Mineral Resources of the 

Cedar Mountain Wilderness 

Study Area, Washakie and 

Hot Springs Counties, Wyoming

U.S. GEOLOGICAL SURVEY BULLETIN 1756-B

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Chapter B

Mineral Resources of the 

Cedar Mountain Wilderness 

Study Area, Washakie and 

Hot Springs Counties, Wyoming

By CURTIS E. LARSEN, RANDALL H. HILL, 

DOLORES M. KULIK, and MARK K. BROWN 

U.S. Geolgical Survey

DAVID C SCOTT 

U.S. Bureau of Mines

U.S. GEOLOGICAL SURVEY BULLETIN 1756

MINERAL RESOURCES OF WILDERNESS STUDY AREAS NORTHERN WYOMING
DEPARTMENT OF THE INTERIOR 

DONALD PAUL MODEL, Secretary

U.S. GEOLOGICAL SURVEY 

Dallas L. Peck, Director

UNITED STATES GOVERNMENT PRINTING OFFICE: 1988

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U.S. Bureau of Mines.

Library of Congress Cataloging-in-Publication Data

Mineral resources of the Cedar Mountain Wilderness Study Area, Washakie 

and Hot Springs Counties, Wyoming.

(Mineral resources of wilderness study areas northern Wyoming ; ch. B) 

(U.S. Geological Survey bulletin ; 1756-B) 

Bibliography: p. 

Supt. of Docs, no.: I 19.3:1756-6

1. Mines and mineral resources Wyoming Cedar Mountain Wilderness.

2. Cedar Mountain Wilderness (Wyo.) I. Larsen, Curtis E. II. Series. 

III. Series: U.S. Geological Survey bulletin ; 1756-B. 

QE75.B9 no. 1756-B 557.3 s [553'.09787'34] 88-600336 

[TN24.W8]
STUDIES RELATED TO WILDERNESS 

Bureau of Land Management Wilderness Study Areas

The Federal Land Policy and Management Act (Public Law 94-579, October 21, 

1976) requires the U.S. Geological Survey and the U.S. Bureau of Mines to conduct mineral 

surveys on certain areas to determine the mineral values, if any, that may be present. Results 

must be made available to the public and be submitted to the President and the Congress. 

This report presents the results of a mineral survey of the Cedar Mountain (WY-010-222) 

Wilderness Study Area, Washakie and Hot Springs Counties, Wyoming.

CONTENTS

Summary Bl

Abstract Bl 

Character and setting Bl 

Mineral resources B3 

Resource potential B3 

Introduction B4

Appraisal of identified resources B4 

Mining history B5 

Energy resources B5 

Coal B5 

Oil and gas B5 

Geolhermal energy B5

Assessment of potential for undiscovered resources B7 

Geology B7 

Geologic structure B9 

Geochemistry BIO 

Geophysics Bll

Mineral and energy resources B14 

Metals B14 

Oil and gas B14 

Coal B15

Geolhermal energy B15 

Uranium B15 

Sand and gravel B15 

References cited B15 

Appendix B19

FIGURES

1-5. Maps of the Cedar Mountain Wilderness Study Area and vicinity:

1. Mineral resource potential and location B2

2. Locations of leases, wells, fields, and geologic structures pertaining to 

oil, gas, and coal production B6

3. General geology B8

4. Thrust faulting along the western margin of the Bighorn Basin BIO

5. Complete Bouguer gravity anomaly and generalized structure B12

6. Residual magnetic anomaly and generalized structure B13

Contents

MINERAL RESOURCES OF WILDERNESS STUDY AREAS-NORTHERN WYOMING

Mineral Resources of the

Cedar Mountain Wilderness Study Area,

Washakie and Hot Springs Counties, Wyoming

By Curtis E. Larsen, Randall H. Hill, 

Dolores M. Kulik, and Mark K. Brown 

U.S. Geological Survey, and

David C. Scott

U.S. Bureau of Mines

SUMMARY 

Abstract

The Cedar Mountain Wilderness Study Area 

(WY-010-222) consists of approximately 21,570 acres along 

the east bank of the Bighorn River, east of the town of Kirby, 

Wyo. The area includes parts of both Hot Springs and 

Washakie Counties. During the summer of 1986, the U.S. 

Geological Survey (USGS) and the U.S. Bureau of Mines 

(USBM) undertook field studies to appraise the identified 

(known) resources and assess the mineral resource potential 

(undiscovered) of the study area. No mines or prospects are 

located within the study area, and it has no identified 

resources. However, coal was mined from thin discontinuous 

coal seams within the Upper Cretaceous Mesaverde 

Formation 2 miles south of the area. This formation is 

covered by as much as 1,200 feet of the Meeteetse and 

Lance Formations beneath Cedar Mountain. The resource 

potential for coal is low in the southernmost part of the study 

area; the remainder of the area has no potential for coal 

resources. Anomalous gold concentrations identified in three 

stream-sediment samples collected near Tie Down Flats 

indicate a moderate potential for gold resources in the three 

small drainage basins those samples represent. The study 

area has no potential for gold resources outside these three 

drainages, and no potential for resources of other metals, 

including uranium. An extension of a known oil and gas 

producing structure, the Neiber anticline, crosses the

Manuscript approved for publication July 15, 19SS.

northeastern part of the area, and another producing 

structure, the Gebo Dome, is 4 miles southwest of Cedar 

Mountain. Based on the proximity of these structures, 

inferred faulting beneath the central part of the area, and oil 

and gas shows in dry wells drilled within the area, the 

potential for oil and gas resources is considered moderate for 

two areas in the north and central parts of the Cedar 

Mountain Wilderness Study Area, and low for the remainder 

of the area. The study area also has no potential for sand and 

gravel resources or for geothermal energy resources.

Character and Setting

The Cedar Mountain Wilderness Study Area (WY010-222) lies within the Bighorn Basin. It is located on the 

east bank of the Bighorn River and straddles the boundary 

between Hot Springs and Washakie Counties. It is 

approximately 9 miles southwest of Worland and 12 miles 

northeast of Thermopolis (fig. 1). The study area covers 

about 21,570 acres. The land surface within the area is 

characterized by a badlands topography and has a 

maximum relief of about 1,200 feet. There are no permanent 

streams within the study area; however, many ravines carry 

intermittent runoff northward and westward into the Bighorn 

River.

Gently dipping sandstones interbedded with siltstone 

and shale underlie most of the area. These dip 10° to 28° to 

the north and northeast, but two prominent folds the Neiber 

anticline and its accompanying syncline trend westnorthwest and east-southeast across the northern portion of 

the area. These are accompanied by faulting at depth. 

Closure on the anticlinal structure is sufficient for oil and

Cedar Mountain Wilderness Study Area B1
108" 10' 108°00'

TIE DOWN 

FLATS

APPROXIMATE

BOUNDARY OF

CEDAR MOUNTAIN

WILDERNESS

STUDY AREA

(WY-010-222)

Washakic County; 

Hot Springs Coun

R.95W.

N/D

R. 94 W.

EXPLANATION

R. 93 W.

Geologic terrane having moderate mineral resource potential for oil and gas, with 

certainty level C

Geologic terrane having moderate mineral resource potential for gold, with certainty 

level C

Geologic terrane having low mineral resource potential for coal, with certainty level C

Geologic terrane having low mineral resource potential for oil and gas, with certainty 

level C Applies only to that part of study area outside the areas of moderate oil and gas 

potential described above

Geologic terrane having no mineral or energy resource potential for any metals, 

including uranium and gold, nor for coal, geothermal energy, sand, or gravel, with 

certainty level D Applies to entire study area for all listed commodities except gold and 

coal, which have no potential only outside the areas of moderate and low potential 

described above 

Levels of certainty:

C Data give a good indication of geologic environment and level of mineral resource 

potential

D Data clearly define geologic environment and level of mineral resource potential

Figure 1. Mineral resource potential and location of Cedar Mountain Wilderness Study 

Area, Hot Springs and Washakie Counties, Wyoming.

B2 Mineral Resources of Wilderness Study Areas Northern Wyoming
gas production 2.75 miles east of the study area. The Neiber 

II Unit field borders the east boundary of the study area in 

sec. 16, T. 45 N., R. 93 W.

The rocks exposed at the surface belong to the Meeteetse and Lance Formations of Late Cretaceous age (see 

geologic time chart in Appendix), the Fort Union Formation of 

Paleocene age, and the Willwood Formation of Eocene age. 

The Meeteetse and Lance Formations are well exposed 

along the southern face of Cedar Mountain. Interbedded 

shales, thin coals, and bentonite beds of the Meeteetse 

Formation are exposed at the base of Cedar Mountain, and 

massive sandstones and interbedded gray shales of the 

Lance Formation form its rugged south-facing slope. The 

Lance Formation dips beneath the Fort Union Formation in 

the southwestern part of the study area, east of the town of 

Kirby. North of that point, most of the study area is covered 

by a repetitious sequence of as much as 3500 feet of 

interbedded thin sandstones and shales of the Fort Union. A 

small part of the overlying Willwood Formation is preserved 

within the core of the syncline adjacent to the Neiber anticline 

at Tie Down Flats. Prominent alluvial terrace remnants 

underlain by sand and gravel locally abut the study area 

along the Bighorn River. These unconsolidated deposits 

represent earlier river flood plains and are preserved locally in 

the mouths of ravines draining into the river.

Mineral Resources

There are no mines or prospects within the Cedar 

Mountain Wilderness Study Area. Resources commonly 

associated with the Bighorn Basin are coal, oil, and gas. 

These resources have been developed near the study area. 

Coal was mined from the Mesaverde Formation at the Gebo 

field, 2 miles southwest of Cedar Mountain. Although much 

of the southern edge of the study area has been leased for 

coal, no thick coal beds are present at or near the surface 

within the study area. The nearest mine is the Cowboy Mine, 

2 miles south-southwest of Cedar Mountain, where coal 

was produced from the Mesaverde Formation. The coalbearing zone in the Mesaverde lies several hundred feet 

below the surface at the south edge of the study area. Beds 

of coal or lignite within the Meeteetse Formation crop out at 

the foot of Cedar Mountain, but they are less than 2 feet thick 

and have not been mined. Similarly, thin bentonitic shale 

beds are present within this same formation along the 

southern edge of the area, but the measured thickness of 

these beds rarely exceeds a few inches.

Oil and gas exploration has a long history in this portion 

of the basin. Drilling of the Neiber anticline, which crosses the 

northern third of the study area, began as early as 1915, but 

a producing well was not completed in this structure until 

1947, when oil was recovered from the Park City Formation. 

This well is approximately 4 miles east of the study area. 

Petroleum exploration of the Neiber anticline has continued. 

An exploratory well was drilled along the crest of this fold 1.5 

miles east of the study area in 1984. In spite of these 

exploratory wells and intensive seismic exploration in the 

1940's, no oil or gas has been produced from the geologic 

structures beneath the study area. Nonetheless, much of the 

study area is covered by oil and gas leases. Geothermal

energy is in evidence at the Thermopolis hot springs, 10 

miles to the south, but there is no surface indication of 

hydrothermal activity within the study area.

Resource Potential

Because identified oil and gas resources exist near the 

study area and anticlinal structures capable of trapping oil 

and gas occur within it, a moderate resource potential for oil 

and gas is assigned to two areas in the north and central 

parts of the study area, whereas the rest of the study area has 

low oil and gas resource potential. A low potential for coal 

resources is assigned to the southernmost part of the study 

area because demonstrated coal beds exist in that vicinity, 

but these are all either too thin or too deeply buried to be 

economically mined; the remainder of the study area has no 

potential for coal resources. Studies show a moderate 

potential for gold resources in three small areas (see below) 

but no potential for gold resources outside these three areas 

and no potential for resources of any other metals, including 

uranium. The area also has no resource potential for geothermal energy or for sand and gravel.

Geochemical analyses of rocks and stream sediments 

taken throughout the area have shown few anomalous 

concentrations of elements. The determined concentrations 

for both types of samples were, with few exceptions, within 

the normal range of background concentrations. Arsenic had 

anomalous concentrations in two rock samples, where it was 

associated with fluorapatite. The nonmagnetic heavy-mineral 

concentrates from stream sediments consistently showed 

high concentrations of barium, zirconium, and titanium. 

These were included in the minerals barite, zircon, and rutile 

respectively. Rock samples from the surrounding areas, 

however, did not reveal anomalous sources for these 

minerals, thus reducing the likelihood that they are present in 

significant amounts. In addition, the alluvium from which the 

samples were taken is too thin and too sparsely distributed to 

provide suitable placer deposits. The data, therefore, show 

no resource potential for these minerals within the study area. 

Three concentrate samples from the vicinity of Tie Down Flats 

showed anomalous concentrations of gold (20, 30, and 100 

parts per million). One of these samples also had anomalous 

silver (3 parts per million). A critical examination of rock and 

stream-sediment samples by atomic-absorption analysis 

suggests that the source for the gold is not the sandstones of 

the Fort Union or Willwood Formations. The fine grain size of 

these sandstones makes them unlikely paleoplacers. 

Possible source deposits, which have not been tested, are 

quartzite-cobble gravels that cap the uplands upstream from 

two of these samples and fine gravel found locally as a basal 

conglomerate to the Willwood Formation. Gold was mined 

from the alluvial gravels of the Bighorn and Wind Rivers south 

of Thermopolis in the early part of this century. These rivers 

drain crystalline and metamorphic rocks of the Owl Creek 

Mountains. The fine grain size of the gold made its recovery 

difficult at that time (Schrader, 1915). The potential for gold 

resources is therefore considered moderate in the three

Cedar Mountain Wilderness Study Area B3
drainages represented by the anomalous samples. The 

study area has no potential for gold resources outside these 

three small drainages.

INTRODUCTION

The U.S. Geological Survey (USGS) and the U.S. 

Bureau of Mines (USBM) studied 21,570 acres of the 

Cedar Mountain Wilderness Study Area (WY-01Q-222) 

during 1986 to appraise the identified (known) mineral 

resources and assess the potential for undiscovered 

mineral resources (mineral resource potential). This 

study was requested by the Bureau of Land Management 

(BLM). The USGS and USBM have a joint role in 

wilderness mineral surveys. Throughout this report, the 

term "study area" means the entire Cedar Mountain 

Wilderness Study Area.

Cedar Mountain is the most prominent landmark 

of the study area. It is an escarpment rising 

approximately 1,200 feet above the surrounding Bighorn 

River valley. Its south-facing slope consists of alternating 

beds of massive sandstone and interbedded mudstones 

and shales of the Upper Cretaceous Lance Formation. 

The name Cedar Mountain comes from the abundant 

juniper vegetation along its slopes and at its summit. This 

vegetation reflects both the altitude of the mountain and 

the moisture-retention properties of the sandstones of 

the Lance Formation. Cedar Mountain lies near the 

southwest corner of the study area. The remainder of the 

area extends northward for about 8 miles. It is bounded 

on the west by the Bighorn River and extends eastward 

from 3 to 7 miles from the river. The eastern boundary is 

marked by a frequently traveled dirt road, which provides 

access to the area from the east. Other access into or 

across the area by vehicle is possible by 4-wheel-drive 

roads that date to seismic exploration in the 1940's.

This report presents an evaluation of the mineral 

endowment (identified resources and mineral resource 

potential) of the study area and is the product of several 

separate studies by the USBM and the USGS. Identified 

resources are classified according to the system of the 

U.S. Bureau of Mines and U.S. Geological Survey 

(1980), which is shown in the Appendix. Identified 

resources are studied by the USBM. Mineral resource 

potential is the likelihood of occurrence of undiscovered 

metals and nonmetals, industrial rocks and minerals, and 

energy sources (coal, oil, gas, oil shale, and geothermal 

sources). It is classified according to the system of 

Goudarzi (1984), which is also shown in the Appendix. 

The potential for undiscovered resources is studied by 

the USGS.

The USGS geological and geochemical teams 

collected data, rock samples, and stream-sediment 

samples during June 1986. Geologic data were used to

map and define formation boundaries and geologic 

structure within the study area and to relate potential 

mineral resources to the geologic setting. Rock and 

stream-sediment samples were collected from stream 

drainages for geochemical analyses. Rock samples were 

taken along traverses at intervals in the uplands. Rock 

and stream-sediment samples representing individual 

drainage basins were collected to identify source areas 

for minerals.

The USBM team visited the area in July 1986 to 

search for mines and prospects and to canvass records on 

file with the BLM District Office in Worland. The USGS 

visited the area again in September 1986 to measure and 

sample a detailed stratigraphic section of the Lance and 

Fort Union Formations. The field data and photogeologic interpretation were used in compiling the 

reconnaissance geologic map shown in figure 3. These 

data amplify the earlier mapping of the study area by 

Weitz and Love (1952), Horn (1963), and Love and 

Christiansen (1985).

Acknowledgments. We owe thanks to the staff of 

the BLM District Office in Worland for their support 

during our field work. Roger Inman, Area Manager, and 

Phil Bigsby, geologist, provided information from their 

files on access roads and previous geologic studies. 

Geologists Jeanne Colmer-Briemont and Cathy Humphrey made available subsurface records from oil and gas 

exploration, and information on the Neiber and Gebo 

known geologic structures. lan Larsen made a 

photographic record of sample localities and the geologic 

setting of the study area.

APPRAISAL OF IDENTIFIED RESOURCES

By David C. Scott 

U.S. Bureau of Mines

A thorough review of pertinent literature on 

geology, mineralization, and mining activity in the region 

of the study area was done by the Bureau of Mines prior 

to the field examination. In July 1986, two Bureau 

geologists spent four days conducting a field examination 

that focused on searching for mines, prospects, and 

mineral occurrences within the study area and as much as 

1 mile outside of its boundaries. The examination 

included reconnaissance by helicopter and four-wheeldrive vehicle. No mines, prospects, or mineral 

occurrences were found in the study area.

Coal samples were taken from two coal outcrops in 

the Mesaverde Formation about 1 mile south of the study 

area (Scott, 1987). Proximate and ultimate analyses of 

the coal samples were made by Chemex Labs, Inc., 

Sparks, Nev. Further inquiries can be directed to U.S.

B4 Mineral Resources of Wilderness Study Areas Northern Wyoming
Bureau of Mines, Branch of Mineral Land Assessment, 

Intermountain Field Operations Center, Building 20, 

Denver Federal Center, Denver, Colo.

Mining History

The study area is within the Bighorn coal basin of 

Wyoming, where coal mining dates back to the 1890's. 

Although no coal was mined in the study area, 

production from the Gebo coal field, 2 miles southwest of 

the area, amounted to about 90 percent of total 

production from the entire Bighorn coal basin. This coal 

was used for railroad locomotives until the mid-1950's 

(Glass and others, 1975, p. 226).

As of June 1986, BLM files contained no patented 

or unpatented mining claims in the study area. 

Approximately 2 square miles of the extreme southern 

part of the study area, south of Cedar Mountain, is under 

coal lease (fig. 2). As of September 1986, more than 90 

percent of the study area was covered by oil and gas 

leases.

Energy Resources

The study area is located in a region known for 

coal, oil and gas, and geothermal resources. These 

commodities are discussed separately. No identified 

resources were found in the study area.

Coal

The coal beds of the Mesaverde Formation, which 

were mined in the nearby Gebo coal field, also occur 

directly south of the study area. Figure 2 shows the 

approximate limits of the coal beds in the Mesaverde 

Formation. Approximately 1 mile south of the 

southwestern boundary of the study area, two prospect 

pits were found in two coal outcrops in the lower unit of 

the Mesaverde Formation (fig. 2). Both pits are shallow 

and expose thin, shaly coal beds. Except for the outcrops 

in these two pits, the extent of the coal is not known.

Coal in the Gebo field ranks as subbituminous A or 

B, with an average as-received heat value of 10,632 

Btu/lb (Glass and others, 1975, p. 226). The two samples 

of weathered coal taken by the Bureau also ranked 

subbituminous A and B. Both proximate and ultimate 

analyses were performed on each coal sample for 

comparison with samples of coal mined from the nearby 

Gebo coal field (Scott, 1987). Coal beds sampled by the 

Bureau were 1 to 1 ¥2. feet thick, whereas those mined in 

the Gebo field are 6 to 11 feet thick.

Coal beds sampled by the USBM generally dip 10° 

toward the study area. Discounting topographic relief, a 

general dip of 10° on a bed gives about 175 feet of vertical 

cover in a horizontal distance of 1,000 feet; therefore, the 

minimum depth of the coal at the southern boundary of 

the study area is about 875 feet. Based on the projected 

depth of the coal at the southern boundary of the study 

area, the thickness of overburden above the coal beds 

would preclude strip or underground mining of the coal. 

Depth of overburden aside, both analytical results and 

thicknesses of these coal beds are not favorable for 

development of this coal.

Oil and Gas

The study area is within the Bighorn Basin oil and 

gas province (Spencer, 1983, p. M7), one of the most 

productive oil and gas basins in the Rocky Mountain 

region. Most of the oil and gas production comes from 

structural traps located around the margins of the basin. 

The primary producing formations are Mississippian 

carbonate rocks, Pennsylvanian sandstone, Permian 

carbonate rocks, and Cretaceous sandstone. The deep 

part of the basin is relatively unexplored by drilling, but 

probably has been extensively mapped by seismic 

methods (Spencer, 1983, p. M7).

Three holes have been drilled in the study area, in 

T. 45 N., R. 93 W. (fig. 2). All of the holes were dry but 

had shows of oil and gas. The earliest hole, drilled in 1954 

in section 29, was 11,972 feet deep and bottomed in the 

Middle and Upper Pennsylvanian Tensleep Sandstone. 

In section 7, a hole was drilled in 1963 to a depth of 8,733 

feet, bottoming in the Lower Cretaceous Mowry Shale. 

The most recent hole was drilled in section 5, in 1982, to 

a depth of 11,582 feet, bottoming in the Tensleep 

Sandstone. Seven other holes have been drilled within 3 

miles of the study area; most of these holes also had 

shows of oil and gas (U.S. Bureau of Land Management, 

Worland District Office, unpublished data). The closest 

producing oil well is 2.75 miles east of the northeast 

boundary of the study area.

Geothermal Energy

Although the region just south of the study area is 

well known for thermal springs, the USBM investigation 

found no record of geothermal waters or leasing activity 

in the study area. The thermal waters near Thermopolis 

are about 10 miles southwest of the study area; the 

source of heat for these thermal waters has not been 

identified (Breckenridge and Hinckley, 1978, p. 40).

Cedar Mountain Wilderness Study Area B5
108° 10' 108°00'

TIE DOWN 

FLATS

APPROXIMATE 

BOUNDARY OF 

CEDAR MOUNTAIN 

WILDERNESS 

STUDY AREA

washakie County ; 

Hot Springs County

R.95W. R. 94 W. R. 93 W.

EXPLANATION

Coal lease

Mesaverde Formation with coal beds

 Approximate boundary of Gebo coal field 

X Coal prospect showing sample number 

-# Dry hole with oil and gas show

Figure 2. Locations of leases, wells, fields, and geologic structures pertaining to oil, gas, 

and coal production in and near the Cedar Mountain Wilderness Study Area.

B6 Mineral Resources of Wilderness Study Areas Northern Wyoming
ASSESSMENT OF POTENTIAL FOR 

UNDISCOVERED RESOURCES

By Curtis E. Larsen, Randall H. Hill, 

Dolores M. Kulik, and Mark K. Brown, 

U.S. Geological Survey

Geology

The Cedar Mountain Wilderness Study Area lies 

near the southern margin of the Bighorn Basin. Along 

the margins of the basin, Paleozoic, Mesozoic, and Cenozoic sedimentary rocks dip toward the axis of the basin. 

The study area includes the contact between the northeastward dipping Mesozoic and Cenozoic rocks (fig. 3). 

Upper Cretaceous sandstones and shales dip beneath 

sandstones and mudstones of Tertiary age at Cedar 

Mountain. Coal-bearing beds of the Upper Cretaceous 

Mesaverde Formation crop out south of the study area 

but lie several hundred feet beneath Cedar Mountain. 

Paleozoic rocks known for oil and gas production 

elsewhere in the basin lie at still greater depth. The 

Tensleep Sandstone, for example, is found between 

11,000 and 12,000 feet beneath the surface near the 

north boundary of the area.

The sedimentary rocks exposed at the surface of 

the study area belong to four formations of Late 

Cretaceous and Tertiary age. The lowermost is the 

Upper Cretaceous Meeteetse Formation. It consists of 

interbedded shale, siltstone, bentonite, and coal (Horn, 

1963). These easily eroded sediments are generally 

poorly exposed, but excellent exposures are found in the 

eastern portion of Freeman Draw, sec. 12, T. 44 N. R. 94 

W. The upper 300 feet of the Meeteetse Formation is 

exposed at the base of Cedar Mountain, where it is 

overlain by massive sandstones of the Upper Cretaceous 

Lance Formation. Near the contact between these 

formations are paleochannels within the lowest 

sandstone beds of the Lance. These are filled with 

apparent siltstone and thin coal beds of Meeteetse 

affinity. This relationship suggests a conformable contact 

between these formations.

The Lance is mostly sandstone and includes gray 

shale and carbonaceous shale in its lower part. The 

sandstones contain ovoid calcareous concretions. Horn 

(1963), on the basis of mappable lithologic units, 

considered it to be 700 to 1,000 feet thick in the study 

area. We found 1,200 feet of Lance strata, including 

about 800 feet exposed on the south face of Cedar 

Mountain. The contact between the Lance and Meeteetse Formations can be traced in outcrop along the 

western boundary of the area until it dips beneath the 

ground surface in sec. 5, T. 44 N., R. 94 W.

The contact between the Lance and the overlying 

Paleocene Fort Union Formation, which contains the 

earliest Tertiary rocks of the Bighorn Basin, is less clear. 

The Lance and Fort Union are difficult to differentiate 

from one another in the Cedar Mountain area. 

Elsewhere in the Bighorn Basin an angular unconformity 

is locally present between the Lance and Fort Union 

Formations (Weitz and Love, 1952; Horn, 1963). In the 

study area, however, depositional environments were 

apparently gradational, leaving few clear lithologic 

breaks to aid mapping. To maintain continuity with the 

earlier mapping efforts, we have followed Horn (1963) by 

placing the Lance-Fort Union contact at the base of the 

first carbonaceous beds above the relatively organic-free 

sandstones and shales of the Lance. This choice is in 

contrast with recent work by Hartman (1986), who has 

studied the fossil vertebrate fauna from the CretaceousTertiary boundary just east of Cedar Mountain and 

argued, on the basis of paleontology, that much of the 

Lance Formation should be included within the Fort 

Union.

A detailed stratigraphic section measured from the 

base of Cedar Mountain to Tie Down Flats identified as 

much as 3,500 feet of Fort Union rocks in the area. This 

is consistent with Moore's (1961) isopach map of the 

Fort Union Formation and Jepsen and Van Houten's 

(1947) type section for the Polecat Bench Formation 

(equivalent to Fort Union) farther to the north in the 

Bighorn Basin. Similarly, as Jepsen and Van Houten 

have suggested, the Fort Union rests conformably on the 

Lance.

The Fort Union Formation covers nearly the entire 

surface of the study area. It dips gently northward at 

about 10° to 15° from its contact with the Lance 

Formation at Cedar Mountain until it is overlain by the 

Willwood Formation of Eocene age in the core of the 

Neiber syncline at Tie Down Flats.

The Fort Union is a drab, repetitive sequence of 

light-gray siltstones and yellowish brown sandstones. 

Using Horn's (1963) definitions, which include coals and 

lignites within the Fort Union rather than in the Lance 

Formation, the base of the Fort Union is marked by a 

yellowish-brown siltstone containing prominent thin 

lignite beds. These organic-rich beds are overlain by 

alternating gray siltstones and thin, yellowish-brown 

sandstones. Calcareous ovoid concretions within 

sandstones, a characteristic of the Lance Formation, 

persist for at least 300 feet above the lignite beds at the 

base of the section before giving way abruptly to ferruginous concretions that cap thin sandstone beds. The 

ferruginous concretions continue upward throughout the 

stratigraphic section.

Siltstone and shale predominate in the Fort Union; 

sandstones in the unit rarely exceed 10 feet in thickness. 

Deposition was apparently cyclic. Fine-grained lacustrine

Cedar Mountain Wilderness Study Area B7
108° 10' 108°00'

'APPROXIMATE

f BOUNDARYOF 

CEDAR MOUNTAIN 

WILDERNESS 

STUDY AREA

R95W. R. 94 W. R93W.

Figure 3 (above and facing page). Generalized geology of the Cedar Mountain 

Wilderness Study Area. Geology mapped in 1986 by C.E. Larsen and M.K. Brown, partly 

based on earlier mapping by Weitz and Love (1952), Horn (1963), and Love and 

Christiansen (1985).

sediments are overlain by sandstones indicative of lakeshore and river environments. Iron oxide concretions and 

crusts many containing plant fossils cap the 

sandstones. Each sandstone, in turn, is covered by 

another siltstone-sandstone-concretion sequence. These 

cyclic units average about 20 feet in thickness in the lower 

portion of the formation. In the middle portion of the 

formation siltstones tend to predominate. Here, some 

individual siltstone beds are 60 to 80 feet thick. These 

fine-grained, easily erodible sediments are well exposed 

along Walters Draw (sees. 33, 34, and 35, T. 45 N., R. 94

W.) and beneath the adjacent high ridge (altitude 5360 

feet) in section 35, where they are protected from further 

erosion by a thick quartzite cobble and gravel deposit of 

probable early Pleistocene or late Tertiary age.

The thick siltstones of the middle portion of the 

section are overlain by approximately 500 feet of closely 

spaced cyclic units that average 10 to 15 feet thick. The 

uppermost 1,000 feet of the Fort Union Formation, 

however, is also predominantly siltstone. While the 

sandstones that cap each cyclic unit are generally less 

than 5 feet thick, the underlying siltstones range in

B8 Mineral Resources of Wilderness Study Areas Northern Wyoming
Unconformity

CORRELATION OF MAP UNITS

QUATERNARY

>- TERTIARY

Tw

Tfu

Kl

Kmt

Kmu

Kmj^ 

--^Kc

H

-Eocene

-Paleocene

^ Upper 

Cretaceous

Qal 

Qt

Tw

Tfu 

Kl

Kmt

Kmu 

Kml 

Kc

>- CRETACEOUS

LIST OF UNITS 

Alluvium (Quaternary) 

Terrace deposits (Quaternary) 

Willwood Formation (Eocene) 

Fort Union Formation (Paleocene) 

Lance Formation (Upper Cretaceous) 

Meeteetse Formation (Upper Cretaceous) 

Mesaverde Formation (Upper Cretaceous):

Upper member

Lower member 

Cody Shale (Upper Cretaceous)

Contact

Subsurface fault Approximately located; U, upthrown side;

D, downthrown side 

Anticline Showing trace of axial plane and plunge

Syncline Showing trace of axial plane and plunge

thickness from 40 to 60 feet. The greater moisture 

content of the sandstones is reflected by the abundance 

of vegetation on sandstone dip slopes of the upper part of 

the Fort Union.

The Fort Union in this part of the Bighorn Basin is 

overlain conformably by the Eocene Willwood 

Formation (Van Houten, 1944, 1948,1952; Bown, 1979, 

1980). The Willwood Formation is the youngest Tertiary 

formation in this portion of the basin. Subsequent 

formations were apparently removed by erosion. These 

varicolored red, purple, and gray mudstones have a 

gradational contact with the underlying gray siltstones 

and mudstones of the upper part of the Fort Union. They 

are interbedded with yellowish-brown sandstone beds. 

Van Houten (1944) measured 2,500 feet of the Willwood 

in Park County, about 85 miles northwest of the study 

area, and proposed the first occurrence of red banding in 

the sediments as the best criterion for distinguishing it 

from the underlying Fort Union Formation. We have 

followed this scheme for our mapping purposes. Only the

basal 200 to 250 feet of the formation is present in the 

study area. This is a remnant preserved within the core of 

the Neiber syncline in sees. 12 and 13, T. 45 N., R. 94 W., 

and sec. 18, T. 45 N., R. 93 W.

Gravels of Quaternary age overlie earlier rocks 

along the Bighorn River. These deposits underlie terrace 

surfaces that reflect former flood plains and runoff 

conditions (Mackin, 1937; Ritter, 1975; Palmquist, 1983; 

Reheis and others, in press). Reworked alluvial deposits 

related to postglacial and modern river systems underlie 

the modern flood plain. Remnants of earlier alluvial 

surfaces, underlain by quartzite cobble gravel deposits, 

are found sporadically on uplands as much as 1,200 feet 

above the modern flood plains (sec. 35, T. 45 N., R. 94 

W.).

Geologic Structure

The geologic structure of the southern Bighorn 

Basin is important to mineral resource potential in the 

Cedar Mountain Wilderness Study Area, as it affects not 

only the distribution of stratigraphic traps for oil and gas 

(Pierce and others, 1947), but also the distribution of 

source terranes for detrital minerals. The Bighorn Basin 

is a downwarped asymmetrical trough whose axis trends 

northwest-southeast. Along its western margin it is 

adjacent to or is overridden by the Oregon Basin and 

Line Creek faults (fig. 4). This faulting, as well as 

downwarping of the basin, occurred chiefly during the 

Paleocene. It was contemporaneous with the uplift of the 

surrounding mountain ranges and deposition of the Fort 

Union Formation. The Fort Union thickens towards the 

axis of the basin (Moore, 1961; Bown, 1980; Parker and 

Jones, 1986). Parker and Jones (1986) indicate that the 

Oregon Basin fault began moving during deposition of 

the Lance Formation and continued throughout the 

Paleocene. Major movement was complete by the time 

Willwood deposition began. As figure 4 shows, the 

Oregon Basin fault is about 75 miles long and extends 

southeastward to the vicinity of Cedar Mountain. Oil and 

gas well logs (BLM district office, Worland, Wyo.) 

identify faulting of the Lower Permian Park City 

Formation that is consistent with movement on the 

Oregon Basin fault. They also show reverse faulting 

within the Pennsylvanian Tensleep Sandstone beneath 

the Neiber anticline and aligned with the Oregon Basin 

fault. These faults, concealed at depth beneath the north 

and south portions of the study area, might have created 

oil and gas traps.

Early research by Stow (1952) indicated structural 

influences on the occurrence of detrital heavy minerals in 

the Lance, Fort Union and Willwood Formations. He 

identified uplifting areas along the flanks of the basin as 

source terranes. The Lance and Fort Union both

Cedar Mountain Wilderness Study Area B9
109°

45°

20 MILES

I

EXPLANATION

Cenozoic basin fill 

Mesozoic and older rocks

Thrust fault Sawteeth on upper plate

Subsurface fault Linked with folding Tertiary rocks. 

U, upthrown side; D, downthrown side

Anticline Showing trace of axial plane and plunge

Figure 4. Thrust faulting along the western margin of the 

Bighorn Basin (modified from Parker and Jones, 1986).

received heavy minerals derived from earlier Mesozoic 

strata. By the Eocene, however, crystalline basement 

rocks were exposed, and these supplied hornblende to 

the Willwood.

Geochemistry

Bulk samples collected from active alluvium at 38 

sites in and near the study area were used to produce 38 

minus-80-mesh stream-sediment samples and 38 heavymineral panned concentrates. These samples were the 

primary medium selected to represent the heavy-mineral 

component of rock and soil exposed in the drainage 

basins upstream from sample sites. Chemical analyses of 

these stream sediments provide data useful in identifying 

basins which contain unusually high concentrations of 

elements that may be related to mineral occurrences. In 

addition, studies have shown that heavy-mineral 

concentrates derived from stream sediments are a useful 

sample medium in arid-semiarid environments or in

areas of rugged topography, where mechanical erosion 

predominates over chemical erosion (Overstreet and 

Marsh, 1981; Bugrov and Shalaby, 1975).

Fresh, unaltered rock samples were collected from 

outcrops near 34 of the stream-sediment sample sites. 

The actual areal extent of terrane represented by 

geochemical information from a specific sample is not 

known; the sampling program was designed only to 

provide some general information on the geochemical 

nature of the rock units present. A separate suite of 118 

grab samples of rock from outcrops was collected along 

upland traverses. All rock samples were analyzed using 

the same techniques.

In preparation for analysis, the dry streamsediment samples were sieved through 80-mesh (0.17- 

mm) stainless steel sieves. The minus-80-mesh material 

was retained for analysis and pulverized with ceramic 

plates to finer than 100 mesh (0.15 mm) prior to analysis.

To produce the heavy-mineral concentrate, bulk 

stream sediment from active alluvium was first sieved 

through a 10-mesh (2.0-mm) screen. Approximately 

10-15 pounds of the minus-10-mesh sediment was 

panned to remove most of the quartz, feldspar, organic 

materials, and clay material. The panned concentrate was 

then separated into light and heavy fractions using bromoform (heavy liquid, specific gravity 2.86). The light 

fraction was discarded. The material of specific gravity 

greater than 2.86 was further separated into three 

fractions (highly magnetic, weakly magnetic, and nonmagnetic) using a modified Frantz Isodynamic 

Separator. The nonmagnetic fraction was hand ground 

and saved for analysis. These procedures result in a 

sample that contains ore-forming and ore-related 

minerals. This selective concentration of minerals 

permits determination of some elements that are not 

easily detected in bulk stream-sediment samples. Rock 

samples were crushed and then pulverized to finer than 

100 mesh with ceramic plates prior to analysis.

Stream sediments, heavy-mineral panned 

concentrates, and unaltered rock samples were then 

analyzed for 31 elements (Ag, As, Au, B, Ba, Be, Bi, Ca, 

Cd, Co, Cr, Cu, Fe, La, Mg, Mn, Mo, Nb, Ni, Pb, Sb, Sc, 

Sn, Sr, Th, Ti, V, W, Y, Zn, and Zr) using a six-step 

semiquantitative emission spectrographic method 

(Grimes and Marranzino, 1968). Because of the small 

size of the nonmagnetic heavy-mineral concentrates, they 

were only analyzed spectrographically. The rock and 

minus-80-mesh stream-sediment samples were also 

analyzed for As, Bi, Cd, Sb, and Zn using an inductively 

coupled argon plasma-atomic emission spectrograph 

(Crock and others, 1987), and they were analyzed fluorometrically for uranium and by atomic absorption 

spectrometry for gold (O'Leary and Meier, 1986). A 

complete listing of all analyses, elements and their lower

B10 Mineral Resources of Wilderness Study Areas Northern Wyoming
limits of determination, a sample locality map, and rock 

sample descriptions are included in Hill and others 

(1988).

Threshold values, defined as the upper limits of 

normal background values, were determined for each 

element by inspection of frequency distribution 

histograms for all three sample media. Geochemical 

concentrations higher than the threshold values are 

considered anomalous and worthy of scrutiny as possible 

indicators of mineralization.

Geochemical analyses show that the unaltered rock 

and minus-80-mesh stream-sediment samples are all well 

within normal background levels, except for two rock 

samples which show concentrations of 21 and 34 ppm 

(parts per million) arsenic. The arsenic probably derives 

from arsenate substituting for phosphate in fluorapatite 

(Palache and others, 1951), which has been identified by 

X-ray diffraction analysis in these samples. It is not 

believed to indicate any mineral deposit.

Geochemical values in nonmagnetic heavy-mineral 

concentrates reflect high concentrations of barium (all 

samples had 10,000 ppm or greater), zirconium (all 

samples had more than 2,000 ppm), and titanium (76 

percent of the samples had 2 percent or more). Barite, 

zircon, and rutile, respectively, were identified by X-ray 

diffraction as the major mineral constituents of the 

heavy-mineral concentrates containing these elements. 

The barite is considered to be authigenic; zircon and 

rutile are believed to be products of mechanical 

weathering and erosion of the surrounding surface rocks. 

All three of these heavy minerals were reported in the 

Fort Union Formation by Stow (1952). They have been 

concentrated in stream alluvium and further 

concentrated by panning. Nominally high strontium 

concentrations in the heavy-mineral concentrates (1,500 

to 3,000 ppm) most likely reflect strontium contained in 

barite in the concentrates. Yttrium, which has high values 

of 300 to 1,000 ppm, may reside in both zircon and 

fluorapatite (Palache and others, 1951). The source of 

detectable tin (20 to 100 ppm) is not known.

Three high concentrations of gold (20, 30, and 100 

ppm) and one high silver value (3 ppm) were detected by 

emission spectrography in the heavy-mineral concentrates. The areal extent of the gold and silver is very 

limited. No other gold or silver was detected in any other 

samples of any type. Even the rock and minus-80-mesh 

stream-sediment samples, which were analyzed for gold 

by the more sensitive atomic absorption spectrometric 

method (lower detection limit of 50 parts per billion), 

had none.

Geophysics

Gravity and magnetic studies undertaken as part of 

the mineral resource evaluation of the Cedar Mountain

Wilderness Study Area provide information on the 

subsurface distribution of rock masses and the structural 

framework. The gravity and magnetic data are of a 

reconnaissance nature and are adequate only to define 

regional geologic features.

The gravity data were obtained in and adjacent to 

the study area by D.M. Kulik in 1986 and were 

supplemented by data maintained in the files of the 

Defense Mapping Agency of the Department of Defense. 

Stations measured were established using a Worden 

gravimeter W-177. The data were tied to the 

International Gravity Standardization Net 1971 (U.S. 

Defense Mapping Agency Aerospace Center, 1974) at 

base station ACIC 16611 at Shoshoni, Wyo., 40 miles 

south of the study area. Station elevations were obtained 

from benchmarks, spot elevations, and estimates from 

topographic maps at 1:24,000 and 1:62,500 scales; most 

are accurate to within 20 feet, though errors as large as 

40 feet are possible for some stations. The error in the 

Bouguer anomaly resulting from the errors in elevation 

control is less than 2.5 milligals. Bouguer anomaly values 

were computed using the 1967 gravity formula 

(International Association of Geodesy, 1976), a 

reduction density of 2.67 grams per cubic centimeter, and 

mathematical formulas given in Cordell and others 

(1982). Terrain corrections were made by computer for a 

distance of 100 miles from the station using the method 

of Plouff (1977). The data are shown in figure 5 as a 

complete Bouguer anomaly map with a contour interval 

of 5 milligals.

Magnetic data are from Bendk Field Engineering 

Corporation (1982). Flight lines were flown east-west at 

2- to 5-milc intervals and at 400 feet elevation above the 

ground. The data are shown in figure 6 as a residual 

intensity magnetic map with a contour interval of 20 

gammas.

In the central part of the Bouguer anomaly map 

(fig. 5), low gravity values in the study area reflect the 

low-density sedimentary rocks of the Bighorn Basin. 

Higher values north and south of the study area derive 

from crystalline rocks of the Owl Creek uplift to the 

south and the Bighorn uplift northeast of the area shown 

on the maps. These data indicate that the gravity axis of 

the basin is offset to the south of the mapped axis. This 

offset suggests either that a deep trough developed in 

front of the northeastward-directed Oregon Basin fault, 

or that the sediments shed from the south into this part of 

the basin were less dense than those deposited elsewhere 

in the basin. In addition, the data indicate that the basin 

narrows in the study area and a lobe of higher density 

rocks extends westward from the Bighorn uplift into the 

area north of Cedar Mountain. The steep gradient at the 

southern boundary of the study area suggests that the 

fault mapped to the east is continuous with the Oregon

Cedar Mountain Wilderness Study Area B11
108°

APPROXIMATE BOUNDARY

OF CEDAR MOUNTAIN 

WILDERNESS STUDY AREA

EXPLANATION

 175 Gravity contour Number shows complete Bouguer anomaly in milligals

 Gravity station

T"" y r~ Thrust fault Sawteeth on upper plate

__ D

" "".."" Subsurface fault U, upthrown side; D, downthrown side

 T > Anticline Showing trace of axial plane and plunge

 " f~~ ^ Syncline Showing trace of axial plane and plunge

Figure 5. Complete Bouguer gravity anomaly and generalized structure in and near Cedar 

Mountain Wilderness Study Area. Geologic structure modified from Ver Ploeg (1985).

B12 Mineral Resources of Wilderness Study Areas Northern Wyoming
108°15' 108"

APPROXIMATE BOUNDARY

OF CEDAR MOUNTAIN 

WILDERNESS STUDY AREA

10 MILES

 -200-

EXPLANATION

Magnetic contour Number shows residual intensity anomaly in gammas

Thrust fault Sawteeth on upper plate

 Subsurface fault U, upthrown side; D, down thrown side

Anticline Showing trace of axial plane and plunge 

Syncline Showing trace of axial plane and plunge

Figure 6. Residual intensity magnetic anomaly and generalized structure in and near the 

Cedar Mountain Wilderness Study Area. Letter A marks an anomaly discussed in text. 

Geologic structure modified from Ver Ploeg (1985).

Cedar Mountain Wilderness Study Area B13
Basin fault, which is associated with a similar basinbounding gradient for at least 75 miles to the northwest. 

A magnetic high (A) near the southern boundary 

of figure 6 is part of a more extensive high that extends to 

the south (Bendix Field Engineering Corporation, 1982) 

and is caused by crystalline rocks of the Owl Creek uplift. 

The magnetic low north of magnetic high A probably is 

due largely to the dipole effect, but may be enhanced by 

nonmagnetic Paleozoic rocks on the flank of the uplift. 

The high magnetic values at the north edge of figure 6 

reflect the crystalline rocks of the Bighorn uplift a few 

miles farther to the northeast. The relatively high 

magnetic values just north of the study area result from 

crystalline rocks beneath the basin in a westward 

extension of the Bighorn uplift, as discussed in the 

previous paragraph. Magnetic values are moderate over 

the Cedar Mountain area. The offset in the -240 and -260 

contours as they cross the area suggests, as do the gravity 

data, that the fault to the east continues through the 

study area and connects with the Oregon Basin fault.

Mineral and Energy Resources

Metals

The available geologic and geochemical data 

suggest that the Cedar Mountain Wilderness Study Area 

has no resource potential for metals other than gold, with 

certainty level D. The geologic terrane consists of finegrained, semi-indurated sedimentary rocks. There are no 

known plutonic sources for metals or mineralizing fluids 

in the vicinity. Similarly, the rocks of the area show no 

evidence of mineralization or hydrothermal alteration.

Minerals present in the surface rocks are mostly 

detrital. Geochemical analyses show that all metals in 

these rocks except gold and silver are at or below the 

normal concentrations for sandstones (Turekian, 1977). 

Gold was detected in the nonmagnetic heavy-mineral 

fractions of three samples, and silver in one of these. A 

sample containing 30 ppm gold and 3 ppm silver was 

collected at the mouth of a short ravine in sec. 6, T. 45 N., 

R. 93 W., adjacent to the Bighorn River. Another sample, 

which had a gold content of 100 ppm, came from a 

stream drainage in sec. 12, T. 45 N., R. 94 W. A third 

sample, with 20 ppm gold, was recovered from a stream 

drainage in sec. 24, T. 45 N., R. 94 W. These drainage 

basins are shown in figure 1. Inasmuch as gold was 

absent from all samples of the surrounding rocks, even 

when they were analyzed by more sensitive atomic 

absorption spectrometry, it is highly unlikely that the gold 

was derived from paleoplacer deposits in the Fort Union 

Formation. It is possible, however, that the gold 

recovered from section 12 was derived from a basal 

conglomerate of fine-gravel size in the adjacent Willwood

Formation. Fine-grained gold has been reported from 

conglomerates in the Upper Cretaceous Harebell 

Formation and the Upper Cretaceous and Paleocene 

Pinyon Formation of Jackson Hole, 130 miles west of the 

study area (Antweiler and Love, 1967; Lindsey, 1972). 

Thus, coarse-grained facies in the Willwood may contain 

reworked gold from earlier paleoplacers. More likely 

sources are the Quaternary terrace gravels that once 

bordered the Bighorn River flood plain, and quartzite 

cobble gravels that cap the uplands upstream from both 

of the latter samples. For example, gold was recovered 

from similar alluvial deposits along the Wind River and 

Bighorn River south of Thermopolis (Schrader, 1915).

The alluvial deposits derived from the surrounding 

rocks in this part of the study area are exceedingly thin. 

Though Quaternary terrace gravels are preserved as 

remnants along the edges of the Bighorn River valley, 

none are present at the three sample sites. However, 

fine-grained gold may have been left as a lag deposit from 

gravels that were eroded from the area. Another possible 

source is the small remnant of quartzite-cobble gravels 

that cap the uplands in sec. 35, T. 45 N., R. 94 W., 

upstream from two of the sample sites. These deposits, 

however, are thin and sparsely distributed in the study 

area. Notwithstanding anomalous gold concentrations in 

three samples, the combined data suggest only a 

moderate potential for the occurrence of undiscovered 

gold resources in the three small drainages these samples 

represent, at certainty level C. There is no potential for 

gold resources in the remainder of the study area, at 

certainty level D.

Oil and Gas

The geologic evidence from this portion of the 

Bighorn Basin presented by Spencer (1983), the results 

of previous oil and gas exploration in the study area, and 

the structural and geophysical data presented here 

suggest a moderate resource potential for undiscovered 

oil and gas, with certainty level C, in two parts of the 

study area. The possible extension of the Oregon Basin 

thrust fault beneath the southern portion of the study 

area and the demonstrated reverse faulting of the Neiber 

anticline, at depth, are subsurface structures that are not 

readily apparent on the surface. The proximity of known 

geologic structures and producing oil fields indicates that 

the subsurface conditions are favorable for the migration 

and accumulation of oil and gas. Traps could exist at 

facies changes within the Middle and Upper Pennsylvanian Tensleep Sandstone and within Lower Permian 

rocks called the Phosphoria Formation by some workers 

and the Park City Formation by others. Traps might also 

exist in porous zones created by movement along the 

Oregon Basin and Neiber anticline faults. Present data 

do not show whether any accumulations of oil or gas exist 

in the study area.

B14 Mineral Resources of Wilderness Study Areas Northern Wyoming
Various groups of researchers have evaluated the 

oil and gas resource potential of the study area with 

various results. Spencer and Powers (1982) assigned it a 

moderate potential. Tetra Tech, Inc. (1983), in a 

consulting study to the BLM, classified the entire study 

area as "highly favorable for the potential occurrence of 

oil and gas resources," on the basis of what they 

considered abundant direct and indirect evidence. The 

BLM (U.S. Bureau of Land Management, 1986) 

similarly suggested a high potential, based on the location 

of the Neiber anticline and the recent lease activity. 

Nevertheless, our assessment of the available data 

suggests only a moderate resource potential for 

undiscovered oil and gas, at certainty level C, along the 

Neiber anticline and the projection of the Oregon Basin 

fault. The oil and gas potential in the remainder of the 

study area is low at certainty level C.

Coal

Coal is found in the Mesaverde Formation at the 

Cowboy Mine, 2 miles south-southwest of Cedar 

Mountain. The beds there are eastward extensions of 

thicker coal beds in the Gebo coal field west of the 

Bighorn River. The Mesaverde at the Cowboy Mine dips 

northward at about 10° to 15°, so it probably lies at a 

depth of 800 to 1,000 feet at the southern boundary of the 

study area and at still greater depth farther to the north. 

Coal from this portion of the Mesaverde Formation in 

the Gebo coal field ranked as subbituminous A and B 

and had a heat value of 10,632 Btu/lb (Glass and others, 

1975, p. 226). Samples taken from the Cowboy Mine by 

the USBM (Scott, 1986, and this study) gave those coals 

a comparable rank.

Other coal or lignite beds crop out within the study 

area, in the Meeteetse and Fort Union Formations. 

Carbonaceous shales mixed with subbituminous coal in 

beds as much as 4 to 5 feet thick are exposed at the base 

of Cedar Mountain. We measured only four thin, 1- to 

2-foot beds of lignite within the Fort Union Formation 

during our field research. The mineral resource potential 

for coal is low in the southern part of the Cedar 

Mountain Wilderness Study Area, at a certainty level of 

C. No resource potential for coal exists in the remainder 

of the study area, at certainty level D.

Geothermal Energy

Although hot springs occur 10 miles south of the 

area at Thermopolis, we found no published information 

regarding geothermal waters or leasing activity. In 

addition, no geologic evidence, such as sinter or hot 

springs, has been found to indicate past or present

geothermal activity in the study area. These data show 

the study area has no potential for geothermal resources, 

with a certainty level D.

Uranium

Tertiary rocks have been a focus of uranium 

prospecting since Love (1952) reported roll-front 

uranium concentrations in sandstones of the Eocene 

Wasatch Formation in the Powder River Basin. The 

Eocene Willwood Formation and the Paleocene Fort 

Union Formation in the Bighorn Basin each contain 

lithologic associations of channel sandstones, lignites, 

and siltstones that host redox or roll-front type uranium 

deposits (Boberg, 1981). Samples of rock and stream 

sediment collected from both of these formations in the 

study area show concentrations of uranium much less 

than 1 ppm. These observations are consistent with those 

of Harris (1983), who reported no uranium anomalies 

within the Fort Union, Willwood, or Tatman Formations 

in the Bighorn Basin. The available geologic and 

geochemical data suggest at a certainty level of D that 

there is no mineral resource potential for uranium in the 

Cedar Mountain Wilderness Study Area.

Sand and Gravel

The proximity of the Bighorn River to the study 

area ensures that ample sand and gravel resources are 

present nearby. The majority of sand and gravel deposits 

are beneath the high Pleistocene river terraces, which are 

generally along the west side of the river, just outside the 

western border of the study area. Gravels beneath 

terrace surfaces are prevalent on the east side of the river 

north of the study area. Indeed, the few sand and gravel 

deposits within the borders of the wilderness study area 

occur as perched remnants of earlier land surfaces as 

much as 1,200 feet above the flood plain of the Bighorn 

River. There is no industrial mineral resource potential 

for sand and gravel, at a certainty level of D.

REFERENCES CITED

Antweiler, J.C., and Love, J.D., 1967, Gold-bearing 

sedimentary rocks in northwest Wyoming A 

preliminary report: U.S. Geological Survey Circular 541, 

12 p.

Bendix Field Engineering Corporation, 1982, Residual 

intensity magnetic anomaly contour map, Thermopolis 

NTMS quadrangle: U.S. Department of Energy Report 

GJM-095(82). Available from U.S. Geological Survey, 

Books and Open-File Reports Section, Box 25425, DFC, 

Denver, CO 80225.

Boberg, W.W., 1981, Some speculations on the development of 

central Wyoming as a uranium province, in Energy 

resources of Wyoming: Wyoming Geological Association 

Guidebook, 32d Annual Field Conference, 1981, p. 

161-180.

Cedar Mountain Wilderness Study Area B15
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the Sand Creek fades, lower Willwood Formation 

(Lower Eocene), Washakie County, Wyoming: 

Geological Survey of Wyoming Memoir 2, 151 p.

____ 1980, Summary of latest Cretaceous and Cenozoic 

sedimentary, tectonic, and erosional events, Bighorn 

Basin, Wyoming, in Gingerich, P.O., ed., Early Cenozoic 

paleontology and stratigraphy of the Bighorn Basin, 

Wyoming: University of Michigan Papers on 

Paleontology 24, p. 25-32.

Breckenridge, R.M., and Hinckley, B.S., 1978, Thermal springs 

of Wyoming: Geological Survey of Wyoming Bulletin 60, 

104 p.

Bugrov, V.A., and Shalaby, I.M., 1975, Geochemical 

prospecting in the Eastern Desert of Egypt, in Elliot, I.L., 

and Fletcher, W.K., eds., Geochemical exploration 1974: 

Amsterdam, Elsevier, Developments in Economic 

Geology, no. 1, p. 523-530.

Cordell, Lindreth, Keller, G.R., and Hildenbrand, T.G., 1982, 

Bouguer gravity map of the Rio Grande rift, Colorado, 

New Mexico, and Texas: U.S. Geological Survey Geophysical Investigations Series Map GP-949, scale 

1:1,000,000.

Crock, J.G., Briggs, P.H., Jackson, L.L., and Lichte, F.E., 1987, 

Analytical methods for the analysis of stream sediments 

and rocks from wilderness study areas: U.S. Geological 

Survey Open-File Report 87-84, 35 p.

Glass, G.B., Westervelt, K., and Oviatt, C.G., 1975, Coal 

mining in the Bighorn Basin of Wyoming, in Exum, F.A., 

and George, G.R., eds., Geology and mineral resources 

of the Bighorn Basin: Wyoming Geological Association 

Guidebook, 27th Annual Field Conference, 1975, p. 

221-227.

Goudarzi, G.H., compiler, 1984, Guide to preparation of 

mineral survey reports on public lands: U.S. Geological 

Survey Open-File Report 84-787, 42 p.

Grimes, D.J., and Marranzino, A.P., 1968, Direct-current arc 

and alternating-current spark emission spectrographic 

field methods for the semiquantitative analysis of 

geologic materials: U.S. Geological Survey Circular 591, 

6 p.

Harris, R.E., 1983, Uranium and thorium in the Bighorn Basin, 

in Geology of the Bighorn Basin: Wyoming Geological 

Association Guidebook, 34th Annual Field Conference, 

1983, p. 171-178.

Hartman, J.E., 1986, Paleontology and biostratigraphy of lower 

part of Polecat Bench Formation, southern Bighorn 

Basin, Wyoming: University of Wyoming Contributions 

to Geology, v. 24, p. 11-63.

Hill, R.H., Hopkins, T.M., Fey, T.L., and Taylor, C.F., 1988, 

Analytical results and sample locality map of rock, 

stream-sediment, and heavy-mineral-concentrate 

samples from the Cedar Mountain Wilderness Study 

Area (WY-010-222), Hot Springs and Washakie 

Counties, Wyoming: U.S. Geological Survey Open-File 

Report, in press.

Horn, G.H., 1963, Geology of the east Thermopolis area, Hot 

Springs and Washakie Counties, Wyoming: U.S. 

Geological Survey Oil and Gas Investigations Map 

OM-213, scale 1:48,000.

International Association of Geodesy, 1976, Geodetic 

reference system, 1976: International Association of 

Geodesy Special Publication 3, 116 p.

Jepsen, G.L., and Van Houten, F.B. [1947], Early Tertiary 

stratigraphy and correlations, Wyoming Geological 

Association Guidebook, [2d Annual] Field Conference, 

Bighorn Basin, Aug. 1947, p. 142-149.

Lindsey, D.A., 1972, Sedimentary petrology and paleocurrents 

of the Harebell Formation, Pinyon Conglomerate, and 

associated coarse clastic deposits, northwestern Wyoming: U.S. Geological Survey Professional Paper 734-B, 

68 p.

Love, J.D., 1952, Preliminary report on uranium deposits in the 

Pumpkin Buttes area, Powder River Basin, Wyoming: 

U.S. Geological Survey Circular 176, 37 p.

Love, J.D., and Christiansen, A.C., compilers, 1985, Geologic 

map of Wyoming: U.S. Geological Survey, 3 sheets, scale 

1:500,000.

Mackin, J.H., 1937, Erosional history of the Big Horn Basin, 

Wyoming: Geological Society of America Bulletin, v. 48, 

p. 813-893.

Moore, D.A., 1961, Isopachous map Fort Union Formation, 

Bighorn Basin, in Symposium on Late Cretaceous rocks, 

Wyoming and adjacent areas: Wyoming Geological 

Association Guidebook, 16th Annual Field Conference, 

1961, p. 200-203.

O'Leary, R.M., and Meier, A.L., 1986, Analytical methods used 

in geochemical exploration, 1984: U.S. Geological Survey 

Circular 948, 48 p.

Overstreet, W.C., and Marsh, S.P., 1981, Some concepts and 

techniques in geochemical exploration, in Skinner, B.J., 

ed., Economic Geology Seventy-fifth anniversary 

volume 1905-1980: Lancaster, Pa., Economic Geology 

Publishing Co., p. 775-805.

Palache, Charles, Berman, Harry, and Frondel, Clifford, 1951, 

Halides, nitrates, borates, carbonates, sulfates, 

phosphates, arsenates, tungstates, molybdates, etc., v. 2 

o/The system of mineralogy of James Dwight Dana and 

Edward Salisbury Dana, 7th ed., revised: New York, John 

Wiley and Sons, 1124 p.

Palmquist, Robert, 1983, Terrace chronologies in the Bighorn 

Basin, Wyoming in Geology of the Bighorn Basin: Wyoming Geological Association Guidebook, 34th Annual 

Field Conference, 1983, p. 217-231.

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Upper Cretaceous-lower Tertiary deposition, Bighorn 

Basin, Wyoming, in Garrison, P.B., ed., Geology of the 

Beartooth uplift and adjacent basins: Guidebook, Montana Geological Society and Yellowstone Bighorn 

Research Association Joint Field Conference and 

Symposium, 1986, p. 137-144.

Pierce, W.G., Andrews, D.A., and Keroher, J.K., 1947, 

Structure contour map of the Big Horn Basin, Wyoming 

and Montana: U.S. Geological Survey Oil and Gas 

Investigations Preliminary Map 74.

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based on topography digitized on a geographic grid: U.S. 

Geological Survey Open-File Report 77-535, 45 p.

B16 Mineral Resources of Wilderness Study Areas Northern Wyoming
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Meers, Brainerd, Jr., Madole, R.F., Nelson, A.R., and 

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Geological Association Guidebook, 27th Annual Field 

Conference, 1975, p. 37-44.

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Rivers, Wyoming, in Ransome, F.L., and Gale, H.S., 

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Wilderness Study Area (WY-010-222), Hot Springs and 

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Wyoming in Miller, B.M., ed., Petroleum potential of 

wilderness lands in the western United States: U.S. 

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Miscellaneous Investigations Series Map 1-1547, scale 

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Cedar Mountain Wilderness Study Area B17

APPENDIX
DEFINITION OF LEVELS OF MINERAL RESOURCE POTENTIAL 

AND CERTAINTY OF ASSESSMENT

Definitions of Mineral Resource Potential

LOW mineral resource potential is assigned to areas where geologic, geochemical, and geophysical characteristics define a geologic environment in which the existence of resources is unlikely. This broad 

category embraces areas with dispersed but insignificantly mineralized rock as well as areas with few 

or no indications of having been mineralized.

MODERATE mineral resource potential is assigned to areas where geologic, geochemical, and geophysical 

characteristics indicate a geologic environment favorable for resource occurrence, where interpretations 

of data indicate a reasonable likelihood of resource accumulation, and (or) where an application of 

mineral-deposit models indicates favorable ground for the specified type(s) of deposits.

HIGH mineral resource potential is assigned to areas where geologic, geochemical, and geophysical characteristics indicate a geologic environment favorable for resource occurrence, where interpretations of 

data indicate a high degree of likelihood for resource accumulation, where data support mineral-deposit 

models indicating presence of resources, and where evidence indicates that mineral concentration has 

taken place. Assignment of high resource potential to an area requires some positive knowledge that 

mineral-forming processes have been active in at least part of the area.

UNKNOWN mineral resource potential is assigned to areas where information is inadequate to assign low, 

moderate, or high levels of resource potential.

NO mineral resource potential is a category reserved for a specific type of resource in a well-defined 

area.

Levels of Certainty

U/A

UNKNOWN

POTENTIAL

H/B

HIGH POTENTIAL

M/B 

MODERATE POTENTIAL

L/B

LOW

POTENTIAL

H/C

HIGH POTENTIAL

M/C 

MODERATE POTENTIAL

L/C

LOW

POTENTIAL

H/D

HIGH POTENTIAL

M/D 

MODERATE POTENTIAL

L/D

LOW POTENTIAL

N/D

NO POTENTIAL

I

o

CL

LU 

O

cc 

o

CO

LU

cc

o

_l

LU

B C 

LEVEL OF CERTAINTY

A. Available information is not adequate for determination of the level of mineral resource potential.

B. Available information suggests the level of mineral resource potential.

C. Available information gives a good indication of the level of mineral resource potential.

D. Available information clearly defines the level of mineral resource potential.

Abstracted with minor modifications from:

Taylor, R. B., and Steven, T. A., 1983, Definition of mineral resource potential: Economic Geology,

v. 78, no. 6, p. 1268-1270. 

Taylor, R. B., Stoneman, R. J., and Marsh, S. P., 1984, An assessment of the mineral resource potential

of the San Isabel National Forest, south-central Colorado: U.S. Geological Survey Bulletin 1638, p.

40-42. 

Goudarzi, G. H., compiler, 1984, Guide to preparation of mineral survey reports on public lands: U.S.

Geological Survey Open-File Report 84-0787, p. 7, 8.
RESOURCE/RESERVE CLASSIFICATION

IDENTIFIED RESOURCES

Demonstrated

Measured Indicated

Inferred

UNDISCOVERED RESOURCES

Hypothetical

Probability Range 

(or)

Speculative

ECONOMIC

MARGINALLY 

ECONOMIC

SUBECONOMIC

Reserves Inferred Reserves

Marginal Reserves

Demonstrated 

Subeconomic Resources

Inferred 

Marginal Reserves

Inferred

Subeconomic

Resources

Major elements of mineral resource classification, excluding reserve base and inferred reserve base. Modified from McKelvey, 1972, Mineral 

resource estimates and public policy: American Scientist, v.60, p.32-40, and U.S. Bureau of Mines and U.S. Geological Survey, 1980, 

Principles of a resource/reserve classification for minerals: U.S. Geological Survey Circular 831, p.5.
GEOLOGIC TIME CHART 

Terms and boundary ages used in this report

EON

Phanerozoic

Proterozoic

Archean 

pre-Ar<

ERA

Cenozoic

Mesozoic

Paleozoic

Late Proterozoic

Middle Proterozoic

Early Proterozoic

Late Archean

Middle Archean

Early Archean 

;hean2

PERIOD

Quaternary

Tertiary

Neogene 

Subperiod

Paleogene 

Subperiod

Cretaceous

Jurassic

Triassic

Permian

Carboniferous 

Periods

Pennsylvanian

Mississippian

Devonian

Si urian

Ordovician

Cambrian

 _3800?~ -

EPOCH

Holocene

Pleistocene

Pliocene

Miocene

Oligocene

Eocene

Paleocene

Late 

Early

Late 

Middle 

Early

Late

Middle 

Early

Late

Early

Late 

Middle 

Early

Late 

Early

Late 

Middle 

Early

Late 

Middle 

Early

Late 

Middle 

Early

Late 

Middle 

Early

 -

BOUNDARY AGE 

IN 

MILLION YEARS

-0.010

- 1.7

- 5

- 38

- 55

_ CC

- 96

1 «5O

- 205

-A/ 240

- 290 

-~ 330

ocn

- 410

- 500 

L~ 570 1

- 900

- 1600

- 2500

- 3000 

- 3400

1 Rocks older than 570m.y. also called Precambrian, a time term without specific rank. 

1 Informal time term without specific rank.

* US. GPO: 1988 573-047/85005
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f * -^ i