REVISION OF THE BECKWITH AND BEAR RIVER FORMATIONS OF 

SOUTHEASTERN IDAHO. 

By G. R. MANsFIELD and P. V. RouNDY. 

INTRODUCTION AND SUMMARY. 

In the detailed geologic mapping of the 

Wayan and Montpelier quadrangles, in southeastern Idaho and adjacent territory, it has 

been found necessary to apply new names to 

strata hitherto referred to the Beckwith and 

Bear River formations or to portions of the 

Laramie as mapped by the Hayden Survey. 

The two quadrangles are contiguous, and the 

Montpelier quadrangle lies south of the Wayan. 

They occupy the corner of the State and include 

a very narrow strip in northeastern Utah and 

a somewhat broader strip in western Wyoming. They lie between parallels 42° and 43° 

N. and meridians 111° and 111° 30' W. The 

Wayan 30-minute quadrangle, the topographic 

map of which has not yet been published, consists of four 15-minute quadrangles, the Freedom, Lanes Creek, Crow Creek, and Slug Creek. 

Topographic maps of these areas are now available. 

The formations to be discussed extend from 

the northeastern part of the Montpelier quadrangle northward through the eastern part of 

the Wayan quadrangle and thence northward 

an undetermined distance, possibly including 

a considerable part of the Caribou Range. 

They include about 17,000 feet of strata, unless 

there are unrecognized repetitions by folding or 

faulting. 

Two large groups of beds are recognizable 

in the field. At first, in accordance with earlier 

interpretations, these groups were assigned 

respectively to the Beckwith formation, of 

Cretaceous and Jurassic age, and the Bear 

River formation, of Upper Cretaceous age. 

On the maps of the Hayden Survey both are 

included in the Laramie. There is, however, 

considerable lack of ~greement both lithologically and faunally between these formations as 

exposed in the district under discussion and as 

30830°-17---6 

exposed in the region of their type localities. 

Descriptions of the Beckwith formation in the 

areas where it has been studied show considerable variety in lithologic character. The fossil 

content is ·meager, and there is uncertainty 

about the upper limit of the formation. 

The Bear River. formation has long been 

known and has been studied by many geologists. It has a distinctive fauna and nearly 

as distinctive a lithology. The lack of agreement between the beds in the Wayan quadrangle heretofore called Bear River and the 

typical Bear River is so marked as to raise the 

question whether any of these beds can properly be assigned to that formation. The beds 

in the Wayan quadrangle resemble somewhat 

the Kootenai of Montana and Canada and may 

in part represent that formation. They may 

furnish a connecting link between the Kootenai 

and the Bear River. 

The strata in this area that were formerly 

called the Bear River are here assigned to the 

Wayan formation, of Cretaceous, possibly 

Lower Cretaceous age, and the so-called Beckwith is divided into seven formations, of which 

the lower two are marine formations of Jurassic age, and the remaining five are nonmarine 

formations assigned to the Gannett group, of 

Cretaceous (?) age. This paper gives a statement of the stratigraphic problems involved 

and a description of the formations. The 

writers are indebted to Mr. T. W. Stanton for 

examination of the fossils and for helpful suggestions. 

GENERAL STRATIGRAPHY OF THE AREA. 

The stratigraphic sequence in southeastern 

Idaho is remarkably full, all the great Paleozoic and later systems being represented. The 

Paleozoic formations are identical in name and 

number with the corresponding formations of 

75 
76 SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY, 1916. 

northern Utah described by Richardson,! 

except that the Threeforks limestone has not 

been recognized. The Idaho formations differ somewhat in thickness and character from 

those of the Utahsection. The subjoined table 

shows the general character of the Mesozoic 

formations of the region and the relations of 

the formations here discussed to the others. · 

Mesozoicjormations in southeastern Idaho. 

System and series. Formation. 

Cretaceous (Lower Cretaceous?). Wayan formation. 

Unconformity 

Cretaceous (?). Gannett group. 

Stump sandstone. 

Jurassic. Preuss sandstone. 

Unconformity 

Twin Creek limestone. 

Jurassic or Triassic. Nugget sandstone. 

Ankareh formation. 

Triassic (Lower Triassic). 

Thaynes limestone. 

Woodside shale. 

THE BECKWITH PROBLEM. 

The Beckwith formation has been identified 

at several localities in western Wyoming and 

adjacent parts of Idaho by a number of geologists, but present knowledge of the formation 

I Richardson, G. B., The Paleozoic section in northern Utah: Am. 

1our. Sci., 4th ser., vol. 36, pp. 406-416, 1913. 

Character. Thickness 

(feet). 

Sandstones, shales, carbonaceous shales, 

limestones, some conglomerate _______ . 11,800 

ryg~e sandstone ................ 100 

Draney limestone ..•.... _ ....... _ 200 

Bechler conglomerate ..... _ ~ . ___ 1, 775 

Peterson limestone_ .... ___ ..... _ 205 

Ephraim conglomerate_ ... ____ .. 1,025 

--- 3,305 

-

Greenish-gray sandstone, with massive 

calcareous bed at base _ . __ .... _______ . 200-600 

Red sandstones and shales ..... _ ... __ . _ . 1,300 

Whitish shaly limestone, some massive 

beds .. --·-·.·--- ............. ··--·--- 3,500± 

Subdivided into four members: Red 

sandstone, with heavy grit at base, sue- ceeded by cherty limestone and red 

shale. Raymond Canyon section .... ·. 1, 900 

Variable, yellow sugary sandstone, thin 

to massive bedded, or red or chocolatecolored shale and sandstone, or mottled 

clays and shale with some sandstone 

and limestone. __ . _ .... _ .... _ ......... 750± 

Limestones, calcareous sandstones, and 

shales .. _ ...... __ ...... _ ......•... _ .. 2,000± 

Thin-bedded calcareous shales and limestones ......... · .•.................... 1,500 

is largely derived from the three principal 

published descriptions, which represent more 

or less separated districts and contain differences sufficient to warrant a brief discussion. 

Their main features are set forth in the following table, which includes also the correlations 

given in the present report: 
Age. 

Upper Cretaceous. 

Cretaceous (Lower 

Cretaceous?). 

Tentative correlation of the Beckwith and Bear River formations in southeastern Idaho and southwestern Wyoming. 

Southeastern Idaho (Mansfield and Roundy). 

Not recognized. 

Wayan formation : Feet. 

Alternating sandstone and 

shales ............... . . 9, 000 

Sandstones, shales, and 

limestones:...... . . . . . . 2, 800 

Idaho-Wyoming border (Breger, U. S. 

Geol. Survey Bull. 430, pp. 562-563, 

1910). 

Higher beds not recognized. 

Southwestern Wyoming (Veatch, U. S. Geol. Survey Prof. Paper 56, pp. 57-61, 1907). 

Bear River. 

Western area. Eastern area. 

Unconformity---! I 

Beckwith: UpJ?er mem- ber time eqmvalent of 

Lower Cretaceous and 

Dakota(?); consists of 

light-colored sandstones and clays; 3,000 

feet. 

Beckwith: Upper 

and lower phases 

merge. Predominant r e d d ish 

color but all light 

color; conglomerates in this sec- tion are white to 

yellow. Entire 

section a b o u t 

4,000 feet. 

Cretaceous (?). 

Jurassic. 

Gannett group: 

Tygee sandstone ....... . Draney limestone ...... . Bechler conglomerate .. . Peterson limestone .... . . Ephraim conglomerate .. 

100+ 

200 

1,775 

205 

1,025 

Stump sandstone........ . . . 200-600 

Preuss sandstone........... 1, 300 

Beckwith: Feet. Upper gray limestone .. 100 

Conglomerate .......... 850 

Lower gray band 

sandstone. . . . . . 250-600 

Red sandstone. . . . 1, 200 

Beckwith: Lower redbed member c om- posed of sandy clays, 

sandstones, and con- glomerates; 2,500 feet; 

Upper Jurassic. 

Beckwith: Lower 

part of section. 

Unconformity I 1--------

Twin Creek limestone. Twin Creek. Twin Creek. Twin Creek. 

Lincoln County, Wyo. (Schultz, 

U.S. Geol. Survey Bull. 543, 

pp. 30, 52-55, 1914). 

Bear River. 

Unconformity-----

Not represented or included with Bear River. 

Beckwith considered 

equivalent of Veatch's 

eastern section, but all 

Jurassic. Light-colored 

shale, sandstone, and 

clay with associated 

beds of white to lightyellow and red con- glomerate and black 

limestone; 900-2,400 

feet. 

Twin Creek. 

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78 SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY, 1916. 

Veatch, 1 who defines and describes the formation, divides it into two unnamed members-

" a lower red-bed member composed of interbedded sandy clays, sandstones, and conglomera.tes 2,500 feet thick, and an upper member 

composed of rather light-colored interbedded 

sandstones and clays with a thickness of 3,000 

feet or more." In the eastern exposures 

within his district these two phases merge. 

"Just west of Hilliard these beds, while having 

a predominant reddish cast, are a~ light in 

color. The conglomerates, which near Beckwith are deep red, are here white to yellow." 

Veatch appears not to have found fossils in the 

Beckwith, but he refers to this formation collections of marine Jurassic fossils previously 

made by Stanton at two localities, one of 

which was outside of the district described. 

On the evidence of these fossils he refers the 

lower part of the Beckwith to the Jurassic; 

the remainder, he thinks, "contains time equivalents of the Lower Cretaceous and Dakota." 

Breger 2 gives the following account of the 

Beckwith formation in the Crow Creek region, 

Idaho, which is included in the Montpelier and 

Wayan quadrangles: 

This formation consists of red sandstone and conglomerates with two conspicuous gray bands. The lower 

gray band is a dark greenish-gray calcareous sandstone 

250 to 600 feet thick and occurs 1,200 feet above the base 

of the formation. The lower 1,200 feet consists of red 

sandstones and shales, apparently without conglomerates. 

The conglomerates seem to be confined * * * to the 

interval above the lower gray . band, constituting most of 

the rocks for a thickness of 850 feet. They are succeeded 

by the second or upper gray band, a massive limestone, 

more or less marly and light blue-gray in color. This 

rock attains a thickness of 100 feet in Stump Canyon and 

northward, where it forms a resistant ledge that may 

easily be traced by its light color. 

Breger makes no mention of fossils in the 

formation. 

Schultz 3 describes the formation as it occurs 

in Lincoln County, Wyo., south of Snake River 

·and east of the Salt River Range and the 

Absaroka Ridge. There it represents the 

direct northward extension of the Beckwith formation of 

the eastern belt of Uinta County [Veatch'sarea], where the 

conglomerate phase merges with the upper sandstone and 

shale. * * * The beds are composed of light-colored 

1 Veatch, A. C., Geography and geology of a portion of southwestern 

Wyoming: U.S. Geol. Survey Prof. Paper 56, pp. 57-58, 1907. 

2 Breger, C. L., The salt resources of the Idaho-Wyoming border, 

with notes on the geology: U. S. Geol. Survey Bull. 430, pp. 562-563, 1910. 

~ Schultz, A. R., Geology and geography of a portion of Lincoln County, 

Wyo.: U.s. Geol. Survey Bull. 543, pp. 30, 53, 54, 1914.· 

shale, sandstone, and clay. The sandstone is usually 

light yellow, pink, or white, and the clay varies from 

yellow or light pinkish red to dark purple. With the 

sandstone, shale, and clay are associated beds of white to 

light yellow and red conglomerate and black limestone. 

In places * * * conglomerate beds constitute an 

important part of the formation. 

Fossils are not numerous, but Schultz obtained collections from four localities. These 

were examined by Stanton, 'Yho referred three 

of the collections to the Jurassic and stated that 

the fourth was not sufficient for age determination but suggested Jurassic. According to 

Schultz two of the lots "come from the top of 

the Beckwith and indicate. that it is Upper 

Jurassic." The thickness of the formation in 

the region ranges from 900 to 2,400 feet. 

Lithologically the descriptions given by 

Veatch and Schultz agree fairly well, except 

that in Schultz's area the red conglomeratic 

phase seems not to be well developed. In both 

areas sandstones and clays predominate in the 

formation. Conglomerates appear to be of 

relatively minor Importance. Veatch makes 

no mention of limestone, but Schultz refers to 

beds of black limestone. Breger, on the other 

hand, does not mention clays, but emphasizes 

two gray bands, one of sandstone and the other 

of limestone, with an intermediate . massive 

conglomerate. He also notes the presence of 

a thick band of red sandstones and shales below 

the lower -gray band. Thus he divides the 

formation into a series of bands which, he says, 

·"maintain these characters throughout the 

area covered by the present reconnaissance, 

* * * a distance of about 35 miles." The 

formation in the Wyoming region appears to 

be more variable, and the subdivisions noted 

by Veatch and Schultz do not · appear to continue over considerable areas. r 

The study of the Wayan and · Montpelier 

quadrangles has given the writers an opportunity to review in some detail Breger's work 

on the Beckwith and to cover a somewhat 

larger area than he examined. They have also 

semi the Beckwith northeast and southeast of 

Evanston, Wyo., but have not been able to 

make extended observations there. In the 

Idaho region they recognized the four bands 

described by Breger and found three additional 

higher ones, but in the portions of the Wyoming 

Beckwith seen they did not observe any similar 

arrangement. Perhaps the most striking differences noted in the two regions were the 
BECKWITH. AND BEAR RIVER. FORMATIONS OF SOUTHEASTERN IDAHO. · 79 

greater abundance of conglomerates and limestones and more intense red color in the Idaho 

area contrasted with the predominance of sandstones and clays of lighter colors in the Wyoming area. 

Faunally there are several differences to be 

noted. Veatch refers the lower part of the 

Beckwith to the Jurassic, but there is an 

element of doubt in this reference, because of 

the possibility that the fossils collected earlier 

by Stanton n1ay have come from unrecognized 

in-faulted Twin Creek beds, although Veatch 

does not regard this as probable. The upper 

beds he considers Cretaceous. SchUltz found 

Jurassic fossils in the top of the Beckwith in 

his area, and yet he regards the forn1ation 

there as the direct northward continuation of 

Veatch's combined section. In the Idaho area 

the writers found marine Jurassic fossils just 

at the base of Breger's lower gray band, but the 

limestone beds higher in the section contain a 

fresh-water fauna that is thought by Stanton 

to be later that Jurassic, having affinities with 

those of the Kootenai and Bear River formations. Nothing comparable to this fresh-water 

fauna has yet been reported from the other 

Beckwith areas. 

Schultz/ from work in Wyoming and Utah, 

the results of which have not yet been published, has come to look upon the Beckwith as a 

group rather than a single formation. It is 

thus seen that the term Beckwith as now used 

has no very definite meaning, that it is applied 

to widely varying beds, some of which may not 

be closely related, and that it probably covers 

beds belonging to two great systems. 

The writers have found it practicable to subdivide the beds hitherto called Beckwith in 

the Wayan and Montpelier quadrangles into 

seven formations, two Jurassic and five Cr~­

taceous ( n. In view of the above discussion 

it seems unwise to .retain the name Beckwith 

for any of these formations and new names 

are therefore assigned. Detailed descriptions 

of the formations are given on pages 82-83. 

THE BEAR RIVER PROBLEM. 

The Bear River formation early attracted 

attention because of its numerous and wellpreserved fossils. It was named by Hayden 2 

1 Personal communication. 

2 Hayden, F. V., U.S. Geol. Survey Terr. Second Ann. Rept., pp. 

91-92, 1873. 

in 1873, but its true stratigraphic position was 

not determined until nearly 20 years later by 

Stanton.3 In 1895 White 4 gave a full description of it, summarizing the information 

available at that date. Since then other 

geologists have contributed additional details. 

(See table on p. 80.) 

Although the stratigraphic position of the 

Bear River has been determined, its relations to 

the underlying formations are not everywhere 

clear. It is probable that in some of the earlier 

accounts strata now assigned to the Beckwith 

have been included in the Bear River. The 

formation has not been recognized outside of 

the region which extends from Old Bear River 

City, about 9 miles southeast of Evanston, 

Wyo., northward through the Wyoming and 

Salt River ranges into the northeastern part 

of Idaho. 5 

In the Yellowstone Park and extending 

northward into Canada there is a thick and 

extensive non1narine formation, the Kootenai, of Lower Cretaceous age, between which 

and the Bear River there are certain affinities, 

but the relations of the two formations to 

each other are not known. In Idaho and 

Wyoming there are great thicknesses of strata 

which have been assigned to the Bear River 

but in which none of the characteristic 

Bear River fossils have been found. Stanton 6 comments as follows on a collection 

made by Schultz on the west flank of the 

Caribou Range about 2 miles east of Hernian. 

Idaho: 

In my opinion this fauna is Cretaceous, but on account 

of the absence of definitely characteristic forms I am 

unable to determine whether it belongs to the Bear River 

formation. Similar imperfect fossils have been collected 

in Montana in rocks that are provisionally referred to the 

Kootenai formation. 

The assignment of these and other doubtful 

beds to the Bear River seems to have been 

based partly on lithologic resemblances and 

partly on the actual occurrence in higher beds 

of characteristic Bear River fossils, as in parts 

of Lincoln County, Wyo./ and of Bonneville 

a Stanton, T. W., The stratigraphic position of the Bear River forma· 

tion: Am. Jour. Sci., 3d ser., vol. 43, pp. 98-115, 1892. 

4 White, C. A., The Bear River formation and its characteristic fauna: 

U. S. Geol. Survey Bull. 128, 1895. 

5 Veatch, A. C., op. cit., p. 60. 

6 Schultz, A. R., and Richards, R. W., A geologic reconnaissance 

in southeastern Idaho: U. S. Geol.'Survey Bull. 530, p. 275, 1913. 

7 Schultz, A. R., Geology and geography of a portion of Lincoln 

County, Wyo.: U.S. Geol. Survey Bull. 543, pp. 54-59, 1914. 
80 SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY, 1916. 

and Fremo~t counties in Idaho, north and 

northeast of the Wayan quadrangle.1 

The rocks in typical exposures of the Bear 

River formation may be described as dark 

shales with calcareous bands and some soft gray 

sandstones, which are abundantly fossiliferous. 

A single section which may be regarded as representative may be quoted from Stanton's 

section on Stowe Creek/ near the type locality. 

Part of Stanton's section on Stowe Creek, Wyo. 

5. Bear River formation: Feet. 

Brown sandstone; dip 75° E................ . 20 

Soft gray shale. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25 

Gray sandstone. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 

Dark shale................................. 60 

Brown sandstone . . . . . . . . . . . . . . . . . . . . . . . . . . 10 

Dark shale with calcareous bands containing 

numerous fossils: Pyrgulijera humerosa, Corbula pyriformis, Unio belliplicatus .......... 250 

Sandstone.................................. 10 

Dark shales with thin bands of limestone and 

sandstone and occasional carbonaceous 

seams; many Bear River fossils ............ 400 

Gray sandstone; dip 75° E. . . . . . . . . . . . . . . . . 10 

Soft shales. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25 

Gray sandstone; dip 75° E . . . . . . . . . . . . . . . . . . 20 

840 

In some places the shales are sufficiently carbonaceous to carry thin seams of coal, but the 

coal is generally too poor to be of economic 

importance. 

At a few localities in the Wayan quadrangle 

there are dark shales with calcareous bands in 

supposed Bear River strata, but these are not 

very fossiliferous, and such fossils as occur are 

not typical of the Bear River. · The strata include two rather prominent sets of limestone 

beds, with which more or less dark shale is interbedded, and great thicknesses of sandstones 

and shales, some of which are of an intense red 

color. Lithologically there is no very close 

agreement between the rocks of the Wayan 

quadrangle and the typical Bear River, and 

faunally the relationship is uncertain. 

The Kootenai /of Canada and Montana contains some coal beds of economic importance. 

In the Cascade coal basin of Alberta the formation includes some 2,800 feet of sandstones and 

shales with many valuable coal seams, there 

being in one locality as many as 14 beds that 

I Unpublished data collected by E. G. Woodruff and A. R. Schultz. 

2 Stanton, T. W., The stratigraphic position of the Bear River formation: Am. Jour. Sci., 3d ser., vol. 43, p. 106, 1892. 

are possibly workable. 3 In the Philipsburg 

qua.drangle, Mont./ the Kootenai formation includes 1,500 feet of variegated beds, chiefly 

sandstones and shales with some limestones and 

conglomerates. The "gastropod limestone " 5 

in that quadrangle is physically much like the 

limestones of the supposed Bear River in the 

Wayan quadrangle. It is described as a pure 

gray limestone rich in fossils, chiefly freshwater snails. The limestones form distinct 

. beds which are separated by shales and crop 

out as reefs. On . fresh fracture the rock is 

dark gray; on the weathered surface, pale bluish gray. The texture is coarse and less compact than that of the lower limestone. The 

rock is crowded with spiral shells which are conspicuous on weathered surfaces. The calcareous shale interbedded with and overlying the 

gastropod limestone is partly of an olive-green, 

ocherous-weathering type. It grades into 

sandstones. The uppermo'st beds consist of 

more or less calcareous shale, gray to nearly 

black on fresh fracture but weathering to bluegray or brown; these beds virtually grade into 

limestone. The limestones of the supposed 

Bear River in the Wayan quadrangle occur in 

the same manner as in the Kootenai of the Philipsburg quadrangle, but they are not so fossiliferous nor so coarse-textured, and the interbedded shales are usually dark gray to blackish, 

although the olive-green color and gradation to 

sandstone have been noted. 

Other lithologic similarities exist between 

the so-called Bear River of the Wayan quadrangle and the Kootenai of the Philipsburg . 

quadrangle and other parts of Montana . . There 

are also many differences, among them being 

the absence of workable coal in the Wayan 

quadrangle. However, the shales are in some 

places carbonaceous, and near Auburn, Wyo., 

a tunnel some 40 feet long has been driven at 

a coal prospect from which a few lumps of 

usable coal have been taken. 

No recognizable flora has been found in the 

Wayan "Bear River," but undeterminable 

stern fragments have been taken from some of 

the olive-yellow sandstones above the band of 

a Dowling, D. B., Report on the Cascade coal basin, Alberta, p. 8, 

Canada Geol. Survey, 1907. 

4 Calkins, F. C., and Emmons, W. H., Geology and ore deposits of 

the Philipsburg quadrangle, Mont.: U.S. Geol. Survey Prof. Paper 78, 

p. 77, 1913. 

5 Idem, pp. 77-79. 
BECKWITH AND BEAR RIVER FORMATIONS OF SOUTHEASTERN IDAHO. 81 

dark shale in the lower part of the formation, 

and some pieces of dark silicified wood have 

been found in dark-gray sandstone beds close 

to the top of the section studied. 

From the above descriptions it is clear that 

the differences between the Wayan ''Bear 

River" and the typical Bear River are so great 

as to make the correlation of the two formations questionable. On the other hand, the 

agreement between the beds of the Wayan area 

and the Kootenai is perhaps not sufficiently 

close to warrant correlation with that formation until such a correlation is supported by 

further and more detailed studies. It seems 

likely that when the detailed stratigraphy of 

the region north of the Wayan quadrangle, 

beyond Snake River, is· better known the formation will be found to grade upward into the 

typical Bear River. If the interesting suggestion that the formation should be correlated 

with the Kootenai of Montana should be substantiated, it might then be possible to determine the stratigraphic relations of the Kootenai 

and the Bear River. 

In the mean time it seems undesirable to 

apply either term to the formation now called 

Bear River in the Wayan quadrangle. To 

avoid ainbiguity these beds are named the 

Wayan formation. The great thickness of the 

formation, more than 11,800 feet, neither top 

nor bottom being exposed, and the arrangement 

of the strata suggest that it may be subdivided 

later, but this seems inadvisable until detailed 

studies have been carried farther north. A 

more detailed description of the formation 1s 

given on pages 83-84. 

THE FORMATIONS. 

reddish gray to deep dull red. The sandstone 

is usually calcareous and more or less argillaceous, becoming very shaly in some places. 

The beds are generally less than 6 inches thick, 

weather to a dull-red soil, and make the slopes 

of subordinate ridges. A graphic measurement 

at the head of Thomas Fork valley gives a 

thickness of 1,300 feet. 

A minor unconformity separates the Preuss 

sandstone from the underlying Twin Creek 

limestone. 

STUMP SANDSTONE. 

The Stump sandstone is named from Stump 

Peak, at the head of the north fork of Stump 

Creek, about the center of T. 6 S., R. 45 E., 

Boise meridian (unsurveyed). It consists 

mainly of thin-bedded gray to greenish-gray 

fine-grained sandstones which weather into 

platy fragments about an inch thick . . Near 

the base are some beds of compact calcareous 

sandstone, locally as thick as 6 feet. The 

grains are very fine and chiefly of colorless 

quartz. The rock tends to break with a conchoidal fracture and to ring under the hammer. 

Fresh surfaces have a steel-gray color, but 

weathered surfaces appear velvety brown. Instead of ledges these beds commonly form lines 

of irregularly weathered blocks that at first 

glance resemble trap rock. At the base is a 

bed of grit, or coarse-grained sandstone, which 

contains marine fossils of Jurassic age. The 

component grains are colorless quartz, with 

some greenish chloritic material, and the 

cement is calcareous and grayish. The fresh 

rock has a slight pinkish cast, and weathered 

surfaces are decidedly pinkish. This is practically the only bed in the entire formation 

PREUSS SANDSTONE. from which fossils were collected, and the colThe Preuss sandstone is named from Preuss lections it yielded at several ·localities gave 

Creek, in the northeastern part of the Mont- practically the same fauna. Fossils identified 

pelier quadrangle, about 12 miles northeast of by T. W. Stanton were Ostrea strigilecula 

Montpelier. With higher formations it occu- White~' Rhynchonella ~ sp., Camptonectes ~ sp., 

pies a synclinorium extending northward from and Pentacrinus sp. A single collection asthe northeastern part of the Montpelier quad- signed tentatively to the same or nearly the 

rangle completely across the Wayan quadran- same horizon included Astarte sp., Trigonia 

gle. The eastern extension of the southern sp., and Belemnites sp. According to Mr. 

part was not traced, but the central and north- Stanton these forms might all be considered as 

ern parts probably do not extend far east of Twin Creek. They are, however, separated 

the area studied. from that formation by an unconformity and 

The formation consists of very fine, even- more than 1,000 feet of unfossiliferous sandgrained sandstones ranging in color from pale stones. 
82 SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY, 1916. 

The Stump sandstone is usually resistant to 

weathering and forms con-spicuous ridges, but 

south of the Halfway House, on the southern 

edge of the Wayan quadrangle, ·it forms a valley. The rock there has probably been weakened by fracturing or. other structural disturbance. 

The essential features of this formation are 

present throughout the region studied, but the 

thickness varies from 200 to 600 feet. Plate 

XIII, A, shows a typical exposure of the Stump 

sandstone. 

GANNETT GROUP. 

NAME AND GENERAL FEATURES. 

The Gannett group is named from the Gannett Hills, which lie in Bannock County, Idaho, 

and Lincoln County, Wyo., in the eastern part 

of the Wayan quadrangle, where all the formations of the group are well exposed. The 

Gannett Hills have been named in honor of the 

late Henry Gannett, topographer of the Green 

River division of the Hayden Survey and subsequently an eminent geographer, who did the 

first topographic work in this region. 

The group includes five distinct subdivisions 

and has a maximum thickness of over 3,300 

feet. It rests, with apparent conformity, upon 

the Stump sandstone. At the top is the Tygee 

sandstone, gray and even grained, .followed by 

the Draney limestone, gray and compact. 

Below are the Bechler and Ephraim conglomerates, separated by the Peterson limestone, 

which is much like the Draney. S.hale appears 

to be nearly absent from the group. 

The fossils thus far collected from the Gannett group are not distinctive, but they are 

apparently later than Jurassic, so that the age 

of the group is probably Cretaceous. 

The group occurs in much the same areas as 

the Preuss sandstone, but is confined more to 

the central portion of the synclinorium. 

EPHRAIM CONGLOMERATE. 

The Ephraim conglomerate, at the base of 

the group, is named from Ephraim VaHey, in 

sec. 36, T. 10 S., R. 45 E., Boise meridian, which 

lies in the formation. The rock is a red conglomerate with minor amounts of sandstone and 

some thin bands of gray to purplish limestone. 

It is about 1,000 feet thick at the type locality, 

but varies much in thickness and character, becoming in some regions practically all conglomerate with pebbles, some of which are nearly a 

foot in diameter. The pebbles represent a wide 

variety of materials, but perhaps 100 feet above 

the base there is an olive-yellow band, 25 feet 

or more thick, in which the pebbles are almost 

exclusively of dark chert, rounded or subangular, and generally an inch or less in diameter. 

The Ephraim conglomerate forms most of the 

mass known as Red Mountain, in the northeastern part of the Montpelier quadrangle, 

where it is well exposed. (See Pl. XIII, B.) 

PETERSON LtMESTONE. 

The Peterson limestone is named from Peterson's ranch, along Tygee Creek, in sec. 34, T. 

7 S., R. 46 E., Boise meridian, east of which 

the formation is well exposed. It is about 200 

feet thick, massively bedded near the top, and 

very persistent throughout the region studied, 

forming prominent ridges that can be followed 

by the eye for miles from some of the higher 

summits. (See Pl. XIV, A.) The following 

fossils from this limestone have been identified 

by T. W. Stanton: Unio sp., Planorbis (Gyraulus) sp. related to P. prrecursoris White, 

Viviparus sp., Goniobasis? sp., and two distinct species of Physa. Fossils of similar types 

occur in the Kootenai, Bear River, and later 

formations. The fresh-water gastropods are 

not distinctive and similar forms of Planorbis 

are found in both the Morrison and Bear River, 

but no species of Physa have been reported 

from beds older than the Bear River. 

BECHLER CONGLOMERATE. 

The Bechler conglomerate is named from 

Bechler Creek, which enters Stump Creek from 

the north about a quarter of a mile north of 

the mouth of Boulder Creek, in T. 6 S., R. 45 

E., Boise meridian (unsurveyed), in Bannock 

County. Bechler Creek is named in honor of 

G .. R. Bechler~ topographer of the Teton division of the Hayden Survey, who did the first 

topographic work in the region adjoining the 

Wayan quadrangle on the north. 

The formation is composed of about 1,700 

feet of gray, reddish, and "salt and pepper" 

sandstones with interbedded conglomerates. 

The "salt and pepper" color predominates, 

and there is probably over twice as much conglomerate as sandstone. The proportion of 
U. S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 98 PLATE XIII 

A. VIEW NORTHWEST ALONG THE RIDGE SOUTH OF THE HEAD OF 

LANES CREEK, IN THE NORTHWESTERN PART OF THE FREEDOM 

QUADRANGLE, IDAHO. 

B. VIEW NORTH NEAR THE SUMMIT OF RED MOUNTAIN, IN THE NORTHEASTERN 

PART OF THE MONTPELIER QUADRANGLE, IDAHO. 
U. S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 98 PLATE XIV 

A. VIEW NORTH ALONG THE WEST FLANK OF THE CARIBOU RANGE, IN 

THE EAST-CENTRAL PART OF THE FREEDOM QUADRANGLE, IDAHO. 

B. SHALY AND LIMY STRATA OF THE LOWER DIVISION OF THE WAYAN FORMATION 

EXPOSED IN TINCUP CANYON, IN THE NORTH-CENTRAL PART OF THE FREEDOM 

QUADRANGLE, IDAHO. 
BECKWITH AND BEAR RIVeR FORMATIONS OF SOUTHEASTERN IDAHO. 83 

sandstone> however, is greater than in the 

Ephraim conglomerate. The pebbles in the 

conglomerate are small, few having a diameter 

of more than 1 inch. 

DRANEY LIMESTONE. 

The Draney limestone is named from the 

Draney ranch, on Tygee Creek, in sec. 10, T. 

8 S., R. 46 E., Boise meridian. The lin1estone 

occurs on the top of the ridge about a mile and 

a quarter east of the ranch. The form:1tion is 

about 200 feet thick and is fairly massive, the 

individual beds reaching a maximum thickness of 1! feet. The rock is much like that of 

the Peterson limestone, but is not so massively 

bedded near the top. It is compact and gray, 

but weathers to a dirty-white color. The following fossils from this limestone have been 

identified by T. W. Stanton: Unio sp. related 

to U. vet1tstus Meek, Viviparus ~ sp., and 

Goniobasis ~ sp., a simple smooth form resembling G:? increbescens Stanton or Arnnicola? 

cretacea Stanton. 

TYGEE SANDSTONE. 

The Tygee sandstone is named from. Tygee 

Creek, east of which, in T. 8 S., R. 46 E., the 

formation is well exposed in association with 

the Draney limestone on the top of the ridge 

along the Idaho-Wyoming boundary. The rock 

is gray to buff, even grained, and without the 

greenish or reddish tinges of some of the higher 

sandstones. The top is not exposed, and in 

much of the region this sandstone with part or 

all of the limestone below it has been eroded 

before the deposition of the Wayan formation. 

At the type locality about 100 feet of this sandstone is exposed. 

WAYAN FORMATION. 

Resting unconformably upon the Gannett 

group is a group of beds con1posed of sandstones, shales, limestones, and some conglomerates. Neither the top nor the botton1 is 

known, but apparently about 11,800 feet of 

beds are exposed. These rocks are confined to 

the northeastern part of the Wayan quadrangle 

and the region to the north. The formation is 

named from the settlement of Wayan, in Bannock County, in the northwestern part of the 

Wayan quadrangle. It occupies the hills immediately east of Wayan and appears to be 

broadly divisible into two units, the upper 

composed chiefly of alternating sandstones and 

shales with some conglomeratic beds, but without significant li1nestones, and the lower compnsmg some eight subdivisions, including 

several thick beds of limestone. 

The lower unit in the section exposed in Tincup Canyon includes four sets of red beds, three 

of lin1estone and shale, and one of yellow sandstone. These beds in ascending order may be 

briefly described as follows: 

1. Beneath the limestone of the dome that forms a fine 

arch about a mile west of the mouth of the South Fork of 

Tincup Creek there is a suggestion of reddish soil that may 

represent red beds not otherwise exposed. 

2. Gray limestones, weathering whitish, with darkcolored shales. The top 20 feet is rather massively bedded 

limestone; shale and limestone are interbedded below, the 

proportion of shale gradually increasing toward the base. 

3. Red beds consisting largely of red-weathering soft 

gray sandstone but including also some gray and red shaly 

beds and some calcareous beds. These rocks generally 

form slopes and soil of a light-red color, a brighter color 

than that of No. 5. 

4. Bands of gray limestone in dark shales. Some of the 

limestone beds are relatively massive, 1! feet or more 

thick, and project from the weaker shales. 

5. Red beds with purplish to reddish-gray sandstone, 

massive near the top but in thinner beds and associated 

with shale below, the whole weathering to a red. soil and 

forming fairly smooth slopes. 

6. Dark gray to black shale with massive buff limestone 

near the top and thinner beds of limestone below. (See 

Pl. XIV, B.) 

7. Greenish-gray sandstones and grit, weathering, yellow and reddish, usually forming marked ridges and 

rough talus slopes of large blocks. The sandstone becomes 

conglomeratic in places. 

8. Red to purplish sandstone with some shaly and some 

calcareous beds. 

Some of these subdivisions may be recognized north and south of Tincup Canyon, but 

their structure is complex, they appear to vary 

in lithology and thickness, and they are in 

places not well expressed topographically. For 

these reasons it is not yet practicable to map 

them separately. Their combined thickness is 

estimated at about 2,800 feet. 

The upper unit of the formation, if there is no 

reduplication by folding and faulting, comprises some 9,000 feet of westward-dipping 

strata that lie along the upper course of Tincup 

Creek above the canyon. These beds are 

chiefly red and gray sandstones, with intervening shales and some calcareous beds. The 

sandstones form a series of low ridges and 

points, but the shales are mainly weathered 

into soil-covered areas. Toward the top yel-
84 SHORTER CONTRIBU'riONS TO GENERAL GEOLOGY, 1916. 

lowish and brownish sandstones appear, and 

the uppermost strata recognized are shown only 

by fragments of dark-gray siliceous sandstone 

and pieces of dark-brown or black silicified 

wood weathered white. 

The upper unit apparently represents the 

east limb of a broad syncline, the axial region 

of which is occupied by the layer containing 

silicified wood. The syncline is broken on the 

west by a fault. The northward continuation 

of. the strata and the structural relations suggest that higher beds may appear in that 

direction. 

The fossils collected from the Wayan formation have come 'almost entirely from the limestone bands. The following forms have been 

identified by T. W. Stanton: Unio ~ sp., 

Rhytophorus ~ sp., Viviparus ~ sp., Limnooa ~' 

opercula of gastropods, and fragments of 

fresh-water shells. An unidentifiable fragment of bone has also been found. In his report on the collections Mr. Stanton remarks: 

The collections from the Wayan quadrangle fail to 

show any characteristic species of the Bear River formation, and if the Bear River is recognized there it must be 

on some other basis than naleontologic correlation. This 

is also true of the Beckwith formation, for the reason that 

in its type area the Beckwith has yielded so few fossils 

that it can not be said to have a characteristic fauna. 

. The few fossils found in both the Wayan 

formation and the Gannett group are poorly 

preserved fresh-water forms belonging to Unio 

and to small, uncharacteristic gastropods referred to several genera. There are, therefore, 

marked faunal similarities between the Gannett 

group and the Wyan formation, and certain 

beds in both, particularly the limestones, are 

also lithologically similar. These likenesses 

sometimes make difficult the distinction between the formations where the similar beds of 

each occur in proximity, and thus the unconformity between them, though in many places 

distinct, is locally hard to detect and probably 

does not represent any great stratigraphic 

interval.