Digital Geologic Map of the Redding 1o x 2o Quadrangle, 

Shasta, Tehama, Humboldt, and Trinity Counties, 

California 

By Luis A. Fraticelli, John P. Albers, William P. Irwin, Milton C. Blake, Jr, and Carl M. Wentworth 

Pamphlet to accompany 

Open-File Report 2012-1228 

DEPARTMENT OF THE INTERIOR 

U.S. GEOLOGICAL SURVEY 

2012 
 

 

 

 

 

 

 

 

 

 

 

 

Contents 

Digital Compilation............................................................................................................................................................................1
 

Description of Map Units ..................................................................................................................................................................2
 

Superjacent Rocks .......................................................................................................................................................................2
 

Surficial Deposits......................................................................................................................................................................2
 

Volcanic Rocks .........................................................................................................................................................................3
 

Sedimentary Rocks ..................................................................................................................................................................4
 

Elder Creek Terrane .................................................................................................................................................................5
 

Plutonic Rocks..........................................................................................................................................................................6
 

Subjacent Rocks...........................................................................................................................................................................6
 

King Range Terrane .................................................................................................................................................................6
 

Yager Subterrane .....................................................................................................................................................................6
 

Coastal Terrane........................................................................................................................................................................6
 

Central Terrane ........................................................................................................................................................................6
 

Yolla Bolly Terrane ...................................................................................................................................................................7
 

Pickett Peak Terrane ................................................................................................................................................................7
 

Western Jurassic Terrane ........................................................................................................................................................7
 

Rattlesnake Creek Terrane ......................................................................................................................................................8
 

Hayfork Terrane........................................................................................................................................................................9
 

Western Hayfork Subterrane ................................................................................................................................................9
 

Eastern Hayfork Subterrane .................................................................................................................................................9
 

North Fork Terrane ...................................................................................................................................................................9
 

Central Metamorphic Terrane.................................................................................................................................................10
 

Eastern Klamath Terrane .......................................................................................................................................................10
 

Trinity Terrane ........................................................................................................................................................................12
 

References Cited............................................................................................................................................................................13
 

Figures 

Figure 1. Index to geologic mapping..........................................................................................................................................18
 

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Digital Geologic Map of the Redding 1° x 2° Quadrangle, 

Shasta, Tehama, Humboldt, and Trinity Counties, 

California 

By Luis A. Fraticelli, John P. Albers, William P. Irwin, Milton C. Blake, Jr, and Carl M. Wentworth 

Digital Compilation 

The original map compiled by Fraticelli and others (1987; Open-File Report 87–257) was 

prepared with ink on mylar and released in 1987 as a black-line map on a screened (gray) base. Here, we 

(Porter Irwin and Carl Wentworth) have converted that original map into a colored digital map 

supported by GIS files. The GIS process involved scanning a paper copy of the original map, vectorizing 

the line work in ArcGIS, and then editing that line work in workstation ArcInfo (v. 8.1) under the 

control of the menu interface ALACARTE (Fitzgibbon and Wentworth, 1991; Wentworth and 

Fitzgibbon, 1991). Label points were then added to identify the geologic units. 

The original map contained many unlabelled polygons and various polygons containing 

conflicting labels, incomplete unit boundaries (hanging lines), and mislabeled areas. We resolved many 

of these problems, in part by consulting more detailed maps of the area. The 543 remaining unlabelled 

polygons (uncolored on the map) are mostly small and probably mostly surficial deposits, but some 

larger unlabelled areas are included, particularly in the southeastern part of the map. Dashed contacts 

and faults in the original are shown as solid on this map. 

The southern half of the map area is covered by two geologic maps at scales of 1:100,000: 

McLaughlin and others (2000) and Blake and others (1999). These, together with five 15-minute 

quadrangles by Irwin (2009; 2010a,b), Irwin and others (2011), and Albers and others (1964), were 

consulted to help identify unlabelled polygons and resolve apparent geologic conflicts. Units Qbt 

(Basalt near Tuscan Buttes, Holocene and (or) Pleistocene), Qeb (Olivine basalt of Eagle Canyon, 

Pleistocene), and Qra (Rockland Ash, Pleistocene), unlabelled on the original map, have been identified 

from Blake and others (1999). 

Map figures 1–3 of the original report (Fraticelli and others, 1987) are not reproduced here. 

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DESCRIPTION OF MAP UNITS 

[This Description of Map Units was taken from Fraticellli and others (1987), with additions as 

noted and other, largely minor, additions and changes] 

SUPERJACENT ROCKS 

SURFICIAL DEPOSITS 

t Man-made materials (Holocene)—Dredge tailings and other disturbed ground 

Qsc Stream channel deposits (Holocene)—Light tan and gray, unweathered deposits of 

open, active stream channels. Deposits are transported under modern 

hydrologic conditions, usually in contact with modern surface waters 

Qa Alluvium and colluvium (Holocene)—Unconsolidated silt, sand, and gravel in 

modern stream channels and on associated low terraces 

Qo Overbank deposits (Holocene)—Sand, silt, and minor lenses of gravel deposited by 

floods and during high water stages 

Qao Alluvial and overbank deposits, undivided (Holocene) 

Qt Terrace deposits (Holocene)—Unconsolidated sand and gravel; closely associated 

with modern stream channels but generally higher than normal modern highwater level; also may include remnants of high-level terraces not necessarily 

related to present streams 

Qls Landslide deposits (Holocene)—Slumped, rotated chaotic mixtures of underlying 

bedrock units and colluvium. Many landslides in areas of the Rattlesnake 

Creek terrane, Pickett Peak terrane, and in the Franciscan rocks of the Coastal 

and Central terranes are not shown although these areas are exceptionally 

unstable, and downslope movement is widespread 

Qg Glacial deposits (Pleistocene and (or) Holocene)—Numerous moraines and debris 

flows that extend down glacial valleys, primarily in the Trinity Alps, north 

central part of the quadrangle 

Qm Modesto formation of Davis and Hall (1959) (Pleistocene)—Consists of tan and 

light-gray gravely sand, silt, and clay, except where derived from volcanic 

rocks of the Tuscan Formation. It then is distinctly red and black with minor 

brown clasts. The Modesto Formation is the youngest unit comprising the 

Pleistocene alluvium. It borders existing stream channels in the southeast 

quarter of the quadrangle 

Qr Riverbank Formation (Pleistocene)—Weathered reddish gravel, sand, and silt, 

forming alluvial terraces and fans. Differentiated from the younger Modesto 

Formation by (1) its geomorphic position in terraces topographically above 

the terraces of Modesto age and (2) the degree of post-depositional soil-profile 

development 

Qrb Red Bluff formation of Diller (1894) (Pleistocene)—Thin veneer of distinctive, 

highly weathered bright-red gravels overlying the Tehama, Tuscan, and 

Laguna Formations. Interpreted as a sedimentary cover on a pediment surface 

QTog Older gravel deposits (Pliocene and (or) Pleistocene)—Moderately well indurated, 

coarse to very coarse gravel with minor sand resting unconformably on a 

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truncated soil profile developed on the Tuscan Formation in the southeast part 

of the quadrangle. In the Rattlesnake Creek and the Hayfork terrane, it 

consists of unconsolidated gravels in patches as much as 700 ft higher than 

modern stream levels 

VOLCANIC ROCKS 

Qip Basalt flows of Paynes Creek (Pleistocene)—Thin, black to dark-gray basalt flows 

with scattered yellowish-brown phenocrysts of olivine and glassy-green 

phenocrysts of clinopyroxene, in a matrix of fine-grained plagioclase, 

clinopyroxene, and glass. Age uncertain but less than 26,000 yr and possibly 

less than 12,000 yr because it overlies upper member of the Modesto 

formation of Davis and Hall (1959) 

Qiu Undifferentiated basalt flows of Inskip Hill (Pleistocene)
 

Qbbb Cinder blanket deposits (Pleistocene)—Black, well-bedded basaltic cinder deposits
 

forming a dissected ejecta blanket ranging in thickness from 10 m to 1.5 m. 

Remaining volume of cinder blanket and cone deposit is estimated at about 6 

x l06 m3 

Qbbf Basalt flow of Black Butte (Holocene)—Dark-gray to black basalt, similar in texture 

and mineralogy to the Paynes Creek flows; olivine and clinopyroxene 

phenocrysts scattered in a diktytaxitic matrix of clinopyroxene and 

plagioclase. Holocene age from Blake and others (1999); Fraticelli and others 

(1987) showed it as Pleistocene 

Qbt Basalt near Tuscan Buttes (Pleistocene and (or) Holocene)—Local extrusions of 

gray to black, glomeroporphyritic to highly vesicular, high-alumina basalt and 

minor amounts of scoria (unlabeled unit identified and described from Blake 

and others, 1999) 

Qvu Volcanic rocks of the Millville quadrangle (Pleistocene)—Dark-gray, moderately 

diktytaxitic, high-alumina basalt (Al2O3, 18.4 to 19.1 %), composed of 

openwork plagioclase laths, fine-grained clinopyroxene, and magnetite with 

small scattered phenocrysts of brownish-green olivine 

Qbs Basalt of Shingletown Ridge (Pleistocene)—Composed of three subunits (not 

differentiated on map) of dark-gray, fine-grained, diktytaxitic, and locally 

porphyritic basalt with rounded phenocrysts of brownish-green olivine 

scattered in an openwork mesh matrix of plagioclase and clinopyroxene. 

High-alumina basalts containing about 47.6 % SiO2, 18.09 % Al203, and 0.19 

% K20 

Qeb Olivine basalt of Eagle Canyon (Pleistocene)—Dark-gray, diktytaxitic, vesicular 

olivine basalt (unlabeled unit identified and described from Blake and others, 

1999) 

Qba Olivine basalt of Devils Half-Acre (Pleistocene)—Gray, glomeroporphyritic, 

vesicular olivine basalt. Maximum thickness 15 m, source unknown. 

Pleistocene age from Blake and others (1999); Fraticelli and others (1987) 

showed the age as a query (?) 

Qab Andesite of Brokeoff Mountain (Pleistocene)—Porphyritic hypersthene andesite 

with abundant white plagioclase phenocrysts, minor amounts of hypersthene, 

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and sparse augite phenocrysts in a fine-grained matrix of plagioclase 

microlites and brown glass 

Qra Rockland ash bed of Sarna-Wojcicki and others (1982) (Pleistocene)—Loosely 

aggregated, dacitic pumice lapilli ash that contains scattered, coarse, white 

pumice fragments as large as 20 cm in diameter (unlabeled unit identified and 

described from Blake and others, 1999) 

Qcb Basalt of Coleman Forebay (PIeistocene)—Dark-gray olivine basalt with 

pronounced diktytaxitic texture and scattered large vesicles and voids. 

Weathers light-rusty gray. The unit is undated but is older than the Red Bluff 

formation of Diller (1894) and has a maximum thickness of 10 m 

Ta Andesite (Pliocene)—Undivided flows of predominantly two-pyroxene andesite; 

commonly platy, medium to light gray, rarely dark gray, locally pink, greenish 

gray, or mottled; locally overlies hornblende-bearing pyroxene andesite 

containing abundant plagioclase phenocrysts and less abundant, smaller 

hornblende phenocrysts 

Tva Andesitic breccia (Pliocene)—Breccias and tuff breccia in area east of Shasta Lake; 

may be correlative with the Tuscan Formation. Fraticelli and others (1987) 

called the unit andesite, here renamed andesitic breccia to contrast with unit 

Ta 

Tvb Basalt (Pliocene)—Undivided basaltic flows east of Shasta Lake 

SEDIMENTARY ROCKS 

Tte Tehama Formation (Pliocene)—Pale-green, gray, and tan sandstone and siltstone 

with lenses of cross-bedded pebble and cobble conglomerate. Interfingers with 

the Tuscan Formation north of Red Bluff. Clastic debris is more andesitic in 

composition and Tuscan-like in appearance eastward in area of interfingering. 

The Tehama and Tuscan Formations are considered coeval because both 

contain the Nomlaki Tuff Member at or near their stratigraphic bases. 

Maximum thickness is about 600 m 

Ttn Nomlaki Tuff (Pliocene)—White, light-gray, locally reddish-tan to salmon dacitic 

pumice tuff and pumice lapilli tuff exposed in widely separated areas at or 

very near the bases of the Tuscan and Tehama Formations. Varies from 

massive non-layered ash flow at Tuscan Springs, Gas Pointe, and Antelope 

Creek to bedded and cross-bedded, reworked pumiceous sediment at 

Richardson Springs. Thickness varies from 1 to 30 m. Evernden and others 

(1964) obtained a K-Ar date of 3.4 Ma on a welded ash-flow tuff at Bear 

Creek Falls, which Anderson and Russell (1939) correlated with the type 

Nomlaki Tuff 

Tt Tuscan Formation, undivided (Pliocene)—Includes interbedded lahars, volcanic 

conglomerate, volcanic sandstone, siltstone, and pumiceous tuff. The Tuscan 

Formation is divided into four subunits: 

Ttd Fragmental deposits—Characterized by large monolithologic masses of gray 

hornblende andesite, augite-olivine basaltic andesite, black pumice, and 

smaller fragments of black obsidian and white and gray hornblende-bearing 

pumice in a grayish-tan pumiceous mudstone matrix. Thickness ranges from 

10 to 50 m 

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Tth Tuff of Hogback Road—Discontinuous thin lapilli tuff, pumiceous sandstone, 

and conglomerate composed of rounded white hornblende-bearing dacitic 

pumice fragments up to 3 cm in diameter and smaller gray and black pumice 

fragments admixed with varying amounts of andesitic tuff about 2.5 m thick at 

the hogback on Hogback Road 

Ttc Lahars with minor interbedded volcanic conglomerate and sandstone—North 

of Antelope Creek, separated from overlying units by partially stripped soil 

horizons. This unit is about 80 m thick near Tuscan Springs 

Tti Ishi Tuff Member—White to light-gray, fine-grained, pumiceous air-fall tuff 

commonly reworked with variable amounts of volcanic sandstone and silt, 

distinguished by abundant black to bronze biotite flakes about 1 mm in 

diameter. A fission-track age of 2.7 Ma obtained from zircons separated from 

the pumice clasts is the best current estimate age of the Ishi Tuff member 

(Blake and others, 1984) 

Twg Wildcat Group (Upper Miocene-Pliocene)—Weakly consolidated mudstone, 

siltstone, sandstone, and conglomerate and minor interbeds of limestone, tuff, 

and lignite. Abundant fossils of a molluscan and foraminiferal fauna indicate a 

Pliocene age, but the oldest part (not differentiated on the map) may be as old 

as late Miocene (Irwin, 1960). Includes the Falor Formation in the northwest 

corner of the quadrangle 

Tw Weaverville Formation (Oligocene and (or) Miocene)—Nonmarine sedimentary 

rocks including conglomerate, sandstone, and thinly laminated, light-colored 

clay and tuff; lignitic coal beds present locally. Fossil plants previously 

indicated Oligocene age (MacGinitie, 1937), but more recent study of pollen 

and spores indicates late Oligocene and (or) Miocene age (Barnett, 1982) 

Tmc Montgomery Creek Formation (Eocene)—Gray, yellowish-orange-weathering, 

arkosic sandstone with conglomerate and shale; commonly massive to thickbedded nonmarine sandstone with scattered lenses of pebble conglomerate 

and shale. The unit is about 80 m thick at its southern limit and thickens to the 

north to about 200 m (Anderson and Russell, 1939) in Montgomery Creek 

Kc Chico Formation (Upper Cretaceous)—Tan, yellowish-brown to light-gray, 

fossiliferous marine sandstone with lenticular beds of pebble to fine cobble 

conglomerate and minor siltstone. Clasts in conglomerate include rounded to 

well-rounded, red, green, and black chert, white vein quartz, quartzite, granite, 

and greenstone 

Ks Sedimentary rocks (Lower Cretaceous)—Mostly marine sedimentary rocks; well 

indurated, buff-weathering sandstone, mudstone, and conglomerate. Contains 

ammonites and other marine fossils; rocks are similar to those of equivalent 

age in the Great Valley sequence. Includes some minor nonmarine rocks in 

western part of quadrangle near Glade Creek and Big Bar 

ELDER CREEK TERRANE 

ecms Mudstone (Upper Jurassic-Lower Cretaceous)—Dark gray, mainly hackly 

fractured, with minor tan siltstones and sandstones. Limestone nodules, 

lenses, and thin beds locally abundant 

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eco Coast Range ophiolite (Upper Jurassic)—Dismembered ophiolite consisting of 

sheared serpentinite and small blocks of gabbro and diabase 

PLUTONIC ROCKS 

Kqd Shasta Bally Batholith (Lower Cretaceous)—Quartz diorite and granodiorite of 

Shasta Bally is dated by K-Ar analysis at 135 Ma by Lanphere and others 

(1978). Unit includes other small plutonic bodies of similar composition and 

age. In the extreme northeast part of the quadrangle, small bodies of coarsegrained quartz diorite yielded radiometric ages of 123 Ma (Paul René, oral 

commun., May 1986) 

SUBJACENT ROCKS 

KING RANGE TERRANE 

krt Turbidites and pillow lava (Eocene(?)-Miocene)—Pillow lava overlain by thinbedded turbidites thought to range in age from early Cenozoic to middle 

Miocene (McLaughlin and others, 1982). Turbidites are characterized by 

closely spaced folds of three generations. Represents youngest known terrane 

within the Franciscan Complex in California. Present only in extreme 

southwest corner of map 

YAGER SUBTERRANE 

ymt 

yst 

Chiefly marine mudstone and sandstone (Paleocene-upper Eocene) 

Chiefly marine sandstone, locally conglomerate (Paleocene-upper Eocene) 

COASTAL TERRANE 

Broken formation consisting largely of arkosic sandstone. Fossils range in age from Late 

Cretaceous to Eocene. Characterized by abundant laumontite veins. Locally isoclinally folded and (or) 

stratally disrupted 

cosa Chiefly broken to coherent, well-bedded sandstone and argillite (Upper 

Cretaceous-Eocene) 

cosas Chiefly sheared argillite and sandstone (Upper Cretaceous-Eocene) 

cov Basalt flows, tuff, breccia, and diabase intrusives (Upper Cretaceous-Eocene)—

Locally contain manganese, pink pelagic limestone, or minor cherty partings 

CENTRAL TERRANE 

Tectonic melange consisting of resistant blocks in a highly sheared argillaceous matrix. The 

matrix, where well exposed and less sheared, is commonly made up of interbedded fine-grain mudstone, 

lithic sandstone, and radiolarian tuff. Pillow lava is probably also part of the matrix but is usually 

detached by faulting. Fossils from the matrix and interbedded chert range in age from Late Jurassic 

(Tithonian) to Early Cretaceous (Valanginian) 

ctmm Melange matrix (Upper Jurassic-Lower Cretaceous)—Chiefly sheared argillite 

and lithic sandstone or graywacke with some interbedded green tuff. Includes 

scattered high-grade blueschist, eclogite, and amphibolite blocks (not shown) 

ctsp Serpentinite (Upper Jurassic-Lower Cretaceous)—Possibly includes some Coast 

Range ophiolite 

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ctcr Coast Range ophiolite (Upper Jurassic-Lower Cretaceous)—Includes peridotite, 

diabase, gabbro, basalt; may include other rocks derived from the Coast 

Range ophiolite 

ctls Pelagic limestone(?)—(only two localities on map) 

ctgs 

ctch 

ctss 

Greenstone(?) 

Chert(?) 

Sandstones(?) 

YOLLA BOLLY TERRANE 

Intercalated graywacke, shale, conglomerate, and radiolarian chert, all intruded by diabasegabbro and quartz keratophyre and subsequently metamorphosed to blueschist facies. Cherts contain 

radiolarians of Middle(?) Jurassic to Middle Cretaceous age (Blake and others, 1981) 

ybt Taliaferro metamorphic complex (Lower Cretaceous(?) metamorphic age)— 

Includes schistose metagraywacke, crumpled phyllite, metagreenstone, and 

metachert 

ybtmm Melange (Upper Jurassic to Lower Cretaceous)—Mostly sheared argillite, 

graywacke, and conglomerate with abundant blocks of fine-grained 

greenstone, chert, plus scarce serpentinite, and rare blueschist and amphibolite 

knockers. Radiolarians extracted from chert are Tithonian-Valanginian in age 

(Blake and others, 1984) 

ybh Metagraywacke of Hammerhorn Ridge (Upper Jurassic-Lower Cretaceous)—

Dominantly graywacke with lesser amounts of argillite and conglomerate and 

abundant interbeds of chert which yield fossils of Upper Jurassic-Lower 

Cretaceous (Tithonian-Valanginian) age (Blake and others, 1984) 

ybtch Chert (Middle(?) Jurassic-Middle Cretaceous) 

PICKETT PEAK TERRANE 

Strongly deformed quartz-mica schist, metagraywacke, metabasalt, and metachert. Contains 

high-pressure blueschist-facies minerals. Includes South Fork Mountain Schist, Colebrooke Schist of 

southwest Oregon, and Valentine Springs Formation. No fossils are known; radiometric ages on 

metamorphic minerals suggest an Early Cretaceous (125 Ma) metamorphic age (Lanphere and others, 

1978) 

sfm South Fork Mountain Schist (Lower Cretaceous(?))—Consists chiefly of finegrained quartz-albite-muscovite-chlorite schist and commonly contains 

microscopic lawsonite. Most of the South Fork Mountain Schist is poorly 

exposed owing to a thick cover of slope debris 

sfmmb Chinquapin Metabasalt Member (Lower Cretaceous(?))—A fine-grained, 

albite-chlorite- actinolite-epidote gneiss with local crossite-rich layers; also 

includes sparse metachert 

vsmv Metavolcanic rocks within the Valentine Springs Formation (Lower 

Cretaceous(?)) 

WESTERN JURASSIC TERRANE 

wJg Galice Formation(?) (Upper Jurassic)—Interbedded mudstone, graywacke, and 

conglomerate ranging in texture from weakly slaty to semischist. Fossils have 

not been found in the Galice Formation(?) in this mapped area, but it is 

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presumed to correlate with similar rocks in southern Oregon containing fossils 

that indicate a Late Jurassic (late Oxfordian and middle Kimmeridgian) age 

(Imlay, 1959). Age of metamorphism is Late Jurassic based on K-Ar analysis 

(148±1.8 Ma,151±4.4 Ma, and 153±4.5 Ma; Lanphere and others, 1978) 

wJr Rogue Formation(?) (Middle to Upper Jurassic(?))—Mafic to intermediate 

volcanic flows(?), breccia, and tuff; includes volcanic conglomerate in upper 

part 

wJsp Serpentinite (Upper Jurassic(?))—Occurs as tectonic slices along South Fork Fault; 

may be related to Josephine ophiolite of Harper (1980), which is more 

completely exposed in the Western Jurassic terrane farther north in the 

Klamath Mountains province 

wJd Diorite-Ammon Ridge Pluton (Upper Jurassic(?))
 

wJgb Gabbro (Upper Jurassic(?))
 

wJgn Friday Camp gneiss (Upper Jurassic(?))—Weakly foliated hornblende-diorite
 

gneiss 

wJgm Meta-Galice (Upper Jurassic(?))—Hornfels and fine-grained chiastolite-biotitechlorite schist adjacent to the Ammon Ridge Pluton (wJd) 

RATTLESNAKE CREEK TERRANE 

rcv Volcanic broken formation and melange (Middle(?) Triassic to Middle 

Jurassic)—Consists of sheared and dislocated mafic volcanic rocks, including 

pillow basalt, flows(?), tuff, volcanic breccia, and volcaniclastic rocks that 

contain locally interbedded red and gray to black, thin-bedded radiolarian 

chert; includes minor intermediate and silicic volcanic rocks, lenses, and 

tectonic blocks of limestone, amphibolite, plutonic rocks, and serpentinite. 

Microfossils in various bodies of chert and limestone have yielded ages 

ranging from Permian to Jurassic. A K-Ar age on blueschist-facies chert is 

185±8.8 Ma (Irwin, 1985). Continuity of lithic units is disrupted by faults and 

obscured by landslides 

rcs Detrital sedimentary rocks (Triassic or Jurassic)—Well-bedded, somewhat slaty 

rocks ranging from mudstone to pebble conglomerate; may be inliers or fault 

slices of Western Jurassic terrane (Irwin, 1985) 

rcp Plutonic rocks (Triassic to Jurassic)—Medium- to coarse-grained rocks that range 

from diorite to granite; includes Eltapom and Grassy Mountain Plutons, Bear 

Wallow diorite, and Tule Creek granite complex. Some are isotopically dated 

as Early Jurassic (207-193 Ma; Wright, 1982) in Chanchelulla Peak and 

Dubakella Mountain quadrangles. May include some intermediate and silicic 

volcanic rocks 

rcsp Serpentinite (age unknown)—Dominantly serpentinized peridotite, but includes 

associated metasomatized mafic rocks of uncertain origin, as well as minor 

sheared-in volcanic rocks and chert. Continuity of serpentinite zone is 

disrupted by faults and obscured by landslides 

rcgb Gabbro (Triassic(?) to Jurassic) 

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HAYFORK TERRANE 

Western Hayfork Subterrane 

hhvc Chert and argillite (Middle Jurassic)—Dominantly thin-bedded radiolarian chert 

locally interlayered with argillite and meta-andesite. Generally overlies 

(conformably(?)) and locally interfingers with the Hayfork Bally Metaandesite (hhb) 

hhb Hayfork Bally Meta-andesite (Middle Jurassic)—Layered mafic volcanogenic 

rocks ranging in texture from coarse agglomerate to crystal tuff, probably 

representing an island-arc deposit. Commonly characterized by euhedral 

augite and plagioclase crystals in a light-to dark-green groundmass. Locally 

includes interlayered thin-bedded radiolarian chert and dark argillite. Age of 

meta-andesite is thought to be Middle Jurassic on basis of a probable 

cogenetic relation with the Ironside Mountain Batholith (him; 170 Ma, revised 

constant) and on K-Ar isotopic ages of 159 Ma (Fahan and Wright, 1983) 

measured on hornblende from meta-andesite 

him Ironside Mountain batholith (Middle Jurassic)—Mostly medium grained 

monzodiorite, but includes quartz diorite and minor gabbro and pyroxenite. 

Fine-grained and hybrid(?) varieties are common along much of the boundary 

between the batholith and the Hayfork Bally Meta-andesite. Age of batholith 

is Middle Jurassic based on isotopic ages of about 170 Ma determined by KAr analysis (Lanphere and others, 1968, revised constant) and by U-Pb 

analysis (Wright, 1982) 

hgb Gabbro (Middle Jurassic(?))—Includes the Goods Creek Pluton and some small 

unnamed intrusives bodies in both the Eastern and Western Hayfork 

subterrane 

hpx Pyroxenites (Middle Jurassic(?))—Includes the Chanchelulla Peak zoned ultramafic 

complex 

Eastern Hayfork Subterrane 

hm Melange (Middle(?) Jurassic)—Slaty argillite and other clastic sedimentary rocks, 

thin-bedded chert, volcaniclastic rocks, sparse recrystallized limestone (ls), 

minor mica schist, amphibolite (ha), and serpentinite (hsp). Unit structurally 

overlies unit hhb 

ha Amphibolite tectonic blocks (age unknown)—Rare occurrences within the 

Eastern Hayfork subterrane 

hsp Serpentinite (age unknown) 

hgd Granodiorite (Middle Jurassic(?))—Unnamed small intrusive body in the 

northern part of the Hayfork terrane 

hd Diorite (Middle Jurassic(?))—Small intrusive bodies mostly in the northern part of 

the Hayfork terrane 

NORTH FORK TERRANE 

nf Tectonically dismembered ophiolite (Upper Triassic-Middle(?) Jurassic)—

Includes overlying siliceous tuff, chert, sandstone, and limestone. Locally a 

mélange containing blocks and slabs of Permian limestone having Tethyan 

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faunal affinities and blueschist knockers. Radiolarians from chert range from 

Late Triassic to Middle(?) Jurassic (Irwin and others, 1982) 

nfsp Serpentinite of the North Fork terrane(?) 

nfgb Gabbro(?) 

nfd Diorite(?)—Small isolated intrusives bodies in the North Fork terrane 

nfdb Diabase 

nfs Metasedimentary rocks of the Stuart Fork Formation (pre-Upper Jurassic(?))—

Includes phyllitic quartzites and dark quartz-mica phyllites, commonly 

graphitic (Davis and others, 1965) 

nfv Metavolcanic rocks of the Stuart Fork Formation (pre-Upper Jurassic(?))—

Fine-grained greenstones and associated schistose metavolcanic rocks 

interfingering with siliceous Stuart Fork rocks in upper part of formation. 

Schistose rocks include mainly actinolite schists and phyllonites (Davis and 

others, 1965) 

CENTRAL METAMORPHIC TERRANE 

cms Salmon Hornblende Schist (Devonian)—Amphibolite-grade hornblende schist and 

gneiss, probably represents mafic volcanic rocks of an island arc; locally 

includes lenses of micaceous schist. Lower part of unit in the Weaver Bally 

area may be a metagabbro; co-metamorphic with Abrams Mica Schist; K-Ar 

isotopic ages of 390 and 399 Ma (Hotz, 1977) of possibly correlative 

amphibolites in the Yreka-Callahan area, north of the Redding map area, 

suggests a Devonian age of metamorphism 

cma Abrams Mica Schist (Devonian)—Schistose metasedimentary rocks; generally 

micaceous and quartzitic; discontinuous lenses of micaceous marble near base 

(m, where distinguished); Rb-Sr isotopic ages of about 380 Ma indicate 

Devonian age of metamorphism (Lanphere and others, 1968); unit equivalent 

to the Grouse Ridge Formation of Davis and Lipman (1962) 

cmsa Undifferentiated Salmon Hornblende and Abrams Mica Schist (Devonian) 

EASTERN KLAMATH TERRANE 

Island-arc volcanic rocks plus intercalated sedimentary rocks of Devonian through Middle 

Jurassic age. Forms a younging-eastward, homoclinal but internally deformed sequence that is faulted 

against the Trinity terrane to the west. Overlain to the south and east, with great angular unconformity, 

by Cretaceous sedimentary strata of the Great Valley sequence 

Jp Potem Formation (Jurassic)—Sandstones, shales, and tuffs; thin-bedded sandstones 

and gray, sometimes slaty, shales predominate in lower part and comprise the 

greater part of the unit. Subordinate lentils of limestone are contained in lower 

part. Tuffaceous conglomerate predominates in upper half of the formation 

mi Mafic intrusive rocks (Jurassic)—Mainly two-pyroxene diorite formerly mapped as 

Bagley Andesite in northeast part of the quadrangle; radiometric age is 160 

Ma (Paul Renne, oral commun., 1986) 

Ja Arvison Formation (Jurassic)—Volcanic breccia, tuff, agglomerate, and volcanic 

conglomerate, named by Sanborn (1960) for exposures in the Big Bend area 

^m Modin Formation (Upper Triassic)—Extensive succession of andesitic tuffaceous 

beds, overlain by shaley sandstone and shale; volcanic conglomerate at the 

10 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

base locally contains limestone fragments with Hosselkus-type (^h) fossils; 

unit here includes underlying Brock Shale of Diller (1906) 

^h Hosselkus Limestone (Upper Triassic)—Medium- to light-gray, lenticular 

limestone as much as 60 m thick 

^p Pit Formation (Permian(?) or Triassic)—Predominantly gray and black shale with 

interbedded layers of tuff in lower part and limestone lenses in upper part. 

Also contains local mafic flows and dome-like bodies of silicic volcanic rock. 

Contains lenses of massive sulfide in lowermost part in local areas. Some 

cherty layers at the base in two localities have yielded radiolarians of Permian 

age (Silberling and Jones, 1982; Fraticelli, 1984) 

Pbh Bully Hill Rhyolite (Permian(?)-Middle Triassic(?))—Dominantly porphyritic and 

non-porphyritic quartz keratophyre; locally includes much volcanic breccia. 

Contains lenticular bodies of massive sulfide in uppermost part. Formation is 

of small areal extent, highly variable in thickness, and extensively altered. 

Age is uncertain, but possibly late Permian based on radiolarians of Permian 

age in chert bed above the Bully Hill Rhyolite in the Shasta Lake area 

(Fraticelli, 1984) 

Ppr Pit River stock (Permian)—Coarse-grained quartz diorite, granodiorite, and albite 

granite, with associated aplite dikes. Isotopic age as determined by U/Pb ratios 

on zircon is 261 Ma (Fraticelli and others, 1985) 

aqd Augite-quartz diorite (Permian(?))—Includes medium-grained augite quartz 

diorite, fine-grained diorite, and minor granodiorite that intrude and surround 

the McCloud Limestone 

md Mafic rocks (Permian(?))—Includes mafic diorites and diabasic rocks that intrude 

Bragdon, Baird, and Nosoni Formations 

Pd Dekkas Andesite (Permian)—Predominantly albitized andesite (keratophyre) and 

subordinate albitized basalt (spilite); forms massive flows and volcanic 

breccia; commonly porphyritic and (or) amygdaloidal. Contains lenses of 

mudstone and tuffaceous mudstone 

Pn Nosoni Formation (Permian)—Predominantly mafic volcanic tuffs and subordinate 

mudstone, tuffaceous sandstone, mafic flows, volcanic conglomerate, and 

breccia. Some mudstone is calcareous and contains abundant fusulinids of 

Permian age (Fraticelli, 1984). Formation thickens from south to north but is 

absent in some areas. Contact with overlying Dekkas Andesite (Pd) is locally 

difficult to ascertain 

Pm McCloud Limestone (Pennsylvanian(?) and Permian)—Light-gray massive 

limestone; locally contains abundant Permian fusulinids; forms individual 

large blocks in many areas owing to disruption by faults and (or) engulfment 

by mafic quartz diorite or other dark fine-grained intrusive rock; may be in 

part Pennsylvanian but fossil evidence is controversial (Skinner and Wilde, 

1965) 

Mb Baird Formation (Mississippian and Pennsylvanian(?))—Predominantly 

volcaniclastic sandstone composed of clasts of intermediate volcanic rocks; 

subordinate interbedded purple-weathering tuff, mudstone, shale, and bluegray bioclastic limestone. Some shale and limestone lenses are highly 

11 
 

 

 

 

 

 

 

 

 

 

 

 

fossiliferous; lowest part of Baird Formation in southern part of its exposed 

area is massive albitized porphyritic andesite flows 

Mbd Bragdon Formation (Mississippian)—Dark-gray to black shale, mudstone, and 

siltstone in lower part; siliceous sandstone, grits, and chert conglomerate 

prominently interlayered with dark pelitic rocks in middle and upper parts; 

some tuffaceous beds near top of formation seem to be comformable with and 

gradational into the overlying Baird Formation. The abundant chert in the 

conglomerate is of unknown source 

Dk Kennett Formation (Devonian)—Lowest part in southern exposure of Kennett 

Formation is silicic volcaniclastic debris derived largely from erosion of 

Balaklala Rhyolite. This is overlain by interlayered black carbonaceous and 

cherty shales containing local volcaniclastic interbeds. Shales typically 

weather medium to light gray. Uppermost part contains massive gray 

limestone lenses, locally with abundant fossils. Contact with overlying 

Bragdon Formation is unconformable and may be a thrust fault of regional 

extent 

Dmm Mule Mountain stock (Devonian)—Highly altered phaneritic igneous body 

consisting of trondhjemite, albite granite, and quartz diorite; U/Pb isotopic age 

is 400 Ma (Albers and others, 1981) 

Dbr Balaklala Rhyolite (Devonian(?))—Silicic flows, breccias, and tuffs; subordinate 

dikes and mafic flows; all rocks are intensely albitized, and protolith was 

probably dacite. Most of the rocks are quartz keratophyres, but through long 

informal usage are usually referred to as hyalite. The unit is divided into three 

informal units (not differentiated on this map); a nonporphyritic rhyolite 

consisting of flows and breccias, with subordinate tuffs and mafic flows; a 

medium-grained porphyritic rhyolite consisting of flows; and a coarse-grained 

porphyritic rhyolite consisting of flows and breccias in the upper part. The 

Balaklala is considered to be a cogenetic extrusive equivalent of the Mule 

Mountain Stock. The lower and middle units are intruded by the stock 

Dcg Copley Greenstone (Devonian(?))—Chiefly keratophyre and subordinate spilite 

pillow lavas and volcanic breccias; includes some metaandesite and 

metabasalt, as well as boninite and shaly tuff lenses in lower part. Pillow lavas 

conspicuously dominate the upper part where it is locally interlayered with, 

and also intruded by, middle facies of Balaklala Rhyolite (Dbr). Probably 

coeval with Balaklala Rhyolite 

TRINITY TERRANE 

tum Trinity ultramafic complex (Ordovician(?))—Strongly deformed and recrystallized 

peridotite, minor layered and intrusive gabbro (tgb, where distinguished), 

diabase dike-sill-complex, plus rare volcanic rocks. Has yielded early 

Paleozoic radiometric ages. May represent an Ordovician ophiolite (LindsleyGriffin, 1977) or a mantle diapir, intrusive into an island-arc or back-arc basin 

environment (Quick, 1981) 

tgb Gabbro (Ordovician(?))—Layered intrusive, minor component, locally 

distinguished 

12 
 

 

 

 

 

 

 

 

 

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16 
 

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17
 
18
1. Carver, G.A., Cashman, S.M., Kelsey, H.M., and Stephens, 

T.A., 1985, Geologic map of the Blue Lake 15-minute 

quadrangle, California (unpublished) 

2 Young (1978) 

3. Charlton (1979) 

4. Irwin, W.P., and Court, B.L., 1985, Reconnaissance map of 

portions of the Ironside Mountain 15-minute quadrangle 

(unpublished) 

5. Hotz and others (1974) 

6. Cox (1967) 

7. Fahan (1982) 

8. Lipman (1962) 

9. Lawson (1986) 

10. Fraticelli, L.A., 1985, Reconnaissance map of portions of 

the Rush Creeks 7.5-minute quadrangle, Trinity County, 

California (unpublished) 

11. Lydon and Klein (1969) 

12. Sorensen, M.L., 1985, Reconnaissance map of the Schell 

Mountain quadrangle, Trinity and Shasta County, 

California (unpublished) 

13. Kingston (1985) 

14. Renne, P.R., 1985, Reconnaissance map of the northern 

Bollibokka Mountain, Shasta County, California, scale 

1:62,500 (unpublished) 

15. unmapped area 

16. Aalto, K.R., 1984, Reconnaissance geologic map of 

portions of the Pilot Creek quadrangle, Humboldt County, 

California (unpublished) 

17. Rowland (1966) 

18. Irwin (1985) 

19. Irwin (1974) 

20. Irwin (1963) 

21. Albers and others (1964) 

22. Kinkel and others (1956) 

23. Hollister and Evans (1965) 

24. Albers and Robertson (1961) 

25. Fraticelli, L.A., 1985, Reconnaissance mapping in parts of 

the Millville 15-minute quadrangle, Shasta County, 

California (unpublished) 

26. Hilton (1975) 

27. Fraticelli (1984) 

28. Helley and Harwood (1985) 

29. Kelsey and Allwardt (1974) 

30. Irwin and others (1974) 

31. Irwin and others (1985) 

32. Huber and others (1983) 

33. Irwin, W.P., Unpublished reconnaissance mapping, in

Blake and others (1984) 

34. Wright (1981) 

35. Peterson (1969) 

36. Maytum (1967) 

37. Murphy and others (1969) 

38. Helley and others (1981) 

39. Harwood and others (1980) 

40. McLaughlin, R.J., 1986, Reconnaissance geologic mapping 

in the western half of the Garberville 1:100,000 quadrangle 

(unpublished) 

41. Blake, M.C., Jr., 1986, Reconnaissance geologic mapping 

in the eastern half of the Garberville 30- x 60-minute 

quadrangle, scale 1:100,000 (unpublished) 

42. Blake (1965) 

43. Worrall (1981) 

44. Blake, M.C., Jr., and Jayko, A.S., 1984, Reconnaissance 

geologic map, southern half of Yolla Bolly 15-minute 

quadrangle (unpublished) 

45. Worrall, D.M. (#44), and Blake, M.C., Jr., and Jayko, A.S. 

(#45) 

46. Bailey and Jones (1973) 

19