REVISION OF THE BECKWITH AND BEAR RIVER FORMATIONS OF SOUTHEASTERN IDAHO.

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

INTRODUCTION AND SUMMARY. exposed in the region of their type localities. In the detailed geologic mapping of the Descriptions of the Beckwith formation in the Wayan and Montpelier quadrangles, in south­ areas where it has been studied show consider­ eastern Idaho and adjacent territory, it has able variety in lithologic character. The fossil been found necessary to apply new names to content is ·meager, and there is uncertainty strata hitherto referred to the Beckwith and about the upper limit of the formation. Bear River formations or to portions of the The Bear River. formation has long been Laramie as mapped by the Hayden Survey. known and has been studied by many geolo­ The two quadrangles are contiguous, and the gists. It has a distinctive fauna and nearly Montpelier quadrangle lies south of the Wayan. as distinctive a lithology. The lack of agree­ They occupy the corner of the State and include ment between the beds in the Wayan quad­ a very narrow strip in northeastern Utah and rangle heretofore called Bear River and the a somewhat broader strip in western Wyo­ typical Bear River is so marked as to raise the ming. They lie between parallels 42° and 43° question whether any of these beds can prop­ N. and meridians 111° and 111° 30' W. The erly be assigned to that formation. The beds Wayan 30-minute quadrangle, the topographic in the Wayan quadrangle resemble somewhat map of which has not yet been published, con­ the Kootenai of Montana and Canada and may sists of four 15-minute quadrangles, the Free­ in part represent that formation. They may dom, Lanes Creek, Crow Creek, and Slug Creek. furnish a connecting link between the Kootenai Topographic maps of these areas are now avail­ and the Bear River. able. The strata in this area that were formerly The formations to be discussed extend from called the Bear River are here assigned to the the northeastern part of the Montpelier quad­ Wayan formation, of Cretaceous, possibly rangle northward through the eastern part of Lower Cretaceous age, and the so-called Beck­ the Wayan quadrangle and thence northward with is divided into seven formations, of which an undetermined distance, possibly including the lower two are marine formations of Juras­ a considerable part of the Caribou Range. sic age, and the remaining five are nonmarine They include about 17,000 feet of strata, unless formations assigned to the Gannett group, of there are unrecognized repetitions by folding or Cretaceous (?) age. This paper gives a state­ faulting. ment of the stratigraphic problems involved Two large groups of beds are recognizable and a description of the formations. The in the field. At first, in accordance with earlier writers are indebted to Mr. T. W. Stanton for interpretations, these groups were assigned examination of the fossils and for helpful sug­ respectively to the Beckwith formation, of gestions. Cretaceous and Jurassic age, and the Bear GENERAL STRATIGRAPHY OF THE AREA. River formation, of Upper Cretaceous age. On the maps of the Hayden Survey both are The stratigraphic sequence in southeastern included in the Laramie. There is, however, Idaho is remarkably full, all the great Paleo­ considerable lack of ~greement both lithologic­ zoic and later systems being represented. The ally and faunally between these formations as Paleozoic formations are identical in name and exposed in the district under discussion and as number with the corresponding formations of 30830°-17---6 75 76 SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY, 1916. northern Utah described by Richardson,! those of the Utahsection. The subjoined table except that the Threeforks limestone has not shows the general character of the Mesozoic been recognized. The Idaho formations dif­ formations of the region and the relations of fer somewhat in thickness and character from the formations here discussed to the others. ·

Mesozoicjormations in southeastern Idaho.

Thickness System and series. Formation. Character. (feet).

Sandstones, shales, carbonaceous shales, Cretaceous (Lower Cretaceous?). Wayan formation. limestones, some conglomerate ______. 11,800 Unconformity ryg~e sandstone ...... 100 Draney limestone ..•.... _...... _ 200 Cretaceous (?). Gannett group. Bechler conglomerate ..... _~ . ___ 1, 775 Peterson limestone_ .... ___ ..... _ 205 Ephraim conglomerate_ ... ____ .. 1,025 --- 3,305 - Greenish-gray sandstone, with massive Stump sandstone. calcareous bed at base _. __ .... ______. 200-600

Jurassic. Preuss sandstone. Red sandstones and shales ..... _... __ . _. 1,300 Unconformity Twin Creek limestone. Whitish shaly limestone, some massive beds .. --·-·.·--- ...... ··--·--- 3,500±

Subdivided into four members: Red sandstone, with heavy grit at base, sue- Jurassic or Triassic. Nugget sandstone. ceeded by cherty limestone and red shale. Raymond Canyon section ....· . 1, 900

Variable, yellow sugary sandstone, thin to massive bedded, or red or chocolate- Ankareh formation. colored shale and sandstone, or mottled clays and shale with some sandstone and limestone. __ . _.... _.... _...... 750±

Triassic (Lower Triassic). Limestones, calcareous sandstones, and Thaynes limestone. shales .. _...... __ ...... _...... •... _.. 2,000±

Thin-bedded calcareous shales and lime- Woodside shale. stones ...... · .•...... 1,500

THE BECKWITH PROBLEM. is largely derived from the three principal The Beckwith formation has been identified published descriptions, which represent more at several localities in western Wyoming and or less separated districts and contain differ­ adjacent parts of Idaho by a number of geolo­ ences sufficient to warrant a brief discussion. gists, but present knowledge of the formation Their main features are set forth in the follow­ ing table, which includes also the correlations I Richardson, G. B., The Paleozoic section in northern Utah: Am. 1our. Sci., 4th ser., vol. 36, pp. 406-416, 1913. given in the present report: Tentative correlation of the Beckwith and Bear River formations in southeastern Idaho and southwestern Wyoming.

Idaho-Wyoming border (Breger, U. S. Lincoln County, Wyo. (Schultz, Age. Southwestern Wyoming (Veatch, U. S. Geol. Survey Southeastern Idaho (Mansfield and Roundy). Geol. Survey Bull. 430, pp. 562-563, Prof. Paper 56, pp. 57-61, 1907). U.S. Geol. Survey Bull. 543, 1910). pp. 30, 52-55, 1914).

Upper Cretaceous. Not recognized. Bear River. Bear River. t:i:i t:zj Unconformity----- 0 P:l Western area. Eastern area. ~ 1-1 1-3 Wayan formation: Feet. Ill Cretaceous (Lower Alternating sandstone and Cretaceous?). shales ...... 9, 000 Beckwith: Upper > and lower phases ~ Sandstones, shales, and Beckwith: UpJ?er mem­ t:1 limestones:...... 2, 800 Higher beds not recognized. ber time eqmvalent of merge. Predom­ inant r e d d ish t;d Unconformity---! I Lower Cretaceous and color but all light Not represented or in­ t;:l Dakota(?); consists of cluded with Bear River. > Gannett group: light-colored sand­ color; conglomer­ !;d ates in this sec­ t:d Tygee sandstone ...... 100+ stones and clays; 3,000 tion are white to Draney limestone ...... 200 feet. Cretaceous (?). yellow. Entire l'j< Bechler conglomerate .. . 1,775 Beckwith: Feet . t:d Peterson limestone ...... 205 Upper gray limestone .. 100 section a b o u t 4,000 feet. l'%j Ephraim conglomerate .. 1,025 Conglomerate ...... 850 0 ~ > Beckwith considered 1-3 1-1 equivalent of Veatch's 0 eastern section, but all ~ Beckwith: Lower red­ r/1 bed member c om­ Jurassic. Light-colored Stump sandstone...... 200-600 Lower gray band shale, sandstone, and 0 posed of sandy clays, Beckwith: Lower l'%j sandstone...... 250-600 sandstones, and con­ part of section. clay with associated Preuss sandstone...... 1, 300 Red sandstone. . . . 1, 200 beds of white to light­ r/1 Jurassic. glomerates; 2,500 feet; 0 Upper Jurassic. yellow and red con­ q glomerate and black 1-3 limestone; 900-2,400 P:: l'j feet. > Unconformity I 1------r/1 ~ Twin Creek limestone. Twin Creek. Twin Creek. Twin Creek. Twin Creek. t:d ~ 1-1 t:;:j > P:: 9

-::r -::r 78 SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY, 1916.

Veatch, 1 who defines and describes the forma­ shale, sandstone, and clay. The sandstone is usually tion, divides it into two unnamed members­ light yellow, pink, or white, and the clay varies from " a lower red-bed member composed of inter­ yellow or light pinkish red to dark purple. With the sandstone, shale, and clay are associated beds of white to bedded sandy clays, sandstones, and conglom­ light yellow and red conglomerate and black limestone. era.tes 2,500 feet thick, and an upper member In places * * * conglomerate beds constitute an composed of rather light-colored interbedded important part of the formation. sandstones and clays with a thickness of 3,000 Fossils are not numerous, but Schultz ob­ feet or more." In the eastern exposures tained collections from four localities. These within his district these two phases merge. were examined by Stanton, 'Yho referred three "Just west of Hilliard these beds, while having of the collections to the Jurassic and stated that a predominant reddish cast, are a~ light in the fourth was not sufficient for age determina­ color. The conglomerates, which near Beck­ tion but suggested Jurassic. According to with are deep red, are here white to yellow." Schultz two of the lots "come from the top of Veatch appears not to have found fossils in the the Beckwith and indicate. that it is Upper Beckwith, but he refers to this formation col­ Jurassic." The thickness of the formation in lections of marine Jurassic fossils previously the region ranges from 900 to 2,400 feet. made by Stanton at two localities, one of Lithologically the descriptions given by which was outside of the district described. Veatch and Schultz agree fairly well, except On the evidence of these fossils he refers the that in Schultz's area the red conglomeratic lower part of the Beckwith to the Jurassic; phase seems not to be well developed. In both the remainder, he thinks, "contains time equiv­ areas sandstones and clays predominate in the alents of the Lower Cretaceous and Dakota." formation. Conglomerates appear to be of Breger 2 gives the following account of the relatively minor Importance. Veatch makes Beckwith formation in the Crow Creek region, no mention of limestone, but Schultz refers to Idaho, which is included in the Montpelier and beds of black limestone. Breger, on the other Wayan quadrangles: hand, does not mention clays, but emphasizes This formation consists of red sandstone and conglom­ two gray bands, one of sandstone and the other erates with two conspicuous gray bands. The lower of limestone, with an intermediate . massive gray band is a dark greenish-gray calcareous sandstone conglomerate. He also notes the presence of 250 to 600 feet thick and occurs 1,200 feet above the base a thick band of red sandstones and shales below of the formation. The lower 1,200 feet consists of red the lower -gray band. Thus he divides the sandstones and shales, apparently without conglomerates. The conglomerates seem to be confined * * * to the formation into a series of bands which, he says, interval above the lower gray. band, constituting most of ·"maintain these characters throughout the the rocks for a thickness of 850 feet. They are succeeded area covered by the present reconnaissance, by the second or upper gray band, a massive limestone, * * * a distance of about 35 miles." The more or less marly and light blue-gray in color. This formation in the Wyoming region appears to rock attains a thickness of 100 feet in Stump Canyon and northward, where it forms a resistant ledge that may be more variable, and the subdivisions noted easily be traced by its light color. by Veatch and Schultz do not · appear to con-

tinue over considerable areas. r Breger makes no mention of fossils in the The study of the Wayan and · Montpelier formation. quadrangles has given the writers an oppor­ Schultz 3 describes the formation as it occurs tunity to review in some detail Breger's work in Lincoln County, Wyo., south of Snake River on the Beckwith and to cover a somewhat ·and east of the Salt River Range and the larger area than he examined. They have also Absaroka Ridge. There it represents the semi the Beckwith northeast and southeast of direct northward extension of the Beckwith formation of Evanston, Wyo., but have not been able to the eastern belt of Uinta County [Veatch'sarea], where the make extended observations there. In the conglomerate phase merges with the upper sandstone and Idaho region they recognized the four bands shale. * * * The beds are composed of light-colored described by Breger and found three additional 1 Veatch, A. C., Geography and geology of a portion of southwestern higher ones, but in the portions of the Wyoming Wyoming: U.S. Geol. Survey Prof. Paper 56, pp. 57-58, 1907. 2 Breger, C. L., The salt resources of the Idaho-Wyoming border, Beckwith seen they did not observe any similar with notes on the geology: U. S. Geol. Survey Bull. 430, pp. 562-563, 1910. arrangement. Perhaps the most striking dif­ ~ Schultz, A. R., Geology and geography of a portion of Lincoln County, Wyo.: U.s. Geol. Survey Bull. 543, pp. 30, 53, 54, 1914.· ferences noted in the two regions were the BECKWITH. AND BEAR RIVER. FORMATIONS OF SOUTHEASTERN IDAHO. · 79 greater abundance of conglomerates and lime­ in 1873, but its true stratigraphic position was stones and more intense red color in the Idaho not determined until nearly 20 years later by area contrasted with the predominance of sand­ Stanton.3 In 1895 White 4 gave a full de­ stones and clays of lighter colors in the Wyo­ scription of it, summarizing the information ming area. available at that date. Since then other Faunally there are several differences to be geologists have contributed additional details. noted. Veatch refers the lower part of the (See table on p. 80.) Beckwith to the Jurassic, but there is an Although the stratigraphic position of the element of doubt in this reference, because of Bear River has been determined, its relations to the possibility that the fossils collected earlier the underlying formations are not everywhere by Stanton n1ay have come from unrecognized clear. It is probable that in some of the earlier in-faulted Twin Creek beds, although Veatch accounts strata now assigned to the Beckwith does not regard this as probable. The upper have been included in the Bear River. The beds he considers Cretaceous. SchUltz found formation has not been recognized outside of Jurassic fossils in the top of the Beckwith in the region which extends from Old Bear River his area, and yet he regards the forn1ation City, about 9 miles southeast of Evanston, there as the direct northward continuation of Wyo., northward through the Wyoming and Veatch's combined section. In the Idaho area Salt River ranges into the northeastern part the writers found marine Jurassic fossils just of Idaho.5 at the base of Breger's lower gray band, but the In the Yellowstone Park and extending limestone beds higher in the section contain a northward into Canada there is a thick and fresh-water fauna that is thought by Stanton extensive non1narine formation, the Koote­ to be later that Jurassic, having affinities with nai, of Lower Cretaceous age, between which those of the Kootenai and Bear River forma­ and the Bear River there are certain affinities, tions. Nothing comparable to this fresh-water but the relations of the two formations to fauna has yet been reported from the other each other are not known. In Idaho and Beckwith areas. Wyoming there are great thicknesses of strata Schultz/ from work in Wyoming and Utah, which have been assigned to the Bear River the results of which have not yet been pub­ but in which none of the characteristic lished, has come to look upon the Beckwith as a Bear River fossils have been found. Stan­ group rather than a single formation. It is ton 6 comments as follows on a collection thus seen that the term Beckwith as now used made by Schultz on the west flank of the has no very definite meaning, that it is applied Caribou Range about 2 miles east of Hernian. to widely varying beds, some of which may not Idaho: be closely related, and that it probably covers In my opinion this fauna is Cretaceous, but on account beds belonging to two great systems. of the absence of definitely characteristic forms I am The writers have found it practicable to sub­ unable to determine whether it belongs to the Bear River divide the beds hitherto called Beckwith in formation. Similar imperfect fossils have been collected the Wayan and Montpelier quadrangles into in Montana in rocks that are provisionally referred to the Kootenai formation. seven formations, two Jurassic and five Cr~­ taceous ( n. In view of the above discussion The assignment of these and other doubtful it seems unwise to .retain the name Beckwith beds to the Bear River seems to have been for any of these formations and new names based partly on lithologic resemblances and are therefore assigned. Detailed descriptions partly on the actual occurrence in higher beds of the formations are given on pages 82-83. of characteristic Bear River fossils, as in parts of Lincoln County, Wyo./ and of Bonneville THE BEAR RIVER PROBLEM. a Stanton, T. W., The stratigraphic position of the Bear River forma· The Bear River formation early attracted tion: Am. Jour. Sci., 3d ser., vol. 43, pp. 98-115, 1892. attention because of its numerous and well­ 4 White, C. A., The Bear River formation and its characteristic fauna: U. S. Geol. Survey Bull. 128, 1895. 2 preserved fossils. It was named by Hayden 5 Veatch, A. C., op. cit., p. 60 . 6 Schultz, A. R., and Richards, R. W., A geologic reconnaissance 1 Personal communication. in southeastern Idaho: U. S. Geol.'Survey Bull. 530, p. 275, 1913. 2 Hayden, F. V., U.S. Geol. Survey Terr. Second Ann. Rept., pp. 7 Schultz, A. R ., Geology and geography of a portion of Lincoln 91-92, 1873. 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 are possibly workable.3 In the Philipsburg northeast of the Wayan quadrangle.1 qua.drangle, Mont./ the Kootenai formation in­ The rocks in typical exposures of the Bear cludes 1,500 feet of variegated beds, chiefly River formation may be described as dark sandstones and shales with some limestones and shales with calcareous bands and some soft gray conglomerates. The "gastropod limestone " 5 sandstones, which are abundantly fossiliferous. in that quadrangle is physically much like the A single section which may be regarded as rep­ limestones of the supposed Bear River in the resentative may be quoted from Stanton's Wayan quadrangle. It is described as a pure section on Stowe Creek/ near the type locality. gray limestone rich in fossils, chiefly fresh­ water snails. The limestones form distinct Part of Stanton's section on Stowe Creek, Wyo. . beds which are separated by shales and crop 5. Bear River formation: Feet. out as reefs. On . fresh fracture the rock is Brown sandstone; dip 75° E...... 20 dark gray; on the weathered surface, pale blu­ Soft gray shale...... 25 Gray sandstone...... 10 ish gray. The texture is coarse and less com­ Dark shale...... 60 pact than that of the lower limestone. The Brown sandstone ...... 10 rock is crowded with spiral shells which are con­ Dark shale with calcareous bands containing spicuous on weathered surfaces. The calcare­ numerous fossils: Pyrgulijera humerosa, Cor- ous shale interbedded with and overlying the bula pyriformis, Unio belliplicatus ...... 250 Sandstone...... 10 gastropod limestone is partly of an olive-green, Dark shales with thin bands of limestone and ocherous-weathering type. It grades into sandstone and occasional carbonaceous sandstones. The uppermo'st beds consist of seams; many Bear River fossils ...... 400 more or less calcareous shale, gray to nearly Gray sandstone; dip 75° E...... 10 black on fresh fracture but weathering to blue­ Soft shales...... 25 Gray sandstone; dip 75° E ...... 20 gray or brown; these beds virtually grade into limestone. The limestones of the supposed 840 Bear River in the Wayan quadrangle occur in In some places the shales are sufficiently car­ the same manner as in the Kootenai of the Phil­ bonaceous to carry thin seams of coal, but the ipsburg quadrangle, but they are not so fossil­ coal is generally too poor to be of economic iferous nor so coarse-textured, and the inter­ importance. bedded shales are usually dark gray to blackish, At a few localities in the Wayan quadrangle although the olive-green color and gradation to there are dark shales with calcareous bands in sandstone have been noted. supposed Bear River strata, but these are not Other lithologic similarities exist between very fossiliferous, and such fossils as occur are the so-called Bear River of the Wayan quad­ not typical of the Bear River. · The strata in­ rangle and the Kootenai of the Philipsburg. clude two rather prominent sets of limestone quadrangle and other parts of Montana . . There beds, with which more or less dark shale is in­ are also many differences, among them being terbedded, and great thicknesses of sandstones the absence of workable coal in the Wayan and shales, some of which are of an intense red quadrangle. However, the shales are in some color. Lithologically there is no very close places carbonaceous, and near Auburn, Wyo., agreement between the rocks of the Wayan a tunnel some 40 feet long has been driven at quadrangle and the typical Bear River, and a coal prospect from which a few lumps of faunally the relationship is uncertain. usable coal have been taken. The Kootenai/of Canada and Montana con­ No recognizable flora has been found in the tains some coal beds of economic importance. Wayan "Bear River," but undeterminable In the Cascade coal basin of Alberta the forma­ stern fragments have been taken from some of tion includes some 2,800 feet of sandstones and the olive-yellow sandstones above the band of shales with many valuable coal seams, there a Dowling, D. B., Report on the Cascade coal basin, Alberta, p. 8, being in one locality as many as 14 beds that Canada Geol. Survey, 1907. 4 Calkins, F. C., and Emmons, W. H., Geology and ore deposits of I Unpublished data collected by E. G. Woodruff and A. R. Schultz. the Philipsburg quadrangle, Mont.: U.S. Geol. Survey Prof. Paper 78, 2 Stanton, T. W., The stratigraphic position of the Bear River forma­ p. 77, 1913. tion: Am. Jour. Sci., 3d ser., vol. 43, p. 106, 1892. 5 Idem, pp. 77-79. BECKWITH AND BEAR RIVER FORMATIONS OF SOUTHEASTERN IDAHO. 81 dark shale in the lower part of the formation, reddish gray to deep dull red. The sandstone and some pieces of dark silicified wood have is usually calcareous and more or less argilla­ been found in dark-gray sandstone beds close ceous, becoming very shaly in some places. to the top of the section studied. The beds are generally less than 6 inches thick, From the above descriptions it is clear that weather to a dull-red soil, and make the slopes the differences between the Wayan ''Bear of subordinate ridges. A graphic measurement River" and the typical Bear River are so great at the head of Thomas Fork valley gives a as to make the correlation of the two forma­ thickness of 1,300 feet. tions questionable. On the other hand, the A minor unconformity separates the Preuss agreement between the beds of the Wayan area sandstone from the underlying Twin Creek and the Kootenai is perhaps not sufficiently limestone. close to warrant correlation with that forma­ STUMP SANDSTONE. tion until such a correlation is supported by further and more detailed studies. It seems The Stump sandstone is named from Stump likely that when the detailed stratigraphy of Peak, at the head of the north fork of Stump the region north of the Wayan quadrangle, Creek, about the center of T. 6 S., R. 45 E., beyond Snake River, is · better known the for­ Boise meridian (unsurveyed). It consists mation will be found to grade upward into the mainly of thin-bedded gray to greenish-gray typical Bear River. If the interesting sugges­ fine-grained sandstones which weather into tion that the formation should be correlated platy fragments about an inch thick . . Near with the Kootenai of Montana should be sub­ the base are some beds of compact calcareous stantiated, it might then be possible to deter­ sandstone, locally as thick as 6 feet. The mine the stratigraphic relations of the Kootenai grains are very fine and chiefly of colorless and the Bear River. quartz. The rock tends to break with a con­ In the mean time it seems undesirable to choidal fracture and to ring under the hammer. apply either term to the formation now called Fresh surfaces have a steel-gray color, but Bear River in the Wayan quadrangle. To weathered surfaces appear velvety brown. In­ avoid ainbiguity these beds are named the stead of ledges these beds commonly form lines Wayan formation. The great thickness of the of irregularly weathered blocks that at first formation, more than 11,800 feet, neither top glance resemble trap rock. At the base is a nor bottom being exposed, and the arrangement bed of grit, or coarse-grained sandstone, which of the strata suggest that it may be subdivided contains marine fossils of Jurassic age. The later, but this seems inadvisable until detailed component grains are colorless quartz, with studies have been carried farther north. A some greenish chloritic material, and the more detailed description of the formation 1s cement is calcareous and grayish. The fresh given on pages 83-84. rock has a slight pinkish cast, and weathered surfaces are decidedly pinkish. This is prac­ THE FORMATIONS. tically the only bed in the entire formation PREUSS SANDSTONE. from which fossils were collected, and the col- The 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 as­ the 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 sand­ grained sandstones ranging in color from pale stones. 82 SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY, 1916.

The Stump sandstone is usually resistant to coming in some regions practically all conglom­ weathering and forms con-spicuous ridges, but erate with pebbles, some of which are nearly a south of the Halfway House, on the southern foot in diameter. The pebbles represent a wide edge of the Wayan quadrangle, ·it forms a val­ variety of materials, but perhaps 100 feet above ley. The rock there has probably been weak­ the base there is an olive-yellow band, 25 feet ened by fracturing or. other structural dis­ or more thick, in which the pebbles are almost turbance. exclusively of dark chert, rounded or subangu­ The essential features of this formation are lar, and generally an inch or less in diameter. present throughout the region studied, but the The Ephraim conglomerate forms most of the thickness varies from 200 to 600 feet. Plate mass known as Red Mountain, in the north­ XIII, A, shows a typical exposure of the Stump eastern part of the Montpelier quadrangle, sandstone. where it is well exposed. (See Pl. XIII, B.) GANNETT GROUP. PETERSON LtMESTONE. NAME AND GENERAL FEATURES. The Peterson limestone is named from Peter­ The Gannett group is named from the Gan­ son's ranch, along Tygee Creek, in sec. 34, T. nett Hills, which lie in Bannock County, Idaho, 7 S., R. 46 E., Boise meridian, east of which and Lincoln County, Wyo., in the eastern part the formation is well exposed. It is about 200 of the Wayan quadrangle, where all the forma­ feet thick, massively bedded near the top, and tions of the group are well exposed. The very persistent throughout the region studied, Gannett Hills have been named in honor of the forming prominent ridges that can be followed late Henry Gannett, topographer of the Green by the eye for miles from some of the higher River division of the Hayden Survey and sub­ summits. (See Pl. XIV, A.) The following sequently an eminent geographer, who did the fossils from this limestone have been identified first topographic work in this region. by T. W. Stanton: Unio sp., Planorbis (Gy­ The group includes five distinct subdivisions raulus) sp. related to P. prrecursoris White, and has a maximum thickness of over 3,300 Viviparus sp., Goniobasis? sp., and two dis­ feet. It rests, with apparent conformity, upon tinct species of Physa. Fossils of similar types the Stump sandstone. At the top is the Tygee occur in the Kootenai, Bear River, and later sandstone, gray and even grained, .followed by formations. The fresh-water gastropods are the Draney limestone, gray and compact. not distinctive and similar forms of Planorbis Below are the Bechler and Ephraim conglom­ are found in both the Morrison and Bear River, erates, separated by the Peterson limestone, but no species of Physa have been reported which is much like the Draney. S.hale appears from beds older than the Bear River. to be nearly absent from the group. The fossils thus far collected from the Gan­ BECHLER CONGLOMERATE. nett group are not distinctive, but they are The Bechler conglomerate is named from apparently later than Jurassic, so that the age Bechler Creek, which enters Stump Creek from of the group is probably Cretaceous. the north about a quarter of a mile north of The group occurs in much the same areas as the mouth of Boulder Creek, in T. 6 S., R. 45 the Preuss sandstone, but is confined more to E., Boise meridian (unsurveyed), in Bannock the central portion of the synclinorium. County. Bechler Creek is named in honor of G .. R. Bechler~ topographer of the Teton divi­ EPHRAIM CONGLOMERATE. sion of the Hayden Survey, who did the first The Ephraim conglomerate, at the base of topographic work in the region adjoining the the group, is named from Ephraim VaHey, in Wayan quadrangle on the north. sec. 36, T. 10 S., R. 45 E., Boise meridian, which The formation is composed of about 1,700 lies in the formation. The rock is a red con­ feet of gray, reddish, and "salt and pepper" glomerate with minor amounts of sandstone and sandstones with interbedded conglomerates. some thin bands of gray to purplish limestone. The "salt and pepper" color predominates, It is about 1,000 feet thick at the type locality, and there is probably over twice as much con­ but varies much in thickness and character, be- glomerate 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 X IV

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 composed chiefly of alternating sandstones and Ephraim conglomerate. The pebbles in the shales with some conglomeratic beds, but with­ conglomerate are small, few having a diameter out significant li1nestones, and the lower com­ of more than 1 inch. pnsmg some eight subdivisions, including several thick beds of limestone. DRANEY LIMESTONE. The lower unit in the section exposed in Tin­ The Draney limestone is named from the cup Canyon includes four sets of red beds, three Draney ranch, on Tygee Creek, in sec. 10, T. of lin1estone and shale, and one of yellow sand­ 8 S., R. 46 E., Boise meridian. The lin1estone stone. These beds in ascending order may be occurs on the top of the ridge about a mile and briefly described as follows: a quarter east of the ranch. The form:1tion is 1. Beneath the limestone of the dome that forms a fine about 200 feet thick and is fairly massive, the arch about a mile west of the mouth of the South Fork of individual beds reaching a maximum thick­ Tincup Creek there is a suggestion of reddish soil that may ness of 1! feet. The rock is much like that of represent red beds not otherwise exposed. 2. Gray limestones, weathering whitish, with dark­ the Peterson limestone, but is not so massively colored shales. The top 20 feet is rather massively bedded bedded near the top. It is compact and gray, limestone; shale and limestone are interbedded below, the but weathers to a dirty-white color. The fol­ proportion of shale gradually increasing toward the base. lowing fossils from this limestone have been 3. Red beds consisting largely of red-weathering soft identified by T. W. Stanton: Unio sp. related gray sandstone but including also some gray and red shaly beds and some calcareous beds. These rocks generally to U. vet1tstus Meek, Viviparus ~ sp., and form slopes and soil of a light-red color, a brighter color Goniobasis ~ sp., a simple smooth form resem­ than that of No. 5. bling G:? increbescens Stanton or Arnnicola? 4. Bands of gray limestone in dark shales. Some of the cretacea Stanton. limestone beds are relatively massive, 1! feet or more thick, and project from the weaker shales. TYGEE SANDSTONE. 5. Red beds with purplish to reddish-gray sandstone, massive near the top but in thinner beds and associated The Tygee sandstone is named from. Tygee with shale below, the whole weathering to a red. soil and Creek, east of which, in T. 8 S., R. 46 E., the forming fairly smooth slopes. formation is well exposed in association with 6. Dark gray to black shale with massive buff limestone the Draney limestone on the top of the ridge near the top and thinner beds of limestone below. (See Pl. XIV, B.) along the Idaho-Wyoming boundary. The rock 7. Greenish-gray sandstones and grit, weathering, yel­ is gray to buff, even grained, and without the low and reddish, usually forming marked ridges and greenish or reddish tinges of some of the higher rough talus slopes of large blocks. The sandstone becomes sandstones. The top is not exposed, and in conglomeratic in places. much of the region this sandstone with part or 8. Red to purplish sandstone with some shaly and some calcareous beds. all of the limestone below it has been eroded before the deposition of the Wayan formation. Some of these subdivisions may be recog­ At the type locality about 100 feet of this sand­ nized north and south of Tincup Canyon, but stone is exposed. their structure is complex, they appear to vary in lithology and thickness, and they are in WAYAN FORMATION. places not well expressed topographically. For Resting unconformably upon the Gannett these reasons it is not yet practicable to map group is a group of beds con1posed of sand­ them separately. Their combined thickness is stones, shales, limestones, and some conglom­ estimated at about 2,800 feet. erates. Neither the top nor the botton1 is The upper unit of the formation, if there is no known, but apparently about 11,800 feet of reduplication by folding and faulting, com­ beds are exposed. These rocks are confined to prises some 9,000 feet of westward-dipping the northeastern part of the Wayan quadrangle strata that lie along the upper course of Tincup and the region to the north. The formation is Creek above the canyon. These beds are named from the settlement of Wayan, in Ban­ chiefly red and gray sandstones, with interven­ nock County, in the northwestern part of the ing shales and some calcareous beds. The Wayan quadrangle. It occupies the hills im­ sandstones form a series of low ridges and mediately east of Wayan and appears to be points, but the shales are mainly weathered broadly divisible into two units, the upper into soil-covered areas. Toward the top yel- 84 SHORTER CONTRIBU'riONS TO GENERAL GEOLOGY, 1916. lowish and brownish sandstones appear, and The collections from the Wayan quadrangle fail to the uppermost strata recognized are shown only show any characteristic species of the Bear River forma­ by fragments of dark-gray siliceous sandstone tion, and if the Bear River is recognized there it must be on some other basis than naleontologic correlation. This and pieces of dark-brown or black silicified is also true of the Beckwith formation, for the reason that wood weathered white. in its type area the Beckwith has yielded so few fossils The upper unit apparently represents the that it can not be said to have a characteristic fauna. east limb of a broad syncline, the axial region . The few fossils found in both the Wayan of which is occupied by the layer containing formation and the Gannett group are poorly silicified wood. The syncline is broken on the preserved fresh-water forms belonging to Unio west by a fault. The northward continuation and to small, uncharacteristic gastropods re­ of. the strata and the structural relations sug­ ferred to several genera. There are, therefore, gest that higher beds may appear in that marked faunal similarities between the Gannett direction. group and the Wyan formation, and certain The fossils collected from the Wayan forma­ beds in both, particularly the limestones, are tion have come 'almost entirely from the lime­ also lithologically similar. These likenesses stone bands. The following forms have been sometimes make difficult the distinction be­ identified by T. W. Stanton: Unio ~ sp., tween the formations where the similar beds of Rhytophorus ~ sp., Viviparus ~ sp., Limnooa ~' each occur in proximity, and thus the uncon­ opercula of gastropods, and fragments of formity between them, though in many places fresh-water shells. An unidentifiable frag­ distinct, is locally hard to detect and probably ment of bone has also been found. In his re­ does not represent any great stratigraphic port on the collections Mr. Stanton remarks: interval.