dark-gray interbedded to interlaminated dolomitic argillite to siltite with some gray dolomite to dolomitic limestone beds, similar to basal unit of the lower part of Wallace. At some places dark-gray argillite, also contains carbonates. At most exposures, rocks are noticeably fissile, and fairly regularly bedded. Thickness is approximately 2,500 to 3,000 feet. The lower contact is gradational.'
2588|'This map units contains two distinguishable members, which were not differentiated on map. The upper unit consists predominantly of alternating black argillite and light-gray to greenish-gray siltite or quartzite; the latter is usually carbonate bearing. Interspersed in the sequence are layers or zones of rock like that in the Wallace units above and below. The lower unit, green to greenish-gray or gray, usually carbonate -bearing, interbedded or interlaminated argillite and siltite, contains many bluish-gray dolomite and dolomitic limestone beds. Blocky weathering molar-tooth structure, and rusty-tan-weathering are characteristic. Mud cracks (nondesiccate in origin) and ripple marks are common; fine-textured cross bedding is evident on etched surfaces of some siltite and quartzite beds. Irregularity in bedding and minor folds are characteristic. Thickness is estimated to vary from 5,000 to 7,000 feet; the thinnest section is in and around the Coeur dAlene district.'
2589|'Dark-red, purplish-red, green, or greenish-gray, interbedded or interlaminated, usually very thin- to thin-bedded argillite and siltite. The unit contains some quartzite beds in its basal part and becomes more argillitic toward top. Some carbonate-bearing beds are found in the upper part. Mud cracks, mud-chip breccia, and ripple marks are very common. It is gradational into units above and below. The unit weathers into platy or flaggy fragments.'
2590|'Blocky, white to light-gray, thick-bedded, fine- to medium-grained, vitreous quartzite that is somewhat feldspathic. Gray to greenish-gray, thin- to thick-bedded siltite with partings and interbeds of argillite are common in upper and lower parts of the unit; siltite may be dominant rock type over zones tens of feet thick. Cross bedding in vitreous quartzite is common, and a rusty speckling due to weathering of small round carbonate segregations is characteristic in some vitreous beds. The thickness ranges from 2,000 to 3,000 feet. The map unit is transitional over hundreds of feet into units above and below.'
2591|'Units are lumped together where individual identity questionable in areas west of south end of Coeur dAlene Lake.'
2592|'Light- to medium-gray to greenish-gray, thin- to thick- bedded siltite with partings and interbeds of argillite. Some light-gray to white quartzite occurs in scattered beds and zones. At some places, mostly peripheral to Coeur dAlene mining district and in the lower middle part of section, rocks are reddish-purple to lavender in color. Ripple marks are common in places; some cross bedding is present. At many exposures, the rocks have a faded weathered rind that contrasts with darker fresh rock. Fine magnetite octahedral pepper many of siltite beds. It is transitional into formations above and below. The thickness ranges from 2,800 to 4,500 feet; at most places, it is between 3,000 and 3,500 feet.'
2593|'The formation was mapped as a single unit in western part of Coeur dAlene district near Kellogg. The upper transitional zone and argillitic rocks have not been mapped separately from the predominantly siltite to quartzite below in the western part of the Coeur dAlene district.'
2594|'Dark- to medium- gray, very thin-bedded argillite commonly interlaminated with light-gray siltite and also containing some siltite beds. This sequence grades upward into a interbedded and interzoned argillite, siltite, and quartzite sequence 500 to 1,000+ feet thick, which forms the transition zone into siltitic and quartzitic units above. Argillite is rust-stained on weathered surfaces; occasional ripple marks are present in the upper part. Total thickness ranges from 2,500 to 3,500 feet.'
2595|'Predominantly medium- to light-gray, thin- and regularly bedded siltite, laminated in part; some argillite is present in laminae and beds. Some beds or zones of gray to white quartzite of lenticular habit are present. Disseminated pyrrhotite concentrated within certain laminae is characteristic, and its weathering results in a persistent rusty-red rind on fracture surfaces. Thickness is over 7,500 feet; the base of the unit is not exposed.'
2596|'Dark-green, fine- to coarse- grained, hornblende-plagioclase-(quartz-biotite) diabasic-textured rocks intruded as sills into Prichard Formation. The sills can be as much as 1,000 feet thick; only the larger bodies are shown on the map.'
2597|'Rusty-weathering, medium-grained, thinly-layered biotite-orthoclase-plagioclase-quartz gneiss and schist that contains minor quartzite. These rocks are foliated and may show lineated, mylontitic fabrics. Sillimanite is common and widespread. Muscovite-biotite schist layers are less than 1 m thick and quartz-feldspar layers are more than 1 m thick. The  gneiss is locally intruded by mafic igneous rocks that now are small bodies of garnet-bearing amphibolite. Abundant felsic dikes and irregular crosscutting bodies with wide range of textures and compositions are present. Griggs (1973) thought the Prichard Formation (Belt Supergroup) was the protolith for the gneiss.'
2598|'Tan to light-gray, coarse-grained quartz-feldspar-mica gneiss; tan, pink, gray, brown, medium to fine-grained micaceous and sillimanitic schist; gray, prominently layered gneiss and schist, and quartzite. Individual layers in prominently layered gneiss and schist are generally less than 6 inches thick and include quartzite, feldspathic quartzite, micaceous quartz-feldspar gneiss, granitic rock, amphibolite, and schist. Finer-grained sillimanitic facies rocks generally have less well-developed schistosity and are commonly intricately folded and contorted on all scales. Intricate folding and contortion on larger-scale is widespread in coarser-grained rocks. Granitic and pegmatitic lenses, pods, and irregular crosscutting bodies are locally abundant. Amphibolite layers and small, irregular amphibolite bodies present in several places. Griggs (1973) thought the Prichard Formation (Belt Supergroup) was the protolith for the gneiss.'
2599|'Medium to coarse-grained, in part vitreous, but mostly micaceous; in zones to hundreds of feet thick with some interlayered, more micaceous rock. Shown separately only in the more highly metamorphosed rocks.'
3000|'Gravel, sand, silt, and clay along active channels of rivers, creeks, and tributaries.'
3001|'Locally derived slope-wash deposits mainly of Gravel, sand, silt, and clay. Typically thin veneer concealing bedrock, but locally as thick as 30 ft. Commonly grades into Qal. Locally contains well-rounded cobbles derived from alluvial terrace gravel.'
3002|'Gravel, sand, silt, and clay deposited in fans being formed by modern streams along major valley margins. Display characteristic fan-shaped map pattern and convex upward profile. Typically grade upstream into Qal. Thickness ranges from very thin at toe to as much as 50 ft at head of fans.'
3003|'Unconsolidated mixture of soil and blocks of bedrock transported down steep slopes by mass wasting. Characteristic hummocky surface with concentric swales and ridges near downslope limits. Common along steep slopes beneath resistant rocks but can occur where slope and moisture content produce unstable conditions.'
3004|'Angular and subangular coarse gravel derived from local bedrock; gravel deposits beneath smooth pediment surfaces sloping away from the Crazy Mountains and Beartooth Mountains. About 10 to 30 ft thick.'
3005|'Unsorted mixture of clay- to boulder-size material transported and deposited by glaciers. Characteristic hummocky surface form. Occur in valleys near the Beartooth Mountains in the southwest corner of the map area. Clasts are predominantly Archean metamorphic rocks with lesser amounts of quartzite, igneous rocks, dolomite and limestone.'
3006|'Gravel underlying terraces about 10 to 20 ft above altitude of Qal (present altitude of rivers). Mostly cobbles and pebbles with minor amounts of sand and silt. Clasts are mainly granitic igneous rocks, granitic gneiss, schist, and quartzite, with much less limestone and sandstone. About 10 to 40 ft thick.'
3007|'Gravel underlying terraces about 20 to 40 ft above Qal. Mostly cobbles and pebbles with minor amounts of sand and silt. Clasts are mainly granitic igneous rocks, granitic gneiss, schist, and quartzite, with much less limestone and sandstone. About 10 to 40 ft thick.'
3008|'Gravel underlying terraces about 50 to 90 ft above present altitude of rivers. Mostly cobbles and pebbles and minor amounts of sand and silt. Clasts are mainly granitic igneous rocks, granitic gneiss, schist, and quartzite, with much less limestone and sandstone. About 10 to 30 ft thick.'
3009|'Gravel underlying terraces about 200 to 300 ft above present altitude of rivers. These terraces locally exhibit a relatively steep gradient toward the Yellowstone River Valley and may actually include several levels of terraces that are difficult to distinguish. Cobble- and pebble-size clasts are mainly granite, granitic gneiss, schist, and quartzite. Thickness as much as 20 ft.'
3010|'Gravel underlying terraces about 400 to 600 ft above present altitude of rivers. Occur mainly as small discontinuous erosional remnants. Cobble- and pebble-size clasts are mainly granite, granitic gneiss, schist, and quartzite. Calcite cement locally present, especially at base. Thickness ranges from a very thin remnant to about 20 ft.'
3011|'Gravel, sand, silt, and clay underlying terraces about 20 to 600 ft above present altitude of modern streams and rivers. Equivalent to Qat1-Qat5.'
3012|'Gravel underlying terrace about 900 ft above present altitude of rivers. Composed mainly of well-rounded cobbles of granitic gneiss, schist, and quartzite. About 30 to 40 ft thick.'
3013|'Gray to grayish-yellow, fine- to medium-grained sandstone, cross-bedded. Interbedded with brownish-gray carbonaceous shale and siltstone and minor thin coal beds. Sandstones ledge forming, commonly support growths of pine trees. A section about 400 ft thick of this member is present in the map area; top not present in the map area.'
3014|'Predominantly dark-gray to olive shale, locally yellowish-gray claystone; thin, interbedded, yellowish-gray sandstones and siltstone. Typically forms smooth grassy slopes below the Tongue River Member. Thickness 200 to 250 ft.'
3015|'Yellowish-gray, fine- to medium-grained, ledge-forming sandstone, cross-bedded in part. Interbedded with gray to greenish-gray claystone, siltstone, and minor carbonaceous shale. Supports growths of pine trees. About 400 to 600 ft thick.'
3016|'Interbedded light-brownish-gray, cliff- and ledge-forming, fine-grained, thin- to thick-bedded sandstone, and gray, pale-greenish-gray and pale-purple-gray mudstones. Sandstone beds support growths of pine trees. Includes basal beds commonly mapped as Lennep Formation that are typical of basal Hell Creek to the east (personal communication, Susan Vuke and Edie Wilde, MBMG). Total thickness of the formation is about 900 to 1, 100 ft.'
3017|'Dark-gray to medium-gray fine-grained diorite and diorite porphyry, phenocrysts of plagioclase, hornblende, pyroxene, and locally biotite. Occurs as stocks in the Sliderock Mountain area and in the core of a dome in the southwest corner of the map area. Also occurs as dikes and smaller stocks of diorite porphyry and andesite porphyry and trachyandesite. In the area of Ellis Mountain includes xenoliths of rocks derived from the Stillwater Complex. Radiometric age is 74-77 m.y. (du Bray and Harlan, 1993, and du Bray and others, 1994).'
3018|'This unit includes all the volcanic rocks erupted from the Sliderock stratovolcano (du Bray and others, 1994). Mostly andesite breccia (lahars) gray, pale purple gray, pale greenish gray. Andesite in clasts is porphyritic with phenocrysts of chalky plagioclase, hornblende, and pyroxene; matrix is similar but lighter in color and slightly finer grained. Very resistant, forming cliffs and very rugged topography especially near the vent zone in Sliderock Mountain area. Near the vent zone, adjacent to stock of Kdi, this unit is intruded by innumerable dikes of andesite porphyry and diorite. In distal areas, as near town of Greycliff, clasts are less angular but otherwise similar to breccias elsewhere. Locally contains minor flows of porphyritic andesite and basaltic andesite, with phenocrysts of plagioclase, hornblende, and pyroxene. Thickness is at least 1,000 ft (du Bray and others, 1994).'
3019|'Dark-gray shale, commonly weathering dark-brownish-gray, fissile, fossiliferous, brownish-gray calcareous concretions and nodules are common. Middle part of formation contains numerous thin, mostly greenish-gray bentonite beds, thin sandstone beds common near the top. The thickness is about 100 to 300 ft, thinning westward.'
3020|'Interbedded brownish-gray sandy shale and light-brown to pale-yellowish-brown, argillaceous, very-fine to fine-grained lenticular sandstone in beds up to 10 ft thick. A basal, massive cliff-forming sandstone is commonly referred to as the Parkman Sandstone and resembles those in the Eagle Sandstone. Sandstones friable to moderately well indurated, cross-bedded, burrowed to bioturbated, and support growths of pine trees. Greenish-gray and pale-maroon-gray mudstones, poor-quality coal, and easily eroded sandstones occur near the top of the formation. The thickness ranges from 700 to 1000 ft.'
3021|'Brownish-gray, fissile shale with minor interbeds of light-brownish-gray, very argillaceous sandstone. Light-brownish-gray to light-brown, calcareous concretions common, commonly fossiliferous. The upper contact is gradational and conformable, and is placed at the change to ledge-forming sandstones of the Judith River Formation. Thickness of the formation is 100 to 300 ft, thinning westward.'
3022|'Light-brownish-gray to very-pale-orange, very fine to fine-grained, cross-bedded sandstone, burrowed to bioturbated in part. Locally contains calcareous, light-brown sandstone concretions up to 15 ft in diameter. Up to four sandstone intervals with interbedded shale. Thickness is about 150 ft.'
3023|'Shale and sandy shale, brownish-gray to medium-dark-gray with thin interbedded sandstone. Dusky-red concretions common near base. Sandstone beds thicker and more abundant upward, grading into Eagle Sandstone. Contact with Eagle is placed at the base of the first cliff-forming sandstone. Maximum thickness about 150 ft.'
3025|'Shale, olive-gray and dark-brownish-gray, fissile, and contains abundant thin bentonite beds. Upper half calcareous, containing few very thin bentonite beds, and near top contains thin beds of very calcareous, laminated sandstone, siltstone, and sandy limestone. Commonly contains medium-light-gray to pale-yellowish-brown concretions from few inches to 1 or 2 ft in diameter. Inoceramus prisms common. Upper contact placed at change from calcareous shales to non-calcareous shales of Telegraph Creek. Zone of dusky-red concretions in the Telegraph Creek, just above contact, also helps establish its position. Basal contact not exposed, thickness unknown.'
3026|'Units mapped together where poorly exposed and where thermally metamorphosed in area of intrusive rocks. Mostly medium-gray to dark-gray shales, partly calcareous, occurring between the Telegraph Creek and Frontier Formations. On cross-section includes the Frontier Formation. Thickness approximately 1000 ft.'
3027|'Light-brownish-gray, fine-grained thick-bedded to massive, "salt and pepper" sandstone. Contains three sandstone intervals interbedded with dark-gray, fissile shale. Thickness about 350 ft.'
3028|'Mowry Shale is interbedded, siliceous, very fine- to fine-grained sandstone, siltstone, and shale. Contains several prominent bentonite beds. Sandstones and siltstones mostly light gray to medium gray, with a silvery sheen. Fish scales on bedding planes of sandstones and siltstones are characteristic of the formation. Thermopolis Shale is predominantly dark-gray, fissile shale, bentonitic shale, containing several beds of bentonite. Has hematitic concretionary zone near base. Fall River Sandstone is brownish-gray, thin-bedded, argillaceous, fine-grained, quartz sandstone. Generally poorly exposed in map area; mostly covered by glacial deposits. Total thickness is about 1,300 ft.'
3029|'Mostly reddish-brown, olive-gray, and dusky-purple mudstones with interbedded, lenticular, fine- to coarse-grained sandstones. Locally thick, lenticular, fluvial, fine-grained sandstone (Greybull Sandstone) is present at the top. The basal Pryor Conglomerate Member is brown conglomerate and pebbly coarse-grained sandstone, 20 to 60 ft thick. The total thickness of the Kootenai Formation is about 500 ft.'
3030|'Variegated, mainly greenish-gray and pale-reddish-brown mudstone. Very fine to fine-grained, quartzose, calcareous, cross-bedded sandstones are commonly present at about midsection, 5 to 10 ft thick, but locally can be as much as 30 ft thick. Fossil dinosaur remains locally present. Upper contact placed at the base of the Pryor Conglomerate. The basal contact is placed at the top of fossiliferous, calcareous sandstone and coquina of the underlying Swift Formation. Thickness is about 200 ft.'
3031|'Individual formations are not mapped separately; includes the Swift, Rierdon, and Piper Formations. The Swift is interbedded medium gray shale, limestone and calcareous sandstone, fossiliferous. Brownish-gray, fossiliferous, very sandy limestone occurs at the top of the formation, and commonly has brownish-gray coquina at the top. The Rierdon Formation is mostly pale-greenish-gray, very fossiliferous shale with minor interbedded, brownish-gray limestone. Typically poorly exposed, forming smooth slopes littered with fossils, including oysters (Gryphaea and Ostrea), belemnites (Pachyteuthis), and crinoids fragments (Pentacrinus). The Piper is interbedded medium-gray, and pale-reddish-gray, thin-bedded limestone and medium-gray shale. Includes thin interbedded gypsum. Forms ledge below smooth slopes of the Rierdon shales. Thickness of the Ellis Group is about 500 ft.'
3033|'Interbedded moderate reddish-brown fine-grained sandstone, siltstone, and mudstone. Maximum thickness is about 100 ft, thinning westward to 0 near the west edge of the quadrangle.'
3034|'Formations not mapped separately because of narrow outcrop width. Phosphoria is light-gray limestone, sandstone and quartzite, commonly grayish-pink, cherty; thickness is 50 to 75 ft. The Tensleep Sandstone is light-brown to very-pale-orange sandstone, fine-grained, well sorted, well rounded, cross-bedded. Locally contains thin limestone beds, locally cherty near the top, and locally silicified to form quartzite; about 250 ft thick. The Amsden Formation is interbedded grayish-pink to light-red mudstone, limestone, and siltstone. Limestones are commonly cherty. Unconformably overlies karst surface developed on limestone of the Madison Group. Characteristically produces pink stain on underlying cliffs of Madison Group; thickness about 200 ft but locally, tectonically thinned to only a few ft along mountain front. Total thickness of lumped unit is about 500 ft.'
3035|'Limestone and dolomitic limestone, light-gray to light-brownish-gray. Thick-bedded to massive in the upper part (Mission Canyon Limestone) and thin-bedded to thick-bedded in the lower part (Lodgepole Limestone). Also contains thin, interbedded, gray shales. Fossiliferous and cherty beds are present throughout. Collapse features and caves are common at the upper karst surface. Thickness of the Madison is 800 to 1,000 ft.'
3036|'The Jefferson is dolomitic limestone, light brownish gray, fetid, poorly exposed, typically occurs as float. The Three Forks is mainly yellowish-weathering, argillaceous limestone and medium-gray shale, very poorly exposed. The Big Horn Dolomite is cliff-forming dolomite and dolomitic limestone, very light gray to very pale orange, lower part massive, thin to thick bedded in upper part. Has characteristic pock-marked surface due to differential weathering. Total thickness of this interval is about 600 ft.'
3037|'Light-reddish sandstone and quartzite, greenish-gray shale and sandy shale, gray thin-bedded limestone and greenish-gray flat-pebble limestone conglomerate. Includes the Flathead, Wolsey, Meagher, Park, and Pilgrim Formations. Thickness is 600 to 800 ft.'
3040|
3041|
3200|'Tendoys Mountain area:  Unconsolidated, poorly sorted deposit of mud, silt, sand, and gravel in modern streams and channels.

Snowcrest Range area:  Silt, sand, and gravel in channels and flood plains of major rivers and streams. May be partly of Pleistocene age.

Red Rock Hills, Sage Creek basin, and upper Blacktail regions:  Well rounded, well sorted cobble gravel deposited in active stream channels and floodplains.'
3201|'Tendoys Mountain area:  Fan-shaped deposit of unconsolidated gravel, sand, and silt.

Snowcrest Range area:  Poorly sorted, silty sand and gravel deposits in broad alluvial fans along valley margins and in valleys of streams tributary to the Ruby and Red Rock Rivers.

Red Rock Hills, Sage Creek basin, and upper Blacktail regions:  Poorly to moderately sorted deposits of locally-derived, sub-angular to sub-rounded, silt- to boulder-sized clasts deposited in debris flow and fluvial environments along valley margins and in tributary valleys.'
3202|'Fine-grained paludal sediments of Lima Reservoir area.'
3203|'Unconsolidated slope wash, talus, and rock fall; locally includes alluvium.'
3204|'Tendoys Mountain area:  Unconsolidated deposits of locally derived, chiefly angular, unsorted debris.

Snowcrest Range area:  Angular fragments of bedrock mixed with soil. Characterized by irregular, hummocky topography. Many landslides are marked by torn sod, tilted or uprooted trees, and steep, unvegetated slopes that indicate very recent continuing movement. Most of the landslides mapped in the Snowcrest Range have moved on underlying beds of shale, especially in the Lombard, Blackleaf, and Frontier Formations, and in the Beaverhead Group.

Red Rock Hills, Sage Creek basin, and upper Blacktail regions:  Unsorted and unstratified mixtures of angular material that have been moved down slope by gravity. Characterized by irregular hummocky topography. Many are still active. Most landslides in this area are developed on underlying Renova Formation, especially on Trev that contains abundant bentonite developed as an alteration product.'
3205|'Unconsolidated to poorly consolidated gravel deposits of mixed or uncertain origins.'
3206|'Tendoys Mountain area:  Chiefly unconsolidated, locally dissected deposits of mud, silt, sand, and gravel.

Red Rock Hills, Sage Creek basin, and upper Blacktail regions:  Well sorted, well rounded boulders, cobbles, gravel, sand, and silt deposited by streams, later incised by modern streams and now stranded up to 15 m above the present watercourses. Includes both terrace deposits along rivers and outwash fan deposits emerging from the mountains.'
3207|'Tendoys Mountain area:  Chiefly fan-shaped deposits of unconsolidated mud, silt, sand, and gravel; locally dissected.

Red Rock Hills, Sage Creek basin, and upper Blacktail regions:  Poorly to moderately sorted deposits of locally-derived, sub-angular to sub-rounded, silt- to boulder-sized clasts deposited in debris flow and fluvial environments along valley margins and in tributary valleys. Includes glacial outwash deposits.'
3208|'Unconsolidated mud and silt at head of Middle Fork of Little Sheep Creek; SE Sec 20 and SW Sec 21, T15S, R8W.'
3209|'Tendoys Mountain area:  Loosely consolidated to unconsolidated, unsorted pebble to boulder gravel in a matrix of silt, sand, and clay in cirques of Lima Peaks and along upper Dutch Hollow.

Snowcrest Range area:  Till containing unsorted boulders, cobbles, and pebbles in a matrix of sand and clay. Unit includes deposits of two major episodes of glaciation; youngest deposits are nearly unweathered in moraine that is not significantly dissected; older till is deeply weathered, in moraines that are rounded and dissected.'
3210|'Tendoys Mountain area:  Unconsolidated, poorly sorted pebble to boulder gravel on sloping surfaces north of Lima Peaks and isolated patches along creeks.

Snowcrest Range area:  Poorly sorted bouldery gravel and sand deposited by glacial meltwater; compositionally similar to glacial moraines, and with similar weathering characteristics. Deposits typically include large angular boulders of Quadrant and younger sandstones as much as 15 ft in diameter that in older outwash are rounded, exfoliated, and deeply weathered and pitted by solution and wind.'
3211|'Unconsolidated to poorly consolidated gravels of uncertain affinity.'
3212|'Dark colored; locally scoriaceous.'
3213|
3214|
3215|'Freshwater limestone; light gray and white, thick-bedded, vuggy; locally quarried for decorative stone.'
3216|'Rhyolitic to basaltic dikes and small intrusive bodies.'
3217|'Light gray to black silicified limestone and other sedimentary rocks.'
3218|'Chiefly unconsolidated, locally cemented, rounded to sub-rounded, quartzite boulder gravel.'
3219|'Coarse-grained clastics of Muddy Creek Basin (Janecke and others, 1999).'
3220|'Contains conglomerate lenses and limestone clasts; restricted to Muddy Creek basin (Janecke and others, 1999).'
3221|'Contains limestone lenses; restricted to Muddy Creek basin (Janecke and others, 1999).'
3222|'Conglomerate, sandstone, limestone, mudstone, and locally gypsum in Nicholia and Medicine Lodge Creek basins; includes thin Quaternary cover in places.'
3223|'Units mapped in Muddy Creek Basin by Janecke and others (1999).

The following description is extracted from Janecke and others (1999, p. 153 and 158).  They called the Challis Volcanics "Facies A" in their report.

"Facies A consists of ash-flow tuffs and lava flows of the Challis Volcanic Group, whereas facies B consists of pebble to boulder conglomerate. The two facies are intimately interbedded and are thickest in the faulted and tilted remnants of two Eocene palaeovalleys in the NW part of the basin (Fig. 2A). Ash-flow tuffs occur throughout the section and, in general, those low in the stratigraphic succession (quartzite-bearing ash-flow tuff and the lower quartz-sanidine tuff) are confined to the two palaeovalleys in the NW part of the Muddy Creek basin. Tuffs high in the stratigraphic succession (e.g. a biotitic ash-flow tuff and the upper quartz-sanidine tuff) persist across most of the basin. A crystal poor and fine-grained massive white tuff at the very top of the Challis Volcanic Group is an exception to this rule because it is localized and very thick in the northern end of the basin, possibly due to initial slip across the Muddy Creek fault zone. Lava flows and cinder cones are andesitic to basaltic and, like the underlying ash-flow tuffs and conglomerates, occur only in the northern half of the basin and in the southern relay ramp. Some units low in facies A and B pinch out laterally along strike and rest on the adjacent Palaeozoic rocks along a buttress unconformity.

"Volcanic rocks of facies A and conglomerate of facies B were deposited during the Middle Eocene Challis magmatic episode between 49.5 Ma and about 46 Ma (Fig. 7). A 40Ar/39Ar single-crystal age determination on sanidine from a quartzite-bearing ash-flow tuff that occurs only in the Lemhi Pass palaeovalley yielded an age of 49.470.05 Ma on the stratigraphically lowest Tertiary unit (Figs 2A, 7 and sample number 1 in Fig. 8). The first widespread volcanic unit in the Muddy Creek basin, a biotitic ashflow tuff (Tbt), was emplaced about 47.1 Ma, based on two 40Ar/39Ar single crystal dates of  47.570.16 (47.070.16) Ma (M''Gonigle & Dalrymple, 1996) and 47.070.26 Ma on sanidine (sample number 2 in Fig. 8).  40Ar/39Ar age determinations of M''Gonigle & Dalrymple (1993, 1996) were multiplied by a factor of 1.010526 to account for slight differences in the ages of monitors used in each laboratory. Their original age determinations are in parentheses. The youngest widespread volcanic unit is a quartz-sanidine rhyolite ash-flow tuff. Correlative ash-flow tuffs at similar stratigraphic positions in adjacent half graben have yielded dates ranging from 46.740.53 (46.250.52) Ma to 45.550.41 (45.080.41) Ma, with most of the age determinations clustered around 46.4 (45.9) Ma (M''Gonigle & Dalrymple, 1996). Most of facies B was deposited after the 49.5 Ma quartzite-bearing ash-flow tuff and before the 47.1 Ma biotitic ash-flow tuff."'
3224|
3225|
3226|
3227|
3228|
3229|
3230|'Locally includes basalt.'
3231|
3232|'Blocks of Archean rocks interbedded in lower part of Challis Volcanic Group in northern Muddy Creek Basin.'
3233|
3234|
3235|'Tendoys Mountain area:  Conglomerate, sandstone, mudstone, and limestone.

Snowcrest Range area:  (Lowell and Klepper, 1953; Nichols and others, 1985; Perry and others, 1988). Interbedded sandstone, siltstone, mudstone, and conglomerate.

Sandstone - Typically yellowish-gray, light olive-gray to light gray, fine-grained to medium-grained, rarely coarse-grained, commonly moderately to well rounded and well sorted; and locally containing abundant grains of dark gray chert, locally calcareous, commonly cross-bedded, locally contains scattered pebbles and pebbly zones of yellowish-gray to dark gray chert; in places contains abundant fragments of partly fossilized wood, charcoal, lignite, and leaf imprints. Beds 0.5 to 6 ft thick in interbedded units 10 to 30 ft thick.

Siltstone and mudstone:: yellowish-gray to olive-gray or dark gray, partly calcareous, locally bentonitic, in interbeds 1 to 4 ft thick, and interbedded units 10 to 60 ft thick.

Conglomerate - Medium gray to yellowish-gray, thin- (0.5 ft) to thick-bedded (up to 40 ft), containing well rounded pebbles or subangular to subrounded chips of medium gray to dark gray or yellowish-gray chert, and less abundant quartzite in a matrix of medium to very coarse sand. Includes limestone conglomerate composed of well rounded cobbles 0.5 to 0.8 ft in diameter and boulders of Madison Group limestone 1 to 2 ft in diameter, thick-bedded to massive, in a matrix of limestone sand and pebbles.

Facies distribution - Chert-pebble conglomerate interbeds are most common in the headwaters area of the Ruby River, where they form about one-third of the basal Beaverhead Group. Between Antone Peak and the Ruby River outcrops, the Beaverhead Group is mainly sandstone that is pebbly and includes relatively sparse interbeds of chert-pebble conglomerate, with some interbeds of mudstone and siltstone and a few thin beds of olive-gray, platy limestone. In the Clover Creek and Little Basin Creek area, south of Antone Peak, Zeigler (1954) mapped a lower member of chert-pebble conglomerate interbeds and lenses in cherty salt-and-pepper sandstone. The unit ranges from about 750 ft to 3,000 or 4,000 ft thick, thickening eastward from Little Basin Creek. The cherty unit is overlain by and intertongues with a limestone cobble and boulder conglomerate of uncertain but great thickness. Zeigler (1954) measured more than 1000 ft in an incomplete section. Haley (1986) and Nichols and others (1985) include the Beaverhead Group rocks of the Snowcrest Range in the Lima Conglomerate and Clover Creek Sandstone units of the Group. The Beaverhead rocks overlie tightly folded and overturned rocks of the Frontier Formation and older formations with profound angular unconformity. The unconformity is best exposed near Stonehouse Mountain and farther south near Little Basin Creek (Zeigler, 1954; Gealy, 1953).

Red Rock Hills, Sage Creek basin, and upper Blacktail regions:  Synorogenic conglomerate with interbedded sandstone, siltstone, mudstone, and conglomerate. Clasts are primarily composed of Precambrian and Paleozoic quartzite and limestone that were shed from advancing thrust sheets. Mostly lithified. In this area, rocks of the Beaverhead Group have been folded and thrust faulted. (See Lowell and Klepper, 1953; Nichols and others, 1985; Perry and others, 1988; and Haley and Perry, 1991.)'
3236|'Tendoys Mountain area:  Limestone conglomerate contains clasts of recycled limestone conglomerate and well-rounded quartzite (Haley and Perry, 1991).

Red Rock Hills, Sage Creek basin, and upper Blacktail regions:  Boulder and cobble conglomerate characterized by clasts of dominantly limestone of Mississippian through Triassic age, but with up to 25% rounded cobbles of Precambrian Belt quartzite (after Haley and Perry, 1991).

Dominantly limestone conglomerate and minor interbedded sandstone and siltstone.  It has included clasts of recycled limestone conglomerate and an admixture of well-rounded quartzite clasts (generally less than 25%, but can be as much as 50% of clasts) recycled from older units of the Beaverhead Group. It includes the Chute Canyon sandstone of Ryder and Scholten (1973).'
3237|'Quartzite roundstone conglomerate; Contains large limestone clasts (Perry and others, 1988).'
3238|'Limestone pebble to cobble conglomerate derived from erosion of Blacktail-Snowcrest uplift (Nichols and others, 1985).'
3239|'Calcareous salt and pepper sandstone; contains limestone fragments (Ryder and Scholten, 1973).'
3240|'Clean, calcareous quartz sandstone (Wilson, 1970; Ryder and Scholten, 1973).'
3241|'Limestone and quartzite conglomerates derived respectively from Triassic and Jurassic rocks and Belt Supergroup rocks (Ryder and Scholten, 1973).'
3242|'(Haley and Perry, 1991)

Conglomerate composed predominately Triassic and Permian limestone clasts. Haley and Perry (1991, Figure 1) label this unit: Conglomerates, sandstones, and siltstones of the upper Beaverhead Group in the McKnight Canyon area.'
3243|'(Haley and Perry, 1991) Oncoid limestones outcrop within the Beaverhead strata in the partial window beneath the Tendoy thrust at McKnight Canyon.'
3244|'(Haley and Perry, 1991) Limestone pebble-cobble conglomerate composed of clasts from no higher in the section than the Mississippian Madison Group and thus is the most attractive source for the conglomerate clasts.'
3245|'Tendoys Mountain area:  Greenish-gray siltstone and mudstone, interbedded with brown-weathering salt-and-pepper sandstone. Upper part locally contains limestone and quartzite conglomerate. (Dyman and others, 1997).

Snowcrest Range area :  Interbedded sandstone, siltstone, mudstone, and limestone. Sandstone ranges from light gray to dark gray, but most commonly is medium light gray to yellowish- or greenish-gray or olive-gray, very fine- to medium-grained, but coarse-grained in places, with subrounded or subangular grains of quartz, dark gray chert, feldspar, and biotite; commonly calcareous, with some beds nearly sandy limestone; laminated or cross-laminated, and thinly platy. Sandstone is pebbly or conglomeratic in places, containing well rounded pebbles 0.1 to 0.2 ft in diameter of quartzite and chert. Sandstone beds 0.5 to 1 ft thick in single beds or in intervals as much as 20 ft thick, interbedded with siltstone and mudstone, make up most of the formation. Basal sandstone of formation is medium gray to medium-light gray, fine- to medium-grained with abundant chert grains and is 10 to 20 ft thick. Siltstone and mudstone are olive-gray to medium gray or medium-dark gray, partly bentonitic, partly porcellanitic, chippy, and typically concealed. Limestone is medium gray to olive-gray, fine-grained, thinly platy, in thin and irregular beds, nodules and concretions.

A faulted and incomplete measured section is about 2,900 ft thick, northeast of the Snowcrest Range (Tysdal and others, 1990). Near the south end of the Snowcrest Range, the formation is about 7,000 ft thick (Dyman and Nichols, 1988). The Frontier Formation overlies the porcellanitic upper Vaughn Member of the Blackleaf Formation with apparent conformity. It is overlain with angular unconformity by the Beaverhead Group.'
3246|'Tendoys Mountain area:  Volcaniclastic mudstone, bentonite, porcellanite, and siltstone (pastel beds) in upper part. Ledge-forming quartz and chert sandstone and minor mudstone in lower part. (Dyman and Nichols, 1988).

Snowcrest Range area:  Includes four lithofacies units (Dyman, 1985a, 1985b, 1985c; Dyman and Nichols 1988; Dyman and Tysdal, 1990; Tysdal and others 1989a, 1989b) not mapped separately in the Snowcrest Range. Thickness ranges from as much as 400 ft to about 1,500 ft and most commonly is 800 to 1,000 ft; the wide range in thickness is a result of tectonic thinning of shale units on the overturned limbs of tight chevron folds, and of concomitant thickening from the upright limbs.

Vaughn Member - Interbedded sandstone, siltstone and mudstone. Sandstone is light olive-gray to medium-light gray, fine- to medium-grained, partly calcareous, poorly to well sorted, subangular to subrounded quartz and locally abundant feldspar. Pebbly or conglomeratic with well-rounded pebbles and cobbles, as much as 0.2 ft in diameter, of mudstone, shale, siltstone, quartzite and chert; thin- to medium-bedded and partly thinly laminated. Siltstone and mudstone are predominant and are medium-dark gray to light brown or pale yellowish-brown and pale red, chippy to blocky, and commonly porcellanitic in upper part of unit; partly calcareous, locally bentonitic. Limestone is rare and is medium gray to grayish-brown, very fine-grained, in platy beds 0.1 to 1 ft thick. Stratigraphically equivalent to part of the Mowry Shale. Thickness as much as 260 ft.

Lower three lithofacies units are included in Flood Member of Blackleaf Formation (Tysdal and others, 1989):  Upper Sandstone unit - Medium-light gray and pale red to yellowish-gray and dusky-yellow, fine- to medium-grained, calcareous, subrounded to subangular grains or quartz and sparse chert, locally cross-laminated, beds 0.3 to I ft thick, and interbedded medium gray to olive-gray, fissile to chippy shales and mudstone. Basal sandstone of unit is thin-bedded to massive and about 10 to 30 ft thick, most commonly 10 to 20 ft thick. Thickness of unit as much as 50 ft Stratigraphically equivalent to Muddy Sandstone.

Middle Shale unit - Dark gray to medium dark gray, fissile to chippy, light olive-gray and brownish-gray to grayish-brown, calcareous, chippy mudstone and silty or muddy limestone; interbedded with sparse beds 0.3- to 1-ft thick of yellowish-gray, fine-grained sandstone. Thickness of unit less than 50 ft to as much as 300 ft. Stratigraphically equivalent to Thermopolis (or Skull Creek) Shale.

Lower Sandstone unit - Sandstone and interbedded sandstone, mudstone, and shale. Sandstone is medium-light gray and light olive-gray and dusky-yellow or pale yellowish-brown, and weathers to distinctive rusty color; very fine- to medium-grained with subrounded to subangular grains; calcareous; partly thinly laminated or cross-laminated and pebbly or conglomeratic in places. Interbedded siltstone, mudstone and shale are medium-light gray and light olive-gray to medium-dark gray, calcareous, partly fissile to chippy. Interbedded limestone is medium gray to grayish-brown, very fine-grained, in platy beds 0.1 to 1 ft thick. Basal sandstone typically is olive-gray or yellowish-gray to pale red, fine-grained with well rounded to subangular grains of quartz and sparse chert, calcareous, in beds 0.3 to 4 ft thick; as much as 25 to 35 ft thick, but absent in places. Thickness of unit about 45 to 50 ft. Stratigraphically equivalent to Fall River Formation.'
3247|'Mollusc-bearing freshwater limestone in upper part; sandstone and mudstone, locally red, in middle part; and ledge-forming conglomerate at base (DeCelles, 1986; Moritz, 1951).'
3248|
3249|'Poorly exposed upper interval of gray and grayish-green calcareous mudstone and argillaceous limestone, containing a ledge-forming oolitic limestone near the base. Lower part is reddish-brown mudstone, siltstone, and sandstone; may include Triassic Ankareh Formation locally. (Sadler, 1980; Perry, 1986; Moritz, 1951).'
3250|'Tendoys Mountain area:  Light gray to brownish gray interbedded limestone, silty limestone, and calcareous siltstone in upper part; recessive red mudstone in middle part; and chocolate-brown, thin-bedded limestone and silty limestone in lower part (Sadler, 1980; Moritz, 1951).

Snowcrest Range area:  Thaynes Formation (Lower Triassic) - Interbedded sandstone, siltstone, and limestone.  Sandstone is predominant and is yellowish-gray and grayish-orange to light gray and medium-light gray, very fine-grained to fine-grained, rarely medium-grained, with well sorted and rounded quartz grains; calcareous, grading into sandy limestone in places; thinly platy and typically in thin (0.2 to 1.0 ft) and irregular beds. Siltstone resembles and is gradational into very fine-grained sandstone. Limestone is yellowish-gray and light gray to pale yellowish-brown, very fine- to medium-grained, commonly sandy, locally dolomitic, in beds 0.5 to 2 ft thick. Abundantly fossiliferous in some beds. Uppermost limestone beds in the central and south parts of the Snowcrest Range contain abundant dark gray to medium-light gray chert in nodules 0.2 to 0.5 ft thick and as much as 2 ft long, in irregular beds up to 0.5 ft thick.

The Thaynes Formation is exposed most completely on Hogback Mountain and Sunset Peak in the central part of the Snowcrest Range. The middle of the formation there includes two zones of grayish-red to moderate reddish-orange siltstone, each about 10 to 15 ft thick separated by about 15 ft of pale yellowish-gray, very fine-grained sandstone. The formation is about 600 ft thick on Hogback Mountain (Gealy, 1953), and the lower contact is gradational through a thickness of about 20 ft from the underlying Woodside Formation. Farther north in the Snowcrest Range the cherty limestones are not present at the top of the formation, probably because of pre-Jurassic erosion, and the lower part of the formation, including the red siltstones and sandstone, apparently was not deposited. The formation thins to about 400 to 450 ft on the west side of Sliderock Mountain, and to about 50 ft at the north end of the Snowcrest Range. It is not present in the Greenhorn Range farther north (Hadley, 1980).

Woodside Formation (Lower Triassic) - Interbedded mudstone, siltstone, and subordinate very fine-grained, sandstone, all reddish brown, reddish-purple and grayish-red to yellowish-brown, calcareous; in beds 0.3 to 1 ft thick. Prominently exposed on the east face of Hogback Mountain, where the formation is about 600 ft thick (Kummel, 1954); also about 600 ft thick near Devils Hole and 450 to 500 ft on Sliderock Mountain. Formation thins to about 180 ft north of Sliderock Mountain but thickens to about 500 feet farther north near Badger Creek; thins to 50 to 100 ft at the north end of the Snowcrest Range; absent farther north. Thickness changes from Hogback Mountain to Badger Creek result from tectonic thinning and thickening; the northward regional thinning is a result of non-deposition (Moritz, 1951).

Dinwoody Formation (Lower Triassic) - Interbedded limestone and sandstone with mudstone and shale principally in bedding partings and thin interbeds. Predominantly limestone that is pale yellowish-brown, olive-gray and brownish-gray to light gray, and medium gray and typically weathers pale brown to moderate brown; fine- to medium-grained, partly sandy or silty, abundantly fossiliferous, in places a fish bone coquina, partly dolomitic; in platy and irregular beds 0.5 to 1 ft thick, many of which are thinly laminated. Sandstone is moderate yellowish-brown and light brownish-gray to light olive-gray and medium to medium-light gray and typically weathers yellowish-gray and brownish-gray to pale brown; very fine- to medium-grained, with well rounded and well sorted quartz grains; calcareous, grading into sandy or silty limestone in thin and platy beds 0.3 to 2 ft thick but with beds as much as 5 ft thick in basal part of formation. Thickness ranges from 500 to 600 ft at the south end of the Snowcrest Range (Gealy, 1953; Kummel, 1954) to about 550 ft near Ledford Creek and Hogback Mountain and to about 500 ft at the north end of the Snowcrest Range.'
3251|'Interbedded gray dolostone, gray to black chert, brown phosphatic mudstone, phosphorite, and minor limestone and salt-and-pepper sandstone (Cressman and Swanson, 1964).'
3252|'Tendoys Mountain area:  Sandstone and minor dolostone or limestone. Upper part pale orange to light gray, medium- to fine-grained quartzose sandstone, some calcareous, with minor thick beds of dolostone or limestone; forms cliffs or ledges. Lower part is dolostone and dolomitic sandstone. (Saperstone, 1986; Sloss and Moritz, 1951).

Snowcrest Range area:  Sandstone, dolomite, and dolomitic limestone. Upper two-thirds of formation is predominantly yellowish-gray to pale olive-gray to pale yellowish-brown and grayish-orange, fine-grained to medium-grained, well sorted and well rounded, commonly cross-bedded, partly calcareous, quartzitic sandstone in beds I to 4 ft thick or massive. Locally includes thin interbeds of light gray to medium gray, sandy limestone or dolomite. Lower one-third of formation is interbedded light gray to medium-dark gray, fine-grained, locally cherty dolomite in beds 0.5 to 5 ft thick, and yellowish-gray to brownish-gray, fine-grained, well sorted and rounded, quartzitic, calcareous sandstone in 1- to 3-ft beds. Basal sandstone of formation, which may be as much as 50 ft thick, is light gray to pale yellowish-gray, fine- to medium-grained, well rounded and sorted, and thin-bedded (0.2 to 1 ft). Thickness of formation ranges from 600 to about 350 ft, thinning northward (Saperstone and Ethridge, 1984; Saperstone, 1986; Gealy, 1953).

Red Rock Hills, Sage Creek basin, and upper Blacktail regions:  Light gray to white and tan, fine- to medium-grained, medium- to thick-bedded, well-sorted quartz sandstone. Trough cross-beds are common. Lower contact is conformable. Commonly forms cliffs and talus slopes. Thickness 680 to 725 feet. (After Pecora, 1981; Tysdal, 1988).'
3253|'Tendoys Mountain area:  Includes Conover Ranch and Lombard Formations. Dark gray, black, and reddish-brown limestone, calcareous mudstone, sandstone, siltstone, and minor gypsum (Wardlaw and Pecora, 1985).

Snowcrest Range area:  Formerly mapped as Amsden Formation and/or Big Snowy Group in this region, but now included in the Snowcrest Range Group which includes the Conover Ranch Formation, Lombard Limestone, and Kibbey Formation (Wardlaw and Pecora, 1985; Pecora, 1987; Key, 1986; Byrne, 1985).

Conover Ranch Formation - Interbedded sandstone, limestone, and shale. Upper half of formation includes relatively abundant interbeds of limestone that typically is medium-light gray to yellowish-brown, very fine-grained, and fossiliferous; gradational into overlying Quadrant Formation. Lower half of formation is predominately olive-gray and yellowish-gray to yellowish-brown, fine- to medium-grained, well sorted and well rounded, thin-bedded, calcareous sandstone with thin interbeds of similarly colored shale, siltstone, and sparse limestone. Estimated thickness about 750 to 800 ft, thinning northward; formation present only southwest of Little Basin Creek at south end of Snowcrest Range.

Lombard Limestone - Includes three units, an upper limestone, a middle sandstone and shale, and a lower limestone:

Upper limestone - Medium-dark gray to medium gray and less commonly medium-light gray to pale brown and light olive-gray, very fine-grained to fine-grained, partly cherty with medium-light gray to dark gray chert in irregular nodules and lenses 0.1 to 0.5 ft thick and up to 5 ft long; fossiliferous, commonly bioclastic, including crinoid coquinas; in beds 0.1 to 6 ft thick separated by thin beds of platy to shaly dark gray limestone or calcareous mudstone and shale. Unit is predominantly thin-bedded, but includes more thick (2 to 6 ft) beds than lower Lombard Limestone. Top of formation commonly is medium-dark gray, very fine-grained to fine-grained, shaly to platy, mud-cracked, thin-bedded limestone as much as 40 ft thick, with yellowish-gray, silty partings on bedding planes; gradational into overlying Quadrant Formation where Conover Ranch Formation is not present in central and northern Snowcrest Range. Thickness of unit ranges from about 200 to 370 ft (Key, 1986; Gealy, 1953).

Middle sandstone and shale - Predominantly dark gray, fissile shale separated by a middle unit, typically 10 to 30 ft thick, of sandstone and conglomerate. The sandstone is yellowish-orange and olive-gray to yellowish-gray and light brown, fine- to medium-grained, calcareous, partly well sorted and rounded, partly poorly sorted with subrounded to subangular quartz grains grading into conglomerate with mostly well rounded pebbles and cobbles of limestone and chert, probably from the Madison limestone, and with siltstone and rip-up clasts of limestone and mudstone. Dark gray to medium-dark gray, fissile shale above sandstone is as much as 100 ft thick, but most commonly is 30 to 50 ft thick, and is gradational both from the sandstone below and into the overlying upper limestone. Shale below sandstone is similar, and also is gradational into the overlying sandstone and into the underlying lower limestone. Middle sandstone and shale unit typically is 30 to 50 ft thick, but may be as much as 100 ft thick.

Lower limestone - Medium-dark gray to medium-light gray and pale olive-gray, fine-grained to very fine-grained or sublithographic, locally abundantly fossiliferous and bioclastic, thinly platy to thin-bedded (0.1 to 0.5 ft), but rarely as much as 3 ft thick; partly cherty with medium-dark gray chert in irregular nodules as much as 0.3 ft thick and up to 5 ft long; partly thinly laminated; bedding partings and thin interbeds of dark gray, fissile shale increase in abundance upward in unit; commonly weathers into splintered pencil-like fragments. Thickness of lower limestone about 175 to 200 ft (Byrne, 1985).

Kibbey Formation - Interbedded limestone, sandstone, siltstone, and mudstone, partly gypsiferous. Limestone is medium-dark gray to bluish-gray and yellowish-brown, fine-grained, silty to sandy, thinly laminated, thin- to medium-bedded. Sandstone is yellowish-gray and grayish-red to pale reddish-brown, fine- to medium-grained, very calcareous, limonite-speckled and stained. Siltstone and mudstone are pale red to moderate reddish-brown and pale reddish-brown, very calcareous, in interbeds up to 0.5 ft thick. Includes dark gray fissile shale in upper part of formation. Formation partly brecciated from solution of gypsum, particularly in lower half. Thickness ranges from about 100 to 200 ft, but in places is tectonically thinned to a few tens of feet, or is absent. Age is late middle Meramecian to early late Meramecian (Byrne, 1985).

Red Rock Hills, Sage Creek basin, and upper Blacktail regions:  Conover Ranch, Lombard, and Kibbey Formations, undivided.

CONOVER RANCH FORMATION (LOWER PENNSYLVANIAN AND UPPER MISSISSIPPIAN)-Brick-red shale and mudstone, siltstone, and sandstone, with minor green shale and gray limestone; 0-100 feet thick; basal unit is limestone pebble conglomerate; conformable with underlying Lombard Limestone. (After Pecora, 1981; Tysdal, 1988).

LOMBARD LIMESTONE (UPPER MISSISSIPPIAN)-Tectonically deformed; consists of an upper sequence of 300 feet of pale-brown to gray, thick-bedded, crinoidal limestone and dark gray limey shale; a 220-580-foot-thick middle sequence of thin- to thick-bedded limestone with interbeds of siltstone and claystone and a 1-foot-thick discontinuous coal seam; and a 125-foot-thick lower sequence of olive-gray to pale-red-purple, thin- to thick-bedded, ostracod-rich limestone. Lower contact is conformable. (After Pecora, 1981; Tysdal, 1988).

KIBBEY SANDSTONE (UPPER MISSISSIPPIAN)-Pale yellow and reddish brown, thin-bedded, argillaceous, fine-grained, quartz sandstone. Limestone and evaporite solution breccia in the middle of the formation. Lower contact is conformable. Thickness 100 to 160 feet.(After Pecora, 1981; Tysdal, 1988).'
3254|'Chiefly limestone and minor sandstone.'
3255|'Railroad Canyon Formation: Medium gray and grayish-black mudstone, limestone, limestone conglomerate, and medium gray sandstone.

Scott Peak Formation: Medium gray, thick bedded, cliff-forming, sandy limestone; locally includes some thin Surrett Canyon and South Creek Formations.

Middle Canyon Formation: Medium to dark gray, thin-bedded limestone and black ribbon chert (up to 60%).

McGowan Canyon Formation: Grayish-black mudstone and sandstone; medium to dark gray limestone at base. Locally includes Devonian rocks of Three Forks.'
3256|'Medium gray and grayish-black mudstone, limestone, limestone conglomerate, and medium gray sandstone.'
3257|'Medium gray, thick bedded, cliff-forming, sandy limestone; locally includes some thin Surrett Canyon and South Creek Formations.'
3258|'Medium to dark gray, thin-bedded limestone and black ribbon chert (up to 60%).'
3259|'Grayish-black mudstone and sandstone; medium to dark gray limestone at base. Locally includes Devonian rocks of Three Forks.'
3260|'Includes, in descending order, McKenzie Canyon, Kibbey (?), Mission Canyon, Middle Canyon, and Paine Formations. Chiefly medium to dark gray limestone, thin- to thick-bedded, with locally abundant ribbon chert and minor sandstone (Sando and others, 1985).'
3261|'Chiefly medium to dark gray, medium- to thick-bedded limestone and calcareous mudstone and siltstone in upper part. Lower part is medium gray, thick-bedded, cliff-forming limestone.'
3262|'Chiefly black shaly mudstone and interbedded limestone and sandstone.'
3263|'Includes Three Forks, Jefferson, and Maywood? Formations. Medium gray, sheared limestone and dolomite; and red and yellow sandstone and siltstone.'
3264|'Sandstone, dolomite, quartzite, and siltstone.'
3265|'White to light gray quartzite and dolomite.'
3266|'Quartzite, sandstone, conglomeratic sandstone, and dolomite (Dubois, 1983).'
3267|'Chiefly reddish-brown feldspathic sandstone.'
3268|'Tendoys Mountain area and Snowcrest Range area:  Light-colored, quartz-feldspar-biotite gneiss and associated foliated granitic pegmatite.'
3269|'Tendoys Mountain area and Snowcrest Range area:  Mainly medium gray to dark brown coarsely crystalline marble composed of calcite and dolomite with subordinate amounts of quartz, diopside, tremolite, forsterite, and talc.'
3276|'Accumulations of unsorted, angular rock fragments in and at the toe of snow avalanche chutes, commonly littered with broken and shattered trees. Common on steep, east-facing slopes in the Snowcrest Range.'
3278|'Active sand dunes in the Centennial Basin; carried by prevailing winds from the southwest. Dunes are underlain by lake deposits of pale yellowish-brown to light brown, unconsolidated sand, silt, and clay that locally contain small pebbles about 3 mm in diameter.'
3282|'Mature soil zone preserved on upland surfaces in Ledford Pass and on Beaver Bench in the central part of the Snowcrest Range; surface has been deeply dissected by Ledford Creek and by the West Fork of the Ruby River and its tributaries. Overlain by till of the Hogback Mountain glaciers, and is clearly pre-glacial in age.'
3283|'Dark gray, fine grained, vesicular; in thin flows overlying boulder gravels in the south part of the Snowcrest Range. May include lavas related to the Tertiary Sage Creek and Blacktail Deer Creek flows (Scholten and others, 1955), and younger flows contemporaneous with Snake River Plain volcanics 3 to 4 M.Y. old (Fields and others, 1985).'
3284|'Snowcrest Range area:  Light yellowish-gray to light gray very fine-grained to fine-grained, vuggy, partly thinly laminated, beds 0.3 to 5 ft thick or massive and cliff-forming; locally tuffaceous or silty. Widespread along west flank of Snowcrest Range from Lone Rock Creek south to Steamboat Rock; in most places 100 ft or more thick, but thins north of Lone Rock Creek. Overlain by as much as 400 ft of quartzite cobble conglomerate cemented by travertine.

Unit deposited in a lake fed by thermal springs, some of which are still active, along the Snowcrest frontal fault zone. Calcium carbonate was leached from rocks in and adjacent to the fault zone, including (a) limestones in the Madison Group, which now is solution breccia heavily veined with calcite and well exposed in the canyon of the West Fork of Blacktail Creek; (b) Quadrant sandstone, which in places is reduced to loose, fine grains of white sand; and (c) limestone in the Lombard Formation of the Snowcrest Range Group, which is bleached, solution-pitted, and brecciated. Gypsum and calcareous rocks in the underlying Kibbey Formation typically have been completely dissolved and the formation in places has been almost totally removed. Large sinkholes in the SW 1/4 Sec. 4, T. 12 N., R. 5 W. show that solution and removal of the formation is continuing today, with accompanying extensive brecciation and solution in the underlying Madison limestone and the overlying Lombard Formation (see Anderson and Diehl, 1999). The original extent of the limestone and of the lake in which it was deposited are unknown, but the present outcrops of the limestone indicate that at least as much as a cubic mile of calcium carbonate was leached from the rocks in and adjacent to the frontal fault zone in the Snowcrest Range.

The source of the hydrothermal fluids is uncertain, but some evidence suggests a heat source near Basin and Little Basin Creeks and near Vinegar Hill in T.12 and 13 S., R.7 W. The curving courses of the creeks define a nearly perfect semi-circle that forms the south edges of a basin filled with coarse gravel in a compound alluvial fan, suggesting rapid collapse along a ring structure. The rocks of the frontal fault zone are thermally metamorphosed near the possible ring structure, and a large hot-spring tufa deposit is adjacent to the fault zone in Sec. 16, T. 13 S., R.7 W. Tufa is vuggy, fine grained algal limestone and travertine cementing angular fragments 1 to 3 inches in diameter of bleached and hydrothermally altered rocks. Locally abundant seams and veinlets of chalcedony and in places cristobalite (Zeigler, 1954). Archean and Mississippian rocks near the hot spring deposit are bleached, brecciated, and indicate extreme and widespread hydrothermal alteration.

Other possible ring fractures are present north of Vinegar Hill, and near Little Sage Creek where a curving fault has been recognized by J. W. Sears (written communication, 1999). In all, these features seem to outline a ring fracture zone about 7 miles in diameter, or possibly as much as 10 miles in diameter, that encloses a collapsed area. At depth, the fracture zone also may have been the source of the abundant basaltic volcanic rocks in the area.

The age of the limestone is only approximately known. It overlies rocks included in the upper Miocene Sixmile Creek Formation, and rhyolitic volcanic rocks that probably are Huckleberry Tuff (Brasher, 1950). It probably is mainly or entirely of Pliocene age (Fields and others, 1985; Zeigler, 1954; Ripley, 1995), but may include Upper Miocene rocks as well.

Red Rock Hills, Sage Creek basin, and upper Blacktail regions:  Light yellowish-gray to light gray, very fine-grained to fine-grained, vuggy, partly thinly banded, beds 0.3-5 feet thick or massive and cliff-forming. Locally tuffaceous or silty. Ranges from 5 to 200 feet thick; averages 100 feet thick. See Ruppel''s discussion on its deposition in this paper (Part B). Probably deposited in a lake formed by the break-up of the late Miocene-early Pliocene Ruby graben (Jim Sears, personal communication, 1999).'
3285|'Snowcrest Range area:  Sandstone, siltstone, and conglomerate commonly correlated with the Sixmile Creek Formation (Fields and others, 1985; Monroe, 1976; Robinson, 1963).

Sandstone and siltstone - Light gray and olive-gray to yellowish-gray, pale brownish-gray and grayish-orange, fine- to medium-grained, calcareous, cross-laminated, partly tuffaceous sandstone and siltstone; in beds 1 to 5 ft thick interbedded with 10- to 50-ft thick units of thicker and more massive, yellowish-gray, partly tuffaceous fine-grained sandstone and siltstone and sandy or silty tuff, and light gray fine- to medium-grained, calcareous crystal tuff in beds I to 3 ft thick. Many beds contain isolated small well rounded pebbles of basalt, quartzitic sandstone, and chert, and thin beds, lenses, and channel fills of pebble conglomerate or conglomeratic sandstone 0.5 to 3 feet thick; many beds thinly laminated or cross-laminated, and some characterized by large, festoon cross laminations.

Conglomerate - Cobbles and pebbles, well rounded, mainly of locally derived quartzitic sandstone, chert, limestone, and dolomite, and rare quartzofeldspathic gneiss, but including basalt, vesicular basalt, and a small percentage of Belt Supergroup pebbles and cobbles derived from the Gravelly Range gravel (Gutmann and others, 1989; Ruppel 1993); commonly well sorted, with cobbles, and rare boulders of vesicular basalt as much as one ft in diameter floating in a pebble-sand matrix; beds 10 to 20 ft thick. And interbedded light gray to pale yellowish-gray calcareous, partly tuffaceous siltstone and very fine-grained sandstone in beds 0.5 to 2 ft thick.

Red Rock Hills, Sage Creek basin, and upper Blacktail regions:  Mostly conglomerate with sand to cobble sized clasts of mainly quartzite, although basalt, limestone, and Belt argillite clasts are also common. Much is reworked Beaverhead Formation. The presence of volcanic clasts distinguishes it from Beaverhead Formation (Jim Sears, personal communication, 1999). Mostly unconsolidated. Age dates from tephra beds (Fritz and Sears, 1993) are consistent with vertebrate fossil ages (Monroe, 1976) and range from 3.7 to 16 Ma. Four members have been described by Fritz and Sears (1993) and Sears and others (1995), but only two were mapped as separate units in this study. Undivided unit Tsc is mostly Bighole River and Sweetwater Creek members, although some Anderson Ranch Member (Tsca) is included.

BIGHOLE RIVER MEMBER, INFORMAL-Well-sorted, well-rounded conglomerate with sand- to boulder-sized clasts of predominantly quartzite, but also including volcanic, limestone, and Belt argillite clasts. Deposited in fluvial environments. Unit recognized but included in undivided Tsc.

SWEETWATER CREEK MEMBER, INFORMAL-Moderate to poorly sorted conglomerate with silt to subrounded boulder clasts up to 2 m in diameter. Deposited in debris flow and alluvial fan environments. Laterally gradational with the Bighole River and Anderson Ranch members. Unit recognized but included in undivided Tsc.'
3287|'Frontier Formation (Upper Cretaceous) -- Interbedded sandstone, siltstone, mudstone, and limestone. Sandstone ranges from light gray to dark gray, but most commonly is medium light gray to yellowish- or greenish-gray or olive-gray, very fine- to medium-grained, but coarse-grained in places, with subrounded or subangular grains of quartz, dark gray chert, feldspar, and biotite; commonly calcareous, with some beds nearly sandy limestone; laminated or cross-laminated, and thinly platy. Sandstone is pebbly or conglomeratic in places, containing well rounded pebbles 0.1 to 0.2 ft in diameter of quartzite and chert. Sandstone beds 0.5 to 1 ft thick in single beds or in intervals as much as 20 ft thick, interbedded with siltstone and mudstone, make up most of the formation. Basal sandstone of formation is medium gray to medium-light gray, fine- to medium-grained with abundant chert grains and is 10 to 20 ft thick. Siltstone and mudstone are olive-gray to medium gray or medium-dark gray, partly bentonitic, partly porcellanitic, chippy, and typically concealed. Limestone is medium gray to olive-gray, fine-grained, thinly platy, in thin and irregular beds, nodules and concretions.

A faulted and incomplete measured section is about 2,900 ft thick, northeast of the Snowcrest Range (Tysdal and others, 1990). Near the south end of the Snowcrest Range, the formation is about 7,000 ft thick (Dyman and Nichols, 1988). The Frontier Formation overlies the porcellanitic upper Vaughn Member of the Blackleaf Formation with apparent conformity. It is overlain with angular unconformity by the Beaverhead Group. 

Blackleaf Formation (Upper and Lower Cretaceous) -- Includes four lithofacies units (Dyman, 1985a, 1985b, 1985c; Dyman and Nichols 1988; Dyman and Tysdal, 1990; Tysdal and others 1989a, 1989b) not mapped separately in the Snowcrest Range. Thickness ranges from as much as 400 ft to about 1,500 ft and most commonly is 800 to 1,000 ft; the wide range in thickness is a result of tectonic thinning of shale units on the overturned limbs of tight chevron folds, and of concomitant thickening from the upright limbs. 

Vaughn Member -- Interbedded sandstone, siltstone and mudstone. Sandstone is light olive-gray to medium-light gray, fine- to medium-grained, partly calcareous, poorly to well sorted, subangular to subrounded quartz and locally abundant feldspar. Pebbly or conglomeratic with well-rounded pebbles and cobbles, as much as 0.2 ft in diameter, of mudstone, shale, siltstone, quartzite and chert; thin- to medium-bedded and partly thinly laminated. Siltstone and mudstone are predominant and are medium-dark gray to light brown or pale yellowish-brown and pale red, chippy to blocky, and commonly porcellanitic in upper part of unit; partly calcareous, locally bentonitic. Limestone is rare and is medium gray to grayish-brown, very fine-grained, in platy beds 0.1 to 1 ft thick. Stratigraphically equivalent to part of the Mowry Shale. Thickness as much as 260 ft. 

Lower three lithofacies units are included in Flood Member of Blackleaf Formation (Tysdal and others, 1989): 

Upper Sandstone unit -- Medium-light gray and pale red to yellowish-gray and dusky-yellow, fine- to medium-grained, calcareous, subrounded to subangular grains or quartz and sparse chert, locally cross-laminated, beds 0.3 to 1 ft thick, and interbedded medium gray to olive-gray, fissile to chippy shales and mudstone. Basal sandstone of unit is thin-bedded to massive and about 10 to 30 ft thick, most commonly 10 to 20 ft thick. Thickness of unit as much as 50 ft Stratigraphically equivalent to Muddy Sandstone. 

Middle Shale unit -- Dark gray to medium dark gray, fissile to chippy, light olive-gray and brownish-gray to grayish-brown, calcareous, chippy mudstone and silty or muddy limestone; interbedded with sparse beds 0.3- to 1-ft thick of yellowish-gray, fine-grained sandstone. Thickness of unit less
than 50 ft to as much as 300 ft Stratigraphically equivalent to Thermopolis (or Skull Creek) Shale. 

Lower Sandstone unit -- Sandstone and interbedded sandstone, mudstone, and shale. Sandstone is medium-light gray and light olive-gray and dusky-yellow or pale yellowish-brown, and weathers to distinctive rusty color; very fine- to medium-grained with subrounded to subangular grains; calcareous; partly thinly laminated or cross-laminated and pebbly or conglomeratic in places. Interbedded siltstone, mudstone and shale are medium-light gray and light olive-gray to medium-dark gray, calcareous, partly fissile to chippy. Interbedded limestone is medium gray to grayish-brown, very fine-grained, in platy beds 0.1 to 1 ft thick. Basal sandstone typically is olive-gray or yellowish-gray to pale red, fine-grained with well rounded to subangular grains of quartz and sparse chert, calcareous, in beds 0.3 to 4 ft thick; as much as 25 to 35 ft thick, but absent in places. Thickness of unit about 45 to 50 ft. Stratigraphically equivalent to Fall River Formation.'
3290|'Kootenai Formation (Lower Cretaceous) - Sandstone and conglomerate, siltstone, mudstone, shale, and limestone. Thickness of formation 350 to 500 ft. From top to base of formation:

Limestone - Limestone and thin interbeds and partings of dark gray, fissile shale. Limestone is medium-light gray to medium gray, very fine- to coarse-grained, typically partly bioclastic, in places sandy in lower and upper beds; fossiliferous containing abundant gastropods and fossil fragments in some beds; beds I to 3 ft thick. Gastropod limestone unit is 35 to 150 ft thick and most commonly is about 40 to 80 ft thick.

Upper shale and mudstone - Shale, mudstone, and subordinate sandstone; typically mostly concealed. Shale and mudstone are fissile, yellowish-gray to olive-gray, rarely pale red; interbedded quartz sandstone is yellowish-gray to olive-gray, fine- to medium-grained, very calcareous, in beds 0.4 to I ft thick. Approximately 50 to 110 ft thick.

Middle sandstone - Salt and pepper sandstone unit of pale yellowish-gray to medium gray, fine- to medium-grained with well rounded to subrounded quartz and chert grains, very calcareous, and cross-laminated. Beds are 0.4 to 1.2 ft thick, separated by medium gray to medium-light gray fissile shale partings and beds as much as 1 ft thick. Unit is 10 to 30 ft thick.

Lower mudstone, shale, and sandstone unit - Pale red mudstone, shale, and fine-grained sandstone, 25 to 35 ft thick, which is in turn underlain by 30 to 50 ft of interbedded shale, mudstone, and sandstone like that in the upper shale unit.

Basal Kootenai sandstone - Salt and pepper sandstone and chert pebble conglomerate, 30 to 100 ft thick. Sandstone is medium gray to light brown and dark yellowish-orange, medium- to coarse grained, with subangular grains of quartz and abundant dark gray chert, in beds I to 2 ft thick to massive; interbedded with chert-pebble conglomerate and pebbly sandstone, with subrounded to well rounded pebbles commonly 0.1 ft or less in diameter of yellowish-gray to dark gray or grayish-red chert. In lenses and beds 1 to 5 ft thick.

Morrison Formation (Upper Jurassic) - Olive-gray, greenish-gray, dusky-yellow and pale red to light brownish-gray and medium-dark gray, fissile to blocky mudstone and shale; includes nodules as much as 3 ft long and thin interbeds of medium gray to medium-light gray to blackish-red, very fine-grained, conchoidal limestone. Includes thin interbeds of olive gray, rusty weathering fine-grained, dirty sandstone. As much as 40 ft thick, but absent in places.

Ellis Group rocks (Middle and Upper Jurassic) -Present in the southern Snowcrest Range and in the canyon of the West Fork of Blacktail Creek (Gealy, 1953). Medium light gray, fine-grained, locally oolitic, partly conglomeratic limestone and grayish green glauconitic siltstone and shale; about 50 ft thick.'
3292|'Dolomite, chert, quartzitic sandstone, mudstone, and shale; partly phosphatic, including thin beds of oolitic phosphate rock. Lithology and thickness differ from place to place, but generally include, from top to bottom: (a) medium-light gray to olive-gray, fine-grained, thick bedded (0.5 to I ft), partly phosphatic and quartzitic, cherty sandstone and interbedded dark gray, phosphatic mudstone and shale, as much as 110 ft thick, but absent in places; (b) light gray to medium gray, thin (0.3 to 1 ft) and irregularly bedded chert, with locally interbedded light gray dolomite, and including light gray, quartzitic sandstone and interbedded phosphatic mudstone and phosphate rock near base of unit; as much as 110 ft thick; (c) light gray to light olive-gray, very fine-grained, dolomite in beds 1 to 5 ft thick or massive, locally very cherty including abundant nodules up to 0.5 ft long and irregular interbeds up to 0.5 ft thick of medium gray chert; locally includes mammillary clusters of quartz crystals; includes about 15 ft of dark gray shale and mudstone in middle of unit; thickness as much as 125 ft; (d) medium gray to yellowish-gray, irregularly bedded (0.5 to 4 ft), partly nodular chert; about 100 to 130 ft thick including a middle unit of yellowish-gray, fine-grained, dolomitic sandstone about 30 ft thick; (e) yellowish-gray, fine-grained sandstone underlain by about 6 ft of phosphatic mudstone and shale and phosphate rock, in all about 40 ft thick; (f) light gray to very light gray, very fine-grained dolomite in beds 0.5 to 2 ft thick, with interbedded thin beds and nodules of medium-light gray chert, and sandy dolomite near base of unit; 75 to 150 ft thick; (g) basal medium-light gray to yellowish-brown and light brown, fine-grained sandstone in beds 0.1 to 0.3 ft thick, with interbedded chert and cherty light gray dolomite; as much as 25 ft thick, but locally absent.

Total thickness of Phosphoria Formation ranges from about 420 ft in the northern Snowcrest Range to more than 900 ft on Olson Peak, and about 600 ft at Wadhams Spring near the south end of the range (Gealy, 1953; Klepper, 1950; Klepper and others, 1953; Cressman, 1955; Swanson, 1970). Thickness variations result from erosion of upper beds, northward thinning by non-deposition of some lower beds, and tectonic thinning.'
3295|'Limestone, dolomitic limestone, and shale included in Mission Canyon and Lodgepole Formations.'
3296|'Snowcrest Range area:  Medium-light gray and medium gray to brownish-gray, generally fine- to medium-grained but coarse-grained in places, medium- and thick-bedded to massive limestone. Locally with nodules and lenses of pale yellowish-brown to light olive-gray chert 0.2 to 0.3 ft thick and 3 to 4 ft long. Occurs only on the west side of Snowcrest Range in fault-bounded and locally solution-brecciated outcrops.

Red Rock Hills, Sage Creek basin, and upper Blacktail regions:  Light gray, medium- to thick-bedded to massive limestone, oolitic limestone, and dolomitic limestone. Dark gray chert stringers in lower part and zones of evaporite-solution breccia in the upper and middle parts. Forms cliffs. Thickness 800 to 1000 feet. (After Pecora, 1981; Tysdal, 1988).'
3297|'Snowcrest Range area:  Medium gray to medium-dark gray, fine- to medium-grained limestone in beds from 0.5 to 2 ft thick, rarely as thick as 4 ft, partly thinly laminated, argillaceous, with thin interbeds and bedding partings of dark gray, calcareous shale. Occurs only on west side of Snowcrest Range in fault-bounded and locally solution brecciated outcrops.

Red Rock Hills, Sage Creek basin, and upper Blacktail regions:  Upper third is thin- to medium-bedded limestone, limey mudstone, and red calcareous siltstone. Lower two thirds is light gray, finely laminated, thin-bedded, limestone with partings of silty mudstone or calcareous siltstone. Thickness 1000 feet. (After Pecora, 1981; Tysdal, 1988).'
3298|'Snowcrest Range area:  Three Forks Formation (Lower Mississippian? and Upper Devonian) -Medium gray and dark gray to dark olive-gray siltstone and very fissile shale with sparse concretions up to 1.5 ft in diameter of dark gray, very fine-grained limestone; subordinate interbedded light brownish-gray to grayish-brown, fine- to medium-grained, poorly sorted, glauconitic, fossiliferous sandstone in beds 0.1 to 2 ft thick, and rare beds of limestone-pebble conglomerate. Thickness ranges from 320-440 ft (Gealy, 1953).

Jefferson Formation (Upper and Middle Devonian) - Medium gray to medium-dark gray to yellowish-gray, fine- to medium-grained, fetid, splendant dolomite; thin- to medium-bedded (0.2 to 3 ft) to massive. About 150-300 feet thick (Gealy, 1953).

Red Rock Hills, Sage Creek basin, and upper Blacktail regions:  Three Forks Formation is grayish-orange siltstone, silty limestone, and evaporite solution breccia, about 60 feet thick. Unconformable contact with the underlying Jefferson Formation, which is grayish black, thick-bedded, fetid dolomite, yellowish-brown, sugary dolomite, and thin beds of yellowish brown calcareous siltstone. Thickness 100-120 feet. (After Pecora, 1981; Tysdal, 1988).'
3299|'Light gray and yellowish-gray to very pale brownish-gray, fine-grained, massive dolomite. Present only near Basin Creek and Little Basin Creek in southern part of Snowcrest Range, the westernmost outcrops of the formation. About 20 to 50 ft thick where present.'
3300|'Descriptions from Upper and Middle Cambrian units:

Sage Dolomite Member: Medium-light gray, fine-grained, thin-bedded dolomite with crinkled and irregular laminae; locally contains thinly laminated algal beds. About 40 to 200 ft thick. Exposed mainly near Little Basin Creek in south part of Snowcrest Range.

Dry Creek Shale Member: Pale red to grayish-red, very fine-grained to medium-grained dolomite and calcareous sandstone, with interbedded yellowish-brown to yellowish-gray, dolomitic and calcareous siltstone, mudstone, and shale. About 10 to 30 ft thick.

Includes Pilgrim, Park, Meagher, Wolsey, and Flathead Formations.

Pilgrim Formation (Upper Cambrian) - Medium-light gray and yellowish-gray to light brownish-gray, fine grained dolomite in beds 0.5 to 6 ft thick, mostly 0.5 to 4 ft Upper part of formation is sandy, particularly on laminae and cross laminae, and includes interbeds of very fine- to medium-grained, well sorted and rounded, dolomitic sandstone. Sandy zone is 40 to 60 ft thick. Uppermost 20 to 40 ft of formation commonly not sandy. Beds beneath sandy zone are irregularly "ribboned" wavy-laminated, yellowish-gray, fine-grained, dolomite and dolomitic limestone about 50 to 100 ft thick, underlain by non-ribboned dolomite. Thickness of formation about 300 to 350 ft.

Park Shale (Middle Cambrian) - Pale olive and grayish-green, micaceous, fissile shale and minor thin interbeds of grayish-red and yellowish-brown to yellowish-gray siltstone and mudstone. About 40 to100 ft thick.

Meagher Formation (Middle Cambrian) - Medium gray and light olive-gray to yellowish-brown, fine-to medium-grained dolomite and dolomitic limestone in beds 1 to 3 ft thick. Partly irregularly mottled light or medium gray, yellowish-gray, or pale red. Thickness about 300 to 350 ft.

Wolsey Shale (Middle Cambrian) - Olive-green to grayish-red or reddish-brown, micaceous, calcareous, glauconitic, very fine-grained sandstone and siltstone, and olive-green, fissile, micaceous shale. Thickness about 50 to 75 ft.

Flathead Sandstone (Middle Cambrian) - Yellowish-gray and yellowish-brown to pale red and grayish-red, fine- to medium-grained, but locally coarse-grained sandstone. Partly thinly laminated; beds commonly 0.5 to 3 ft thick or massive; partly glauconitic, particularly in lower part of formation about 3 ft above base, and in uppermost beds gradational into overlying Wolsey Shale. Basal beds, 1 to 3 ft thick, are locally coarse-grained and conglomeratic, containing well rounded white quartz pebbles up to 0.1 ft in diameter. Thickness of formation 0 to 50 ft.'
3301|'Sage Dolomite Member: Medium-light gray, fine-grained, thin-bedded dolomite with crinkled and irregular laminae; locally contains thinly laminated algal beds. About 40 to 200 ft thick. Exposed mainly near Little Basin Creek in south part of Snowcrest Range.

Dry Creek Shale Member: Pale red to grayish-red, very fine-grained to medium-grained dolomite and calcareous sandstone, with interbedded yellowish-brown to yellowish-gray, dolomitic and calcareous siltstone, mudstone, and shale. About 10 to 30 ft thick.'
3302|'Includes Pilgrim, Park, Meagher, Wolsey, and Flathead Formations.

Pilgrim Formation (Upper Cambrian) - Medium-light gray and yellowish-gray to light brownish-gray, fine grained dolomite in beds 0.5 to 6 ft thick, mostly 0.5 to 4 ft Upper part of formation is sandy, particularly on laminae and cross laminae, and includes interbeds of very fine- to medium-grained, well sorted and rounded, dolomitic sandstone. Sandy zone is 40 to 60 ft thick. Uppermost 20 to 40 ft of formation commonly not sandy. Beds beneath sandy zone are irregularly "ribboned" wavy-laminated, yellowish-gray, fine-grained, dolomite and dolomitic limestone about 50 to 100 ft thick, underlain by non-ribboned dolomite. Thickness of formation about 300 to 350 ft.

Park Shale (Middle Cambrian) - Pale olive and grayish-green, micaceous, fissile shale and minor thin interbeds of grayish-red and yellowish-brown to yellowish-gray siltstone and mudstone. About 40 to100 ft thick.

Meagher Formation (Middle Cambrian) - Medium gray and light olive-gray to yellowish-brown, fine-to medium-grained dolomite and dolomitic limestone in beds 1 to 3 ft thick. Partly irregularly mottled light or medium gray, yellowish-gray, or pale red. Thickness about 300 to 350 ft.

Wolsey Shale (Middle Cambrian) - Olive-green to grayish-red or reddish-brown, micaceous, calcareous, glauconitic, very fine-grained sandstone and siltstone, and olive-green, fissile, micaceous shale. Thickness about 50 to 75 ft.

Flathead Sandstone (Middle Cambrian) - Yellowish-gray and yellowish-brown to pale red and grayish-red, fine- to medium-grained, but locally coarse-grained sandstone. Partly thinly laminated; beds commonly 0.5 to 3 ft thick or massive; partly glauconitic, particularly in lower part of formation about 3 ft above base, and in uppermost beds gradational into overlying Wolsey Shale. Basal beds, 1 to 3 ft thick, are locally coarse-grained and conglomeratic, containing well rounded white quartz pebbles up to 0.1 ft in diameter. Thickness of formation 0 to 50 ft.'
3303|'Snowcrest Range area:  Metamorphic rocks about 2.75 to 3 b.y. old (Zell E. Peterman, written communication, 1982); includes quartzofeldspathic gneiss, complexly interlayered granitic, tonalitic quartz-feldspar-biotite, and hornblende-plagioclase gneiss.

Red Rock Hills, Sage Creek basin, and upper Blacktail regions:  Mostly pink to pale orange, medium- to coarse-grained, quartz-microcline granitic gneiss, with light gray, banded, medium- to coarse-grained biotite-plagioclase-quartz gneiss also common. Hornblende gneiss layers a few tens of feet thick also present. (After Tysdal, 1988).'
3327|'White, fluvial tephra, interbedded with light brown silt, sand, and gravel. Distinguished from tephra-rich members of the Renova Formation by clean appearance and lack of bentonitic clay.'
3328|'A single olivine basalt flow that Sears and others (1995) traced for 50 km along the ancestral northeast-trending Ruby graben. Age is 6 Ma (Kreps and others, 1992). Found with gravels of the Big Hole River member or unconformable overlying Archean to Miocene rocks.'
3329|'BLACKTAIL DEER MEMBER, INFORMAL (EARLY MIOCENE): Gritty sandstone, tuffaceous mudstone commonly with abundant bentonite, and thin brown limestone. Sandstone contains angular clasts of quartz, volcanic rock fragments, and black chert. Late Arikareean vertebrate fossil assemblages have been found (Fields et.al., 1985). 

WHITE HILLS MEMBER, INFORMAL (LATE OLIGOCENE):  Light gray tuffaceous mudstone containing abundant bentonitic clay. Yielded Whitneyan vertebrate fossils (Fields and others, 1985). Trc COOK RANCH MEMBER, INFORMAL (OLIGOCENE)  Very light brown tuffaceous mudstones with lesser amounts of conglomeratic sandstone and volcanic ash. Abundant calcareous nodular horizons. Includes only the Cook Ranch Member of Tabrum (1996).

BASALT CAP, DILLON VOLCANIC MEMBER, INFORMAL (EOCENE?): Black, dense olivine basalt forms a cap on the Trev unit in the north-central part of the map. Tentatively correlated with basalts to the north in Grasshopper Canyon that yielded age dates of 40.5 to 47.1 Ma (Leeth, 2000).

HALL SPRING BASALT AND OTHER OLDER BASALT, DILLON VOLCANIC MEMBER, INFORMAL (EOCENE): Altered and weathered vesicular and amygdaloidal basalt flows, breccias, and agglomerates. Rests unconformably on Beaverhead Group rocks, but Tabrum (1996) found it separating Sage Creek and Dell beds, making it about 48 Ma. This is the Sage Creek basalt of Scholten and others.(1955).

SAGE CREEK AND DELL BED MEMBERS, INFORMAL (EOCENE): Poorly sorted tuffaceous mudstone, pebbly to cobbly tuffaceous mudstone, sandstone, and conglomerate. Brightly colored cobbles and pebbles of rhyolitic tuff containing sanidine phenocrysts are diagnostic (Tabrum, 1996). Bridgerian Sage Creek sediments unconformably underlie Uintan Dell Beds (Tabrum, 1996), but the distinction is hard to make, and Sage Creek Member is exposed over only a small area.

RHYOLITIC PYROCLASTIC ROCKS, DILLON VOLCANIC MEMBER, INFORMAL (EOCENE?): Air fall and pyroclastic flow tuff, and tuffaceous mudstone. Light gray to light brown. Commonly altered to bentonitic clays. Includes some interbedded basalt flows, sometimes distinguished as Trvh. Tentatively correlated with the 40.5-47.1 Ma tuffs (Leeth, 2000) north of the map area in Grasshopper Canyon and with the 41-43 Ma tuffs (Fritz and others, 1989) of Frying Pan Basin. Unit may also be correlative with the Sage Creek and Dell beds in the Renova Formation (Fields and others, 1985; Tabrum, 1996) to the south. Unit is the same as Cook Ranch Volcanics of Pecora (1981, 1987). Landslides commonly develop in this unit.

RHYOLITIC FLOWS, DILLON VOLCANIC MEMBER, INFORMAL (EOCENE?): Brick-red to maroon rhyolite lava flows with an aphanitic groundmass and tiny phenocrysts of quartz and plagioclase (after Tysdal, 1988). Found on the southeast flank of the Blacktail Range, far from the postulated Dillon volcanic center.'
3330|'Gritty sandstone, tuffaceous mudstone commonly with abundant bentonite, and thin brown limestone. Sandstone contains angular clasts of quartz, volcanic rock fragments, and black chert. Late Arikareean vertebrate fossil assemblages have been found (Fields et.al., 1985).'
3331|'Light gray tuffaceous mudstone containing abundant bentonitic clay. Yielded Whitneyan vertebrate fossils (Fields and others, 1985).'
3332|'Very light brown tuffaceous  mudstones with lesser amounts of conglomeratic sandstone and volcanic ash. Abundant calcareous nodular horizons. Includes only the Cook Ranch Member of Tabrum (1996).'
3333|'Black, dense olivine basalt forms a cap on the Trev unit in the northcentral part of the map. Tentatively correlated with basalts to the north in Grasshopper Canyon that yielded age dates of 40.5 to 47.1 Ma (Leeth, 2000).'
3334|'Altered and weathered vesicular and amygdaloidal  basalt flows, breccias, and agglomerates. Rests unconformably on Beaverhead Group rocks, but Tabrum (1996) found it separating Sage Creek and Dell beds, making it about 48 Ma. This is the Sage Creek basalt of Scholten and others (1955).'
3335|'Poorly sorted tuffaceous mudstone, pebbly to cobbly tuffaceous mudstone, sandstone, and conglomerate. Brightly colored cobbles and pebbles of rhyolitic tuff containing sanidine phenocrysts are diagnostic (Tabrum, 1996). Bridgerian Sage Creek sediments unconformably underlie Uintan Dell Beds (Tabrum, 1996), but the distinction is hard to make, and Sage Creek Member is exposed over only a small area.'
3336|'Air fall and pyroclastic flow tuff, and tuffaceous mudstone. Light gray to light brown. Commonly altered to bentonitic clays. Includes some interbedded basalt flows, sometimes distinguished as Trvh. Tentatively correlated with the 40.5-47.1 Ma tuffs (Leeth, 2000) north of the map area in Grasshopper Canyon and with the 41-43 Ma tuffs (Fritz and others, 1989) of Frying Pan Basin. Unit may also be correlative with the Sage Creek and Dell beds in the Renova Formation (Fields and others, 1985; Tabrum, 1996) to the south. Unit is the same as Cook Ranch Volcanics of Pecora (1981, 1987). Landslides commonly develop in this unit.'
3337|'Brick-red to maroon rhyolite lava flows with an aphanitic groundmass and tiny phenocrysts of quartz and plagioclase (after Tysdal, 1988). Found on the southeast flank of the Blacktail Range, far from the postulated Dillon volcanic center.'
3338|'Gray, tan, or white dense masses of quartz and locally jasperoid; commonly vuggy, fractured, and layered. Replaces gneiss and fills open spaces on the northeast flank of the Blacktail Range, and appears to be associated with the Jake Canyon Reverse Fault. (After Tysdal, 1988).'
3340|'Conglomerates containing mainly clasts of Paleozoic limestone.'
3341|'Conglomerates containing mainly clasts of quartzite.'
3349|'Pilgrim dolomite is gray to pinkish-gray medium- and thick-bedded sugary dolomite, 100-140 feet thick. Lower contact with Park is conformable. Park Shale is olive-green fissile chippy clay shale with thin limestone beds in the middle part, 150-200 feet thick. Conformable with underlying Meagher limestone, which is yellowish-brown to gray, mottled, medium- to thick-bedded dolomite, and a cliff former. Thickness 575 feet. (After Pecora, 1981; Tysdal, 1988).'
3350|'Wolsey shale is olive-green, finely micaceous, clay shale with thin layers of brown glauconitic quartzose siltstone. 50-100 feet thick. The underlying Flathead sandstone is light-gray, tan, and maroon, medium- to coarse-grained, medium bedded quartz sandstone. Cross-bedded, and contains some quartz pebbles; thickness 30-120 feet. (After Pecora, 1981; Tysdal, 1988).'
3351|'Greenish-black, fine- to medium-grained biotite-plagioclase-clinopyroxene metamorphic rock, commonly serpentinized.'
3353|'Talus deposit - Not described in publication, but shown on map.'
3375|'Stream deposits in modern drainages. Most deposits are composed of stratified and laterally discontinuous beds of pebbles, cobbles, sand, and silt. Includes reworked loess in the western part of the area near Tensed.'
3376|'Unconsolidated poorly sorted rubble, typically as boulders of basalt in a finer grained matrix. Includes large blocks of Columbia River Basalt Group near St. Maries interpreted by Griggs (1973) as landslide deposits, but which lack hummocky topography and other obvious landslide features. Few deposits are known with certainty to be landslides, perhaps because they are relatively old features without recent movement.'
3378|'Unsorted boulders and finer grained unconsolidated material in the valleys of the highest drainages. Possibly outwash.'
3379|'Mostly deeply weathered yellow to orange silt and clay, but also quartzite pebbles and cobbles, and sand. Clasts derived primarily from the Belt Supergroup. Near Clarkia, lakebeds of clay and silt contain extremely well-preserved leaf fossils (Smiley and Rember, 1979; Rember, 1991). Locations taken largely from unpublished maps of M.D. Jenks (written commun., 1998) and C.N. Savage (Idaho Geological Survey, unpublished files, 1979). Most deposits overlie flows of the Columbia River Basalt Group or rocks of the Belt Supergroup at elevations well above present stream levels, but several ages of deposits are preserved in the area. Younger (late Miocene? or Pliocene?), more bouldery terrace remnants are present at lower elevations along the major rivers. These remnants are deeply eroded and lack subhorizontal upper surfaces that would be expected if they were Quaternary terraces. Thickness of Ts is varied, but a well in the Tensed area passed through 265 feet (81 m) of sediment before encountering basalt (well 44/4-18N1; Ko and others, 1974). Typical thickness is about 30 feet (10 m).'
3380|'Medium gray to dark gray basalt that typically has a grainy, felty texture caused by abundant small plagioclase and olivine phenocrysts and by microvesicles and diktytaxitic cavities. The denser parts of the flows are dark gray to black and fine grained; they lack the grainy texture, although small plagioclase phenocrysts are apparent. Outcrops weather gray-brown to reddish brown. In thick flows, large, poorly defined basal columns 3-6 m thick change upward to slabby, platy zones that are typically medium bluish gray on fresh surfaces. Above the platy zones, flows commonly have a thick blocky to hackly entablature that is 15 m or more thick, and in places well-developed thin, vertical to radiating columns. The top of the entablature grades into an increasingly vesicular, rubbly in places, flow top. Thin flows are more vesicular throughout and generally have only weakly developed basal columns and a vesicular flow top. Pillow-palagonite complexes are locally common at the base of flows or flow units (series of chemically similar thin flows that grade laterally into a single flow). Hyaloclastic material is also present locally at the top of some units; this material is well exposed on a logging road built in 1998 on the southeast side of Trout Creek, about 4 miles west of Calder.

The Priest Rapids Member typically consists of one or more flows of Rosalia chemical type and has reversed magnetic polarity. A flow of Lolo chemical type is present in the Clarkia area. The Priest Rapids Member is the uppermost unit in the Plummer-St. Maries-St. Joe River area and directly overlies basement rocks in the upper St. Joe River drainage, where it partly fills the prebasalt topography. In the St. Maries area, it overlies the Ted unit, and near Harrison it overlies Tgn2 flows. Thicknesses of individual flow units ranges from 8 to 25 m for thin units to >180 m for thick, valley-filling sequences in the St. Joe River drainage.'
3381|'Medium gray, coarse-grained and highly plagioclase phyric basalt to dark gray and dense basalt with fewer but still abundant plagioclase phenocrysts. Freshly broken fragments have a coarse, irregular surface texture. Phenocrysts range in size from less than 1 mm to at least 5 mm. The smaller phenocrysts are typically lath shaped, and the larger ones are more equant. Most exposures are of  the massive basal columnar part of the unit. The well-formed basal columns are 1-2 m in diameter and in places 7 m or more in length. The unit commonly weathers gray-brown to dark gray. Hyaloclastic material is associated with the Dodge basalt exposed in the railroad tunnel portal north of Benewah Lake campground.

The basalt of Dodge is a valley- and basin-filling unit of normal magnetic polarity exposed around the southern end of Coeur dAlene Lake, and near and south of St. Maries. The Dodge basalt was not found in the basalt section south of Harrison along State Highway 97, although it is present on the west side of the lake south of Browns Bay. A probable Dodge vent is at Cedar Creek campground 3 miles north of Clarkia (Swanson and others, 1979a). The Dodge basalt overlies Tgn2 basalt and is overlain by Tpr flows. Maximum thickness is approximately 40 m.'
3382|'Dark gray to black, fine-grained aphyric to very sparsely plagioclase-phyric basalt. Locally at least one flow near the top of this unit has a Priest Rapids-like grainy, felty texture. Large columns of the basal colonnade are generally exposed only in quarry cuts. Natural exposures are typically of the thick entablature, consisting of either thin, well-developed and commonly radiating columns, or poorly developed columns with a blocky, hackly character. These entablature exposures are typically cliff-forming masses that can be traced laterally for several miles. Individual flows are usually over 30 m thick and may be more than 60 m thick. Locally, hyaloclastic material is associated with the top of individual flows, especially near contacts with basement rocks. In the Hells Gulch section north of St. Maries, an extensive hyaloclastic unit, with incorporated pods of ropy spatter and other ejecta-like debris, is at least 25 m thick and forms erosional hoodoo pillars at several locations. In other areas, the hyaloclastic material has crude stratification.

Grande Ronde N2 has normal magnetic polarity and is the lowermost basalt unit exposed on most of the St. Maries quadrangle; generally, its base is either not exposed or lies directly on prebasalt basement rocks. However, on the east side of Coeur dAlene Lake near the north edge of the St. Maries quadrangle, the top of a Tgr2 flow is exposed along the shoreline beneath the base of Tgn2. This Tgr2 flow is also present beneath the Tgn2 along the west shoreline at Rockford Bay, but is too thin to show at map scale. Tgn2 is overlain by either Ted or Tpr flows.'
3383|'Dark gray to black, fine-grained aphyric to very sparsely plagioclase-phyric basalt similar to Tgn2. One flow, with reversed magnetic polarity, is the lowermost basalt unit exposed in the map area. Only the vesicular flow top and upper part of the entablature are exposed along the east shoreline of Coeur dAlene Lake north of Harrison.'
3384|'Dark gray, fine-grained porphyritic basalt. Mapped south of the study area by Duncan (1998) who noted a distinctive brown weathering rind in places and plagioclase phenocrysts that average 1 cm in length but may exceed 5 cm. Flows have normal magnetic polarity. Originally thought to be either the upper part of the Wanapum Formation (Camp, 1981) or part of the Saddle Mountains Formation (Bush and others, 1995) of the Columbia River Basalt Group. Recent work by John Bush (personal commun., 1999) indicates that these flows are actually older than the Columbia River Basalt Group. Extruded from local vents and flowed into valleys. May also have flowed over and intruded into sediments (Ts). Thickness uncertain, but may locally exceed 60 m.'
3385|'Light gray, aphanitic to very fine-grained rhyolite with sparse (2-10%) phenocrysts of quartz and rare potassium feldspar. Large mass along the St. Joe River east of St. Maries is a composite body containing dikes of sparsely porphyritic rhyolite and subordinate dikes of porphyritic rhyolite (or dacite?) with conspicuous K-feldspar, quartz, and plagioclase phenocrysts.'
3386|'Gray dacite, typically porphyritic, with an aphanitic groundmass. Phenocrysts, where present, include quartz (up to 8 mm in diameter, commonly embayed) as well as plagioclase, biotite, and hornblende. Present east of Fernwood as well as north of the Merton Creek stock.'
3387|'Gray, medium-grained, porphyritic biotite granodiorite of the Merton Creek stock, and hornblende-biotite granodiorite and biotite granodiorite of the Herrick stock (Holland, 1947). Potassium feldspar phenocrysts, 1 to 2 cm in length, compose 5 to 10 percent of the rock in some areas. Contains mafic inclusions and sparse aplite and pegmatite dikes. Weathers to a coarse grus. Plagioclase in Merton Creek stock is compositionally zoned (An16 to An28); most zoning is oscillatory. The southern margin of the Herrick stock is compositionally diverse and includes intermingled hornblende-rich phases, some of which are well foliated. Foliation there is subhorizontal and may result from igneous flow. Foliation at Mud Cabin Creek near the northern margin is mylonitic. Age unknown, but rock resembles the Roundtop pluton to the southeast that has been dated at 527 Ma by U-Pb methods (Marvin and others, 1984).'
3388|'Mafic dikes mapped by Hobbs and others (1965) and Campbell and Good (1963) in and near the Coeur dAlene mining district.'
3389|'Mafic dikes with biotite phenocrysts mapped in and near the Coeur dAlene mining district by Hobbs and others (1965) and Campbell and Good (1963). Single dike analysis indicates high K2O content (6.15%).'
3390|'Black to dark gray, medium- to fine-grained pyroxene gabbro. Typically has red weathering rind and develops red soil. Largest body northeast of Clarkia has squarish outline, perhaps because its emplacement was controlled by orthogonal faults or fractures; smaller intrusions are dike-like elsewhere in the south-central part of the map area. Includes diabase and gabbro dikes of Clark (1963) and Hietanen (1963a), who report plagioclase compositions of An47 and An53. Major-element concentrations similar to those of Tpr, but trace-element concentrations dissimilar to any known Columbia River basalt.'
3391|'Gray, strongly foliated, moderately lineated hornblende-biotite tonalite, biotite tonalite, granodiorite, and quartz diorite. Exposed on the eastern, upthrown side of the White Rock fault in the southeast quarter of the map area. Orthogneiss is medium grained and contains allotriomorphic granular to recrystallized mosaics of quartz and feldspar between larger biotite flakes. Hornblende typically blocky. Contains euhedral epidote interpreted as a magmatic phase. Rocks mapped as Kog are heterogeneous and samples contain a range of SiO2 from 57 to 74 percent; K2O varies from 0.75 to 4.25 percent. Some of the compositional variation may have originated as schlieren or mafic inclusions. Contains amphibolite bodies up to 100 m wide with contacts approximately parallel to foliation. Intercalated with muscovite schist. Foliation is overprinted locally by s-c fabric (Simpson and Schmid, 1983) with top-to-the-west sense of shear. Cut by irregular masses of pegmatite that lack flattening fabric, and on Freezeout Ridge, by a north-striking undeformed rhyolitic dike. Includes Marble Creek gneiss bodies of Reid and others (1981) and Cockrum (1986). Age is poorly known but orthogneiss is considered to be Cretaceous based on similarities with approximately 94 Ma deformed phases of the Cretaceous Idaho batholith near Lowell (Toth and Stacey, 1992).'
3392|'Black to dark gray, fine- to medium-grained, foliated to lineated hornblende-plagioclase rock. Mostly garnetiferous, with garnets up to 2 cm in diameter locally; some contain biotite instead of or in addition to hornblende. Present in schist correlated as metamorphosed Prichard Formation (Hietanen, 1967; Cockrum, 1986) and thus may be metamorphosed Proterozoic sills. However, those associated with Kog unit and those with pyroxene are probably Cretaceous.'
3393|'Light green to dark gray siltite, darker green argillite, dolomitic siltite,  and white, very fine-grained quartzite. Rocks low in the unit have mud-chips and mudcracked and rippled surfaces in siltite. Quartzite increases upward. Minor dark gray argillite, alone and as carbonate-free caps on reddish weathering ferroan calcitic or dolomitic siltite and quartzite northwest of Emida, possibly in the middle of the unit. Locally, one or more stromatolite horizons occur in this interval. Siltite and white quartzite dominate the upper part to the erosional top. The presence of carbonate led Savage (1973) to assign these rocks to the Wallace Formation. Stratigraphic relations are more consistent with the carbonate being part of the Libby Formation, as mapped by Griggs (1973).'
3394|'Gray to white to pale red quartzite with lesser amounts of siltite and argillite. Shown where a lack of mapping or poor exposure prevented subdivision. Consists largely of Ysp1 and Ysp4 as defined by Harrison and Jobin (1963) near Clark Fork. Thin intervals of carbonate (Ysp2) and dark gray, thinly laminated argillite (Ysp3) were noted at a few localities but not mapped as separate units. Includes rocks along Renfro Creek northeast of Santa previously mapped as Striped Peak Formation (Griggs, 1973), but which are more highly deformed and possibly at higher metamorphic grade than Striped Peak rocks to the southwest. An alternative explanation is that these are quartzitic rocks of the Ravalli Group in thrust contact with the Wallace Formation.'
3395|'Light gray to red, medium- to fine-grained arkosic quartzite. Beds up to 1 m thick with some intervening siltite and argillite. Fine-grained beds are similar to the Ysp1 quartzites but have less magnetite, more yellow rusty spots, and more K-feldspar. Characteristic, however, are well-rounded, medium-size (0.3-0.5 mm) quartz grains, either as isolated grains (floaters) in a finer grained matrix or as major constituents of the rock. Ripple cross lamination and rippled surfaces more abundant than cross lamination. Includes plane lamination, some of which has hematite concentrations. Rocks are characteristically but not ubiquitously feldspathic. Visual estimates of twelve etched and stained hand specimens indicate 9 to 23 percent K-feldspar (mean of 17 %) and 5-15 percent plagioclase (mean of 8%). Some K-feldspar appears detrital, but much is present as diagenetic(?) rims on plagioclase. Common yellow-brown spots may result from weathering of ferroan calcite. Equivalent to Ysp4 near Clark Fork (Harrison and Jobin, 1963) and to the Bonner Quartzite in the Missoula area (Nelson and Dobell, 1961). Thickness uncertain but may be as much as 1,000 m in the southwestern part of the area.'
3396|'Purplish red and subordinate green siltite and argillite. Layering typically 1 to 3 cm thick, with some rippled and mudcracked surfaces. Salt casts present in western part of area south of Plummer, but unit not subdivided in that region. Minor carbonate occurs within and at the top of the member in the northeastern part of the area. This uppermost carbonate interval thickens north of the area and is mapped as Ysp2 by Harrison and Jobin (1963) near Clark Fork. Unit is equivalent to member three of the Mount Shields Formation, described to the northeast (Harrison and others, 1986). Thickness uncertain but probably about 90 to 120 m in the northeastern part of the area and 300 m in the east-central part (north of Calder at Spooky Butte) and in the western part (southwest of Emida at West Dennis).'
3397|'Pale purplish red, fine-grained, flat-laminated quartzite, and subordinate argillite and siltite. Rare ripple cross lamination and even rarer trough cross lamination in 10-30 cm thick beds. Commonly contains macroscopic magnetite octahedra and some mud flakes. Base of unit is placed at lowest quartzite beds. Above them is an interval of very thinly laminated green argillite-siltite similar to that of the Ywu3 unit below, with color grading upward from dark to light and the reverse. This argillite-siltite gives way upward to the quartzite-dominated part of the unit. Visual estimates of eleven etched and stained hand specimens indicate 12-20 percent plagioclase (mean of 17%). Only three of these samples contain K-feldspar (7% or less), in contrast to the K-feldspar-rich Ysp4 quartzite. Equivalent to the lower part of Ysp1 mapped by Harrison and Jobin (1963) near Clark Fork. Also equivalent to the lower two members of the Mount Shields Formation to the northeast described by Harrison and others (1986). Thickness at Striped Peak, immediately east of the map area, is about 820 feet (250 m; Vance, 1981). Thickens to 300 m at Spooky Butte north of Calder and to more than 450 m at West Dennis southwest of Emida.'
3398|'Predominantly dark gray siltite and argillite, but locally contains unmapped carbonate intervals equivalent to member two. Shown where a lack of mapping or poor exposure prevented subdivision. Includes rocks at Lolo Pass 6 miles northeast of Tensed mapped as Ywu by Griggs (1973) but which could alternatively be Ysp3 of Harrison and Jobin (1963) mapped to the north near Clark Fork. Total thickness at Striped Peak, immediately east of area, is 1,500 feet (460 m; Shenon and McConnel, 1939). Thickens to about 1,200 m in south-central part of area at Baby Grand Mountain southeast of Emida.'
3399|'Microlaminated and thinly laminated light green siltite and darker green argillite, green siltite, and black argillite. Subordinate 10 to 20 cm thick, locally carbonate-bearing siltite and very fine-grained quartzite. Bedding commonly uneven and wavy. Weathers yellowish brown. Thickness about 500 feet (150 m) on north side of Striped Peak just east of area (Shenon and McConnel, 1939). Thickens to the southwest, with approximately 230 m at Spooky Butte north of Calder, 335 m at St. Maries, and 490 m in the area south of Bald Mountain Lookout south of Emida.'
3400|'Green dolomitic siltite that weathers orange, green thinly laminated and microlaminated siltite and argillite, and thin lenticular quartzite beds. Contains mudcracks and ripple marks, which are uncommon in the other two members of the upper Wallace Formation. Equivalent to the Shepard Formation present in western Montana (Lemoine and Winston, 1986). Thickness about 500 feet (150 m) on the north side of Striped Peak immediately east of the area (Shenon and McConnel, 1939). Thickens to approximately 335 m at St. Maries, but apparently thins to the southwest where it has not been mapped separately.'
3401|'Dark gray to white, thinly laminated siltite and black argillite. Lower and upper parts have uneven, wavy laminations with graded bedding and rare ripple lamination. Middle(?) part is typically parallel laminated without grading. It commonly contains pyrite (or pyrrhotite?) and weathers rusty brown. Scapolite occurs low in the unit, mostly south of the St. Joe River, as 2-5 mm diameter poikiloblastic white ovoids and more rarely as green-brown prisms with square cross sections (Hietanen, 1967; Mora and Valley, 1989). Thickness about 500 feet (150 m) on northeast side of Striped Peak (Shenon and McConnel, 1939), and 450 to 900 m to the southwest.'
3402|'Quartzite and siltite, typically carbonate-bearing, and argillite. Shown where lack of mapping or poor exposure prevented subdivision. Equivalent to the lower Wallace unit of Griggs (1973) and Hobbs and others (1965).'
3403|'White quartzite, siltite, and black argillite. Siltite and quartzite commonly contain dolomite and calcite. Characterized by uneven bedding (pinch and swell sediment type of Winston, 1986a) that consists of graded couples or couplets of quartzite or siltite-argillite in which scours and loads of quartzite cut or deform tops of subjacent black argillite. Argillite caps commonly contain ptygmatically folded siltite-filled cracks that taper downward. Carbonate typically confined to coarsest parts of bases; some carbonate-bearing quartzites develop open cross fractures that do not continue into the bounding argillite. White quartzite also occurs as hummocky cross-stratified planar beds 15-30 cm thick. Similarly thick siltite beds with the highest concentration of carbonate in the unit contain calcite ribbons, pods, and molar tooth structures. Rare stromatolites and brecciation are associated with carbonate-rich zones. Argillite in this material is typically gray instead of black and lacks siltite-filled cracks. South of the St. Joe River, scapolite is also commonly spatially associated with these zones. Where contact metamorphosed by the Herrick stock along the St. Joe River in the eastern part of the area, quartzites commonly contain abundant fine-grained epidote, and argillite is converted to hornfels. Equivalent to the middle member of the Wallace Formation as mapped by Harrison and others (1986). Thickness highly uncertain, but probably as much as 1200-1500 m.'
3404|'Massive green siltite and thinly laminated green siltite-argillite couplets with lesser amounts of carbonate, commonly as pods in siltite. Subdivided only in a few localities northwest of Calder. Equivalent to the lower member of the Wallace Formation as mapped by Harrison and others (1986). Thickness uncertain, but probably as much as 250-300 m.'
3405|'Gray muscovite and muscovite-biotite phyllite and schist, and fine-grained biotite-feldspar quartzite or granofels. Schistosity at small to large angle to relict bedding. Commonly contains pale lavender to more opaque red garnet and is the source for the Emerald Creek garnet deposits northwest of Clarkia. Is continuous with Ywu along the west boundary of the garnet zone, with distinction drawn at the garnet isograd. Toward the south also contains normally small, rarely 1-2 cm long, staurolite porphyroblasts, perhaps confined to certain layers. Also retains 1-2 cm wide, 10-30 cm long muscovite concentrations with square cross sections interpreted as pseudomorphs after andalusite (Hietanen, 1963a). Atypical garnet-poor schist east of Clarkia may be metamorphosed Ywu3, Ywl, or Ysr.'
3406|'Fine-grained white quartzite, biotite quartzite, granofels, and calc-silicate horizons. Most of unit probably is a metamorphic equivalent of Ywm; some in Emerald Creek drainage northwest of Clarkia may be metamorphosed Ywu2, and that east of Clarkia possibly represents more carbonate-rich parts of Ywl. Metamorphic grade increases southward, as indicated by a southward progression from small muscovite porphyroblasts to phlogopite or biotite clots around 1 to 4 mm void spaces, and then to amphibole and rare diopside. Tremolite-actinolite is more common toward the east and hornblende toward the west. Voids are interpreted as former calcite grains. Red-brown weathering, carbonate-rich siltite zones persist at this grade. Scapolite occurs in some of the biotite-rich (black argillite protolith) layers as poikiloblastic white, stubby, irregular prisms and ovoids. At the highest metamorphic grade, stubby, ragged prisms of light green tremolite occur in calc-silicate granofels.'
3407|'Pale purple to gray siltite, argillite, and quartzite. Also light green siltite and darker green argillite or dark green siltite-light green argillite couplets. Typically mudcracked 1 cm siltite-argillite couplets, but with thin (2-5 cm) and rarer thick (10-20 cm) fine-grained quartzite beds with green argillite caps, similar to those of the Revett Formation. Thickness uncertain, but probably as much as 450 to 600 m.'
3408|'Muscovite-rich schist, thin quartzite intervals, and minor calc-silicate rocks. Exposed only in the extreme eastern part of map. Unit is probably equivalent to the St. Regis Formation of the Ravalli Group, but may include part of the Revett Formation. Tentatively assigned to the Ravalli Group on the basis of stratigraphic position.'
3409|'A combined unit utilized by Griggs (1973) where rocks are poorly exposed in isolated hills and ridges. Mostly light gray to greenish gray siltite and white vitreous quartzite.'
3410|'Quartzite with siltite and argillite. Characteristically 20 cm to rare 1 m thick beds of fine-grained to rare medium-grained quartzite. Some vitreous; most feldspathic with orange-brown spots. Much is flat laminated. Rippled tops and cross lamination more common than trough cross lamination. Rare mud clasts 2-10 cm long occur in lower parts of some thicker beds; also rare load casts and convolute bedding. Zones of white-weathering quartzite 10-50 m thick alternate with zones of brown-stained, thinner bedded quartzite and siltite with mud cracked surfaces; thickest beds appear low in the unit. Brown color associated with higher density of brown spots, perhaps the residue from weathering of ferroan calcite. Visual estimates of nine etched and stained hand specimens indicate 5 to 12 percent K-feldspar (mean of 10%) and 8-17 percent plagioclase (mean of 12%). One sericitized(?) sample from along Big Creek in the northeastern corner of the area lacks feldspar. Some K-feldspar appears detrital, but much is present as diagenetic(?) rims on plagioclase. Thickness ranges from 1,800 feet (550 m) at the junction of Calusa Creek and Pine Creek in the northeast part of the map area (Campbell and Good, 1963) to 3,400 feet (1,035 m) for a nearby(?) section along Pine Creek (Shenon and McConnel, 1939).'
3411|'Pale green siltite, typically with macroscopic magnetite octahedra, in 10-20 cm beds. Darker green argillite partings. Includes flat-laminated, fine-grained, gray to white quartzite. Total thickness of partial sections in the Twin Crags area is about 3,000 feet (915 m; Campbell and Good, 1963). Clough (1981) reports a thickness of about 2,600 feet (800 m) at a location west of Silver Hill in the northeast part of map area.'
3412|'Fine- to medium-grained, commonly foliated to lineated micaceous to feldspathic quartzite with muscovitic parting spaced at 2-30 cm intervals. Garnets occur on some parting surfaces. Unit occurs within the southeastern metamorphic complex, but most or all is probably equivalent to the Burke and Revett formations. Mapped where metamorphic grade, deformation, or lack of exposure makes internal division difficult.'
3413|'Gray, rusty-weathering siltite and minor quartzite. Minor discontinuous carbonate layers. Rare mudcracks. See Griggs (1973) or Cressman (1989) for more detail.'
3414|'Map unit of Griggs (1973) described as dark to medium gray, very thinly bedded argillite commonly interlaminated with light gray siltite and also containing some siltite beds. Grades upward into interbedded and interzoned argillite, siltite, and quartzite sequence. Griggs (1973) suggests a range in total thickness of 2,500 to 3,500 feet (760-1,070 m).'
3415|'Map unit of Griggs (1973) described as predominantly medium to light gray, thin- and regularly bedded siltite, and laminated in part; some argillite laminae and beds. Some beds or zones of gray to white quartzite have been subdivided locally (Yqp unit). Thickness 7,500+ feet (2,290+ m) according to Griggs (1973); base not exposed.'
3416|'Nearly white to light gray impure to pure quartzite mapped by Hobbs and others (1965) in the northeast part of the area. Individual quartzite zones may be as much as 50 feet thick and are discontinuous. Contains about 5 percent plagioclase and no K-feldspar on the basis of two etched and stained samples.'
3417|'Gray to dark gray, white to brown weathering, medium- to coarse-grained micaceous quartzite. Most is foliated, some highly lineated. Some has lighter (muscovitic) and darker (biotitic) layers 1-2 cm thick. Parting on micaceous layers 1 to 40 cm. Micaceous interlayers contain  flattened and elongated garnet in highly lineated and sheared rocks.'
3418|'Dark brown, muscovite-quartz, biotite-muscovite-quartz, and muscovite-biotite-feldspar-quartz schist. Includes some biotite quartzite and locally preserves compositional layering that reflects probable siltite-argillite protolith. Schistosity is locally axial planar to folds in compositional layering and is itself commonly folded and crenulated. Farthest southeast exposures are migmatitic and multiply deformed. Rarely contains garnet, but northeast of Grandmother Mountain, east of Clarkia, porphyroblasts are 1-2 cm in diameter and in close association to kyanite(?). Includes schists correlated with Prichard and St. Regis formations (Hietanen, 1967; Cockrum, 1986).'
3419|'Fine-grained garnetiferous schist. Meta-igneous rocks to the north and northwest within this complex have been dated at about 1580 and 2650 Ma, indicating a pre-Belt age (Evans and Fischer, 1986; Armstrong and others, 1987). However, the unit may include younger overlying Belt rocks (Prichard?) as well. Mapped as Prichard Formation by Griggs (1973).'
3420|'Strongly lineated and foliated light gray to white quartzite. Coarsely recrystallized and feldspar-poor (2% plagioclase).'
3421|'Man-made'
3422|'Unconsolidated poorly sorted rubble, typically as boulders of basalt in a finer grained matrix. Includes large blocks of Columbia River Basalt Group near St. Maries interpreted by Griggs (1973) as landslide deposits, but which lack hummocky topography and other obvious landslide features. Few deposits are known with certainty to be landslides, perhaps because they are relatively old features without recent movement.'
3423|'Predominantly dark gray siltite and argillite, but locally contains unmapped carbonate intervals equivalent to member two. Shown where a lack of mapping or poor exposure prevented subdivision. Includes rocks at Lolo Pass 6 miles northeast of Tensed mapped as Ywu by Griggs (1973) but which could alternatively be Ysp3 of Harrison and Jobin (1963) mapped to the north near Clark Fork. Total thickness at Striped Peak, immediately east of area, is 1,500 feet (460 m; Shenon and McConnel, 1939). Thickens to about 1,200 m in south-central part of area at Baby Grand Mountain southeast of Emida.'
3550|'Alluvium; alluvial fans; landslide and related deposits; talus; avalanche deposits; flood, stream terrace, pediment, or alluvial gravel; rock streams; colluvium; protalus ramparts; creep and solifluction deposits; glacial deposits; travertine; and locally, basalt.  Includes slide blocks of Pennsylvanian to Mississippian carbonate rocks in the Methodist Creek area, southern Lost River Range.'
3551|'Basalt flows of the Snake River Group.  Includes a Quaternary to Tertiary late Cenozoic cinder cone in the central Lost River Range.'
3552|'Gravel and older alluvium, undifferentiated.'
3553|'Clastic rocks, sandstone, conglomerate, tuff and tuffaceous conglomerate, gravel, fanglomerate, brecciated limestone; generally younger than extrusive rocks (Te).'
3554|'Mostly Challis Volcanic Group.  Includes rocks of the Idavada Volcanics and the Heise volcanic field.  Contains volcaniclastic rocks, rhyolite, dacite, latite, trachyte, andesite, shoshonite, and basalt lava flows, tuff breccia, crystal-lithic tuff, rhyolite to dacite ash-flow tuff, and air-fall tuff.'
3555|'Plutons, dikes, and sills primarily of Challis Volcanic Group.  Includes rhyodacite porphyry, granodiorite (described as quartz monzonite by Dover; 1969, 1981) plutonic rocks; rhyolite, basalt and andesite dikes.'
3556|'Jasperoid, diffuse jasperoid, and silicified sedimentary rocks.'
3557|'Conglomerate, breccia, and sandstone at or near the base of the Challis Volcanic Group.'
3558|'Silty and sandy limestone, calcareous sandstone and siltstone, quartzite, limestone, and conglomerate.'
3559|'Includes Snaky Canyon (Wolfcampian to Chesterian), Bluebird Mountain (Morrowan and Chesterian), and Arco Hills (Chesterian) Formations.  Locally, may include unit Mcb (below).  Primarily limestone, sandy limestone, dolostone, and sandstone.'
3560|'Upper Mississippian part is chiefly shallow-water mudstone to conglomerate containing scattered lenses of fossiliferous limestone and dolostone and thin coal seams.  Lower Mississippian part is mostly proximal turbidite deposits consisting of graded beds composed of terrigenous detrital rocks ranging in grain size from mudstone to boulder conglomerate, and subordinate detrital limestone.'
3561|'Limestone, interbedded with conglomerate and sandstone in the middle part; locally fossiliferous.'
3562|'Includes Surrett Canyon (Chesterian), South Creek (Chesterian), Scott Peak (Chesterian and Meramecian), and Middle Canyon (Meramecian) Formations.  Locally, may include some Permian to Upper Mississippian mixed carbonate and siliciclastic rocks.  Primarily limestone, silty and sandy limestone, and calcareous siltstone; locally fossiliferous.'
3563|'Locally includes Upper Devonian Three Forks Formation.  Chiefly distal turbidites composed of fine- to coarse-grained terrigenous detrital rocks containing local chert-quartzite-granule and pebble conglomerate, sandstone, siltstone, mudstone, and minor silty limestone.'
3564|'Dark gray to black, cleaved argillite interbedded with chert, quartzite, dolomitic siltstone, limestone, and minor conglomerate.'
3565|'Includes Three Forks Formation (except where locally mapped with McGowan Creek Formation in the central Lost River Range and southern Lemhi Range), Picabo, Grand View, and Jefferson Formations, and Carey Dolostone.  Includes unnamed sandstone, channel sandstones, and carbonates in the central Lemhi Range. Primarily dolostone, including carbonate conglomerate and breccia,argillaceous limestone, and calcareous argillite.'
3567|'Carbonate rocks of units Dc and DOc, undivided.  Only mapped in southern Lost River Range.  Primarily dolostone; includes carbonate conglomerate and breccia, argillaceous limestone, and calcareous argillite.'
3568|'Includes Roberts Mountains Formation (Lower Devonian to Middle Silurian), Laketown Dolostone (Silurian), Saturday Mountain Formation (Lower Silurian to Middle Ordovician), and Fish Haven Dolostone (Upper Ordovician). Primarily cliff-forming, crystalline dolostone; some interbeds of sandstone, limestone, argillaceous limestone, and calcareous argillite.  Metamorphosed to marble in the Pioneer Mountains and in some areas adjacent to intrusive rocks.'
3569|'Fine- to medium-grained, white to light gray, vitreous quartzite; local conglomerate.  Locally mapped with Summerhouse Formation (Os).'
3570|'Mostly white to pale pink, bimodal, vitreous quartzite; also Scolithus-bearing and glauconitic sandstone, silty and sandy dolostone; local fossiliferous limestone in central Lemhi Range.'
3573|'Includes Tyler Peak (Lower Cambrian) and Wilbert (Lower Cambrian and Late Proterozoic(?)) Formations.  Locally includes some Summerhouse Formation (Os) in the southern Lemhi Range and interbedded quartzite, dolomite and argillite in the Lost River Range.  Contains purple quartzite, sandstone and siltstone; sandy slate; quartz pebble conglomerate.'
3574|'Includes Lawson Creek and Swauger Formations; Lemhi Group, which is divided in descending order into Gunsight, Apple Creek, Big Creek, West Fork, and Inyo Creek Formations; Hoodoo Quartzite; and Yellowjacket Formation.  Contains phyllitic quartzite, slate, siltstone, arkose, and sandstone.  Mostly lower greenschist metamorphic facies; Yellowjacket Formation is biotite-grade facies.  The Lawson Creek and Swauger Formations are included in this unit though the Lawson Creek Formation and uppermost Swauger Formation are glauconitic, a characteristic restricted to Late Proterozoic and Paleozoic rocks in eastern Idaho and southwestern Montana.  Includes banded calc-silicate, gneissose quartzite and pelitic schist in the Pioneer Mountains.'
3600|'Silt, sand, and gravel in modern floodplains and in undissected alluvial fans; locally includes lacustrine and eolian silts and organic deposits.'
3601|'Chiefly massive eolian silt and fine sand ranging in color from light tan to yellow-brown to dark-red or orange-brown.  Older loess layers typically have deeper coloration.  Thickness of the unit ranges from 75 m to less than 2 m.  Accumulations of less than 2 m are not shown on Plate I (Kiver and others, 1979).

Regionally, as many as six sequences of fining upward, unconformity-bounded loess layers are present (McDonald and Busacca, 1989).  The base of each loess sequence consists of (1) basaltic gravel, lenses of basaltic sand, and indurated gravel- to sand-size clasts of paleosols; or (2) poorly to well-bedded and laminated silt and sand, commonly containing lag layers.  The overlying mixed quartzo-feldspathic and basaltic dune sand grades upward into the massive and unstratified eolian silt that typifies the unit.  Locally, eolian sand and silt directly overlie unconformities.  Paleosols generally cap each loess layer.  The paleosols range from soil profiles with weakly to well-developed B and C horizons (accumulation of clays, Fe- and Al-oxides, and carbonate minerals) to profiles with well-developed siliceous petrocalcic (caliche) layers (Patton and Baker, 1978).  Unconformities are characterized by scoured and channeled paleosol surfaces.  Tephras erupted from Mount St. Helens and Mount Mazama are also locally present in the loess sequences.

In the Rosalia quadrangle, loess deposits reflect both wind deposition and erosion by multiple cataclysmic glacial outburst floods through the Cheney-Palouse tract of the Channeled Scabland during the Pleistocene.  The Channeled Scabland is a system of anastomosing channels (coulees) cut by flood waters into basalt flows of the Columbia River Basalt Group.  The scabland morphology combines erosional and depositional landforms and consists of coulees, intervening buttes, streamlined loess islands and uplands, dry falls and plunge pools, and giant ripples and gravel bars.  Streamlined loess islands preserve the best sections of multiple, unconformity-bounded loess sequences.  Gravels at the base of the loess sequences were deposited by high-energy currents of outburst floods, whereas basal laminated silts and sands were deposited by ponding of flood waters.  The silt comprising the bulk of each loess sequence was deposited by prevailing southwest winds.  The silt was probably derived from the voluminous outburst flood slackwater sediments or the Pliocene-late Miocene Ringold Formation occurring southwest of the map area in the Pasco Basin.  Paleosols represent periods of landscape stability during which soil formed (McDonald and Busacca, 1988, 1989).

Age of the loess ranges from Holocene to early Pleistocene. The youngest loess sequence blankets both erosional and depositional scabland topography formed by the last glacial (late Wisconsin) outburst flooding, and it locally contains Mount Mazama tephra erupted about 7 ka (Patton and Baker, 1978).  The youngest loesses display only weakly developed soil profiles and lack petrocalcic horizons.

The oldest recognized loess sequences are reversely magnetized and therefore were deposited in the early Pleistocene, prior to 790 ka (McDonald and Busacca, 1988).  Stratigraphic position, the degree of soil development present, and the various degrees of oxidation, glass hydration, and weathering rind development on basalt clasts along basal unconformity surfaces suggest a pre-last glacial age for loess above reversely magnetized layers and below the youngest unconformity.  Mount St. Helens tephra correlations and an accelerator radiocarbon age determination (McDonald and Busacca, 1988; 1989) indicate a minimum age of about 36 to 40 ka for the most recent episode of pre-last glacial outburst floods.

The unit includes the Palouse Formation of Treasher (1925).  As defined, the Palouse Formation of Treasher (1925) consisted of as many as three laterally accreted loess sequences unconformably underlying the youngest loess sequence (Patton and Baker, 1978).  More recently, McDonald and Busacca (1988) suggested all Palouse-region Holocene and Pleistocene loess sequences be informally referred to as the Palouse loess.'
3602|'Dominantly poorly sorted coarse gravel and sand composed of subrounded to angular clasts of diverse composition.  Gravels commonly display foreset bedding.  Locally, the unit includes poorly laminated and massive silt and sand, as well as tephra layers.  Deposits of two ages are contained in the mapped unit.  Younger last-glacial (late Wisconsin) deposits are most common in coulees of the Cheney-Palouse tract of the Channeled Scabland; they have only weakly developed soil profiles.  These deposits are commonly overlain by a thin veneer of loess. Older (pre-last glacial) outburst flood sediments are sparsely preserved in coulees and loess islands. These sediments commonly possess soil profiles with well-developed B horizons; clasts are deeply weathered, with well-developed weathering rinds, or are so completely weathered that a weathering rind is no longer discernible (Moody, 1987).  Older and younger flood gravel deposits are not distinguished on Plate I.

Deposition of the younger flood sediments occurred during the last-glacial (late Wisconsin) episode of outburst flooding from glacial Lake Missoula (and possibly other ice-dammed glacial lakes) between 16 ka and 12 ka (McDonald and Busacca, 1989).  The coarse gravel and sand were deposited by the high-energy currents, while sand and massive silt were deposited as distal turbidites (Rigby, 1982).  Poorly laminated silt layers were deposited by slackwater where the outburst flood waters ponded.

The sparsely preserved, older flood gravels are considered pre-last glacial in age on the basis of their stratigraphic position, correlation of tephra layers, limited radiocarbon age estimates, degree of soil development, and degree of weathering (Moody, 1987; Richmond and others, 1965).  Tephra correlations and an accelerator radiocarbon age determination (McDonald and Busacca 1988, 1989) suggest a minimum age of about 36 ka to 40 ka for the most recent of these deposits.'
3603|'Consists of two sequences; most of the unit is contained in a lower sequence of numerous cyclic sets of cross-bedded, poorly sorted sand and gravel overlain by finely laminated clay, silt, and fine sand; locally the lower sequence is overlain unconformably by a channel-fill (upper) sequence of sand, silt, and gravel.  In the map area, the unit is restricted to the northern part of the Hangman Creek valley (R. 43-44 E., T. 23 N.).

Coarse-sediment layers of the cyclically bedded lower sequence generally fine upward and consist predominantly of granule-size clasts with subordinate pebble- to cobble-size clasts; boulders are locally abundant.  Coarse layers range from 1 to 5 m thick.  Cross-bedding is generally present in the central or upper part of the coarse grained layers; the basal part is typically graded and commonly contains rip-up clasts from the finely laminated layer of the underlying cyclic set.  Finely laminated layers form the upper part of each cyclic set and contain 10 to 60 couplets made up of alternating light- and dark-colored laminae.  Laminae are typically continuous but are locally contorted (pinch-and-swell), disrupted by clastic dikelets, or truncated.  Finely laminated layers range from 2 to 20 cm thick.  The finely laminated layers are interpreted as varves deposited in a glacial lake occupying the Spokane River valley and its tributaries (glacial Lake Spokane).  Coarse sediments are interpreted as turbidites deposited during outburst floods into the glacial lake (Rigby, 1982).  Field relationships and 14C dates from outside the map area suggest that these deposits are pre-last glacial (Rigby, 1982).

Locally, a sequence of sand, silt, and gravel fills channels 8 to 9 m deep that were cut into the lower sequence.  Coarse, unsorted gravels as much as 1 m thick are present at the base of the channel fill.  The basal gravel is overlain by cyclic sets of poorly bedded gravel-rich sand capped by massive to graded to laminated silt-rich sand layers.  The upper parts of gravel-rich layers are locally cross-bedded, and silt-rich layers are locally cross-laminated.  Beds generally pinch and swell or pinch out altogether, and silt-rich layers are deformed by load casts, flame structures, and clastic dikelets.  The thickness of cyclic sets ranges from about 2 m near the base of the channels to just less than a meter in the upper part of the sequence.  Reworked Mount Mazama ash (erupted about 7 ka) is locally present in cut-and-fill channels eroded into the channel-fill sequence.  The channel-fill sequence was deposited by slackwater in a lake-free Hangman Creek valley during the last-glacial (late Wisconsin) outburst floods from glacial Lake Missoula (Kiver and Stradling, 1980; Rigby, 1982).'
3604|'"Sparsely plagioclase-phyric flow or flows occupying [a] shallow ancient valley eroded into [the] Priest Rapids Member in the Lamont-Sprague area.  Chemically distinct from most other flows of Columbia River Basalt Group" (Swanson and others, 1979a, p. 6).  In hand specimen, the basalt is gray on fresh surfaces and reddish-brown on weathered surfaces.  It is fine grained and generally diktytaxitic, and plagioclase laths are evenly distributed.  Olivine phenocrysts (< 1 mm) generally are not visible in hand specimen.  In thin section, the rock has an intergranular texture and consists of about 50 percent plagioclase, 40 percent augite, <10 percent olivine, and <5 percent opaque minerals.

The Sprague Lake flow(s) possess normal magnetic polarity, which helps to distinguish them from flows of the Priest Rapids Member of the Wanapum Basalt (reversed polarity).  The rock has a fairly well-defined geochemical signature (Fig. 5, Tables 1 and 2) very similar to the that of the basalt of Lewiston Orchards of the Weissenfels Ridge Member (Saddle Mountains Basalt) (Table 3).  Because of its similarity to the basalt of Lewiston Orchards, the basalt of Sprague Lake was assigned to the Weissenfels Ridge Member of the Saddle Mountains Basalt (Anderson and others, 1987; Hooper and Swanson, 1987; Swanson and others, 1979a; Wright and others, 1989).  The basalt of Sprague Lake is the northernmost exposure of the Saddle Mountains Basalt.  Flows of the Weissenfels Ridge Member were erupted between about 13 Ma and 12 Ma (Reidel and Fecht, 1987) (Fig. 4).'
3605|'Flows of fine- to coarse-grained basalt with reversed magnetic polarity (Swanson and others, 1979a).  The Priest Rapids Member consists of flows of two geochemical units--the Rosalia and the Lolo (Table 3).  The two geochemical units are not distinguished on Plate I.  The Rosalia unit is characterized by high TiO2-low MgO composition; flows are generally aphyric to sparsely phyric with olivine commonly visible in hand specimen.  The Lolo unit has a relatively high MgO content; flows generally contain olivine (<1 mm) and plagioclase phenocrysts or glomerophyric clots of olivine and plagioclase (Swanson and others, 1979b).  Lolo flows consistently overlie Rosalia flows.  Lolo flows were extruded about 14.5 Ma (Beeson and others, 1985; Reidel and Fecht, 1987) (Fig. 4).

The Priest Rapids Member is the most widely exposed rock unit in the map area (Plate I).  It overlies progressively older rocks from west to east (Roza Member, Grande Ronde unit N2, and Precambrian Belt Supergroup).  Near the eastern margin of the map area the Priest Rapids Member commonly includes thin, discontinuous interbeds of the Latah Formation (not shown on Plate I).  The Latah Formation is defined as poorly indurated sedimentary rocks interlayered with flows of the Columbia River Basalt Group in the northeastern part of the Columbia Basin (Swanson and others, 1979b).  Locally, flows of the Priest Rapids Member are invasive into the Latah Formation (Swanson and other, 1979a).  The basal flow (Rosalia geochemical unit) of the Priest Rapids Member is pillowed in exposures southwest of Malden (R. 42 E., T. 20 N.) (Plate I).'
3606|'Flows characterized by numerous (5-8 percent) plagioclase phenocrysts (average, 10 mm) generally evenly distributed as single laths.  Flows of the Roza Member are geochemically similar to the geochemical units of the Frenchman Springs Member of the Wanapum Basalt.  (The Frenchman Springs Member is not present in the map area, but where present, it underlies the Roza Member; see Fig. 4).  The Roza Member is distinguished from the Frenchman Springs by a greater MgO content (Swanson and others, 1979b; Wright and others, 1989, table 13).  The Roza Member generally consists of no more than two flows with a total thickness of about 50 m; the member pinches out in the central part of the map area, between Rock Lake and Bonnie Lake (R. 41-42 E., T. 21-19 N.) (Plate I).  In the map area, the Roza Member overlies the N2 unit of the Grande Ronde Basalt.

The Roza Member records the transition from normal polarity, during Frenchman Springs time, to reversed polarity during Priest Rapids time.  Where the Roza consists of two flows, the upper flow generally has reversed polarity and the lower flow generally has transitional polarity (Swanson and others, 1979b).  Additionally, in the western part of the Columbia Basin (outside the map area), the presence of sedimentary interbeds (Squaw Creek Member of the Ellensburg Formation) between flows of the Roza Member and the underlying flows of the Frenchman Springs Member (Fig. 5) implies that a significant amount of time elapsed between eruptions of the two members.  Thus, the Roza Member is inferred to be nearer in age to the overlying Priest Rapids Member (about 14.5 Ma) than to the underlying Frenchman Springs Member (Fig. 4).'
3607|'Black, dense, fine-grained basalt flows; aphyric to slightly phyric; phyric varieties have sparse plagioclase phenocrysts and plagioclase-clinopyroxene clots visible in both hand specimen and thin section.  Olivine is absent as phenocrysts but is present in the groundmass in minor amounts (<0.5 percent).  Flows range from 1 m to 100 m thick but average 20 m thick (Swanson and others, 1979a).

Grande Ronde flows have a range in composition and include many geochemical units and chemical types.  Chemical types are flows of similar composition in different stratigraphic positions, whereas geochemical units are flows of similar composition in a specific stratigraphic position (Wright and others, 1989).  Within the Grande Ronde Basalt, flows of both high- and low-MgO compositions are common (Swanson and others, 1979b); generally the rock has low TiO2 and P2O5 contents (Wright and others, 1989, table 13).

The N2 unit of the Grande Ronde Basalt is the oldest rock of the Columbia River Basalt Group exposed in the map area.  Flows of the Grande Ronde Basalt erupted between about 15.5 Ma and about 16.5 Ma (Beeson and others, 1985; Reidel and Fecht, 1987).  In the western part of the Columbia Basin, outside the map area, the N2 unit is commonly separated from the overlying Wanapum Basalt by a 15.5 Ma sedimentary interbed known as the Vantage Member of the Ellensburg Formation (Long and Duncan, 1983) (Fig. 4).  In the map area, flows of the Grande Ronde Basalt underlie flows of both the Roza Member and Priest Rapids Member of the Wanapum Basalt and overlie Tertiary-Cretaceous intrusive rocks and Precambrian metasedimentary rocks.  In the eastern part of the Rosalia quadrangle, near the pre-basalt topographic highs, the Grande Ronde basalt contains sedimentary interbeds and overlies weakly lithified sedimentary rocks of the Latah Formation (Griggs, 1976).  The Latah Formation in the Rosalia quadrangle is not mappable at the 1:100,000 scale and is not shown on Plate 1.'
3608|'Porphyritic quartz monzonite exposures in sec. 10, T. 23 N., R. 43 E. (Plate I).  Phenocrysts (1.2-2.5 cm) consist of white to gray K-feldspar and are poikilitic with biotite inclusions.  Biotite is the only mafic mineral visible in hand specimen.  Locally, the rock contains small inclusions of igneous rock and is generally deeply weathered, forming a mantle of grus (DGER mapping, this report).  Unit is probably Tertiary or Cretaceous in age (Griggs, 1973).'
3609|'Predominantly gray, green, and red siltite with subordinate light-colored quartzite and minor pink dolomite lenses or beds.  Dark argillite partings are common.  A 150-m-thick zone of gray to reddish-gray, medium- to coarse-grained feldspathic quartzite is commonly present about 300 m below the top of the formation.  Most outcrops are characterized by a micaceous sheen on bedding surfaces.  Mud cracks, ripple marks, and mud-chip breccia are common in red and green rocks.  The rock is locally punky and bleached.

The unit''s basal contact with the upper unit of the Wallace Formation is gradational over a narrow zone; the upper contact is nowhere exposed in the map area.  East of the map area, south of Coeur d''Alene Lake, the formation has a maximum thickness of about 1,500 m (Griggs, 1973).'
3610|'Dominantly thin-bedded or laminated, dark-gray argillite with minor beds or zones of light-colored siltite; some carbonate-bearing argillite beds or laminae.  A gray carbonate-bearing argillite zone 60 m thick consisting of dolomitic argillite or dolomitic siltite interbedded with dolomite or dolomitic limestone is generally found near the middle or near the top of unit (Griggs, 1973).  The unit is evenly bedded and fissile and ranges from approximately 760 m to 900 m thick (Griggs, 1973).  The lower contact is gradational into the lower unit of the Wallace Formation.'
3611|'Typically composed of an upper part and a lower part.  The upper part consists chiefly of beds of black argillite alternating with beds of carbonate-bearing, gray siltite and/or quartzite.  Siltite and/or quartzite are dominant in zones about 60 m thick.  The lower part is mostly green to gray, carbonate-bearing, interbedded or interlaminated argillite and siltite with lesser blue-gray dolomite and dolomitic limestone.  Rocks of this unit are characterized by tan weathering rinds and molar-tooth structures; irregular bedding and minor folds are also characteristic.  Syneresis cracks and ripple marks are common throughout unit.  Some siltite and quartzite beds display fine cross-bedding on etched surfaces.

The lower contact is not exposed in the map area.  East of the map area, north of the St. Joe fault, the formation ranges in thickness from about 1,500 m to 2,100 m (Griggs, 1973).'
3612|'Chiefly red, green, and gray interbedded or interlaminated argillite and siltite; argillite content increases upward.  Minor quartzite beds are present near the base, and minor carbonate-bearing beds are present in the upper part.  Mud cracks, mud-chip breccia, and ripple marks are common throughout formation.  The rock unit typically displays flaggy weathering.

The upper contact is not exposed in the map area; the lower contact is gradational into the underlying Revett-Burke Formations (undivided).  East of the map area, near Plummer, Idaho, the formation is about 600 m thick (Griggs, 1973).'
3613|'Mostly light-gray to greenish-gray, commonly micaceous siltite and white, commonly feldspathic quartzite.  The quartzite is generally vitreous and locally contains rounded grains of opaque, bluish quartz.  Because of the limited extent and isolation of the exposures in the map area, the position of these strata in the stratigraphic sequence is difficult to determine; as a result, the individual formations can not be reliably separated.

North of the St. Joe fault, which extends from the southern arm of Coeur d''Alene Lake east-southeast to near the Idaho-Montana border, the formations are divisible.  There, the Revett Formation consists of thick-bedded, white to light-gray, fine- to medium-grained, vitreous quartzite with a feldspathic matrix; orange-weathering carbonate spots common.  Gray siltite is common in upper and lower parts of formation.  The gray siltite is dominant over zones several meters thick.  The thickness ranges from about 600 m to about 900 m (Griggs, 1973).

The Burke Formation consists of light- to medium-gray to grayish-green siltite with argillite partings and interbeds; locally, the formation includes minor light-colored quartzite.  Lavender and purple-red rocks are generally present near the middle of the formation.  Magnetite specks are common, and a light-colored weathering rind is characteristic.  Ripple marks and cross-bedding are present locally.  The thickness of the unit averages between about 900 m and about 1,100 m (Griggs, 1973).

Exposures at Badger Lake (center, sec. 34, T. 22 N., R. 41 E.) consist of light-gray, fine-grained, vitreous quartzite with a feldspathic matrix, orange-weathering carbonate spots, and minor magnetite specks.

Webster and Nunez (1982, p. 49) described rocks on Steptoe Butte (T. 18 N., R. 44 E.) as reddish-brown, tan, and white, muscovite-bearing quartzite of the Revett Formation.  Additionally, they described the exposure south of Rosalia as "Quartzite, schist and gneiss of the Prichard Formation" and the exposures in sec. 6, T. 19 N., R. 44 E., as part of the Prichard Formation or the Striped Peak Formation.  For this report, the rocks at those localities are shown on Plate I as Revett-Burke, undivided, after Griggs (1973).'
3614|'Chiefly fine- to medium-grained garnet-biotite-muscovite-quartz schist and coarse-grained phyllite with subordinate medium- to fine-grained micaceous quartzite and micaceous siltite.  The schist is shades of gray or brown on fresh surfaces.  Disseminated iron sulfide is common throughout rocks of this unit; weathering surfaces are generally rusty brown.  Quartzite and siltite are commonly banded; banding appears to parallel relict bedding.  The schist contains garnet porphyroblasts (<1 mm) not typically visible in hand specimen; however, on cut surfaces, garnet porphyroblasts are visible and are pale pink.  Thin sections show that the rock lacks plagioclase.  Garnets are late-growth (post-mica), have no apparent rotation and are colorless with abundant inclusions (quartz?).  Although foliation in the quartzite beds is not well developed, complete metamorphic recrystallization has occurred.

In the schist and phyllite, foliation strikes northwest and dips shallowly to the southwest and appears to parallel relict bedding.  Bedding appears to have been regular and continuous.  The rock has two distinct cleavages; both strike north, one dipping about 60oE and the other dipping about 60oW.

The only exposure of this rock examined by the author is in the west half, sec. 14, T. 20 N., R. 41 E. near the north end of Rock Lake (Plate I).  The other probable exposure of this rock is on the island in Bonnie Lake (sec. 36, T. 21 N., R. 41 E.)(J. E. Schuster, DGER, oral commun., 1988).

The rocks at Rock Lake have been categorized as high-grade metamorphic rocks for the following reasons: (1) The garnet-mica-quartz assemblage could represent the greenschist or albite-epidote-amphibolite facies (low-grade) of Williams and others (1954, p. 210); however, the rock lacks albite, and garnet is more common in this rock than it generally is in these low-grade assemblages.  (2) The rock is more representative of the garnet-biotite-muscovite-quartz ( oligoclase) mineral assemblage of the amphibolite facies (high-grade) of Williams and others (1954, p. 232), in which porphyroblasts of pink garnet are common and feldspar is commonly absent.

According to Williams and others (1954, p. 232) the garnet-mica-quartz mineral assemblage is characteristic of metamorphosed pelitic sedimentary rocks.  On the assumption that rocks of the unit were originally pelitic sedimentary rocks and because of their similar weathering characteristics and lithology, the rocks may be correlative with the Precambrian Y Prichard Formation.  The Prichard Formation is the lowermost formation of the Belt Supergroup.  The Prichard consists dominantly of evenly bedded argillite and siltite with lesser quartzite.  Layers and/or disseminated grains of pyrite and/or pyrrhotite are present in most rocks of the formation, resulting in characteristic rusty weathering surfaces.'
3615|'Light-gray, coarse-grained muscovite-quartz-feldspar schist exposed in sec. 7, T. 23 N., R. 46 E.  Contains less than 50 percent muscovite;  are present locally (Weis, 1968).  .  Layering is locally contorted.  Concordant and discordant granitic intrusions make up as much as 50 percent of the unit. Amphibolite is locally present.  Extensive exposures of this unit lie north of the map area in the Spokane 1:100,000-scale quadrangle.'
3700|'Stream deposits in modern drainages; gravel, silt, and sand.'
3701|'Poorly sorted and poorly stratified, unconsolidated deposits principally of glacial origin. Includes till in lateral and ground moraines as well as outwash and modern stream alluvium.'
3702|'Tan-weathering, aphanitic to very fine-grained phaneritic rock that contains less than 10 percent phenocrysts of potassium feldspar and quartz.'
3703|'Rhyodacite and subordinate rhyolite, typically porphyritic, with phenocrysts of orthoclase or sanidine, plagioclase, quartz, biotite, and hornblende.'
3704|'Dark gray nonfoliated dikes characterized by sparse hornblende and plagioclase phenocrysts in an aphanitic matrix.Dark gray nonfoliated dikes characterized by sparse hornblende and plagioclase phenocrysts in an aphanitic matrix.'
3705|'Biotite granite. Stock in northeast corner is light gray, fine grained, and muscovite-bearing. It lacks perthitic feldspar typical of Eocene granite in the region, but is similar chemically (K2O > Na2O; SiO2 > 72%).'
3706|'Medium-grained equigranular to porphyritic monzogranite and granodiorite. Porphryritic rocks have light pink potassium feldspar phenocrysts 6 mm long in a medium-grained groundmass. Mapped as the Paradise pluton by Toth (1983a, 1983b).'
3707|'Dark gray, sparsely porphyritic to equigranular fine-grained dikes of uncertain age. Equivalent to either Ta or Ka units.'
3708|'Dark gray, weakly porphyritic to equigranular fine-grained dikes that consist primarily of plagioclase, biotite, quartz, and hornblende.'
3709|'Medium-grained, equigranular muscovite-biotite granite and granodiorite. Muscovite is in books that locally coarsen to 1 cm in diameter.'
3710|'Slightly porphyritic to equigranular granodiorite and granite containing 2-5 percent biotite and varied amounts of muscovite. Weakly developed primary flow foliation present. Local development of a mylonitic foliation, particularly at higher elevations. Includes the Bear Creek pluton of Toth (1983b).'
3711|'Granodiorite, granite, and tonalite containing poikilitic potassium feldspar megacrysts 3 to 8 cm long. Muscovite bearing in southwest part of quadrangle (Toth, 1983), and hornblende bearing and foliated in northwest part (Lewis and others, 1992).'
3712|'Medium-grained hornblende-biotite tonalite and quartz diorite. Strongly developed flow foliation and a down-dip flow lineation defined by biotite and hornblende.'
3713|'Dikes and small bodies of fine- to medium grained equigranular (pyroxene-) biotite-hornblende diorite and quartz diorite.'
3714|'Migmatite consisting of 20-95 percent granitic rocks intruded into quartzofeldspathic schist and gneiss, amphibolite, biotite quartzite, and calc-silicate gneiss. Studied in detail by Bittner-Gaber (1987).'
3715|'Gray to pinkish gray, fine- to medium-grained porphyritic hornblende-biotite granite. Phenocrysts are orthoclase feldspar. Mapped as a chill zone capping the Whistling Pig pluton (Lund, 1980; Motzer, 1985).'
3716|'Includes centimeter-scale, layered, hornblende-diopside-quartz plagioclase gneiss, garnet-diopside quartzite, amphibolite, and minor amounts of garnet-biotite schist and gneiss.'
3717|'Cream colored biotite leucogranite. Commonly contains miarolitic cavities. Graphic and myrmekitic textures are abundant. Mapped as a textural phase of the Whistling Pig pluton (Lund, 1980; Motzer, 1985).'
3718|'White quartzite and micaceous granofelsic quartzite, commonly interlayered with pelitic schist. Quartz (31-97 percent) is found as granoblastic grains 2-4 mm across and in elongate platy grains parallel to the schistosity.'
3719|'Stream deposits in modern drainages; gravel, silt, and sand; includes gravels reworked by dredging.'
3720|'Unconsolidated deposits of landslide origin.'
3721|'Unconsolidated glacial drift; includes, till and outwash; landforms include moraines and outwash terraces.'
3722|'Unconsolidated, poorly sorted sediment, primarily clay, sand, and silt, that locally contains cobbles. Sediment lies beneath, within, and above Tcb unit, but is only mapped separately in a few localities in west of quad.'
3723|'Flow of Pomona chemical type.  Petrographically similar to Pomona Member.  Probably equivalent to Pomona Member, but mapped separately.'
3724|'Sparsely plagioclase-phyric basalt flows of Wilbur Creek chemical type (Swanson and other, 1979a; Wright and others, 1979).'
3725|'Higher MgO and lower SiO2 than rest of member.  Chemically intermediate between Wilbur Creek and Asotin chemical types. Contains rare small plagioclase and olivine phenocrysts. Field relations suggests source northeast of Orofino, Idaho.'
3726|'Two or more fine- to medium-grained basalt flows containing scattered plagioclase phenocrysts as long as 10 mm and common groundmass olivine. Invasive into subarkosic sandstone and siltstone.  Occurs only west of Headquarters, Idaho, in drainage of North Fork of Clearwater River. Underlies Wilbur Creek Member of the Saddle Mountains Basalt.'
3727|'Generally  fine- grained and petrographically non distinctive. May contain numerous  plagioclase phenocrysts. Grande Ronde flows are the thickest of the Columbia River Group. Thickest at SW of map. Covers and laps out on rugged topography on older rocks at flow margins: pillows common.  Flow also commonly hackly jointed and pillowed at or near contact with older rocks. Flows of the Grande Ronde Basalt are divided magnetostratigraphic units.'
3728|'Generally  fine- grained and petrographically non distinctive. May contain numerous  plagioclase phenocrysts. Grande Ronde flows are the thickest of the Columbia River Group. Covers and laps out on rugged topography on older rocks at flow margins: pillows common.  Flow also commonly hackly jointed and pillowed at or near contact with older rocks. Flows of the Grande Ronde Basalt are divided magnetostratigraphic units.'
3729|'Includes overlying unconsolidated sediment (Ts unit) in areas.'
3730|'Black, aphanitic, tabular dikes, typically 1-3 m thick, that consist principally of plagioclase, augite, glass, and opaque oxides.  Most likely related to Columbia River Basalt Group.'
3731|'Tan-weathering, aphanitic to very fine-grained phaneritic rock that contains less than 10 percent potassium feldspar and quartz phenocrysts.'
3732|'Highly porphyritic rock consisting of about 40% quartz,  alkali feldspar, and plagioclase phenocrysts in an aphanitic groundmass.'
3733|'Dark- to medium-gray, porphyritic dikes that contain plagioclase and hornblende phenocrysts up to 1 cm in length.'
3734|'Following description taken from U.S. Geological Survey Open File Report 79-1636.  Sparsely plagioclase- and olivine-phyric, commonly ophitic basalt flow of Asotin chemical type (Camp, 1976; Swanson and others, 1979: Wright and others, 1979).  Normal magnetic polarity.  Occurs extensively in the Clearwater embayment of Lewiston, Idaho.  Includes the Huntzinger flow of Mackin (1961) in the Saddle Mountains, Pasco Basin and along Yakima Ridge.'
3735|'May include any of the types of dikes described above, but most are either rhyolite (Tr) or dacite (Td).'
3736|'Fine- to coarse-grained, equigranular to slightly porphyritic granite that contains equant to bipyramidal smoky quartz, white to pinkish feldspar, biotite, and sparse amphibole.  Contains miarolitic cavities, which are most common in associated aplite dikes.  Pegmatites are rare.  Contacts sharp and discordant.  Weathers to form rounded outcrops and spires.  Includes the Lolo Hot Springs batholith mapped by Nold (1968, 1974) and the Horseshoe Lake stock (Lewis and others, 1992).'
3737|'Porphyritic quartz syenite, syenite, and quartz monzonite.  Similar to Tg, but quartz poor.  Contains hornblende, clinopyroxene cores in hornblende, and biotite.  Commonly occurs as resistant, iron-stained stocks and dikes.  Locally contains miarolitic cavities.  Includes unit mapped as the monzonite of Junction Lake by Childs (1982).'
3738|'Light-gray, medium- to fine-grained, porphyritic hornblende-biotite granodiorite that contains small (4-8mm) phenocrysts of potassium feldspar.  Biotite and hornblende form diffuse clots.  Exposed in a small stock southeast of Stanley Hot Springs.  The northern part of the stock is dioritic.'
3739|'Four large sills of pyroxene gabbro intrude the rocks of the Belt series. The centers of these sills consist of medium-grained, massive rock in which dark augite crystals and light-colored plagioclase (An74) are clearly visible.  Toward the borders and locally also in the centers of the sills all augite is altered to hornblende. Plagioclase occurs in clusters of small lath-shaped crystals between the large rounded augite crystals.  There is every gradation from this massive gabbro that occurs in the center to foliated amphibolite and to a fine-grained dark hornblende gabbro near the contacts of the sills.'
3740|'Dark-gray, sparsely porphyritic to equigranular fine-grained dikes of uncertain age.  Equivalent to either the Ta or Ka units.'
3741|'Irregular bodies of intermixed very coarse-grained biotite- and (or) muscovite-bearing pegmatite and fine-grained aplite.  Generally lacks fabric, but locally occurs as small ptygmatic dikes in schist and gneiss.'
3742|'Medium-grained, equigranular muscovite-biotite granite.  Muscovite is in books that locally coarsen to 1 cm in diameter in the eastern part of the area.  The mass south of Mex Mountain in the western part of the area is biotite-poor and contains abundant.'
3743|'Medium- to fine-grained, equigranular to slightly porphyritic biotite granodiorite. Hornblende-bearing and tonalitic near some contacts with metasedimentary rocks. Associated pegmatite and aplite dikes and sills are common.  Similar rocks along the Lochsa River south of the area have yielded U-Pb dates on zircon of 719 Ma and 755 Ma (Toth and Stacey, 1992).   Mass along the lower part of Cayuse Creek is atypical in that it contains perthitic alkali feldspar and has chemical i compositions intermediate between Tg and Kgd.'
3744|'Medium-grained biotite granodiorite and granite that contains phenocrysts of alkali feldspar 1-3 cm in length.'
3745|'Medium- to coarse-grained, equigranular to slightly porphyritic, hornblende-biotite granodiorite.  Contains conspicuous books of biotite as thick as 4 mm.  Weathers to a coarse-grained grus.  Mafic inclusions are common north of Blacklead Mountain.'
3746|'Small bodies of foliated and lineated, fine- to medium-grained, muscovite-biotite granite and quartz monzonite.  Present only in the central part of the map area.  Characteristically iron-stained and pegmatite-rich.  May be anatectic in origin (R. Kell, pers. comm., 1990).'
3747|'Granodiorite and tonalite in the lower part of Black Canyon and in the upper part of Collins Creek.  Includes unit mapped as quartz dioritic orthogneiss by Childs (1982) and tonalite orthogneiss by R. Kell (pers. comm., 1990).'
3748|'Tonalite and quartz diorite.  Distinguished by stubby hornblende crystals that locally define a linear fabric parallel to that in the host rocks.  Locally contains inclusions of fine-grained hornblende diorite.  Includes unit mapped as the quartz diorite of Junction Mountain by Childs (1982).'
3749|'Coarse-grained rock in which  the dark constituents, hornblende and biotite, are strongly  contrasted against the light-colored mixture of quartz and  plagioclase Part of the hornblende is in stubby prisms 5 to 15 mm long; smaller  grains form clusters with biotite. Some of the central part  of the largest body is somewhat coarser, with less biotite  and less mineral orientation than the common variety. In  many places near the contacts, variation in the  distribution of biotite produces dark- and light colored portions.'
3750|'Several small bodies of gneissic medium-grained gabbro occur within quartz diorite and tonalite or in their vicinity. Thin sections show that the gabbro consists of about 55 percent hornblende, 40 percent plagioclase (An3s), and 5 percent quartz in small round grains, and that accessories are sphere, epidote, apatite, and magnetite.  Hornblende and plagioclase occur in groups of small polygonal grains, giving an impression of granulation and recrystallization.'
3751|'Most of this body consists of fine-grained, dark greenish-gray serpentine with rust-colored specks, but a small portion contains radiating crystals of anthophyllite interleaved with chlorite.  The mineralogy and texture of the serpentine suggest that originally most of it was dunite and that only a small part contained anthophyllite in addition to olivine.'
3752|'Mapped where nearly equal amounts of metamorphic rocks and granitic rocks are contorted and intermixed.  Migmatitic rock in the drainages  of Hemlock Creek, Middle Creek, and Beaver Dam Creek in the southwestern part of the area was not delineated.  Despite an abundance of injected granitic material in that area, preexisting metasedimentary units could still be distinguished.'
3753|'Small dike- and sill-like bodies of medium- to coarse-grained pyroxenite that are in places altered to amphibole.   Present on Little Moose Ridge and Hanson Ridge in the east-central part of the map area and on Green Point in the west-central part of the area.'
3754|'plagioclase-hornblende rock.  Contains garnet on Flat Mountain.  Typically lineated, but interiors of some larger masses (e.g. on Indian Henry Ridge) are equigranular.   Interpreted to have an igneous protolith on the basis of uniform composition and texture and apparent cross-cutting relations at many places.  May include some Proterozoic mafic bodies, but a Cretaceous age is probable for most.  One dike cross-cuts the Kfg pluton along Kelly Creek, but no dikes cross-cut younger Cretaceous plutons.  Includes biotite-rich rock that occurs both as dikes and as thin borders on amphibolite dikes near pegmatitic intrusions.'
3755|'northwestern part of the map area, at Pole Mountain and Bacon Creek, this unit typically consists of parallel microlaminated and laminated black- to dark-gray argillite, and grayish-white siltite and black argillite couplets north, in the Chamberlain Mountain-Gospel Hill area, the uppermost part of the unit is sparsely calcareous, cross-laminated white quartzite with vertical extension fractures. along the Idaho-Montana border, the uppermost exposures consist of unevenly laminated and microlaminated siltite and argillite, and subordinate fine-grained quartzite.'
3756|'Biotite-garnet-sillimanite schist with interbedded layers of biotite gneiss. The schist is coarse grained and many outcrops contain abundant pegmatitic veins. The major constituents are quartz, plagioclase (An24), and biotite. Garnet, sillimanite, and muscovite are in places abundant but can be sparse or lacking. Magnetite and zircon are the common accessories. The amount of quartz is usually much larger than that of oligoclase.  The biotite gneiss interbedded with the schist is medium grained and contains more oligoclase and less biotite than the schist.'
3757|'Three types of quartzite occur in the lowest unit of the Wallace formation: medium-grained light-colored biotite quartzite, white granular quartzite, and thin-bedded biotite quartzite with or without plagioclase. Medium-grained biotite quartzite  weathers readily to coarse quartz sand. The beds are thicker than those in the other types of quartzite, ranging from 1 to 5 m in thickness.  Beds of white granular quartzite, ranging from 5 to 20 cm in thickness, are interbedded with thinner layers of biotite and biotite-plagioclase quartzite along the road leading from Bertha Hill to the river.'
3758|'At least two units consisting of a fairly heterogeneous sequence of diopside-plagioclase gneiss, biotite gneiss, and quartzite are interbedded with the schist of the Wallace formation. Most of the gneiss and quartzite is thin bedded and the mineral content of the individual beds varies considerably. A few thick beds are of more homogeneous diopside-plagioclase gneiss. In typical gneiss along Orogrande Creek, light-green diopside-bearing layers, 1 to 5 cm thick, are separated by biotite-bearing laminae or are interbedded with layers of plagioclase quartzite. Thick beds of diopside-plagioclase gneiss are exposed in many localities along French and Orofino Creeks.'
3759|'Areas where exposure and degree of metamorphism prevented subdivision into middle and lower members.'
3760|'Tan-weathering, grayish-white, dolomitic siltite and fine-grained quartzite overlain by black argillite ("black and tan" rock type), brownish-orange-weathering carbonate-bearing white quartzite, greenish-gray siltite and argillite, and syndepositional breccia that weathers brownish-orange. The siltite and fine-grained quartzite is mostly 1 to 3 cm thick, and the clay drapes range from less than 1 mm to 5 cm in thickness.  Breccia is composed of clasts of black- and tan-weathering argillite and siltite of the middle member, white- and brownish-orange-weathering quartzite, and rusty-weathering dolomite in a carbonate-rich, brownish-orange matrix.'
3761|'(1) gray, laminated or massive-weathering limestone that contains abundant molar-tooth structure; (2) tan or dark-gray, orange-weathering, conchoidally fracturing dolomite; (3) non-calcareous and calcareous, ripple cross-laminated and planar-laminated, tan siltite and fine-grained quartzite; (4) fine-grained, planar-laminated, ripple cross-laminated, and low-angle cross-bedded white to light-gray quartzite with extension fractures normal to layering; (5) non-calcareous, microlaminated couplets of light-green siltite; (6) massive-weathering dark-green siltite that contains dark-gray limestone pods;  (7) wavy-bedded, tan-weathering, dolomitic siltite and rhythmically interbedded black argillite.'
3762|'Muscovite-biotite schist that grades into schistose biotite gneiss.  Commonly contains sillimanite and as much as 60% quartz and feldspar.  Unit is spatially associated with calc-silicate gneiss in the southwestern part of the map area and is probably equivalent to argillite-rich portions of the Wallace Formation.  Mapped as Wallace Formation by Hietanen (1963).'
3763|'Includes centimeter-scale layered hornblende-diopside-quartz-plagioclase gneiss, diopside quartzite, amphibolite, quartzites with more than 5% garnet, and minor amounts of garnetiferous schist and gneiss.  Compositional layering or variation in grain size of amphibolite distinguishes it from the more homogeneous rock of the meta-igneous amphibolite (Yam).  Unit probably represents carbonate-bearing lower and middle members of the Wallace Formation, but is too highly recrystallized to apply a formational name.'
3764|'impure, thin-bedded quartzite that contains abundant feldspar and biotite. Grades into quartz-rich biotite gneiss where migmatized; also contains as much as 5% diopside, hornblende, or garnet and grades into calc-silicate gneiss.  Quartzite with sparse flattened quartz pebbles as much as 6 cm long occurs along the Lolo "motorway" on the west end of Rocky Ridge in the southwest corner of the map area. Smaller quartz pebbles (1 cm long) are present along Cayuse Creek  Unit probably represents quartzite-rich portions c,f the Wallace Formation. Hietanen (1963) mapped the qi and cs units as gneiss of the Wallace Formation, and Childs (1982) mapped the qi unit as quartz gneiss of the Wallace Formation.'
3765|'Most of the anorthosite is a white to light-gray, coarse-grained, inequigranular rock that consists principally of two kinds of plagioclase: bytownite  and andesine with hornblende present in varying amounts.   Bytownite grains are mostly 0.1-0.3 mm, andesine 1-5 mm. Ilmenite, magnetite, and rutile or sphene are common accessory minerals and small amounts of chlorite and epidote occur in places.'
3766|'Schist interbedded with the quartzite in the lowest part of the Wallace formation is medium to coarse grained and contains abundant biotite and garnet, and muscovite in varying amounts.  Sillimanite is not as common as it is in the upper part of the Wallace formation. In most outcrops the muscovite occurs as larger flakes than the biotite and forms thin laminae between the biotite-bearing layers.  Garnet crystals are small and their number is far less than that in the upper part of the formation.'
3767|'schist and thin-bedded quartzite. In the thin-bedded quartzite north of the mouth of Robinson Creek, gray biotite quartzite layers alternate with light-colored plagioclase-bearing layers.  Some light-greenish layers containing diopside also are interbedded. The thickness of the individual beds ranges mostly from 2 mm to 3 cm. Paper-thin laminae of biotite are common between the individual layers.  This quartzite grades over to a coarse-grained muscovite-biotite-garnet-sillimanite schist, which is very similar to the schist of the Wallace formation.'
3768|'Beds of biotite-sillimanite schist.'
3769|'Coarse grained and light bluish. The individual beds, 1 to 30 cm thick, are separated by paper-thin laminae of mica. About 85 to 95 percent of the rock is quartz; the rest is plagioclase, microcline, biotite, and muscovite.'
3770|'Biotite schist which separates the Revett quartzite from the underlying hornblende-bearing diopside plagioclase gneiss south of the mouth of Robinson Creek is coarse grained and contains impure quartzite layers.  A similar schist is exposed under the Revett quartzite in many other localities near Robinson Creek.'
3771|'light-gray quartzite in beds from several cm to 1m in thickness interbedded with subordinate phyllite or schist.  Unit is too highly metamorphosed to be definitively assigned to a known group or formation.  Upper part of Black Canyon the unit consists of decimeter- to rare meter-thick beds of light-gray quartzite and thin interbeds of phyllite or schist.  The quartzite is typically fine grained and friable and forms tabular beds.  Middle part of Black Canyon the unit consists of medium-grained quartzite in decimeter- to meter-thick beds with lesser amounts of biotite schist. Snow Creek area, the unit consists of quartzite "beds" 1 m thick that occur'
3772|'Quartz-muscovite-biotite schist, quartz-biotite-muscovite schist, muscovite-biotite-gneiss micaceous quartzite.  Schist grades into biotite gneiss and locally contains sillimanite.  Coarse schist has compositional layering at angles to foliation; more commonly centimeter-scale compositional layering is preserved by fine-grained biotite quartzite and schist.  Most layers are parallel to foliation, but are probably transposed bedding as indicated by rare isoclinal fold hinges to which foliation is axial planar.  Schist is variably garnetiferous.'
3773|'Coarsely recrystallized quartzite that occurs as small bodies in sp unit and as larger bodies to the west.  Ranges from laminated dark and light gray to uniform white to dark gray.  Includes either muscovite and biotite or both, and rarely magnetite.  Parting typically 5 to 30 cm thick, rarely over 1 m.  Some quartzites in the northwestern part of the area have garnet on parting surfaces, apparently from thin argillaceous interlayers.  Internal lamination and schist interlayers commonly tightly folded or discontinuous due to inhomogeneous strain.  Unit includes rocks previously correlated with Revett, Burke, and Prichard Formations (Hietanen, 1968; Childs, 1982).'
3774|'Fine grained and contains a considerable amount of biotite. The thickness of the individual beds ranges from a few millimeters to several centimeters.  Microscopic study shows that quartz in this fine-grained gray quartzite occurs in small round or polygonal grains, with biotite filling the interstices. Sphene, small grains of magnetite, graphite, and zircon are common accessories.'
3775|'Calc-silicate-bearing layers that were found about half a mile west and south of Crescendo Peak are rather thin (1-5 cm thick) and are interbedded with coarse-grained pure quartzite.  The scarcity of lime-silicate minerals and scapolite in the northern part of the area suggests that very little calcareous material was deposited there with the quartz-rich sediment.'
3776|
3777|'Stream deposits in modern drainages; gravel, silt, and sand. Includes some glacial deposits, terrace gravels, and alluvial and debris-flow fan deposits.'
3778|'Unconsolidated deposits of landslide origin.'
3779|'Unconsolidated glacial drift; includes, till and outwash; landforms include moraines and outwash terraces. Also includes some modern alluvium.'
3780|'Unconsolidated sediment, primarily pebbles and cobbles. Restricted to a single small exposure south of Cayuse Creek.'
3781|'Black, aphanitic, tabular dikes, typically 1 m thick, that consist principally of plagioclase, augite, glass, and opaque oxides. Most likely related to Columbia River Basalt Group.'
3782|'Tan-weathering, aphanitic to very fine-grained phaneritic rock that contains less than 10 percent potassium feldspar and quartz phenocrysts.'
3783|'Highly porphyritic rock consisting of about 40% quartz,  alkali feldspar, and plagioclase phenocrysts in an aphanitic groundmass.'
3784|'Dark- to medium-gray, porphyritic dikes that contain plagioclase and hornblende phenocrysts up to 1 cm in length.'
3785|'Dark gray, massive, fine-grained dikes characterized by acicular hornblende and lath-shaped plagioclase phenocrysts in an aphanitic matrix. Some have chilled margins.'
3786|'Pink, fine- to coarse-grained, equigranular to slightly porphyritic granite that contains equant to bipyramidal smoky quartz, white to pinkish feldspar, biotite, and sparse amphibole. Contains miarolitic cavities, which are most common in associated aplite dikes. Pegmatites are rare. Contacts sharp and discordant. Weathers to form rounded outcrops and spires. Includes the Lolo Hot Springs batholith mapped by Nold (1968, 1974). Small stock at Ranger Peak lacks the miarolitic cavities, perthitic feldspar, and pink color characteristic of the Lolo Hot Springs batholith and is only tentatively assigned to the Tg unit on the basis of chemical similarity.'
3787|'Porphyritic quartz syenite, syenite, and quartz monzonite. Similar to Tg, but quartz poor. Contains hornblende, clinopyroxene cores in hornblende, and biotite. Commonly occurs as resistant, iron-stained stocks and dikes, some of which have intruded along fault zones. Locally contains miarolitic cavities.'
3788|'Intrusive(?) breccia consisting of angular to subrounded, matrix-supported clasts of gray siltite, quartzite, and buff-colored rhyolite ranging in size from 5 mm to 5 cm enclosed in a matrix of light gray, aphyric to porphyritic rhyolite. Termed the Crooked Fork plug by Nold (1968, 1974).'
3789|'Principally dacitic tuff(?) breccia, but also includes andesite flows, rhyolite tuff(?), and volcaniclastic rocks. Subdivided locally by Simpson (1985), but grouped on this map. All rock types are phenocryst poor. Clasts are angular to subangular dacite and quartzite, mostly 0.5 to 1.0 cm across.'
3790|'Dark gray, sparsely porphyritic to equigranular fine-grained dikes of uncertain age.'
3791|'Medium-grained, equigranular muscovite-biotite granite. Exposed only in southwest corner of map.'
3792|'Medium-grained, equigranular, biotite-, and hornblende-biotite granodiorite. Comprises the western part of the Skookum Butte stock of Nold (1974), now known to be a composite intrusion.'
3793|'Foliated, coarse-grained, porphyritic (hornblende)-biotite granodiorite and tonalite containing potassium feldspar megacrysts up to 8 cm in length.  Megacrysts commonly form augen with rapakivi texture.'
3794|'Fine- to medium-grained biotite granite grading to quartz monzonite. Resembles Kgd, but plagioclase more strongly zoned and euhedral. Perthitic alkali feldspar.'
3795|'Biotite-hornblende and pyroxene-biotite-hornblende diorite and quartz diorite. Typically as small inclusions in Kgd, but present also as two small mappable bodies in the southern part of the map area.'
3796|'Medium- to fine-grained, equigranular to porphyritic biotite granodiorite and granite. Includes the White Sand Creek and Brushy Fork stocks of Nold (1968, 1974). Similar rocks along the Lochsa River southwest of the area have yielded U-Pb dates on zircon of 719 Ma and 755 Ma (Toth and Stacey, 1992). May include unmapped Eocene plutons along the state line near Rocky Point.'
3797|'Three small bodies of medium- to coarse-grained pyroxenite. Present on Little Moose Ridge and Hanson Ridge in the northern part of the map area.'
3798|'Small roof pendant north of Blacklead Mountain. Magnetite-epidote skarn near margins and interbedded gray limestone marble and pure white dolomite marble in core. Marble is too pure to be part of the Wallace Formation. Probable correlative units are the Hasmark or Jefferson Formations in western Montana.'
3799|'Fine- to medium-grained plagioclase-hornblende rock. May include some Proterozoic mafic bodies, but a Cretaceous age is probable for most.'
3800|'Clastic rocks of the Snowslip and Shepard Formations. Uppermost exposures consist of unevenly laminated and microlaminated siltite and argillite, and subordinate fine-grained quartzite; local scapolite. Grades downward into light gray, fine- to very-fine grained quartzite in decimeter-scale beds and then downward into siltite and argillite. Quartzite is correlated to Yms2 by Chester Wallace (pers. commun. 1990) but is interpreted here as uppermost Snowslip Formation. Equivalent to upper part of Wallace Formation. Small exposure northwest of Shale Mountain is dolomitic siltite and green argillite and is probably correlative with the Shepard Formation in western Montana.'
3801|'Gray to pale red, fine-grained quartzite in tabular, decimeter- to meter-thick beds with green siltite and argillite along partings. Planar-laminated and ripple cross-laminated. Simpson (1985) reports about 10% feldspar, most of which is potassium feldspar. Correlation is based on similarities with member 2 of the Mount Shields Formation in the Missoula area to the northeast, (Lewis, 1998).'
3802|'Banded green (diopside and actinolite) and white (plagioclase and quartz) calc-silicate gneiss and calc-silicate quartzite. Bedding typically preserved. Diopside is replaced by hornblende adjacent to intrusive bodies. Layers of breccia (open triangles) consist of angular to subrounded clasts in a calc-silicate matrix. Breccia is metamorphic equivalent of carbonate breccia found in Ywm. Unit also includes metamorphic equivalents of Ywl.'
3803|'Black, layered lens-like body interbedded with diopside gneiss of the Wallace Formation. Composed of subequal amounts of hornblende and plagioclase with accessory quartz, epidote, magnetite, and garnet. Although interpreted as orthoamphibolite by Nold (1968, 1974) and as a layered mafic intrusion by Jens (1972, 1974), its gradational character with surrounding diopside gneiss and close association with biotite granodiorite suggest a metasomatic origin.'
3804|'Tan-weathering, grayish-white, dolomitic siltite and fine-grained quartzite overlain by black argillite ("black and tan" rock type), brownish-orange-weathering carbonate-bearing white quartzite, greenish-gray siltite and argillite, and syndepositional breccia that weathers brownish-orange. The siltite and fine-grained quartzite is mostly 1 to 3 cm thick, and the clay drapes range from less than 1 mm to 5 cm in thickness. Breccia is composed of clasts of black- and tan-weathering argillite and siltite of the middle member, white- and brownish-orange-weathering quartzite, and rusty-weathering dolomite in a carbonate-rich, brownish-orange matrix.'
3805|'Carbonate-rich clastic rocks consisting of noncalcareous and calcareous siltite and fine-grained quartzite, noncalcareous green siltite and argillite that locally contain gray limestone pods, tan-weathering dolomitic siltite and interbedded black argillite ("black and tan" rock type), white quartzite beds, 2 to 30 cm thick, orange-weathering dolomite, and gray limestone.'
3806|'Feldspathic quartzite and calc-silicate quartzite. Metamorphic equivalent of Ywm. Contains sedimentary breccia.'
3807|'Light gray, fine- to medium-grained quartzite and minor interbeds of muscovite schist. Plagioclase is the principle feldspar. Includes rocks mapped as the Ravalli Group by Nold (1968, 1974).'
3808|'Tightly folded and intermixed feldspathic quartzite and calc-silicate gneiss. Interpreted as an undivided unit of Yqrv and Yqcw.'
3809|'Quartz-muscovite-biotite schist and gneiss exposed in the eastern part of the map area. Locally contains sillimanite. Generally coarse-grained with crenulated or multiply crenulated foliation.'
3810|'Medium- to coarse-grained, equigranular to slightly porphyritic hornblende-biotite granodiorite. Contains conspicuous books of euhedral biotite as thick as 4 mm and subhedral hornblende up to 6 mm long. Weathers to a coarse-grained grus. Mafic inclusions are common north of Blacklead Mountain.'
3811|'Stream deposits in modern drainages.'
3812|'Unconsolidated deposits of landslide origin.'
3813|'Poorly sorted and poorly stratified, unconsolidated deposits principally of glacial origin (Lewis and others, 1992b). Includes till in lateral and ground moraines as well as outwash and modern stream alluvium.'
3814|'Unconsolidated, poorly sorted sediment, primarily clay, sand, and silt, that locally contains cobbles (Lewis and others, 1992b). Only mapped in a few localities in the western part of quadrangle.'
3815|'Medium- to coarse-grained basalt flow with sparse plagioclase phenocrysts less than 7 mm long, and abundant, commonly altered, olivine phenocrysts and microphenocrysts; reverse magnetic polarity (Swanson and others, 1979, 1981).

Sparse plagioclase phenocrysts less than 7mm and abundant, commonly altered, olivine phenocrysts and microphenocrysts. May be associated with Pomona and Dodge flows (chemistry is similar). Equivalent to Amphitheater flow of Bard (1978). (R.S. Lewis, unpub.data, July 8, 2002).'
3816|'Medium- to coarse-grained flow of Pomona chemical type with abundant olivine and reverse magnetic polarity (Swanson and others, 1979,1980; Kauffman, unpub.).  Petrographically similar and probably equivalent to Pomona Member, but mapped separately because the easternmost outcrops of the Pomona, in the Lewiston Basin, are 35 km west of the westernmost outcrops of the basalt of Weippe.  Feeder dikes occur east and northeast of Orofino in the drainage of the North Fork of the Clearwater River.  Age date of a sample collected by Kauffman (2001, unpub.) northeast of Orofino (west of the Kooskia quadrangle) resulted in a date of 12.90.8 M.Y. (Lewis, written communications, 2002).'
3817|'Fine- to medium-grained, sparsely plagioclase- and olivine-phyric, commonly ophitic basalt with normal magnetic polarity (Swanson and others, 1979, 1981).  It is closely associated with and physically resembles the Wilbur Creek Member (which includes the basalt of Lapwai).  These units have been separated in the past (Camp, 1981; Swanson and others, 1979, 1981), but recent mapping in the Clearwater embayment has shown that lateral continuity of these units is often irregular and inconsistent (Kauffman, 2000, 2001, unpub.; Garwood, 2001); therefore these units have been combined.  The basalt of Lapwai is chemically intermediate between the Wilbur Creek and the Asotin.  On the Kooskia quadrangle, only the Asotin unit has been documented chemically.  (Lewis, written communications, 2002).'
3818|'Fine- to coarse-grained basalt flows, sparse to common small plagioclase and olivine phenocrysts, reverse magnetic polarity (Swanson and others, 1979, 1981).  Flows in this area are generally of the Lolo chemical type, although some with Rosalia chemical type also have been documented.  Commonly invasive into weakly lithified subarkosic sandstone, siltstone, and claystone near the eastern margin of the Columbia Plateau. (Lewis, written communications, 2002).'
3819|'Generally  fine- grained and petrographically non distinctive. May contain numerous  plagioclase phenocrysts. Grande Ronde flows are the thickest of the Columbia River Group. Thickest at SW of map.  Covers and laps out on rugged topography on older rocks at flow margins: pillows common.  Flow also commonly hackly jointed and pillowed at or near contact with older rocks.  Flows of the Grande Ronde Basalt are divided magnetostratigraphic units.  (R.S. Lewis, unpub.data, July 8, 2002).

Generally fine-grained aphyric to sparsely plagioclase-phyric, petrographically non-distinctive basalt flows of the R2 magnetostratigraphic unit (Swanson and others, 1979, 1981).  Thins eastward and pinches out at about longitude 116 degrees 30'', except for isolated patches farther east.  Chemical composition varies within a broad field termed Grande Ronde chemical type (Yakima chemical type of Wright and others, 1973).  Flows are generally between 15-25 m but thinner near margins of the Columbia Plateau.  Many flows near the margin of the plateau are invasive into interbedded sand, silt and clay sediments. (Lewis, written communications, 2002).'
3820|'Generally  fine- grained and petrographically non distinctive. May contain numerous  plagioclase phenocrysts. Grande Ronde flows are the thickest of the Columbia River Group. Thickest at SW of map.  Covers and laps out on rugged topography on older rocks at flow margins: pillows common.  Flow also commonly hackly jointed and pillowed at or near contact with older rocks.  Flows of the Grande Ronde Basalt are divided magnetostratigraphic units.  (R.S. Lewis, unpub.data, July 8, 2002).

Generally fine-grained, aphyric to microphyric or sparsely plagioclase-phyric and petrographically non-distinctive flows of the N1 magnetostratigraphic unit (Swanson and others, 1979, 1981).  Chemical composition varies within a broad field termed Grande Ronde chemical type (Yakima chemical type of Wright and Swanson, 1973).  Flows are generally between 15-25 m.  Many flows near the margin of the Columbia Plateau are invasive into interbedded sand, silt and clay sediments. (Lewis, written communications, 2002).'
3821|'Generally  fine- grained and petrographically non distinctive. May contain numerous  plagioclase phenocrysts. Grande Ronde flows are the thickest of the Columbia River Group.  Covers and laps out on rugged topography on older rocks at flow margins: pillows common.  Flow also commonly hackly jointed and pillowed at or near contact with older rocks.  Flows of the Grande Ronde Basalt are divided magnetostratigraphic units.  (R.S. Lewis, unpub.data, July 8, 2002).

Generally fine-grained, aphyric to microphyric, rarely sparsely plagioclase-phyric, petrographically non-distinctive flows of the R1 magnetostratigraphic unit (Swanson and others, 1979, 1981).  Chemical composition varies within a broad field termed Grande Ronde chemical type (Yakima chemical type of Wright and Swanson, 1973).  Flows are generally between 15-25 m.  Many flows near the margin of the Columbia Plateau are invasive into interbedded sand, silt and clay sediments. (Lewis, written communications, 2002).'
3822|'Undivided basalt in areas where no basalt was mapped by Swanson and others (1979) but where other workers have shown basalt. If indeed basalt is present, it may consist of Saddle Mountains, Wanapum and/or Grande Ronde units, and may include interbedded and overlying sediments. (Lewis, written communications, 2002).'
3823|'Black, aphanitic, tabular dikes, typically 1-3 m thick, that consist principally of plagioclase, augite, glass, and opaque oxides (Lewis and others, 1992b).  Most likely related to Columbia River Basalt Group.'
3824|'Tan-weathering, aphanitic to very fine-grained phaneritic rock that contains less than 10 percent potassium feldspar and quartz phenocrysts (Lewis and others, 1992b).'
3825|'Highly porphyritic rhyolite consisting of about 40% quartz,  alkali feldspar, and plagioclase phenocrysts in an aphanitic groundmass (Lewis and others, 1992b).'
3826|'Dark- to medium-gray, porphyritic dacite dikes that contain plagioclase and hornblende phenocrysts up to 1 cm in length (Lewis and others, 1992b).'
3827|'Dark gray nonfoliated andesite dikes  characterized by sparse hornblende and plagioclase phenocrysts in an aphanitic groundmass (Lewis and others, 1992b). Plagioclase phenocrysts are more elongate than those in Td.'
3828|'May include Td, Tr, and Ta, but according to Lewis and others (1992b) most are either rhyolite (Tr) or dacite (Td).'
3829|'Porphyritic gray monzogranite and medium-grained equigranular hornblende-biotite syenogranite of the Whistling Pig pluton (Toth, 1983), medium- to coarse-grained hornblende-biotite monzogranite and fine-grained equigranular to porphryritic syenogranite of the Running Creek pluton (Toth, 1983), and fine- to coarse-grained, equigranular to slightly porphyritic biotite granite and hornblende-biotite granite of the Horseshoe Lake stock (Lewis and others, 1992).  Contains miarolitic cavities, which are most common in associated aplite dikes.  Pegmatites are rare.  Contacts sharp and discordant.  Weathers to form rounded outcrops and spires.   (Lewis, written communications, 2002).'
3830|'Small body of medium- to fine-grained, equigranular pyroxene-hornblende diorite along Rocky Ridge Creek in the northern part of the quadrangle (Lewis and others, 1992a).'
3831|'Porphyritic hornblende-biotite granodiorite that contains small phenocrysts of potassium feldspar (Lewis and others, 1992b).  Biotite and hornblende form diffuse clots.  Exposed in small stock SE of Stanley Hot Springs. North part of stock is dioritic.'
3832|'Porphyritic biotite granite (Lewis and others, 1992b). Phenocrysts of K-feldspar 5-15 mm. Like Tg, it weathers to rounded outcrops, contains smoky quartz, has high background radioactivity, but contains less magnetite than Tg and lacks miarolitic cavities.'
3834|'Weakly porphyritic to equigranular andesite dikes with plagioclase, biotite, quartz, and hornblende (Lewis and others, 1992b). Distinguished from Ta unit by weak to moderate foliation and presence of cross-cutting pegmatites of probable Cretaceous age.'
3835|'Medium-grained, equigranular biotite-muscovite granite (Lewis and others, 1992b). Exposed in two biotite-poor masses near Mex Mountain that contain abundant hematite.'
3836|'Medium-grained biotite granodiorite and granite that contains phenocrysts of alkali feldspar 1-3 cm in length (Lewis and others, 1992b).'
3837|'Composite unit of foliated, medium-grained biotite granodiorite.  Includes variably deformed megacrystic biotite granodiorite and minor hornblende-biotite tonalite.  Typically associated with abundant aplite and pegmatite.  Occurs in thin and irregular bodies situated between rock units where intrusion and deformation likely were fault controlled.  Also mapped as border facies of Ktc unit. (R.S. Lewis, unpub.data, July 8, 2002).'
3838|'Foliated, coarse-grained, porphyritic (hornblende)-biotite granodiorite and tonalite containing potassium feldspar megacrysts up to 8 cm in length.  Megacrysts commonly form augen with rapakivi texture.  In part equivalent to "Proterozoic" augen gneiss at Badger Creek described by Toth and Stacey (1992) (R.S. Lewis, unpub.data, July 8, 2002).'
3839|'Strongly foliated, fine-grained biotite tonalite that occurs in a single homogenous elongate body spanning Coolwater Ridge and the Selway River.  Pronounced foliation, fine grain size, and ribboned quartz indicate shearing of intrusion during(?) and after emplacement.  Includes minor indistinct intermediate composition autoliths or xenoliths and some highly flattened(?) mappable inclusions of tourmaline-kyanite(?)-garnet schists and amphibolite.  Planar fabric is locally folded about shallow to steep eastward-plunging axes.  Includes Coolwater Ridge orthogneiss of Morrison (1968). (R.S. Lewis, unpub.data, July 8, 2002).'
3840|'Foliated and non foliated, biotite tonalite.'
3841|'Medium-grained, equigranular, massive to well-foliated tonalite, quartz diorite, and quartz monzodiorite (Lewis and others, 1992b).  Distinguished by stubby hornblende crystals that locally define a linear fabric parallel to that in the host rocks.'
3842|'Quartz diorite in which dark constituents, hornblende and biotite, are strongly contrasted against light-colored mixture of quartz and plagioclase (Hietanen, 1963). Part of hornblende in stubby prisms 5 -15 mm; smaller grains form clusters with biotite.'
3843|'Fine- to medium-grained equigranular (pyroxene)-biotite-hornblende diorite and quartz diorite (Lewis and others, 1992b).  Includes hornblende- and pyroxene-rich rock having a cumulate texture at the mouth of Bald Mountain Creek along Highway 12. Commonly has complex interdigitating and locally gradational contacts with Kgd. Also occurs as inclusions (or intrusions?) too small to map in Kgd,  (Lewis, written communications, 2002).'
3844|'Areas where metamorphic rocks are intruded by 30-70% granitic rock and intermixed at a scale of centimeters to decimeters (Lewis and others, 1992b).'
3845|'Small pod-like bodies of medium- to coarse-grained pyroxenite and dunite (Lewis and others, 1992b).  Dunite occurs at mouth of Swiftwater Ck, and altered to amphibole, talc, and chlorite.  Pyroxenite occurs south of Stillman Pt as well as north of Lowell.'
3846|'Well-foliated biotite-hornblende quartz diorite, but includes more felsic phases, as well as hornblende gabbro.  Unit is exposed along Highway 12 west of the mouth of Suttler Creek and is similar to quartz diorite exposed near Greer, northwest of the map area. Initial 87Sr/86Sr ratios are low (<0.704; Armstrong and others, 1977; Criss and Fleck, 1987) relative to plutonic rocks of the Idaho batholith exposed to the east.  (R.S. Lewis, unpub.data, July 8, 2002).'
3847|'Light-gray, medium-grained marble, consisting of essentially pure calcite, is exposed along the West Fork of Clear Creek in the southwest part of the map area.  It is interbedded with fine-grained, diopside-bearing, calcareous quartzite.  Marble is also exposed along strike to the north, in a small outcrop northeast of the Middle Fork of the Clearwater River.  There it is medium gray and highly deformed.  Both masses probably represent isolated fault slices of marble within the Riggins Group, now engulfed in younger plutonic rocks.  (R.S. Lewis, unpub.data, July 8, 2002).'
3848|'Garnetiferous biotite-hornblende schist and diopside-bearing quartzite (Lewis and others, 1992b). Contains marble beds immediately to south (Myers, 1982). Probable correlative with Square Ck schist exposed to south near Riggins, Id. (Hamilton, 1963).'
3849|'Garnet-biotite-hornblende gneiss, hornblende-biotite schist, and calc-silicate quartzite exposed west of Woodrat Mtn (Lewis and others, 1992b). Calc-silicate quartzite contains variable amounts of plagioclase, hornblende, diopside, epidote, and garnet.'
3850|'Mylonitic, fine- to medium-grained chlorite-actinolite-epidote schist containing stringers of quartz, plagioclase, and epidote interlayered with lens-shaped pods of unsheared andesite tuff (Lewis and others, 1992b). These schistose rocks were probably derived from andesitic, pyroclastic, and sedimentary rocks containing abundant dikes of plagiogranite. Correlated with similar rocks of the Seven Devils Volcanic Group exposed to the southwest (Myers, 1982).  (Lewis, written communications, 2002).'
3851|'Fine- to medium-grained plagioclase-hornblende rock.  Interpreted to have an igneous protolith on the basis of uniform composition and texture and apparent cross-cutting relations at many places.  May include some Proterozoic mafic bodies, but a Cretaceous age is probable for most. One such dike cross-cuts a deformed pluton of suspected Cretaceous age along Kelly Creek, north in the Hamilton 30 x 60 quad.  (R.S. Lewis, unpub.data, July 8, 2002).'
3852|'Biotite-garnet-sillimanite schist with interbedded layers of biotite gneiss. The schist is coarse grained and many outcrops contain abundant pegmatitic veins. The major constituents are quartz, plagioclase (An24), and biotite. Garnet, sillimanite, and muscovite are in places abundant but can be sparse or lacking. Magnetite and zircon are the common accessories. The amount of quartz is usually much larger than that of oligoclase.  The biotite gneiss interbedded with the schist is medium grained and contains more oligoclase and less biotite than the schist.  (R.S. Lewis, unpub.data, July 8, 2002).

Biotite-garnet-sillimanite schist with interbedded layers of biotite gneiss (Hietanen, 1963). The schist is coarse grained and many outcrops contain abundant pegmatitic veins. The major constituents are quartz, plagioclase (An24), and biotite. Garnet, sillimanite, and muscovite are in places abundant but can be sparse or lacking. Magnetite and zircon are the common accessories. The amount of quartz is usually much larger than that of oligoclase.The biotite gneiss interbedded with the schist is medium grained and contains more oligoclase and less biotite than the schist. Although assigned to the Wallace Formation (Hietanen, 1963), some or all of these rocks may be part of the Syringa metamorphic sequence, particularly the northwesternmost bodies present within the quartz diorite unit (Kqd).  (Lewis, written communications, 2002).'
3853|'At least two units consisting of a fairly heterogeneous sequence of diopside-plagioclase gneiss, biotite gneiss, and quartzite are interbedded with the schist of the Wallace formation. Most of the gneiss and quartzite is thin bedded and the mineral content of the individual beds varies considerably. A few thick beds are of more homogeneous diopside-plagioclase gneiss. In typical gneiss along Orogrande Creek, light-green diopside-bearing layers, 1 to 5 cm thick, are separated by biotite-bearing laminae or are interbedded with layers of plagioclase quartzite. Thick beds of diopside-plagioclase gneiss are exposed in many localities along French and Orofino Creeks.  (R.S. Lewis, unpub.data, July 8, 2002).'
3854|'Muscovite-biotite schist that grades into schistose biotite gneiss (Lewis and others, 1992a).  Contains sillimanite and as much as 60% quartz and feldspar. Mapped as Wallace Fm. by Hietanen (1963). May alternatively be part of Syringa metamorphic sequence.'
3855|'Includes centimeter-scale layered hornblende-diopside-quartz-plagioclase gneiss, light-colored diopside quartzite, amphibolite, quartzites with more than 5% garnet, and minor amounts of garnetiferous schist and gneiss.  Compositional layering or variation in grain size of amphibolite distinguishes it from the more homogeneous rock of the meta-igneous amphibolite (Yam). The unit probably represents carbonate-bearing lower and middle members of the Wallace Formation  (R.S. Lewis, unpub.data, July 8, 2002).'
3856|'Impure, thin-bedded quartzite that contains abundant feldspar and biotite (Lewis and others, 1992a).  Grades into quartz-rich biotite gneiss where migmatized; also contains up to 5% diopside, hornblende or garnet and grades into calc-silicate gneiss.'
3857|'Fine- to medium-grained white quartzite and micaceous granofelsic quartzite, commonly interlayered with pelitic schist (Toth, 1983). Quartz (31-97 percent) is found as granoblastic grains 2-4 mm across and in elongate platy grains parallel to the schistosity and elongate within the schistosity parallel to other mineral lineations. Plagioclase (0-40 percent) is unzoned, untwinned, and pervasively altered. Microcline (2-5 percent) is associated with muscovite and rare sillimanite. Biotite (1-19 percent) is locally replaced by muscovite (0-39 percent). Accessory magnetite, zircon, baddeleyite, thorite, apatite, epidote, and schorl.  (Lewis, written communications, 2002).'
3858|'Biotite-muscovite quartzite and quartz-rich schist (Lewis and others, 1992b). In locations adjacent to the Ycsm unit, rocks include coarse-grained, crenulated, muscovitic schists. In locations away from the Ycsm contact, the mica grains are smaller, and schistose zones are separated by 1-2 cm layers (or rods where more deformed) of fine-grained quartzite. Sillimanite is present locally.  Calc-silicate rocks occur throughout.  (Lewis, written communications, 2002).'
3859|'Dark gray, laminated to thinly laminated amphibole-diopside-quartz gneiss exposed at the southern edge of the quadrangle (Lewis and others, 1992b).'
3860|'Thin bedded or laminated schist that contains layers of thin bedded biotite quartzite and biotite gneiss (Hietanen, 1963). The major constituents are quartz, plagioclase, biotite, sillimanite, garnet, and muscovite. In the laminated schist, layers (2 to 3 mm thick) of quartz, plagioclase, and small flakes of biotite, are separated by paper-thin micaceous laminae. Biotite exceeds muscovite; sillimanite and garnet range from 0 to about 15 percent. Although assigned to St. Regis Formation (Hietanen, 1963), correlation is tenous at best. May alternatively be part of Syringa metamorphic sequence or Wallace Formation.  (Lewis, written communications, 2002).'
3861|'Very pure coarse-grained quartzite with little mica (Hietanen, 1963). Sillimanite locally abundant. Assigned to Revett Formation (Hietanen, 1963) but correlation unlikely given lack of significant feldspar. Likely quartzite of Syringa metamorphic sequence.'
3862|'Coarse-grained mica schist that dips under the Revett quartzite between Hemlock Butte and Dan Lee Lookout is mapped as the Prichard formation. This schist is poorly exposed along the south slope of a wooded ridge.  The outcrops on the western end of the ridge south of Orofino Creek consist of bedded biotite gneiss and biotite-muscovite schist containing garnet and sillimanite.  The southern part of this schist is granitized and grades into a coarse-grained quartz monzonitic rock which includes remnants of schist and gneiss.  (R.S. Lewis, unpub.data, July 8, 2002).

Coarse-grained mica schist that dips under the Revett(?) quartzite between Hemlock Butte and Dan Lee Lookout is mapped as the Prichard Formation (Hietanen, 1963). This schist is poorly exposed along the south slope of a wooded ridge. The outcrops on the western end of the ridge south of Orofino Creek consist of bedded biotite gneiss and biotite-muscovite schist containing garnet and sillimanite. The southern part of this schist is granitized and grades into a coarse-grained quartz monzonitic rock which includes remnants of schist and gneiss. Although assigned to the Prichard Formation (Hietanen, 1963), that correlation is highly tenuous.  (Lewis, written communications, 2002).'
3863|'Quartz-muscovite-biotite schist, quartzofeldspathic gneiss, and dark-colored micaceous quartzite (Lewis and others, 1992b). Grades into biotite gneiss/schist unit (pCbg). Sillimanite/muscovite in lenses 1-4 cm diameter that resemble flattened pebbles.'
3864|'Quartz-feldspar-biotite(-muscovite) gneiss/muscovite-biotite (-quartz) schist (Lewis and others, 1992b). More schistose rocks locally contain sillimanite; garnet rare. Possible fault contact with Syringa metamorphic sequence, but contact relations not exposed.'
3865|'Impure quartzite and biotite schist (Lewis and others, 1992b).  Compositional layering on the scale of decimeters is defined by thin layers of schist alternating with massive quartzite. Quartzite typically contains 10 to 20 percent feldspar (principally alkali feldspar) and about 10 percent mica. Quartz grains are commonly 0.25 to 1 mm in size, but range up to 5 mm in highly recrystallized rocks. These recrystallized quartzites are also highly strained and foliated.  In places this unit includes calc-silicate quartzite.  (Lewis, written communications, 2002).'
3866|'Impure quartzite and biotite schist.  Compositional layering on the scale of decimeters is defined by thin layers of schist alternating with massive quartzite.  Quartzite typically contains 10 to 20 percent feldspar (principally alkali feldspar) and about 10 percent mica.  Quartz grains are commonly 0.25 to 1 mm in size, but range up to 5 mm in highly recrystallized rocks.  These recrystallized quartzites are also highly strained.  In places this unit includes calc-silicate quartzite similar to the qcs unit. (R.S. Lewis, unpub.data, July 8, 2002).'
3867|'Diopside quartzite and hornblende gneiss; locally epidote-rich (Lewis and others, 1992b). Also contains subordinate amounts of biotite schist. Hornblende gneiss is presumed by its association with calc-silicates of this unit to have a sedimentary origin.'
3868|'Biotite granodiorite and granite. Grades into biotite tonalite on the southwest side of the Bitterroot lobe of the Idaho batholith, southwest of Old Man Creek.  Associated pegmatite and aplite dikes and sills are common. Zircon U-Pb dates of 719 Ma and 755 Ma from samples along the Lochsa River (Toth and Stacey, 1992) are the best estimates of the age of this unit.  Includes the Skookum Butte, White Sand Creek, and Brushy Fork stocks of Nold (1968, 1974), part of the Grave Peak pluton of Toth (1987), and the Tom Beal Park granite of Williams (1977).  (R.S. Lewis, unpub.data, July 8, 2002).'
3869|'Stream deposits in modern drainages; gravel, silt, and sand; includes gravels reworked by dredging.'
3870|'Unconsolidated deposits of landslide origin.'
3871|'Gravel, silt and sand deposited on benches above modern drainages.'
3872|
3873|'Poorly sorted, unconsolidated sediments of clay, silt, sand, and gravel.'
3874|'Chemically distinct from other flows in CRB Group (V.E. Camp, unpublished data, 1979. Wright and others, 1980). Occurs just north of Grangeville, Idaho.  Upper age limit unknown.'
3875|'Basalt has some resemblance chemically to Pomona and Dodge chemical types (V.E. Camp, unpublished. data, 1979; Wright and others, 1980). Occurs near Grangeville, Idaho and in scattered outcrops farther west.  Equivalent to the Amphitheater flow of Bard (1978).'
3876|'Med- to coarse- grained flow of Pomona chemical type.  Petrographically similar to Pomona Member.  Probably equivalent to Pomona Member, but mapped separately.'
3877|'Sparsely plagioclase- and olivine- phyric, commonly ophitic basalt flow of Asotin chemical type (Camp, 1976; Swanson and others, 1979a; Wright and others, 1979).'
3878|'Fine- to med- grained flow with higher MgO and lower SiO2 than rest of member. Chemically intermediate between Wilbur Ck. and Asotin chemical types. Contains rare small plagioclase and olivine phenocrysts.'
3879|'Sandstone with lenses of quartzite and quartz clast. Also silts and clays.'
3880|'Fine- to coarse- grained basalt flows. Lolo chemical type (Wright and others, 1973); such flows generally contain phenocrysts of olivine and commonly plagioclase.'
3881|'Generally  fine- grained and petrographically non distinctive. May contain numerous  plagioclase phenocrysts. Grande Ronde flows are the thickest of the Columbia River Group. Thickest at SW of map.  Covers and laps out on rugged topography on older rocks at flow margins: pillows common.  Flow also commonly hackly jointed and pillowed at or near contact with older rocks.  Flows of the Grande Ronde Basalt are divided magnetostratigraphic units.'
3882|'Generally  fine- grained and petrographically non distinctive. Grande Ronde flows are the thickest of the Columbia River Group.  Covers and laps out on rugged topography on older rocks at flow margins: pillows common.  Flow also commonly hackly jointed and pillowed at or near contact with older rocks.  Flows of the Grande Ronde Basalt are divided magnetostratigraphic units.'
3883|'Generally  fine- grained and petrographically non distinctive. May contain numerous  plagioclase phenocrysts. Grande Ronde flows are the thickest of the Columbia River Group. Thickest at NW of map.  Covers and laps out on rugged topography on older rocks at flow margins: pillows common.  Flow also commonly hackly jointed and pillowed at or near contact with older rocks.  Flows of the Grande Ronde Basalt are divided magnetostratigraphic units.'
3884|'Generally coarse-grained, grusy-weathering, and plagioclase-phyric with phenocrysts between 5 and 25   cm.  In Harpster area, vesicular pyroxene diabase containing up to 30% random labradorite laths up to 14 cm.'
3885|
3886|'Biotite granodiorite with weak, local! foliation. Ages determined for older plutons within map area and for younger plutons east of map area (Lund, 1984; Snee and others, 1985; Lund and Snee, 1988) bracket age of granodiorite between 74 and 90 Ma.'
3887|'Hornblende-biotite tonalite containing primary epidote (Zen, 1988) and weak, local foliation.  Sphene commonly visible in hand specimen. Emplacement age of 90.43.0 Ma determined by U/Pb.'
3888|'Foliated trondhjemite composed of oligoclase, quartz , biotite, muscovite, and orthoclase. Plagioclase is twice as abundant as quartz. A common coarse-textured variant is a strongly foliated trondhjemite containing bent sheets of biotite up to 1cm.  Pegmatites include abundant muscovite and occasional garnet.'
3889|'Hornblende-biotite tonalite. Epidote and sphene common. Rock contains well-developed foliation of variable orientation. Foliated tonalite may be same age as tonalite (Kt).'
3890|'Gneissic hornblende- biotite tonalite. locally contains epidote and sphere. Mineralogic variation may indicate presence of multiple strongly deformed plutons or may indicate variation within a single intrusive unit.  Strong fabric developed during deformation of North Fork block  may be either foliation dominated (north-northeast trend, moderate to steep east-southeast dip) or mineral lineation dominated (moderately steep southeast plunge).'
3891|
3892|'Black shale and argillite sandstone, pebble conglomerate, and thin limestone beds.'
3893|
3894|
3895|'Granodiorite, quartz diorite, diorite, and gabbro.'
3896|'Gabbro, diorite, quartz diorite, norite, and albite granite.'
3897|'Predominantly calcareous phyllite to schist; textural gradation depends on metamorphic grade, which increases from lower greenschist facies in west to upper greenschist facies in east. Lesser amounts of marble, conglomeratic calcareous schist.  Outcrops in canyon along east side of Salmon River are silver-gray, calcareous, graphitic phyllite stratigraphically interfingered with very fine grained blue-gray marble in lenses and layers 5-100 m thick.  Outcrops in core of Slate Creek antiform are predominantly calcareous schist; abundance of amphibole and other calc-silicate minerals as well as grain size increase eastward across fold.'
3898|'Gray calcareous slate and phyllite.'
3899|'Green and maroon, metavolcanic rocks and interlayered volcaniclastic sedimentary rocks. Predominantly muscovite-chlorite schist; may contain relict phenocrysts, such as euhedral quartz, that have rims of replaced plagioclase and uralitic amphibole.  Layers of fine- to medium-grained marble and calcareous phyllite (as much as 50 m thick), similar to lithologies of the Martin Bridge Formation, are found interbedded with and gradational with metavolcanic lithologies near top of the Doyle Creek.  Volcaniclastic conglomerate layers, as much as 20 m thick, found at several horizons, contain clasts of weakly schistose, stretched, multilithologic volcanic and volcaniclastic rocks. Top gradational with the Martin Bridge Formation. Base'
3900|'Metamorphosed basalt and andesite flows and volcaniclastics, graywackes, argillites, and limestones.'
3901|'Intensely sheared rock.'
3902|'Primarily green-gray to maroon, lower-greenschist-facies muscovite-chlorite schist: protolith consists of sheared and metamorphosed keratophyre, quartz keratophyre, and spilite.  Also contains volcaniclastic conglomerate beds,  nonnvolcanic sedimentary beds, and limestone lenses. Crops out mainly on west side of Salmon River.'
3903|'Metamorphosed and deformed, biotite quartz diorite cropping out in floor of lower Slate Creek and along its north wall. Quartz diorite is metamorphosed to similar grade as metavolcanic host rocks and is deformed concordantly with host rocks.  May be same age as the Permian gneissic quartz diorite  that intruded the Permian Hunsaker Creek or Windy Ridge Formations.  Exposures in floor of lower Slate Creek are sericitized and silicified. Sericitized plagioclase forms mats intergrown with other minerals. Exposures along north wall of lower Slate Creek are higher metamorphic grade; biotite is common mafic phase.'
3904|'Gray biotite calc-silicate gneiss; contains centimeter-scale quartz-rich and marble layers; also includes outcrops of marble and biotite schist.  Protolith probably calcareous sediment and volcanic-derived sediment. Found on east side of North Fork block along Little Slate Creek, and along same trend east of Allison Creek.'
3905|'Metamorphosed mafic volcanic rocks forming  compositionally interfingered lithologic units having gradational contacts;  could not be mapped separately. Chlorite schist is green and gray and commonly contains muscovite  as major constituent.  Chlorite schist metamorphosed to lower greenschist  facies in westernmost exposures; contains prekinematic garnet,  intergrown biotite and muscovite after chlorite,  and fibrous intergrowths of muscovite and sillimanite.  Hornblende-biotite schist and gneiss is gray, (from near mouth of Little Van Buren Creek to North Fork of Slate Creek), and commonly contains garnet and epidote; retrograde chlorite in some areas defines secondary foliation.'
3906|'Garnet-biotite-hornblende quartzofeldspathic gneiss and schist and garnet amphibolite gneiss predominate. Less common garnet-muscovite-biotite schist occurs along west side of North Fork block in several isolated exposures from Waterspout Creek to ridge north of Willow Creek. Mafic volcanic protolith; no primary features preserved.'
3907|'Orange-stained, silvery gray muscovite schist and minor silvery green muscovite-chlorite schist; amphibolite facies equivalents of intermediate and silicic volcanic rocks. Found discontinuously around Slate Creek antiform above Rapid River thrust fault.  Muscovite schist in lower Slate Creek, middle John Day Creek, and upper Long Gulch is fine to medium grained, contains garnet, and lacks other porphyroblasts.  Muscovite schist from John Day Mountain to north of Slate Point and in middle Slate Creek contains prekinematic garnet porphyroblasts and postkinematic chlorite porphyroblasts replaced by biotite.'
3908|'Gray, sheared, recrystallized quartz diorite and associated (but unmapped) quart, monzonite and mafic dikes, which intruded unit Phw of the Seven Devils Group along Salmon River at Box Canyon.  Mineralogy altered by lower-greenschist facies regional metamorphism.'
3909|'Brown-weathering, green-gray, muscovite-chlorite schist; protolith consists of metamorphosed keratophyre, quartz keratophyre, and spilite; textural varieties include metavolcanic flow, tuffaceous, and conglomerate or breccia rocks (Vallier, 1977).  Metamorphic muscovite and (or) chlorite define foliation. Calcite found both as thin layers and disseminated grains. Although some primary volcanic textures are preserved, primary layering and most primary features are obliterated by shearing and formation of metamorphic minerals. Early Permian age (Walker, 1986) of cross-cutting gneissic quartz.'
3910|'Green and white schists.'
3911|'Stream deposits in modern drainages; gravel, silt, and sand; includes gravels reworked by dredging.'
3912|'Alluvial, colluvial, and morainal deposits (Lund and Esparza, 1990).'
3913|'Unconsolidated landslide debris.'
3914|'Poorly sorted and poorly stratified, unconsolidated deposits principally of glacial origin. Includes till in lateral and ground moraines as well as outwash and modern stream alluvium.'
3915|'Poorly sorted, unconsolidated sediments of clay, silt, sand, and gravel which commonly contain rounded cobbles of quartzite.  Unit is well exposed on the north side of the American River 1.5 kilometers south of Elk City; cross-bedded sands, gravels and boulder conglomerates there contain wood fragments and cedar(?) bark.  Sediments have been locally placered for gold, but grade is lower than that of Quaternary stream deposits (Shenon and Reed, 1934).  Also includes gravel of Blacktail Butte area (Meyers, 1983). In the Meadow Creek area: coarse fossiliferous sand, silt, and gravel. (R.S. Lewis, unpub.data, July 8, 2002).

Poorly sorted, unconsolidated sediments of clay, silt, sand, and gravel which commonly contain rounded cobbles of quartzite (Lewis and others, 1990). Unit is well exposed on the north side of the American River 1.5 kilometers south of Elk City; cross-bedded sands, gravels and boulder conglomerates there contain wood fragments and cedar(?) bark.  Sediments have been locally placered for gold, but grade is lower than that of Quaternary stream deposits (Shenon and Reed, 1934). Also includes gravel of Blacktail Butte area, clay and silt in McComas basin, and fossiliferous sand, silt, and gravel at Fisher placer east of the mouth of Meadow Creek (Myers, 1982). Locations and mapping of this unit in the Newsome Creek drainage taken in part from Reid (1959). (Lewis, written communication, 2002).'
3916|'Medium- to coarse-grained basalt flow of Pomona chemical type with abundant olivine and reverse magnetic polarity (Swanson and others, 1979,1980; Kauffman, unpub.).  Petrographically similar and probably equivalent to Pomona Member, but mapped separately because the easternmost outcrops of the Pomona, in the Lewiston Basin, are 35 km west of the westernmost outcrops of the basalt of Weippe.  Feeder dikes occur east and northeast of Orofino in the drainage of the North Fork of the Clearwater River.  Age date of a sample collected by Kauffman (2001, unpub.) northeast of Orofino (west of the Kooskia quadrangle) resulted in a date of 12.90.8 M.Y. (Lewis, written communication, 2002).'
3917|'The Asotin consists of fine- to medium-grained, sparsely plagioclase- and olivine-phyric, commonly ophitic basalt with normal magnetic polarity (Swanson and others, 1979, 1981).  It is closely associated with and physically resembles the Wilbur Creek Member (which includes the basalt of Lapwai).  These units have been separated in the past based on chemistry (Camp, 1981; Swanson and others, 1979, 1981), but recent mapping in the Clearwater embayment has shown that lateral continuity of these chemical units is often irregular and inconsistent (Kauffman, 2000, 2001, unpub.; Garwood, 2001); therefore these units have been combined.  The basalt of Lapwai is chemically intermediate between the Wilbur Creek and the Asotin. (Lewis, written communication, 2002).'
3918|'Gneissic hornblende tonalite (Khtg unit of Myers, 1982). Accessory minerals in decreasing abundance are sphene, epidote, muscovite, chlorite, apatite, allanite, zircon, pyrite, and calcite. Sphene, allanite, zircon, and apatite are exceptionally large.'
3919|'Fine- to coarse- grained basalt flows. Lolo chemical type (Wright and others, 1973); such flows generally contain phenocrysts of olivine and commonly plagioclase. (R.S. Lewis, unpub.data, July 8, 2002).

Fine- to coarse-grained basalt flows, sparse to common small plagioclase and olivine phenocrysts, reverse magnetic polarity (Swanson and others, 1979, 1981).  Flows in this area are generally of the Lolo chemical type, although some with Rosalia chemical type also have been documented.  Commonly invasive into weakly lithified subarkosic sandstone, siltstone, and claystone near the eastern margin of the Columbia Plateau. (Lewis, written communication, 2002).'
3920|'Generally  fine- grained and petrographically non distinctive. Grande Ronde flows are the thickest of the Columbia River Group.  Covers and laps out on rugged topography on older rocks at flow margins: pillows common.  Flow also commonly hackly jointed and pillowed at or near contact with older rocks. Flows of the Grande Ronde Basalt are divided magnetostratigraphic units. (R.S. Lewis, unpub.data, July 8, 2002).

Generally fine-grained, aphyric to microphyric or sparsely plagioclase-phyric and petrographically non-distinctive flows of the N1 magnetostratigraphic unit (Swanson and others, 1979, 1981).  Chemical composition varies within a broad field termed Grande Ronde chemical type (Yakima chemical type of Wright and Swanson, 1973).  Flows are generally between 15-25 m.  Many flows near the margin of the Columbia Plateau are invasive into interbedded sand, silt and clay sediments. (Lewis, written communication, 2002).'
3921|'Generally  fine- grained and petrographically non distinctive. May contain numerous  plagioclase phenocrysts. Grande Ronde flows are the thickest of the Columbia River Group. Thickest at NW of map.  Covers and laps out on rugged topography on older rocks at flow margins: pillows common.  Flow also commonly hackly jointed and pillowed at or near contact with older rocks.  Flows of the Grande Ronde Basalt are divided magnetostratigraphic units. (R.S. Lewis, unpub.data, July 8, 2002).

Generally fine-grained, aphyric to microphyric, rarely sparsely plagioclase-phyric, petrographically non-distinctive flows of the R1 magnetostratigraphic unit (Swanson and others, 1979, 1981).  Chemical composition varies within a broad field termed Grande Ronde chemical type (Yakima chemical type of Wright and Swanson, 1973).  Flows are generally between 15-25 m.  Many flows near the margin of the Columbia Plateau are invasive into interbedded sand, silt and clay sediments. (Lewis, written communication, 2002).'
3922|'Generally coarse-grained, grus-like weathering, plagioclase-phyric basalt with phenocrysts between 5 and 25 mm (Swanson and others, 1979, 1981).  Uppermost units have normal to transitional magnetic polarity.  In Harpster area, vesicular pyroxene diabase containing up to 30% random labradorite laths up to 14 mm (Myers, 1982).  Generally equivalent to lower basalt of Bond (1963). (Lewis, written communication, 2002).'
3923|'Light-colored dikes, commonly iron-stained, with sparse (0-10 percent) phenocrysts of quartz, alkali feldspar, and plagioclase (Lewis and others, 1990).  Most common in the eastern part of the area, both within and near Eocene granite unit (Tg).'
3924|'Porphyritic, gray to greenish-gray dikes, with plagioclase, hornblende, biotite, and embayed quartz phenocrysts.  Dikes are most common in the eastern part of the area east of the Blanco Creek shear zone.  Variants include coarsely porphyritic rocks in the south part of the area near the Salmon River that have conspicuous feldspar and quartz phenocrysts averaging 1 cm in length.  Some of these dikes near the Salmon River are mylonitized, presumably as a result of motion along the Bargamin Ck. shear zone. (R.S. Lewis, unpub.data, July 8, 2002).'
3925|'Dark greenish-gray andesite dikes with microphenocrysts of plagioclase and hornblende (Lewis and others, 1990).  Some of these dikes may be Cretaceous in age.'
3926|'Hydrothermally altered porphyritic dacite or rhyodacite plug southeast of Orogrande. Similar in composition and texture to (Td) dikes.'
3927|'Dikes of various compositions. Most are probably rhyolite or dacite. This unit includes dikes located on aerial photographs (Lewis, 1990) and not field checked.'
3928|'Poorly exposed areas consisting of greater than 50 percent dike rock (Lewis and others, 1990).  Unit is dominated by dacite and rhyodacite (Td).'
3929|'Massive, pink to light-gray, fine- to medium-grained, equigranular hornblende-biotite granite; locally miarolitic.  Unit also contains smaller amounts of seriate to porphyritic, medium- to coarse-grained, magnetite-hornblende quartz syenite to quartz monzonite.  These latter rock types contain less quartz than is typical for this unit and were only subdivided in the Vermilion Peak area. All phases contain highly perthitic alkali feldspar; mafic minerals are typically interstitial. Includes rocks of Running Creek pluton (Motzer, 1985) and Casto pluton (Cater, 1973).Unit includes foliated plutonic rocks of uncertain correlation on Burnt Knob E of Bargamin Ck, and a stock of leucocratic granite E of Red River Hot Spring both of could be Cretaceous age. (R.S. Lewis, unpub.data, July 8, 2002).'
3930|'Seriate, quartz monzonite phase of Eocene granite subdivided only in vicinity of Vermilion Peak (Lewis and others, 1990). Hornblende cored by relict pyroxene, and magnetite common. Probably equal to coarse-grained hornblende quartz syenite of Pawlowski (1981).'
3931|'Fine-grained, leucocratic, biotite granite and lesser amounts of biotite granodiorite and hornblende-biotite diorite.   The biotite granodiorite is similar to Kgd  and is medium grained, equigranular, and foliated to massive.  Hornblende-biotite diorite is fine grained, and present as inclusions in the biotite granodiorite and the leucocratic granite of this unit.  Although the leucocratic granite was considered by Pawlowski (1982) to be Eocene in age, its low magnetic susceptibility and lack of strongly perthitic alkali feldspar and miarolitic cavities are more characteristic of Cretaceous rocks in the area.

Consists principally of fine-grained, leucocratic, biotite granite and lesser amounts of hornblende-biotite diorite and biotite granodiorite.  Unit is present only in the southeastern part of the area.  The hornblende-biotite diorite is fine grained, and present both as inclusions in the leucocratic granite, and intermixed with it.  Textural evidence such as crenulate margins of diorite inclusions and the presence of composite dikes of leucocratic granite and diorite indicates that felsic and mafic magmas are at least in part contemporaneous, as does the presence of hybrid rocks of intermediate composition.  The biotite granodiorite is similar to the Kgd unit, but is finer grained.  Unlike typical Eocene granite (Tg) the leucocratic granite has variable, but generally low magnetic susceptibility, lacks strongly perthitic alkali feldspar, and lacks miarolitic cavities.  However, its spatial association with more typical, coarser-grained Eocene units suggests an Eocene age, as proposed by Pawlowski (1982). (Lewis, written communication, 2002).'
3932|'Gray, seriate, medium-grained, granodiorite to granite. Alkali feldspar is perthitic, interstitial, and locally in granophyric intergrowths with quartz. Plagioclase is strongly zoned oligoclase-andesine.  Biotite is present in pseudohexagonal books and clinopyroxene forms relict cores in hornblende. Unit is cross-cut by numerous Td dikes, and by sparse dikes of aplite and pegmatite with miarolitic cavities.   Weathers to rounded boulders. (R.S. Lewis, unpub.data, July 8, 2002).'
3933|'Dark-colored, equigranular, hornblende-rich rocks.  These rocks are present both as xenoliths 3-20 m in length within Tg and as map-scale units in the southeastern part of the area.  Hornblende is euhedral and commonly contains cores of clinopyroxene.  Plagioclase is strongly zoned and subhedral, whereas quartz and perthitic alkali feldspar are interstitial.(R.S. Lewis, unpub.data, July 8, 2002).'
3934|'Densely welded dacitic vitric tuff with sparse phenocrysts of plagioclase, quartz, and biotite.  The tuff contains inclusions of biotite granodiorite, dacite, and schist.  Although the unit is resistant to weathering, outcrops are preserved across an area less than one kilometer in width in the central-east part of the map area along the road to Darby, Montana. This unit is probably correlative with the Challis Volcanics. (R.S. Lewis, unpub.data, July 8, 2002).'
3935|'Medium-grained, equigranular, biotite granodiorite to granite.  In places the unit is foliated and hornblende-bearing.  The alkali feldspar exhibits microcline grid twins and myrmekitic textures are common.  Represents the NE-most exposures of the South lobe of the Idaho batholith and is well exposed in the west part of the area.  Included in this unit are muscovite-bearing phases south and west. of Orogrande and in Dixie area, and masses of pegmatite and aplite.  K-Ar determinations  were obtained on a sample of this unit collected in the western part of the area along the South Fork of the Clearwater River west of Peasley Creek (Criss and Fleck, 1987) (R.S. Lewis, unpub.data, July 8, 2002).'
3936|'Porphyritic hornblende-biotite granodiorite; granite. Contains euhedral alkali feldspar phenocrysts up to 3 cm in length. Plagioclase weakly zoned; hornblende contains cores of clinopyroxene. Cretaceous age by Lewis and others (1990), but may be Eocene.'
3937|'Foliated, equigranular to weakly porphyritic, medium-grained biotite granodiorite; locally mylonitic. Includes migmatite and unfoliated biotite granodiorite. Includes rocks mapped as gneissic adamellite of Granite Ck pluton in nw of area (Myers, 1982).

Composite unit that consists principally of foliated biotite granodiorite, but includes areas of megacrystic granodiorite similar to Kpgd, as well as smaller masses of hornblende diorite. (R.S. Lewis, unpub.data, July 8, 2002).'
3938|'Leucocratic and generally undeformed varieties of biotite granodiorite (Kgd) containing 30 percent to 60 percent inclusions of biotite gneiss, less common schist and augen gneiss, and rare calc-silicate rocks.  In most occurrences, foliation and folds in inclusions have attitudes similar to nearby country rocks which  suggests passive emplacement of the granitic material after the ductile deformation and metamorphism of the metasedimentary rocks.  In other occurrences, foliation of the granitic material and the presence of biotite selvages around the inclusions indicate partial melting or assimilation during earlier (syndeformational) emplacement. (R.S. Lewis, unpub.data, July 8, 2002).'
3939|'Foliated to lineated, hornblende-biotite granodiorite to quartz diorite typified by alkali feldspar megacrysts 2 to 6 cm in length. A nonporphyritic variety occurs along the contact in several places, particularly in the area SE of Red River Hot Springs.  Subhedral sphene and epidote are common accessory minerals. The epidote, some of which is cored by allanite, is interpreted as a magmatic phase. A subhorizontal foliation defined by biotite is present, as is a lineation defined by aligned alkali feldspar phenocrysts and hornblende  that parallels a lineation in the surrounding country rocks. The lineation in the Kmgd is interpreted to be a result of deformation that was taking place as the magmas intruded and cooled.  Locally, a steep foliation. (R.S. Lewis, unpub.data, July 8, 2002).

Foliated to lineated, hornblende-biotite granodiorite to quartz diorite typified by alkali feldspar megacrysts 2 to 6 cm in length (Lewis and others, 1990). A nonporphyritic variety occurs along the contact in several places, particularly in the area southeast of Red River Hot Springs. Subhedral sphene and epidote are common accessory minerals. The epidote, some of which is cored by allanite, is interpreted as a magmatic phase. A subhorizontal foliation defined by biotite is present, as is a lineation defined by aligned alkali feldspar phenocrysts and hornblende that parallels a lineation in the surrounding country rocks. The lineation in the Kmgd is interpreted to be a result of deformation that was taking place as the magmas intruded and cooled.  Locally, a steep foliation from submagmatic flow during continuing (or later?) deformation dominates.  Unit differs from the Proterozoic augen gneiss (Yag) in that it contains hornblende. Relative to the Yag unit it is enriched in Al, Ca, Na, Ba, and Sr, and depleted in K, Rb, and Y. (Lewis, written communication, 2002).'
3940|'Metamorphic lense subdivided in more detail to the north by Myers (1983) and part of his Khtg unit. Most of the metamorphic screens are probably units within the Syringa metamorphic sequence (coarse grained schist and massive quartzite).  Intruded in vicinity of western Idaho suture zone. (R.S. Lewis, unpub.data, July 8, 2002).'
3941|'Gneissic biotite tonalite and metamorphic rocks. Biotite tonalite and metamorphic rocks mapped separately to the north by Myers (1982).

Metamorphic lenses, subdivided to north by Myers (1983). Part of Kbtg unit of Myers (1983). Split out from tonalite to the west which is within or west of the suture zone. (R.S. Lewis, unpub.data, July 8, 2002).'
3942|'Poorly mapped mixed unit of biotite granodiorite, biotite tonalite, and metamorphic rocks. Metamorphic lenses subdivided to north by Myers (1983). Intrusive rocks of this unit have intruded along and immediately east of the western Idaho suture zone.

Metamorphic lenses subdivided to north by Myers (1983). Most of the metamorphic lenses are probably units within the Syringa metamorphic sequence (coarse grained schist  and massive quartzite). rock have intruded along western Idaho suture zone. (R.S. Lewis, unpub.data, July 8, 2002).'
3943|'Foliated trondhjemite composed of oligoclase, quartz , biotite, muscovite, and orthoclase. Plagioclase is twice as abundant as quartz. A common coarse-textured variant is a strongly foliated trondhjemite containing bent sheets of biotite up to 1cm.  Pegmatites include abundant muscovite and occasional garnet. Wedge-shaped fault slice of foliated trondhjemite between Castle Ck. and Browns Ck. is an uplifted segment of the Blacktail pluton. (R.S. Lewis, unpub.data, July 8, 2002).'
3944|'Mafic rocks along western and southern margins of Harpster pluton (Myers, 1982). Western roof zone of pluton is mostly hornblende-clinopyroxene gabbro, norite. Roof zone contains numerous mafic xenoliths, pendants that diminish eastward.'
3945|'Mixed tonalite, granodiorite, migmatite, and metamorphic rocks. Metamorphic rocks subdivided in more detail to north by Myers (1983).  Most of the metamorphic rocks are probably units within the Syringa metamorphic sequence (coarse grained schist and massive quartzite). (R.S. Lewis, unpub.data, July 8, 2002).'
3946|'Biotite granodiorite/biotite tonalite in and e of western Idaho suture zone. Plutonic rocks with transitional  initial 87Sr/86Sr values (0.704 to 0.708). Myers (1982) gneissic biotite tonalite, but includes granodiorite; quartz monzodiorite(Hoover, 1986).'
3947|'Sheared, highly altered granodiorite and tonalite of the Lightning Creek pluton (Myers, 1982). Nearly flat roof with abundant greenstone xenoliths and pendants. Chilled margins. Imbricated along northeast-trending faults and contains tectonic slices of phyllonitic greenstone and granitoid rocks. Plagioclase partly replaced by sericite or mixtures of epidote, clinozoisite, and quartz; microcline is sericitized; hornblende is replaced by chlorite and epidote; and biotite is thoroughly chloritized. Tentatively assigned a Jurassic age by Myers (1982) because it shows more alteration and mylonitization than other plutons in the area. (Lewis, written communication, 2002).'
3948|'Eastern and lower part of the Harpster pluton described by Myers (1982) as hornblende tonalite. Low silica contents (55-61 weight percent) reported by Myers indicate low quartz content and a more likely composition of quartz diorite or diorite.'
3949|'Calcareous metasedimentary rocks thought by Myers (1982) to be equivalent to the upper part of Squaw Creek schist. Includes fine-grained calcareous schist with thin compositional interlensing. Schist assemblages are: quartz-phlogopite-calcite+/-actinolite; quartz-clinozoisite-calcite-actinolite+/-tremolite+/-plagioclase; quartz-diopside-actinolite-clinozoisite+/- grossularite; and quartz-hornblende-almandite+/-biotite. Hornblende, epidote, and almandite increase in abundance eastward at the expense of calcite, phlogopite, and quartz. Also includes fine-grained, thinly laminated and strongly lineated hornblende-garnet schist with lesser amounts of quartz, sodic plagioclase (commonly as augen), thin seems of epidote, and accessory disseminated graphite. Hornblende-garnet schist locally contains quartz-biotite-garnet layers and subordinate hornblende-diopside-plagioclase layers and was probably a mafic tuffaceous siltstone prior to metamorphism. Unit also includes banded siliceous marble and and calc-silicate gneiss. The gneiss contains two or more of the following: quartz, actinolitic hornblende, calcite, diopside, andesine, and clinozoisite. Coarse clinozoisite and prochlorite replace plagioclase and hornblende, respectively. (Lewis, written communication, 2002).'
3950|'Thinly laminated, fine-grained, graphitic quartz-mica schist thought by Myers (1982) to be equivalent to the lower part of Squaw Creek schist. Discordant quartz and pegmatite stringers are abundant. Includes a 15 m thick layer of sheared and partly recrystallized coarse crystal tuff composed of ovoid plagioclase porphyroclasts in a mylonitic matrix of quartz, muscovite, and biotite. (Lewis, written communication, 2002).'
3951|'Metagabbro and metaperidotite mapped by Myers (1982) that now is mainly talc-serpentine-chlorite schist. Basal layer of sheared and metamorphosed olivine-pyroxene gabbro, central layer of metaperidotite, and discontinuous upper layer of highly altered pyroxenite. Considerable local variation of in texture and mineral composition. Moderately resistant to erosion. Relict olivine and pyroxene in metaperidotite have been almost completely altered to antigorite, talc, tremolite, prochlorite, zoisite, and magnetite.  Accessory minerals include phlogopite and actinolite. (Lewis, written communication, 2002).'
3952|'Quartz keratophyric crystal and lithic tuffs, tuffaceous siltstone, chert, graywacke, and volcanic conglomerate intercalated with porphyritic basalt and andesite flows (Myers, 1982). Layered rocks are cut by dikes and sills of diabase and coarsely porphyritic andesite. Graywackes and siltstones display graded and disturbed bedding characteristic of turbidites. Chert beds and clasts in siltstone turbidites contain siliceous microfossils. (Lewis, written communication, 2002).'
3953|'Igneous protolith  Relict pyroxene in the eastern part of the area at Green Mountain suggests the protolith was a medium-grained gabbro.  The amphibolite does not intrude into qm, csm, and mq which may indicate that it is older than these units. The small, folded, metamorphosed and boudinaged biotitic bodies located within the Yag and bg units are interpreted as sills or dikes of amphibolite, which may be genetically related to Yag.  These biotitic rocks may reflect replacement of hornblende in a retrograde reaction. (R.S. Lewis, unpub.data, July 8, 2002).'
3954|'Biotite-rich granitic gneiss with augen of alkali feldspar, alkali feldspar rimmed by plagioclase, and plagioclase. Augen are up to 5 cm in length and range from blocky in less strained rocks to asymmetric with strain shadows in more highly strained rock.  Local absence of augen in highly foliated rock is attributed to their destruction from metamorphic processes rather than original absence.  Fine-grained, compositionally layered angular blocks and tabular bodies concentrated near the margins are interpreted as inclusions of surrounding biotite gneiss (bg).  The protolith of the augen gneiss was probably rapakivi granite. (R.S. Lewis, unpub.data, July 8, 2002).'
3955|'White to tan clean quartzite or quartzitic gneiss (Lund and Esparza, 1990). Part of Buffalo Hump roof pendant. Correlated with Belt Supergroup or with equivalent-age rocks of east-central Idaho. May be the same quartzite as that in pCqs unit.'
3956|'Gray to tan calc-silicate gneiss and schist (Lund and Esparza, 1990). Part of Buffalo Hump roof pendant. Correlated with Belt Supergroup or equivalent-age rocks of east-central Idaho.'
3957|'Light-colored, fine- to medium-grained quartzite and calc-silicate rocks with centimeter- to decimeter-scale relict bedding locally preserved. Distribution modified from Lewis and others (1990).'
3958|'Light-colored quartzite, muscovitic quartzite, and fine-grained quartz-muscovite-biotite schist. Quartzite is typically fine grained; some is sugary to friable but most is well recrystallized and hard.  Locally contains up to 20 percent alkali feldspar.  Kyanite is present in biotite-rich layers SE of Copper Butte in the northern part of the area, and near Anderson Butte in the north-central part of the area. Partings on micaceous interlayers appear to define "beds" 2 to 60 cm thick. Schistosity commonly parallels compositional layering, but in the northern part of the area at Disgrace Butte bedding is defined by magnetite laminations and is at a high angle to the schistosity defined by aligned muscovite. (R.S. Lewis, unpub.data, July 8, 2002).

Light-colored quartzite, muscovitic quartzite, and fine-grained quartz-muscovite-biotite schist (Lewis and others, 1990). Quartzite is typically fine grained; some is sugary to friable but most is well recrystallized and hard.  Locally contains up to 20 percent alkali feldspar. Kyanite is present in biotite-rich layers southeast of Copper Butte in the northern part of the area, and near Anderson Butte in the north-central part of the area. Partings on micaceous interlayers appear to define "beds" 2 to 60 cm thick. Schistosity commonly parallels compositional layering, but in the northern part of the area at Disgrace Butte bedding is defined by magnetite laminations and is at a high angle to the schistosity defined by aligned muscovite. Probably correlative with either the Ravalli Group or the Striped Peak Formation of the Belt Supergroup. (Lewis, written communication, 2002).'
3959|'Dark, laminated to thinly laminated amphibole (actinolite?)-diopside-quartz rock (Lewis and others, 1990).  Unit is at or near the transition between the quartzite of Meadow Creek and the underlying rocks of the micaceous quartzite unit (mq).'
3960|'Mixed tonalite, granodiorite, migmatite, and metamorphic rocks. Metamorphic rocks subdivided in more detail to north by Myers (1983).'
3961|'Fine- to medium-grained quartz-feldspar-biotite(-muscovite) gneiss and muscovite-biotite (-quartz) schist. More schistose rocks locally contain sillimanite; garnet is rare.  Gneissic varieties include:1) granular biotite gneiss, which  is a fine-grained quartzo-feldspathic meta-graywacke(?); 2) layered granular biotite gneiss, which is similar to granular rocks but has centimeter-scale layering that possibly is relict bedding; and 3) medium- to coarse-grained gneiss, which has a layered appearance produced by variations in biotite content and which locally grades into migmatite.  Unit includes some dark-colored quartzite and may include augen gneiss where high strain, deep weathering, and the abundance of pegmatites make detection of feldspar augen (R.S. Lewis, unpub.data, July 8, 2002).

Fine- to medium-grained quartz-feldspar-biotite(-muscovite) gneiss and muscovite-biotite (-quartz) schist. Distribution modified from Lewis and others (1990). More schistose rocks locally contain sillimanite; garnet is rare.  Gneissic varieties are quartz rich and include:1) granular biotite gneiss, which  is a fine-grained quartzo-feldspathic meta-graywacke(?); 2) layered granular biotite gneiss consisting of thin interbeds of gneiss and feldspathic quartzite with a range of biotite content which is similar to granular rocks but has centimeter-scale layering that possibly is relict bedding; and 3) medium- to coarse-grained gneiss, which has a layered appearance produced by variations in biotite content and which locally grades into migmatite.  Unit includes some dark-colored quartzite and may include augen gneiss where high strain, deep weathering, and the abundance of pegmatites make detection of feldspar augen difficult. Unit may be in fault contact with the Syringa metamorphic sequence, but lack of adequate exposure prevents determination of contact relations. (Lewis, written communication, 2002).'
3962|'Medium- to coarse-grained quartz-muscovite-biotite schist, medium-grained quartzofeldspathic gneiss, and dark-colored micaceous quartzite; grades into biotite gneiss and schist unit (pCbg).  Commonly contains sillimanite and muscovite in lenses 1-4 cm in diameter that resemble flattened pebbles. (R.S. Lewis, unpub.data, July 8, 2002).'
3963|'Consists of interlayered quartz-mica schist and variably micaceous quartzite.  Schists have relatively abundant, medium- to coarse-grained muscovite, less abundant magnetite, and minor sillimanite and garnet.  Quartzites are dark (from included biotite?) coarse grained (2-5 mm), and locally iron stained from weathering of 2-4 mm magnetite octahedra.  Partings typically are 5 to 30 cm apart.  Unit may be in fault contact with the Elk City metamorphic sequence, but lack of adequate exposure prevents determination of contact relations (R.S. Lewis, unpub.data, July 8, 2002).'
3964|'Impure quartzite and biotite schist.  Compositional layering on the scale of tens of centimeters is defined by thin layers of schist in more massive quartzite.  Quartzite typically contains 10 to 20 percent feldspar (principally alkali feldspar) and about 10 percent mica.  Quartz grains are commonly 0.25 to 1 mm in size, but range up to 5 mm in highly recrystallized rocks.  These recrystallized quartzites are also highly strained.  In places this unit includes calc-silicate quartzite similar to the qcs unit.  Schists adjacent to Cretaceous plutons are gneissic.  Unit differs from qm by having a coarser grain size, more feldspar, and larger amounts of biotite schist. (R.S. Lewis, unpub.data, July 8, 2002).'
3965|'Garnetiferous quartzite and hornblende gneiss; locally epidote- or diopside-rich.  Map unit includes some amphibolite presumed by its association with more clearcut calc-silicates of this unit to have a sedimentary origin.'
3966|'Medium- to coarse-grained impure quartzite in layers 2 to 140 ft thick that core many of the ridges in the northwest part of the area (Myers, 1982). Most or all may belong to the Syringa metamorphic sequence. In addition to quartz the rocks contain variable amounts of muscovite, biotite, actinolite, diopside, calcite, tremolite, almandite, grossularite, epidote, graphite, pyrite, sillimanite, tourmaline, and cordierite. (Lewis, written communication, 2002).'
3967|'Biotite-muscovite schist and gneiss (Myers, 1982). Schist intervals become more gneissic with attendant increase in feldspar toward granitic plutons. Muscovite, the principle mica, is preferentially distributed along axial planes of folded biotite foliation. Schorl and sillimanite increase markedly in the the contact aureole of the Granite Creek pluton. The appearance of sillimanite and subordinate cordierite is accompanied by a decrease in the abundance of biotite. The schist grades into biotite gneiss composed predominantly of sodic andesine or oligoclase, microcline, and quartz. Common accessory minerals are biotite, muscovite, almandite, schorl, sillimanite, allanite, zoisite, clinozoisite, epidote, sphene, magnetite,  pyrite, apatite, and zircon. (Lewis, written communication, 2002).'
3968|'Quartzite, calc-silicate gneiss, marble, apatite-pyrite quartzite, and quartzite-pebble conglomerate (Lund and Esparza, 1990). Gospel Peak roof pendants that exhibit diverse rock compositions and abrupt vertical lithologic changes.'
3970|'Includes stream deposits, colluvium, and glacial deposits.'
3971|'Unconsolidated glacial drift; includes, till and outwash; landforms include moraines and outwash terraces.'
3972|'Light-colored dikes, commonly iron-stained, with sparse (0-10 percent) phenocrysts of quartz, alkali feldspar, and plagioclase (Lewis and others, 1990).  Most common within and near Eocene granite unit (Tg).'
3973|'Porphyritic, gray to greenish-gray dacite and rhyodacite dikes with plagioclase, hornblende, biotite, and embayed quartz phenocrysts (Lewis and others, 1990).'
3974|'Dark gray porphyritic andesite containing plagioclase and pyroxene phenocrysts and glomerocrysts (Toth, 1983). These narrow, vertical dikes crosscut all lithologic units. Groundmass consists of plagioclase, minor iron-titanium oxide minerals, and rare biotite and or hornblende.'
3975|'Porphyritic rhyodacite, rhyolite, and dacite dikes and porphyry stocks; irregularly shaped rhyodacite porphyry bodies form stocks (Lund and others, 1992). Probably a textural variation of the other plutonic units rather than having crystallized from a separate magma. Phenocrysts include quartz, sanidine, plagioclase, biotite, and hornblende. Includes rhyodacite and rhyolite dike unit of Toth (1983).'
3976|'Area near the western map boundary consisting of greater than 50 percent dike rock.  Unit is dominated by rhyolite (Lewis and others, 1990).'
3977|'Rhyolite flows and tuffs and rhyodacite and andesite flows (Lund and others, 1992). Rhyolite flows and welded tuffs are gray, green, or purple and stained brownish orange with Fe-oxide. Less common rhyodacite and andesite flows are near base. Massive to laminated; lithic fragments, including volcanic and metamorphic cobbles, common near base. Quartz, sanidine, plagioclase, biotite, and hornblende phenocrysts.'
3978|'Massive, pink to light-gray, fine- to medium-grained, equigranular hornblende-biotite granite (Lewis and others, 1990); locally miarolitic.  Unit also contains smaller amounts of seriate to porphyritic, medium- to coarse-grained, magnetite-hornblende quartz syenite to quartz monzonite.  These latter rock types contain less quartz than is typical for this unit. All phases contain highly perthitic alkali feldspar; mafic minerals are typically interstitial. Includes rocks of Running Creek pluton (Motzer, 1985). Unit includes foliated plutonic rocks of uncertain correlation on Burnt Knob E of Bargamin Ck. (Lewis, written communications, 2002).'
3979|'Pink to orange, medium- to coarse-grained hornblende-biotite syenogranite and hornblende biotite quartz syenite to quartz monzonite (Lund and others, 1992). May be equivalent to similar rocks in the Tg unit. Perthitic orthoclase dominates over plagioclase (albite-oligoclase, An7-An24). Hornblende is not present in all outcrops and biotite is commonly chloritized. Includes light-gray, medium- to coarse-grained biotite-hornblende quartz monzonite to quartz syenite exposed at the northwest corner of the Painted Rocks pluton (Toth, 1983) that has weak primary flow foliation defined by aligned biotite and hornblende grains and is commonly sheared and altered to chlorite, epidote, and calcite. (Lewis, written communications, 2002).'
3981|'Fine-grained leucocratic biotite granite and lesser amounts of  biotite granodiorite and hornblende-biotite diorite (Lewis and others, 1990). Biotite granodiorite is similar to the Kgd unit. Hornblende-biotite diorite is fine grained, and present as inclusions in the biotite granodiorite and the leucocratic granite of this unit.  Although the leucocratic granite was considered by Pawlowski (1982) to be Eocene in age, its low magnetic susceptibility and lack of strongly perthitic alkali feldspar and miarolitic cavities are characteristic of Cretaceous rocks. May be equivalent to the Tmg unit. (Lewis, written communications, 2002).'
3982|'Gray, fine- to medium-grained biotite monzogranite (Lund and others, 1992). Contains polygonized quartz grains; nearly equal parts of slightly zoned, albite-twinned, subhedral to euhedral white oligoclase and anhedral to subhedral, commonly microperthitic, gray orthoclase; and less than 10 percent chloritized biotite. Trace amounts of secondary and primary(?) muscovite (Hall, 1980). Miarolitic cavities are common in some areas. See Lund and others (1983) for additional descriptions for southeasternmost Tmg. May be equivalent to Tlg unit. (Lewis, written communications, 2002).'
3984|'Gray, salmon, or white granophyric granite, which grades to rhyodacite porphyry and porphyritic rhyodacite (Lund and others, 1983, 1992). Contains slightly more orthoclase than oligoclase and less than 10 percent biotite. Fine-grained to very fine grained groundmass constitutes as much as 50 percent of the rock and has spectacular mineral intergrowths (granophyric texture). Fluorite, magnetite, zircon, apatite, and sphere are accessory minerals. Miarolitic cavities are common. Represents roof phases of granitic plutons. (Lewis, written communications, 2002).'
3985|'Medium-grained equigranular to porphyritic monzogranite and granodiorite of the Paradise pluton (Toth, 1983). Locally mylonitic. Biotite and hornblende comprise 5-20 percent of the rocks and are highest in concentration in the pluton margins. Sphene and allanite trace to 1 percent.'
3986|'Dark-colored, equigranular, hornblende-rich rocks (Lewis and others, 1990).  These rocks are present both as xenoliths 3-20 m in length within Tg and as one map-scale unit northwest of Salmon Mountain.  Hornblende is euhedral and commonly contains cores of clinopyroxene.'
3987|'Abundant narrow dikes and composite bodies as large as 0.3 mi by 0.3 mi of gray to black diorite, quartz diorite, and tonalite (Toth, 1983). Fine- to medium-grained equigranular rocks are dominant over porphyritic varieties. Porphyritic diorite has euhedral phenocrysts of plagioclase 2-4 mm long that are locally flow aligned in an aphanitic groundmass. In both textural varieties hornblende is dominant over biotite and the two comprise 29-60 percent of the rock. Quartz ranges from 0 to 30 percent and plagioclase comprises the remainder of the rock. (Lewis, written communications, 2002).'
3988|'Muscovite-biotite granodiorite and monzogranite (Toth, 1983). Slightly porphyritic to equigranular. Biotite constitutes 2-5 percent of the rock and muscovite is present in variable amounts rarely exceeding 2 percent. Abundant fined-grained equigranular granodiorite to monzogranite dikes.'
3989|'Medium- to coarse-grained porphyritic hornblende-biotite granodiorite and granite.  Contains euhedral alkali feldspar phenocrysts as much as 3 cm in length. Plagioclase is weakly zoned and hornblende contains cores of clinopyroxene. Assigned Cretaceous age by Lewis and others (1990), but may be Eocene. (Lewis, written communications, 2002).'
3990|'Migmatitic quartzofeldspathic schist and gneiss, smaller amounts of amphibolite and biotite quartzite, and sparse calc-silicate gneiss (Toth, 1983; Bittner-Gaber, 1981). Intruded by 20-95 percent granitic rocks. Migmatites are both lit-par-lit style and strongly disharmonic and deformed.'
3991|'Composite unit that consists principally of foliated biotite granodiorite, but includes areas of megacrystic granodiorite similar to Kmgd, as well as smaller masses of hornblende diorite (Lewis and others, 1990).'
3992|'Megacrystic muscovite-biotite granodiorite, monzogranite; subhedral  pink poikilitic potassium feldspar 3-8 cm long (Toth, 1983). Sericite, chlorite alteration. Megacrysts may be late stage, forming from pegmatite-related fluids (Lund, 1980).'
3993|'Medium-grained, gray, hornblende-biotite tonalite and quartz diorite (Toth, 1983). Contains oligoclase, quartz, minor microcline (1-5 percent), biotite, and variable amounts of hornblende (0-26 percent). Accessory minerals are sphene, epidote, apatite, zircon, allanite, magnetite, and thorite. Unit has strongly developed flow foliation and a down-dip flow lineation. (Lewis, written communications, 2002).'
3994|'Gray to brown-gray, foliated, fine- to coarse-grained granite-granodiorite and granite-granodiorite augen gneiss (Lund and others, 1992). Mostly porphyritic; some minor amounts equigranular. Foliated and lineated groundmass of quartz, plagioclase, orthoclase, biotite, and muscovite wraps around subhedral to subrounded orthoclase and plagioclase megacrysts; rapakivi textures common. Hornblende present in a few outcrops. Zircon, tourmaline, apatite and sphene are accessory minerals. (Lewis, written communications, 2002).'
3995|'White to tan quartzite; contains 10-20 percent plagioclase, as much as 10 percent muscovite and (or) biotite, apatite is a very common accessory mineral. Quartz is highly recrystallized and smeared parallel to the mica foliation, and original grain shapes and sizes are not well preserved; plagioclase is very fresh and commonly albite twinned.  Despite the metamorphic features throughout the unit, some outcrops show sedimentary features; planar and tangential cross stratification outlined by heavy mineral laminae is common. (Lewis, written communications, 2002).'
3996|'Dark gray to black, fine- to medium-grained amphibolite gneiss (Lund and others, 1992). Contains plagioclase, hornblende, and minor amounts of quartz; biotite and pyroxene are common in some zones. Iron- and titanium-oxide are accessory minerals. Massive to well foliated and intruded into schist and quartzite. Includes some augen gneiss (Yag unit). (Lewis, written communications, 2002).'
3997|'Light-colored quartzite, muscovitic quartzite, and fine-grained quartz-muscovite-biotite schist (Lewis and others, 1990). Quartzite is typically fine grained; some is sugary to friable but most is well recrystallized and hard.  Locally contains up to 20 percent alkali feldspar. Partings on micaceous interlayers appear to define "beds" 2 to 60 cm thick. Schistosity (Lewis, written communications, 2002).'
3999|'Fine- to medium-grained quartz-feldspar-biotite(-muscovite) gneiss and muscovite-biotite (-quartz) schist. More schistose rocks locally contain sillimanite; garnet is rare.  Gneissic varieties include:1) granular biotite gneiss, which  is a fine-grained quartzo-feldspathic meta-graywacke(?); 2) layered granular biotite gneiss, which is similar to granular rocks but has centimeter-scale layering that possibly is relict bedding; and 3) medium- to coarse-grained gneiss, which has a layered appearance produced by variations in biotite content and which locally grades into migmatite.  Unit includes some dark-colored quartzite and may include augen gneiss where high strain, deep weathering, and the abundance of pegmatites make detection of feldspar augen (Lewis, written communications, 2002).'
4000|'Reddish-brown-weathering, gray schist consisting Tourmaline, epidote, and calcite are along layers. Zircon, apatite, and monazite are common accessory minerals. Copper minerals occur in numerous outcrops.  pCgs probably correlates with the Middle Proterozoic Yellowjacket Formation (R.S. Lewis, unpub.data, July 8, 2002).

Reddish-brown-weathering, gray schist consisting mainly of quartz (50 percent), plagioclase (20-30 percent), biotite (10-20 percent), and less than 10 percent muscovite (Lund and others, 1992). Tourmaline, epidote, and calcite are along layers. Zircon, apatite, and monazite are common accessory minerals. Copper minerals and bedded iron-formation occur in (Lewis, written communications, 2002).'
4001|'Light-colored quartzite, muscovitic quartzite, fine-grained quartz-muscovite-biotite schist (Lewis and others, 1990). Quartzite fine grained; some friable.Locally up to 20% alkali feldspar. Partings on micaceous interlayers define "beds" 2 to 60 cm thick.'
4002|'Quartzite, biotite gneiss, and calc-silicate rocks.  Calc-silicate rocks contain quartz, garnet, diopside, and plagioclase.'
4008|'Glacial deposits including till, outwash, and alluvium.  Landforms common include moraines.'
4009|'Gravel, silt and sand deposited on benches above modern drainages.'
4010|'Generally  fine- grained and petrographically non distinctive. Grande Ronde flows are the thickest of the Columbia River Group. Covers and laps out on rugged topography on older rocks at flow margins: pillows common.  Flow also commonly hackly jointed and pillowed at or near contact with older rocks.  Flows of the Grande Ronde Basalt are divided magnetostratigraphic units.'
4012|'Generally  fine- grained and petrographically non distinctive. May contain numerous  plagioclase phenocrysts. Grande Ronde flows are the thickest of the Columbia River Group. Thickest at NW of map.  Covers and laps out on rugged topography on older rocks at flow margins: pillows common.  Flow also commonly hackly jointed and pillowed at or near contact with older rocks.  Flows of the Grande Ronde Basalt are divided magnetostratigraphic units.'
4013|'Generally coarse-grained, grusy-weathering, and plagioclase-phyric with phenocrysts between 5 and 25   cm.  In Harpster area, vesicular pyroxene diabase containing up to 30% random labradorite laths up to 14 cm.'
4026|'Gabbro, diorite, quartz diorite, norite, and albite granite.'
4027|'Predominantly calcareous phyllite to schist; textural gradation depends on metamorphic grade, which increases from lower greenschist facies in west to upper greenschist facies in east. Lesser amounts of marble, conglomeratic calcareous schist.'
4028|'Gray calcareous slate and phyllite.'
4030|'Metamorphosed basalt and andesite flows and volcaniclasitics, graywackes, argillites, and limestones.'
4031|'Intensely sheared rock.'
4032|'Shear layered and interbedded with greenstone.'
4033|'Primarily green-gray to maroon, lower-greenschist-facies muscovite-chlorite schist: protolith consists of sheared and metamorphosed keratophyre, quartz keratophyre, and spilite.  Also contains volcaniclastic conglomerate beds,  nonnvolcanic sedimentary beds, and limestone lenses. Crops out mainly on west side of Salmon River.'
4039|
4100|'Banded green and white calc-silicate gneiss. Metamorphic equivalent of Ywl.'
4101|'Biotite-hornblende quartz diorite. Intrusion in southeast part of map is foliated and locally mylonitic. Intrusion north of Kelly Creek contains inclusions of fine-grained biotite-hornblende diorite and may be younger (Eocene?).'
4110|'Pink, medium-grained, biotite-hornblende granite to quartz syenite. Miarolitic cavities are common. Mapped as a textural phase of the Whistling Pig pluton (Lund, 1980; Motzer, 1985).'
4111|'Pink, coarse-grained, biotite-hornblende granite to quartz syenite. Grain size averages greater than 5 mm. Sparse to no miarolitic cavities. Mapped as a textural phase of the Whistling Pig pluton (Lund, 1980; Motzer, 1985).'
4112|'Abundant narrow dikes and composite bodies of gray to black diorite, quartz diorite, and tonalite. Fine- to medium-grained equigranular rocks are dominant over porphyritic varieties.'
4113|'Medium- to fine-grained, equigranular to slightly porphyritic biotite granodiorite. Hornblende-bearing and tonalitic near some contacts with metasedimentary rocks. Associated pegmatite and aplite dikes and sills are common.'
4114|
4325|'Shown only in dam area of Cooney Reservoir.'
4326|'Gravel, sand, silt, and clay along active stream channels.'
4327|'Locally derived slope-wash deposits mainly of sand, silt, and clay. Typically thin veneer concealing bedrock, but locally as thick as 30 ft (9 m). Commonly grades into Qal. Locally contains wellrounded cobbles derived from alluvial terrace gravel. May also contain glacial lake deposits behind end moraines.'
4328|'Gravel, sand, silt, and clay deposited in fans being formed by modern streams along major valley margins display characteristic fan-shaped map pattern and convex upward profile. Typically grade upstream into Qal. Thickness ranges from very thin at toe, to as much as 50 ft (15 m) at head of fans.'
4329|'Angular blocks and clasts of bedrock that accumulate below cliffs and steep slopes along the mountain front.'
4330|'Unconsolidated mixture of soil and blocks of bedrock transported down steep slopes by mass wasting. Characteristic hummocky surface with concentric swales and ridges near down-slope limits. Common along steep slopes below resistant rocks but can occur where steep slopes and moisture content produce unstable conditions. Large landslides are common in glacial moraines along the mountain front.'
4331|'Angular and Subangular, coarse gravel derived from local bedrock; gravel deposits occur beneath smooth, concave-upward, pediment surfaces sloping away from the Beartooth Mountains. About 10 (3 m) to about 30 ft (9 m) thick.'
4332|'Unsorted clay- to boulder-size material transported and deposited by glaciers. Characteristic hummocky surface form. Occur in valleys along the mountain front. Clasts are predominantly Archean metamorphic rocks with lesser amounts of quartzite, igneous rocks, dolomite and limestone.'
4333|'Gravel underlying terraces 10 to 20 ft (3.6 m) above altitude of Qal (present altitude of rivers). Mostly cobbles and pebbles with minor amounts of sand and silt. Clasts are mainly granitic igneous rocks, granitic gneiss, schist, and quartzite, with much less limestone and sandstone. Ten to 40 ft (3-12 m) thick.'
4334|'Gravel underlying terraces 20 to 40 ft (6-12 m) above Qal. Mostly cobbles and pebbles with minor amounts of sand and silt. Clasts mainly granitic igneous rocks, granitic gneiss, schist, and quartzite, with much less limestone and sandstone. Ten to 40 ft (3-12 m) thick.'
4335|'Gravel underlying terraces50 to 90 ft (15-27 m) above present altitude of rivers. Mostly cobbles and pebbles and minor amounts of sand and silt. Clasts are mainly granitic igneous rocks, granitic gneiss, schist, and quartzite, with much less limestone and sandstone. Ten to 30 ft (3-9 m) thick.'
4336|'Gravel underlying terraces 200 to 300 ft (60-90 m) above present altitude of rivers. Cobble- and pebble-size clasts are mainly granite, granitic gneiss, schist, and quartzite. Thickness as much as 20 ft (6 m).'
4337|'Gravel underlying terraces 400 to 600 ft (120-185 m) above present altitude of rivers. Occur mainly as small discontinuous erosional remnants. Cobble- and pebble-size clasts are mainly granite, granitic gneiss, schist, and quartzite. Calcite cement locally present, especially at base. Thickness from a very thin remnant to about 20 ft (6 m).'
4338|'Gravel, sand, silt, and clay underlying terraces about 20 to about 600 ft (6-185 m) above present altitude of modern streams and rivers. Equivalent to Qat1- Qat5.'
4339|'Dikes, sills, and irregular-shaped bodies. Andesite, quartz latite, dacite, and rhyolite; commonly porphyritic (Van Gosen and others, 2000).'
4340|'ln the Homestake Mine and Alice E Mine areas, north of Cooke City, composed of clasts of Cambrian sedimentary rocks, Precambrian rocks, altered porphyritic intrusive rocks, and volcanic rocks, and intruded by younger dikes of rhyolite and quartz latite. In the Fisher Mountain area (about 2.8 miles north of Cooke City), composed of aphanitic and fine grained porphyritic dacite, rhyolite, quartz latite and felsite breccia; intruded by quartz-rich dacite and porphyritic and aphanitic dikes, and strongly hydrothermally altered (Van Gosen and others, 2000).'
4341|'Laccoliths, stocks, dikes, and sills in the Lulu Pass and Homestake Mine areas north of Cooke City (Van Gosen and others, 2000)'
4342|'Stock and irregular-shaped intrusive bodies at Scotch Bonnet Mountain, about 3.3 miles north of Cooke City (Van Gosen and others, 2000).'
4343|'Sills in the Cooke City area (Van Gosen and others, 2000).'
4344|'Part of the Absaroka Volcanics in southwest corner of map area. Include basaltic, andesitic, and dacitic flows and flow breccias; rhyolitic ash-flow tuff and vitrophyre, tuff breccias, lahars, agglomerates, agglutinates, conglomerate, and minor andesitic and dacitic intrusive bodies (Van Gosen and others, 2000).'
4345|'Unit named by Calvert (1916) after exposures near the community of Linley (Linley no longer exists but was about 1 mile east-southeast of Luther). These rocks occur along the northern mountain front of the Beartooth Uplift (Calvert, 1916; Jobling, 1974; DeCelles and others, 1991) and are considered to be Laramide synorogenic deposits. Similar rocks occur along the eastern front of the Beartooth Uplift (Laramide synorogenic deposits of Flueckinger, 1970, and Beartooth Conglomerate of DeCelles and others, 1991), and are included here with the Linley Conglomerate. Unconformably overlies the Tongue River Member of the Fort Union Formation, but also overlies an erosional unconformity cut into Upper Cretaceous rocks just south of the map area in Wyoming (DeCelles and others, 1991). The unit consists of mainly reddish brown to gray brown, interbedded conglomerate, coarse-grained sandstone, siltstone, and mudstone; the coarsest facies being generally near the mountain front. Conglomerate cobbles are mostly less than 6 inches in diameter and composed mainly of limestone, andesite porphyry, black chert, metamorphic rocks, and granitic rocks. Paleontologic data indicate the deposits are Paleocene (Flueckinger, 1970; Jobling, 1974; DeCelles and others, 1991). Changes in clast composition in the conglomerates record the unroofing of the Beartooth Uplift, that is, clasts of younger stratigraphic units generally occur near the base and clasts of older rocks occur higher in the section (Flueckinger, 1970; Jobling, 1974; DeCelles and others, 1991). Thickness is about 600 ft (185 m) along the north front (Jobling, 1974). Flueckinger (1970) reports a total thickness of the section along the east front, including exposures in Wyoming, of about 4,200 ft (1,280 m), but exposures on the Red Lodge sheet appear to be about 2,000 ft (610 m) thick. DeCelles and others (1991) report a thickness of more than 2,300 ft 1700 m).'
4346|'Gray to grayish-yellow, fine- to medium-grained sandstone, cross-bedded. Interbedded with brownish-gray carbonaceous shale and siltstone and coal beds. Sandstones ledge forming, commonly support growths of pine trees. Thickness is variable but is as much as 2,800 ft (850 m) (Rawlins, 1986).'
4347|'Predominantly dark-gray to olive shale, and thin, interbedded, yellowish-gray sandstones and siltstone, locally includes yellowish-gray claystone. Typically forms smooth grassy slopes below the Tongue River Member. Thickness 200 to 500 ft (60-150 m).'
4348|'Yellowish-gray, fine- to medium-grained, ledge-forming sandstone, cross-bedded in part. Interbedded with gray to greenish-gray claystone, siltstone, and minor carbonaceous shale. Supports growths of pine trees. Thickness is variable; from about400 ft (120 m)to as much as 1,500 ft (460 m) in the Bear Creek area (Rawlins,1986).'
4349|'Laccoliths, plugs, dikes, sills and irregular-shaped bodies of fine-grained and porphyritic rhyolite, dacite, quartz latite, andesite, and diorite (Van Gosen and others, 2000). '
4350|'Interbedded light-brownish-gray, cliff- and ledge-forming, fine-grained, thin- to thick-bedded sandstone, and gray, pale-greenish-gray and pale-purple-gray mudstones. Sandstone beds support growths of pine trees. Includes basal beds commonly mapped as Lennep Formation that are typical of basal Hell Creek to the east (personal communication, Susan Vuke and Edith Wilde, MBMG). Total thickness of the formation is 900 to l'' 100 ft (275-335 m).'
4351|'Interbedded light-brownish-gray, cliff- and ledge-forming, fine-grained, thick-bedded to massive sandstone, and medium-gray, fissile shale. Sandstone beds are much thicker and more continuous than sandstone beds in the Hell Creek. Sandstone beds support growths of pine trees. Occurs only in the southeast part of the quadrangle, interfingers and changes facies into Hell Creek lithologies in the Joliet area; Lance is used on the map south of Rock Creek and Hell Creek is used to the north. Total thickness of the formation is about 350 ft (105 m).'
4352|'Multiple phases of syenite and monzonite of variable grain sizes and textures, locally altered and mineralized, occurs in a stock near Goose Lake about 7 miles northeast of Cooke City (Van Gosen and others,2000).'
4353|'Dark-gray to medium-gray, fine-grained diorite and diorite porphyry, phenocrysts of plagioclase, hornblende, pyroxene, and locally biotite. Occurs as stocks in the Sliderock Mountain area (Big Timber 30''X 60'' quadrangle, Lopez, 2000) and in the cores of domes in the northwest corner of the map area.  Also occurs as dikes and smaller stocks of diorite porphyry and andesite porphyry and trachyandesite. In the Lodgepole intrusive (Brozdowski, 1983), and in the Ellis Mountain area (on the Big Timber quadrangle, Lopez, 2000) includes xenoliths of rocks derived from the Stillwater Complex. Radiometric age is 74-77 ma (du Bray and Harlan, 1993; du Bray and others, 1994).'
4354|'This unit includes all the volcanic rocks erupted from the Sliderock stratovolcano (du Bray and others, 1994).  Mostly andesite breccia (lahars) gray, pale purple gray, pale greenish gray. Andesite in clasts is porphyritic with phenocrysts of chalky plagioclase, hornblende, and pyroxene; matrix is similar but lighter in color and slightly finer grained. Very resistant, forming cliffs and very rugged topography especially in the northwest part of the quadrangle, which is near the vent zone in Sliderock Mountain area (on Big Timber 30''X 60'' quadrangle, Lopez, 2000). In distal areas, as near town of Fishtail, contains interbeds of andesitic conglomerate and coarse-grained andesitic conglomerate, and clasts are less angular. Locally contains minor flows of porphyritic andesite and basaltic andesite, with phenocrysts of plagioclase, hornblende, and pyroxene. Thickness is at least 1,000 ft (305 m) (du Bray and others, 1994).'
4355|'Dark-gray shale, commonly weathering dark-brownish-gray, fissile, fossiliferous; brownish-gray calcareous concretions and nodules are common. Middle part of formation contains numerous thin, mostly greenish-gray bentonite beds; thin sandstone beds common near the top. The thickness is 100 to 300 ft (30-90 m), thinning westward.'
4356|'Interbedded brownish-gray sandy shale and light-brown to pale-yellowish-brown, argillaceous, very-fine- to fine-grained lenticular sandstone in beds as much as 10 ft (3 m) thick. A basal, massive cliff-forming sandstone is commonly referred to as the Parkman Sandstone and resembles those in the Eagle Sandstone. Sandstones friable to moderately well indurated, cross-bedded, burrowed to bioturbated, and support growths of pine trees. Greenish-gray and pale-maroon-gray mudstones, poor-quality coal, and easily eroded sandstones occur near the top of the formation. The thickness from 700 to 1,000 ft (215-305 m).'
4357|'Brownish-gray, fissile shale with minor interbeds of light-brownish-gray, very argillaceous sandstone. Light-brownish-gray to light-brown, calcareous concretions common, commonly fossiliferous. The upper contact is gradational and conformable, and is placed at the change to ledge-forming sandstones of the overlying Judith River Formation. Thickness of the formation is 100 to 300 ft (30-90 m), decreasing westward.'
4358|'Light-brownish-gray to very-pale orange, very fine- to fine-grained, cross-bedded sandstone, burrowed to bioturbated in part. Locally contains calcareous, light-brown sandstone concretions as much as 15 ft (5 m) in diameter. Usually two or more sandstone intervals with interbedded shale. Contains at least one coal bed west of the town of Bridger, about 4 miles east of the quadrangle, and north of Nye. Thickness is about 150 ft (45 m).'
4359|'Shale and sandy shale, brownish-gray to medium-dark-gray with thin interbedded sandstone. Dusky-red concretions common near base. Sandstone beds thicker and more abundant upward, grading into Eagle Sandstone. Contact with Eagle is placed at the base of the first cliff-forming sandstone. Maximum thickness about 150ft (45 m).'
4360|'Includes Bearpaw Shale, Judith River Formation, Claggett Shale, Eagle Sandstone, and Telegraph Creek Formation.'
4361|'Telegraph Creek Formation: Shale and sandy shale, brownish-gray to medium-dark-gray with thin interbedded sandstone. Dusky-red concretions common near base. Sandstone beds thicker and more abundant upward, grading into Eagle Sandstone. Contact with Eagle is placed at the base of the first cliff-forming sandstone. Maximum thickness about 150ft (45 m).

Niobrara Formation: Mostly medium-gray to dark-gray shales, partly calcareous.'
4363|'Light-brownish-gray fine-grained thick-bedded to massive, "salt and pepper" sandstone. Contains three sandstone intervals interbedded with dark-gray, fissile shale. Full interval not exposed on the Red Lodge quadrangle. Total thickness about 350 ft (106 m) on the Livingston quadrangle to the west (Berg and others, 2000).'
4364|' Mowry Shale is interbedded, siliceous, very fine- to fine-grained sandstone, siltstone, and shale. Contains several prominent bentonite beds. Sandstones and siltstones mostly light gray to medium gray, with a silvery sheen. Fish scales on bedding planes of sandstones and siltstones are characteristic of the formation. Thickness about 300 ft (90 m).'
4365|'Thermopolis Shale is predominantly dark-gray, fissile shale, bentonitic shale, containing several beds of bentonite. Has hematitic concretionary zone near base. Fall River Sandstone is brownish-gray, thinbedded, argillaceous, fine-grained, quartz sandstone. Generally poorly exposed in map area; mostly covered by glacial deposits. About 1,000 ft (305 m) thick.'
4366|'Brownish-gray, thin-bedded, argillaceous, fine-grained, quartz sandstone. Generally poorly exposed in map area; mostly covered by glacial deposits. Thickness about 100 ft (30 m).'
4368|'Mostly reddish-brown, olive-gray, and dusky-purple mudstones with interbedded, lenticular, fine- to coarse-grained sandstones. Locally thick, lenticular, fluvial, fine-grained sandstone (Greybull Sandstone) is present at the top. The basal Pryor Conglomerate Member is brown to gray conglomerate and pebbly coarse-grained sandstone, 20 to 60 ft(6-18 m) thick. Thickness of the Kootenai Formation is about 500 ft (150 m).'
4369|'Variegated, mainly greenish-gray and pale-reddish-brown mudstone. Very fine- to fine-grained, quartzose, calcareous, cross-bedded sandstones are commonly present at about mid-section, 5 to 10 ft (1-3 m) thick, but locally can be as much as 30 ft (9 m) thick. Fossil dinosaur remains locally present. Upper contact placed at the base of the Pryor Conglomerate. The basal contact is placed at the top of fossiliferous, calcareous sandstone and coquina of the underlying Swift Formation. Thickness is about 200 ft (60 m).'
4370|'Kootenai Formation mostly reddish-brown, olive-gray, and dusky-purple mudstones with interbedded, lenticular, fine- to coarse-grained sandstones. Locally thick, lenticular, fluvial, fine-grained sandstone (Greybull Sandstone) is present at the top. The basal Pryor Conglomerate Member is brown to gray conglomerate and pebbly coarse-grained sandstone, 20 to 60 ft(6-18 m) thick. Thickness of the Kootenai Formation is about 500 ft (150 m).

Morrison Formation variegated, mainly greenish-gray and pale-reddish-brown mudstone. Very fine- to fine-grained, quartzose, calcareous, cross-bedded sandstones are commonly present at about mid-section, 5 to 10 ft (1-3 m) thick, but locally can be as much as 30 ft (9 m) thick. Fossil dinosaur remains locally present. Upper contact placed at the base of the Pryor Conglomerate. The basal contact is placed at the top of fossiliferous, calcareous sandstone and coquina of the underlying Swift Formation. Thickness is about 200 ft (60 m).'
4371|'Individual formations are not mapped separately; includes the Swift, Rierdon, and Piper Formations. The Swift is interbedded medium gray shale, limestone, and calcareous sandstone; fossiliferous. Brownish-gray, fossiliferous, very sandy limestone occurs at the top of the formation, and commonly has brownish-gray coquina at the top.'
4372|'Interbedded moderate reddish-brown fine-grained sandstone, siltstone, and mudstone. Maximum thickness is about 100 ft (330 m), thinning westward to o near the west edge of the quadrangle.'
4373|'Includes Morrison Formation, Ellis Group, and Chugwater Formation.'
4374|'Formations not mapped separately because of narrow outcrop width. Phosphoria is light-gray limestone, sandstone and quartzite, commonly grayish-pink, cherty; thickness is 50 to 75 ft (15-23 m). The Tensleep Sandstone is light-brown to very pale-orange sandstone, fine-grained, well sorted, well rounded, cross-bedded. Locally contains thin limestone beds, locally cherty near the top, and locally silicified to form quartzite; about 250 ft (75 m)thick. The Amsden Formation is interbedded grayish-pink to light-red mudstone, limestone, and siltstone. Limestones are commonly cherty. Unconformably overlies karst surface developed on limestone of the Madison Group. Characteristically produces pink stain on underlying cliffs of Madison Group; thickness about 200 ft (60 m) but locally, tectonically thinned to only a few ft along mountain front. Total thickness of lumped unit is about 500ft (150 m).'
4375|'Limestone and dolomitic limestone, light-gray to light-brownish-gray. Thick-bedded to massive in the upper part (Mission Canyon limestone) and thin-bedded to thick-bedded in the lower part (Lodgepole Limestone).  Also contains thin, interbedded, gray shales. Fossiliferous and cherty beds are present throughout. Collapse features and caves are common at the upper karst surface. Thickness of the Madison is 800to 1,000 ft (240-305 m).'
4376|'Includes Jefferson and Three Forks Formations, and Big Horn Dolomite. The Jefferson is dolomitic limestone, light brownish gray, fetid, poorly exposed, typically occurs as float. The Three Forks is mainly yellowish-weathering, argillaceous limestone and medium-gray shale, very poorly exposed. The Big Horn Dolomite is cliff-forming dolomite and dolomitic limestone, very light gray to very pale orange, lower part massive, thin to thick bedded in upper part. Has characteristic pock-marked surface due to differential weathering. Total thickness of this interval is about 600 ft (185 m).'
4377|'Cliff-forming dolomite and dolomitic limestone, very light gray to very pale orange, lower part massive, thin to thick bedded in upper part. Has characteristic pock-marked surface due to differential weathering. Thickness about 400ft (120 m).'
4378|'Light-reddish sandstone and quartzite, greenish-gray shale and sandy shale, gray thin-bedded limestone and greenish-gray flat-pebble limestone conglomerate. Includes the Flathead, Wolsey, Meagher, Park, and Pilgrim Formations. Thickness is 600 to 800 ft (180-245 m).'
4379|'Descriptions below taken from Ordovician and Cambrian descriptions:  Cliff-forming dolomite and dolomitic limestone, very light gray to very pale orange, lower part massive, thin to thick bedded in upper part. Has characteristic pock-marked surface due to differential weathering. Thickness about 400ft (120 m).

Light-reddish sandstone and quartzite, greenish-gray shale and sandy shale, gray thin-bedded limestone and greenish-gray flat-pebble limestone conglomerate. Includes the Flathead, Wolsey, Meagher, Park, and Pilgrim Formations. Thickness is 600 to 800 ft (180-245 m).'
4380|'Descriptions below taken from Paleozoic descriptions:

Formations not mapped separately because of narrow outcrop width. Phosphoria is light-gray limestone, sandstone and quartzite, commonly grayish-pink, cherty; thickness is 50 to 75 ft (15-23 m). The Tensleep Sandstone is light-brown to very pale-orange sandstone, fine-grained, well sorted, well rounded, cross-bedded. Locally contains thin limestone beds, locally cherty near the top, and locally silicified to form quartzite; about 250 ft (75 m)thick. The Amsden Formation is interbedded grayish-pink to light-red mudstone, limestone, and siltstone. Limestones are commonly cherty. Unconformably overlies karst surface developed on limestone of the Madison Group. Characteristically produces pink stain on underlying cliffs of Madison Group; thickness about 200 ft (60 m) but locally, tectonically thinned to only a few ft along mountain front. Total thickness of lumped unit is about 500ft (150 m).

Limestone and dolomitic limestone, light-gray to light-brownish-gray. Thick-bedded to massive in the upper part (Mission Canyon limestone) and thin-bedded to thick-bedded in the lower part (Lodgepole Limestone).  Also contains thin, interbedded, gray shales. Fossiliferous and cherty beds are present throughout. Collapse features and caves are common at the upper karst surface. Thickness of the Madison is 800to 1,000 ft (240-305 m).

Descriptions below taken from Ordovician and Cambrian descriptions:  Cliff-forming dolomite and dolomitic limestone, very light gray to very pale orange, lower part massive, thin to thick bedded in upper part. Has characteristic pock-marked surface due to differential weathering. Thickness about 400ft (120 m).

Light-reddish sandstone and quartzite, greenish-gray shale and sandy shale, gray thin-bedded limestone and greenish-gray flat-pebble limestone conglomerate. Includes the Flathead, Wolsey, Meagher, Park, and Pilgrim Formations. Thickness is 600 to 800 ft (180-245 m).'
4381|'Includes dikes, sills, stocks and irregular-shaped bodies of alkali-olivine dolerite, metadolerite, metagabbro, and quartz dolerite (Van Gosen and others, 2000). Ages of dikes are in three sets: 2.5-2.8 b.y., about 1.37 b.y., and about 740 Ma (Mueller and others, 1985).'
4382|'Small bodies associated with quartz monzonite (Agr) south of the Stillwater Complex (Van Gosen and others, 2000).'
4383|'Stocks and irregular bodies of fine-, medium-, and coarse-grained quartz monzonite and aplite south of the eastern exposures of the Stillwater Complex. Occur in intrusive contact with the Stillwater Complex (Van Gosen and others, 2000).'
4384|'Layered ultramafic and mafic rocks from peridotites and pyroxenites at the base (ultramafic series) to gabbros and anorthosite in the upper part (banded series). Maximum exposed thickness in Beartooth Mountains is about 22,000 ft (6,700 m). Only units 1-5 are exposed on Red Lodge quadrangle.'
4385|'Middle mixed zone - Contains three cycles. Sequence from top to bottom in each cycle is plagioclase-olivine and (or) plagioclase-orthopyroxene cumulate, and plagioclase cumulate. Though it is dominant throughout, the cumulus plagioclase component decreases and the cumulus olivine component increases from one cycle to the next lower one. Only the lowermost cycle seems to be present west of the Boulder River. The zone is cut out by unconformity on Mount Rae, to the west, and by the Horseman Thrust, on the ridge between Picket Pin Creek and West Fork Stillwater River to the east. However, part of the unit reappears from under the unconformity near the east end of the complex. About 90 m of plagioclase cumulate with a little postcumulus clinopyroxene is exposed along the road to Benbow Mine. Plagioclase-olivine cumulate occurs on a ridge northwest of the road. Thickness of the Middle mixed zone is 0-400 m.

Middle gabbro zone - Chiefly plagioclase-orthopyroxene-clinopyroxene cumulate and plagioclase-clinopyroxene cumulate on Contact Mountain, where the zone was first described and defined by Segerstrom and Carlson (1977). West of the Boulder River the lower third of the zone is plagioclase cumulate. A sharp change of lithofacies eastward across the East Boulder River brings in more plagioclase cumulate and cumulus olivine. A distinctive feature of the zone near Picket Pin Mountain is augen-like segregations of plagioclase parallel to regional foliation. Four-phase rock, plagioclase-orthopyroxene-clinopyroxene-olivine cumulate is identified in some outcrops, especially on the eastern part of the ridge between Picket Pin Creek and Iron Creek. To the west the zone is truncated by the un-conformity on Mount Rae. Near West Fork Stillwater River the unit is cut out along the Horseman Thrust, but farther east it reappears south of Horseman Flats. It is cut out again in the Stillwater River valley and farther east until it finally reappears near the road to Benbow Mine. There, the zone is chiefly plagioclase cumulate with post-cumulus orthopyroxene. Some plagioclase-clinopyroxene cumulate present. Thickness 0-280 m.

Lower mixed zone - Principally plagioclase-olivine cumulate with 5-40 percent cumulus olivine and smaller amounts of post-cumulus clinopyroxene. Plagioclase cumulate and plagioclase-clinopyroxene cumulate with scattered grains of cumulus olivine (<5 percent) make up some beds. The middle third of the zone is almost all plagioclase cumulate on the west side of the Boulder River. Alternating bands of plagioclase cumulate and plagioclase-olivine cumulate characterize outcrops at the bottom of the zone on the first spur ridge east of the Stillwater River. The exposure is discontinuous, as it is cut out by faulting and unconformity at five different places. The westernmost exposure of the unit is just south of Mount Rae. Thickness of the zone is 0-300 m.'
4386|'Mostly plagioclase cumulate with oikocrysts of clinopyroxene. The upper contact is defined at the top of a relatively thick plagioclase cumulate layer: sulfides were noted in this rock near the east end of Contact Mountain and on the first spur ridge east of the Stillwater River. Along the road to Benbow Mine cumulus olivine occurs in varying amounts throughout the zone, mostly <5 percent; some of the olivine is poikilitic in oikocrysts of clinopyroxene. Poikilitic olivine in plagioclase cumulate is also noted at the bottom of the zone on the first spur ridge east of the Stillwater River. The zone is exposed continuously along the entire outcrop of the Stillwater Complex, except where it is concealed by Quaternary deposits and except for one short stretch at West Fork Stillwater River and another a little west of the main Stillwater River that are cut out along the Horseman Thrust. Thickness 0-480 m.'
4387|'Lower gabbro zone - Largely plagioclase-two pyroxene cumulate. Layers of plagioclase cumulate, plagioclase-clinopyroxene cumulate, and plagioclase-orthopyroxene cumulate are interspersed throughout the sequence. "Pillow troctolite" (Hess, 1960, p. 82-83), a pegmatoid plagioclase-olivine cumulate, occurs as a crosscutting injection or replacement in fine-grained plagioclase cumulate and plagioclase-clinopyroxene cumulate at the top of the zone about 750 m west of the 10,056-ft summit of Contact Mountain. Lenses of plagioclase-olivine cumulate and olivine cumulate occur at the top of the zone southeast of Contact Mountain and southwest of Picket Pin Mountain. "Inch-scale" layered rock is exposed a few tens of meters below the top of the zone at various localities along the strike of layering. The classic exposure of this unusual rock is in a landslide along the road to the Mountain View mine on west side of valley of Stillwater River, where disc-shaped oikocrysts of clinopyroxene are alined edgewise to form vertical dark layers a few millimeters to 2 or 3 cm thick. The repeating dark layers are generally separated by 2-3 cm of light-colored plagioclase cumulate. Alternation of layers is fairly uniform for 10-20 m across strike, but deviations occur in which the layers are paired or even more complexly grouped. Other exposures of inch-scale layering, at the same stratigraphic position, are: (1) on both sides of the gorge of lower Brownlee Creek, about 1 km west of the East Boulder River, (2) on the spur ridge about 1.8 km east of the Stillwater River (a little olivine is present in the upper part of the layered zone here), and (3) on the spur ridge immediately west of Prairie Creek. A thick sequence of plagioclase cumulate is sandwiched in plagioclase-two pyroxene cumulate of the Lower gabbro zone between Brownlee Creek and Iron Creek. The middle of the Lower gabbro zone is interrupted by a few meters of plagioclase-olivine cumulate and olivine cumulate overlain by plagioclase cumulate well exposed as vertical beds in a cut on the road to Mountain View Mine in SW corner sec. 16, T. 5 S., R. 15 E. Plagioclase-olivine cumulate is interbedded with plagioclase cumulate through much of the sequence on the spur ridge about 1.8 km east of the Stillwater River, so that the Lower gabbro zone there bears little resemblance to a typical section on the south side of the 10,065-ft summit of Contact Mountain. Olivine gradually diminishes toward the eastern end of the complex, and it is not seen in exposures of the Lower gabbro zone along the road to Benbow Mine.  Repeating cycles of plagioclase cumulate, plagioclase-orthopyroxene cumulate, and plagioclase-two pyroxene cumulate can be recognized in the middle of the Lower gabbro zone for a short distance westward from Brownlee Creek.  There are at least two showings of inch-scale layering in plagioclase cumulate a little over 100m above the bottom of the zone.  One of these is on the spur ridge east of the Stillwater River. The other is about 75 m north of down-faulted limestone on the spur ridge west of Prairie Creek. Contact of the zone with the underlying Norite zone tends to be transitional, particularly from the East Boulder River westward to the divide between the East Boulder and main Boulder River. The transition is between plagioclase-two pyroxene cumulate above and plagioclase-orthopyroxene cumulate below. All gradations between these two rocks are exhibited within a stratigraphic range of about 200 m, where interstitial clinopyroxene and fine-grained cumulus clinopyroxene occur in varying proportions with coarser-grained cumulus orthopyroxene. Except where the unit is covered with fill deposits in the main river valleys, the Lower gabbro zone is continuously exposed from southwest of Mt. Rae to the east side of Black Butte, a distance of 40 km. Thickness 0-590 m. Near where it is cut off at either end by unconformity, the zone is only 100-200 m thick.

Norite zone - The upper contact is where rock containing cumulus orthopyroxene readily seen in hand specimen underlies rock devoid of easily recognizable cumulus orthopyroxene. The upper part of the zone is mainly plagioclase-orthopyroxene cumulate. Oikocrysts of clinopyroxene are common in this rock and also in interlayers of plagioclase cumulate. A group of mixed layers provides a major break in continuity about halfway down the sequence. There, through a stratigraphic interval of about 100 m, 28 distinguishable layers a meter or so thick have been counted in one section. This section includes eight olivine-bearing layers interspersed between layers of plagioclase cumulate and plagioclase-orthopyroxene cumulate. Among these strata lies a zone, centered approximately at the divide between Brownlee Creek and Graham Creek that for a distance of 5.5 km and through a thickness of 2.1 m, has an average grade of 0.65 troy oz of Pt and Pd per short ton. This is one of the richest known deposits of platinum-group metals (PGM) in the world. The PGM zone there occurs where a layer of olivine cumulate and a layer of plagioclase cumulate together first became dominant upsection from the base of the Norite zone (Todd and others, 1979, p. 461-462, 464). The Pt and Pd are contained in sulfides, native alloys, arsenides, antimonides, bismuthinites (Cabri and La Flamme, 1974). The principal PGM-bearing minerals are pyrrhotite and pentlandite. Geochemical sampling and the driving of two adits by Johns-Manville in 1976-1980 have shown that the package of mixed layers containing one or more zones of PGM anomalies extends through the entire 40 km of strike length of the Norite zone. Drilling and the driving of an adit by Anaconda in 1979-1980 confirmed the existence of ore-grade PGM near the main Stillwater River. Facies changes within the zone result locally in fewer olivine-rich layers, lensing of pegmatite, and changes in stratigraphic position and grade of PGM anomalies. Two ore zones with a stratigraphic separation of 6-8 m have been locally encountered by Johns-Manville (E. L. Mann, oral commun., August 1980). Ore-grade PGM is encountered through a stratigraphic interval of 20-26 m by Anaconda in the Minneapolis adit (R. N. Miller, oral commun., August 1980). Below the group of mixed layers there is an interval of plagioclase-two pyroxene cumulate, then a much wider interval of principally plagioclase-orthopyroxene cumulate to the bottom of the section. Off-lap and slump structures indicating floor tilt, as well as graded bedding are seen in the lower interval of plagioclase-orthopyroxene cumulate on the west side of the Stillwater River. Scattered injections of pegmatoid orthopyroxene cumulate (bronzite), irregular in shape, crosscutting the layering, and locally rich in sulfides occur at the base of the Norite zone in two areas: (1) for about 1 km northwest of the East Boulder River, and (2) between Iron Mountain and Iron Creek. These sulfides also contain anomalous concentrations of platinum-group metals and were intensively drilled and trenched by Johns-Manville before the more persistent zone of interest was discovered higher in the Norite zone. At the maximum thickness of the zone, across the east end of Contact Mountain, the generalized sequence from top to bottom is: plagioclase-orthopyroxene cumulate, 250 m; mixed group (distinctively plagioclase cumulate and plagioclase-olivine cumulate), 100 m; plagioclase-two pyroxene cumulate, 75 m; and plagioclase-ortho-pyroxene cumulate 275 m making a total thickness of 700 m. The plagioclase-two pyroxene interval thins considerably west of the Brownlee Creek-Graham Creek divide and east of the West Fork of the Stillwater. To the west, the entire Norite zone is faulted out by the Lost Creek fault, near the Boulder River, and to the east the outcropping zone disappears in the moraine of West Fishtail Creek.'
4388|'orthopyroxene (bronzite) cumulate of the Ultramafic series. At the contact between the Banded upper series and the underlying Ultramafic series plagioclase abruptly ceases to occur as a cumulus mineral, and immediately below the contact the only cumulus mineral present is orthopyroxene. "The units are fine to coarse grained. Units in which grain size changes from fine to coarse upward appear to form repeated cycles throughout the sequence. From 3-6 m below the top of the Bronzitite zone in the Benbow area, a concentration of cumulus chromite can be traced for several meters along strike" (Page, 1977, p. 28). This chromite zone is also exposed on the north slope of the 9,587-ft hill 1.5 km east of Chrome Mountain, where it manifests itself in several layers a few millimeters thick and in local disseminations of very fine-grained cumulus chromite. Interstitial plagioclase and oikocrysts of clinopyroxene are common throughout the zone. Through most of the exposed length of the Stillwater Complex the Bronzitite zone is 350-1,000 m thick. West of the Boulder River it is cut out by the Lost Creek Fault and to the east the zone disappears in the moraine of West Fishtail Creek.'
4389|'Peridotite zone - The lower of the two zones that comprise the Ultramafic series. It consists of cyclic units of bronzite cumulates, olivine-bronzite cumulates, olivine cumulates, and chromite cumulates. At least 15 cyclic units have been recognized in the Peridotite zone. Cyclic units are of two types: (1) normal, complete units, and (2) beheaded units, (Jackson 1970, p. 390-401) that lack an olivine plus bronzite layer or bronzite layer or both. "Cumulus chromite and cumulus chromite plus olivine occur in at least 13 of the cyclic units near the base or in the lower part of the olivine cumulates" (Jackson, 1963). Chromite has been produced at three principal mines in the Stillwater Complex: Benbow, to the east; Mountain View, near the center; and Gish, in the western part. The Peridotite zone has an average thickness of about 1,000 m. It is probably not over 100 m thick where it is the only Stillwater rock exposed at the east end of the complex. There it is directly overlain by Paleozoic strata and in fault contact with older granite and metamorphic rocks. Near the Boulder River, to the west, the Peridotite zone is cut out by the Lost Creek fault.

Basal series - Shown as two separate zones on the Page and Nokleberg map (1974). Has spotty outcrop distribution along the southern edge of the Stillwater Complex. Locally as much as several hundred meters thick.

From Zientek and others (2002): The Basal series is a laterally persistent, but locally heterogeneous unit made up of bronzite-rich cumulates containing minor segregations of noncumulate mafic rock and inclusions of Archean metamorphosed sedimentary rocks (Page, 1979; Zientek, 1983; Zientek and others, 1985). It is approximately 150-m thick. The Basal series can be divided into two zones, an upper Basal bronzite cumulate zone and a lower Basal norite zone (Page, 1979). The Basal norite zone is characterized by locally-variable textures and proportions of minerals; orthopyroxene is the predominant cumulus mineral, but cumulus plagioclase, olivine, augite, inverted pigeonite, and chromite occur locally. The Basal bronzite cumulate zone consists predominantly of bronzite cumulates. Sulfide mineral accumulations are typical of the lower part of the Basal series; generally, the proportion of sulfide minerals increases toward the base of the complex (Page, 1979).

The Basal norite zone as mapped by Page and Nokleberg (1974) includes a suite of sills and dikes that intrude metasedimentary rocks near the base of the complex (Zientek, 1983; Helz, 1985). Zientek and others (1985) and Helz (1985) refer to the sill and dike rocks as Stillwater-associated sills and dikes because they are spatially and compositionally distinct from the layered cumulates that make up the bulk of the complex. At least five distinct compositional types of sills and dikes were recognized by Helz (1985), who referred to them as groups 1 through 5. Diabasic-textured rocks are slightly older than the Stillwater Complex (Premo and others, 1990) and include group 1-gabbro norites (2,7111 Ma) and group 4 high Ti-norite (2,7123 Ma). Sulfide-bearing ultramafic sills and dikes (groups 2 and 3) are comprised of lithologies that range from cumulates to more liquid-like compositions that resemble siliceous high-magnesium basalts (Sun and others, 1989); the age of these rocks is indistinguishable from the age of the Stillwater Complex (2,70310 Ma). The group 2 and 3 sills may be petrologically related to cumulates in the overlying Basal series (Zientek, 1983). Group 3 sills and dikes contain disseminated (less than 10 volume percent), matrix (10 to 60 volume percent), and massive (greater than 60 volume percent) accumulations of sulfide minerals. However, accumulations of matrix and massive sulfide minerals are largely restricted to the group 3 mafic norite sills and dikes near mineralized Basal series cumulates (Zientek, 1983).'
4390|'Predominantly granitic gneiss and migmatite; commonly consists of alternating bands of more felsic and more mafic gneiss; formation and amphibolite (Van Gosen and others, 2000). Contains inclusions of metasedimentary rocks (granitic gneiss of Van Gosen and others, 2000).'
4391|'Stock-like mass composed of metanorite and metagabbro.  Occurs in southeastern part of map area (Van Gosen and others, 2000).'
4392|'Irregular-shaped bodies and lenses of olivine-bearing rocks and serpentinite in the southeast part of the map area (Van Gosen and others, 2000).'
4393|'Biotite schist that includes minor quartzite, iron.'
4394|'Mostly tabular and lenticular bodies enclosed in granitic gneiss and migmatite (Van Gosen and others, 2000).'
4395|'Metasedimentary rocks consisting predominantly of schist and hornfels and minor quartzite, amphibolite, and iron-formation; contact metamorphosed to hornblende-hornfels and pyroxene hornfels facies at and near the base of the Stillwater Complex (Van Gosen and others, 2000).'
4396|'Amphibolite, micaceous quartzite, and gneiss. Also includes some small bodies of chromite-bearing serpentinite. Occurs only in southeastern part of map area (Van Gosen and others, 2000).'
4397|'Thermopolis Shale is predominantly dark-gray, fissile shale, bentonitic shale, containing several beds of bentonite. Has hematitic concretionary zone near base. Fall River Sandstone is brownish-gray, thinbedded, argillaceous, fine-grained, quartz sandstone. Generally poorly exposed in map area; mostly covered by glacial deposits. About 1,000 ft (305 m) thick.

Kootenai Formation mostly reddish-brown, olive-gray, and dusky-purple mudstones with interbedded, lenticular, fine- to coarse-grained sandstones. Locally thick, lenticular, fluvial, fine-grained sandstone (Greybull Sandstone) is present at the top. The basal Pryor Conglomerate Member is brown to gray conglomerate and pebbly coarse-grained sandstone, 20 to 60 ft(6-18 m) thick. Thickness of the Kootenai Formation is about 500 ft (150 m).'
4401|'Fault related Tertiary andesitic vent breccia dikes trending approximately N 65 degrees W.  At Nellies Butte and several others in vicinity including Fishtail Butte.  Contact of Claggett and Judith River formations near base of intrusion. Structurally this area is along the crest of the Dean Dome. This dome and several others (McKay, Golden, Dry Creek) are located along the Nye-Bowler lineament.  Dean Dome is a faulted dome with the trace of the fault following the andesitic dikes at a strike of N 65 W.  (Chadwick, 1989, p. 481).'
4500|'Sand, silt, and clay deposited in broad, open stream valleys and in confined ephemeral stream channels.  Maximum thickness unknown.'
4501|'Sand, silt, clay, and pebble to cobble gravel deposited in narrow stream channels and on broad alluvial slopes at base of low hills and mountain fronts.  Locally includes thin colluvial deposits.  Generally less than 5 m thick.'
4502|'Unconsolidated deposits of silt, sand, angular pebbles and cobbles formed by mass movement downslope.  Thickness generally less than 2 m.'
4503|'Sand, silt, clay, and pebble to cobble gravel deposited in narrow stream channels and on broad alluvial slopes at base of low hills and mountain fronts.  Locally includes thin colluvial deposits.  Generally less than 5 m thick.

Unconsolidated deposits of silt, sand, angular pebbles and cobbles formed by mass movement downslope.  Thickness generally less than 2 m.'
4504|'Poorly sorted silty sand and gravel deposited in small alluvial fans along valley margins and around hills and mountains.  Maximum thickness unknown.'
4505|'Active, small to large alluvial fans along valley margins.'
4506|'Inactive, generally large alluvial fans, most of which were deposited along the east side of the Madison Valley; fans are weakly dissected and locally cut by Holocene fault scarps.'
4507|'Translucent tan to brown, well-sorted, moderately frosted quartz sand grains comprise sand dune field in northern Centennial Valley.  Maximum thickness (dune height) about 10 m.'
4508|'Unsorted, unstratified angular clasts and slabs as much as 2 m across that accumulate at the base of cliffs and very steep slopes.'
4509|'Unconsolidated lobate to elongate deposits of coarse gravel and boulders in glacial cirques or at the base of cliffs above timberline.  Older deposits are locally covered by thin soil and vegetation.  Thickness generally less than 20 m.'
4510|'Unsorted accumulation of angular boulders on steep slopes.'
4511|'Pebble- to boulder-size gravel and sand on low terraces adjacent to major streams.  Maximum exposed thickness about 5 m.'
4512|'Unconsolidated gravels deposited on lowest terraces of modern streams.'
4513|'Unconsolidated gravels deposited on terraces above lowest terraces in modern stream valleys.'
4514|'Coarse, unconsolidated deposits of locally derived, angular pebbles, cobbles, and boulders associated with fine-grained matrix of silt and sand. On south and east sides of Gravelly Range, huge landslides where length and width are measured in km include large toreva blocks of Huckleberry Ridge Tuff (Thr) deposited on unconsolidated sand and silt of the Neogene Six Mile Creek Formation (Tsc); on the west side of the Gravellys, landslides of similar size reflect massive dip-slip slope failure of clay-rich, tuffaceous, weakly indurated Cretaceous formations. Maximum thickness probably near 60 m.'
4515|'Light-brown to brown, well-sorted, unconsolidated sand, silt, and clay veneer on undissected surfaces underlain mainly by basin-fill deposits.  Marked, in part, by multiple strand lines that outline limit of dwindling glacial lake.  Thickness unknown;  probably less than 2 m.'
4516|'Generally poorly sorted, bouldery, layered sand and gravel deposited by glacial meltwater.'
4517|'Poorly sorted, unconsolidated deposits of silt, sand, gravel, and boulders in, commonly adjacent to, and locally at the mouths of major alpine valleys.  Deposits are both Pinedale and Bull Lake in age; cirque moraines and pretalus ramparts are Holocene in age.  Maximum thickness is unknown.'
4518|'Weakly dissected deposits of pebbles and cobbles of generally angular to subrounded, unsorted and unconsolidated sedimentary and crystalline rocks in a fine-grained, pale-yellowish-brown matrix.  Deposited on gently dipping surfaces related to the development of the Madison Valley.  Maximum thickness about 5 m.'
4519|'Sand and pebble- to boulder-size gravel deposits on terraces along the Ruby River that are about 60-100 m above adjacent stream level.'
4520|'Isolated sand and pebble- to boulder-size gravel deposits at high elevations in the Gravelly and Centennial Ranges.'
4521|'Thin alluvial and fluvial sand and pebble-size gravel deposits restricted to abandoned stream valleys in the Gravelly Range.'
4522|'Rhyolitic flows erupted from vents in the Yellowstone Caldera; flows contain abundant phenocrysts of mainly quartz and sanidine; plagioclase phenocrysts are conspicuous in their absence. Maximum thickness about 300 m.'
4523|'Rhyolitic ash-flow tuff, light-gray, dense, fine-grained to aphanitic with angular to rounded phenocrysts of quartz, sanidine, pyroxene, and olivine that make up as much as 25 percent of volume of rock.'
4524|'Medium- to light-gray, dense basalt that contains moderately abundant plagioclase phenocrysts and rare olivine phenocrysts; occurs as scattered, thin flows in the vicinity of West Yellowstone.'
4525|'Light-gray, locally pale-red, fine-grained to aphanitic, densely welded ash-flow tuff, with phenocrysts composing as much as 20 percent of rock.  Thickness to east of map area ranges from 180 to 300 m.'
4526|'Ash-flow tuff lithologically similar to overlying upper member; the two members are separated by a partially welded tuff locally associated with a sorted and bedded crystal ash several cm thick.'
4527|'Light-gray rhyolite flows conformably underlie Lava Creek Tuff; rhyolite is variable in appearance but contains conspicuous phenocrysts of sanidine, quartz, and plagioclase that make up 30-50 percent of the volume of the rock.  Maximum thickness to east of map area is 450 m.'
4528|'Tuff, mapped in the Gravelly Range, where it thins dramatically to less than 1 m in the north, and in the northern Gallatin Mountains in the northeast part of the quadrangle.'
4529|'Pinkish-gray, gray, to brown welded tuff containing abundant phenocrysts of sanidine and quartz (25 and 10 percent, respectively); uppermost part is locally nonwelded, light pink on weathered surfaces, and contains noncompacted pumice fragments.'
4530|'Medium- to dark-gray welded tuff with sparse (less than 5 percent) phenocrysts; base of the unit is a vitrophyre overlain by densely welded tuff that becomes only partly welded at the top.'
4531|'Dark-gray to black, dense, fine-grained flow rock, commonly vesicular or columnar jointed, and containing sparse olivine phenocrysts.  Maximum thickness in southern Gravelly Range along the West Fork of the Madison River is near 120 m.  In Centennial Range, divided into two similar mafic flow sequences separated by rhyolitic flows (Tfv).  Upper flows are basalt to basaltic andesite, sparsely porphyritic, and interlayered with thin, discontinuous beds of mudflow breccia; lower sequence consists of lava flows and flow breccias of dark-gray to brownish-black basalt, basaltic andesite, and gray, brown, and yellowish-brown andesite with fewer mafic flows lowermost in the sequence.  All rocks are porphyritic; basaltic rocks contain plagioclase and olivine phenocrysts whereas andesite contains sparse to abundant phenocrysts of plagioclase and at least one mafic mineral in a glassy to aphanitic groundmass. Total thickness about 870 m.'
4532|'In Centennial Mountains, consists of two units: upper sequence consists of light-gray, yellowish-gray, and brown porphyritic dacite and rhyodacite flows and flow breccias interlayered with thin, discontinuous beds of mudflow breccia; maximum thickness about 350 m; lower sequence is light- to brownish-gray mudflow breccia and mudstone containing poorly sorted volcanic rock fragments in an ashy matrix; lower sequence ranges in thickness from 0 to 60 m.  '
4533|'Large to small plugs and sills of basalt and basaltic andesite exposed in western part of map area; largest plug is Black Butte in the Gravelly Range.  In eastern part of map area includes sills of dacite porphyry and minor shoshonite.'
4534|'In Centennial Mountains consists of dark-gray to black, fine-grained to aphanitic pyroxene trachyte porphyry; augite, olivine, and andesine are common phenocrysts.  Thickness unknown.'
4535|'Weakly consolidated. tan to light-orange-brown, laminated, tuffaceous mudstone, siltstone, sandstone, and lithic pebble conglomerate; maximum exposed section along the West Fork of Madison River is about 70 m.'
4536|'Weakly consolidated, cream-colored, tuffaceous mudstone commonly containing calcareous concretions, interlayered with lesser amounts of sandy siltstone and granule-pebble conglomerate; maximum exposed thickness at Lion Mountain at the crest of the Gravelly Range, is about 260 m.'
4537|'Unconsolidated cobbles and boulders of subrounded metamorphic rock in scattered exposures along the crest of the Gravelly Range; maximum preserved thickness about 10 m.'
4538|'Limestone and limestone conglomerate interbedded with varying amounts of siltstone and sandstone.  Best exposures are at Red Hill in the Gravelly Range where basal siltstone and limestone conglomerate are interlayered with lenses of well-rounded quartzite gravel in an angular quartz sand matrix; gravel is similar to underlying stream gravel deposits (Kbeg) and may have been derived, in part, from these fluvial deposits.  The lacustrine limestone consists of medium- to coarse-crystalline, light-gray limestone locally containing abundant snails, stromatolites, and oncolites; also commonly interlayered with coarse-grained sandstone, siltstone, and intraformational limestone rip-up conglomerate.  Many of the conglomerate lenses consist of clasts of locally derived  Paleozoic rocks upon which these rocks rest; they are confined to paleovalleys that, in the Gravelly Range, drained from west to east.  Maximum thickness is about 20 m.'
4539|'Unconsolidated, well-rounded pebble- to cobble-size stream deposits composed chiefly of quartzite derived from Mesoproterozoic Lemhi Group and Belt Supergroup exposed to the northwest and west of Gravelly Range, beyond the borders of the Hebgen Lake quadrangle; thickness about 10 m or less.'
4540|'Poorly exposed buff to brown, silty sandstone interlayered with lenses of well-rounded to subrounded cobbles and boulders of metamorphic rock; present in the northern Centennial Valley and southernmost Gravelly Range; thickness may be as much as 725 m.'
4541|'Everts(?) Formation - Light- to dark-gray, thin- to thick-bedded, fine- to medium-grained, quartz-rich sandstone and interbedded siltstone; includes sparse mudstone, porcellanite, and dark gray limestone.  Lower 60-90 m are thinly interbedded mudstone, siltstone, shale, coal, and minor crossbedded sandstone.  Formation is about 425 m thick.

Virgelle Sandstone - Thin- to thick-bedded, medium- to coarse-grained, crossbedded sandstone forming prominent white-weathering ledges.  Thickness ranges from 23 to 50 m.'
4542|'Upper half consists of light-brown-weathering mudstone and siltstone with thin interbeds of light-gray sandstone that locally contain chert-pebble lags and glauconite.  Middle 20 m consists of conspicuous white-weathering, finely laminated tuffaceous siltstone.  Lower 75 m consists of slope-forming siltstone and mudstone in upper part that overlies lowermost  salt and pepper, ripple-marked sandstone.  Total thickness about 206 m.'
4543|'Dark-gray, thin-bedded, locally micaceous and silty mudstone with thin interbeds of gray-green siltstone and fine-grained sandstone.  About 300 m thick.'
4544|'Interbedded sandstone, siltstone, mudstone, carbonaceous shale and coal seams, and minor limestone.  Sandstone is predominantly medium light gray to yellowish or greenish gray, very fine to medium grained and commonly calcareous.  Coarse-grained varieties include subangular lithic sand grains of chert, feldspar, and biotite; locally conglomeratic, containing well-rounded pebbles of quartzite and chert. Sandstone beds generally less than 1 m, but occur in layered units as much as 7 m in thickness.  Siltstone and mudstone are olive gray and medium to dark gray and are bentonitic and porcellanitic.  Limestone is thin-bedded to nodular, light to medium gray, and micritic.  Thickness ranges from about 870 m directly north of the Gravelly Range, to 2100 m near the southern part of the Gravellys, and thins to 120 m in the Madison Range.'
4545|'Slope-forming dark-gray mudstone and silty mudstone interbedded with minor siltstone, sandstone and bentonite with organic-rich shale in the upper part.  Lower part is light colored pink, gray green, green, and orange-cream colored mudstone, bentonitic mudstone, and porcellanite interlayered with welded tuff, mudstone, siltstone, and minor quartz sandstone.  Generally poorly exposed because of slumping; in the Gravelly Range the Mowry is the site of pronounced landsliding.  Formation is about 150 to 180 m thick.'
4546|'Formation consists of three parts:  upper part consists of light-gray, thin- to medium-bedded, fine- to coarse-grained quartz sandstone, feldspathic sandstone, and arkose; middle part is dark-gray, thin-bedded siltstone, sandstone, and shale; lower part is greenish-gray to tan, fine- to medium-grained sandstone.  The middle member thins to the west and is absent in the Gravelly Range.  Thickness ranges from 0 to about 110 m.'
4547|'Dark-gray to black, fissile, organic-rich shale in the upper part overlies light- to dark-brown-weathering, thin- to medium-bedded, fine- to medium-grained sandstone.  Thickness ranges from about 50 to 75 m.'
4548|'Upper 15 m consists of conspicuous, ledge-forming, medium- to thick-bedded, light-gray fresh water limestone that contains abundant gastropods.  Middle part is a slope-forming gray, maroon, yellow, red, and purple mudstone with siltstone, sandstone, and, in the lower part, minor limestone. Lower part is thick-bedded, cherty, crossbedded, quartz-rich sandstone and minor, well-rounded chert-pebble conglomerate.  Thickness about 125 m.'
4549|'Morrison Formation - Interbedded red, green, gray, and yellowish siltstone, mudstone, and shale locally interlayered with thin beds of dense, fine-grained limestone; in Madison Range the upper part includes yellowish-tan, medium-bedded sandstone lenses as much as 20 m thick; formation is generally poorly exposed and forms reddish-colored slopes.  Maximum thickness is about 100 m.

Ellis Group:
Swift Formation - Thin- to medium-bedded, medium- to coarse-grained, calcareous, locally chert-bearing quartz sandstone that contains abundant ooids and shell fragments; lowermost part is olive-green shale and claystone.  The Swift is the only formation of the Ellis Group exposed in the western part of the map area. Thickness ranges from about 1 to 30 m.

Rierdon Formation - Light-gray to pale brown, thin- to thick-bedded, dense, oolitic limestone locally containing sparse chert pebbles. Formation is absent in western part of map area; maximum thickness is about 30 m.

Sawtooth Formation - Thin-bedded, light- to dark-gray limestone with local shaly to silty limestone interbeds; locally fossiliferous and oolitic.  Formation absent in western part of map area; maximum thickness about 55 m.'
4550|'Interbedded red, green, gray, and yellowish siltstone, mudstone, and shale locally interlayered with thin beds of dense, fine-grained limestone; in Madison Range the upper part includes yellowish-tan, medium-bedded sandstone lenses as much as 20 m thick; formation is generally poorly exposed and forms reddish-colored slopes.  Maximum thickness is about 100 m.'
4551|'Swift Formation - Thin- to medium-bedded, medium- to coarse-grained, calcareous, locally chert-bearing quartz sandstone that contains abundant ooids and shell fragments; lowermost part is olive-green shale and claystone.  The Swift is the only formation of the Ellis Group exposed in the western part of the map area. Thickness ranges from about 1 to 30 m.

Rierdon Formation - Light-gray to pale brown, thin- to thick-bedded, dense, oolitic limestone locally containing sparse chert pebbles. Formation is absent in western part of map area; maximum thickness is about 30 m.

Sawtooth Formation - Thin-bedded, light- to dark-gray limestone with local shaly to silty limestone interbeds; locally fossiliferous and oolitic.  Formation absent in western part of map area; maximum thickness about 55 m.'
4552|'Woodside Formation - Brick-red to orange-red, thin-bedded siltstone and mudstone interbedded with gypsum and thin, discontinuous limestone beds; uppermost strata are silty and locally crossbedded.  Thickness ranges from 0 to about 220 m.

Dinwoody Formation - Tan to pale-brown-weathering, finely laminated, calcareous siltstone in the upper part; grades downward into chocolate-brown-weathering gray to tan limestone, silty limestone and siltstone.  Thickness is variable, ranging from about 20 to 80 m.'
4553|'Brick-red to orange-red, thin-bedded siltstone and mudstone interbedded with gypsum and thin, discontinuous limestone beds; uppermost strata are silty and locally crossbedded.  Thickness ranges from 0 to about 220 m.'
4554|'Tan to pale-brown-weathering, finely laminated, calcareous siltstone in the upper part; grades downward into chocolate-brown-weathering gray to tan limestone, silty limestone and siltstone.  Thickness is variable, ranging from about 20 to 80 m.'
4555|'Uppermost medium-bedded, fine- to coarse-grained sandstone with minor chert lenses grades downward into yellowish- to dark-brown, thin-bedded chert with silty, locally phosphatic partings; lower part is brown to gray, thin- to medium-bedded sandstone that grades downward into yellowish-gray, medium-bedded dolomite and sandy dolomite locally containing abundant chert fragments.  Equivalent to Phosphoria Formation.  Thickness is variable, ranging from about 35 to 70 m.'
4556|'White to tan, medium- to thick-bedded, clean, well-sorted quartz sandstone; lower part contains thin interbeds of pale-brown dolomite and gray limestone.  Thickness is 60-100 m.'
4557|'Dark-red, gray-red, and pinkish-red, thin-bedded, calcareous siltstone, silty shale, and shale; upper part of formation contains interbeds of medium- to coarse-grained, calcareous sandstone whereas the lower part is interbedded with thin-bedded limestone, limestone-pebble conglomerate, and dolomite. Thickness ranges from about 10 to 50 m.'
4558|'Group ranges in thickness from about 400 to 700 m. 

Mission Canyon Limestone (Upper and Lower Mississippian) - Commonly cliff-forming, thick-bedded, light-gray-weathering, cherty, fine-grained limestone and minor dolomite; uppermost few meters of formation contain prominent orangish-gray-weathering solution breccia.

Lodgepole Limestone (Lower Mississippian) - Slope- to ledge-forming, thin- to medium-bedded, light-gray, finely crystalline, fossiliferous limestone with brownish silty limestone partings.'
4559|'Consists of three members, from top to bottom: Yellowish-tan calcareous siltstone and silty limestone (Sappington Member, maximum thickness 25 m); gray-green, fissile, micaceous shale (Trident Member, maximum thickness 6 m); yellowish-grey vuggy limestone and dolomite underlain by olive-green micaceous shale (Logan Gulch Member, maximum thickness 12 m).'
4560|'Light-gray, tan, yellowish-brown, and dark-gray, fine-crystalline to sucrosic dolomite locally interbedded with 1-m-thick silty, shaly, laminated dolomite; in Madison Range, includes uppermost, massive, ledge-forming dolomite breccia (Birdbear Member).  Maximum thickness about 100 m.'
4561|'Bighorn(?) Dolomite (Ordovician) - Light-gray, thin-bedded, dense cryptocrystalline dolomite.  About 11 m thick.

Snowy Range Group (Upper Cambrian) - Tan, thin-bedded limestone with reddish mottles underlain by greenish, thin-bedded dolomite and dolomitic mudstone that grades downward into red, calcareous siltstone and green sandy shale. Formation is about 300 m thick.

Pilgrim Limestone (Upper Cambrian) - Light-gray, yellowish-brown to gray-brown, thin- to medium-bedded, glauconitic dolomitic limestone; mud-chip conglomerate and oolitic beds are locally common.  Thickness is approximately 60 m.'
4562|'Pilgrim Limestone - Light-gray, yellowish-brown to gray-brown, thin- to medium-bedded, glauconitic dolomitic limestone; mud-chip conglomerate and oolitic beds are locally common.  Thickness is approximately 60 m.

Park Shale - Greenish-gray to reddish-gray, fissile, locally waxy-looking shale interbedded with minor limestone, limestone-pebble conglomerate, and oolitic limestone.  Poorly exposed everywhere and perhaps locally missing in the Gravelly Range. Locally included with the underlying Meagher Formation where too thin to show on map.  Thickness 0 to 30 m.

Meagher Formation - Light-gray to brownish-gray, thin to medium-bedded, finely crystalline limestone with thin partings of calcareous shale in upper and lower parts;  characteristically contains irregular orange-yellow silty mottles; locally interbedded with cm-thick oolitic limestone.  Basal few meters of formation in the Gravelly Range, where it directly overlies Paleoproterozoic metasedimentary rocks, are characterized by calcareous-cemented lag gravel deposits.  In Gravelly Range, locally includes thin, unmapped deposits of Wolsey and Flathead Formations.  Maximum thickness about 150 m.'
4564|'Greenish-gray to reddish-gray, fissile, locally waxy-looking shale interbedded with minor limestone, limestone-pebble conglomerate, and oolitic limestone.  Poorly exposed everywhere and perhaps locally missing in the Gravelly Range. Locally included with the underlying Meagher Formation where too thin to show on map.  Thickness 0 to 30 m.'
4565|'Light-gray to brownish-gray, thin to medium-bedded, finely crystalline limestone with thin partings of calcareous shale in upper and lower parts;  characteristically contains irregular orange-yellow silty mottles; locally interbedded with cm-thick oolitic limestone.  Basal few meters of formation in the Gravelly Range, where it directly overlies Paleoproterozoic metasedimentary rocks, are characterized by calcareous-cemented lag gravel deposits.  In Gravelly Range, locally includes thin, unmapped deposits of Wolsey and Flathead Formations.  Maximum thickness about 150 m.'
4566|'Wolsey Formation - Gray-green to dark-gray, fissile, micaceous shale interbedded with minor, thin limestone beds similar to mottled limestone of the overlying Meagher Formation as well as thin, glauconitic, quartzose sandstone similar to underlying Flathead Sandstone.  Locally missing in the Gravelly and Centennial Ranges.  Thickness 0 to 60 m.

Flathead Sandstone - White, tan to reddish-brown, hematitic, thin-to medium-bedded, fine- to medium-grained quartz to feldspathic sandstone; interlayered with greenish shale in upper part; glauconitic locally.  Where unmapped in the Centennial and Gravelly Ranges, formation may be missing or so thin that it is included in the overlying Meagher Formation.  Thickness 0 to 30 m.'
4567|'Gray-green to dark-gray, fissile, micaceous shale interbedded with minor, thin limestone beds similar to mottled limestone of the overlying Meagher Formation as well as thin, glauconitic, quartzose sandstone similar to underlying Flathead Sandstone.  Locally missing in the Gravelly and Centennial Ranges.  Thickness 0 to 60 m.'
4568|'White, tan to reddish-brown, hematitic, thin-to medium-bedded, fine- to medium-grained quartz to feldspathic sandstone; interlayered with greenish shale in upper part; glauconitic locally.  Where unmapped in the Centennial and Gravelly Ranges, formation may be missing or so thin that it is included in the overlying Meagher Formation.  Thickness 0 to 30 m.'
4569|'Mylonitization of rocks occurred about 1.8 Ga, coeval with the mylonitic rocks to the east, in the Madison Range.'
4570|'A granitic stock in the north part of the Gravelly Range.'
4571|'Gabbroic intrusive rocks are weakly tectonized and are associated with contact metamorphic aureoles marked by porphyroblasts of andalusite or staurolite or both in pelitic rocks around their perimeters.  Exposed only in Gravelly Range.'
4572|'Gabbroic intrusive rocks are weakly tectonized and are associated with contact metamorphic aureoles marked by porphyroblasts of andalusite or staurolite or both in pelitic rocks around their perimeters.  Exposed only in Gravelly Range.'
4573|'This is one unit in a weakly metamorphosed rock sequence interpreted to represent a sequence of late Paleoproterozoic clastic foreland basin deposits (ONeill, 1999) consisting mainly of sandstone and shale.  Exposed only in Gravelly Range.'
4574|'This is one unit in a weakly metamorphosed rock sequence interpreted to represent a sequence of late Paleoproterozoic clastic foreland basin deposits (ONeill, 1999) consisting mainly of sandstone and shale.  Exposed only in Gravelly Range.'
4575|'This is one unit in a weakly metamorphosed rock sequence interpreted to represent a sequence of late Paleoproterozoic clastic foreland basin deposits (ONeill, 1999) consisting mainly of sandstone and shale.  Exposed only in Gravelly Range.'
4576|'This is one unit in a weakly metamorphosed rock sequence interpreted to represent a sequence of late Paleoproterozoic clastic foreland basin deposits (ONeill, 1999) consisting mainly of sandstone and shale.  Exposed only in Gravelly Range.'
4577|'Exposed only in Gravelly Range.'
4578|'Sedimentary iron formation occurs in the middle of the sequence of Late Paleoproterozoic tectonites, metasedimentary rocks, and associated igneous rocks and is a marker horizon throughout the Gravelly Range.'
4579|'This is one unit in a weakly metamorphosed rock sequence interpreted to represent a sequence of late Paleoproterozoic clastic foreland basin deposits (ONeill, 1999) consisting mainly of sandstone and shale.  Exposed only in Gravelly Range.'
4580|'This is one unit in a weakly metamorphosed rock sequence interpreted to represent a sequence of late Paleoproterozoic clastic foreland basin deposits (ONeill, 1999) consisting mainly of sandstone and shale.  Exposed only in Gravelly Range.'
4581|'Exposed only in Gravelly Range.'
4582|'This is one unit in a weakly metamorphosed rock sequence interpreted to represent a sequence of late Paleoproterozoic clastic foreland basin deposits (ONeill, 1999) consisting mainly of sandstone and shale.  Exposed only in Gravelly Range.'
4583|'Exposed only in Gravelly Range.'
4584|'Exposed only in Gravelly Range.'
4585|'Foliated granodiorite occurs as intrusive sills that locally show crosscutting relationships and chilled margins.  The rock is equigranular and composed of plagioclase, quartz, microcline, hornblende, and biotite.'
4586|'Amphibolite dikes and sills in the Madison Range range from infolded, disjointed units to tabular sheets with sharp, planar contacts; mapped units were probably originally gabbroic intrusive rock.  In the Centennial Range and Horn Mountains, amphibolite is green to greenish brown, schistose to massive, generally fine grained, and locally porphyroblastic; actinolite makes up as much as 50-90 percent of rock.'
4587|'Massive, light-gray to cream-colored dolomitic marble interlayered with thin quartzite bands; schistosity defined by aligned chlorite and phlogopite, and flattened dolomite grains.  In thin section, dolomite dominates the marble; calcite is associated with quartzite layers only; quartz is present generally as granular bands within marble.'
4588|'Light-green, poorly banded quartzite interfingers with adjacent biotite schist and marble; quartzite has been completely recrystallized and does not show clastic textures or graded bedding.'
4589|'Interlayered rusty-yellow-weathering, quartz-rich muscovite schist and thin quartzite; locally contains abundant magnetite, chlorite, biotite, and poikiloblastic garnet.'
4590|'Well-banded chlorite-biotite schist and gneiss containing variable amounts of quartz and epidote are interlayered with green phyllonite, chloritic schist with quartz augen, and granulated amphibolite.'
4591|'Compositional layering of biotite-rich metamorphic rocks is defined by relative proportions of quartz, biotite, garnet, and muscovite. One- to 3-m-thick beds of biotite-rich metasandstone with well-preserved clastic textures separated by thinner beds of metapelite are common.  Biotite schist is also interlayered with marble and is associated with chlorite-quartz schist and well-banded quartzite similar to banded cherts associated with iron formation.'
4592|'Pods and lenses of hornblende-rich rock consisting mainly of, from rim to core, hornblende and biotite, actinolite and biotite, chlorite, talc and carbonate, anthophyllite, and a core of serpentine.

[Middle Archean amphibolite- to granulite-grade metamorphic tectonites and associated igneous rocks; relative ages uncertain. Middle Archean (>3.1 Ga) age has been confirmed by U-Pb zircon ages from crystalline rocks collected from southern Madison Range (Shuster and others, 1987)].'
4593|'Pink, foliated granitic rocks show weakly to strongly discordant contacts with adjacent rocks.  Rock composition and texture is variable, ranging from medium-grained and equigranular with faint layering defined by aligned biotite, to highly folded and contorted leucogranite enclosing granodioritic xenoliths, to mafic, folded granite and granite gneiss.  Northernmost exposures of granitic gneiss in Madison Range contain conspicuous elongate feldspar augen.

[Middle Archean amphibolite- to granulite-grade metamorphic tectonites and associated igneous rocks; relative ages uncertain. Middle Archean (>3.1 Ga) age has been confirmed by U-Pb zircon ages from crystalline rocks collected from southern Madison Range (Shuster and others, 1987)].'
4595|'Weakly foliated granitic gneiss; locally strongly deformed.  Commonly cut by veins of equigranular granite and pegmatite.  Similar in texture to granitic gneiss (Ag) but is less mafic and generally concordant.

[Middle Archean amphibolite- to granulite-grade metamorphic tectonites and associated igneous rocks; relative ages uncertain. Middle Archean (>3.1 Ga) age has been confirmed by U-Pb zircon ages from crystalline rocks collected from southern Madison Range (Shuster and others, 1987)].'
4596|'White-and-green-spotted, well-foliated plagioclase-hornblende-quartz rock occurs as thin sills and small stocks.  Sills typically consist of 60-80 percent plagioclase, hornblende, and minor quartz; stocks are more felsic and include biotite and as much as 30 percent quartz.

[Middle Archean amphibolite- to granulite-grade metamorphic tectonites and associated igneous rocks; relative ages uncertain. Middle Archean (>3.1 Ga) age has been confirmed by U-Pb zircon ages from crystalline rocks collected from southern Madison Range (Shuster and others, 1987)].'
4597|'Tonalitic migmatite-gneiss and tonalitic biotite gneiss are highly variable both texturally and compositionally; gneiss includes amphibolitic migmatite breccia, leucotonalite gneiss, and dark-gray tonalitic biotite gneiss with moderate migmatite banding.  Locally tonalite gneiss is interlayered with a mixed gneiss composed of green quartzite, biotite-garnet gneiss, amphibolite and garnet amphibolite, and gedrite-cordierite-bearing gneiss.  All tonalitic rocks consist of essential plagioclase, quartz, hornblende, and biotite with a granoblastic texture.  Also included with these rocks is migmatitic granite gneiss characterized by granite leucosomes containing abundant microcline between thin layers enriched in plagioclase, biotite and, locally, hornblende.

[Middle Archean amphibolite- to granulite-grade metamorphic tectonites and associated igneous rocks; relative ages uncertain. Middle Archean (>3.1 Ga) age has been confirmed by U-Pb zircon ages from crystalline rocks collected from southern Madison Range (Shuster and others, 1987)].'
4598|'Basaltic scoria, flows, and volcanic ejectamenta in a cone-shaped deposit on Lion Mountain.'
4603|'Well foliated, fine-to medium-grained granitic gneiss cut by abundant, coarse-grained quartz-feldspar pegmatite.  Unit is intruded by adjacent granite (Xgr).

[Middle Archean amphibolite- to granulite-grade metamorphic tectonites and associated igneous rocks; relative ages uncertain. Middle Archean (>3.1 Ga) age has been confirmed by U-Pb zircon ages from crystalline rocks collected from southern Madison Range (Shuster and others, 1987)].'
4604|
4700|'Composite unit of unconsolidated gravel, sand, silt, and clay deposits of present streams, rivers, and washes; hillside colluvium; landslide material; and glacial moraines and outwash.'
4701|'Composite unit of volcaniclastic sedimentary rocks, limestone, conglomerate, sandstone, shale, and mudstone, deposited as the present basin-range topography formed during extensional faulting.  Unconsolidated and slightly consolidated boulder to pebble conglomerate is interbedded with sandstone and mudstone near top of unit where it accumulated as colluvium, landslide debris, and some glacial outwash.  Limestones are laminated and platy, and formed in fresh-water lakes and hot springs.  Tuffaceous sedimentary rocks and volcanic-derived conglomerates are dominant in lower part of unit.  Well-exposed outcrops indicate that angular unconformities are common within unit (Lucchitta, 1966).'
4702|'Mainly very light gray, friable, vitric, well-sorted tuff in beds as much as 1 m thick, interbedded with very light grayish brown, medium-grained tuff and tuffaceous conglomerate, and very light gray, very finely crystalline to aphanitic limestone in beds 0.3-1 m thick.  Unit is commonly veneered with angular chips of vitreous quartzite lag gravel derived from tuffaceous conglomerate and from sparse quartzite fragments scattered throughout tuff.  Fossil vertebrate fauna, gastropods, and diatoms indicate an age span from Miocene to Pliocene (Ruppel and Lopez, 1988).'
4703|'Tuffaceous, basin-fill strata, tentatively divided into two sequences (Ruppel and Lopez, 1988).  Upper sequence consists of light-olive-gray and yellowish-gray to yellowish-brown or yellowish-orange, tuffaceous mudstone and shale; fine- to medium-grained, tuffaceous sandstone; and lenticular beds of conglomerate with a sandy, tuffaceous matrix.  Shale and mudstone dominate the base of the upper sequence but decrease up section where they are locally absent altogether.  Upper sequence is at least 600-700 m thick.  Lower sequence overlies the Challis Volcanic Group with angular unconformity and is predominantly olive-gray and yellowish-gray to grayish-orange, tuffaceous, bentonitic mudstone and shale with 2 to 15-cm-thick beds of lignite, lignitic mudstone, and beds with abundant woody fragments.  This lower sequence also contains some interbeds of fine-grained to very fine grained, crossbedded sandstone as thick as 1 m and lenticular interbeds of conglomerate 1-8 m thick.  The thickest unfaulted section of lower sequence is about 250 m but total thickness is unknown.  Harrison (1985) interpreted the unit to represent eight depositional facies based on a transition from proximal alluvial fans to shallow lacustrine basins.'
4704|'Poorly consolidated sandstone, mudstone, boulder conglomerate, and tephra that are locally carbonaceous; includes large landslide masses of variegated volcanic rocks.  Unit was deposited in the rapidly subsiding Panther Creek graben during regional rifting concurrent with Challis volcanism.  Strata are easily eroded and subject to a considerable degree of landsliding.'
4705|'Composite unit used in areas where the volcanic rocks have not been subdivided or where units have been combined in order to show at map scale.  Most of the group was erupted from 45 to 51 Ma, although minor activity persisted to about 39 Ma (Fisher and Johnson, 1995).'
4710|'Five cooling units of reddish ash-flow tuff and thin interbeds of ash-fall tuff within the cauldron.  Upper cooling unit is a cliff-forming, densely welded tuff about 228 m thick; beneath it are two thin, partly welded, lithic-rich cooling units each about 30 m thick; these are underlain by a cliff-forming, moderately welded cooling unit about 150 m thick; a lowermost slope-forming, partly welded cooling unit is rich in lithic fragments and about 190 m thick.  Phenocrysts assemblages are similar throughout but vary considerably in relative proportions; minerals include quartz, alkali feldspar, plagioclase, biotite, hornblende, and pyroxene.  Quartz is slightly smoky in all cooling units and chatoyant alkali feldspar is common.  Total thickness about 620 m.'
4711|'Cauldron-filling sequence of mostly very densely welded quartz latite to rhyodacite ash-flow tuff consisting of 10 or more separate cooling units that are characterized by small (about 2 mm) phenocrysts.  Phenocryst content (11-40 percent) in upper part of unit consists of trace quartz and alkali feldspar, 65-75 percent plagioclase, as much as 10 percent biotite, trace altered hornblende, and 10-20 percent altered pyroxene.  Phenocryst content (5-25 percent) in middle part of unit consists of trace quartz, as much as 20 percent alkali feldspar, 65-77 percent plagioclase, as much as 9 percent altered biotite, as much as 3 percent altered hornblende, and 3-10 percent altered pyroxene.  Phenocryst assemblage (3-15 percent) in lower part of unit consists of 2-12 percent quartz, 2-8 percent alkali feldspar, 60-75 percent plagioclase, 2-10 percent altered biotite, as much as 3 percent altered hornblende, and up to 10 percent altered pyroxene.  Thickness from 0 to 3,000 m.'
4712|'Andesitic to basaltic lava flows that are predominantly aphyric reddish brown weathering, gray and greenish gray, brittle, columnar jointed, and blocky to platy; locally interbedded with oxidized flow breccias.  Pyroxene phenocrysts are visible in some specimens; microphenocrysts include olivine, clino- and orthopyroxene, and common xenocrystic quartz.  Groundmass is rich in trachytic and pilotaxitic plagioclase and may contain reddish-brown, strongly pleochroic mica and considerable apatite.  Thickness from 0 to 700 m.'
4713|'Light-gray and greenish-gray, massive-weathering, partly welded and densely welded quartz latite to rhyodacite. Unit is megascopically similar to unit Tce but is distinguished by presence of alkali feldspar, more quartz, and less biotite and hornblende.  Phenocryst assemblage (25-35 percent of rock) consists of 13-17 percent quartz, 12-16 percent alkali feldspar, 45-55 percent plagioclase, 9-12 percent biotite, as much as 2 percent hornblende, and trace clinopyroxene.  K-Ar biotite analysis yields age of 48.41.7 Ma (Fisher and others, 1992).  Thickness from 0 to 300(?) m.'
4714|'Light-greenish-gray, massive-weathering, densely welded, crystal-rich rhyodacite ash-flow tuff. Unit represents outflow from major collapse of the Van Horn Peak cauldron complex.  Phenocrysts (36-50 percent) consist of 4-15 percent quartz (as long as 4 mm and "worm-eaten"), 60-75 percent plagioclase (as long as 6 mm), 12-20 percent biotite, 8-16 percent hornblende, and trace clinopyroxene.  Unit contains abundant pumice lapilli.  K-Ar biotite analysis yields age of 48.41.6 Ma (Fisher and others, 1992).  Thickness from 0 to 300 m.'
4715|'Small, poorly exposed basaltic, andesitic, and granitic plutons scattered throughout the eastern part of the Salmon National Forest.  Most abundant in the Lemhi Range and along the Salmon River north of Salmon.'
4716|'Mixed sequence of gray and greenish-gray extrusive and intrusive rocks of intermediate composition exposed in the Camas Creek drainage at the southwestern margin of the Salmon National Forest.  Some exposures display flow layering indicating that they are lavas; most are massive with crystalline groundmasses.  Phenocrysts constitute 30-45 percent of the rock and have the following proportions:  quartz, as much as 5 percent; plagioclase, 60-75 percent; biotite, 1-12 percent; hornblende, as much as 25 percent; pyroxene, as much as 20 percent (Ekren, 1988).  Intrusive contacts of the massive rock with lavas of the Challis Volcanic Group suggest an age for the unit of 48-51 Ma or less.'
4717|'Medium- to coarse-grained, phaneritic to porphyritic hornblende-biotite syenogranite and gray monzogranite that occur predominantly as large plutons in western part of the Salmon National Forest.  Pink to tan syenogranite is composed of 45-55 percent alkali feldspar, 15-20 percent plagioclase, 15-20 percent quartz, 5-8 percent biotite, 3-5 percent hornblende, and accessory magnetite (Schmidt and others, 1994).  Gray monzogranite is composed of 35-40 percent alkali feldspar, 25-30 percent plagioclase, 25-30 percent quartz, 5-8 percent biotite, and minor hornblende.  Weathering produces exfoliated outcrops and coarse grus.  This unit includes parts of the Painted Rocks pluton (Lund, Rehn, and Holloway, 1983), the Casto pluton (Cater and others, 1973), and the Chamberlain Basin pluton (Lund and others, 1998) with its easternmost extension known as the Bighorn Crags pluton (Cater and others, 1973; Lund and others, 1998).  K-Ar biotite ages range from 44 to 49 Ma (recalculated from Armstrong, 1974).'
4718|'Discrete plutons in the Lemhi Range west and southwest of Leadore ranging in composition from monzogranite to granodiorite and quartz monzodiorite (Ruppel and Lopez, 1988).  Granite is medium-light-gray to medium-dark-gray, porphyritic biotite monzogranite with subhedral phenocrysts (4-6 mm long) of plagioclase, alkali feldspar, quartz, biotite, and hornblende set in a fine-grained groundmass.  The granite in the core of the Big Eightmile stock, southeast of Big Eightmile Creek has been intensely hydrothermally altered.  Granodiorite is commonly medium dark gray and porphyritic with phenocrysts (2-3 mm long) of plagioclase, hornblende, and biotite set in a fine-grained groundmass.  Quartz monzodiorite is medium dark gray to medium gray and porphyritic with phenocrysts (1-3 mm long; rarely 8 mm) of plagioclase, hornblende, biotite, and pyroxene set in a very fine grained to fine-grained groundmass.  K-Ar biotite data suggest an age of about 50 Ma (Ruppel and Lopez, 1988).'
4719|'Dikes and plugs of light-gray, dense, phenocryst-poor rhyolite.  Locally, unit has conspicuous phenocrysts of sanidine as long as 8 mm and sparse phenocrysts of quartz.  Unit crops out in the southwestern part of the Salmon National Forest.'
4720|'Mostly composite plutons of the Carmen stock in the headwaters of Carmen Creek in the northern Beaverhead Mountains, and the Chief Joseph plutonic complex near Lost Trail Pass, Idaho-Montana.  The Carmen stock is mostly granite, granodiorite, and quartz monzodiorite; Ar ages about 48-55 Ma; eastern part of stock is more mafic and yields ages of about 80-83 Ma (Kilroy, 1981).  The Chief Joseph plutonic complex is located mostly outside the Salmon National Forest in Montana, and includes granite, hornblende-biotite granodiorite, biotite granodiorite, and tonalite.  K-Ar, U-Pb zircon, and fission track ages indicate an age range of about 43-78 Ma (Desmarais, 1983).'
4721|'Dark-gray, slightly foliated, medium-grained, phaneritic hornblende-biotite tonalite with local mafic enclaves; poorly exposed in the northwestern part of the Salmon National Forest.  Pluton is 40-50 percent feldspar (<5 percent alkali feldspar), 15-20 percent quartz, 5-10 percent hornblende, 15-20 percent biotite, and less than 5 percent brown pyroxene(?) (Schmidt and others, 1994).  Unit Kt is intruded by unit Tg and intrudes Kpg and Ybgn, suggesting a Cretaceous age similar to that of tonalitic rocks in the Payette National Forest to the west (Lund and others, 1998).'
4722|'Light-gray, nonfoliated, medium-grained, phaneritic two-mica granite in upper Owl Creek, west of Shoup and north of the Salmon River.  Rock consists of 20-30 percent alkali feldspar, 30-40 percent plagioclase, 25-30 percent quartz, 5-10 percent muscovite (euhedral books), and less than 5 percent biotite (Schmidt and others, 1994).  Outcrops tend to exfoliate and weather to a coarse, light-gray grus.  Pluton intrudes units Ybgn, Ymg, and Kgd with sharp contacts.  Unit Kg commonly crops out to the west in the Payette and Nez Perce National Forests, Idaho, where it has been dated by 40Ar/39Ar methods at about 74 Ma (Lund and others, 1986).'
4723|'Light-gray, nonfoliated to weakly foliated, medium-grained, porphyritic granite and granodiorite exposed within the Salmon River canyon at the northwest margin of the Salmon National Forest and along Camas Creek in the southwestern part of the forest.  Similar in composition to unit Kgd but contains pink alkali feldspar phenocrysts generally 5-7 cm in length.  Weathering characteristics are similar to those of unit Kgd.'
4724|'Light-gray, nonfoliated to weakly foliated, medium-grained, phaneritic biotite granodiorite in the western part of the Salmon National Forest; forms plutons, dikes, and sills within Mesoproterozoic units.  Made up of 20-25 percent alkali feldspar, 45-55 percent plagioclase, 15-25 percent quartz, and 3-10 percent biotite, with accessory sphene and magnetite (Schmidt and others, 1994).  Locally, near contacts with Proterozoic rocks, unit Kgd can contain as much as 10 percent muscovite.  Outcrops weather to a light-gray, coarse grus.  Unit Kgd is a major component of the Idaho batholith to the west in the Payette National Forest (Lund and others, 1998).'
4725|'Light-gray, medium-grained, foliated biotite granodiorite in the southwestern part of the Salmon National Forest along and near the Middle Fork Salmon River.  Ekren (1988), based on one thin section, described a composition of about 11 percent alkali feldspar, 51 percent plagioclase, 28 percent quartz, and 10 percent biotite.  Although exposures underlie only a small part of the Salmon National Forest, unit Kgdf is widespread west of the Thunder Mountain caldera in the Payette National Forest (Lund and others, 1998).'
4726|'Yellow-brown-weathering, dark-gray, fissile shale and calcareous shale, with interbeds of medium-gray and brownish-gray limestone and calcareous sandstone; present in the Beaverhead Mountains southeast of Leadore.  Coarse-grained recrystallized limestone contains distinct, abundant fossil debris.  Spaced cleavage is prevalent and locally obscures bedding.  The upper contact is disconformable and the lower contact with the Phosphoria Formation (Pp) is abrupt.  Unit poorly exposed.  Although structurally deformed, the formation is probably about 300 m thick (Lucchitta, 1966).'
4727|'Crops out in the Beaverhead Mountains; definition follows usage of Lucchitta (1966).  Upper part is bedded black chert with thin beds of dolomite and limestone.  Bluish-white phosphatic spots are found in the chert beds.  Chert is about 50 m thick and is equivalent to the Tosi Chert Member (McKelvey and others, 1959).  Lower part is dark-gray dolomite and minor limestone with dark-gray to black, ropy chert nodules, (mapped as Phosphoria and Park City Formations, undivided, by Lucchitta, 1966).  Lower part may belong to the upper Juniper Gulch Member of the Snaky Canyon Formation, but structural complexity and lack of definitive age information make it difficult to assign these beds. Lowest part exposed is a bluish siltstone less than 30 m thick. The upper contact, with the Dinwoody Formation (TRd), is abrupt; the lower contact with the undivided Snaky Canyon and Bluebird Mountain Formations (PMs), where preserved, is gradational.  Thickness difficult to measure but probably about 260 m (Lucchitta, 1966).'
4728|'Combined unit present in the Beaverhead Mountains in the southeastern part of the Salmon National Forest.  The upper member of the Snaky Canyon (Juniper Gulch Member) is medium-bluish-gray, sandy dolomite with interbedded quartz sandstone layers.  The amount of interbedded sandstone decreases upward so that light- to medium-gray cherty dolomite predominates.  The underlying Gallagher Peak Sandstone Member of the Snaky Canyon Formation is similar to the Bluebird Mountain strata but has more calcareous cement.  The lower member of the Snaky Canyon Formation (Bloom Member) is medium- to dark-gray, cherty limestone with common chert nodules and interbedded thin quartz sandstone similar to Bluebird Mountain sandstone.  Sandstone of the Bluebird Mountain Formation is light-brown-weathering, fine-grained, light-gray quartzitic sandstone and minor quartzite.  Unit PMs totals about 560 m thick (Lucchitta, 1966).  The type section for these units is south of the Salmon National Forest in the extreme southern Beaverhead Mountains, where the total thickness is 1,350 m (Skipp, Hoggan, and others, 1979).  The upper contact is gradational and some cherty dolomite beds included in the Phosphoria Formation (Pp) on this map may belong to the upper part of the Snaky Canyon Formation.  The lower contact is abrupt.  Intense structural disruption is common in this unit.'
4729|'Combined unit of limestones in the Beaverhead Mountains that are either so brecciated or sheared that original bedding characteristics are obscured and the strata cannot be assigned to particular formations.  This unit may include strata correlative with the South Creek and Surrett Canyon Formations, although these two units have not been recognized in this part of the Beaverhead Mountains.'
4730|'Combined unit of limestone and silty limestone that crop out low on the eastern side of the southern Lemhi Range.  Shaly beds at top of unit may be equivalent to the Railroad Canyon Formation.  Underlying minor thin-bedded silty limestone, preserved locally above massive limestone, is probably equivalent to parts of the South Creek and Surrett Canyon Formations.  Thickest part of unit is massive cherty bioclastic limestone that is equivalent to the Scott Peak Formation.  Lower part of unit is thin-bedded, cherty, yellow- to red-weathering silty bioclastic limestone that is highly cleaved and deformed.  Although not mapped separately, these lower rocks are equivalent to the Middle Canyon Formation.  Originally mapped as the White Knob Limestone (Hait, 1965), the rocks were subsequently subdivided and renamed (Huh, 1967; Skipp, Sando, and Hall, 1979).  Total thickness about 700 m (Hait, 1965).'
4731|'Dark-gray, pink-, and yellow- to orange-weathering shale, mudstone, silty limestone, and calcareous siltstone present in the Beaverhead Mountains north and east of Leadore.  Strata are mostly thin bedded and flaggy, though some dark shale is fissile and flaggy.  Dark shale and siltstone have a musty odor.  Unit is poorly exposed and underlies swales and valleys, where springs and slumps are preferentially located in it.  Shaly strata commonly acts as locus for faults that in many places excise all or part of the formation.  Slivers of unit Mr are preferentially silicified along fault zones; narrow zones of silicified siltstone are common indicators of low-angle faults.  Formation was mapped previously as Big Snowy Group (Lucchitta, 1966) and Big Snowy Formation (Skipp and others, 1984).  Unit Mr is 205 m thick at the type section on the west side of upper Railroad Canyon northeast of Leadore and is considered equivalent to the Surrett Canyon and Arco Hills Formations of the foredeep carbonate bank sequence of Idaho (Wardlaw and Pecora, 1985; Skipp, Sando, and Hall, 1979).  Upper and lower contacts are conformable.'
4732|'Medium-dark-gray, medium- to thick-bedded, mostly pure limestone with bedded chert horizons in the Beaverhead Mountains in the vicinity of Leadore and in the Lemhi Range near Gilmore.  Much of the unit contains orange-weathering, wispy and bedded, dark-gray chert.  Beds are fossiliferous with corals and brachiopods dominant; encrinite layers are common but not diagnostic.  Unit typically forms cliffs.  Thin-bedded strata, recognized in the upper part by Lucchitta (1966) but not mapped separately, may be correlative with the South Creek and Surrett Canyon Formations.  Near low-angle normal faults, the unit is brecciated and recemented with calcite.  Throughout the study area the Scott Peak is strongly cleaved as a result of deformation associated with thrust faulting.  Although commonly thinned by low-angle normal faults, the unit may be as much as 700 m thick (Skipp and others, 1984).'
4733|'Medium- to dark-gray, thin-bedded cherty limestone and silty limestone crop in the southeastern part of the Salmon National Forest.  Bedding is commonly 0.5-5 cm thick.  Silty interbeds weather tannish-orange and give the unit a tannish-gray appearance.  Unit forms smooth slopes and generally only crops out on canyon walls.  Exposures in the range front north of Leadore indicate that the strata are strongly ductilely deformed, having undergone multiple deformations.  In the Lemhi Range west of the hamlet of Lemhi, near junction of Hayden and Basin Creeks, unit Mm forms prominent outcrops in the footwall of the Poison Creek thrust fault.  Some of these strata are silicified adjacent to rocks of the Eocene Challis Volcanic Group and locally were misinterpreted as Beaverhead Conglomerate (now Beaverhead Group) (Cretaceous and Paleocene) by Anderson (1961).  Total thickness about 160 m (Lucchitta, 1966).'
4734|'Gray to pink calcareous siltite, argillite, and shale poorly exposed in the Lemhi Range in the southeastern part of the Salmon National Forest.  Thickness about 200 m in southern part of the Lemhi Range (Hait, 1965).'
4735|'Widespread in the Lemhi Range and Beaverhead Mountains in the southeastern part of the Salmon National Forest.  Uppermost part of unit locally includes limey siltstone beds that were not mapped separately, but which may correlate with the McGowan Creek Formation.  The Three Forks Formation consists of dark-gray siliceous mudstone, tan to gray to pink siltstone, and platy fine-grained dark-gray limestone. The underlying Jefferson Formation is primarily dark-gray dolomite with lesser amounts of limestone, limestone evaporite-solution breccia, and sandy dolomite.  Strong tectonic brecciation of unit in most locations makes identification of bedding difficult.  Beneath (east of) the Hawley Creek thrust (east-southeast of Leadore) in the Beaverhead Mountains, base of unit is an angular unconformity with underlying Ordovician and Mesoproterozoic strata.  Above (west of) the Hawley Creek thrust in the Lemhi Range and north of Leadore in the Beaverhead Mountains, the unconformity is less profound and Silurian and Upper Ordovician rocks are present.  Ruppel and Lopez (1988) reported a maximum thickness in the Lemhi Range, near Gilmore, of about 825 m of Jefferson and 90 m of Three Forks strata, but both units (especially the Jefferson) thin rapidly to the south and east.'
4736|'Where present in the Lemhi Range south of Poison Creek, the Laketown Dolomite is too thin to show separately and has been combined with the underlying Saturday Mountain Formation (see description of unit SOs).  The Laketown Dolomite is a light-olive-gray to medium-light-gray and light-gray, fine- to medium-crystalline dolomite in beds 0.6-3 m thick.  Fresh surfaces of the Laketown are characterized by a sparkling appearance, in contrast to the Saturday Mountain Formation.  Vugs (1-2 mm in diameter) are moderately abundant but fossils are rare.  Thickness of the Laketown Dolomite in the central Lemhi Range is about 60 m; total thickness of unit SOs as much as 430 m.'
4737|'Medium-light- to medium-dark-gray, very fine grained dolomite located in the Poison and Warm Spring Creeks area of the Lemhi Range and in the Beaverhead Mountains near Leadore.  South of Poison Creek in the Lemhi Range the unit has been combined with the overlying Laketown Dolomite into unit SOu.  Unit SOs consists of four members (Ruppel and Lopez, 1988).  The uppermost member consists of medium-gray to medium-light-gray, finely crystalline, thick- to massive-bedded dolomite that weathers to a mottled appearance.  Black chert nodules are present but notably less abundant than in lower members; however the member is quite fossiliferous.  Underlying this is medium-dark-gray to medium-gray, finely crystalline dolomite that weathers to distinctly mottled lighter gray colors; black chert nodules are also common as well as numerous beds with abundant fossils and fossil fragments.  This grades downward into yellowish-gray to medium-gray, finely crystalline dolomite characterized by a network of irregular, interlaced, hair-like wisps and veinlets of white dolomite and locally by abundant black chert nodules.   The basal Lost River Member consists of interbedded clastic deposits of generally dark-colored sandstone, quartzite, shale, and mudstone.  Ruppel and Lopez (1988) reported fossil data that indicate an age in the central Lemhi Range of mostly Ordovician with the top part being Lower Silurian; in the southern Lemhi Range, however, the unit is wholly Ordovician.  It is overlain along a deeply weathered, erosional unconformity by the Silurian Laketown Dolomite.  Maximum thickness of unit SOs in the central Lemhi Range is about 370 m, but it thins to the south and east.'
4738|'White to light-gray, fine- to medium-grained, vitreous quartzite present in the Beaverhead Mountains and Lemhi Range.  Unit is compositionally supermature and well sorted with tightly cemented subrounded grains; as a result, bedding is usually difficult to identify.  The lower contact is conformable with the underlying Summerhouse Formation (Os), although locally the Kinnikinic rests unconformably on Mesoproterozoic strata (Ruppel, 1980).  Thickness about 300 m in the Lemhi Range (Ruppel, 1980).'
4739|'White and light-gray to pale-yellowish-orange, fine- to coarse-grained (locally bimodal) quartzite and dolomitic quartzite; locally includes an uppermost unit of massive dolomite.  Unit exposed in the Rattlesnake Creek area of the Salmon River Mountains.  Bedding is commonly 50-100 cm thick.  Beds virtually identical to those of the Kinnikinic Quartzite (Ok) are intercalated with medium- to coarse-grained, locally bimodal quartzite with dolomitic cement, consistent with relationships in the type section of unit Os in the central Lemhi Range (Ruppel and others, 1975; McCandless, 1982).  Quartzites grade upward through an approximately 10-m-thick transition zone of dolomitic quartzite into about 30 m of medium-gray, fine-grained, locally massive dolomite (which in this study has been included in map unit Os).  Conodonts and brachiopods from the dolomite suggest an age of Middle or Late Ordovician, possibly equivalent in part to the Middle Ordovician Ella Dolomite of the Challis area (Ekren, 1988).  This is in accord with the interpretation that the quartzites are pre-Kinnikinic and best correlated with the Summerhouse Formation.  Because the dolomite is too thin to show at the scale of the map and because regional relationships of the Ella Dolomite and the Summerhouse Formation are undefined (McCandless, 1982; Hobbs and Hays, 1990), the dolomite is tentatively mapped as part of the Summerhouse Formation.  In the Rattlesnake Creek area, the dolomite is truncated upward by the Poison Creek thrust but the base of the quartzites is thrust onto the Gunsight Formation (Yg) along one of several imbricate faults below the Poison Creek thrust.    Total thickness about 230 m.'
4740|'Map unit used only in the northern Lemhi Range where poor exposure and the map scale used for compilation prevented the two units from being shown separately.  In the Goldbug Ridge area north of the Poison Creek thrust fault, the dolomite is overlain (conformably?) by the Kinnikinic Quartzite but unfoliated quartzite of the basal Summerhouse rests unconformably on locally strongly cleaved Swauger Formation.  Further south near Poison Peak and the thrust fault, coplanar cleavage presumably produced by thrusting occurs in both quartzites and post-unit Ok carbonates.  Total thickness about 530 m.'
4741|'Predominantly quartzite pebble to cobble conglomerate and quartzite with minor carbonate-cemented sandstone and sandy dolostone.  Unit crops out in small area in the Beaverhead Mountains north of Leadore.  Most recognized exposures are quartzite with interbedded conglomerate, but where conglomerate is lacking parts of this unit may include some underlying Gunsight Formation (Yg).  Quartzite shows bimodal grain size distribution, and is cemented by silica in lower part of unit.  Conglomerate layers are as thick as 2 m; cobbles derived primarily from quartzite of the Mesoproterozoic Swauger (Ys) and Gunsight Formations; minor clasts of vein quartz and rare chips of light-colored siltite.  Amount of carbonate cement increases upward where the carbonate-cemented sandstone is interbedded with sandy dolomite.  Unit is probably correlative with the Wilbert Formation as defined in the Lemhi Range (Ruppel and others, 1975; McCandless, 1982).  Total thickness of unit CZw is unknown because it only crops out in fault slivers; maximum thickness observed is about 10 m.'
4743|'Medium-grained, phaneritic to porphyritic, alkali-feldspar syenite, alkali-feldspar quartz syenite, and alkali-feldspar granite with generally lesser amounts of gabbro and mafic-rich quartz syenite. Crops out in the Beaverhead Mountains (Beaverhead pluton of Scholten and Ramspott, 1968; Skipp, 1984), west of Salmon (Deep Creek and Arnett Creek plutons, Evans and Zartman, 1988), and near Yellowjacket and Middle Fork Peak (Ekren, 1988).  U-Pb zircon dates indicate an age of about 490 Ma, in contrast to compositionally similar alkalic plutons to the west in the Payette National Forest (Lund and others, 1998), where preliminary data indicate an age of about 650 Ma (Evans and Zartman, 1988; J.N. Aleinikoff and K.V. Evans, unpub. data, 2002).'
4745|'Intercalated siltite and metasandstone to orthoquartzite.  Strata are gray to grayish green and blueish green, and range from near equal parts quartz and feldspar in a fine-grained chloritized matrix to orthoquartzite.  Beds are 1 cm to 1.5 m thick and planar to cross-laminated, and locally contain "floating" rip-up clasts of argillite.  A few beds are light gray, fine-grained metasandstone with fine laminations and dark-gray, heavy-mineral laminae 1-2 grains thick.  Other metasandstones are poorly sorted with well-rounded, medium- to coarse-grained quartz, minor plagioclase, and medium- to coarse-grained silt.  Siltite is medium to dark gray and forms sequences as thick as 10 m in which siltite and metasandstone are interlayered in beds 0.5-5 cm thick.  These strata are planar to ripple cross-laminated and show abundant flaser and lenticular bedding, as well as cut and fill structures.  Hobbs (1980) named the unit for strata in the Lost River Range and Tysdal (1996a) and Tysdal and Moye (1996) extended the term to rocks in fault slivers south of the Lem Peak fault in the Lemhi Range.  The description is from Tysdal (1996a).  Tysdal (2000a) interpreted the unit to have formed in an intertidal environment.  Total thickness in the type section is about 1,200 m, but only about 300 m is preserved in the Salmon National Forest due to thinning by faults.'
4746|'Light-gray, pale-green, and pale-red-purple, medium- to coarse-grained quartzite.  Unit is widespread in the Lemhi Range and present in the Beaverhead Mountains near Leadore and in the Salmon River Mountains west of Salmon.  Quartz content typically ranges from 90 to 95 percent; well-rounded, well-sorted, tightly cemented, and glassy grains.  Feldspar content seldom exceeds 5-10 percent.  A speckled appearance is quite common and results from 0.5 to 3-mm-diameter (usually reddish) spots of hematite, local limonite, and rare chlorite commonly concentrated along cross-laminae.  Beds are 0.5-2 m thick and commonly show trough cross-laminations and lesser herringbone cross-laminae.  Two-dimensional ripples and dunes are quite well developed in places; dunes have wavelengths of 4-8 m and heights of 0.7-1 m and ripples have wavelengths of 2-15 cm and heights of 0.3-3 cm.  Tysdal (2000a) interpreted the bulk of the Swauger to have been deposited in a tidal environment, based on the compositional maturity of the quartzites, presence of herringbone cross-beds, subordinate current cap deposits (de Mowbray and Visser, 1984) on some dunes, rare antidunes, and local flaser and lenticular bedding.  The Swauger grades upward into the Lawson Creek Formation.  Total thickness about 3,100 m.'
4747|'The Gunsight Formation was defined by Ruppel (1975) for rocks at Gunsight Peak in the Lemhi Range west-southwest of Leadore, Idaho.  McBean (1983) further studied the type section and much of the following description for the Gunsight south of the Lem Peak fault is taken from his work.  North of the Lem Peak fault and in the Beaverhead, Salmon River, and Clearwater Mountains, strata previously mapped as the upper unit of the Yellowjacket Formation (unit Yyu of Evans, 1998) are now correlated with the Gunsight (Tysdal, 2000b). Accordingly, the Gunsight is separately described as follows:  south of Lem Peak fault (that is, type section), north of Lem Peak fault (that is, mostly former unit Yyu), and in the Beaverhead and Clearwater Mountains.

South of Lem Peak fault-Pale-brown to gray, very fine grained to medium-grained metasandstone typifies most of the type section.  Quartz and feldspar are the dominant components, with feldspar content ranging from 25 to 50 percent; matrix content is 0-8 percent.  Sedimentary structures include trough and planar cross-beds; parallel ripple and climbing ripple cross-laminations; ripple and climbing ripple laminations; straight-crested, asymmetrical and oscillation ripples; and dewatering structures.  In the uppermost 100+ m, where the unit is transitional into the compositionally mature Swauger Formation (Ys), quartz content increases to 80-90 percent.  Lower 450 m of unit consist of interbedded siltite, argillite, and very fine grained metasandstone transitional into the underlying siltite of the Apple Creek Formation.  Matrix content in this lower part can reach 40 percent.  Total thickness is 1,700+ m.  McBean (1983) interpreted the formation to have been deposited in a shallow marine setting, but Tysdal (2000a) considered most of the unit to be fluvial.  Trough crossbedded metasandstone (as thick as 1-2 m) that fines upward into siltite is indicative of channel and overbank deposits and strongly supports Tysdal''s reevaluation.  Upper part of formation may be shoreface deposits transitional into marine deposits of the Swauger (Tysdal, 2000a).  Lower part of formation, with its intercalated siltite and argillite, probably formed in an intertidal to subtidal environment transitional into the turbidites of the Apple Creek Formation.

North of Lem Peak fault-Light- to dark-gray, very fine grained to medium-grained, feldspathic metasandstone (arkose) typifies this unit in the northern Lemhi Range and Salmon River Mountains.  Bed thickness ranges from 10 to 100 cm.  Decimeter-thick trough and planar cross-beds are typical; hummocky cross-stratification is present locally in the Salmon River Mountains.  Conglomeratic beds exist locally, containing clasts that are angular and rounded.  Deposition was probably in fluvial to shallow marine environments, with features such as the local conglomerates probably representing slumping of partially lithified channel margins into tidal(?) channels.  Total thickness probably exceeds 4,000 m.  In the Salmon River Mountains the unit is transitional downward into the banded siltite unit of the Apple Creek Formation (Yab), and upward into the Swauger Formation (Ys).'
4748|'The Apple Creek Phyllite was defined by Anderson (1961) for foliated rocks near Hayden Creek in the central Lemhi Range.  Ruppel (1975) redefined the unit as the Apple Creek Formation and Tietbohl (1981, 1986) studied a diamictite unit within the formation.  Tysdal (1996a, b, c, 2000a, b; Tysdal and Moye, 1996) slightly redefined and subdivided the formation into mappable informal subunits, described below.  On our geologic map, Tysdal''s subunits are used where recent mapping is available; where it is not available or distinctions could not be made in the field, the undivided designation (Ya) is used.'
4749|'Centimeter-scale layers of light-gray siltite to very fine grained metasandstone alternating with black siltite or argillite characterize the easily identified banded member.  The thickness of layers and the percentage of metasandstone versus siltite/argillite vary considerably.  Layers range from 0.5 to 10 cm thick and percentages of metasandstone to siltite/argillite range from equal to 95 percent dominance by either component.  These couples and couplets of the unit are interpreted to be turbidites (Sobel, 1982; Tysdal, in press).  In addition to the visually striking light and dark layering, argillite beds in virtually any outcrop exhibit predominantly (but not exclusively) downward-penetrating dikelets of coarser sediment from the overlying layer.  Commonly the dikelets are ''ptygmatically'' folded due to compaction of the originally very water laden argillaceous layers.  Unit is widespread in the Salmon River Mountains northeast of the Iron Lake fault, and reaches a thickness of at least 2,000 m.  Unit apparently thins to the southeast due to erosion so that only a thin sliver is preserved in the footwall of the Poison Creek thrust in the Lemhi Range.  Unit is the primary host for the stratabound Blackbird Co-Cu-Au deposit.  Base of unit is gradational downward into the coarse siltite unit (Yac), and top grades upward through a relatively abrupt transition into the overlying Gunsight Formation (Yg).  As previously noted, in the Lemhi Range unit Yab thins below the Gunsight due to erosion.

Unit was called the "middle subunit of the Yellowjacket Formation" by Connor and Evans (1986), but because the unit lies conformably above the coarse siltite unit of the Apple Creek Formation, Tysdal (in press) assigned it to the Apple Creek Formation.  The "banded siltite" name resurrects an informal name that was used originally by Connor and Evans (1986).'
4750|'Grayish-green, medium- to coarse-grained siltite and fine-grained quartzite (metasandstone) best preserved between Bear Valley Lakes and Basin Lake in the Lemhi Range.  In the Salmon River Mountains southwest of the town of Salmon, strata previously mapped as the lower unit of the Yellowjacket Formation (unit Yyl of Evans and Connor, 1993) are now identified as the coarse siltite member of the Apple Creek Formation (Tysdal, 2000a, b; Tysdal and others, 2000).  Unit is named for distinctive light-gray, quartz-rich graded beds of coarse-grained siltite to fine-grained quartzite that are most abundant in the lower part of this member.  Light-gray beds have erosional bases, show Bouma sequences (Tb-c, Tb-c-d, locally also Ta), and grade upward into gray-green medium siltite.  Graded beds commonly are 10-30 cm thick but are as thick as 1 m.  Upper part of unit is dominated by graded beds of grayish-green siltite and minor beds of argillite and fine-grained quartzite.  Bedding ranges from 1 to 100 cm; most about 10-25 cm thick.  Magnetite bands are present both in the Lemhi Range where this unit was defined by Tysdal (1996a, b, c, 2000a) and in the redefined strata (formerly lower Yellowjacket Formation) in the Salmon River Mountains (Nash, 1989).  Soft-sediment deformation structures are common in this unit, including convolute lamination, dish, pillar, and flame structures, syneresis cracks, and ball-and-pillow structures.  Unit Yac is interpreted to be primarily a turbidite deposit with minor debris flows indicated by rare pebbly beds.  Total thickness about 2,000-2,500 m.  Unit grades upward through a transition into the Gunsight Formation (Tysdal, 2000a).'
4751|'Grayish-green argillite, argillaceous siltite, and fine- to medium-grained siltite forms the matrix and interbeds to matrix-supported, poorly sorted conglomerate, first characterized as diamictite by Tietbohl (1981).  Unit is generally intensely cleaved, obscuring sedimentary features; however graded beds are commonly recognized in those siltite beds that are less pervasively deformed.  Conglomeratic beds are tabular in shape with thicknesses of as much as several meters and lateral extent of several tens of meters.  Clasts in conglomeratic beds are subangular to well rounded and commonly 1-5 cm in long dimension; locally, some clasts are 20-25 cm long and one observed clast was 50 cm.  Matrix material is composed of sericite, muscovite, chlorite, and silt of quartz and plagioclase.  Tietbohl (1986) indicated that about 90 percent of clasts are detrital rock fragments ranging from argillite to fine-grained metasandstone.  Tysdal (2000a) described sparse laminae and beds (=1 cm) of magnetite locally present in the Lemhi Range.  He interpreted graded bedding in the siltite beds to indicate an origin by turbidity currents, and attributed conglomeratic beds that lack grading to subaqueous debris flows.  Thickness estimates are complicated by deformation but the unit is about 600 m thick on the west side of the Lemhi Range and 1,000-1,500 m on the east side.  Unit grades upward into the conformably overlying coarse siltite member (Yac) (Tysdal, 2000a).'
4752|'Greenish-gray to olive-gray, planar-laminated and ripple-cross-laminated, fine-grained siltite and argillaceous siltite well exposed in upper reaches of Bear Valley Creek drainage in the Lemhi Range.  Some beds contain planar laminations that grade upward to small-scale (1-3 cm) sets of ripple-cross-laminated siltite.  Planar-laminated strata locally developed water-escape structures.  Beds commonly beds graded from 1 to 2-cm-thick, light-gray, medium- to fine-grained siltite upward into dark-gray, fine-grained siltite.  Upper part of fine siltite member contains sparse, local, matrix-supported, gravel-size argillite clasts in horizons 1-2 clast diameters thick.  Fine silt and clay content also is more abundant in upper part of unit.  Graded beds with Bouma sequences and sedimentary structures indicate most of unit consists of turbidites, with lesser debris flows and some reworking by bottom currents (Tysdal, 2000a).  Base of unit is unconformable on the Big Creek Formation (Yb) and top is conformably overlain by the abrupt appearance of the diamictite member (Yad).  Total thickness about 1,000 m (Tysdal, 2000a).'
4753|'The Big Creek strata are primarily exposed in the Lemhi Range and Beaverhead Mountains.  In the Lemhi Range, the Lem Peak (normal) fault separates somewhat different sequences of unit Yb; the following descriptions from Tysdal (2000a) focus on these two areas (Tysdal, 1996a, b, c; Tysdal and Moye, 1996).

North of Lem Peak fault-Light-gray, coarse-grained siltite to medium-grained quartzite (metasandstone); prominent silty laminae of rusty-brown-weathering carbonate and dark-gray, heavy-mineral laminae.  Quartzite is composed of 50-60 percent quartz, 10-20 percent feldspar, 5-15 percent matrix, and as much as 5 percent heavy-mineral laminae, including such minerals as tourmaline, zircon, and ilmenite.  Beds commonly are composed of two-dimensional dunes (megaripples) with planar cross-lamination in sets 0.5-1 m high; dune wavelengths as much as 3 m, and dune heights 0.3-0.5 m.  Other beds show three-dimensional dunes with trough cross-laminae; dune wavelengths 3-5 m, and dune heights of 0.3-0.5 m.  In upper part of formation, dark-gray argillaceous siltite in sequences less than 5 m thick is intercalated with light-gray, coarse-grained siltite and fine-grained quartzite.  Locally, double clay drapes and reactivation surfaces are developed, indicating deposition by tidal current processes.  Other sedimentary features indicating or consistent with bipolar tidal currents include herringbone cross-lamination, flaser and lenticular bedding, interbedded dunes and mudstone lenses, and tidal channel deposits.  Locally, an amygdaloidal andesite flow is 2-4 m thick in upper Big Creek strata.  Thickness about 2,700 m.  Bottom of the Big Creek is not exposed in the Salmon National Forest and top is unconformably overlain by the Apple Creek Formation (Tysdal, 2000a).

South of Lem Peak fault-Light-gray, coarse-grained siltite to medium-grained quartzite is also the dominant lithology south of the Lem Peak fault, including the area designated the type section by Ruppel (1975).  Upper part of the Big Creek in the type area consists of stacked two-dimensional dunes with heights of 0.5-1.5 m and wavelengths of 2-3 m.  Reactivation surfaces and double clay drapes indicate deposition in a tidal environment with bipolar currents trending northeast-southwest (present coordinates). Lower part of formation is typified by heavy-mineral laminae commonly as thick as 3 cm and extending laterally in gently inclined cross-beds for as much as 100 m.  These strata have been interpreted as beach deposits (Tysdal, 2000a). Total thickness about 3,100 m.'
4754|'Composite unit generally used for areas where Mesoproterozoic strata were mapped prior to the definition of current stratigraphic nomenclature, and have not been re-examined during this mapping and compilation effort.'
4755|'Predominantly dark gray (but ranging from light to dark gray), thin- and thick-bedded, fine-grained and very fine grained, feldspathic and micaceous quartzite interlayered with lesser amounts of medium-gray argillaceous siltite (Ekren, 1988; Tysdal, 2000b); crops out in and near upper Shovel Creek in southwestern part of map area.  Sedimentary structures include abundant cross-beds, ripple cross-laminations, and local rip-up clasts.  Unit grades downward through a conformable transition zone into the Hoodoo Quartzite (Yh), as noted by Ross (1934), Ekren (1988), Evans and Connor (1993), and Tysdal and others (2000).  An intertidal depositional environment is suggested by sedimentary structures and alternating lithologies, which reflect contrasting energy conditions.  Top of unit not exposed; minimum thickness 500 m.

Unit Yaq was recognized by Ross (1934) as a separate unit from the Yellowjacket Formation (Yy), which occurs below the Hoodoo, but he did not assign a stratigraphic name.  Ekren (1988) also did not assign a formal name to the unit, preferring instead to use the informal "argillaceous quartzite."  Evans and Connor (1993), following the lead of Evans and Ekren (1985), included both Ross'' Yellowjacket below the Hoodoo Quartzite and the argillaceous quartzite above the Hoodoo in their "lower Yellowjacket."  This tentative correlation implied that the Hoodoo could be a tongue of clean white quartzite interfingering with the "expanded" Yellowjacket.  To further complicate the issue, Evans and Connor (1993), as well as other workers, also extended use of their "lower Yellowjacket" to include rocks to the east now interpreted to be Lemhi Group (see Yellowjacket Formation description).  Subsequent work indicates that the sequence Yellowjacket Formation (as defined by Ross)-Hoodoo Quartzite-argillaceous quartzite reflects a genetically related package of shallow-water strata that occur in a thrust plate which has later been cut by high-angle faults.  This package is fault-bounded and, as shown on the geologic map, is structurally isolated from Lemhi Group strata to which it has been correlated previously.  Tysdal (2000b) provided a detailed account of the geology and history of correlations relevant to this stratigraphic package.'
4756|'White to light-gray (locally brownish gray), medium-grained, thin- to thick-bedded quartzite composed of about 80-90 percent well-rounded quartz, 5-10 percent feldspar (orthoclase, microcline, and albite), and 5-10 percent biotite, chlorite, sericite, and iron oxide (Ekren, 1988).  Unit is generally massive, making identification of bedding difficult where fracturing is well developed.  Cross-lamination is locally distinct and oscillatory and current ripples are present throughout unit.  Marble and calcareous quartzite is irregularly present in basal part of formation (Ekren, 1988; Evans and Connor, 1993).  Total thickness estimated at about 1,100 m (Ekren, 1988).  The Hoodoo Quartzite grades downward into the Yellowjacket Formation (Yy) through a thickness of about 200 m, with thin-bedded white Hoodoo strata intercalated with thin-bedded, dark-gray argillaceous metasandstone and gray, fine-grained metasandstone typical of the Yellowjacket.  Transitional zone is reasonably well exposed in upper Lake Creek (about 7 km west of the townsite of Yellowjacket) and in the cirque wall about 0.7 km north of McEleny Mountain (Ekren, 1988; Evans and Connor, 1993).  Upper contact is gradational into unit Yaq.  The Hoodoo Quartzite is interpreted to be a shallow subtidal to intertidal deposit, winnowed under high-energy conditions as evidenced by the lack of silt and clay and the common presence of high-angle cross-laminations.'
4757|'Unit (as defined by Ross, 1934, and Tysdal, 2000b; see discussion below) consists of 518 m of calcareous strata, with no base exposed, overlain by 2,225 m of quartzitic clastic rocks.  Calcareous beds are gray to dark green and black, containing varying amounts of carbonate and calc-silicate minerals in lenses that intertongue with quartzite.  Upper greenschist metamorphism resulted in beds that are banded or mottled, depending on the presence of dark metamorphic minerals.  The presence of metamorphic scapolite indicates some of the beds were formerly evaporite horizons (Tysdal and Desborough, 1997).  The upper quartzitic part of the section is dark-gray, dark-bluish-gray, or locally white, generally thin bedded quartzite, with lesser intercalations of thin-bedded, dark gray siltite and argillite.  Metasandstone commonly consists of about 70 percent quartz, 15 percent biotite (or chlorite altered from biotite), and 15 percent feldspar (Ekren, 1988).  Common sedimentary structures include ripple cross-lamination, mud-chips, fluid-escape structures, local herringbone cross-lamination, climbing ripples, mudcracks, and millimeter-scale load casts (Ekren, 1988; Tysdal, 2000b).  Some argillite layers show "pull apart" structures probably formed as clay layers dried and shrank.  Locally, mud-chips are imbricated in opposite directions, indicating reversal of current directions.  These features are most consistent with deposition in a tidal environment, confirming the original shallow-water interpretation of Ross (1934) and later Ekren (1988).  Yellowjacket strata grade upward into the conformably overlying Hoodoo Quartzite (Yh) (Ross, 1934; Ekren, 1988; Evans and Connor, 1993).

Because this report uses a revised definition of unit Yy that differs from most recent applications [summarized to 1993 by Evans (1998)], a short summary of the nomenclatural history of this unit it required.  Ross (1934) originally included gray, slightly calcareous, shallow-water deposits of metasandstone and siltite near the townsite of Yellowjacket in his description of the reference section (technically, there is no formal type section).  Subsequent workers extended use of the Yellowjacket name to other gray quartzites and siltites that are widespread in the eastern Salmon River Mountains and northern Lemhi Range (Vhay, 1948; Ruppel, 1975; Bennett, 1977; Lopez, 1981; Hughes, 1983; Connor and Evans, 1986; Ekren, 1988; Evans and Connor, 1993; Evans, 1998).  Recent detailed mapping and stratigraphic studies indicate that the term Yellowjacket Formation should be restricted to the genetically related shallow-water strata originally designated by Ross (1934), which are preserved in a fault-bounded structural block (Tysdal, 2000b; Tysdal and others, 2000).  Similar, though not identical, conclusions have been reached by D. Winston (University of Montana) and P.K. Link (Idaho State University) in their attempt to relate the Middle Proterozoic strata of east-central Idaho to the classic Belt Supergroup (Winston and others, 1999).  Other rocks to which the Yellowjacket name had been extended (see references cited above) are now correlated with formations of the Lemhi Group (Tysdal, 2000a, b).'
4758|'White to light gray, medium- to coarse-grained feldspathic metasandstone; feldspar is 15 to 45 percent of rock; quartz grains are generally subangular to subrounded.  Dark-gray heavy mineral laminae are common in lower parts of beds; mud chips of siltite are present in some beds.  Beds commonly range from 30-100 cm thick. and are trough cross bedded, with troughs in sets that decrease in size upward in each bed.  Local 1-25 cm thick, discontinuous interbeds of medium-gray siltite.  Unit present only northwest of Carmen Creek in northwestern part of Beaverhead Mountains and in the eastern part of the Clearwater Mountains, northeast of the Cabin thrust fault. Unit displays characteristics of fluvial strata in both areas (R.G. Tysdal, unpub. data).  Neither the top nor bottom of the unit is exposed.  Total thickness is unknown, but it is greater than 2,000 m.'
4759|'Light-gray, fine- to coarse-grained, arkosic metasandstone composed chiefly of quartz and feldspar (both microcline and plagioclase); matrix ranges from 1-10 percent.  Dark-gray heavy minerals are abundant and are concentrated in basal laminae of beds; some heavy-mineral laminae are so concentrated as to form sags and convolute layers.  Beds composed of trough cross-laminae are abundant, and commonly are overlain by beds of planar to ripple cross-laminated metasandstone.  Fragments of dark-gray siltite (mud-chips) occur at the base of some beds, some forming lenses as thick as 1 m and extending along strike for several meters.  Climbing ripples were observed in a few beds.  Pebble conglomerate layers occur at the base of some beds, forming lenses as thick as 10 cm and extend at least 50 m along strike.  Pebbles commonly are rounded and are1-4 cm in diameter.  Clast compositions are mainly vein quartz, but include crystalline metamorphic rocks, granite, and metasandstone.  Water-escape structures occur locally.  Unit is interpreted as fluvial (Tysdal, unpub. data).  Unit is present only along the northeast flank of the northwestern part of the Beaverhead Mountains.  Unit is more than 5,000 m thick.  Unit was assigned to the Mount Shields Formation (Ruppel and others, 1993).'
4760|'Alternating sequence of quartzitic and calc-silicate strata.  A basal, upward-fining, fine-grained, and laminated metasandstone grades upward into calc-silicate argillite, siltite, and quartzite.  Basal quartzitic units vary in thickness from 0.1 to 2 m; capped by thin-bedded calc-silicate units 0.1-1 m thick.  Calc-silicate rocks are medium to dark green and contain abundant porphyroblasts of actinolite and tremolite.  Exposure of this unit is poor but the strata have been correlated to clastic and calcareous units of the Helena and Empire Formations of the Belt Supergroup as exposed in the Anaconda Range, Mont., east of the Salmon National Forest (Ruppel and others, 1993).'
4761|'Dark-gray to dark-greenish-gray, well-laminated argillite and silty argillite in uneven beds generally less than 5 cm thick; commonly contains uneven, parallel laminations of white to tan, very fine grained quartzite and siltstone.  Apparently overlying is a unit of light-gray to white, fine- to medium-grained quartzite interlayered with minor dark-gray argillite and siltite.  Ruppel and others (1993) interpreted these strata as being correlative to the Spokane and Greyson Formations of the Belt Supergroup as seen in the Highland Mountains, Mont., to the east.  Unit is poorly exposed at the northern end of the Salmon National Forest but appears to underlie the strata mapped as undivided Helena and Empire Formations (Yhe).'
4762|'Dark gray-green to grayish blue-green rock, cleaved; metamorphosed to lower greenschist facies.  Some intrusions are diabase, but others are so well cleaved that classification is uncertain.  Some of the rock contains yellowish-brown carbonate clots that weather readily, leaving a vuggy surface texture.  Forms sills, dikes, and in western part of Lemhi Range, a small plug-like intrusive.  Thickness of tabular bodies ranges from 1 to 30 m, generally too thin and discontinuous to show on map; only a very few are shown.  Present mainly in the Lemhi Range and eastern part of the Salmon River Mountains.  Age is uncertain.'
4763|'Pink and light-gray, medium- to coarse-grained, porphyritic to coarsely porphyritic, slightly peraluminous granite and augen gneiss underlying large areas in the north-central part of the Salmon National Forest.  Composed of 20-40 percent alkali feldspar, 15-25 percent plagioclase, 20-40 percent quartz, 20-30 percent biotite, and locally minor muscovite.  Microcline phenocrysts are commonly 1-4 cm long in the strongly foliated augen gneiss but generally range from 4 to 10 cm in the less foliated granite; locally, as long as 15 cm.  Phenocrysts typically are rounded oblate spheroids with rapakivi texture and internal growth rings commonly defined by small biotite inclusions.  Unit occurs both as plutonic bodies and as sills ranging from 1 to 1,000 m thick.  Outcrops weather to spheroidal shapes studded with gray or pink microcline phenocrysts and produce coarse grus with whole microcline phenocryts and augen typically preserved.  U-Pb zircon dates yield an age of about 1,370 Ma (Evans and Zartman, 1990; Doughty and Chamberlain, 1996).'
4764|'Dark-gray to black, fine- to medium-grained amphibolite and magnetite-hornblende gneiss in north-central part of the Salmon National Forest and extending to the north into Montana (Berg, 1977).  Composed of 40-70 percent hornblende, 20-50 percent plagioclase, 5-40 percent biotite, and less than 5 percent quartz (Schmidt and others, 1994).  Typically, amphibolite occurs as 1- to 15-m-thick sills with foliation defined by hornblende and biotite; magnetite-hornblende gneiss probably was comagmatic with the amphibolite.  Magnetite-hornblende gneiss contains 55-70 percent feldspar, 20-30 percent quartz, 10-20 percent hornblende, and 3-5 percent magnetite (Schmidt and others, 1994).  Outcrops of unit Yam are uncommon and weathering produces a dark micaceous soil.  Field relations between unit Yam and the megacrystic granite (Ymg) indicate mingling of the two magmas; U-Pb isotopic dating of both units confirms a comagmatic relationship at about 1,370 Ma (Berg, 1977; Evans and Zartman, 1990; Doughty and Chamberlain, 1996).'
4765|'Medium- to dark-gray, fine- to medium-grained, thinly layered biotite gneiss well exposed in the lower Middle Fork Salmon River and along the main Salmon River west of Shoup (Maley, 1974).  Composed of 50-90 percent subrounded to subangular quartz, 5-50 percent biotite, and 0-20 percent feldspar (Schmidt and others, 1994; Lund, Evans, and Esparza, 1983).  Biotite-rich and quartz-rich layers alternate and range from 0.5 to 10 cm thick.  Metamorphism reached garnet and sillimanite grade with migmatization common along the Middle Fork Salmon River.  Locally, gneiss interfingers with unit Yq and is cut by sills of units Ymg and Yam.  Some biotite-rich layers contain greater than 50 percent biotite and are similar to biotitites associated with the cobalt-deposit at Blackbird mine (Evans, 1998), suggesting at least part of unit Ybgn is equivalent to identifiable lower-grade strata.'
4766|'Light-gray to white, fine- to medium-grained quartzite present in both walls of the Salmon River canyon west of Shoup and northeast of Papoose Creek.  Compositionally 80-100 percent subrounded quartz, 0-5 percent biotite, and 0-10 percent feldspar, with local concentrations (=5 percent) of muscovite (Schmidt and others, 1994).  Bedding commonly massive except where biotite-rich laminae define thin layers.  Rare tourmaline breccias are present as 0.5- to 3-m-thick concordant lenses with angular quartzite clasts surrounded by a matrix of tourmaline.  Units Ymg and Yam intrude the quartzite, as do deformed and undeformed pegmatite and aplite.  Unit interfingers with unit Ybgn at both outcrop and map scale.

The stratigraphic relationship of units Yq and Ybgn is similar to that of the much less metamorphosed Hoodoo Quartzite and Yellowjacket Formation at their reference section near Yellowjacket (Ross, 1934; Tysdal and others, 2000).  In addition, local tourmaline breccias are present in the Hoodoo Quartzite (Evans and Connor, 1993), possibly strengthening the argument for such a correlation.  However, if biotitite layers are present in unit Ybgn, this suggests correlation with rocks at Blackbird mine (formerly considered Yellowjacket Formation, but now correlated with the Apple Creek Formation (compare, Evans, 1998; Tysdal, 2000b)).  In such a case, unit Yq may correlate with part of the Gunsight Formation (Yg).'
4768|'Predominantly light-gray to red-brown, coarse-grained granite gneiss locally present near Deadman Pass in the Beaverhead Mountains, but widely exposed in Montana immediately east of the Salmon National Forest in the Maiden Peak spur area northeast of Leadore (M''Gonigle, 1994).  Average composition is 38 percent microcline, 25 percent quartz, 12 percent orthoclase, 11 percent plagioclase, 12 percent hornblende and (or) biotite, and 2 percent apatite, zircon, ilmenite, and leucoxene.  Preliminary U-Pb zircon data suggested an Archean age (reported in M''Gonigle, 1994), but recent work suggests a Paleoproterozoic age of about 2,450 Ma (Kellogg and others, 1999).'
4769|'Light-gray, pale-green, and pale-red-purple, medium- to coarse-grained quartzite.  Unit is widespread in the Lemhi Range and present in the Beaverhead Mountains near Leadore and in the Salmon River Mountains west of Salmon.  Quartz content typically ranges from 90 to 95 percent; well-rounded, well-sorted, tightly cemented, and glassy grains.  Feldspar content seldom exceeds 5-10 percent.  A speckled appearance is quite common and results from 0.5 to 3-mm-diameter (usually reddish) spots of hematite, local limonite, and rare chlorite commonly concentrated along cross-laminae.  Beds are 0.5-2 m thick and commonly show trough cross-laminations and lesser herringbone cross-laminae.  Two-dimensional ripples and dunes are quite well developed in places; dunes have wavelengths of 4-8 m and heights of 0.7-1 m and ripples have wavelengths of 2-15 cm and heights of 0.3-3 cm.  Tysdal (2000a) interpreted the bulk of the Swauger to have been deposited in a tidal environment, based on the compositional maturity of the quartzites, presence of herringbone cross-beds, subordinate current cap deposits (de Mowbray and Visser, 1984) on some dunes, rare antidunes, and local flaser and lenticular bedding.  The Swauger grades upward into the Lawson Creek Formation.  Total thickness about 3,100 m.'
4770|'The Gunsight Formation was defined by Ruppel (1975) for rocks at Gunsight Peak in the Lemhi Range west-southwest of Leadore, Idaho.  McBean (1983) further studied the type section and much of the following description for the Gunsight south of the Lem Peak fault is taken from his work.  North of the Lem Peak fault and in the Beaverhead, Salmon River, and Clearwater Mountains, strata previously mapped as the upper unit of the Yellowjacket Formation (unit Yyu of Evans, 1998) are now correlated with the Gunsight (Tysdal, 2000b). Accordingly, the Gunsight is separately described as follows:  south of Lem Peak fault (that is, type section), north of Lem Peak fault (that is, mostly former unit Yyu), and in the Beaverhead and Clearwater Mountains.

South of Lem Peak fault-Pale-brown to gray, very fine grained to medium-grained metasandstone typifies most of the type section.  Quartz and feldspar are the dominant components, with feldspar content ranging from 25 to 50 percent; matrix content is 0-8 percent.  Sedimentary structures include trough and planar cross-beds; parallel ripple and climbing ripple cross-laminations; ripple and climbing ripple laminations; straight-crested, asymmetrical and oscillation ripples; and dewatering structures.  In the uppermost 100+ m, where the unit is transitional into the compositionally mature Swauger Formation (Ys), quartz content increases to 80-90 percent.  Lower 450 m of unit consist of interbedded siltite, argillite, and very fine grained metasandstone transitional into the underlying siltite of the Apple Creek Formation.  Matrix content in this lower part can reach 40 percent.  Total thickness is 1,700+ m.  McBean (1983) interpreted the formation to have been deposited in a shallow marine setting, but Tysdal (2000a) considered most of the unit to be fluvial.  Trough crossbedded metasandstone (as thick as 1-2 m) that fines upward into siltite is indicative of channel and overbank deposits and strongly supports Tysdal''s reevaluation.  Upper part of formation may be shoreface deposits transitional into marine deposits of the Swauger (Tysdal, 2000a).  Lower part of formation, with its intercalated siltite and argillite, probably formed in an intertidal to subtidal environment transitional into the turbidites of the Apple Creek Formation.

North of Lem Peak fault-Light- to dark-gray, very fine grained to medium-grained, feldspathic metasandstone (arkose) typifies this unit in the northern Lemhi Range and Salmon River Mountains.  Bed thickness ranges from 10 to 100 cm.  Decimeter-thick trough and planar cross-beds are typical; hummocky cross-stratification is present locally in the Salmon River Mountains.  Conglomeratic beds exist locally, containing clasts that are angular and rounded.  Deposition was probably in fluvial to shallow marine environments, with features such as the local conglomerates probably representing slumping of partially lithified channel margins into tidal(?) channels.  Total thickness probably exceeds 4,000 m.  In the Salmon River Mountains the unit is transitional downward into the banded siltite unit of the Apple Creek Formation (Yab), and upward into the Swauger Formation (Ys).'
4771|'The Apple Creek Phyllite was defined by Anderson (1961) for foliated rocks near Hayden Creek in the central Lemhi Range.  Ruppel (1975) redefined the unit as the Apple Creek Formation and Tietbohl (1981, 1986) studied a diamictite unit within the formation.  Tysdal (1996a, b, c, 2000a, b; Tysdal and Moye, 1996) slightly redefined and subdivided the formation into mappable informal subunits, described below.  On our geologic map, Tysdal''s subunits are used where recent mapping is available; where it is not available or distinctions could not be made in the field, the undivided designation (Ya) is used.'
4772|'Centimeter-scale layers of light-gray siltite to very fine grained metasandstone alternating with black siltite or argillite characterize the easily identified banded member.  The thickness of layers and the percentage of metasandstone versus siltite/argillite vary considerably.  Layers range from 0.5 to 10 cm thick and percentages of metasandstone to siltite/argillite range from equal to 95 percent dominance by either component.  These couples and couplets of the unit are interpreted to be turbidites (Sobel, 1982; Tysdal, in press).  In addition to the visually striking light and dark layering, argillite beds in virtually any outcrop exhibit predominantly (but not exclusively) downward-penetrating dikelets of coarser sediment from the overlying layer.  Commonly the dikelets are ''ptygmatically'' folded due to compaction of the originally very water laden argillaceous layers.  Unit is widespread in the Salmon River Mountains northeast of the Iron Lake fault, and reaches a thickness of at least 2,000 m.  Unit apparently thins to the southeast due to erosion so that only a thin sliver is preserved in the footwall of the Poison Creek thrust in the Lemhi Range.  Unit is the primary host for the stratabound Blackbird Co-Cu-Au deposit.  Base of unit is gradational downward into the coarse siltite unit (Yac), and top grades upward through a relatively abrupt transition into the overlying Gunsight Formation (Yg).  As previously noted, in the Lemhi Range unit Yab thins below the Gunsight due to erosion.

Unit was called the "middle subunit of the Yellowjacket Formation" by Connor and Evans (1986), but because the unit lies conformably above the coarse siltite unit of the Apple Creek Formation, Tysdal (in press) assigned it to the Apple Creek Formation.  The "banded siltite" name resurrects an informal name that was used originally by Connor and Evans (1986).'
4773|'White to light-gray (locally brownish gray), medium-grained, thin- to thick-bedded quartzite composed of about 80-90 percent well-rounded quartz, 5-10 percent feldspar (orthoclase, microcline, and albite), and 5-10 percent biotite, chlorite, sericite, and iron oxide (Ekren, 1988).  Unit is generally massive, making identification of bedding difficult where fracturing is well developed.  Cross-lamination is locally distinct and oscillatory and current ripples are present throughout unit.  Marble and calcareous quartzite is irregularly present in basal part of formation (Ekren, 1988; Evans and Connor, 1993).  Total thickness estimated at about 1,100 m (Ekren, 1988).  The Hoodoo Quartzite grades downward into the Yellowjacket Formation (Yy) through a thickness of about 200 m, with thin-bedded white Hoodoo strata intercalated with thin-bedded, dark-gray argillaceous metasandstone and gray, fine-grained metasandstone typical of the Yellowjacket.  Transitional zone is reasonably well exposed in upper Lake Creek (about 7 km west of the townsite of Yellowjacket) and in the cirque wall about 0.7 km north of McEleny Mountain (Ekren, 1988; Evans and Connor, 1993).  Upper contact is gradational into unit Yaq.  The Hoodoo Quartzite is interpreted to be a shallow subtidal to intertidal deposit, winnowed under high-energy conditions as evidenced by the lack of silt and clay and the common presence of high-angle cross-laminations.'
4774|'Unit (as defined by Ross, 1934, and Tysdal, 2000b; see discussion below) consists of 518 m of calcareous strata, with no base exposed, overlain by 2,225 m of quartzitic clastic rocks.  Calcareous beds are gray to dark green and black, containing varying amounts of carbonate and calc-silicate minerals in lenses that intertongue with quartzite.  Upper greenschist metamorphism resulted in beds that are banded or mottled, depending on the presence of dark metamorphic minerals.  The presence of metamorphic scapolite indicates some of the beds were formerly evaporite horizons (Tysdal and Desborough, 1997).  The upper quartzitic part of the section is dark-gray, dark-bluish-gray, or locally white, generally thin bedded quartzite, with lesser intercalations of thin-bedded, dark gray siltite and argillite.  Metasandstone commonly consists of about 70 percent quartz, 15 percent biotite (or chlorite altered from biotite), and 15 percent feldspar (Ekren, 1988).  Common sedimentary structures include ripple cross-lamination, mud-chips, fluid-escape structures, local herringbone cross-lamination, climbing ripples, mudcracks, and millimeter-scale load casts (Ekren, 1988; Tysdal, 2000b).  Some argillite layers show "pull apart" structures probably formed as clay layers dried and shrank.  Locally, mud-chips are imbricated in opposite directions, indicating reversal of current directions.  These features are most consistent with deposition in a tidal environment, confirming the original shallow-water interpretation of Ross (1934) and later Ekren (1988).  Yellowjacket strata grade upward into the conformably overlying Hoodoo Quartzite (Yh) (Ross, 1934; Ekren, 1988; Evans and Connor, 1993). 

Because this report uses a revised definition of unit Yy that differs from most recent applications [summarized to 1993 by Evans (1998)], a short summary of the nomenclatural history of this unit it required.  Ross (1934) originally included gray, slightly calcareous, shallow-water deposits of metasandstone and siltite near the townsite of Yellowjacket in his description of the reference section (technically, there is no formal type section).  Subsequent workers extended use of the Yellowjacket name to other gray quartzites and siltites that are widespread in the eastern Salmon River Mountains and northern Lemhi Range (Vhay, 1948; Ruppel, 1975; Bennett, 1977; Lopez, 1981; Hughes, 1983; Connor and Evans, 1986; Ekren, 1988; Evans and Connor, 1993; Evans, 1998).  Recent detailed mapping and stratigraphic studies indicate that the term Yellowjacket Formation should be restricted to the genetically related shallow-water strata originally designated by Ross (1934), which are preserved in a fault-bounded structural block (Tysdal, 2000b; Tysdal and others, 2000).  Similar, though not identical, conclusions have been reached by D. Winston (University of Montana) and P.K. Link (Idaho State University) in their attempt to relate the Middle Proterozoic strata of east-central Idaho to the classic Belt Supergroup (Winston and others, 1999).  Other rocks to which the Yellowjacket name had been extended (see references cited above) are now correlated with formations of the Lemhi Group (Tysdal, 2000a, b).'
4775|'Alternating sequence of quartzitic and calc-silicate strata.  A basal, upward-fining, fine-grained, and laminated metasandstone grades upward into calc-silicate argillite, siltite, and quartzite.  Basal quartzitic units vary in thickness from 0.1 to 2 m; capped by thin-bedded calc-silicate units 0.1-1 m thick.  Calc-silicate rocks are medium to dark green and contain abundant porphyroblasts of actinolite and tremolite.  Exposure of this unit is poor but the strata have been correlated to clastic and calcareous units of the Helena and Empire Formations of the Belt Supergroup as exposed in the Anaconda Range, Mont., east of the Salmon National Forest (Ruppel and others, 1993).'
4776|
4777|'Description from Apple Creek Formation (coa_id 4748).  The rocks in this unit have been tectonically altered and silicified.

The Apple Creek Phyllite was defined by Anderson (1961) for foliated rocks near Hayden Creek in the central Lemhi Range.  Ruppel (1975) redefined the unit as the Apple Creek Formation and Tietbohl (1981, 1986) studied a diamictite unit within the formation.  Tysdal (1996a, b, c, 2000a, b; Tysdal and Moye, 1996) slightly redefined and subdivided the formation into mappable informal subunits, described below.  On our geologic map, Tysdal''s subunits are used where recent mapping is available; where it is not available or distinctions could not be made in the field, the undivided designation (Ya) is used.'
4778|'Description from Gunsight Formation (coa_id 4747).  The rocks in this unit have been tectonically altered and silicified.

The Gunsight Formation was defined by Ruppel (1975) for rocks at Gunsight Peak in the Lemhi Range west-southwest of Leadore, Idaho.  McBean (1983) further studied the type section and much of the following description for the Gunsight south of the Lem Peak fault is taken from his work.  North of the Lem Peak fault and in the Beaverhead, Salmon River, and Clearwater Mountains, strata previously mapped as the upper unit of the Yellowjacket Formation (unit Yyu of Evans, 1998) are now correlated with the Gunsight (Tysdal, 2000b). Accordingly, the Gunsight is separately described as follows:  south of Lem Peak fault (that is, type section), north of Lem Peak fault (that is, mostly former unit Yyu), and in the Beaverhead and Clearwater Mountains.

South of Lem Peak fault-Pale-brown to gray, very fine grained to medium-grained metasandstone typifies most of the type section.  Quartz and feldspar are the dominant components, with feldspar content ranging from 25 to 50 percent; matrix content is 0-8 percent.  Sedimentary structures include trough and planar cross-beds; parallel ripple and climbing ripple cross-laminations; ripple and climbing ripple laminations; straight-crested, asymmetrical and oscillation ripples; and dewatering structures.  In the uppermost 100+ m, where the unit is transitional into the compositionally mature Swauger Formation (Ys), quartz content increases to 80-90 percent.  Lower 450 m of unit consist of interbedded siltite, argillite, and very fine grained metasandstone transitional into the underlying siltite of the Apple Creek Formation.  Matrix content in this lower part can reach 40 percent.  Total thickness is 1,700+ m.  McBean (1983) interpreted the formation to have been deposited in a shallow marine setting, but Tysdal (2000a) considered most of the unit to be fluvial.  Trough crossbedded metasandstone (as thick as 1-2 m) that fines upward into siltite is indicative of channel and overbank deposits and strongly supports Tysdal''s reevaluation.  Upper part of formation may be shoreface deposits transitional into marine deposits of the Swauger (Tysdal, 2000a).  Lower part of formation, with its intercalated siltite and argillite, probably formed in an intertidal to subtidal environment transitional into the turbidites of the Apple Creek Formation.

North of Lem Peak fault-Light- to dark-gray, very fine grained to medium-grained, feldspathic metasandstone (arkose) typifies this unit in the northern Lemhi Range and Salmon River Mountains.  Bed thickness ranges from 10 to 100 cm.  Decimeter-thick trough and planar cross-beds are typical; hummocky cross-stratification is present locally in the Salmon River Mountains.  Conglomeratic beds exist locally, containing clasts that are angular and rounded.  Deposition was probably in fluvial to shallow marine environments, with features such as the local conglomerates probably representing slumping of partially lithified channel margins into tidal(?) channels.  Total thickness probably exceeds 4,000 m.  In the Salmon River Mountains the unit is transitional downward into the banded siltite unit of the Apple Creek Formation (Yab), and upward into the Swauger Formation (Ys).'
4800|'Modern stream alluvium; sand, gravel, cobbles, and boulders. Includes some glacial outwash gravel and alluvial fans mostly composed of debris-flow deposits.'
4801|'Medium to coarse sand interbedded with silty fine sand and silt. Mostly derived from weathered granite (Othberg and Stanford, 1992).'
4802|'Sandy pebble and cobble gravel; sand and granule gravel where formed from weathered granite.  Primarily formed by debris flows and local high-energy streams (Pierce and Scott, 1982).'
4803|'Slope failure in Kbgd.'
4804|'Sand, gravel, cobbles, and boulders.  Partially derived from glacial advances upstream. Benches as much as 600 feet (183 m) above modern streams. Commonly capped by alluvial fans mostly composed of debris-flow deposits.'
4805|'Includes till, glaciolacustrine sediments, outwash gravel, and some stream alluvium. Landforms include moraines, lake basins, outwash plains, and terraces.  Deposited by small isolated glaciers, valley glaciers, and large ice outlet glaciers originating in the Sawtooth and Trinity Mountains.  Relative dating of deposits indicates at least three glaciations in the Sawtooth Mountains (Stanford, 1982).'
4806|'Basalt flows of uncertain age.'
4807|'One canyon-filling flow from unknown vent in Mores Creek valley (Howard and others, 1982). Dark gray, vesicular, olivine-rich basalt. It is composed of lathlike crystals of plagioclase (labradorite) set in a matrix that is chiefly augite, ilmenite, and magnetite but which also contains olivine. Normal magnetic polarity. Thickness of 20 feet (6 m).'
4808|'Basalt erupted from Red Mountain and flowed down Fall Creek (Bennett, 1980).'
4809|'Fan gravel and sand deposited onto, and stream deposits formed in water dammed behind, Smith Prairie Basalt and mostly coarse sand deposited onto the basalt of Gowen Terrace. Thickness up to 100 feet (30 m) adjacent to canyon walls.'
4810|'Includes three canyon-filling basalts (Howard and Shervais, 1973): two porphyritic basalts separated by a microporphyritic basalt. Normal magnetic polarity. Mostly diktytaxitic and dark gray. Contains plagioclase, brown clinopyroxene, olivine, and opaques. Maximum measured thickness of 400 feet (120 m).'
4811|'Fan gravel deposited onto, and stream deposits formed in water dammed behind, basalt of Lava Creek.'
4812|'Dark to medium gray, very fine-grained basalt. Normal magnetic polarity.'
4813|'Four flows of medium gray olivine basalt. Canyon-filling basalt probably erupted in Smith Prairie (Howard and others, 1982). Normal magnetic polarity. Olivine phenocrysts up to 1-3 mm in diameter. Age of 0.5720.210 Ma (potassium-argon date from Othberg and Stanford, 1992). Forms terrace up to 600 feet (183 m) above the river. Thickness of about 200 feet (61 m).'
4814|'Single flow of dark gray to black, aphyric, very fine-grained basalt. Canyon-filling basalt probably erupted in Smith Prairie (Howard and others, 1982). Normal magnetic polarity. Thickness of about 121 feet (37 m).'
4815|'Fan gravel deposited onto, and stream deposits formed in water dammed behind, Smith Creek and Steamboat Rock basalts.  Also includes some fan gravels deposited on the Steamboat Rock Basalt surface downstream from Long Gulch.'
4816|'Medium to light gray and almost aphyric basalt. Xenocrysts and xenoliths of granitic rocks are common. Reverse magnetic polarity.'
4817|'Numerous flows of olivine basalt. Upper flows are medium gray plagioclase-phyric basalt and diabase. Lower flows are dark to medium gray microporphyritic basalt. Reverse magnetic polarity.  Maximum thickness of 580 feet (180 m; Howard and Shervais, 1973). Age of 1.80.3 Ma (potassium-argon date from Howard and others 1982).'
4818|'Two basalt flows and gravel above and between the flows. Light gray and very fine-grained aphyric upper flow. The lower flow is black and mostly glass. Normal magnetic polarity. May be basalt of Lucky Peak (Othberg and others, 1995).'
4819|'Consists of poorly sorted to unsorted sand, gravel, cobbles, and boulders eroded from rocks of the Idaho batholith and from various dikes. Gravel may be equivalent to the gravel of Bonneville Point of Othberg and Stanford (1992).'
4820|'Stratified, tan to gray, loosely consolidated arkosic sandstone and siltstone and interstratified conglomerate and thin-bedded, dark gray to black shale in which are abundant impressions of upper middle to lower upper Miocene leaves and plant fragments. Minimum thickness of 574 feet (175 m).'
4821|'Dark gray to black basalt, commonly porphyritic with euhedral lathlike phenocrysts of plagioclase (andesine to labradorite) up to 4 mm in length. Olivine is a common mineral in most samples, occurring as phenocrysts larger than those of plagioclase.'
4822|'Dark green microporphyritic basaltic andesite and basalt dikes consisting mostly of labradorite and augite. Most probably correlate with the Columbia River Basalt Group, but those in the southernmost part of the Idaho batholith may be younger.'
4823|'Light gray, almost white, very fine-grained, crystal poor rhyolite. It consists of a matrix of quartz and potassium feldspar in which are angular pieces of quartz, sanidine, and oligoclase that range from 1 to 3 mm long. Age of about 342.4 Ma (zircons using the fission track method; Kiilsgaard and others, 1997).'
4824|'Water-lain rhyolitic ash, conglomerate, and arkose. Age of 32.72.7 Ma (zircons using the fission track method; Kiilsgaard and others, 1997).'
4825|'Dark gray to black, fine-grained, and weakly porphyritic. The phenocrysts are plagioclase and commonly 2 to 4 mm long.'
4826|'Includes diabase with medium grained, ophitic to subophitic texture and lamprophyric dikes in which ferromagnesium phenocrysts are set in a dark aphanitic groundmass.'
4827|'Pink, tan, and light gray, highly to sparsely porphyritic rhyolite with phenocrysts of potassium feldspar, quartz, plagioclase, and biotite.'
4828|'Pink to gray-green, porphyritic rhyodacite with phenocrysts of plagioclase, hornblende, biotite, and embayed quartz.'
4829|'Dark greenish to gray porphyritic dacite. Most of the phenocrysts are plagioclase, but some are quartz, which is commonly resorbed and rounded. Small phenocrysts of hornblende and biotite are common.'
4830|'Pink to light gray, coarse- to medium-grained, equigranular to porphyritic biotite granite in which perthitic potassium feldspar and dark quartz are the principal components.'
4831|'Granodiorite grading to quartz monzodiorite and granite. Gray to dark gray, medium-grained, equigranular to porphyritic rock in which zoned andesine is the principal component; hornblende and sphene are common.'
4832|'Greenish gray, highly porphyritic stocks and dikes with a fine-grained groundmass. Commonly contains 10 to 30 percent green hornblende. Phenocrysts in the rock are chiefly strongly zoned plagioclase, although some are quartz. Another conspicuous feature is fresh appearing, vitreous, euhedral biotite.'
4833|'Dark gray, equigranular, and fine- to medium-grained. Green hornblende is the principal mafic mineral and may account for as much as 40 percent of the rock. Augite and hypersthene also are common constituents.'
4834|'Undifferentiated dikes with compositions that may range from basalt through aplite (tf).'
4835|'Dark gray, equigranular, and medium- to fine-grained. It is layered and consists chiefly of cumulus aggregates of plagioclase (labradorite grading to andesine), hypersthene, augite, and olivine.'
4836|'Pink, fine-grained aplite.'
4837|'Coarsely crystalline dikes consisting principally of quartz, feldspar, biotite, and muscovite.'
4838|'Light gray, fine-textured aplite with quartz and feldspar minerals the principal constituents. Pegmatites are light gray to white and distinguished by the large grain size of contained minerals.'
4839|'Aplite and pegmatite dikes crosscutting subordinate amounts of biotite granodiorite.'
4840|'Light gray and fine- to medium-grained biotite granite with a distinctive anhedral texture. Similar to aplite.'
4841|'Massive, light gray, medium- to coarse-grained, and equigranular to porphyritic muscovite-biotite (two-mica) granite, grading to granodiorite.'
4842|'Light gray, medium- to coarse-grained, equigranular to porphyritic granodiorite in which oligoclase is the chief component. Grades to granite.'
4843|'Iron-stained, medium- to coarse-grained, equigranular to porphyritic granodiorite. Biotite is altered to chlorite or to iron oxides, which account for the characteristic reddish stain. Feldspars in the rock are altered to clay minerals or sericite.'
4844|'Gray, medium-grained hornblende-biotite granodiorite. Present only as two small exposures southwest of Atlanta.'
4845|'Gray to dark gray, medium-grained, equigranular tonalite in which andesine is the principal component. May contain as much as 20 percent biotite and hornblende. Contains primary epidote. Locally foliated; grades to granodiorite.'
4846|'Garnet-diopside gneiss, quartzite, and biotite-sillimanite schist of uncertain age.'
4847|
4900|'Unconsolidated boulder, gravel, sand, clay, and peat deposits of Pleistocene and Holocene age.  These include moraine, glacial outwash, stream, talus, and landslide deposits.  Four glacial episodes, pre-Bull Lake, Bull Lake (BLM on Plate 2), Pinedale (BLM on Plate 2), and Neoglaciation are recognized in some areas based on outwash terraces and moraines.'
4901|'Post-basalt arkosic sedimentary rocks found along southern margin of Weiser embayment (Figure A-3) and along fault troughs in Long Valley area (southeastern Plate 1).'
4902|'Thin discontinuous soil horizons as well as ash beds and locally derived sediments that were deposited as interbeds and in local basins.  Those interbedded with Imnaha and Grande Ronde Basalts are considered to be lower Payette Formation whereas those associated with basalt of Weiser are considered to be upper Payette Formation (Fitzgerald, 1982).'
4903|'Basalt flows that are post-Grande Ronde Basalt (Tcrg).  These are aerially restricted basalt flows found in south-central Plate 1.  Includes three members and several local units based on stratigraphy, geochemistry, and paleomagnetism (Fitzgerald, 1982).  Locally includes interbedded pyroclastic deposits of Weiser (Twp).'
4904|'Voluminous pyroclastic materials including pumice breccia, scoria, volcaniclastic debris, and ash are closely related to the basalt of Weiser.  Pyroclastic rocks are particularly important near vent areas east of Cambridge and south of Midvale (southern Plate 1; Fitzgerald, 1982) where mapped separately from basalt of Weiser.'
4905|'Slightly to highly porphyritic (phyric) basalt flows with coarse pyroxene and plagioclase phenocrysts.  Restricted to Cuddy Mountain and the eastern edge of the Cuddy Mountain uplift (west-central Plate 1).  Mostly deposited on pre-Tertiary rocks of the uplift.  On southwestern part of Cuddy Mountain, a lower flow of basalt of Cuddy Mountain is overlain by a Grande Ronde Basalt (Tcrg) flow and elsewhere; an upper flow of basalt of Cuddy Mountain may overlie Grande Ronde Basalt (Fitzgerald, 1982).  This suggests that basalt of Cuddy Mountain may at least span the time of Grande Ronde Basalt (Fitzgerald, 1982) but basalt of Cuddy Mountain has also been included with basalt of Weiser and correlated with the Strawberry Volcanics of Oregon (Hooper and Swanson, 1990).'
4906|'Includes Imnaha and Grande Ronde Basalts (Tcri and Tcrg, respectively) where they have not been mapped separately (northern Plate 1).  Exposures are part of the eastern fringe of Columbia River Plateau known as the Weiser embayment (Figure A-3, Plate 1; Fitzgerald, 1982).  Faulting and erosion have caused the discontinuous exposures that are remnants of more complete basalt cover to west.'
4907|'Nonporphyritic (aphyric) basalt with fine plagioclase laths in some flows.  Sugary texture.  Medium dark gray color with some green mottling on fresh surfaces at tops of flows.  Weathered tops of flows are reddish colored.   Flows are 10-20 m thick.  Total thickness in Weiser embayment (Figure A-3) is less than 300 m (Fitzgerald, 1982).  Flows are geochemically homogeneous and are subdivided based on paleomagnetism (Swanson and others, 1979).  Deposited conformably on Imnaha Basalt (Tcri).  Age is 16.5-15.6 Ma (Long and Duncan, 1982).'
4908|'Coarsely porphyritic (phyric) basalt flows at base of Columbia River Basalt Group.  Phenocrysts are plagioclase, olivine, and augite.  Color is black except tops of some flows are purplish.  Flows are 20-60 m thick; as many as 19 flows are exposed in areas in and near the Forest.  A total thickness of at least 700 m exists in the Weiser embayment (Figure A-3; Fitzgerald, 1982).  Age is 17.5-16.5 Ma (McKee and others, 1981).'
4909|'Porphyritic rhyolite to dacite, granite porphyry, and hornblende-biotite granodiorite.  Dikes are 1-100 m wide and structurally controlled.  Most intense concentration is Profile Gap-Smith Creek dike swarm (Lund and others, 1997), which has average strike about N10oE and was first mapped at Profile Gap (central Plate 2) by Shenon and Ross (1936) where intruded into Profile Gap-Johnson Creek shear zone (Lund and others, 1997).  Dikes are dated by K-Ar on hornblende at about 46-47 Ma (Leonard and Marvin, 1982).  These rocks also comprise the areally larger Pistol Creek dike swarm (south-central Plate 2; Fisher and others, 1992) with similar north-northeast trend.  They also form the Rainbow Ridge-Quartz Ridge dike swarm and the dikes near Van Meter Hill (3 km northwest of Yellow Pine, central Plate 2) that trend about N65oE and that are primarily formed of hornblende-biotite granodiorite and porphyritic dacite, respectively.'
4910|'Unit composed of several textural varieties, undivided on map: 1) Green rhyolite with aphanitic groundmass having up to 50 percent quartz and feldspar phenocrysts. 2) Light tan-pink, miarolitic cavity-rich, rhyolite porphyry containing quartz and potassium feldspar phenocrysts and aphanitic groundmass of the same mineralogic composition. 3) Tan-pink syenogranite porphyry (Figure B-1) having fine-grained groundmass and as much as 75 percent fine- to medium-grained quartz, potassium feldspar, biotite, and hornblende phenocrysts; also has as much as 20 percent miarolitic cavities, some lined with bi-pyramidally terminated quartz crystals.  4) Gray monzogranite porphyry having fine-grained groundmass with common plagioclase phenocrysts and lesser amounts of potassium feldspar, biotite and hornblende, and minor quartz phenocrysts.

Forms core of Savage Point pluton (Figure A-3; Lund and others, 1997) along east-west-trend from Rock Lake to upper Logan Creek (central Plate 2).  Unit crops out in Wolf Fang Peak area as the southwestern arm of the roof zone of the Chamberlain Basin pluton (Figure A-3; north-central Plate 2).  A minor amount of this unit is on Quartz Ridge (central Plate 2) associated with Eocene hornblende-biotite granodiorite (Tgd) of the Rainbow Ridge-Quartz Ridge dike swarm (Lund and others, 1997).  Unit also present in roof areas of Casto pluton and intruding Challis Volcanic group at southeast corner of Plate 2.'
4911|'Unit composed of two compositional varieties, both common in Eocene plutons of central Idaho.  1) Tan-pink equigranular medium- to coarse-grained hornblende-biotite syenogranite (Figure B-2) found as major unit in Casto pluton, western part of Chamberlain Basin pluton, and eastern phase of Chamberlain Basin pluton (Figure A-3) known as Bighorn Crags pluton (eastern Plate 2).  2) Light gray porphyritic medium-grained hornblende-biotite monzogranite has less hornblende than syenogranite and forms major part of Chamberlain Basin, Savage Point, and Casto plutons.'
4912|'Light gray, fine-grained hornblende-biotite granodiorite.  Early phase of Eocene plutons intruded by and fringing the granites (Tg) in Savage Point, Chamberlain Basin, and Casto plutons (Figure A-3).  Forms major part of Rainbow Ridge-Quartz Ridge dike swarm (Lund and others, 1997).'
4913|'Dark brown-gray, medium-grained hornblende-biotite diorite.  Coarse-grained strongly zoned plagioclase; medium- to coarse-grained hornblende and biotite; and dark fine-grained felted masses of plagioclase, quartz, hornblende, biotite, and opaque minerals as groundmass. Forms oldest phase of the Eocene intrusions in Casto pluton (Fisher and others, 1992) and in western part of Chamberlain Basin pluton (Figure A-3).'
4914|'Dacitic to rhyolitic ash flows and lahars and minor volcaniclastic sedimentary rocks (Cater and others, 1973; Fisher and others, 1992) in the northern half of Thunder Mountain Caldera (Figure A-3; central Plate 2) which remains mapped only at reconnaissance level.  Based on extension of units from areas mapped in southern part of caldera, the lower part of the Sunnyside Tuff (Tcs), buff rhyolite (Tcbr), and lapilli tuff (Tct) are probably the major units in the northern unsubdivided part of the caldera.  In northwestern part, exposed rocks are dominantly basal lahar units that contain at least 25 percent pre-volcanic metamorphic and igneous cobbles.  Samples from this area have been preliminarily dated by K-Ar at about 48-51 Ma (Leonard and Marvin, 1982).'
4915|'Black, nearly aphyric, vesicular latite lava containing cinder layers and volcanic bombs. Thickness 0-50 m.  Located in central part of caldera complex near Sunnyside mine (central Plate 2; Fisher and others, 1992).  K-Ar dates from whole rocks are 41.01.4 and 43.41.4 Ma (Leonard and Marvin, 1982).'
4916|'Caldera-filling sedimentary rocks.  Includes bedded volcaniclastic ash, varved lake-bed siltstone, volcaniclastic conglomerate, talus, and landslide deposits.  Carbonaceous debris in this unit chemically fixed gold in the hydrothermal system at the Dewey mine (central Plate 2; Ross, 1933).'
4917|'Complex rhyolitic unit making up most of Thunder Mountain caldera complex (Figure A-3; central Plate 2) as subdivided by Fisher and others (1992).  Upper part of Sunnyside Tuff is a multiple-flow compound-cooling unit of red-weathering densely-welded, devitrified rhyolite tuff that contains rock fragments and flattened pumice lapilli and has a black vitrophyric base.  Upper and lower parts of unit separated by megabreccia unit wherein fragments from lower part of unit are included in matrix of tuff from upper part of unit.  This megabreccia may have formed from collapse of caldera walls at beginning of eruption of tuffs of upper part of unit.  Lower part of Sunnyside Tuff from  bottom to top is 1) three or more cooling units of white to pink, only slightly welded, pumice-bearing, slightly porphyritic rhyolite bases and gray, vertically jointed, densely welded, phenocryst-rich (as much as 50 percent) quartz latite tops; 2) at least two cooling units of red flow-layered lava or hot-ash-flow tuff with black vitrophyre and intercalated black vesicular latite flow; and 3) a single cooling unit of reddish-gray, densely welded rhyolite tuff.  Thickness as much as 1,000 m (Fisher and others, 1992).  Originally named in Thunder Mountain mining district (Figure A-4; Shannon and Reynolds, 1975).  Biotite K-Ar date of 47.71.6 Ma and sanidine K-Ar dates on two samples of 46.31.1 and 46.31.0 (Leonard and Marvin, 1982).'
4918|'Nearly aphyric buff rhyolite.  Flow laminated and layered. Thickness 0-300 m.  In same stratigraphic position on western margin of caldera complex as lapilli tuff (Tct) is around southern and eastern margins (Fisher and others, 1992).'
4919|'Rhyolite ash-flow tuffs with three recognized cooling units (Fisher and others, 1992).  Finely porphyritic rhyolite with predominant plagioclase phenocrysts; phenocrysts are 14 percent of unit and less than 2 mm long.  Cooling units have black vitrophyric bases, lavender to salmon devitrified or densely welded tops, and green epiclastic sedimentary rocks as interbeds.  Thickness 0-300 m.  Found as thin unit in central part of caldera (Fisher and others, 1992).'
4920|'Complex unit of lapilli-bearing ash-flow latite tuff, tuffaceous sedimentary rocks, and black latite lava.  Green-gray or buff lapilli tuff is densely welded with plagioclase and pyroxene phenocrysts and conspicuous dark green, 1.5-2.5 cm, collapsed pumice lapilli.  Ash-flow tuffs are interbedded with tuffaceous sandstone and siltstone.  Thin unit of black latite is a local interbed.  Quartz-rich densely welded gray tuff forms base of unit on southwest side of caldera.  Thickness 0-500 m.  Unit has undergone pervasive propylitic alteration.  Eruption of this unit caused initial collapse of Thunder Mountain caldera (Fisher and others, 1992).'
4921|'Dark-gray and dark-purplish-gray flow-layered latite lava.  Crystal-poor latite lava layered with porphyritic dacite-rhyolite flows having plagioclase, biotite, hornblende, and pyroxene phenocrysts.  Thickness 0-500 m.  Found on fringes of Thunder Mountain caldera (Fisher and others, 1992).  Sanidine K-Ar age of 50.81.7 Ma (Leonard and Marvin, 1982).'
4922|'Crystal-rich, gray-green, rhyodacite ash-flow tuff.  Subequal amounts of plagioclase, resorbed quartz, biotite, and hornblende phenocrysts.  Pumice lapilli common.  Two outflow units recognized.  Thickness in Forest unknown, but as much as 2000 m in localities to east.  Unit formed as outflow from Van Horn Peak caldera on east side of Middle Fork of Salmon River (directly east of Plate 2).  Biotite K-Ar date of 48.41.6 Ma (Fisher and others, 1992).'
4923|'Gray, medium-grained biotite-muscovite granite (Figure B-3).  Muscovite equal to biotite or more abundant.  Rock is equigranular and minerals are subhedral.  Texture is structurally homogeneous (nonfoliated).  Pegmatite zone commonly observed at roof of biotite-muscovite granite (Kg) near contact with unit Kpg.   Cross-cutting relationships were not found.  However, based on map relations (central Plate 2), biotite-muscovite granite intruded the porphyritic muscovite-biotite granite-granodiorite (Kpg).'
4924|'Unit consists of varieties of gray porphyritic muscovite-biotite granite-granodiorite, gray biotite granite-granodiorite, and gray muscovite-biotite granite.  In porphyritic variety, potassium feldspar phenocrysts, generally about 1 cm long, range from very common (15 percent) to sparse (<1 percent).  In nonporphyritic variety, minerals are medium grained and subhedral.  Quartz grains form fine-grained aggregates.  Muscovite varies from trace amounts to subequal with biotite and increases near the contact with the younger biotite-muscovite granite (Kg); some muscovite may be secondary.  Monazite and xenotime are common accessory minerals and are ubiquitous heavy minerals in placers in the Warren mining district (Figure A-4).  In western exposures, foliation is present but is inconsistently oriented; in eastern exposures, texture is nonfoliated.  Muscovite-bearing varieties may be equivalent to Warm Lake quartz monzonite but much of this unit is probably equivalent to Gold Fork granodiorite of Schmidt (1957).'
4925|'Gray, fine- to medium-grained biotite granodiorite (Figure B-4).  Hornblende may be present in trace amounts.  Plagioclase phenocrysts are present locally.   Prominent foliation is formed by planar alignment of biotite and locally by flattening of quartz.  Lineation of biotite is present locally.  Inclusions, schlieren, and screens of country rock are common.  Foliated biotite granodiorite is closely associated with foliated tonalite (Ktf) near Salmon River suture (eastern Plate 1 and western Plate 2) and at roof of Idaho batholith in Plate 2.   Equivalent to Little Valley quartz diorite of Schmidt (1957).'
4926|'Coarsely porphyritic biotite granodiorite with large pink potassium feldspar phenocrysts and hornblende in some areas.  Unit is more mafic than other Cretaceous granite and granodiorite (Kgdf or Kpg), having up to 15 percent mafic minerals.  Foliation is common.  This is a minor unit that is dated by K-Ar on biotite between 75 and 81 Ma (Fisher and others, 1992).  Intruded by Kg and Kpg.'
4927|'Gray, medium-grained, foliated and commonly lineated hornblende-biotite tonalite.  Hornblende generally subsidiary to biotite and abundance of each ranges from trace to 10 percent.  Primary epidote found in some areas (Manduca, 1988).  Foliation formed by planar alignment of biotite flakes and elongation and flattening of quartz grains.  Lineation formed by orientation of elongate hornblende grains.  Schlieren and screens of metamorphic country rock are common near Salmon River suture (eastern Plate 1 and western Plate 2).  Preserved at top of Idaho batholith in isolated locations in Plate 2.  Equivalent to tonalite of Payette River of Manduca (1988) and probably equivalent to quartz dioritic gneiss of Donnelly of Schmidt (1957).'
4928|'Porphyritic biotite granodiorite gneiss with coarse phenocrysts of microcline in medium-grained quartz-plagioclase-microcline-biotite groundmass.  5-15 percent biotite present.  Fabric ranges from foliated granodiorite to mylonitic augen gneiss.  Dated at 1151 Ma (by SHRIMP U-Pb zircon; K. Lund and J.N. Aleinikoff, unpublished data, 2002; previously dated at 1115 Ma, Manduca, 1988).  Equivalent to porphyritic orthogneiss of Little Goose Creek complex of Manduca (1988) and only differentiated from heterogeneous orthogneiss complex (Kgn) where in large unmixed body forming much of West Mountain (east central Plate 1).'
4929|'Gneissic coarse-grained hornblende tonalite gneiss, porphyritic granodiorite gneiss (possibly the same rock as unit Kpgdm), and medium-grained biotite granodiorite gneiss (eastern Plate 1).  Rocks are strongly deformed together (Figure B-5) such that they can not be mapped separately at this scale (for detail, see Manduca, 1988).  Equivalent to Little Goose Creek complex of Manduca (1988), gneissic quartz monzonite and quartz diorite unit of Hamilton (1969), and part of migmatite of McCall of Schmidt (1957).'
4930|'Heterogeneous mixture of Jurassic to Permian island arc rocks that underwent Cretaceous intrusion, metamorphism, and deformation during accretion along the Salmon River suture (eastern Plate 1).  Considerable variation exists among different rock types; protoliths not identifiable for much of complex and complexity of intrusion and deformation too great to be shown at this scale (for detail, see Hamilton, 1969; Manduca, 1988).  Includes amphibolitic and biotitic paragneisses that formed from volcanogenic sedimentary and volcanic rocks during Cretaceous dynamothermal processes; protoliths probably all Jurassic to Permian volcanic and sedimentary rocks of the Blue Mountains island arc.  Also includes tonalitic, trondhjemitic, and granodioritic orthogneisses, some of which formed from Cretaceous intrusions into the Triassic and Permian protolith and others of which may have originated as Jurassic to Permian island arc plutons.  The youngest pluton (orthogneiss) in the complex (based on cross-cutting relationships) is about 123 to 113 Ma (Manduca, 1988).  In northwestern exposures, metavolcanic parts of this unit are gradational with undifferentiated metamorphosed rocks of the Blue Mountains island arc (JPmcs, JPgn, and JPam).  Orthogneisses and parts of the unit that were predominantly plutonic are equivalent to Hazard Creek complex of Manduca (1988) and gneissic quartz diorite unit of Hamilton (1969); entire complex is equivalent to gneiss of Council Mountain of Schmidt (1957).'
4931|'The Deep Creek pluton and nearby unnamed plutons in the Seven Devils Mountains (north-central Plate 1) are hornblende quartz diorite and tonalite compositions.  The Deep Creek pluton is dated by K-Ar on hornblende at about 127 Ma (White, 1968; 1973).  Based on absence of oriented fabric and dating, White (1968) suggested that these are part of a younger group of plutons that intruded the Wallowa terrane.  Assuming the date is approximately the age of emplacement, these plutons may represent early stages of the accretionary processes after building of the island arc had ceased in the Jurassic.'
4932|'Greenstone volcaniclastic rocks and minor latite-andesite tuff of the Weatherby Formation are exposed in the southwestern part of Plate 1.  Volcaniclastic rocks are primarily sandstone and shale containing largely volcanic and chert grains.  Sedimentary features such as flute casts, grooves, and fining upward sequences indicate deposition by turbidites.  Individual andesitic tuff (Jwa) and rhyolite tuff (Jwr) members have been mapped separately (below).  Lower part contains several volcanic conglomeratic horizons especially a distinctive red and green conglomerate below the rhyolite tuff member (Jwr).  Conglomerate matrix is tuffaceous and clasts are predominantly andesitic and basaltic (Frankhauser, 1969; Bruce, 1971; Henricksen, 1975).  Volcanic conglomerates were derived from the Huntington Formation (TRh) that in part unconformably (Slater, 1969; Bruce, 1971) and in part structurally underlies the Weatherby Formation (Livingston, 1932; Skurla, 1974; Henricksen, 1975).  This shows that the Huntington Formation (Olds Ferry terrane) must have been near the Izee terrane during the Jurassic.  Additionally, the large percentage of chert detritus in sandstones indicates a cherty provenance probably from the Baker terrane which must have been nearby in the Jurassic as well (Vallier, 1995).  Jurassic dates are from fossil assemblages and particularly from ammonite fossils in the unit (Brooks, 1979).  Formation is greater than 1300 m thick (Mann, 1991).'
4933|'Light green, greenstone andesitic tuff layer in the Weatherby Formation (west-central Plate 1; Mann, 1991).  Rock is composed of weathered plagioclase phenocrysts in a glassy perlitic matrix.  Contacts in most exposures are gradational.  Absence of thermal alteration of underlying rocks indicate that andesitic tuff may have formed as a subaqueous ash fall (Mann, 1991).  Approximately 130 m thick (Mann, 1991).'
4934|'Rhyolite to rhyodacite crystal tuff can be traced across Hitt and Cuddy Mountains (southwestern Plate 1) above the red and green volcanic conglomerate of the Weatherby Formation.  Dated at 200 Ma by K-Ar methods (C. Field in Mann, 1989).   Thickness is from 100 to 230 m (Skurla, 1974).'
4935|'Moderately porphyritic biotite granodiorite having plagioclase phenocrysts as much as 2 cm long and, locally, quartz phenocrysts.  Groundmass is medium-grained.  Commonly weakly foliated.  Age of these rocks not well documented.  Spatially and genetically related to quartz diorite (KJqd) and gabbro (KJgb) that all crop out in the Hitt, Cuddy, and Seven Devils Mountains (western Plate 1; White, 1968; Frankhauser, 1969; Slater, 1969; Bruce, 1971; King, 1971; Skurla, 1974; Henricksen, 1975).  This granodiorite is the youngest of these units as demonstrated by cross-cutting relationships.  The only available age information is a K-Ar date on hornblende from a sample in the Cuddy Mountains that gives an age of 195 to 205 Ma (Frankhauser, 1969).  This date indicates that this granodiorite unit (KJgd) is significantly older than and has a different origin than the similar looking foliated granodiorite (Kgdf) in and east of the suture zone.'
4936|'Light-gray, medium-grained, equigranular hornblende-biotite quartz diorite is found associated with gabbro (KJgb) and granodiorite (KJgd) in the Hitt and Cuddy Mountains (south-central and southwestern Plate 1, respectively).  Samples from the Cuddy and Hitt Mountains are dated by K-Ar on biotite and hornblende at 196 to 225 Ma (Henricksen, 1975).'
4937|'Medium-gray, medium- to coarse-grained hornblende gabbro plutons in central Plate 1.  Hornblende is the common mafic mineral seen in hand specimen; pyroxene and magnetite are commonly seen in thin section.  Intruded by granodiorite (KJgd) and quartz diorite (KJqd) in the Hitt and Cuddy Mountains (Frankhauser, 1969; Slater, 1969; Bruce, 1971; King, 1971; Skurla, 1974; Henricksen, 1975).  K-Ar biotite dates from samples from the Cuddy Mountains gives an age of 182 to 197 Ma (Henricksen, 1975) which is contrary to the cross-cutting relationships described above.'
4938|'Greenstone volcaniclastic, volcanic, and minor intrusive rocks comprise the Middle to Late Triassic Huntington Formation (southwestern Plate 1; Mann, 1991).  Volcanic sandstone and conglomerate and minor limestone and chert are prevalent in the Cuddy Mountains.  Volcanic rocks are tuffs, tuff breccias, and flows that are compositionally andesite, dacite porphyry, spilite, and keratophyre.  To the southeast, volcaniclastic and volcanic rocks of the Huntington Formation are intruded by granodiorite, quartz diorite, and gabbro plutons (KJgd, KJqd, KJgb).  Rocks of the Huntington Formation are the southeastern most of the oceanic terranes exposed in western Idaho.  At least 2600 m are exposed in the Cuddy Mountains (Mann, 1991).'
4939|'Diorite and quartz diorite plutons in the Seven Devils Mountains have not been dated but were mapped as part of an older group of plutons (White, 1968) that intruded greenschist metamorphic rocks of the Seven Devils Group (northwestern Plate 1).  This older group of plutons is thought to be related to island arc volcanism but, without dating, the age may be Triassic-Jurassic as suggested by White (1968) or Permian-Triassic as suggested by Vallier (1995).'
4940|'Recrystallized limestone and calcareous shale in the Snake River Canyon (northwestern edge Plate 1) increases in metamorphic grade northeastward across thrust faults to: 1) marble and calcareous phyllite and 2) coarse-grained marble to calcareous schist in the area of Pollack Mountain (north-central Plate 1).  Calcareous phyllite to schist contains calcite, plagioclase, biotite or phlogopite, muscovite, chlorite, rounded fine-grained quartz, epidote, siderite, and graphite.  Limestone to marble is medium to light gray calcite with minor phlogopite and graphite at highest grades.  In the Snake River Canyon, the limestone unconformably overlies the Doyle Creek Formation (TRd; Vallier, 1977).  However, along trend to the northeast, the Martin Bridge Formation gradationally overlies volcaniclastic sediments of the Doyle Creek Formation (TRd; McCollough, 1984; Lund and others, 1993).  Herein, the name "Martin Bridge Formation" is used in preference to "Martin Bridge Limestone" (Hamilton, 1963) because, both in its type locality in Oregon (Ross, 1938; Follo, 1986; 1994) and in central Idaho (Lund and others, 1993), the unit is an interlayered sequence of limestone and calcareous shale.  In some studies, the interfingered limestone and shale (or their metamorphic equivalents) have been given separate names (Hamilton, 1963; Aliberti, 1988) which has complicated the understanding of the stratigraphy and structure.  Additionally in areas where structure is complex, lenses of limestone in the upper Seven Devils Group have been mistakenly called Martin Bridge Limestone  (Hamilton, 1963; Aliberti, 1988).  Usage in this report is that Martin Bridge Formation refers to the interbedded limestone and calcareous shale above the volcanic and volcaniclastic rocks of the Seven Devils Group.  Formation is as much as 580 m thick (Vallier, 1977).'
4941|'Greenstone basalt, andesite, and keratophyre of the Seven Devils Group that have not been subdivided in mapping.  Named and described by Vallier (1977) for exposures in northwestern Plate 1.  Although most places divided into formations, the Seven Devils Group is undivided in areas of difficult access between the Snake and Rapid Rivers in the Seven Devils Mountains (northwestern Plate 1).'
4942|'Greenschist facies red and lesser green volcaniclastic strata derived from underlying volcanic units and lesser basalt flows.  Named and described by Vallier (1977) for exposures in northwestern Plate 1.  Doyle Creek Formation totals more than 300 m thick at the top of the Seven Devils Group.  Volcaniclastic rocks include sandstone, siltstone, conglomerate, and volcanic breccia.  Beds vary greatly in thickness and in composition along trend.  The amount of clastic material increases upward in the section (Vallier, 1977).'
4943|'Greenschist facies basalt, basaltic andesite, andesite, lesser volcaniclastic rocks, and minor limestone named and described by Vallier (1977) for exposures in northwestern Plate 1.  Volcanic flow rocks are now mostly altered to spilite and keratophyre.  Volcaniclastic rocks include volcanic breccia, sandstone, and siltstone in layers 5-50 m thick.  A limestone layer as much as 50 m thick is in the upper third of the formation.  Base is dominantly keratophyric andesite, middle part is mainly spilitic basalt, and upper part is mainly volcaniclastic and limestone beds.  Unit is primarily green in contrast to the mostly reddish Doyle Creek Formation that is gradationally overlying.  Faunal dates indicate latest Middle Triassic to early Late Triassic age.  Unit is about 2500 m thick (Vallier, 1977).'
4944|'Pyroclastic rocks, water-laid tuffs, and volcaniclastic rocks are dominant with minor keratophyre and spilite flow units named and described by Vallier (1977) for exposures in northwestern Plate 1.  Graded bedding in the tuffs is characteristic.  Volcaniclastic rocks are conglomerate, breccia, sandstone, and siltstone.  Clasts commonly contain some plutonic rocks indicating deeply eroded source terrain.  Upper contact is unconformable.  Faunal dates are Early Permian.  Formation is more than 2500 m thick (Vallier, 1977).'
4945|'Greenschist facies quartz keratophyre tuff, tuff breccia, and flows named and described by Vallier (1977) for exposures in northwestern Plate 1.  The rocks are all grayish-green with little evidence of bedding.  Formation is distinguished from overlying units by lack of clastic units.  Base is not exposed, top may be unconformable, and unit may be a local deposit rather than regionally continuous.  Not well dated but probably Early Permian.  Thickness estimated at 250 m (Vallier, 1977).'
4946|'Strongly deformed quartz diorite to tonalite plutons that intruded into the basement of the Wallowa terrane (MzPzgn).  U-Pb date on zircon from plutonic rock at Oxbow (west-central edge Plate 1) gives a Late Permian age of 249 Ma (Walker, 1982; 1986) and indicates that these plutons formed as part of and were emplaced during early stages of arc volcanism.'
4947|'Amphibolite, hornblende schist, metabasalt, and metagabbro form a mylonitized and sheared mafic gneiss complex that is basement to the volcanic rocks of the Wallowa terrane. These rocks are exposed at Oxbow on the Snake River (west-central edge Plate 1) as part of the Oxbow-Cuprum shear zone (Ave Lallemant and others, 1985).  Minimum age is given by 249 Ma quartz diorite (TRPqd) that intruded the complex (U-Pb zircon methods, Walker, 1986).  Deformation in these rocks indicates left-lateral shearing probably during amalgamation of the Blue Mountains island arc (Ave Lallemant and others, 1985).  Metamorphic hornblende and biotite related to the deformation are dated by 40Ar/39Ar between 224 and 217 Ma (Ave Lallemant and others, 1980).'
4948|'Massive and ribbon cherts, cherty phyllite, cherty argillite, cherty limestone, phyllitic argillite, limestone, and all gradations among those lithologies, characterize the Baker terrane.  Cherts, argillites, and phyllites are well bedded but limestones are lensoid.  Rocks are conspicuously folded, mostly into isoclinal folds, but beds can be traced along strike.  Some strongly deformed metagabbro is included as part of the unit (Mann, 1991).  Unit is lower greenschist facies metamorphic grade.  Faulted over the Izee terrane along the Cuddy Mountain fault (west-central Plate 1).'
4949|'Serpentinized melange with fragments of the Baker terrane (MzPzb) and Weatherby Formation (Jws) of the Izee terrane.  Unit only found in the Cuddy Mountain fault zone (west-central Plate 1) where Baker and Izee terranes are juxtaposed.'
4950|'Calcareous schist, chlorite-biotite schist, and amphibolite gneiss that lie along the western side of the Salmon River suture (central Figure A-3; eastern Plate 1) and that have not been mapped separately.  Metamorphic grade ranges from greenschist to middle amphibolite facies.  Premetamorphic protoliths were volcanic and volcanogenic sedimentary rocks of an allochthonous island-arc terrane.  Compositions suggest that these are metamorphic equivalents of the Wallowa terrane of the Blue Mountains island arc.    Gradational to south and east with the metamorphosed volcanic components of the metamorphosed volcanic/plutonic complex (KJPvp).'
4951|'Silver-green muscovite-chlorite schist forms a structural plate along the east side of upper Rapid River (northeastern Plate 1).  Unit originated as volcanic and volcanogenic sedimentary rocks metamorphosed to upper greenschist facies.  The terrane of origin is unknown but the thrust sheet came from the east, closer to the suture.  This plate is sandwiched between underlying low-grade rocks of the Wallowa terrane and overlying high-grade metamorphosed island arc rocks (JPgn and JPam).  In metamorphic grade and lithologic composition, this thrust sliver is most like rocks of the Rapid River plate (Hamilton, 1963; Onasch, 1977, 1987; Lund, 1984; Onasch, 1987; Lund and others, 1993, 1997) which are along strike to the north-northeast.  Compositionally, these may be a higher metamorphic grade equivalent of the Seven Devils Group of the Wallowa terrane or the Huntington Formation of the Olds Ferry terrane.'
4952|'Biotite-quartz-feldspar gneiss with lesser amphibolite gneiss and biotite schist.  Originated as volcanic and volcanogenic sedimentary rocks metamorphosed to amphibolite facies.  This unit was thrust westward over lower-grade island-arc rocks and includes most of the metamorphosed island arc rocks near the Salmon River suture (northeastern Plate 1) where differentiated in mapping from enveloping plutonic rocks.'
4953|'Strongly deformed amphibolite and garnet amphibolite gneiss (Figure B-7a); retains some evidence of original volcanic textures such as possible layering and volcanic conglomerate (Figure B-7b).  Unit originated primarily as volcanic rock now metamorphosed to amphibolite facies.  Between the Rapid and Little Salmon Rivers (northeastern Plate 1), these rocks were thrust over muscovite-chlorite schist (JPmcs) and upper greenschist facies rocks of the Wallowa terrane.'
4954|'Light- to medium-colored syenite to quartz syenite and dark-colored syenodiorite to amphibolite with minor pyroxenite and gabbro form three bimodal intrusive complexes that crop out in a west-northwest line along Big Creek (Cater and others, 1973), named Ramey Ridge (Leonard, 1963), Acorn Butte, and Rush Creek Point complexes from northwest to southeast, respectively (Cater and others, 1973).  The light-colored syenites are mainly composed of intergrown K-feldspar and albite with hornblende, biotite, and minor quartz and magnetite.  The dark-colored syenodiorite and amphibolite are nearly equal mixtures of albite and the mafic minerals (biotite and hornblende).  Syenite and syenodiorite have mutual cross-cutting relationships and complicated segregations of light and dark varieties indicating mixing of two chemically different magmas.  Thin section observation shows that these rocks have undergone greenschist facies metamorphism and deformation but this is not readily apparent in hand specimen.  U-Pb dating on zircons indicates that these are Neoproterozoic intrusive complexes (J.N. Aleinikoff and K.V. Evans, USGS, unpublished data).  A similar complex near Middle Fork Peak (southeastern edge Plate 2) is the same composition but intruded the Yellowjacket Formation and Hoodoo Quartzite; dating indicates it may be Cambrian (K.V. Evans, USGS, oral communication, 2000).'
4955|'Amphibolite gneiss consisting mostly of hornblende and biotite with lesser plagioclase is mapped as a separate unit near Buckhorn Lake in the western side of Plate 2 and as dikes in Neoproterozoic and Mesoproterozoic rocks near Big Creek in the central part of Plate 2.  Amphibolite is also a major component of gneiss units (PzYs and Ygn).  It is possible that these occurrences may be equivalent to the Mesoproterozoic amphibolites that are closely related to augen gneiss (Yagn; Evans and Zartman, 1990; Doughty and Chamberlain, 1996).  Alternatively, some may be higher metamorphic grade equivalents to the Neoproterozoic mafic metavolcanic rocks (Ze) or syenodiorite (Zsd) or dikes related to them.'
4956|'Foliated porphyritic biotite granite and granitic augen gneiss.  K-feldspar phenocrysts are commonly 1 to 3 cm in length.  Unit is exposed in the far eastern part of the Forest along the Middle Fork of the Salmon River both as discrete plutons (Figure B-8) and as migmatitic stringers and veins (Figures B-9a and b) in metasedimentary biotite gneiss (Ygn).  Equivalent to the Mesoproterozoic granitic augen gneiss and porphyritic granite near Shoup 20 km to the east and Elk City 30 km to the northwest of the Forest (Evans and Fischer, 1986; Evans and Zartman, 1990).'
4957|'Medium- to dark-gray marble.  Fine- to medium-grained calcite with minor actinolite-tremolite needles as long as 2 cm.  Centimeter-scale layers (Figure B-10a), some that are tan silty carbonate, may represent bedding.  Mottled bedding surfaces suggest bioturbation or mud cracks (Figure B-10b).  Calc-silicate minerals are more abundant at base and top of unit and growth of these minerals has obscured primary features.  Calcareous layers are gradational and interlayered with quartzite layers near top and base of unit at Cinnabar Peak (central Plate 2).  Preserved in Gospel Peak and Stibnite roof pendants (Figure A-3; northwestern and southcentral Plate 2, respectively).  A maximum of about 250 m, estimated from mapped exposures, is exposed at Cinnabar Peak.'
4958|'Quartzite, quartzite-pebble conglomerate, and minor biotite-quartz schist form the Umbrella Butte Formation.  Quartzite is predominant in the upper part of the unit.  Planar cross-beds with slightly concave laminae are prevalent in quartzite at Sugar Mountain (Figure B-11c, southcentral Plate 2) and in overturned exposures at Cinnabar Mountain in the Stibnite roof pendant (Figure A-6, southcentral Plate 2).  5- to 10-m thick marble, calc-silicate metasandstone, and schist layers are traced at wide intervals in the upper quartzite-dominant parts of the formation.  Pebble conglomerate is near the base of the formation and possibly in lenses higher in the unit; conglomerate layers are about 10 m thick and contain well-rounded pebbles that are as much as 3 cm long and 1 cm wide (Figure B-11b).  Biotite-quartz schist layers are commonly at or near the base of the unit (Figure B-11a) below the conglomerate lenses.  Part of the Umbrella Butte Formation is multiply repeated in Stibnite roof pendant probably due to unmapped thrust faults or tight folds.  Exposures in the Forest are only about 150 m thick because of fault truncation but this unit is estimated to be about 1,500 m thick in the Gospel Peaks roof pendant (at the northwestern margin of Plate 2; Lund, 1984).'
4959|'Carbonaceous metasiltite and thinly layered calcsilicate-bearing marble in 5 to 15 m thick compositional zones form the unique ribbon-laminated calcareous Missouri Ridge Formation (Figure B-12a).  A siliceous carbonate rock forms alternating fine-grained quartzo-feldspathic layers intercalated with thin marble and calc-silicate bearing layers (Figure B-12b).   Individual beds are generally 0.5 to 2 cm thick.  The lower contact is a narrow gradational zone of calcsilicate-dominant metasiltites.  The upper contact may be an unconformity but is poorly preserved.  The Missouri Ridge Formation overlies the Moores Lake Formation in the Big Creek and Stibnite roof pendants.  Missouri Ridge Formation is estimated to be about 450 m thick but exposures are complicated by deformation and intrusion.'
4960|'Primarily quartzite with lenses of quartzite-cobble conglomerate.  Quartzite composed of recrystallized and intergrown quartz grains.  Upper parts of the unit are more than 95 percent quartz with minor feldspar and mica making up the rest of the rock.  The upper part of the unit is massive and bedding is difficult to identify but, in the middle and lower parts of the unit, faint uncommon layering is defined by muscovite- and biotite-rich laminae.  Minor cross bedding is the only primary feature and is important for indicating stratigraphic younging directions for much of the section.  Base of unit in Gospel Peaks roof pendant contains lenses of quartzite-cobble conglomerate.  Cobbles as much as 15 cm across are in micaceous feldspathic quartz-rich matrix.  Where this part of the section is well exposed in the Gospel Peaks roof pendant, the presence of the conglomerate lenses and the absence of the Goldman Cut Formation, suggest that the base of this formation is an unconformity. Thickness of the incomplete unit exceeds 500 m.'
4961|'Rusty brown weathering fine-grained silvery gray andalusite-mica schist is preserved only in the Big Creek and Stibnite pendants.  The foliation and layering in the rock causes flaggy partings.  The layering is defined by micas and andalusite.  Andalusite needles are aligned with foliation but not lineated.  Primary features or compositional layering are not well preserved but original sedimentary layering with possible graded bedding was found in the Big Creek roof pendant (Figure A-3; central Plate 2).  About 250 m of this unit is at the intruded base of the Big Creek roof pendant.  A thinner interval, about 50 m thick, is traced in a thrust sheet across the southeastern part of the Stibnite roof pendant (Figure A-3; central Plate 2).'
4962|'Composite unit of interbedded gray marble, rusty-weathering fine-grained black quartzite, rusty-weathering muscovite schist, and calc-silicate gneiss.  Marble lenses are about 2 to 15 m thick and are interbedded with lenses of red- to gray-weathering, apatite- and pyrite-rich, fine-grained black quartzite that are also about 15 to 25 m thick (Figure B-13).  Orange-stained quartzite intervals, only about 10 m thick, are locally exposed.  Muscovite schist commonly contains some garnet, biotite, staurolite, calcic amphibole, and(or) epidote.  No primary features were found but the distinct compositional layers in this unit suggest original bedding.  The unit probably formed as an alternating black shale and limestone unit with compositional gradations; it is a very important and distinct regional marker unit.  Structural complication makes thickness estimates difficult but, based on map exposure width, unit is probably as much as 300 m thick.'
4963|'Compound metamorphosed bimodal volcanic sequence and associated glaciogenic conglomerate.  The section is described based on exposures west of the settlement of Big Creek (center of Plate 2). The most widely recognized members of the formation are layered amphibolite and associated mafic greywacke conglomerate containing quartzite and meta-carbonate clasts.

Hogback Rhyolite Member--Metamorphosed porphyritic rhyolite tuff with relict potassium feldspar, plagioclase, and bipyramidal quartz phenocrysts (Figure B-14a).  Groundmass biotite and muscovite form a faint metamorphic foliation.  Eutaxitic and fiamme structures as well as flow breccia are preserved in the metarhyolite, indicating that the Hogback Rhyolite is a rhyolite flow (rather than intrusive) that is only preserved near the settlement of Big Creek.  The Hogback Rhyolite Member is dated at 6877 Ma by U-Pb zircon methods (Lund and others, in press).  The Hogback Rhyolite Member is about 40 m thick.

Placer Creek Member--More regionally widespread than, and probably laterally interfingering with, the Hogback Rhyolite Member.  The Placer Creek Member is made up of volcanogenic matrix conglomerates.  An upper conglomerate contains an heterogeneous mixture of volcanic, quartzite, and calc-silicate gneiss pebbles (Figure B-14b).  Pebbles in the upper conglomerate are stretched and as much as 4 cm wide by 10 cm long.  A lower volcanic conglomerate contains a heterogeneous mixture of volcanic clasts of diverse compositions (Figure B-14c).  Pebbles in the lower conglomerate appear to be stretched and are mostly about 1 cm wide by 2 cm long.

Golden Cup Member--Metamorphosed mafic volcanic rocks that form the middle of the Edwardsburg Formation.  The mafic volcanic rocks are medium- to coarse-grained amphibolite containing relict pyroxene (now plagioclase and chlorite) and plagioclase phenocrysts (Leonard, 1962) and fine-grained indistinctly layered amphibolite containing hornblende, biotite, plagioclase, and quartz.  In the coarser grained porphyritic amphibolites, stretched calcite-filled cavities suggest amygdaloidal texture (Figure B-14d).  Possible fragmental and pillow textures are also found.  These porphyritic amphibolites were volcanic flows and are mostly in the middle of the Golden Cup Member.  The fine-grained indistinctly layered amphibolite may have originated as mafic volcaniclastic rocks.  At Big Creek, this member is approximately 400 m thick.

Wind River Meadows Member--Interfingered rhyodacite tuffs and conglomerates at the base of the Edwardsburg Formation.  Regionally widespread massive matrix-supported greywacke conglomerate with quartzite and calc-silicate gneiss cobbles and pebbles (Figure B-14e) is 2 to 15 m thick.  The clasts are as much as 20 cm long but mostly less than 4 cm long.  The clasts are rounded and structurally stretched.  The matrix-supported conglomerate is as much as 200 m thick.  Rhyodacite flow breccia, tuff, and water-worked tuff is locally found low in the unit.  The rhyodacite has relict plagioclase and potassium feldspar phenocrysts.  Volcanic breccia fragments of similar lithology are common (Figure B-14f).  Primary sedimentary structures, including flow-breccia tuff and water-laid tuff with graded bedding are locally preserved.  Rhyodacite of the Wind River Meadows Member is dated at 68710 Ma (Lund and others, in press).  The rhyodacite is about 20 m thick west of Big Creek.  A thin unit of mafic volcanic rocks about 5 m thick is found on a ridge about 6 km west of Big Creek (central Plate 2).  Fine-grained quartzite 2 to 3 m thick is found at base in several localities.

Thickness of the Edwardsburg Formation, estimated from map width of exposures, is 700 m.  Graded bedding in the volcaniclastic sedimentary part of the rhyodacite in the Wind River Meadows Member shows that the section is overturned in the exposure west of Big Creek.  Where preserved, contacts at the top and base are gradational.'
4964|'Marble and calc-silicate metasiltite lie below the diamictite and volcanogenic rocks of Gospel Peaks sequence B.  Coarse-grained light-gray-green tremolite marble is predominant at the top of the unit and medium-grained dark green and purple layered calc-silicate metasiltite rock is predominant at the bottom.  Tremolite marble contact may be gradational with Edwardsburg Formation (Ze) in overturned exposures on ridge west of Big Creek (center of Plate 2) but may be unconformable in other locations because pebbles of this unit are incorporated into diamictites of the Edwardsburg Formation.  Basal contact is gradational.  Unit is about 100 m thick.'
4965|'Fine-grained, white to light-buff quartzite with subrounded bimodal quartz grains, minor mica, feldspar, and oxide grains.  A few lenses contain remnant subrounded quartz granules and pebbles and subrounded iron oxide granules (Figure B-15a).  Small quartzite pebbles, only as large as 1 cm across, were noted on the ridge south of Smith Creek and at Snowshoe Peak (central Plate 2).  Ripple cross bedding and ripple-marked surfaces are present (Figure B-15b).  Compositionally, this quartzite is cleaner than Mesoproterozoic biotite-feldspar-quartz metasandstone that is correlated with the Gunsight Formation (Ylg).  The Square Mountain Formation structurally overlies units of both the Neoproterozoic and Mesoproterozoic strata on ridge northwest of Big Creek (center of Plate 2).  At this same location, quartzite of the Square Mountain Formation is intruded by amphibolite sills (ZYam) that cut the quartzite but not the dated Neoproterozoic (and possible Cambrian) units that are structurally below but younger.  Actual thickness not known because of structural disruption but probably greater than 500 m.'
4966|'Reddish gray-weathering medium-grained muscovite-biotite schist and amphibolite that in places contains garnet-, sillimanite-, or quartz-rich layers.  No primary sedimentary features were found.  The Plummer Point Formation is consistently found above Mesoproterozoic rocks and below dated Neoproterozoic rocks.  Metamorphic grade, structural features, and bedding orientation are commonly different below this unit suggesting that the base may be an unconformity.  The schist is about 200 m thick.'
4967|'Dark-gray and white, massive quartz-rich metasandstone.  Rock contains 5 to 15 percent feldspar.  Muscovite and biotite amount to as much as 5 percent of the rock.  Quartz grains are rounded to subrounded and medium-grained.  Unit is massive to medium-bedded with beds .1-.5 m thick.  Ripple cross-bedding is found in isolated locations (Figure 16).  Base is gradational with underlying Gunsight Formation (Ylg) and strata belonging to the Swauger Formation may be mapped with Gunsight Formation, particularly in Profile Creek.  Top is structurally overlain by higher grade gneisses and by Neoproterozoic units.'
4968|'Centimeter-thick, prominent, tan to gray fine- to medium-grained metasandstone layers alternate with rusty-weathering millimeter- to centimeter-thick biotite phyllite layers (Figure B-17a).  Lower to middle greenschist facies metamorphism.  Cross-bedding is preserved locally in rocks that are from the Gunsight-Swauger transition (Figure B-17b).  Formation becomes more quartz-rich upward in the section and is gradational with the Swauger Formation (Yls).  The base of the unit is exposed near Center Mountain, where this unit gradationally overlies biotite phyllite of the probable upper Apple Creek Formation (Ylau).  Accurate thickness is not possible to determine but unit is estimated to be about 1000 m thick.  This unit is similar to and correlated with rocks that are described near the Blackbird mine area (about 30 km east of Plate 2; Connor and Evans, 1986; Nash and Hahn, 1989; Connor, 1990, 1991) and that are now mapped as Mesoproterozoic Gunsight Formation (Tysdal, 2000a).

Higher grade exposures in Profile Creek (center of Plate 2) are interpreted as primarily upper Gunsight Formation and probably include undifferentiated rocks of the Swauger Formation.  Exposures in Profile Creek were previously called "older quartzite" by White (1941) to distinguish these from other quartzites that White mapped nearby as younger rocks and that are herein mapped as part of the Neoproterozoic Windermere Supergroup and related strata.  Biotite-feldspar metasandstone (Ybfq) in Marshall Mountain roof pendant (Figure A-3) may be metamorphic equivalent (Figure B-17c)'
4969|'Laminated, gray and green chlorite-biotite phyllite and gray quartzose phyllite.  Where cleavage is weak or parallel to layering, this rock has prominent fine light-and-dark laminations on millimeter to centimeter scale, graded bedding, and sedimentary water-escape structures of light-colored more quartzose material from some layers that appear to cut up into intervening dark micaceous layers (Figure B-18).  Metamorphic grade is lower- to middle-greenschist facies.  Crops out along Big Creek (east-central Plate 2).  Upper contact with biotite metasandstone-phyllite of the probable Gunsight Formation (Ylau) is gradational near Center Mountain (central Plate 2) but elsewhere upper contact is faulted.  Lower contact is not exposed.   Estimated thickness is more than 1000 m. 

Previously correlated with the Mesoproterozoic Yellowjacket Formation (Cater and others, 1973) because of similar composition as strata mapped as Yellowjacket Formation to the east (Connor and Evans, 1986).  With revision of the Mesoproterozoic stratigraphy near Blackbird, Idaho (Tysdal, 2000a, 2000b; Tysdal and others, 2000) and based on sedimentary structures and stratigraphic succession, this unit is probably correlative with the banded siltite member of the Apple Creek Formation.'
4970|'Biotite phyllite and quartzite are interlayered in centimeter-scale layers that are a preserved sedimentary lamination.  Metamorphosed to middle and upper greenschist facies.  Stratigraphically overlies Hoodoo Quartzite in lower Big Creek drainage (R.S. Lewis, personal communication, 1996; central Plate 2).  Top of unit not exposed.  Thickness in study area is unknown.'
4971|'Light gray and tan biotite-feldspar metasandstone and feldspathic quartzite.  Some layering preserves cross-bedding.  Metamorphosed to middle and upper greenschist facies.  Crops out from eastern edge of Forest (east-central side of Plate 2), where it is traced from the reference section (Ross, 1934; Ekren, 1988; Tysdal, 2000; Tysdal and others, 2000), across the Middle Fork of the Salmon River to lower Big Creek (this study) where this lithologic unit stratigraphically overlies phyllites (R.S. Lewis, personal communication, 1996) herein correlated with the Yellowjacket Formation.  Thickness in study area is unknown.'
4972|'Gray biotite-feldspar metasiltite and phyllite is finely layered.  Compositional layering is, in part, preserved sedimentary lamination.  Centimeter-thick layers with preserved ripple-cross lamination found in Middle Fork of the Salmon River drainage.  Metamorphosed to middle and upper greenschist facies.  Crops out from eastern edge of Forest (east-central side of Plate 2), where it is traced from the reference section (Ross, 1934; Ekren, 1988; Tysdal, 2000; Tysdal and others, 2000), across the Middle Fork of the Salmon River to lower Big Creek (this study) where mapped underlying quartzite (R.S. Lewis, personal communication, 1996) of the Hoodoo Quartzite.  Thickness in study area is unknown.'
4973|'This unit is mapped in the Marshall Mountain roof pendant and south of Yellow Pine where lit-par-lit injection and possible partial melting have destroyed primary features (Figure B-16b).  Metamorphosed to upper amphibolite facies.  Thickness unknown.  Probably equivalent to the lower grade metamorphosed biotite arkosic metasandstone correlated with the Swauger and Gunsight Formations (Yls and Ylg).'
4974|'Biotite-quartz-feldspar phyllite and gneiss.  Some augen gneiss probably equivalent to Yagn and amphibolite probably equivalent to ZYam is present in places (Figures B-8 and B-9).  Difficult access into areas underlain by these rocks resulted in inadequate information for subdivision into separate map units.  Rocks have undergone amphibolite facies metamorphism and sedimentary structures are mostly not preserved.  Thickness unknown.  However, compositions and location of unit indicate that much of this unit may be metamorphosed upper part of the Mesoproterozoic Apple Creek Formation (Ylau).'
4975|'Lower quartzite and feldspathic quartzite unit contains less than ten percent biotite and muscovite.  Ripple cross-lamination and small-scale interference ripple patterns are present on bedding surfaces (Lund, 1984).  Lower quartzite is gradational with upper layered quartz-rich metasandstone.  The upper quartz-rich metasandstone is interlayered with cm-scale calc-silicate and phyllitic layers.  Probable mud cracks preserved in one location (Lund, 1984).  Base is structurally detached from underlying biotite phyllite and calc-silicate gneiss unit (Ybc); top is eroded.  Crops out in Nez Perce National Forest along the northern part of Plate 2.  Thickness estimated to be about 3200 m (Lund, 1984).  May be equivalent to the Hoodoo Quartzite and Argillaceous Quartzite units (Yh and Yaq).'
4976|'Well-layered green to black medium-grained calc-silicate and biotite gneiss.  Calc-silicate gneiss layers composed of epidote, tremolite-actinolite, quartz, biotite, and feldspars.  Interlayered with biotite-quartz-feldspar gneiss and well-layered phyllite to schist.  Primary sedimentary features destroyed by medium-grade metamorphism in most areas.  Lower metamorphic grade exposures in the Gospel Hump Wilderness area (northern margin, Plate 2) contain cm-scale climbing ripple lamination and load structures (Lund, 1984).  Thickness estimated at about 3200 m (Lund, 1984).  This unit may be in part equivalent to biotite gneiss unit (Ygn) and to the lower metamorphic grade biotite phyllite and calcareous phyllite of the Yellowjacket Formation (Yy).'
4977|'Undivided metasedimentary rocks and minor metavolcanic rocks.  Compositions include quartzite, feldspathic quartzite, calc-silicate gneiss, biotite gneiss, micaceous schist, and amphibolite.  Mapped mostly as screens and schlieren in foliated tonalite (Ktf) and biotite granodiorite (Kgdf, extreme eastern edge of Plate 1 and western edge of Plate 2), where because of shearing, structural dismemberment, and strongly intruded nature of these outcrops, the rocks were not subdivided into discrete map units.  Also shown in southeastern parts of Plate 2 where rocks in roof pendants were not remapped and subdivided.  Only limited observations of these outcrops were made during this study and, from these observations, it is not possible to determine if these rocks are part of the Neoproterozoic or Mesoproterozoic sections.'