GEOLOGICAL SURVEY CIRCULAR 358 

URANIUM IN THE MAYOWORTH AREA 

JOHNSON COUNTY, WYOMINGA PRELIMINARY REPORT 

This report concerns work done on 

behalf of the U.S. Atomic Energy 

Commission and is published with 

the permission of the Commission. 

UNITED STATES DEPARTMENT OF THE INTERIOR 

Douglas McKay, Secretary 

GEOLOGICAL SURVEY 

W. E. Wrather, Director 

GEOLOGICAL SURVEY CffiCULAR 358 

URANIUM IN THE MA YOWORTH AREA, JOHNSON COUNTY, WYOMINGA PRELIMINARY REPORT 

ByJ. D. Love 

This report concerns work done on 

behalf of the U. S. Atomic Energy 

Commission and is pubJished with 

the permission of the Commission. 

Washington. ·D. C., 1954 

Free on application to the Geological Survey, Washington 25, D. C. 
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Alluvium }I 0 

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Frontier formation 

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Mowry shale (.) 

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Thermopolis shale 

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Cloverly formation 

[8 I Morrison formation u 

f--;;. .... 1 ~ js'j~~~ ~~~~~~~~ ~ 

Chuowoter ~ formation J~ ct 'lema, Crow Mountain sandstone and it: Alcova limestone members ~ 

(undifferentiated J 

Phosp~o~: fo~motlon } j G.z 

~i Tensleep sandstone 

.L!3 Strike and dip of beds 

X2 

Locality where uronium-beoring 

limestone wos sampled 

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GeoloCJY from unpublished mop by A.L.Richordson 

Geolooy in Sundance formation near localities I and 2 by J. D. Love 

Figure 1. -Geologic map of Mayoworth area, Wyoming. 

ii 
URANIUM IN THE MAYOWORTH AREA, JOHNSON COUNTY, WYOMINGA PRELIMINARY REPORT 

ByJ. D. Love 

CONTENTS 

Page 

Abstract..................................... 1 

Introduction. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 

Geography . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 

Geology...................................... 2 

Stratigraphy. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 

Uranium deposits............................. 3 

Page 

Uranium deposits -Continued 

Description of localities. . . . . . . . . . . . . . . . . . 3 

Analyses of samples . . . . . . . . . . . . . . . . . . . . . . . . . . 6 

Origin of uranium in the Mayoworth area. . . . . . . . 6 

Literature cited.............................. 7 

Unpublished reports.. . . . . . . . . . . . . . . . . . . . . . . . . . ·7 

ILLUSTRATIONS 

Page 

Plate 1. 

Figure 1. 

2. 

3. 

4. 

Section from Bighorn Mountains through Mayo worth to North Pumpkin Butte, Wyoming ....... Inside cover 

Geologic map of Mayoworth area . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . • . . . ii 

Stratigraphic section of rocks near Mayoworth . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 

Uranium locality 1 in oolitic basal limestoi1e of Sundance formation. . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 

Photomicrograph x 40 of polished surface of oolites in basal limestone 

of Sundance formation replaced by metatyuyamunite at locality 1 . . . . . . . . . . . . . . . . . . . . . . . . . . 5 

ABSTRACT 

The uranium mineral, metatyuyamunite, occurs 

in the basal limestone of the Sundance formation of Late 

Jurassic age along the east flank of the Bighorn Mountains, about 2 miles southwest of the abandoned Mayoworth post office. This deposit is of particular interest because it is the first occurrence of uranium mineralization reported from a marine limestone in Wyoming. The first uranium claims were filed in July 1953, 

by J. S. Masek, Dan Oglesby, and Jack Emery of 

Casper, Wyo. Subsequent reconnaissance investigations have been made by private individuals and geologists of the U. S. Geological Survey and Atomic 

Energy Commission. 

The metatyuyamunite is concentrated in a 

hard gray oolitic limestone that forms the basal 

bed of the Sundance formation. A selected sample 

of limestone from a fresh exposure in the northernmost deposit known at the time of the field examination contained 0. 70 percent equivalent uranium 

and 0. 71 percent uranium. Eight samples of the 

limestone taken at the same place by the Atomic 

Energy Commission contained from 0. 007 to 

0. 22 percent uranium. A chip sample from the 

weathered outcrop at the top of this limestone 

half a mile to the southeast contained 0. 17 percent equivalent uranium and 0. 030 percent uranium. 

A dinosaur bone from the middle part of the Morrison 

formation contained 0. 044 percent equivalent uranium 

and 0. 004 percent uranium. 

1 

Metatyuyamunite forms a conspicuous yellow 

coating along fractl'l'e planes cutting the oolitic limestone and has also replaced many of the oolites within 

the solid limestone even where fractures are not present. 

Many radioactive anomalies in the basal limestone of the Sundance formation were examined in a 

reconnaissance along the outcrop for a distance of half 

a mile south of the initial discovery. Samples were 

taken for analysis only at the northern and southern 

margins of this interval. Outcrops farther north and 

south were not studied. 

Sufficient data are not available to make even rough 

estimates of tonnage and grade of these deposits. 

The extent of the limestone, the approximate boundaries of the area of above-normal radioactivity, and 

the possibilities of other radioaclive zones have not 

been thoroughly invesFgated. Although dinosaur bones 

in the Morrison formation were r~;djoactive wherever 

they were tested, no significant amount of radioactivity 

was observed in adjacent rocks. 

INTRODUCTION 

The Mayoworth area is in the southwestern part 

of Johnson County, Wyo. (fig. 1). Several detailed 

stratigraphic sections were measured by the writer in 

this area in 1944 and additional studies were made in 

1949-50 as part of oil and gas investigations of the 

Geological Survey. The first uranium claims were 
filed in July 1953, by J. S. Masek, Dan Oglesby, and 

Jack Emery of Casper, Wyo. Subsequently, reconnaissance investigations of the area were made by 

private individuals and geologists of the U. S. Geological 

Survey and the U. S. Atomic Energy Commission 

(Geslin, 1953). The writer examined the uranium deposits to study their geology and to obtain data on their 

origin. No mining or detailed exploration has been 

done, as of April 1, 1954. 

The writer is indebted to Robert S. Houston for 

the photograph of the polished section of mineralized 

limestone {fig. 4). Except where specified otherwise, 

the Denver laboratory of the U. S. Geological Survey 

made the chemical analyses. Alice D. Weeks of the 

Geological Survey identified the uranium mineral as 

metatyuyamunite. 

Stratigraphic and structural studies of the 

Mayoworth area and the region directly north have 

been made by several geologists {Love and others, 

1945a; Richardson, 1950, and Hose, in preparation). 

Topographic maps of the area, scale 1:24,000, 

having a 20-foot contour interval, compiled for the 

Bureau of Reclamation, are not published but are available through the Bureau. 

Reconnaissance examination of the Mayoworth area 

was made on behalf of the Division of Raw Materials of 

the U. S. Atomic Energy Commission. 

GEOGRAPHY 

The Mayoworth area lies along the western margin 

of the Powder River Basin. Directly to the west, the 

land surface rises onto the east flank of the Bighorn 

Mountains. The altitude of the uranium deposit is about 

5, 450 feet. On the crest of the mountains 10 miles to 

the west, the altitude is about 8, 000 (pl. 1). The area 

is drained by intermittent streams, all tributaries to 

the North Fork of Powder River. There are no towns, 

and the Mayoworth post office, which was in the northeast corner of the area {fig. 1), has been discontinued. 

At Mayoworth, a graded county road that crosses the 

area from south to north intersects an oiled road from 

Kaycee, which is the nearest town, 12 miles to the south 

east. Alternating sets of hard and soft strata have been 

dissected into strike ridges and valleys, resulting in 

a rough topography. Vegetation is sparse and bedrock 

is comparatively well exposed. Livestock raising is the 

only industry. 

GEOLOGY 

The Mayoworth area is at the foot of the east 

flank of the Bighorn Mountains, where the rugged 

mountain topography flattens out into the Powder River 

Basin (pl. 1). The exposed rocks are of Triassic, 

Jurassic, and Early Cretaceous ages and have monoclinal dips of 10° to 15° to the northeast {fig. 1). The 

rocks probably were folded at the close of Paleocene 

time, when the principal arching of the Bighorn Mountains occurred. There may have been slight subsequent 

movement here, but it cannot be proved or disproved. 

Data from adjacent localities indicate that the Powder 

River Basin was largely filled with Eocene, Oligocene, 

and probably younger rocks (Love, 1952, pls. 2 

and 3, and p. 5). Remnants of Oligocene and 

2 

Miocene ( () tuffaceous claystones and sandstones 

occur on the crest of the Bighorn Mountains 

northwest of Mayoworth at altitudes of 7, 500 to 

9, 000 feet. These remnants were laid down on a 

rugged topography {pl. 1) and are still essentially 

undeformed. 

STRATIGRAPHY 

Figure 2 presents summary descriptions and 

thicknesses of the rock units in the vicinity of the uranium deposits in the Mayoworth area. Richardson (1950) 

and Hose {in preparation) have described the stratigraphy of the Paleozoic and Mesozoic rocks of this area 

in some detail. Love and others (1945b) described the 

lithology and correlated sections of the Morrison, 

Cloverly, and Thermopolis formations. 

The Chugwater formation, of Triassic age, directly 

underlies the Sundance formation in this area, is about 

800 feet thick, and consists of 3 members. At the base 

is the Red Peak member, which is about 700 feet thick 

and composed of brick-red soft shale, siltstone, and 

silty sandstone. The uppermost 20 feet is massive red 

silty sandstone in the vicinity of the uranium deposits. 

Overlying the Red Peak member is the Alcova limestone 

member, which consists of gray to pink thin-bedded 

slabby limestone ranging in thickness from a feather 

edge to 2 feet. The Alcova limestone member is 

lenticular and wedges out, only to reappear at the same 

stratigraphic horizon farther along the outcrop. 

Overlying the Alcova limestone member is the 

Crow Mountain sandstone member which consists of 

about 100 feet of salmon-pink massive to crossbedded 

fine-grained sandstone. The Crow Mountain was 

originally described by Love {1939). The member 

characteristically crops out in cliffs. In places where 

the Alcova limestone member is absent, it is difficult 

to distinguish the Crow Mountain sandstone member 

from the uppermost sandstone in the Red Peak member. The upper part of the Crow Mountain is commonly 

silty and soft and forms a slope capped by the resistant 

basal limestone of the overlying Sundance formation. 

The Crow Mountain sandstone member has been 

mistaken for the somewhat younger Nugget sandstone of 

areas farther west by many geologists because both 

sequences have almost identical lithology. ' 

The Gypsum Spring formation occurs along the 

east flank of the Bighorn Mountains farther north but 

wedges out at about the north boundary of the Mayoworth 

area. 

The Sundance formation consists of two sequences, a lower one called the "lower Sundance," 

comprising about 200 feet of nonglauconitic sandstone and shale containing uranium-bearing oolitic 

limestone at the base, and an upper sequence 

called the "upper Sundance" composed of greenish 

glauconitic shale and sandstone about 150 to 175 feet 

thick. Both sequences contain marine fossils. The 

basal limestone of the "lower Sundance" is oolitic, 

hard, and forms a conspicuous ledge in the Mayoworth area but thins and disappears to the north 

and to the south. Its maximum thickness is about 

20 feet. This limestone superficially resembles 

the nonoolitic Alcova limestone member of the 

Chugwater formation and has been mistaken for it 
by some geologists. Peterson (1954) has described the 

Sundance rocks in this general region and illustrated 

oolitic beds in the upper part of the "lower Sundance. 11 

The Morrison, Cloverly, and Thermopolis formations have been described (Love, and others, 1945b) and 

the lithology is summarized in figure 2. 

URANIUM DEPOSITS 

Uranium has been found in the basal limestone of the 

Sundance formation and in dinosaur bones in the overlying 

Morrison formation. Other rocks in the area were not examined in detail for uranium by the writer. An airborne 

surveyhasbeenmade (Jones, 1952, p. 10) bythe Atomic 

Energy Commission. 

Description of localities 

Locality 1 (NEtNWtswt sec. 31 T. 44 N. I 

R. 83 W. ). -The site oflocality 1 is the claim discovered 

and staked by J. S. Masek and associates, in the marine 

basal limestone of the Sundance formation of Late Jurassic 

age. The outcrops are on a northeastward-facing dip slope 

(fig. 3). Strata strike N. 30° W., and dip 12° northeast. 

The stratigraphic section, shown below, was measured at 

the place of best exposed uranium mineralization. Unit 1 

is the oldest. 

Unit 

no. 

Top of section. 

Lithologic character Thickness 

(feet) 

5 Shale, pale green, soft; forms valley at 20+ 

base of dip slope. 

4 Limestone, brown, oolitic, hard, but 4 

softer than underlying unit; irregularly 

bedded in upper half; contains metatyuyamunite in middle 2 feet (fig. 3); 

top of unit forms prominent dip slope 

(fig. 3); contains fragments of oysters, 

bryozoans, and other marine fossils. 

3 Limestone, brown, oolitic, very hard, 2.5 

evenly bedded, weathering into conspicuous slabs one-half to l inch thick. 

2 Limestone, grayish-brown, massive, very 2.5 

sandy, containing some small chert 

pebbles; highly oolitic. 

Contact between Sundance formation and Crow 

Mountain sandstone member of Chugwater formation. Contact is very sharp and even. 

l Siltstone, brick-red, sandy, soft. Under- 3+ 

lying strata are not exposed at this 

locality. 

Metatyuyam unite is visible in the middle 2 feet of unit 

4 throughout a distance of 27 f.eet in an east-west direction 

and 7 feet in a north-south direction. The most conspicuous 

yellow coating is along fracture faces, but, as is shown in 

figure 4, the metatyuyamunite has replaced oolites within 

unfracturedlimestone. The most radioactive areas are 

along ferruginous brown clayey partings, where a scintillation counter shows 1. 5 mr /hr. A 1-pound selected sample of the limestone taken for mineral identification contained 0. 70 percent equivalent uranium, 0. 71 percent uranium, and 0. 56 percent V 20 :>· The average uranium content of this limestone face is much lower. Analyses of 

additional samples taken at locality 1 are shown in the table 

presentedonp. 6ofthis report. The replacementof the 

3 

oolites indicates that uranium was introduced after the 

sediments were deposited. The limes tone contains 

oysters, bryozoans, and other fossils of marine origin. 

About 100 feet southwest of the largest mineralized 

exposure, and at the same stratigraphic position, metatyuyamunite is visible in an area about. 6 feet in diameter. 

This area had not been dug out at the time of examination 

so its extent and thickness could not be determined. 

On the same dip slope with these two mineralized 

spots are many other spots where radioactivity is considerably above background, but no metatyuyamunite is 

visible and no digging was done. At the time of examination, no drilling had been done in the area and the 

deepest pit was about 3 feet, so conclusions as to the 

economic possibilities of this locality are not warranted 

at present. 

Locality 2 (SWi-SEtswt sec. 31 T. 44 N. I 

R. 83 W. ) . -The site of locality 2 is about half a mile 

southeast of locality 1, along strike and in the same 

oolitic limestone bed at the base of the Sundance formation. A scintillation counter showed a maximum reading 

of 2. 0 mr jhr (as compared with 1. 5 mr /hr at locality 1) 

at the contact between the brown ooliUc limestone and 

the overlying green shale. At this place a 1-poundsample of the limestone contained 0.17 percent equivalent 

uranium, 0. 30 percent uranium1 and 0. 10 percent V 2051 

The sample was taken from a bedding -plane surface and 

the limestone was so hard that it could be dug to a depth of 

only about 3 inches with the tools at hand. No uranium 

was observed in this near-surface sample, but the relatively high radioactivity suggests that if a pit or drill 

hole were put down at this spot, uranium minerals 

might be found. 

Radioactivity much higher than background was recorded in many places along the dip slope of this limestone 

for the next quarter mile to the south. At one place a 

maximum radioactivity of 1 mr /hr was observed. Lack 

of time prevented more detailed reconnaissance or 

mapping of the extent of this oolitic limestone, but 

it is likely that the richest and most extensive uranium deposits were not found. 

In the middle part of the Morrison formation about 

2miles southeastoflocality 2 (NEt sec. 14, T. 44N., 

R. 83 W. ) , radioactive dinosaur bones occur in considerable abundance in a medium-grained gray and brown 

sandstone (fig. 2). A sample of bones containedO. 044percent equivalent uranium, 0. 004 percent uranium, and 

0. 08 percent V 20 5. The sandstone in which the bones are 

embedded shows radioactivity slightly above background 

and the underlying green and dully variegated claystone is 

slightly more radioactive than the sandstone. 

Neither the Morrison formation nor the overlying 

Cloverly formation, or the Muddy sandstone member of 

the Thermopolis shale has been examined in sufficient 

detail for radioactivity by the writer to justify any conclusion as to the possibility of uranium deposits in these 

rocks. Carbonaceous material occurs in the sandstones, 

and lenticular beds of lignitic material are present in 

several places. Jones (1952, p. 10) indicates that he 

made complete radiometric flight coverages of outcrops 

of the Sundance, Morrison, and Cloverly formations and 

the Muddy sandstone member, throughout this region 

without discovering any anomalies. This survey would 

suggest that the radioactivity in the v:_cinity of localities 

1 and 2 is difficult to detect from the air, an observation 

that has been corroborated by commercial geologists who 

flew the area after uranium was discovered. 
(/) 

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2 

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..., 

Mowry shale 

Thermopolis 

shale 185 1 

Cloverly 

formation 

205' 

Morrison 

formation 

190-200' 

Sundance 

formation 

350-395' 

Chugwater 

formation 

Shale, black, soft 

Sandstone, gray, coarse-grained 

Shale, block, soft 

Sandstone, gray, silty, interbedded with block shale 

Sandstone, gray to brown; variegated claystone near bose 

Sandstone, gray to brown, conglomeratic near base 

Claystone, green to variegated; dinosaur bones in lower part 

San~stone,gray, hard, dinosaur bones contain 0.004 percent uronrum 

Claystone, dully variegated 

Claystone and limestone with Jurassic invertebrate fossils 

Claystone, dully variegated 

Sandstone, gray, fine-grained Shale, red and green, and glauconitic sandstone 

Shale, green, sandy, glauconitic, fossiliferous 

Sandstone, gray to brown, fine-grained 

Shale, gray to brown, sandy 

Sandstone, gray to brown, fine-grained 

Limestone, gr9y, hard, oolitic; contains as much as 0.71 

percent uronrum 

Sandstone, salmon pink; forms massive cliff 

Figure 2. -Stratigraphic section of rocks near Mayoworth, Wyoming. 

4 
Figure 3.-Uranium locality· 1 in oolitic basal limestone of Sundance formation. Slope in background is stripped dip 

slope on top of basal limestone. Arrow indicates camera case for scale. A selected sample at this point contained 

0. 71 percent uranium. 

Figure 4. -Photomicrograph x 40 of polished surface of oolites in basal limestone of Sundance formation replaced 

by metatyuyamunite at locality 1. Light- colored oolites and parts of oolites, and wbJte irregular deposits between 

oolites are metatyuyamunite. 

5 
ANALYSES OF SAMPLES .!:-='ROM MAYO\ roRTh AREA 1 

Laboratory Locality eU u V205 Location (fig. l), lithology, and formation sampl_e no. (percent) (percent) (percent) 

99511 l 0.70 0.71 0.56 NEtNW-&sw-& sec. 3, T • 44 N. , R . 83 W. , oolitic 

93857 2 limestone in basal part of Sundance formation. 

l .015 .019 .08 Do. 

93858 2 l .10 .017 .07 Do. 

93859 2 l .012 .007 .12 Do. 

94559 2 l .017 .025 .20 Do. 

94560 2 l .17 .18 .17 Do. 

94561 2 l .21 .22 .12 Do. 

94562 2 l .12 .17 .24 Do. 

94563 2 l .30 .040 .29 Do. 

99510 2 .17 .030 .10 swl}sE-&swi_- sec. 3, T. 44 N., R. 83 w., oolitic 

limestone in basal part of Sundance formation • 99512 --------- • 044 .004 .08 NEt sec. 14, T. 44 N., R. 83 W., dinosaur bone 

in Morrison formation. 

1

Samples analyzed in Denver laboratory, U. S. Geological Survey. Analysts: Furman, Mountjoy, Schuch, Wilson, Fennelly, McGurk, and Meadows._ 2Samples collected by geologists of the Atomic Energy Commission, suboffice, Douglas, Wyo. 

ORIGIN OF URANIUM IN THE MA YOWORTH AREA 

The origin of the uranium in the Mayoworth 

area has not been determined and can only be inferred from a study of regional relationships. As 

shown in figure 4, metatyuyamunite has replaced 

some of the limestone oolites, in addition to being 

concentrated along fracture planes that developed 

after the limestone was lithified. The area is 

essentially unfaulted, although a thrust fault is 

present a short distance to the north. The folding probably took place at the close of Paleocene 

time. It is reasonable to assume that most of 

the fracturing occurred at the time of folding. 

There is no evidence of vein deposits other than, 

perhaps, the metatyuyamunite concentrated along 

fractures, or of Mesozoic or Tertiary igneous activity of any kind in the region. Reflection seismograph 

and magnetometer surveys of the Powder River Basin 

have not indicated any buried intrusive rocks younger 

than pre-Cambrian. The nearest outcrop of preCambrian rocks is 6 miles to the north on an anticlinal nose called :'The Horn, " which is separated 

from the Mayoworth area by a thrust fault, south of 

which is a syncline (Love and Weitz, 1951). 

Slightly more than 1 mile northeast of the 

map area (fig. 1), in the SEtswtsEt sec. 24, 

T. 45 N., R. 83 W., the Stanolind Oil and Gas Co., 

Brock No. 1 dry hole was drilled to a depth of 

4, 011 feet, starting in the Frontier formation of 

Late Cretaceous age and bottoming in the Madison 

limestone of Mississippian age. A radioactivity log 

of this test shows no zones of abnormally high radioactivity in any formation penetrated. 

A study of radioactivity .logs in the Powder 

River Basin indicates that the basal part of the 

Sundance formation is typically not radioactive. However, a conspicuous exception is in the Little Buck 

Creek oilfield, 130 miles to the southeast, where the 

basal sandstone in the Sundance formation is moderately 

radioactive at a depth of 4, 500 feet. This sandstone is 

6 

in a comparable stratigraphic position and about the 

same age as the oolitic limestone in the Mayoworth area. 

It seems pertinent to make a comparison of 

the structural and stratigraphic relationship, because the origin of radioactivity in the Sundance 

formation in the Mayoworth and Little Buck Creek 

areas probably is similar, and because the sedimentary record at Little Buck Creek is more complete .. 

At the north end of the Hartville uplift is a northwardplunging anticline in Paleozoic and Mesozoic rocks, 

named the Lusk Dome by Denson and Botinelly (1949). 

This dome is 12 miles south of the Little Buck Creek 

oilfield. The White River formation of Oligocene age 

was deposited in deep valleys and on rugged topography cut in the rocks on this northward-plunging structural nose. The basal sandstone in the Sundance 

formation is very porous and permeable and outcrops 

of this sandstone are directly overlain by the White 

River formation. Radioactivity logs show that the 

White River formation in this area is radioactive, and 

eight samples taken from it southeast of Little Buck 

Creek show equivalent uranium contents averaging 

0. 003 percent, having a maximum of 0. 008 percent. 

Radioactivity anomalies in the White River formation have been reported by Mallory (1953) 

6 miles north and 7 miles southwest of Little Buck 

Creek. 

Water samples taken by M. L. Troyer (personal communication, 1953) from the White River 

formation of this general area contain moderately 

high concentrations of uranium. In past geologic time 

uranium probably was leached out of the White River 

formation as readily as at present, and was carried 

in solution in ground water downdip along the porous 

basal sandstone of the Sundance formation. This 

sandstone contains hydrocarbons in small quantity in 

the Little Buck Creek oilfield, and it is possible that 

uranium was deposited where the hydrocarbons were 

concentrated. It is also conceivable that the structure 

of the area prohibited further migration of the uraniumbearing ground water. 
It is possible to account for the uranium deposit in 

the Mayoworth area in the same manner. Many remnants 

of tuffaceous claystone' sandstone' and conglomerate of 

the Oligocene White River formation (pl. 1} occur about 

13 miles to the northwest, on top ofthe Bighorn Mountains, 

at an altitude of about 8, 000 feet. These rocks are slightly 

radioactive (Love, 1952, p. 17}. They were depositedon 

a surface of high relief. Similar remnants are present 

on Pumpkin Buttes, 40 miles to the east, at anal titude 

of 6, 000 feet (pl. 1}. These remnants, thought to be the 

source rocks for the uranium deposits in the underlying 

Wasatch formation (Love, 1952, p. 17 -19}, contain as much 

as 0. 007 percent uranium. The strata at Pumpkin Buttes 

are of early Oligocene (Chadronian} age on the basis of 

the following vertebrate fossils (M. J. Hough, personal 

communication, 1954): Hyracodon? priscidens, 

Hyracodon sp., Archaeotherium sp., Triqonias 

osborni. Mesohippus cf. M. westoni, Leptomeryx 

sp., and a rhinocerotid, probably Subhyracodon. 

The White River formation probably extended eastward from the crest of the Bighorn Mountains to Pumpkin 

Buttes (pl. 1). The White River strata were deposited 

across the upturned and eroded edges of the Jurassic rocks 

about 2, 500 feet structurally higher than the uranium deposit near Mayoworth. It is known that the uraniumbearing oolitic limestone grades laterally into coarsegrained sandstone. The limestone is directly underlain 

by the soft, porous, andpermeable Crow Mountain sandstone member of the Chugwater formation which is 100 feet 

thick. Uranium leached from the White River formation 

could easily have migrated in solution in ground water downdip along these porous rocks and have been deposited in the 

oolitic limestone. The factors that caused deposition in 

the limestone are not known. Some of the brown color, 

which is associated with the greatest radioactivity, may 

be caused by the presence of hydrocarbons. 

Metatyuyamunite from the White River formation 

occurs at several localities and is the principal mineral 

in a few of the deposits in the underlying Wasatch 

formation of the Pumpkin Buttes area (M. L. Troyer, 

personal communication). 

7 

LITERATURE CITED 

Denson, N. M., and Botinelly, Theodore, 1949, Geology of the Hartville uplift, eastern Wyoming: U. S. 

Geol. Survey Oil and Gas Map OM 102. 

Hose, R. K., Geology of the Crazy Woman Creek area, 

Johnson County, Wyo.: U. S. Geol. Survey Bull. 1015. 

[In preparation. ] 

Love, J. D., 1939, Geology along the southern margin 

of the Absaroka Range, Wyoming: Geol. Soc. 

America Special Paper 20, 134 p. 

-..,......-.,..,......., 1952, Preliminary report on uranium 

deposits in the Pumpkin Buttes area, Powder River 

Basin, Wyoming: U. S. Geol. Survey Circ. 176. 

Love, J. D., and others, 1945a, Stratigraphic sections 

and thickness maps of Triassic rocks in central Wyoming: U. S. Geol. Survey Oil and Gas Chart 17. 

-----::-::1945b, Stratigraphic sections and thickness 

maps of Lower Cretaceous and non-marine Jurassic 

rocks of central Wyoming: U. S. Geol. Survey Oil 

and Gas Chart 13. ·· , 

Love, J. D., and Weitz, J. L., 1951, Geologic map 

of the Powder River Basin and adjacent areas, Wyoming: U. S. Geol. Survey Oil and Gas Map OM 122. 

Peterson, J. A. , 19b4, Marine Upper Jurassic, eastern Wyoming: Am. Assoc. Petroleum Geologists 

Bull., v. 38, p. 463-507. 

UNPUBLISHED REPORTS 

Geslin, H. E., 1953, Mayoworth district, Johnson 

County, Wyo.: U. S. Atomic Energy Comm., 

Prelim. Recon. Rept. DEB-RRD-726. 

Jones, E. E., 1952, Airborne radiometric survey of the 

east flank of the Big Horn Mountains, Wyoming and 

Montana: U. S. Atomic EnergyComm. RME-4006. 

Mallory, N. S., 1953, Airborne radiometric survey of 

Lusk area, Niobrara, Platte, and Goshen Counties, 

Wyo.: U. S. Atomic Energy Comm. RME-46. 

Richardson, A. L. , 1950, Geology of the Mayoworth 

region, Johnson County, Wyo.: L Unpub. master of 

arts thesis in files of Univ. Wyo.] 

INT.-DUP. SEC., WASH .. D.C.71610