DEPARTMENT OF THE INTERIOR 

FRANKLIN K. LANE, Secretary 

UNITED STATES GEOLOGICAL SURVEY 

GEORGE OTIS SMITH, Director 

Professional Paper 108-D 

WASATCH FOSSILS IN SO-CALLED FORT UNION BEDS 

OF THE POWDER RIVER BASIN, WYOMING 

AND THEIR BEARING ON THE STRATIGRAPHY OF THE REGION 

BY 

CARROLL H. WEGEMANN 

Published May 29,1917 · 

Shorter contributions to general geology, 1917 

(Pages 57-60) 

WASHINGTON 

GOVERNMENT PRINTING OFFICE 

1917 
ILLUSTRATIONS. 

PLATE XXII. A, Sandstone bed in Lance formation showing large "concretions"; B, Great Pine Ridge, Wyo., 

formed by outcrop of Fort Union formation ......................................... : .... . 

XXIII. A, Badlands in Wasatch formation at fossil locality near the Davis ranch, Sussex, Wyo.; B, 

Kingsbury conglomerate on Kingsbury Ridge, 8 miles southwest of Buffalo, Wyo ........... . 

FIGURE 16. Map of northeastern Wyoming ..•.................••..•.............•.....•....•..•.••........ 

II 

Page, 

58 

59 

57 
W~SATCH FOSSILS IN SO-CALLED FORT UNION BEDS OF THE POWDER 

RIVER BASIN, WYOMING, AND THEIR BEARING ON THE STRATIG-

. RAPHY OF THE REGION. 

By CARROLL H. WEGEMANN. 

Northeastern Wyomipg is occupied by a 

broad structural basin opening to the north 

and bounded on the ea~t, south, and west by 

three mountain upliftsTthe Black Hills, the 

Laramie Mountains, and the 

Big Horn Mountains. (See 

fig. 16.) Throughout much 

of this basin the suriface 

rocks are of Tertiary! age. 

They contain the pr~cipal 

coal beds of the region and 

have been classified in all the 

more recent Survey reports as 

Fort Union. The true age of 

these rocks and the general 

stratigraphyofthefresh-water 

beds that underlie them are 

the theme of this paper. 

tion, the transition being marked by thin beds 

of coal and carbonaceous shale. Neither at 

the base nor at the top has evidence of unconformity been observed in this region. 

104 

The rocks above the Fox 

Hills sandstone on the southwest side of the basin may 

be separated, on lithologic 

grounds, into three divisions. 

TheLanoofurmation, about ~~~~~~~~~~~~~~~~~~~~~~~~~· 

3,200 feet thick, consisting of 

gray shale and buff finegrained slabby or concretionary sandstone, is at the base. 

It conta-ins a few thin coal 

beds at various horizons in 

the formation, particularly 

near the base and top, but 

they are so thin and the coal 

is so poor as to be· of no commercial value. 

One of the most characteristic features of the 

Lance consists of large round concretionary 

masses that weather from the sandstone beds. 

(See Pl. XXII, A.) These masses resemble 

great boulders, and some of them are as much 

as 10 or 15 feet in diameter. 

At its top the Lance grades almost imperceptibly into the beds of the overlying forma77482°-17 

10 20 30 40 50 60 Mll.ES 

FIGURE 16.-Map of northeastern Wyoming. 

The Lance formation, as a whole, is a unit 

that is not susceptible of division on lithologic 

grounds. The vertebrate remains, however 

(for the most part Triceratops and Trachodon), 

are not distributed through the w:hole formation, but are found only in the lower 2,000 feet. 

The upper 1,200 feet of beds, although identical in appearance with those below, are apparently barren of vertebrate fossils. 

57 
58 SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY, 1917. 

Above the Lance formation is about 2,000 

feet of very fine grained bluish-white sandstone interbedded with gray shale and with a 

few beds of coarser sandstone, containing 

grains one-eighth of an inch in diameter. 

This formation is distinguished from the underlying Lance by its bluish-white color, the absence of large round concretionary masses, 

and the presence of beds of highly ferruginous 

sandstone only a few inches thick. The iron 

in many of these ferruginous beds appears to 

be of secondary origin, having probably been 

deposited from ground water. Some . of it 

may represent swamp deposits, although this 

is difficult to demonstrate. · 

The formation as a whole is more resistant 

to erosion than the formations above and below it, so that its outcrop around the margin 

of the great basin already described forms a 

prominent escarpment, which is generally timber covered, and to which the writer has referred in several reports as the ''Great Pine 

Ridge." (See Pl. XXII, B.) Fossil leaves, 

that are found in abundance in some of the 

ferruginous beds, have been determined by 

F. H. Knowlton as of Fort Union age, but 

the strata have heretofore been considered as 

comprising only the basal mmnber of that 

formation. 

The bluish-white shale and sandstone of the 

Great Pine Ridge are overlain by about 2,500 

feet of beds that are the principal coal-bearing 

rocks of the upper Powder River valley and 

that have in the past been considered by most 

workers in the region, the writer included, as 

of Fort Union age, constituting the upper division of that formation. (See Pl. XXIII, A.) 

These beds consist mainly of gray shale and. 

fine-grained dirty-white sandstone. They include some beds of coarser sandstone, especially 

in the upper part of the formation, and at the 

bases of these are found in many places thin 

layers of conglomerate. At certain horizons 

there are layers of pink shale and pink sandstone whose color-in the sandstone at leastis variable from place to place. Ferruginous 

layers, so abundant in the underlying formation, are here absent. Distributed through the 

formation at various horizons are beds of sub bituminous coal, which range in thickness from 

a few inches to 50 feet. Some of the beds are 

apparently very lenticular and can be traced for 

only a few miles along their outcrop. Others 

are very persistent and underlie hundreds of 

square miles of territory. 

During the season of 1915 R. W. Howell and 

the writer examined an area of about 2,000 

square miles, extending from northwest Converse County northward ~ong the divide on 

which are situated the Pumpkin Buttes to the 

Powder River valley. In the Pumpkin Buttes 

are exposed the highest beds that are present 

in this general region. About 12 miles west of 

the buttes lies the Great Pine Ridge, and between this ridge and the buttes is the most advantageous locality at which to measure the 

thickness and study the characteristics of the 

overlying formation, the so-called upper division of the Fort Union. To Mr. Howell belongs 

the credit of finding the first tooth of Ooryphodon discovered by the party. The specimen was 

found between the Middle and North buttes 

at about 950 feet below the top of the formation as there exposed. Mr. Howell and the 

writer afterward returned to the place and obtained several other teeth. All came from a 

blue shale underlying a thick sandstone bed; at 

the base of which is one of the small local unconformities characteristic of the formation. 

Later in the season we obtained from Mr. William Black, a rancher, other specimens of Coryphodon teeth, which ~e described as having 

been found at the top of Dome Butte, an outlier 

of North Pumpkin Butte. The sandstone that 

caps this butte is the same as the basal part of 

the thick sandstone bed that caps all the Pumpkin Buttes. Mr. Black gave the locality accurately, and Mr. Howell afterward visited it. 

He did not discover any more teeth but did 

find fragments of bone embedded in sandstone, 

that correspond in texture to that ·in which 

the specimens which we had received were embedded. J. W. Gidley states, with regard to · 

this as well as the former collection, that . the 

teeth belong to Goryphodon molest us, a genus 

knownonlyfrom the Wasatch. Itw<;mldseem, 

therefore, that. these remains afford definite 

evidence for correlating the rocks that form 

the Pumpkin Buttes, or the upper 1,000 feet of 

the formation heretofore called Fort Union, 

with theW asatch. The 1,400 feet of beds from 

the base of the Pumpkin Buttes down to the top 

of the Great Pine Ridge are lithologically similar to the rocks of the buttes themselves, and 

there is every reason, on lithologic grounds, to 

suppose that they belong to the same formation 
U. S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 108 PLATE XXII 

A . SANDSTONE BED IN LANCE FORMATION, SHOWING LARGE "CONCRETIONS." 

B. GREAT PINE RIDGE, WYO., FORMED BY OUTCROP OF FORT UNION FORMATION. 
U. S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 108 PLATE XXIII 

A. BADLANDS IN WASATCH FORMATION AT FOSSI.L LOCALITY NEAR THE DAVIS RANCH, 

SUSSEX, ·WYO. 

Photograph byT. W. Stanton. 

B. KINGSBURY CONGLOMERATE ON KINGSBURY RIDGE, 8 MILES SOUTHWEST OF 

BUFFALO, WYO. 
WASATCH FOSSILS OF THE POWDER RIVER BASIN, WYO. 59 

as the rocks from which Ooryphodon has been 

obtained. 

In 1910 T. W. Stanton, A. R. Schultz, and 

the writer made a collection of small mammal 

"teeth from a horizon about 700 feet above the 

top of the beds forming the Great Pine Ridge, 

at a place 20 miles west of Pumpkin Buttes. 

(See Pl. XXIII, A.) · Some shale beds in the 

vicinity are pink or red and resemble the Wasatch beds of southwestern Wyoming. The 

writer was directed to this loc!;tlity by Mr. H. W. 

Davis, an old-time rancher of the region, who 

stated that some years before students from 

Amherst, Mass., had made a collection from 

the locality and found the jaw of a fossil horse. 

Concerning this statement Prof. F. B. Loomis, 

of Amherst, has informed the writer that a 

party under his direction made a collection 

near the Davis ranch in 1904 which included 

teeth regarded by him as belonging to Eohippus 

and Ooryphodon. With regard to the 1910 

collection near the Davis ranch, Mr. Gidley has 

very kindly prepared the following statement: 

On a former preliminary examination of the material 

from the vicinity of the Davis ranch, Sussex, Wyo., I was 

led to believe that it indicated Fort Union deposits at that 

locality. My · conclusion was based principally on the 

presence in the collection of a little insectivorous mammal 

represented by a portion of a lower jaw containing two 

teeth. This or a closely related species occurs also in 

the Fort Union beds of Sweet Grass County, Mont., and 

so far as I know has never been found elsewhere. Its 

presence, however, is by no means conclusive-evidence of 

the Fort Union age of these b~ds. For, while this particular animal has not yet been found in other formations, 

there are several forms commonly found in the Fort Union 

(or the Torrejon) which are known to extend beyond the 

limits of this formation and occur in beds recognized as 

lower Wasatch. 

Of the three mammal molars also included in the collection from the Davis ranch, I stated five years ago that 

they represented undescribed species but seemed to be 

generically identical with certain forms of the Torrejon. 

To this I can now add that one of these (catalogue No. 

6734) is very close to if not identical with Polycodus ralstoni, recently described by Matthew 1 from beds in the 

Clark Fork basin, Wyo., designated by Granger 2 the 

Sand Coulee beds and regarded as transitional in age between the Fort Union (represented in northwestern New 

Mexico by the Puerco and Torrejon) and the Wasatch. 

This suggests that the other specimens may also prove to 

belong to this horizon, especially as it now seems very 

evident that many of the Fort Union forms have passed 

without much change into the basal Wasatch. 

I Matthew, W. D., The Cretaceous-Tertiary problem: Geol. Soc. 

America Bull., vol. 25, pp. 387-402, 1914. 2 Granger, Walter, On the names of lower Eocene faunal horizons of 

Wyoming and New Mexico: Am. Mus. Nat. Hist. Bull., vol. 33, pp. 

204-205, 1914. 

As the Clark Fork beds and Sand Coulee beds of Granger, 

which contain both Fort Union and Wasatch forms are 

regarded as a transitional phase, there appears to have 

been no great time break between the Fort Union and 

Wasatch formations. A series of beds near Ignacio, Colo;, 

mapped by Gardner 3 as Wasatch, also appears to contain 

a fauna intermediate between Fort Union and Wasatch. 

The fossils from this locality are not numerous, but they 

show the presence of Coryphodon (species not determinable) in the upper levels. The lower levels contain a 

phenacodont, intermediate between Phenacodus of the 

Wasatch and Euprotogonia of the Torrejon; He:miacodon 

(probably a new species); a Bridger genus; and Nothodectes sp., a genus from Granger's Clark Fork beds 2 (species 

may also be identical). A few other teeth in the collection appear to be species belonging to the Clark Fork beds. 

Coryphodon and Eohippus are not known to occur lower . 

than the beds designated by Granger Sand Coulee beds. 

Therefore, as Coryphodon has been found in the Pumpkin 

Buttes locality and as Loomis has reported Coryphodon 

and Eohippus from the Davis ranch locality it seems 

reasonable that these beds should be classed with the 

Wasatch formation and that those at the Davis ranch 

should be regarded as probably equivalent to one of the 

lower ·members of this group, either the Sand Coulee or 

the Clark Fork of Granger. 

It is evident, then, that the fresh-water beds 

above the Fox Hills sandstone in this part of 

Wyoming comprise at the base a formation 

3,200 feet in thickness which bears Triceratops 

in its lower 2,000 feet and which is unquestionably Lance, at the top a formation 2,400 feet 

in thickness which ·bears Coryphodon and is 

therefore Wasatch, and intermediate between 

these two a formation 2,000 feet in thickness 

which bears Fort Union leaves in abundance 

and which probably represents that formation. We may therefore refer to the rocks of 

the Great Pine Ridge as the Fort Union of 

this region, and to the formation overlying it 

as Wasatch. 

That theW asatch rests unconformably upon 

the Fort Union would seem to be indicated by 

the following observations: At Kmgsbury 

Ridge, 8 miles ·southwest of Buffalo and about 

50 miles northwest of the Pumpkin Buttes, is a 

thick conglomerate named by Darton 4 the 

Kingsbury, which appears to represent a great 

alluvial fan, its outcrop being some 40 miles in 

length from north to south and 2 to 5 miles in 

width from east to west. (See PL XXIII, B.) 

It was apparently deposited by streams which 

flowed from the highest part of the Big Horn 

Mountains and which had, pnor. to the deposia Unpublished material. 

• Darton, N. H., Geology of the Bighorn Mountains: U.S. Geol. 

Survey Prof. Paper 51, p. 61, 1906. 
60 SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY, 1917. 

tion of the conglomerate, cut deep valleys in the 

underlying beds. The conglomerate thus rests 

unconformably on the rocks below it, transgressing at Kingsbury Ridge strata ranging in 

age from Tertiary to Carboniferous. Its greatest thickness is estimated by Darton 1 as 2,500 

feet. In recent Survey reports it has been 

treated as a member of the Fort Union formation. It is certainly younger than the Fort 

Union beds on which it rests toward the south, 

and in that direction also the conglomerate as a 

member thins out within a few miles, although 

layers a few inches to several feet in thickness 

can be found at or near its horizon as far south 

as Powder River. To the east the Kingsbury 

conglomerate appears to become finer grained 

and to :finger out into the shale and sandstone 

of the coal-bearing beds that are now believed 

to be of Wasatch age. In other words, it is the 

writer's opinion that the Kingsbury conglomerate is equivalent to part of the Wasatch, and 

that the unconformity at its base separates that 

formation, in the Kingsbury region at least, 

from all older rocks. 

Along the Dry Fork of Cheyenne River 35 

miles south of Pumpkin Buttes and 90 miles 

southeast of Kingsbury Ridge there is some 

evidence of an unconformity between the 

Wasatch and underlying Fort Union beds. The 

Dry Fork of the Cheyenne heads in the Great 

Pine Ridge, and along its valley there are exposed two beds of coal stratigraphically about 

160 feet apart. The lower coal bed is only a few 

feet above the top of the Fort Union as exposed 

in the Great Pine Ridge. The upper coal bed 

may be traced eastward along the Cheyenne 

I Darton, N.H., Geology of the Bighorn Mountains: U.S. Geol. Survey 

Prof. Paper 51, p. 61, 1906. 

Valley for about 10 miles from the ridge to a 

point where both the lower and upper beds are 

exposed, together with about 50 feet of strata 

underlying the lower bed. There is no indication at this locality of the highly ferruginous 

layers characteristic of the Fort Union. Still 

farther east along the Cheyenne lower rocks are 

exposed, including a third coal bed that lies 

about 220 feet below the lower coal bed above 

described. The rocks associated with this 

third bed are in appearance Wasatch rather 

than Fort Union. A coal bed, therefore, which 

at the head of the Dry Fork of the Cheyenne 

rests almo_st directly on the Fort Union beds 

has below it in an area 15 miles farther east at 

least 27 5 feet of strata that appear to be W asatch, and it seems probable that an unconformity is here present between the two formations. Inasmuch, however, as the coal beds in 

the lower part of theW asatch do not extend for 

any great distance north and south in the region 

of the Fort Union outcrop, and as there are, besides the coal beds, no· other key rocks that are 

easily recognizable in the lower part of the W asatch, it is impossible to prove conclusively the 

amount of the unconformity. 

In summary, we :find in the region southeast 

of the Big Horn Mountains three fresh-water 

formations above the marine sandstone of the 

Fox Hills; the lowest of these is Lance, the highest Wasatch, and the intermediate formation 

may reasonably be considered to be Fort Union. 

A local unconformity is known to exist in the 

vicinity of Buffalo between the Wasatch and 

Fort Union, and there is evidence to indicate 

that this u,nconformity is present, although less 

evident in other parts of the Powder River 

basin. 

0