U.S. Department of the Interior

U.S. Geological Survey

Scientific Investigations Report 2016–5089–E

Version 1.1, October 2016

Prepared in cooperation with the Bureau of Land Management

Geology and Mineral Resources of the Southwestern and 

South-Central Wyoming Sagebrush Focal Area, Wyoming, 

and the Bear River Watershed Sagebrush Focal Area, 

Wyoming and Utah

Chapter E of

Mineral Resources of the Sagebrush Focal Areas of Idaho, Montana, Nevada, 

Oregon, Utah, and Wyoming
COVER. View looking southeast from the east flank of South Mountain, Wyoming (between the Fossil Basin and Fontenelle blocks). 

Topography and vegetation is typical of much of the study area. Phosphate was mined from the Phosphoria Formation at South Mountain for 

a few years after World War II. The target bed was less than 1.4 m thick and contained 21 percent P2

O5. Photograph by Anna Wilson, U.S. 

Geological Survey, 2010.
Geology and Mineral Resources of the 

Southwestern and South-Central Wyoming 

Sagebrush Focal Area, Wyoming, and the 

Bear River Watershed Sagebrush Focal Area, 

Wyoming and Utah

By Anna B. Wilson, Timothy S. Hayes, Mary Ellen Benson, Douglas B. Yager, Eric D. 

Anderson, Donald I. Bleiwas, Jacob DeAngelo, Connie L. Dicken, Ronald M. Drake II, 

Gregory L. Fernette, Stuart A. Giles, Jonathan M.G. Glen, Jon E. Haacke, John D. Horton, 

Heather L. Parks, Barnaby W. Rockwell, and Colin F. Williams

Chapter E of

Mineral Resources of the Sagebrush Focal Areas of Idaho, Montana, 

Nevada, Oregon, Utah, and Wyoming

Edited by Warren C. Day, Thomas P. Frost , Jane M. Hammarstrom, and Michael L. Zientek

Prepared in cooperation with the Bureau of Land Management

Scientific Investigations Report 2016–5089–E

Version 1.1, October 2016

U.S. Department of the Interior

U.S. Geological Survey
U.S. Department of the Interior

SALLY JEWELL, Secretary

U.S. Geological Survey

Suzette M. Kimball, Director

U.S. Geological Survey, Reston, Virginia 

First release: 2016

Revised: October 26, 2016 (ver. 1.1)

For more information on the USGS—the Federal source for science about the Earth,

its natural and living resources, natural hazards, and the environment—visit

http://www.usgs.gov/ or call 1–888–ASK–USGS (1–888–275–8747).

For an overview of USGS information products, including maps, imagery, and publications,

visit http://store.usgs.gov.

Any use of trade, firm, or product names is for descriptive purposes only and does not imply

endorsement by the U.S. Government.

Although this information product, for the most part, is in the public domain, it also may

contain copyrighted materials as noted in the text. Permission to reproduce copyrighted items

must be secured from the copyright owner.

Suggested citation:

Wilson, A.B., Hayes, T.S., Benson, M.E., Yager, D.B., Anderson, E.D., Bleiwas, D.I., DeAngelo, J., Dicken, C.L., Drake, 

R.M., II, Fernette, G.L., Giles, S.A., Glen, J.M.G., Haacke, J.E., Horton, J.D., Parks, H.L., Rockwell, B.W., and Williams, 

C.F., 2016, Geology and mineral resources of the Southwestern and South-Central Wyoming Sagebrush Focal Area, 

Wyoming, and the Bear River Watershed Sagebrush Focal Area, Wyoming and Utah, (ver. 1.1, October 26, 2016): U.S. 

Geological Survey Scientific Investigations Report 2016–5089–E, 128 p., http://dx.doi.org/10.3133/sir20165089E.

ISSN 2328-0328 (online)
 iii

Acknowledgments

We appreciate the many people, both named and unnamed, who have made contributions to this 

report. For all they have done, we are grateful.

We wish to thank Tom Drean, Wayne Sutherland, and Bob Gregory from the Wyoming State Geological Survey, who not only discussed Wyoming geology by phone but also came to Colorado to 

participate in the initial delineation of mineral resources tracts. We also thank their colleagues 

Chris Carroll, for his advice on the coal assessment, and Karl Taboga, Jim Rodgers, David Lucke, 

and Suzanne Luhr, who provided a variety of information.

Ken Krahulec and Andrew Rupke of the Utah Geological Survey helped clarify questions on the 

geology and mineral resources of Utah and participated in the mineral assessment tract delineation by conference call and WebEx.

Scott Murrellwright and Adam Merrill of the Bureau of Land Management (BLM) made suggestions to improve the accuracy of the report introduction and citations to BLM regulations and 

procedures.

Within the U.S. Geological Survey (USGS), contributions have come from many corners. The National Minerals Information Center (NMIC) group, collectively, has been a huge help in providing 

production information and expertise in the industrial (mostly nonmetallic) minerals.

From the USGS Central Energy Science Center, we thank Mark Hannon and Susan Hall, who 

directed us to additional uranium information, and Gregory L. Gunther and Aimee E. Graeber, who 

provided GIS support for the oil and gas section. Jeremy Havens redrafted a number of the nonGIS-based figures.

The geographic information system (GIS) team, including Carma San Juan and Paul Denning, has 

performed miracles.

Thanks to providers of all the data relied on for the report, especially those not involved in writing the Wyoming-Utah report—Kathy Tureck, Steve Smith, and Karen Kelley.

Leaders of the related Sagebrush Mineral Resource Assessment (SaMiRA) studies based in 

Denver, Colorado—Karen Lund for Idaho and Jeff Mauk for Montana—encouraged teamwork 

and supplied support and encouragement of many kinds.

Thank you to Rob Robinson and Jane Hammarstrom for their guidance through the assessment 

process and to Ed du Bray for sharing his understanding of specific deposit types.

Michael L. Zientek wrote the template that this report is based on: without it, the writing process 

would not have gone so quickly or smoothly. Warren Day and Tom Frost provided project leadership and kept us on track.

Reviewers of the manuscript, Klaus Schulz and Bill Cannon, are gratefully acknowledged.

Finally, thank you to the staff of the USGS Science Publishing Network, especially our primary 

editor, James Hendley, and Claire Landowski, who did both an edit and a geologic names review.
iv 

Contents

Acknowledgments........................................................................................................................................iii

Executive Summary.......................................................................................................................................1

Mining and Mineral Exploration Activity in the Study Areas ........................................................1

Southwestern and South-Central Wyoming 

Study Area.......................................................................................................................2

Past Mining Activity ...........................................................................................................2

Recent Mining Activity.......................................................................................................2

Mine Production Data........................................................................................................3

Active Exploration ..............................................................................................................3

Bear River Watershed Study Area............................................................................................4

Past Mining Activity ...........................................................................................................4

Recent Mining Activity.......................................................................................................4

Mine Production Data........................................................................................................4

Active Exploration...............................................................................................................4

Leasable ........................................................................................................................................4

Locatable.......................................................................................................................................4

Mineral-Potential Tracts....................................................................................................5

Salable...........................................................................................................................................5

Introduction.....................................................................................................................................................5

Lands Involved.......................................................................................................................................6

Southwestern and South-Central Wyoming Study Area.......................................................6

Bear River Watershed Study Area............................................................................................6

Organization of this Report and Terminology ...................................................................................7

Who Did the Work?...............................................................................................................................7

Description of Geology................................................................................................................................14

Physiography ......................................................................................................................................15

Regional Geology and Tectonic Setting..........................................................................................15

Archean and Proterozoic Rocks .............................................................................................15

Paleozoic Rocks.........................................................................................................................15

Mesozoic Rocks.........................................................................................................................19

Cretaceous Rocks......................................................................................................................19

Eocene Magmatism and Contemporaneous Lake System.................................................20

Neogene Extensional Faulting and Volcanism .....................................................................20

Leasable Minerals .......................................................................................................................................21

Oil and Gas...........................................................................................................................................21

Mineral Description...................................................................................................................21

Geology and Occurrence .........................................................................................................21

Exploration and Development..................................................................................................21

Production...................................................................................................................................21

Results of Previous USGS Assessments ...............................................................................22

Geothermal Energy.............................................................................................................................36

Mineral Description...................................................................................................................36
 v

Geology and Occurrence .........................................................................................................37

Exploration and Development..................................................................................................37

Southwestern and South-Central Wyoming Sagebrush Study Area.......................37

Bear River Watershed Study Area.................................................................................37

Results of Previous USGS Assessments ...............................................................................37

Coal........................................................................................................................................................42

Mineral Description...................................................................................................................42

Geology and Occurrence in the Study Area .........................................................................42

Recent Exploration and Mining Activity.................................................................................43

Southwestern and South-Central Wyoming Study Area............................................43

Bear River Watershed Study Area.................................................................................43

Results of Previous USGS Assessments ...............................................................................43

Phosphate ............................................................................................................................................47

Mineral Description...................................................................................................................47

Geology and Occurrence in the Study Area .........................................................................47

Exploration and Mining Activity ..............................................................................................51

Results of Previous USGS Assessments ...............................................................................51

Trace Elements as Potential Byproducts of Elemental Phosphorus and Phosphoric 

Acid Production............................................................................................................51

Vanadium............................................................................................................................51

Uranium ..............................................................................................................................54

Rare Earth Elements.........................................................................................................54

Potash...................................................................................................................................................54

Mineral Description...................................................................................................................54

Geology and Occurrence .........................................................................................................54

Exploration, Development, or Mining and Results of Previous USGS Assessments .....55

Locatable Minerals......................................................................................................................................55

Mineral Potential.................................................................................................................................56

Metallic Locatable Minerals.............................................................................................................57

Hydrothermal-Metamorphic Mineral System.......................................................................64

Orogenic Low-Sulfide Gold-Quartz Veins (Gold Veins)...............................................64

Mineral Description.................................................................................................64

Geology and Occurrence in the Study Area .......................................................64

Exploration and Mining Activity ............................................................................65

Potential for Occurrence........................................................................................65

Economic Analysis ..................................................................................................71

Sedimentary Mineral System ..................................................................................................71

Sediment-Hosted Stratabound Copper Deposits ........................................................74

Mineral Description.................................................................................................74

Geology and Occurrence in the Study Area .......................................................74

Exploration and Mining Activity ............................................................................75

Potential for Occurrence........................................................................................75

Economic Analysis of the Deposit Types.............................................................77

Banded-Iron Formation....................................................................................................77

Mineral Description.................................................................................................77

Geology and Occurrence in the Study Area .......................................................77
vi 

Economic Analysis ..................................................................................................80

Sandstone Roll-Front Uranium .......................................................................................80

Mineral Description.................................................................................................80

Geology and Occurrence in the Study Area .......................................................81

Exploration and Mining Activity ............................................................................91

Potential for Occurrence........................................................................................91

Economic Analysis ..................................................................................................94

Surficial Mineral Deposits System, Including Placers........................................................94

Mineral Description..........................................................................................................95

Geology and Occurrence in the Study Area ................................................................95

Paleoplacer Gold Deposits in the Study Area.....................................................95

Quaternary Placer Gold ........................................................................................101

Coastal Titanium Placer Deposits .......................................................................102

Nonmetallic Locatable Minerals....................................................................................................103

Diatreme-Hosted Diamond (Diamonds in Lamproite)........................................................103

Mineral Description........................................................................................................103

Geology and Occurrence in the Study Area ..............................................................103

Exploration and Mining Activity ...................................................................................104

Potential for Occurrence...............................................................................................106

Economic Analysis .........................................................................................................107

Dolomite.....................................................................................................................................107

Mineral Description........................................................................................................107

Geology and Occurrence in the Study Area ..............................................................107

Exploration and Mining Activity ...................................................................................107

Potential for Occurrence and Economic Analysis ....................................................107

Strategic and Critical Materials ..............................................................................................................107

Salable Minerals........................................................................................................................................107

Sand and Gravel................................................................................................................................107

References Cited........................................................................................................................................108

Appendixes .................................................................................................................................................122

Appendix 1. Mineral Potential Classification System..........................................................................123

Appendix 2. Table of Mineral-Potential Assessment Tracts for Locatable Minerals in the 

Southwestern and South-Central Wyoming Study Area, Wyoming, and Bear River 

Watershed Study Area, Wyoming and Utah............................................................................125

Appendix 3. Geochemical Samples for the Southwestern and South-Central Wyoming Study 

Area, Wyoming, and Bear River Watershed Study Area, Wyoming and Utah ..................126

Appendix 4. Table of Oil and Gas Plays and Assessment Units in the Southwestern and SouthCentral Wyoming Study Area, Wyoming, and Bear River Watershed Study Area, 

Wyoming and Utah.......................................................................................................................127

Appendix 5. Table of Producing Properties in Southwestern Wyoming and 

Northeastern Utah .......................................................................................................................128
 vii

Figures

1. Map showing the Southwestern and South-Central Wyoming and Bear River Watershed 

study areas, Wyoming and Utah, and U.S. Geological Survey study area boundaries ....8

2. Surface land-management map of the Southwestern and South-Central Wyoming and Bear 

River Watershed study areas, Wyoming and Utah...............................................................10

3. Map showing the physiography of the Southwestern and South-Central Wyoming and Bear 

River Watershed study areas, Wyoming and Utah...............................................................12

4. Map showing the geologic and tectonic setting, with mountain ranges and structural 

basins, in Wyoming and surrounding areas...........................................................................14

5. Simplified geologic map of the Southwestern and South-Central Wyoming and Bear River 

Watershed study areas, Wyoming and Utah .........................................................................16

6. Stratigraphic chart of Phanerozoic rock units for the Southwestern and South-Central Wyoming and Bear River Watershed study areas, Wyoming and Utah....................................18

7. Illustration showing categories of oil and natural-gas accumulations ......................................22

8. Generalized stratigraphic column of Southwestern Wyoming Province with numbered total 

petroleum systems .....................................................................................................................23

9. Map showing well type by quarter cell summary of exploration and well type in the Southwestern and South-Central Wyoming and Bear River Watershed study areas, Wyoming and Utah .............................................................................................................................24

10. Maps showing cumulative liquid production from Wyoming oil and gas fields by township 

in the Southwestern and South-Central Wyoming study area, Wyoming, and Bear River 

Watershed study area, Wyoming and Utah ...........................................................................26

11. Maps showing cumulative gas production from Wyoming oil and gas fields by township in 

the Southwestern and South-Central Wyoming study area, Wyoming, and Bear River 

Watershed study area, Wyoming and Utah ...........................................................................30

12. Map showing Federal oil and gas leases and oil and gas provinces within the 

Southwestern and South-Central Wyoming and Bear River Watershed study areas, 

Wyoming and Utah .....................................................................................................................34

13. Map showing the locations of low-, moderate-, and high-temperature geothermal systems 

and geothermal development sites, as well as hydrothermal favorability from the 

2008 U.S. Geological Survey geothermal assessment for an area encompassing the 

Southwestern and South-Central Wyoming and Bear River Watershed study areas, 

Wyoming and Utah .....................................................................................................................38

14. Map showing the locations of low-, moderate-, and high-temperature geothermal systems 

and geothermal development sites, as well as the estimated temperature at 6 km 

depth, for an area encompassing the Southwestern and South-Central Wyoming and 

Bear River Watershed study areas, Wyoming and Utah .....................................................40

15. Map showing the coal regions and mine-permit boundaries in and near the Southwestern 

and South-Central Wyoming and Bear River Watershed study areas..............................44

16. Illustration showing stratigraphic column for southwest Wyoming..........................................46

17. Map showing the Public Land Survey System township and range grid for the entire region 

of the Southwestern and South-Central Wyoming and Bear River Watershed study 

areas .............................................................................................................................................48

18. Correlation chart of Permian Phosphoria and Park City Formations from the northeastern 

Great Basin to the Wyoming shelf ...........................................................................................50

19. Map of the surface extent of Permian and Mississippian phosphorite and phosphatic shale 

in the Southwestern and South-Central Wyoming and Bear River Watershed study 

areas .............................................................................................................................................52
viii 

20. Map showing active and pending mine claims for locatable commodities in the 

Southwestern and South-Central Wyoming and Bear River Watershed study areas, 

Wyoming and Utah...................................................................................................................58

21. Map showing 43 CFR 3809 surface-management authorizations for locatable commodities 

in the Southwestern and South-Central Wyoming and Bear River Watershed study 

areas, Wyoming and Utah.......................................................................................................60

22. Map showing mineral deposits, mines, and important exploration prospects for locatable 

commodities in the Southwestern and South-Central Wyoming and Bear River Watershed study areas, Wyoming, and Utah .................................................................................62

23. Map showing the geology of the South Pass block, Southwestern and South-Central 

Wyoming study area, Wyoming .............................................................................................66

24. Map showing location of orogenic-gold mines and claims, with geology and resource 

potential tracts, in the South Pass block, Southwestern and South-Central Wyoming 

study area, Wyoming ...............................................................................................................68

25. Map showing the mineral-potential tracts for orogenic low-sulfide gold veins in the South 

Pass block, Southwestern and South-Central Wyoming study area, Wyoming............72

26. Map showing sediment-hosted stratabound copper locations relative to thrust faults and 

oil and gas fields in the thrust belt.........................................................................................76

27. Map showing the mineral-potential tracts for sedimentary-hosted copper deposits in the 

Bear River Watershed study area, Wyoming and Utah.....................................................78

28. Schematic showing schematic cross section of a sandstone roll-front uranium deposit..82

29. Map addressing potential for sandstone roll-front uranium deposits in the Big Sandy 

and Continental Divide blocks of the Southwestern and South-Central Wyoming

study area ..................................................................................................................................84

30. Map showing Landsat 7 spectral mineral signature of sandstone roll-front uranium system alteration at the Red Rim area........................................................................................86

31. Map showing Landsat-7 spectral mineral signatures of sandstone roll-front uranium 

system alteration in the Sweetwater district, central Great Divide Basin, Wyoming ..88

32. Map showing Landsat 7 spectral mineral signatures from the intertongued Wasatch and 

Green River Formations in the Fontenelle block, Bear River Watershed study area, 

Wyoming, and their relation to sandstone roll-front uranium system alteration...........92

33. Map showing mineral-potential tracts for sandstone roll-front uranium deposits in the 

Southwestern and South-Central Wyoming and Bear River Watershed study areas, 

Wyoming and Utah...................................................................................................................96

34. Map showing mineral-potential tracts for paleoplacer gold and placer gold in the 

South Pass block of the Southwestern and South-Central Wyoming study area, 

Wyoming ....................................................................................................................................98

35. Map showing mineral-potential tracts for diamonds in lamproites, Leucite Hills, Southwestern and South-Central Wyoming study area, Wyoming..........................................105

1–1. Matrix showing the classification system used for qualitative mineral-resource potential 

for locatable minerals in the Sagebrush Mineral-Resource Assessment......................124
 ix

Tables

1. Status and number of mining claims, mineral leases, mineral material sales sites, and 43 

CFR 3809 surface management authorizations in the proposed withdrawal area within 

the Southwestern and South-Central Wyoming study area, Wyoming, and Bear River 

Watershed study area, Wyoming and Utah .............................................................................2

2. Production data for mines in the Southwestern and South-Central Wyoming study area .......3

3. Acreage of Southwestern and South-Central Wyoming and Bear River Watershed study 

area, Wyoming and Utah.............................................................................................................6

4. Cumulative oil and gas production per township in the Southwestern and South-Central 

Wyoming and Bear River Watershed study areas, Wyoming and Utah............................22

5. Assessed oil and gas potential in the Wyoming Thrust Belt and Southwestern Wyoming 

Provinces .....................................................................................................................................36

6. Summary of mining claims for locatable minerals in sections containing the proposed 

withdrawal area within the Southwestern and South-Central Wyoming study area, 

Wyoming, and Bear River Watershed study area, Wyoming and Utah.............................55

7. Summary of status and number of 43 CFR 3809 surface-management authorizations for 

locatable minerals in the proposed withdrawal area within the Southwestern and 

South-Central Wyoming study area, Wyoming, and Bear River Watershed study area, 

Wyoming and Utah .....................................................................................................................56

8. Active 43 CFR 3809 surface-management authorizations summarized by commodity in the 

proposed withdrawal area within the Southwestern and South-Central Wyoming study 

area, Wyoming, and Bear River Watershed study area, Wyoming and Utah ..................56

9. Mineral deposits, mines, and important exploration prospects that occur in or near the 

Southwest and South-Central Wyoming study area, Wyoming..........................................57

10. Active Bureau of Land Management mineral material authorizations in the proposed 

withdrawal area within the Southwestern and South-Central Wyoming study area, 

Wyoming, and Bear River Watershed study area, Wyoming 

and Utah .....................................................................................................................................108
x 

[U.S. customary units to International System of Units]

Conversion Factors

Multiply By To obtain

Length

inch (in.) 2.54 centimeter (cm)

inch (in.) 25.4 millimeter (mm)

foot (ft) 0.3048 meter (m)

mile (mi) 1.609 kilometer (km)

yard (yd) 0.9144 meter (m)

Area

acre 4,047 square meter (m2

)

acre 0.4047 hectare (ha)

acre 0.4047 square hectometer (hm2

) 

acre 0.004047 square kilometer (km2

)

square foot (ft2

) 929.0 square centimeter (cm2)

square foot (ft2

) 0.09290 square meter (m2)

square inch (in2

) 6.452 square centimeter (cm2)

square mile (mi2

) 259.0 hectare (ha)

square mile (mi2

) 2.590 square kilometer (km2) 

Volume

barrel (bbl; petroleum, 1 barrel=42 gal) 0.1590 cubic meter (m3

) 

Mass

ounce, troy (oz) 31.103 gram (g) 

pound, avoirdupois (lb) 0.4536 kilogram (kg) 

ton, short (2,000 lb) 0.9072 metric ton (t) 

ton, long (2,240 lb) 1.016 metric ton (t) 

[International System of Units to U.S. customary units]

Multiply By To obtain

Length

centimeter (cm) 0.3937 inch (in.)

millimeter (mm) 0.03937 inch (in.)

meter (m) 3.281 foot (ft) 

kilometer (km) 0.6214 mile (mi)

kilometer (km) 0.5400 mile, nautical (nmi) 

meter (m) 1.094 yard (yd) 

Area

square meter (m2

) 0.0002471 acre 

square kilometer (km2

) 247.1 acre

square centimeter (cm2

) 0.001076 square foot (ft2)

square meter (m2

) 10.76 square foot (ft2) 

square centimeter (cm2

) 0.1550 square inch (ft2) 

square kilometer (km2

) 0.3861 square mile (mi2)

Volume

cubic meter (m3

) 6.290 barrel (petroleum, 1 barrel = 42 gal)

cubic meter (m3

) 264.2 gallon (gal) 

cubic meter (m3

) 0.0002642 million gallons (Mgal) 

cubic centimeter (cm3

) 0.06102 cubic inch (in3) 
 xi

Multiply By To obtain

cubic meter (m3

) 35.31 cubic foot (ft3)

cubic meter (m3

) 1.308 cubic yard (yd3) 

cubic kilometer (km3

) 0.2399 cubic mile (mi3) 

cubic meter (m3

) 0.0008107 acre-foot (acre-ft) 

Mass

gram (g) 0.032 ounce, troy (oz)

gram (g) 0.03527 ounce, avoirdupois (oz)

kilogram (kg) 2.205 pound avoirdupois (lb)

metric ton (t) 1.102 ton, short [2,000 lb]

metric ton (t) 0.9842 ton, long [2,240 lb]

Density

kilogram per cubic meter (kg/m3

) 0.06242 pound per cubic foot (lb/ft3) 

gram per cubic centimeter (g/cm3

) 62.4220 pound per cubic foot (lb/ft3) 

Supplemental Information

Temperature in degrees Celsius (°C) may be converted to degrees Fahrenheit (°F) as °F = (1.8 × 

°C) + 32.

Temperature in degrees Fahrenheit (°F) may be converted to degrees Celsius (°C) as °C = (°F – 

32) / 1.8.

Datum

Vertical coordinate information is referenced to the North American Datum of 1983 (NAD 83).

Horizontal coordinate information is referenced to the North American Datum of 1983 (NAD 83).

Altitude, as used in this report, refers to distance above the vertical datum.
xii 

Abbreviations

Ad andradite (iron-rich garnet)

AMIS Automated Minerals Information System

AOC Assessment Oversight Committee

API American Petroleum Institute

AR “as received”

ASTER Advanced Spaceborne Thermal Emission and Reflection Radiometer

ASTM American Society for Testing and Materials

AU assessment unit (oil and gas)

BCF, BCFG billion cubic feet (of gas) 

BHT bottom-hole temperature

BLM Bureau of Land Management

BRW Bear River Watershed (Sagebrush Focal Area)

BV “best value”

CAGR compound annual growth rate

CAI conodont alteration index

CFR Code of Federal Regulations 

CIGS copper-indium-gallium selenide

CSA Canadian Standards Association

CSM clay-sulfate-mica

CSAMT controlled-source audiofrequency magnetotellurics

DLA Defense Logistics Agency

DOD U.S. Department of Defense

DOE U.S. Department of Energy

DOI U.S. Department of the Interior

EGS enhanced geothermal system

EIS Environmental Impact Statement

ETM+ Landsat 7 Enhanced Thematic Mapper Plus

FLPMA Federal Land Policy and Management Act of 1976

f.o.b. free on board

FWS U.S. Fish and Wildlife Service

g/t gram per metric ton

Ga giga-annum or billions of years ago

GFTZ Great Falls Tectonic Zone

GHC Geo-Heat Center
 xiii

GIS geographic information system

HSSR Hydrogeochemical and Stream Sediment Reconnaissance

IDW inverse distance weighted

LEDs light-emitting diodes

LLD lower limit(s) of determination

m.y. millions of years

Ma mega-annum or millions of years ago

MAS Minerals Availability System

MCF thousand cubic feet of gas

MILS Mineral Industry Location System

MMBO million barrels of oil

MMBNGL million barrels of natural gas liquids

MOP muriate of potash

Moz million troy ounces

MRDS Mineral Resources Data System

Mt million metric tons

MTU metric ton unit

MVT Mississippi-Valley-type

MW megawatt

MWe megawatt electricity

NASGLP North American Soils Geochemical Landscape Project

NBMG Nevada Bureau of Mines and Geology

NDS National Defense Stockpile

NEPA National Environmental Policy Act of 1989

NGDB National Geochemical Database

NGL natural gas liquids

NGS National Geochemical Survey

NMIC USGS National Minerals Information Center

NOAA National Oceanic and Atmospheric Administration

NOGA USGS National Oil and Gas Assessment

NURE National Uranium Resource Evaluation

NWR National Wildlife Refuge

opt troy ounce per short ton

oz troy ounce 

PGE platinum-group element
xiv 

PGM platinum-group metal

PLSS Public Land Survey System

ppm parts per million

REE rare earth element

REOE rare earth oxide equivalent(s)

RMOTC Rocky Mountain Oilfield Testing Center

ROD Record of Decision

RTP reduction-to-the-pole or reduced-to-pole

SaMiRA Sagebrush Mineral-Resource Assessment

SEDAR Canadian System for Electronic Document Analysis and Retrieval

SEDEX sedimentary exhalative

SFA Sagebrush Focal Area

SG specific gravity

SI structural index

SOP sulfate of potash

SWIR shortwave-infrared (region of the electromagnetic spectrum)

t metric ton

TCM Tax Court Memorandum

Th/K thorium/potassium ratio

TMI total magnetic intensity

TOMS Topographically Occurring Mine Symbols

TPS total petroleum system

UMOS Utah Mineral Occurrence System

USBM former U.S. Bureau of Mines

USFS U.S. Forest Service

USGS U.S. Geological Survey

USMIN USGS Mineral Deposit Database

VMS volcanogenic massive sulfide

wt.% weight percent

WYO Southwestern and South-Central Wyoming (Sagebrush Focal Area)
 xv

Chemical Symbols and Formulas Used 

Ag silver Gd gadolinium

Al aluminum Ge germanium

Al2

O3 aluminum oxide H hydrogen

Ar argon H2

S hydrogen sulfide

As arsenic Hf hafnium

Au gold Hg mercury

B boron Ho holmium

Ba barium In indium

BaSO4 barium sulfate Ir iridium

Be beryllium K potassium

Bi bismuth K2

O potassium oxide

Br bromine La lanthanum

C carbon Li lithium

Corg organic carbon Lu lutetium

CO carbon monoxide Mg magnesium

CO2 carbon dioxide MgO magnesium oxide

Ca calcium Mn manganese

CaO calcium oxide Mo molybdenum

Cd cadmium N nitrogen

Ce cerium NH3 ammonia

CH4 methane Na sodium

Cl chlorine NaCl sodium chloride

Co cobalt Na2

O sodium oxide

Cr chromium Nb niobium

Cs cesium Nd neodymium

Cu copper Ni nickel

Dy dysprosium O oxygen

Er erbium Os osmium

Eu europium P phosphorous

F fluorine P4 elemental (white) phosphorus

Fe iron PO4 phosphate

Fe2

O3 ferric iron oxide P2O5 phosphorous pentoxide

Ga gallium Pb lead

GaAs gallium arsenide Pd palladium

GaN gallium nitride Pr praseodymium
xvi 

Pt platinum Te tellurium

Rb rubidium Th thorium

Re rhenium Ti titanium

Rh rhodium TiO2 titanium dioxide

Ru ruthenium Tm thulium

S sulfur Tl thallium

Sb antimony U uranium

Sc scandium U3

O8 triuranium octaoxide (yellowcake)

Se selenium V vanadium

Si silicon V2

O5 vanadium pentoxide

SiO2 silicon dioxide (silica) W tungsten

Sm samarium WO3 tungsten trioxide

Sn tin Y yttrium

Sr strontium Yb ytterbium

Ta tantalum Zn zinc

Tb terbium Zr zirconium

Mineral Formulas Used

adularia KAlSi

3

O8

alunite KAl3(SO4)

2

(OH)

6

andradite (garnet) Ca3Fe3+

2

(SiO4)

3

ankerite Ca(Fe,Mg,Mn)(CO3)

2

argentite Ag2S

arsenopyrite FeAsS

barite BaSO4

bornite Cu5FeS4

cassiterite SnO2

chalcocite Cu2S

chalcopyrite CuFeS2

cinnabar HgS

clinoptilolite (zeolite) (Ca,Na,K)2-3Al3

(Al,Si)2Si13O36·12(H2O)

coffinite U[SiO4

,(OH)4]

corderoite Hg3

S2Cl2

dolomite CaMg(CO3)

2

erionite (zeolite) (Ca,Na,K)10[Al10Si26O72]·~30H2O

fluorite CaF2

galena PbS

hectorite (smectite clay) Na3

(Mg,Li)3Si4O10(F,OH)2
 xvii

hematite Fe

2

O

3

ilmenite FeTiO

3

kaolinite Al

2

Si

2

O

5

(OH)

4

leucite K(AlSi

2

O

6

)

magnetite Fe

3

O

4

molybdenite MoS

2

molybdite MoO

3

monazite (Ce,La,Th,Nd)PO

4

montmorillonite (Na,Ca)0.33(Al,Mg)

2

(Si

4

O10)(OH)

2 · nH2

O

nepheline Na

3

KAl

4

Si

4

O16

opal SiO

2

·nH

2

O

phillipsite (zeolite) (Ca,Na,K)4-7[Al4-7Si2-9

O32]·12H

2

O

powellite CaMoO

4

pyrite FeS

2

quartz SiO

2

rutile TiO

2

scheelite CaWO

4

siderite FeCO

3

sillimanite Al

2

SiO

5

sylvite KCl

sylvinite KCl+NaCl

sphalerite (Zn,Fe)S

staurolite Fe

2

Al

9

Si

4

O23(OH)

stilpnomelane (K,Ca,Na)(Fe2+,Mg,Fe3+

)

8

(Si,Al)12(O,OH)27·nH

2

O

tetrahedrite (Cu,Fe,Ag,Zn)12Sb

4

S13

uraninite UO

2

xenotime YPO

4

zircon ZrSiO

4

Geology and Mineral Resources of the Southwestern and 

South-Central Wyoming Sagebrush Focal Area, Wyoming, 

and the Bear River Watershed Sagebrush Focal Area, 

Wyoming and Utah

By Anna B. Wilson, Timothy S. Hayes, Mary Ellen Benson, Douglas B. Yager, Eric D. Anderson, Donald 

I. Bleiwas, Jacob DeAngelo, Connie L. Dicken, Ronald M. Drake, II, Gregory L. Fernette, Stuart A. Giles, 

Jonathan M.G. Glen, Jon E. Haacke, John D. Horton, Heather L. Parks, Barnaby W. Rockwell, and Colin F. 

Williams

Executive Summary

The U.S. Department of the Interior has proposed to 

withdraw approximately 10 million acres of Federal lands 

from mineral entry (subject to valid existing rights) from 

12 million acres of lands defined as Sagebrush Focal Areas 

(SFAs) in Idaho, Montana, Nevada, Oregon, Utah, and Wyoming (for further discussion on the lands involved see Day and 

others, 2016).The purpose of the proposed action is to protect 

the greater sage-grouse (Centrocercus urophasianus) and its 

habitat from potential adverse affects of locatable mineral 

exploration and mining. To inform the decision on whether to 

withdraw the SFAs from mineral entry, the Bureau of Land 

Management requires a mineral-resource assessment be completed to identify mineral resources within the proposed withdrawal area. The USGS Sagebrush Mineral-Resource Assessment (SaMiRA) project was initiated in November 2015 and 

supported by the BLM to (1) assess locatable mineral-resource 

potential and (2) to describe leasable and salable mineral 

resources for the seven SFAs and Nevada additions. 

 This report provides information about mineral 

resources and their potential to occur within study areas that 

include proposed withdrawal areas within the central part 

of the Southwestern and South-Central Wyoming and Bear 

River Watershed, Wyoming and Utah, SFAs. Together, the 

Public Land Survey System (PLSS) townships that contain 

these parcels are referred to as the Wyoming-Utah study area 

(figs. 1 and 2). The methodology used for the assessment for 

locatable mineral resource potential and levels of certainty are 

reviewed in Day and others (2016) and classification criteria 

are described in appendix 1.

Most of the study area is in the greater Green River 

Basin, a paleobasin whose modern topographic expression 

is an intermontane desert covering 51,800 square kilometers 

(km2

) (20,000 square miles, mi2) in southwest Wyoming, 

northeast Utah, and northwest Colorado (Roehler, 1992). The 

structural framework of the greater Green River Basin was 

established during the Laramide orogeny (70–35 million years 

ago or mega-annum, Ma), beginning in the Late Cretaceous. 

Three intrabasin anticlines subdivide the basin into four structural and topographic subbasins (Roehler, 1992).

Eocene sedimentary deposits of lacustrine and fluvial origin dominate the greater Green River Basin area, where they 

are as much as 3,050 m (about 10,000 feet, ft) thick. Important 

rock formations include parts of the intertongued Wasatch, 

Green River, and Bridger Formations. These three Eocene 

strata are important, economically, for their energy, and metallic and nonmetallic resources, and for their abundance of fossil 

fauna and flora (Roehler, 1992).

The “thrust belt” (variously termed overthrust belt, Sevier 

fold and thrust belt, Sevier orogenic belt, fold and thrust belt, 

Wyoming thrust belt, and Wyoming-Idaho-Utah thrust belt in 

the cited literature) forms the western boundary of the Green 

River Basin on the western margin of Wyoming. Folding and 

thrust faulting occurred during the Cretaceous-to-Paleocene 

Sevier orogeny (~130–60 Ma) (Link and DeGrey, 2016).

In Utah, the study area is in Bear River Range (fig. 3) 

and the Wasatch Range (fig. 4). The Wasatch Range is a 

north-south oriented mountain range that extends from Idaho 

south to central Utah. The western flank is very steep and 

relatively straight as a result of displacement along the stillactive Wasatch Fault. The eastern flank rises more gently. The 

Wasatch Range has a core of Archean quartzites, gneisses, and 

schists overlain by Mesozoic sandstones, shales, mudstones, 

and limestones (Moyle, 1981). Locally, Cenozoic conglomerates and shales, interspersed with volcanic tuffs and breccias, 

form the surface layers of strata (Moyle, 1981). By contrast 

to the Wasatch Range, the Bear River Range, located between 

Cache Valley and Bear Lake, is relatively small in area (Banner, 1992).

Mining and Mineral Exploration Activity in the 

Study Areas

Recent mining and mineral activity in the study areas is 

sparse. Currently (2016), there are no active mines or mineral processing plants within the proposed withdrawal area. 
2 Geology and Mineral Resources of the Southwestern and South-Central Wyoming and Bear River Watershed Sagebrush Focal Areas

Beyond the margins of the proposed withdrawal area, but 

inside the study area, there are uranium sites in the Great 

Divide Basin; iron at South Pass; and lode and placer gold 

at South Pass, Atlantic City, and Lewiston, Wyoming. Of 

the nearly 3,000 claims in the study areas, only 13 are active 

(table 1); all are placer claims, and all are in the Southwestern 

and South-Central Wyoming study area. All of these active 

claims fall within the area outlined in this report as having 

potential for lode or placer gold. There are no active claims in 

the Bear River Watershed study area; therefore, none of these 

active claims is within the proposed withdrawal areas. Table 1 

shows the number and status type of all cases that intersect the 

proposed withdrawal area in a specific study area.

Southwestern and South-Central Wyoming 

Study Area

Past Mining Activity

There are 105 mine features shown on USGS 7.5-minute topographic maps of the Southwestern and South-Central 

Wyoming study area, of which 10 are adits, 14 are mineshafts, 

and 39 are prospect pits (Fernette and others, 2016b). These 

types of features are commonly associated with mining of 

locatable minerals and give a general indication of the extent 

of past mining activity in the area. The remainder of the mine 

features shown on the topographic maps are borrow pits and 

(or) gravel pits. The U.S. Geological Survey (USGS) Mineral 

Resource Data System (MRDS) database contains 20 records 

within the study area, which are reported as “producer” 

or “past producer” (U.S. Geological Survey, 2016). These 

include 18 with metallic minerals (predominantly gold) as 

the commodity and 2 with sand and gravel. MRDS contained 

no production data for these mines but the data do provide 

an indication of the level and nature of past mining activity. 

These MRDS records may include duplicates.

Recent Mining Activity

The Wyoming Department of Environmental Quality 

permit data (Wyoming Department of Environmental Quality, 2015) were used to compile locations of active mines 

within the study area. Three active mine sites were found 

within the area. These included one gold mine and two sand 

Table 1. Status and number of mining claims, mineral leases, mineral material sales sites, and 43 CFR 3809 surface management 

authorizations in the proposed withdrawal area within the (A) Southwestern and South-Central Wyoming study area, Wyoming, and (B) 

Bear River Watershed study area, Wyoming and Utah.

[Source: Bureau of Land Management (BLM) LR2000 database, March 6, 2016. The number of cases is for the complete section that includes a proposed withdrawal area. ND, no data]

A. Southwestern and South-Central Wyoming study area, Wyoming.

Type Mineral 

type

Number of 

unique cases Active Authorized Pending Closed Cancelled Expired Rejected Withdrawn

Mining claims locatable 2,955 13 ND ND 2,942 ND ND ND ND

Coal leases leasable ND ND ND ND ND ND ND ND ND

Geothermal leases leasable ND ND ND ND ND ND ND ND ND

Non-energy solid 

mineral leases leasable ND ND ND ND ND ND ND ND ND

Oil and gas leases leasable 468 ND 14 1 452 1 ND ND ND

Mineral materials 

sales sites salable 11 ND ND ND 11 ND ND ND ND

Surface management 3809 plans locatable 18 ND ND 1 17 ND ND ND ND

B. Bear River Watershed study area, Wyoming and Utah.

Type Mineral 

type

Number of 

unique cases Active Authorized Pending Closed Cancelled Expired Rejected Withdrawn

Mining claims locatable 106 ND ND ND 106 ND ND ND ND

Coal leases leasable ND ND ND ND ND ND ND ND ND

Geothermal leases leasable ND ND ND ND ND ND ND ND ND

Non-energy solid 

mineral leases leasable 1 ND ND ND 1 ND ND ND ND

Oil and gas leases leasable 792 ND 29 ND 763 ND ND ND ND

Mineral materials 

sales sites salable 22 ND 3 1 16 ND 2 ND ND

Surface management 3809 plans locatable ND ND ND ND ND ND ND ND ND
Executive Summary 3

and gravel operations. According to the Wyoming Mines 

Inspector (Adcock, 2014), the South Marble Mine, owned 

by Sublette County Road and Bridge, produced 42,180 short 

tons of sand and gravel in 2014 (Fernette and others, 2016a). 

A sand and gravel operation, called 15 Mile Knoll and owned 

by Sweetwater County, is reported to be active (Fernette and 

others, 2016a). Lastly, although the Mary Ellen gold mine has 

an active permit, there is no report of activity or production in 

the annual report of the State Inspector of Mines of Wyoming 

(Adcock, 2014). 

Mine Production Data

Production data were found for 16 past-producing mines 

located within the study area (table 2). All are gold mines that 

are located in the South Pass-Atlantic City gold district, which 

is within the study area but outside the proposed withdrawal 

area. The exact activity dates for these specific mines are not 

provided, but the periods of active mining in the district are 

shown in table 2. Another mine, South Marble, recently produced sand and gravel.

The largest of the mines, the Carissa Mine (immediately northeast of the proposed withdrawal area), produced 

more than 53,000 troy ounces (troy oz) of lode gold before 

1911 (Hausel, 1980). The study area, but not the proposed 

withdrawal area, also covers parts of the Rock Creek placer 

deposit, which produced 11,500 troy oz of placer gold from 

1933 to 1953 (Hausel, 1991). 

Active Exploration 

No site-specific information was found on active exploration projects within the study area. The Wyoming State 

Geological Survey (Wayne Sutherland, Wyoming Geological 

Survey, written commun., January 21, 2016) and the USGS 

Minerals Yearbook (U.S. Geological Survey, 2008, 2010, 

2013) report that within the past 10 years, companies have 

conducted exploration in the Dickie Springs-Oregon Gulch 

gold placer area, which is within the southern part of the South 

Pass block of the study area.

One site within the study area was found to have reported 

resource data. The Carissa deposit (at the Carissa Mine) has a 

reported resource of 100,000 short tons, with an average grade 

of 0.368 troy oz of gold per ton based on exploration in 1994 

(Fernette and others, 2016a). These values have been revised 

downwards from the 252,405 tons at 432 troy oz/ton reported 

in 1989 (Hausel, 1991, p. 47).

The southern part of the South Pass block (fig. 1) of the 

study area covers the eastern one-third of the Dickie SpringsOregon Gulch gold paleoplacer area, which Love and others 

(1978) estimate may contain over 28 million [troy] oz of gold 

(Hausel, 1989).

Table 2. Production data for mines in the Southwestern and South-Central Wyoming study area.

[ND, no data; troy oz, troy ounce; NA, not applicable; Au, gold]

Mine name From To Commodities Ore, in short tons Au, in troy oz

Caribou Mine ND 1911 Au ND 26,450

Carissa Mine ND 1954 Au ND 53,683

Carrie Shields Mine ND 1911 Au ND 1,850

Diana Mine ND 1911 Au ND 530

Doc Barr Mine ND 1911 Au ND 900

Duncan Mine ND 1956 Au ND 3,830

Empire State Mine ND 1911 Au ND 260

Franklin Mine ND 1911 Au ND 15,860

Garfield (Buckeye) Mine ND 1911 Au ND 21,150

Ground Hog Group ND 1911 Au ND 1,585

Mary Ellen ND 1911 Au ND 6,600

Midas Mine ND 1911 Au ND 1,380

Rock Creek Placers 1933 1953 Au ND 11,500

Rose Mine ND 1911 Au ND 260

Soules and Perkins Mine ND 1911 Au ND 25,000

South Marble 2014 2014 Sand and Gravel 42,180 NA

St. Louis Mine ND 1911 Au ND 400
4 Geology and Mineral Resources of the Southwestern and South-Central Wyoming and Bear River Watershed Sagebrush Focal Areas

Bear River Watershed Study Area

Past Mining Activity

An initial estimate of the level of past mining activity was 

made by summarizing the number of mining-related features 

shown on USGS topographic maps of the study area (Fernette 

and others, 2016b). Of the 117 mine features shown on USGS 

7.5-minute topographic maps within the study area, 13 are 

adits, 2 are shafts, 19 are open-pit mines, and 36 are prospect 

pits. These types of features are most commonly associated 

with mining of locatable minerals and give a general indication of the extent of past mining activity in the area. The other 

mine features shown on the topographic maps are borrow pits 

and (or) gravel pits.

A second estimate of past mining activity was made by 

extracting records for mines with a status of “producer” and 

“past producer” from the USGS Mineral Resources Data 

System (MRDS) database. The MRDS database contains 82 

records within the study area that are reported as “producer” or 

“past producer” (U.S. Geological Survey, 2005). These include 

5 that were mined for metallic minerals, 22 for phosphate, and 

55 for stone or sand and gravel. MRDS contained no production data for these mines but the data provide an indication of 

the level and nature of past mining activity. Not all of these 

MRDS records are unique—some may be duplicate records.

Recent Mining Activity

Permit data (Wyoming Department of Environmental 

Quality, 2015) were used to compile locations of active permits within the Wyoming part of the study area. For the Utah 

part of the study area, permit data from the Minerals Program 

of the Utah Division of Oil, Gas, and Mining (Utah Division 

of Oil, Gas, and Mining, 2016), and mine locations from the 

Utah Geological Survey’s Utah Mineral Occurrence System 

(Utah Geological Survey, 2015) were used to locate active 

mines.

Fifteen active mine sites were found within the study area 

(Fernette and others, 2016b). Fourteen of these sites are for 

stone and (or) sand and gravel. The remaining site is the Kemmerer coal mine, which produces an average of 4.8 million 

tons of coal annually (Westmoreland Coal Company, 2016). 

No production data were found for any of the other active 

mines.

Mine Production Data

No production data were found for any past producing 

mines located within the study area.

Active Exploration

No information was found on active exploration projects 

within the proposed withdrawal area of the study area.

Leasable

Leasable minerals, as defined by the Mineral Leasing Act 

of 1920 (30 U.S.C. 181 et seq.), include the subsets leasable 

fluid and solid minerals. Leasable fluid minerals include oil 

and gas and geothermal resources, and leasable solid minerals include coal, oil shale, native asphalt, phosphate, sodium, 

potash, potassium, and sulfur.

The potential for the occurrence within the study area of 

six leasable minerals (oil and gas, coal, geothermal, phosphate, 

potash, and trona) was evaluated. Of these commodities, only 

oil and gas and phosphate resources were identified in or near 

the study areas and are discussed in detail in this report.

With the exception of phosphate, no additional leasable 

minerals are known to have been produced or to occur in the 

study area. Phosphate was mined in the past from deposits 

adjacent to the study area at South Mountain, Leefe, Cokeville, 

and several small mines in the Wyoming part of the thrust belt. 

Sodium, in the form of trona (and converted to soda ash), is 

produced to the south and west of the study area but not within 

it. Potash occurs to the southwest of the study area, nearer to 

the Great Salt Lake, but is not present in the study area. An 

area near the Leucite Hills was prospected as a potential source 

of potassium; however, those deposits never proved feasible 

for mining. There is no record of native asphalt, sulfur, or 

bentonite in the area.

Locatable

Locatable minerals are those for which the right to 

explore, develop, and extract on Federal land open to mineral 

entry is established by the location (or staking) of lode or 

placer mining claims (General Mining Act of 1872 [30 U.S.C. 

22–42], as amended, or “Mining Law”). Locatable minerals 

are divided into metallic minerals, industrial minerals, and 

uncommon varieties of mineral materials. Examples of metallic 

minerals that have been historically mined and are currently 

being mined in the vicinity of the study area include gold, silver, copper, iron, and uranium. Examples of industrial minerals 

are certain types of limestone and dolomite.

Although no locatable commodities have been produced 

in significant amounts from the proposed withdrawal areas, 

four locatable commodities have been produced in significant 

amounts immediately adjacent to the proposed withdrawal 

areas in Wyoming. Uranium is being mined by in situ recovery 

methods to the southeast of the study area. Gold (from both 

orogenic-type vein deposits and from placers) was mined in 

the South Pass/Atlantic City/Lewiston area, and there are still 

a few active placers and possibly lode claims in the area. Iron 

was produced from the Atlantic City mine, to the northeast 

of the study area. Copper from a sedimentary-hosted copper 

deposit was produced in unknown quantity from the Griggs 

Mine, more than 25 km north of the study area. Although 

there are no mines within the proposed withdrawal area that 
Introduction 5

are known to have produced ore, at least one similar mineral 

occurrence is within the study area: the Rock Creek Valley 

copper occurrence within the Fossil Basin block. A second 

copper prospect occurs south of the study area at Cockscomb 

(U.S. Geological Survey, 2016).

Mineral-Potential Tracts

Mineral-potential tracts are outlined for specific deposit 

types (appendix 2). A summary of mineral potential and levels 

of certainty are shown in appendix 1. For orogenic low-sulfide 

gold-quartz veins there are four tracts. The first is rated high 

with certainty level D encompassing the South Pass and Lewiston areas. South of the Lewiston tract there is an extension 

with high potential but certainty level B, and beyond that, 

where the tract is buried under Tertiary rocks, the potential 

drops to moderate with certainty level A. For sediment-hosted 

stratabound copper deposits there is one tract with moderate 

potential and certainty level C. Tracts for sandstone roll-front 

uranium are rated moderate potential with certainty level B in 

the Big Sandy area and low potential with certainty level C in 

the Fontenelle area. There are two paleoplacer gold tracts: one 

is evaluated as having high potential with certainty level D in 

the Dickie Springs-Oregon Gulch area and the other as having 

low potential with certainty level A in the Sand Creek area. 

Potential for placer gold deposits is rated high with certainty 

level D in the South Pass area and moderate with certainty 

level C in the rest of the Sweetwater River drainage system, 

where there is placer potential. There is low potential with certainty level B, C, and D for diatreme-hosted diamond deposits 

in the Leucite Hills. Details of each of the tracts are discussed 

in the Locatable Minerals section of this report.

Salable

Salable minerals, also referred to as mineral materials, are 

sand and gravel, aggregates, dimension stone, petrified wood, 

cinders, clay, pumice, and pumicite, as described under the 

Mineral Materials Act of 1947 (30 U.S.C. 601 et seq.) and the 

Surface Resources Act of 1955 (30 U.S.C. 611–614).

With the exception of sand and gravel, there are no 

known sources of salable minerals in the study area. Most of 

the sand and gravel deposits are in Quaternary unconsolidated 

deposits. As of March 6, 2016, there were only three approved 

mineral material authorizations for sand and gravel (two for 

sand and gravel, one for shale) and one site pending (for sand) 

in the proposed Bear River Watershed study area and none 

in the Southwestern and South-Central Wyoming study area 

(Dicken and San Juan, 2016b). All other previous mineral 

material authorizations for sand and gravel seem to be closed, 

but this is not quite in accordance with reports of a productive 

South Marble sand and gravel operation in the northeastern 

part of the Big Sandy block (table 2).

Introduction

The U.S. Department of the Interior has proposed to 

withdraw approximately 10 million acres of Federal lands 

from mineral entry (subject to valid existing rights) from 

12 million acres of lands defined as Sagebrush Focal Areas 

(SFAs) in Idaho, Montana, Nevada, Oregon, Utah, and Wyoming (for further discussion on the lands involved see Day and 

others, 2016).The purpose of the proposed action is to protect 

the greater sage-grouse (Centrocercus urophasianus) and its 

habitat from potential adverse affects of locatable mineral 

exploration and mining. To inform the decision on whether to 

withdraw the SFAs from mineral entry, the Bureau of Land 

Management requires a mineral-resource assessment be completed to identify mineral resources within the proposed withdrawal area. The USGS Sagebrush Mineral-Resource Assessment (SaMiRA) project was initiated in November 2015 and 

supported by the BLM to (1) assess locatable mineral-resource 

potential and (2) to describe leasable and salable mineral 

resources for the seven SFAs and Nevada additions.

The purpose of this report is to summarize the current 

status of locatable, leasable, and salable mineral commodities 

and assess the potential for the occurrence of locatable minerals in the Southwestern and South-Central Wyoming and Bear 

River Watershed study area in Wyoming and Utah. A mineralpotential assessment for these study area was done by the 

U.S. Geological Survey (USGS) as part of the USGS Sagebrush Mineral Resource Assessment (SaMiRA) project being 

undertaken for BLM. This report was prepared as required by 

the Federal Land Policy and Management Act of 1976 (Pub. 

L. 94–579; 90 Stat. 2743) for an application for withdrawal 

of lands. This report by the U.S. Geological Survey follows 

guidance provided in BLM Manual Sections 3031 (Bureau of 

Land Management, 1985) and 3060 (Bureau of Land Management, 1994) for mineral assessments and mineral reports. The 

information and interpretations provided herein relied on the 

best publically available data and information sourced from 

Federal and State agencies, academic literature, and company 

reports.

The methodology followed for this resource assessment 

is described in detail in Hammarstrom and Zientek (2016) and 

the classification scheme used is described in appendix 1. Key 

datasets included geophysics (Anderson and Ponce, 2016), 

geochemistry (appendix 3; also, Smith and others, 2016), 

remote sensing (Rockwell, 2016), and mineral occurrence data 

(Fernette and others, 2016a, b; U.S. Geological Survey, 2016). 

Resource assessment tracts are assigned high (H), moderate (M), or low (L) potential at certainty ratings D (available 

data provide abundant direct and indirect evidence to support 

or refute the possible existence of mineral resources) to A 

(available data are insufficient and (or) cannot be considered 

as direct or indirect evidence to support or refute the possible 

existence of mineral resources within the respective area) 

(appendix 1).
6 Geology and Mineral Resources of the Southwestern and South-Central Wyoming and Bear River Watershed Sagebrush Focal Areas

Lands Involved

This report describes the mineral potential of a USGS 

study area that encompasses the proposed withdrawal areas in 

two Sagebrush Focal Areas: Southwestern and South-Central 

Wyoming and the Bear River Watershed in Wyoming and 

Utah. The area of interest ranges from southwestern Wyoming 

to northeastern Utah (fig. 1). Within this area there are two 

study areas—a 1,943 square kilometer (km2) (480,180 acres) 

part of the Southwestern and South-Central Wyoming Sagebrush Focal Area and a 4,192 km2

 (1,035,789 acres) part of the 

Bear River Watershed Sagebrush Focal Area (fig. 2; table 3). 

Together, the proposed withdrawal areas within these larger 

focal areas cover 1,680 km2 (415,173 acres), of which the 

BLM manages 1,475 km2 (364,477 acres) in parts of Lincoln, 

Fremont, Sublette, and Sweetwater Counties, Wyoming, and 

Rich and Cache Counties, Utah. Surface management for the 

remaining lands is coded as Forest Service, Bureau of Reclamation, and private or unknown. The study area is the aggregation of all Public Land Survey System (PLSS) townships 

containing proposed withdrawal areas, which are a subset of 

the lands in the SFAs, as provided by the BLM (San Juan and 

others, 2016). These outer boundaries containing the proposed 

withdrawal areas are referred to as the “study area” in this 

report. The boundaries of the proposed withdrawal areas are 

presented in BLM (2105a) and amended in BLM (2015b).

Southwestern and South-Central Wyoming Study 

Area

For ease of description in this report, each subarea, or 

block, of the study area has been assigned a geographic name 

(figs.1 and 2). The Southwestern and South-Central Wyoming 

study area is subdivided into South Pass, Continental Divide, 

Big Sandy, and Boars Tusk blocks. Bear River Watershed 

study area is subdivided into the Fontenelle, Fossil Basin, and 

Bear Lake Plateau blocks. The Bear Lake Plateau block is in 

Utah; all the other blocks are in Wyoming. These names are 

strictly for use in this report and do not reflect any official 

names used by BLM or other land-management agencies.

The Southwestern and South-Central Wyoming study 

area (figs. 1 and 2; table 3) covers 138,470 acres in parts 

of Fremont, Sublette, and Sweetwater Counties, of which 

138,459 acres are managed by BLM. Most of the study area 

lies north of a band of lands across the State:

. . . that is 40 miles wide; 20 miles to the north and 

south of the Union Pacific Railroad right-of-way 

known as the “railroad checkerboard lands” . . . 

Every other section of land for 20 miles on either 

side of the railroad right-of-way is privately owned.

(Bureau of Land Management, 2012)

Most of the Southwestern and South-Central Wyoming 

study area is located in the Wyoming Basin Province (fig. 

3), a structural basin covering southwestern Wyoming and 

extending into northeastern Utah and northwestern Colorado. 

The greater Green River Basin is bordered by the north-south 

trending Wyoming Range (fig. 3) of the thrust belt (fig. 4) 

on the west, by the northwest-southeast trending Wind River 

Range (fig. 3) on the north, by the Ferris Mountains (fig. 3) 

on the northeast, by the Rawlins Uplift and Sierra Madre (fig. 

3) on the east, and by the Uinta Mountains (fig. 4) and Axial 

Basin Uplift on the south in Utah and Colorado respectively. 

In Wyoming, the Green River Basin is subdivided into three 

smaller basins that are separated by the Rock Springs Uplift. 

The Green River Basin is located on the west side of the uplift, 

the Great Divide Basin is located on the northeast side, and the 

Washakie and Sand Wash Basins are located on the southeast 

(Bureau of Land Management, 2012), outside the study area 

(fig. 4).

Bear River Watershed Study Area

Straddling the Utah-Wyoming State line, the Bear 

River Watershed study area (figs. 1 and 2) covers 4,192 km2

(1,035,789 acres) in parts of Lincoln County, Wyoming, and 

Table 3. Acreage of Southwestern and South-Central Wyoming 

and Bear River Watershed study area, Wyoming and Utah.

[The study area refers to the outer boundary of the Public Land Survey System 

(PLSS) townships that contain proposed withdrawal areas. BLM, Bureau of 

Land Management]

Subdivision 

(block)

Study area

acreage

BLM 

acreage in 

study area

Proposed 

withdrawal 

area 

acreage

BLM 

acreage in 

proposed 

withdrawal 

area

Southwestern and South-Central Wyoming study area

South 

Pass

181,898.31 140,075.72 58,175.16 58,175.16

Continental 

Divide

23,058.82 21,776.89 19,323.62 19,323.62

Big 

Sandy

228,417.89 181,707.56 58,522.25 58,511.58

Boars 

Tusk

46,805.28 32,270.86 2,449.01 2,449.01

Subtotal 480,180 375,831 138,470 138,459 

Bear River Watershed study area

Fontenelle230,330.26 194,070.97 79,307.32 79,307.32

Fossil 

Basin

303,169.43 175,747.47 31,939.98 31,939.98

Bear 

Lake 

Plateau

502,289.29 153,709.92 165,455.36 114,770.7

Subtotal 1,035,789 523,528 276,703 226,018 

Total 1,515,969 899,369 415,173 364,477
Introduction 7

Rich and Cache Counties, Utah, of which the BLM manages 

276,703 acres in the actual proposed withdrawal area (table 3). 

Bear River forms a broad floodplain between the States (fig. 3).

Study area lands in Wyoming primarily are in the thrust 

belt (fig. 4). Lands in Utah are in the Wasatch Range and Bear 

River Range west of Bear River and south of Bear Lake (fig. 

3).

Organization of this Report and Terminology

The outline of this report is based on guidance published 

in the BLM Manual Sections 3060 and 3031 (Bureau of Land 

Management, 1985, 1994). To the extent possible, this report 

is organized to reflect BLM technical and legal language. 

Information is grouped by the legal classification of minerals 

recognized by BLM. Potential for occurrence is only discussed 

for locatable minerals.

Several schemes are used to classify types of minerals in 

scientific and technical literature. For example, a distinction 

is made between materials from which metals are extracted 

(metallic) from those that are not used as a source of metal or 

energy (nonmetallic or industrial). Another scheme differentiates material that is extracted from solid rock (lode) from that 

which was concentrated by moving water in sediment (placer). 

Common variety minerals do not possess a distinct or special 

value. Uncommon variety minerals have unique commercial value. Strategic and critical minerals are distinguished 

according to their importance to the Nation. Other classification schemes distinguish material based on the ultimate source 

of the valuable material—magma, hydrothermal fluid, surficial 

water, or weathered material. 

The BLM differentiates locatable, leasable, and salable minerals; these terms are based on U.S. mining law and 

Departmental decisions and are not widely used in scientific 

literature. Locatable minerals in the United States are those 

that may be acquired under the Mining Law, as amended. 

Locatable minerals include metallic minerals, industrial 

minerals, and certain varieties of mineral materials if they are 

uncommon because they possess a distinct and special value. 

Leasable minerals refers to commodities acquired through the 

Mineral Leasing Act of 1920, 30 U.S.C. 181–287, as amended; 

the Geothermal Steam Act of 1970, 30 U.S.C. 1001–1026, 

as amended; or the Acquired Lands Act of 1947, 30 U.S.C. 

351–359, as amended. Examples of leasable minerals include 

oil, gas, coal, oil shale, sodium, potash, phosphate, and all minerals within acquired lands. Salable minerals on Federal lands 

are those sold by sales contract from the Federal Government, 

and by free use permit to governmental agencies and nonprofit 

organizations. The applicable statute is the Mineral Materials 

Act of 1947, 30 U.S.C. 601–604, as amended. Salable minerals 

are generally common varieties of materials; examples include 

construction materials and aggregates, such as sand, gravel, 

cinders, roadbed, and ballast material.

Rights to locatable minerals are established by the location (or staking) of lode or placer mining claims. Acquisition of 

leasable minerals is by application for a Government lease and 

permits to mine or explore after lease issuance. Salable minerals on Federal lands are sold by sales contract. Surface disturbance associated with locatable mineral development must 

be approved and permitted according to Surface Management 

regulations (43 CFR 3809). Table 1 summarizes information 

on mining claims, leases, and salable mineral sites, along with 

surface management permits in the study areas.

The mining laws applicable to Federal lands of the United 

States were not developed with specific knowledge of geology and types of mineral materials. Even so, the various legal 

types of minerals do have some broad geologic associations. 

Leasable minerals include areally extensive types of valuable earth materials most commonly occurring in sedimentary 

basins: oil and gas fields, coal fields, oil shales, large bedded 

deposits of soluble sodium and potassium salts, and large 

bedded deposits of phosphorite. Salable minerals are common, 

widely distributed earth materials with low unit value. They 

must be obtained near where the need exists. If the material is 

not leasable or salable, it is locatable. Most, but not all, of this 

type of material occurs in spatially restricted areas.

A glossary of terms is provided in chapter A (Day and 

others, 2016), the companion report to this assessment. In 

some parts of this report, a brief discussion is provided to 

clarify usage of specific terms and to relate how concentrations of valuable earth materials form to the legal definitions 

that determine their ownership and development. However, 

for other terms, like “minerals,” the intended meaning must be 

inferred from context.

Who Did the Work?

This report represents contributions from a multidisciplinary team of USGS geologists, geophysicists, geochemists, 

mineral-commodity specialists, and geographic information 

system (GIS) experts. These geoscientists reached out to 

personnel from the Wyoming State Geological Survey and the 

Utah Geological Survey to gather the most recent geologic and 

mineral resource information available. Representatives from 

these groups also provided helpful feedback on the preliminary tracts that we developed for the study area. 

Anna Burack Wilson and Timothy Hayes wrote the 

majority of the text in this report. Tim took the lead on the 

major mineral deposit models for which tracts were drawn, 

whereas Anna compiled the salable and other commodities 

while stitching the rest of the manuscript pieces together. 

Doug Yager wrote the section on geology, and it was revised 

by both Mary Ellen Benson and Anna. John Horton and 

Stuart Giles, in Denver, Colorado; Heather Parks, in Spokane, 

Washington; and Connie Dicken, in Reston, Virginia, undertook much of the GIS work that underpins this report. John 

constructed the digital tracts in this report, and Stuart produced 

most of the figures from the GIS. Connie also compiled and 

delivered information from BLM, and helped us to understand 

its meaning and significance. The “Leasable Minerals” section 
8 Geology and Mineral Resources of the Southwestern and South-Central Wyoming and Bear River Watershed Sagebrush Focal Areas

BEAR LAKE PLATEAU

BLOCK

FOSSIL BASIN BLOCK

FONTENELLE BLOCK

BIG SANDY

BLOCK

Bear

Lake

Evanston

Green R

UTAH

IDAHO

LINCOLN COUNTY

SUBLETTE COUNTY

UINTA COUNTY

RICH

COUNTY

BEAR LAKE

COUNTY

CARIBOU COUNTY

CACHE

COUNTY

FRANKLIN

COUNTY

WEBER

COUNTY

MORGAN

COUNTY

80

189

30 89

30

89

189

30

1

111°0' 110°0' 

42°30'

42°0'

41°30'

0 10 20 30 40 

0 10 20 30 40 50 KILOMETERS

Base modified from U.S. Geological Survey DEM data, 2016.

Roads and political data © 2014 Esri and its licensors.

Boundary data from San Juan and others (2016).

USA Contiguous Albers Equal Area Conic Projection.

Central meridian, 110° W., latitude of origin, 37.5° N.

North American Datum of 1983.
Introduction 9

Figure 1. Map showing the Southwestern and South-Central 

Wyoming and Bear River Watershed Sagebrush Focal Areas, 

Wyoming and Utah, and U.S. Geological Survey (USGS) study area 

boundaries. Darker areas on the inset map depict all of the study 

areas in six western states. BLM, Bureau of Land Management.

BOARS TUSK BLOCK

CONTINENTAL

DIVIDE BLOCK

SOUTH PASS

BLOCK

River

Rock Springs

WYOMING

SWEETWATER COUNTY

FREMONT COUNTY

80

287

191

191

91

109°0'

Map

area

Study areas

IDAHO

MONTANA

OREGON

WYOMING

NEVADA UTAH

WASHINGTON

County boundaries

State boundaries

USGS study area boundaries

Base data

Southwestern and South Central Wyoming

Bear River Watershed

BLM Sagebrush Focal Areas

EXPLANATION

50 MILES

Proposed withdrawal areas
10 Geology and Mineral Resources of the Southwestern and South-Central Wyoming and Bear River Watershed Sagebrush Focal Areas

Bear

Lake

BEAR LAKE PLATEAU

BLOCK

FOSSIL BASIN BLOCK

FONTENELLE

BLOCK

BIG SANDY

BLOCK

80

189

30 89

30

89

189

30

1

LINCOLN COUNTY

SUBLETTE COUNTY

UINTA COUNTY

RICH

COUNTY

BEAR LAKE

COUNTY

CARIBOU COUNTY

CACHE

COUNTY

FRANKLIN

COUNTY

WEBER

COUNTY

MORGAN

COUNTY

UTAH

IDAHO

Evanston

Green R

111°0' 110°0' 

42°30'

42°0'

41°30'

0 10 20 30 40 

0 10 20 30 40 50 KILOMETERS

Base modified from U.S. Geological Survey DEM data, 2016.

Roads and political data © 2014 Esri and its licensors.

Boundary data from San Juan and others (2016).

Surface management data from BLM, 2015.

USA Contiguous Albers Equal Area Conic Projection.

Central meridian, 110° W., latitude of origin, 37.5° N.

North American Datum of 1983.
Introduction 11

Figure 2. Surface land-management map of the Southwestern 

and South-Central Wyoming and Bear River Watershed study 

areas, Wyoming and Utah. USGS, U.S. Geological Survey.

BOARS TUSK BLOCK

CONTINENTAL

DIVIDE

BLOCK

SOUTH PASS

BLOCK

80

287

191

191

91

SWEETWATER COUNTY

FREMONT COUNTY

WYOMING

River

Rock Springs

109°0'

Map

area

Study areas

IDAHO

MONTANA

OREGON

WYOMING

NEVADA UTAH

WASHINGTON

County boundaries

State boundaries

Proposed withdrawal areas

USGS study area boundaries

Base data

U.S. Forest Service

U.S. Fish and Wildlife

State

Private, unknown, or water

National Park Service

Department of Defense

Bureau of Reclamation

Bureau of Land Management

Bureau of Indian Affairs

Surface management status

EXPLANATION

50 MILES
12 Geology and Mineral Resources of the Southwestern and South-Central Wyoming and Bear River Watershed Sagebrush Focal Areas

BEAR LAKE

PLATEAU

BLOCK

FOSSIL BASIN

BLOCK

FONTENELLE

BLOCK

BIG SANDY

BLOCK

BOARS TUSK

BLOCK CONTINENTA

DIVIDE BLOC

SOUTH PASS

BLOCK

Bear River

Bear

Lake

GREAT

SALT

LAKE

Evanston

Green River

Rock Springs

UTAH

IDAHO

80

287

189

191

89 30

30

89

189

30

191

191

SWEETWATER COUNTY

LINCOLN

COUNTY

SUBLETTE

COUNTY

UINTA COUNTY

RICH

COUNTY

BEAR LAKE

COUNTY

CARIBOU COUNTY

CACHE

COUNTY

FRANKLIN

COUNTY

WEBER

COUNTY

MORGAN

COUNTY

DAGGETT

COUNTY

SUMMIT

COUNTY

BONNEVILLE

COUNTY

BINGHAM

COUNTY

BOX

ELDER

COUNTY

BANNOCK

COUNTY WIND RIVER RANGE

TUNP RANGE

WYOMING RANGE

BEAR RIVER RANGE

CRAWFORD

MTS.

UINTA MOUNTAINS

CACHE VALLEY

TRONA

AREA

MIDDLE ROCKY

MOUNTAINS

PROVINCE

MIDDLE ROCKY

MOUNTAINS

PROVINCE

BASIN AND RANGE

PROVINCE

COLUMBIA

PLATEAU

PROVINCE 

112°0' 111°0' 110°0' 109°0' 

43°30'

43°0'

42°30'

42°0'

41°30'

41°0'

LEUCITE

HILLS

0 10 20 30 40 50 MILES

0 10 20 30 40 50 KILOMETERS

Base modified from U.S. Geological Survey DEM data, 2016.

Roads and political data © 2014 Esri and its licensors.

Boundary data from San Juan and others (2016).

USA Contiguous Albers Equal Area Conic Projection.

Central meridian, 110° W., latitude of origin, 37.5° N.

North American Datum of 1983.
Introduction 13

Figure 3. Map showing the physiography of the Southwestern 

and South-Central Wyoming and Bear River Watershed study 

areas, Wyoming and Utah. USGS, U.S. Geological Survey.

AL

K

Sweetwater River

Rawlins

WYOMING

COLORADO

80

FREMONT COUNTY

MOFFATT

COUNTY

CARBON

COUNTY

NATRONA

COUNTY

Sand

Basin

SIERRA MADRE

FERRIS

MOUNTAINS

RATTLESNAKE HILLS

Crooks Gap

GRANITE

MOUNTAINS

GREEN

RIVER

BASIN

WYOMING BASIN

PROVINCE

GREAT

PLAINS

PROVINCE

SOUTHERN

ROCKY

MOUNTAINS

PROVINCE

108°0' 107°0'

Map

area

Study areas

IDAHO

MONTANA

OREGON

WYOMING

NEVADA UTAH

WASHINGTON

COLORADO

BASIN AND RANGE

GREAT PLAINS

WYOMING

BASIN

NORTHERN

ROCKY MOUNTAINS

MIDDLE ROCKY

MOUNTAINS

COLUMBIA

PLATEAU

County boundaries

State boundaries

Proposed withdrawal areas

Southwestern and South Central Wyoming

Bear River Watershed Area

USGS study area boundaries

Base data

Trona mineralized area outline

Greater Green River Basin (Approximate boundary of

 Bridger, Great Divide, Kindt, Washakie, Green River, 

 and Hoback Basins)

Wyoming Basin

Southern Rocky Mountains

Middle Rocky Mountains

Columbia Plateau

Basin and Range

Great Plains

Provinces

Physiography

EXPLANATION

Green River Basin data from USGS Southwest WY Province Assessment Team, (2005a).

Trona area from Fernette and others (2016).

Physiographic provinces from USGS (2014).
14 Geology and Mineral Resources of the Southwestern and South-Central Wyoming and Bear River Watershed Sagebrush Focal Areas

Bighorn

Mts.

Black

Hills

Laramie

Mts.

Wind River Mts.

A bsaroka Mts.

 Thrust b elt

Green

River

Basin

Washakie

Basin

Rock 

Springs

Uplift

Hartville uplift

Medicine Bow Mts.

North

Park

Sierra

Madre

Owl Creek Mts.

Powder River

Basin

Wind River

Basin

Bighorn

Basin

DenverJulesburg

Basin

Laramie

Basin

Hanna

Basin

Great Divide

Basin

Shirley

Basin

Gros Ventre

Mts.

Teton Mts.

Yellowstone

Plateau

 Washakie Mts.

Uinta Mts.

Wasatch

Range

Fossil Basin

Madison

Gallatin

Mts. Pryor 

Mts.

Continental Fault

S . Granite Mts. Fault

 Beartooth Mts.

Granite Mts.

100 Kilometers

50 100 Miles

50

0

0

Figure 4. Map showing the geologic and tectonic setting, with mountain ranges and structural basins (dotted lines), in Wyoming and 

surrounding areas (modified from Roberts, 1989). Faults (solid lines) are generalized from Snoke (1993) for southwest Wyoming (bar and 

ball on down-dropped block of normal fault; teeth on upper plate of thrust fault).

of this report was produced by several authors—Ronald Drake 

wrote the “Oil and Gas” section; Colin Williams, Jonathan 

Glen, and Jacob DeAngelo wrote the “Geothermal Energy” 

section; Jon Haacke wrote the “Coal” section; Mary Ellen 

Benson wrote the “Phosphate” section; and Doug Yager wrote 

the “Potash” section. Eric Anderson compiled the geophysical results in this report, and he also compiled the simplified geologic map for Doug Yager to illustrate the geologic 

framework. Barnaby Rockwell provided expert knowledge of 

remote sensing data, which helped to inform and validate the 

tracts, especially for sandstone roll-front uranium. Greg Fernette made available the preliminary version of U.S. Geological Survey Mineral Deposit Database project (USMIN) and 

provided helpful feedback about past production and possible 

resources in the study area. Don Bleiwas provided the marketdemand commodity profiles that are referenced in this report.

Description of Geology

A general geologic and tectonic history for Wyoming and 

northeastern Utah is presented in this section to provide context for discussions of mineral tracts delineated as part of this 

report. The diverse physiography of uplifted mountain blocks, 

adjacent intermountain basins, and sinuous folded and thrusted 

mountain ranges in the study area is a result of a long and 

complex geologic history of the study area. Geologic maps of 

Wyoming (Love and Christiansen, 1985; Green and Drouillard, 1994) and Utah (Hintze, 1980; Hintze and others, 2000) 

provide additional geologic background.

This section summarizes, from oldest to youngest, the 

geologic history of the area. It is beyond the scope of this 

report to discuss all rock units within each geologic period. 
Description of Geology 15

Selected formations are discussed as they pertain to important 

geologic or tectonic events or are of economic interest. 

Physiography 

Most of the study areas covered in this report are in the 

Wyoming Basin (physiographic) Province (fig. 3) (Sullivan, 

1980). The Wyoming Basin includes all or parts of the Green 

River, Great Divide and Washakie Basins, and the Rock 

Springs Uplift (figs. 3 and 4). This province is made up of high 

plains and plateau areas and is bordered by mountain ranges 

and major uplifts of the Middle Rocky Mountains Province. 

The southern end of the Wind River Range extends into the 

South Pass block of the Southwestern and South-Central 

Wyoming study area on its northern border. Surface features 

reflect erosion by wind and water in an arid, cold-temperature 

environment. In some instances, they have been modified by 

faulting or volcanic activity (Bureau of Land Management, 

2012). 

Regional Geology and Tectonic Setting

The geologic history of the study area spans nearly 4 

billion years from Archean through the Holocene. Archean 

and Proterozoic rocks (together, the Precambrian) are present 

in the Wind River Range north of the study area and around 

Atlantic City and South Pass in the northeastern part of the 

study area. Much of the Paleozoic section is exposed in the 

thrust belt in western Wyoming. Mesozoic sedimentary rocks 

fill the basins. Cenozoic rocks blanket the landscape, especially along waterways. A generalized geologic map of the 

study area is shown in figure 5.

The Southwestern and South-Central Wyoming study 

area extends from the southwestern side of the Wind River 

Mountains, a northwest-trending basement uplift, which is 

composed of Archean gneisses and granites that were thrust 

westward over Paleozoic and Mesozoic sedimentary rocks in 

the Late Cretaceous through Eocene Laramide orogeny (Frost 

and others, 2000) and southwestward into the northern greater 

Green River Basin, a sedimentary basin also formed during the 

Laramide orogeny (Ryder, 1988). The Bear River Watershed 

study area extends from the northern Green River Basin across 

the thrust belt to the eastern boundary of the Basin and Range 

Province in northern Utah (fig. 3).

Archean and Proterozoic Rocks

Some of the oldest known Archean rocks of the North 

American craton (Laurentia) underlie much of Wyoming 

(Snoke, 1993). Basement-cored Laramide uplifts provide 

excellent bedrock exposures of these rocks. The Precambrian 

history of Wyoming is characterized by continental-arcmagmatism terrane accretion that formed the continental 

craton named the Wyoming Province (Mueller and Frost, 

2006). Subduction along the southern margin of the Archean 

Wyoming craton during the Proterozoic resulted in accretion 

of oceanic island arc terranes along a tectonic suture zone 

named the Cheyenne belt (Karlstrom and Houston, 1984; 

Jones and others, 2010). This zone of tectonism was a zone 

of crustal weakness that was subsequently intruded by mafic 

(low SiO2

) to felsic (high SiO2) composition magmas during 

the Mesoproterozoic. A billion-year gap in the geologic record 

occurred between the Mesoproterozoic and the Phanerozoic 

(Snoke, 1993). The Proterozoic gap is known throughout the 

world as the Great Unconformity and is characterized by erosion of the ancient continental crust and sedimentation that 

occurred throughout this area, and globally (Peters and Gaines, 

2012). The gap in the geologic record is shorter in some places 

west of Laurentia and east of the thrust belt. Areas of younger 

Proterozoic terrain are identified in central Idaho and western 

Montana, as well as in southern Idaho and northern Utah (Foster and others, 2006). Precambrian basement in northeast Utah 

consists of Paleoproterozoic rocks of the Mojave Province 

(Yonkee and Weil, 2011). Neoproterozoic rocks are exposed in 

Utah north of the study area in the Bear River Range northeast 

of Bear Lake.

A fragment of an Archean greenstone belt exposed in 

the southern Wind River Range is of economic importance 

(Bayley and others, 1973). The greenstone belt is composed 

of variably metamorphosed, mafic to ultramafic volcanic 

rocks and associated sedimentary rocks. Greenstone is named 

for the greenish hue caused by such minerals as chlorite and 

green amphibole. Gold deposits, discovered between 1867 

and 1871, occur in greenstone of the Miners Delight Formation metagraywacke at South Pass (Bayley and others, 1973). 

Banded-iron deposits in metasedimentary rocks of the Goldman Meadows Formation have been mined near South Pass 

(Bayley and others, 1973).

Paleozoic Rocks

Lower- to middle-Paleozoic rocks (units MPs, _Ds, and 

|s, upper part of unit Z_s on fig. 5) form a thin sedimentary 

veneer on Precambrian basement rocks. Where Precambrian 

basement rocks were uplifted during Paleozoic mountain 

building that formed the Pennsylvanian-Permian ancestral 

Rocky Mountains, Paleozoic rocks were eroded exposing Precambrian-cores of the uplifts. The Sierra Madre and Medicine 

Bow Mountains (fig. 4) are the northern-most manifestation 

of the ancestral Rocky Mountains, which extended southward 

from Wyoming into Colorado. Continentally derived sediments of the Upper Mississippian to Middle Pennsylvanian 

Amsden Formation (fig. 6) were eroded from uplifted crustal 

blocks and deposited in adjacent basins (Snoke, 1993). 

Pennsylvanian-age rocks unconformably overlie Precambriancored uplifts where older Paleozoic strata had been eroded 

during mountain building. An unconformity separates clastic 

terrestrial Pennsylvanian deposits from overlying Permian marine sedimentary strata. Permian marine rocks of the 

Phosphoria Formation (fig. 6) in central and western Wyoming 

are composed of phosphatic shale, phosphorite, and bedded 
16 Geology and Mineral Resources of the Southwestern and South-Central Wyoming and Bear River Watershed Sagebrush Focal Areas

Evanston

Green River

Ro

WYOMING

UTAH

IDAHO

SWEETWATER COUNTY

LINCOLN

COUNTY

SUBLETTE COUNTY

UINTA COUNTY

RICH

COUNTY

BEAR LAKE

COUNTY

CARIBOU COUNTY

CACHE

COUNTY

FRANKLIN

COUNTY

WEBER

COUNTY

MORGAN

COUNTY

80

189

191

30

89

30

89

189

30

191

191

Tes

Ks

Ks

Ds

Js

Qs

Ds

Ks

Zs

Ks

Qs

Zs

MPs

Ks

Tpls

Tpgs

Qvm 

Ks

Qs

Tpls

W

MPs

Ks

Wg

Zs

Wg

W

Ks

Ds

Ks

Qs

Zs

Teosv

Ds

Wsv

Qs

MPs

Tos

Tes

Tes

Tes

Tes

Tpas

Js

Js

Js Js

Js

Js Js

s

s

s

s

s

s

s

s

MPs

Ds

Bear

Lake

Fontenelle

Reservoir

Flaming

Gorge

Reservoir

BEAR LAKE

PLATEAU

BLOCK

FOSSIL BASIN BLOCK

FONTENELLE

BLOCK

BIG SANDY BLOCK

BOARS TUSK

BLOCK

111°0' 110°0' 

42°30'

42°0'

41°30'

0 10 20 30 40 50 MILES

0 10 20 30 40 50 KILOMETERS

Base modified from U.S. Geological Survey DEM data, 2016.

Roads and political data © 2014 Esri and its licensors.

Boundary data from San Juan and others (2016).

USA Contiguous Albers Equal Area Conic Projection.

Central meridian, 110° W., latitude of origin, 37.5° N.

North American Datum of 1983.
Introduction 17

Figure 5. Simplified geologic map of the Southwestern and 

South-Central Wyoming and Bear River Watershed study areas, 

Wyoming and Utah. Geologic units simplified from Garrity and 

Soller, 2009. USGS, U.S. Geological Survey.

ck Springs

FREMONT

COUNTY

80

287

Tes

Ks

Wp

Tpas 

Tms

s

s

Wsv

Tos

Wg

Wn

Tms

Ks

Wg

Wp

Tes Ks

Wg

Tos

Qvm

MPs

Qvm

s

CONTINENTAL

DIVIDE BLOCK

SOUTH PASS BLOCK

109°0'

Map

area

Study areas

IDAHO

MONTANA

OREGON

WYOMING

NEVADA UTAH

WASHINGTON

CO

CA

Geologic data from Garrity and Soller (2009).

EXPLANATION

Tpls

Tpgs

Tpas

Tos

Tms

Teosv

Tes

Zs

Zs

Wsv

Wn

Wp

Wg

Js

Qvm

Qs

s

s

MPs

Ks

Ds

County boundaries

State boundaries

USGS study area boundary

Base data

Unclassified fault

Thrust fault

Normal fault

Formation contact

Cambrian through Devonian sedimentary rocks

Cretaceous sedimentary rocks

Mississippian through Permian sedimentary rocks

Mesozoic sedimentary rocks

Paleozoic sedimentary rocks

Quaternary sedimentary rocks

Quaternary mafic volcanic rocks

Triassic and Jurassic sedimentary rocks

Late Archean granitic rocks

Late Archean intermediate plutonic rocks

Late Archean gneissic rocks

Late Archean interlayered sedimentary and

 volcanic rocks 

Neoproterozoic sedimentary rocks

Neoproterozoic and Cambrian sedimentary rocks

Tertiary (Eocene) sedimentary rocks 

Tertiary (Eocene and Oligocene) interlayered

 sedimentary and volcanic rocks

Tertiary (Miocene) sedimentary rocks

Tertiary (Oligocene) sedimentary rocks

Tertiary (Paleocene) sedimentary rocks 

Tertiary (Paleogene, includes Paleocene, Eocene,

 and Oligocene) sedimentary rocks

Tertiary (Pliocene) sedimentary rocks

Lithostratigraphy

Structure
18 Geology and Mineral Resources of the Southwestern and South-Central Wyoming and Bear River Watershed Sagebrush Focal Areas

Wasatch Fm.

Epoch Green River Basin,

Wyoming

Rock Springs Uplift,

Wyoming

 Great Divide Basin,

Washakie Basin, WY

Holocene

Lava Creek B ash Lava Creek B ash

Pleistocene

Miocene

Oligocene

Eocene

Paleocene

Tertiary

Browns Park Fm.,

Miocene & Oligocene

rocks

Camp Davis Fm. 

Teewinot Fm.

Conglomerate 

Split Rock, Browns

 Park Formations 

Bishop Conglomerate 

Bridger Formation

Green River Fm.

Wasatch Formation

Fort Union Formation

Hoback, Almy Fm.

of Wasatch Group 

Cretaceous

Mesaverde

Formation 

Cody, Baxter Shales

Lance Formation

Fox Hills Sandstone

Lewis Shale

Almond Formation

Mesaverde

Baxter Shale Cody Sh. 

Frontier Formation

Aspen Shale Mowry Shale

Lower

Upper

Middle

Lower

Jurassic

Bear River Formation Thermopolis Shale

Dakota

Sandstone

Morrison Formation

Entrada Sandstone Sundance Formation

Carmel Formation

Darwin Ss. Darwin Ss.

Ankareh Formation

Woodside

Formation 

Chugwater Group Triassic

Permian

Pennsylvanian

Mississippian

Devonian

Silurian

Ordovician

Cambrian

Upper

Middle

Lower

Dinwoody Formation

Phosphoria Formation

Tensleep

Sandstone

Weber

Sandstone

Tensleep

Sandstone

Morgan Amsden Fm. Formation

Madison Limestone

Gallatin Limestone

Flathead

Buck

Spring

Formation

Muddy Sandstone

Upper

Pliocene

Sandstone

Erosion or nondeposition

Alkalic extrusions & intrusions

Cloverly Formation

Quaternary

 Thrust Belt, 

Fossil Basin, WY

Northeastern

Utah

White River Fm.,

Bishop Conglomerate 

Miocene (?) rocks

Bridger Formation

Green River Fm.

Intrusives

Fowkes Fm.

Green River,

Evanston Formation

Wasatch Fms.

Gannett Group

Cokeville,

Bear River

Formations

Sage Junction Fm.,

Aspen Sh.

Group

Meeteetse Fm.

Ericson Sandstone of Mesaverde Group

Rock Springs Formation

Hilliard Sh. Steele,

Niobrara Fm. 

Adaville Fm. Blind Bull

 Fm.

 Salt Lake

Formation

 Intrusives &

Volcanic rocks

Fowkes Fm.

Wasatch

Formation

Kelvin Formation

Aspen Shale

Henefer Formation

 Echo Canyon

Conglomerate

Basaltic rocks

Twin Creek Limestone

Nugget Sandstone

Thaynes Limestone 

Preuss Sandstone

Stump Formation

Morrison Formation

Park City, Phosphoria Formations

Weber Quartzite

Morgan Formation,

 Round Valley Ls.

Chainman Sh., Humbug &

Woodman Fms., Deseret

& Lodgepole Ls.

Laketown Dolomite

Fish Haven Dolomite, 

 Garden City Ls.

 Beirdneau Ss., Hyrum

Dol., Water Canyon Fm.

Tintic Quartzite

Bloomington Fm.,

Maxfield Limestone,

Ophir Fm.

 St. Charles Fm.,

Nounan Dolomite

Wells Formation

Amsden Formation

Darby Formation

Bighorn Dolomite

Gros Ventre Formation

Cloverly Formation

Sundance Formation

Gypsum Spring Fm.

Battle Spring

Fm.

Stratigraphic units from Northeastern Utah to South-Central Wyoming

Period

Carboniferous

Figure 6. Stratigraphic 

chart of Phanerozoic 

rock units for the 

Southwestern and SouthCentral Wyoming and 

Bear River Watershed 

study areas, Wyoming 

and Utah (compiled from 

Love and others, 1993; 

and Hintze and others, 

2000). Fm., Formation; 

Ls., Limestone; Ss., 

Sandstone; Sh., Shale; 

Dol., Dolostone.
Description of Geology 19

chert, and are a significant source of phosphate (Snoke, 1993). 

Where organic-rich, the Phosphoria Formation is a hydrocarbon source rock.

The Paleozoic history in northeastern Utah is recorded 

in marine, lower Paleozoic limestone, dolomite, and quartzite 

that form the Bear River Range, east and south of Bear Lake. 

Lower Paleozoic rocks also crop out along the thrust belt at 

the border with Wyoming. The dolomite may have economic 

potential and will be discussed later in the report.

Mesozoic Rocks

Mesozoic strata were unconformably deposited on an 

eroded, stable platform of the continental western interior. 

Mesozoic rocks are represented by units }s, Ks, and ^J

on figure 5. In Wyoming, Triassic rocks are mainly exposed 

adjacent to uplifts along basin margins and in the Sevier fold 

and thrust belt (fig. 4). Triassic red beds of the Chugwater 

Group (fig. 6), composed mainly of siltstone, very fine-grained 

sandstone, and intertonguing limestone, were deposited in a 

tidal flat environment. Marine siltstone and limestone of the 

Dinwoody and Thaynes Formations (fig. 6) that are contemporaneous with deposition of the Chugwater Group to the east 

were deposited in western Wyoming. The Jurassic, aeolian 

Nugget Sandstone (fig. 6) was widely distributed throughout 

northeastern Utah, and western and south-central Wyoming. It 

is equivalent in age to other continental interior, ancient dunesand deposits such as the Navajo Sandstone of the Colorado 

Plateau. The Nugget Sandstone has historically been a target 

for hydrocarbons in Wyoming and locally may host copper 

deposits. Terrestrial lacustrine and fluvial deposition of the 

Morrison Formation during the Late Jurassic, consisted of variegated, green to gray claystone, siltstone, silty sandstone and 

conglomerate and followed incursion of a shallow sea that was 

the precursor to the Cretaceous continental interior seaway.

Jurassic units, including the terrestrial Nugget Sandstone 

and marine Preuss Sandstone and Twin Creek Limestone, are 

exposed along the eastern margin of Bear Lake, in Utah.

Cretaceous Rocks

A Middle Cretaceous seaway inundated much of the 

continental interior of the United States including much of 

Wyoming (Blakey, 2011). The seaway deposited marine 

sediments along the eastern margin of the Rocky Mountain 

Cordillera and in basins within or adjacent to the Southwestern and South-Central Wyoming study area. Cretaceous rocks 

deposited in the foreland basin east of the Rocky Mountain 

Cordillera are mainly shale, siltstone, sandstone, and conglomerate (unit Ks on fig. 5).

Lower Cretaceous rocks unconformably overlie the 

Jurassic Morrison Formation and include two episodes of 

marine to nonmarine sequences. The first sequence is represented by the Bear River Formation marine shale, limestone, 

and sandstone and the age-equivalent Dakota Sandstone. The 

second sequence, marked by deposition of the marine Mowry 

Shale, conformably overlies the Dakota Sandstone (Ryer and 

others, 1987). A sequence of marine to nonmarine sandstone 

and shale, the Upper Cretaceous Frontier Formation, was 

deposited unconformably on the eroded Mowry Shale surface. 

Marine to nonmarine Upper Cretaceous strata of the Baxter, 

Steele, Niobrara, and Cody Shales were deposited on the Frontier Formation. Nonmarine to near-shore marine, sandstone, 

and shale units (Mesaverde Group including Almond Formation, Lewis Shale, Fox Hills Sandstone, and Lance Formation) 

cap the Upper Cretaceous sequence. Cretaceous sedimentary 

rocks do not occur in northeastern Utah because the Cretaceous seaway did not inundate this area (Blakey, 2011).

Late Cretaceous east-west compressive stresses were 

caused by subduction of oceanic crust beneath continental 

crust of western North America. Subduction-related (arc) magmatism formed along the western margin of North America 

above the subducting oceanic slab. Volcanic eruptions along 

the magmatic arc resulted in volcanic ash being transported 

eastward and deposited in Cretaceous basins in Wyoming. 

These volcanic ash deposits were later converted through 

burial and diagenesis into bentonite (rock composed of smectite group clay minerals), which has a number of economic 

uses such as an additive to drilling-mud additive and sorbent 

for environmental contaminants. There are no known occurrences of bentonite in the study area.

Another manifestation of compressional tectonics during 

the Late Cretaceous is an area of mountain building known 

as the Sevier orogenic belt. The belt forms a sinuous fold and 

thrust belt along much of the border of western Wyoming 

and into northeastern Utah (figs. 4 and 5; Yonkee and Weil, 

2015). The thrust faults transported Proterozoic to Mesozoic 

rocks eastward in an area that had been the passive margin of 

western North America, inland from the active volcanic arc 

to the west. This period of compressional tectonics continued 

as part of the Laramide orogeny from the Late Cretaceous to 

the Eocene. Before Laramide deformation, Upper Cretaceous 

marine shale was relatively continuous across southwestern 

Wyoming. However, the depositional continuity of the marine 

strata was interrupted during the Laramide orogeny as basement-cored mountains with extreme topographic relief and 

deep intermountain nonmarine basins formed (Snoke, 1993; 

Fan and Carrapa, 2014). The topographic relief developed at 

that time set the stage for a period of erosion and deposition 

of thick sequences of sediments in subsiding basins (Love, 

1960). The transition in tectonic regime is recorded in basins 

where marine Lewis Shale (fig. 6) is overlain by thick terrestrial sedimentary rock sequences of Late Cretaceous to early 

Eocene strata. Terrestrial nonmarine continental basin rocks 

include the Upper Cretaceous Lance Formation (fig. 6), Paleocene coal-bearing Fort Union Formation, and Eocene Wasatch 

Formation (Snoke, 1993). Extensive deposits of the Wasatch 

and Evanston Formations (undivided) occur in the Bear Lake 

Plateau in northeastern Utah.

The lower Eocene arkosic, and locally conglomeratic, 

sandstone of the Battle Spring Formation in Wyoming is 
20 Geology and Mineral Resources of the Southwestern and South-Central Wyoming and Bear River Watershed Sagebrush Focal Areas

economically important for uranium mineralization. The 

uplifted Granite Mountains were a source of both sediment 

and uranium; uranium occurs in tabular, sandstone roll-front 

uranium deposits in the Battle Spring Formation (Wilson, 

2015). Crooks Gap in the western Granite Mountains is an 

example of this style of uranium mineralization (Stephens, 

1964). Sandstone roll-front uranium deposits are discussed 

and assessed later in this report.

Eocene Magmatism and Contemporaneous Lake 

System

Paleogene magmatism in Wyoming is recorded in a 

group of chronologically and compositionally diverse igneous 

centers scattered throughout the State. Igneous rocks synchronous with the episode of Laramide tectonism include iron-rich, 

alkalic intrusions and lava flows in the Black Hills (in western 

South Dakota, not shown on figures in this report) (Snoke, 

1993). Post-Laramide Eocene magmatic centers include the 

Rattlesnake Hills (fig. 3) north of the Granite Mountains 

(Hoch and Frost, 1993) and the Absaroka volcanic field in 

northwestern Wyoming (Smedes and Prostka, 1972). The 

Rattlesnake Hills are characterized by alkaline to subalkaline 

plugs, dikes, and flows; igneous rocks of the Absaroka volcanic field are mostly calc-alkaline intermediate- to felsic- composition lava flows and volcanoclastic rocks covering 23,000 

km2 (Smedes and Prostka, 1972; Feeley, 2003). 

A widespread lake system (Lake Gosiute) developed 

contemporaneously with mid-Eocene magmatism. The lake 

is thought to have formed when an earlier eastward-flowing 

drainage system was cut off by westward tilting of the Wyoming foreland (Snoke, 1993). Although lakes developed in 

other parts of Wyoming during this time, Lake Gosiute was 

established in southwestern Wyoming in the areas of the 

Green River and Washakie basins (fig. 4). Sedimentary lake 

deposits are represented by the Tipton Shale, Wilkins Peak, 

and Laney Members of the Green River Formation (fig. 6). 

Members of the Green River Formation are thought to have 

developed in conditions in which lake water became chemically stratified and did not mix. These conditions contributed to precipitation of continuous stratiform beds of trona 

(Na3

(CO3)(HCO3)∙2H2O) and oil shale (organic-rich carbonate 

and siliceous mudstone) (Jagniecki and Lowenstein, 2015). 

The mineral trona is economically important in Wyoming and 

is used in manufacturing of glass, detergents, and textiles. 

The Green River Basin trona deposit (fig. 3), located beyond 

the study area west of the Rock Springs Uplift, is the largest 

known occurrence in the world.

The early Oligocene was characterized by deposition of 

volcaniclastic rocks and fluvial sediments of the White River 

Formation (fig. 6) deposited unconformably on an Eocene erosion surface. The volcanic debris is thought to be derived from 

volcanic activity in the Great Basin to the west (Snoke, 1993). 

Deposition of the White River Formation marked the end of an 

extensive episode of Eocene erosion (Epis and Chapin, 1975; 

Snoke, 1993).

Neogene Extensional Faulting and Volcanism 

Some preexisting Laramide-age structures, including 

those of the Sevier fold and thrust belt, were reactivated during 

a period of Neogene extension (Snoke, 1993). Fault systems in 

or adjacent to the Southwestern and South-Central Wyoming 

study area include the Continental Fault system that borders the 

southwest Wind River Range and, farther east, the South Granite Mountains fault system (fig. 4). South of the Continental 

Fault system near Dickie Springs, paleoplacer gold occurrences 

thought to have been deposited during Neogene extension 

have been mined from White River Formation sandstone and 

conglomerate deposited in alluvial fans along the flanks of the 

southern Wind River Range. The paleoplacers are south of lode 

gold occurrences and are likely sourced by Archean greenstone 

rocks in the South Pass-Atlantic City mining district (Antweiler 

and others, 1980; Hausel and Love, 1991). Paleoplacers are 

discussed in detail and evaluated later in this report.

Neogene normal faulting in Wyoming appears to have 

occurred in a geographically transitional tectonic setting, as 

evidenced by the presence of non-extended terrain of the Great 

Plains (fig. 3) to the east, the highly extended Basin and Range 

physiographic province, and the northern extent of the Rio 

Grande Rift in central Colorado to the south (Snoke, 1993).

The Bear Lake Plateau block (fig. 2) of the Bear River 

Watershed study area is located on the northeast of the Basin 

and Range province (fig. 3). The Bear River valley, occupied 

by Bear Lake, is bounded by Neogene normal faults along the 

Bear River Range and Bear Lake Plateau (Reheis and others, 

2009).

The Leucite Hills volcanic field is located partially 

within and adjacent to the Boars Tusk block of the Southwestern and South-Central Wyoming study area along the 

northeastern flank of the Rock Springs Uplift. The field is one 

of the youngest magmatic centers in Wyoming and is dated 

at 1.1 Ma (McDowell, 1971). Rock types consist of peralkaline (sodium+potassium>aluminum) ultrapotassic, mafic to 

ultramafic (very low silica) flows, dikes, necks, and plugs. 

These ultrapotassic rocks were investigated early in the 20th 

century as a potential source for potash fertilizer (Schulz and 

Cross, 1912). Pathfinder minerals for diamonds (pyrope garnet, 

chrome diopside, and orthopyroxene) have also been identified 

64–80 km southwest of the Leucite Hills, although the source 

of the indicator minerals is uncertain (Hausel and others, 1995).

The Neogene was also characterized by voluminous, 

felsic caldera-forming eruptions of the Yellowstone volcanic 

field. Ash was deposited throughout the region for hundreds 

of kilometers from the caldera source areas. Ash units (Lava 

Creek B ash) are preserved in young sediments (fig. 6) in the 

Green River, Rock Springs, Great Divide, and Washakie Basin 

areas (Love and others, 1993). An active geothermal system, 

complex Holocene deformation history, and progression of 

young volcanism that occurred toward the northeast along the 

Yellowstone Hot Spot track are indicators of the potential for 

future active volcanism in this area (Girard and Stix, 2012).

The present topography of the study area—mountains 

that have high relief relative to surrounding sedimentary 
Leasable Minerals 21

basins—has been strongly shaped by a late Cenozoic period 

of erosion. Large quantities of sediment were eroded from the 

basins during the Pliocene, when deep canyons were also cut 

into the southern Rocky Mountains (Scott, 1975). Erosion and 

glacial activity during this time sculpted mountains in Wyoming, eroded basin fill, and formed the present day landscape.

Leasable Minerals

Leasable minerals include both fluid and solid minerals. 

Leasable fluid minerals include oil and gas and geothermal 

resources, and leasable solid minerals include coal, oil shale, 

native asphalt, phosphate, sodium salts such as halite and 

trona, potassium (potash), and sulfur (in Louisiana and New 

Mexico). Of these resources, because they are important in or 

immediately adjacent to the study area, oil and gas, geothermal, coal, phosphate, and potassium (potash) are discussed 

below. The world’s largest deposit of trona, although important to the economy of Wyoming, is outside the study area and 

therefore is not discussed.

Oil and Gas

The Southwestern and South-Central Wyoming and Bear 

River Watershed study areas lie within the Southwestern Wyoming and Wyoming Thrust Belt Oil and Gas Provinces (note 

that, although they have similar names, these provinces are not 

exactly the same areas as the Southwestern and South-Central 

Wyoming study area or the thrust belt). According to IHS 

ENERDEQ well data (IHS Energy Group, 2016), there has 

been no significant oil or gas production within the proposed 

withdrawal area within the study area (one inactive well in 

Sweetwater County, Wyoming, produced a minor amount of 

oil and gas). However, there has been oil and significant gas 

produced within some of the townships that contain the proposed withdrawal areas.

Mineral Description

Petroleum is a naturally occurring mixture of gaseous, 

liquid, and solid hydrocarbons derived from the remains of 

plants and animals that lived millions of years ago. The USGS 

National Oil and Gas Assessment (NOGA) team assesses the 

potential undiscovered petroleum (oil, natural gas, and natural 

gas liquids (NGLs), such as propane and butane) resources 

throughout the country. The results of these assessments are 

discussed in more detail within the published reports referred 

to in this report.

Geology and Occurrence

The total petroleum system (TPS) concept is used by the 

USGS to assess the potential petroleum resources within an 

area. As defined by Magoon and Schmoker (2000), the TPS 

has

. . . the essential elements (source rock, reservoir 

rock, seal rock, and overburden rock) and processes 

(generation-migration-accumulation and trap formation) as well as all genetically related petroleum that 

occurs in seeps, shows, and accumulations, both 

discovered and undiscovered, whose provenance is 

a pod or closely related pods of active source rock. 

The TPS is a naturally occurring hydrocarbon-fluid 

system in the lithosphere that can be mapped, and 

includes the essential elements and processes needed 

for oil and gas accumulations to exist. The TPS concept presumes that migration pathways must exist, 

either now or in the past, connecting the provenance 

with the accumulations. . . The goal, then, is to map 

this natural fluid system, or TPS, in three dimensional space through time to locate, define, and 

evaluate those areas for undiscovered hydrocarbons.

Within the Southwestern Wyoming Province there are nine 

TPSs defined, and in the Wyoming Thrust Belt Province there 

are two TPSs defined.

Within the Southwestern and South-Central Wyoming 

and Bear River Watershed study area, there are conventional 

and unconventional (continuous) resources (fig. 7). The 

hydrocarbon source rocks in the area are Eocene to Permian 

in age and include the Wasatch, Green River, Lance, and Fort 

Union Formations; Mesaverde Group; Lewis Shale; Niobrara 

Formation; the Hilliard, Baxter, and Mowry Shales; and the 

Phosphoria Formation (fig. 8). The reservoir rocks in the area 

include the Frontier, Morrison, and Sundance Formations; 

the Dakota, Muddy, Nugget, and Tensleep Sandstones; and 

the Madison Limestone. Conventional oil and gas have been 

produced from both stratigraphic and structural traps.

Exploration and Development

Of the 72 townships containing proposed withdrawal 

areas in the Southwestern and South-Central Wyoming and 

Bear River Watershed study areas, only five are not associated 

with an oil and gas assessment unit (appendix 4). Although 

there are many assessed potential oil and gas resources in the 

area and near the study area, there has not been any significant 

hydrocarbon production within the study area, and the overall 

potential appears to be low to moderate, considering the presence of several dry wells within the study area.

Production

As previously mentioned, one well, now inactive, in 

Sweetwater County, Wyoming, produced a minor amount of 

oil and gas within the proposed withdrawal area (IHS Energy 

Group, 2016). Oil and gas has been produced within the townships surrounding some of the study areas. As table 4 shows, 

there have been almost 2.4 million barrels of oil (MMBO) and 
22 Geology and Mineral Resources of the Southwestern and South-Central Wyoming and Bear River Watershed Sagebrush Focal Areas

Land surface

Conventional

structural gas

accumulation

Coalbed gas

Conventional

stratigraphic gas

accumulation

Conventional

structural oil

accumulation

Continuous

basin-centered

gas accumulation Continuous

chalk gas or shale gas

accumulation

Continuous

chalk oil or shale

oil accumulation

Transition 

zones

Tens of miles

Gas generation window

Oil generation window

Oil

Gas

Water

Figure 7. Illustration showing categories of oil and natural-gas accumulations (after U.S. Geological Survey Southwestern Wyoming 

Province Assessment Team, 2005b).

Table 4. Cumulative oil and gas production per township in 

the Southwestern and South-Central Wyoming and Bear River 

Watershed study areas, Wyoming and Utah (Gunther and others, 

2016b). 

[PLSSID, Public Land Survey System Identifier, a concatenation of the state, 

principal meridian, township, range, and duplicate code; MCF, thousand cubic 

feet; WYO, Southwestern and South-Central Wyoming; Bear River Watershed, Bear River Watershed. See figure 17 for location of townships with these 

PLSSIDs]

PLSSID Study 

area

Cumulative 

liquid 

(barrels)

Cumulative gas 

(MCF)

WY060260N1070W0 WYO 581 582

WY060270N1070W0 WYO 4,171 29,191

WY060270N1080W0 WYO 4,431 466,026

WY060240N1140W0 BRW 4,595 11,068,643

WY060220N1040W0 WYO 11,556 421,780

WY060230N1150W0 BRW 12,168 2,364,158

WY060220N1150W0 BRW 20,226 1,942,695

WY060270N1060W0 WYO 24,031 570,037

WY060230N1130W0 BRW 200,012 12,122,880

WY060240N1120W0 BRW 301,983 799,513

WY060220N1130W0 BRW 737,378 36,012,018

WY060210N1180W0 BRW 1,070,774 5,222,511

Total 2,391,906 71,020,034

more than 71 billion cubic feet (BCF) of gas produced in the 

townships containing the study areas.

Results of Previous USGS Assessments

This area has been extensively assessed for potential 

hydrocarbon resources (figs. 9, 10, 11). Within the USGS 

Southwestern Wyoming and Wyoming Thrust Belt Oil and 

Gas Provinces (fig. 12), there are 35 assessed units (U.S. Geological Survey, 2004, 2005a). Of these, the 15 prior to 1995 

are termed ‘plays’ (Law, 1995); the 20 after 1995 are referred 

to as ‘assessment units.’ (Appendix 4 lists oil and gas plays 

and assessment units the Southwestern and South-Central 

Wyoming and Bear River Watershed study areas.)

Within the Wyoming Thrust Belt Province, there are 

assessed mean potential resources (table 5) of almost 39 

million barrels of oil (MMBO), 556.92 billion cubic feet of 

gas (BCFG) and 57.27 million barrels natural gas liquids 

(MMBNGL), as well as mean potential coalbed gas resources 

of 361 BCFG (U.S. Geological Survey, 2004). Within the 

Southwestern Wyoming Province, the USGS has assessed 

potential mean resources of 131 MMBO, 84,590 BCFG, and 

2,578 MMBNGL (U.S. Geological Survey Southwestern 

Wyoming Province Assessment Team, 2002). For more details 

about the geologic oil and gas assessment of this area, please 

see the aforementioned USGS oil and gas assessment reports 

and U.S. Geological Survey Southwestern Wyoming Province 

Assessment Team (2005a). 
Leasable Minerals 23

AGE

STRATIGRAPHIC UNITS

WEST EAST WESTCENTRAL

EASTCENTRAL

TERTIARY CRETACEOUS JURASSIC

Eocene

Paleocene

Late

Late

Middle

Early

Early

TRIASSIC

PERMIAN

DEVONIAN

SILURIAN

ORDOVICIAN

PENNSYLVANIAN

MISSISSIPPIAN CAMBRIAN

Late

Early

Middle

Bridger Formation

Green River Formation

Fort Union Formation

Hanna and

Ferris Fms.

Lance Formation

Cloverly Formation

Sundance Formation

Dinwoody Formation

Phosphoria Formation

Ankareh Formation

Nugget Sandstone

Morrison

Frontier Formation

Baxter Shale Steele Shale Niobrara Fm.

Fox Hills Sandstone

Lewis Shale

Almond Formation

Mesaverde Group

Hilliard Shale

Aspen Shale Mowry Shale

Thermopolis Shale

Muddy Sandstone Bear

River

Formation Dakota

Sandstone

Preuss

Sandstone

Twin Creek

Limestone

Entrada Sandstone

Carmel Formation

Gannett Group

Stump Formation Formation

Thaynes

Limestone Woodside

Formation

Chugwater Group

Goose Egg

Formation

Casper

Formation Tensleep

Sandstone

Amsden

Formation Amsden Fm. Morgan

Formation

Tensleep

Sandstone

Weber

Sandstone

Madison Limestone

Darby Formation

Unnamed

Bighorn Dolomite Unnamed

Gallatin Limestone

Gros Ventre Formation

Flathead

Sandstone

Buck

Spring

Formation

Flathead Sandstone

Fountain

Fm.

Darwin Ss.

Mesaverde

Group

Wasatch Formation

Hoback and

Almy Fms.

3

1

2

4

5

7 6

9

8

1. Wasatch–Green River Composite TPS

2. Lance–Fort Union Composite TPS

3. Mesaverde–Lance–Fort Union Composite TPS

4. Lewis TPS

5. Mesaverde TPS

6. Niobrara TPS

7. Hilliard–Baxter-Mancos TPS

8. Mowry Composite TPS

9. Phosphoria TPS

Figure 8. Generalized stratigraphic 

column of Southwestern Wyoming 

Province with numbered total 

petroleum systems (TPSs) (from U.S. 

Geological Survey Southwestern 

Wyoming Province Assessment Team, 

2005b). Fm., Formation; Ss., Sandstone.
24 Geology and Mineral Resources of the Southwestern and South-Central Wyoming and Bear River Watershed Sagebrush Focal Areas

Evanston

WYOMING

UTAH

IDAHO

SWEETWA

LINCOLN COUNTY

S

UINTA COUNTY

RICH

COUNTY

BEAR LAKE

COUNTY

CARIBOU COUNTY

CACHE

COUNTY

FRANKLIN

COUNTY

WEBER

COUNTY

MORGAN

COUNTY

80

189

30 89

30

89

189

30

19

Bear

Lake

BEAR LAKE

PLATEAU

FOSSIL BASIN

BLOCK FONTENELLE

BLOCK

BOAR

B

111°0' 110°0' 

42°30'

42°0'

41°30'

100 20 30 40 50 KILOMETERS

0 10 20 30 40 

Base modified from U.S. Geological Survey DEM data, 2016.

Roads and political data © 2014 Esri and its licensors.

Boundary data from San Juan and others (2016).

Exploration well status data from Gunther and others (2016a).

USA Contiguous Albers Equal Area Conic Projection.

Central meridian, 110° W., latitude of origin, 37.5° N.

North American Datum of 1983.
Leasable Minerals 25

Figure 9. Map showing well type by quarter cell (0.25 mile) 

summary of exploration and well type (Gunther and others, 2016a) 

in the Southwestern and South-Central Wyoming and Bear 

River Watershed study areas, Wyoming and Utah. USGS, U.S. 

Geological Survey.

Green River

Rock

Springs

ATER COUNTY

UBLETTE COUNTY

FREMONT COUNTY

80

287

191

191

1

BIG SANDY

BLOCK

RS TUSK

LOCK

CONTINENTAL

DIVIDE

BLOCK

SOUTH PASS

BLOCK

109°0'

Map

area

Study areas

IDAHO

MONTANA

OREGON

WYOMING

NEVADA UTAH

WASHINGTON

CO

CA

County boundaries

State boundaries

Proposed withdrawal areas

USGS study area boundary

Base data

Dry

Oil and gas

Gas

Oil

Exploration well type (0.25-mile cells)

EXPLANATION

MILES50
26 Geology and Mineral Resources of the Southwestern and South-Central Wyoming and Bear River Watershed Sagebrush Focal Areas

BIG SANDY

BLOCK

BOARS TUSK

BLOCK

SWEETWATER COUNTY

SUBLETTE COUNTY

191

191

581

4,431 4,171

11,556

24,031

110°0' 109°30' 109°0' 

42°30'

42°0'

0 5 10 15 20 MILES

0 5 10 15 20 KILOMETERS

Base modified from U.S. Geological Survey DEM data, 2016.

Roads and political data © 2014 Esri and its licensors.

Boundary data from San Juan and others (2016).

USA Contiguous Albers Equal Area Conic Projection.

Central meridian, 110° W., latitude of origin, 37.5° N.

North American Datum of 1983.

A
Leasable Minerals 27

Figure 10. Maps showing cumulative liquid (oil) production from 

Wyoming oil and gas fields by township (Gunther and others, 

2016b) in the (A) Southwestern and South-Central Wyoming 

study area, Wyoming, and (B) Bear River Watershed study area, 

Wyoming and Utah. USGS, U.S. Geological Survey.

CONTINENTAL

DIVIDE BLOCK

SOUTH PASS

BLOCK

FREMONT COUNTY

108°30'

Map

area

Study areas

IDAHO

MONTANA

OREGON

WYOMING

NEVADA UTAH

WASHINGTON

County boundaries

Proposed withdrawal areas

USGS study area boundary

Base data

15,001 - 24,031

5,001 - 15,000

581 - 5,000

Cumulative liquid production per township (barrels)

Oil and gas

Oil

Gas

Wyoming oil and gas fields

EXPLANATION

Liquid production data from Gunther and others (2016b).

Oil and gas field data from Wyoming State Geological Survey (2012).
28 Geology and Mineral Resources of the Southwestern and South-Central Wyoming and Bear River Watershed Sagebrush Focal Areas

BEAR LAKE

PLATEAU

BLOCK

FOSSIL BASIN

BLOCK

FON

B

Bear

Lake

1,070,774

30

189

89

111°30' 111°0' 

42°0'

41°30'

20151050 KILOMETERS

0 5 10 15 MILES20 Base modified from U.S. Geological Survey DEM data, 2016.

Roads and political data © 2014 Esri and its licensors.

Boundary data from San Juan and others (2016).

USA Contiguous Albers Equal Area Conic Projection.

Central meridian, 110° W., latitude of origin, 37.5° N.

North American Datum of 1983.

B
Leasable Minerals 29

Figure 10.—Continued

NTENELLE

BLOCK

Fontenelle

Reservoir

4,595

12,168

301,983

737,378

200,012

80

30

Kemmerer

110°30'

20,226

IDAHO

MONTANA

OREGON

WYOMING

NEVADA UTAH

WASHINGTON

Map

area Study areas

County boundaries

Proposed withdrawal areas

USGS study area boundary

Base data

300,001 - 1,070,774

25,001 - 300,000

15,001 - 25,000

5,001 - 15,000

581 - 5,000

Cumulative liquid oil production per township (barrels)

Oil and gas

Oil

Gas

Wyoming oil and gas fields

EXPLANATION

Liquid production data from Gunther and others (2016b).

Oil and gas field data from Wyoming State Geological Survey (2012).
30 Geology and Mineral Resources of the Southwestern and South-Central Wyoming and Bear River Watershed Sagebrush Focal Areas

BIG SANDY

BLOCK

BOARS TUSK

BLOCK

SWEETWATER COUNTY

SUBLETTE COUNTY

191

191

582

466,026 29,191 570,037

421,780

110°0' 109°30' 109°0' 

42°30'

42°0'

20151050 KILOMETERS

0 5 10 15 MILES20 Base modified from U.S. Geological Survey DEM data, 2016.

Roads and political data © 2014 Esri and its licensors.

Boundary data from San Juan and others (2016).

USA Contiguous Albers Equal Area Conic Projection.

Central meridian, 110° W., latitude of origin, 37.5° N.

North American Datum of 1983.

A
Leasable Minerals 31

Figure 11. Maps showing cumulative gas production from 

Wyoming oil and gas fields by township (Gunther and others, 

2016b) in the (A) Southwestern and South-Central Wyoming 

study area, Wyoming, and (B) Bear River Watershed study area, 

Wyoming and Utah. USGS, U.S. Geological Survey.

CONTINENTAL

DIVIDE BLOCK

SOUTH PASS

BLOCK

FREMONT COUNTY

108°30'

Map

area

Study areas

IDAHO

MONTANA

OREGON

WYOMING

NEVADA UTAH

WASHINGTON

County boundaries

Proposed withdrawal areas

USGS study area boundary

Base data

500,001 - 570,037

100,001 - 500,000

582 - 100,000

Cumulative gas production per township (million cubic feet)

Oil and gas

Oil

Gas

Wyoming oil and gas fields

EXPLANATION

Production data from Gunther and others (2016b).

Oil and gas field data from Wyoming State Geological Survey (2012).
32 Geology and Mineral Resources of the Southwestern and South-Central Wyoming and Bear River Watershed Sagebrush Focal Areas

BEAR LAKE

PLATEAU

BLOCK

FOSSIL BASIN

BLOCK

FON

B

Bear

Lake

30

189

89

5,222,511

5,497,846

IDAHO

UTAH

BEAR LAKE COUNTY

FRANKLIN

COUNTY

CACHE

COUNTY

RICH COUNTY

111°30' 111°0' 

42°0'

41°30'

20151050 KILOMETERS

0 5 10 15 MILES20 Base modified from U.S. Geological Survey DEM data, 2016.

Roads and political data © 2014 Esri and its licensors.

Boundary data from San Juan and others (2016).

USA Contiguous Albers Equal Area Conic Projection.

Central meridian, 110° W., latitude of origin, 37.5° N.

North American Datum of 1983.

B
Leasable Minerals 33

NTENELLE

BLOCK

Fontenelle

Reservoir

80

30

Kemmerer

799,513

2,364,158

1,942,695

11,068,643

36,012,018

12,122,880

WYOMING

UINTA COUNTY

LINCOLN COUNTY 

110°30'

Map

area Study areas

IDAHO

MONTANA

OREGON

WYOMING

NEVADA UTAH

WASHINGTON

County boundaries

Proposed withdrawal areas

USGS study area boundary

Base data

Cumulative gas production per township (million cubic feet)

Oil and gas

Oil

Gas

Wyoming oil and gas fields

EXPLANATION

582 - 800,000

800,001 - 2,000,000

2,000,001 - 5,000,000

5,000,001 - 13,000,000

13,000,001 - 36,012,018

Production data from Gunther and others (2016b).

Oil and gas field data from Wyoming State Geological Survey (2012).

Figure 11.—Continued
34 Geology and Mineral Resources of the Southwestern and South-Central Wyoming and Bear River Watershed Sagebrush Focal Areas

BEAR LAKE

PLATEAU

BLOCK

FOSSIL BASIN

BLOCK

FONTENELLE

BLOCK

BOARS TU

BLOCK

Bear

Lake

Evanston

WYOMING

UTAH

IDAHO

SWEETWAT

LINCOLN COUNTY

UINTA COUNTY

RICH

COUNTY

BEAR LAKE

COUNTY

CARIBOU COUNTY

CACHE

COUNTY

FRANKLIN

COUNTY

WEBER

COUNTY

MORGAN

COUNTY

80

189

30 89

30

89

189

30

191

111°0' 110°0' 

42°30'

42°0'

41°30'

0 10 20 30 40 50 MILES

0 10 20 30 40 50 KILOMETERS

Base modified from U.S. Geological Survey DEM data, 2016.

Roads and political data © 2014 Esri and its licensors.

Boundary data from San Juan and others (2016).

USA Contiguous Albers Equal Area Conic Projection.

Central meridian, 110° W., latitude of origin, 37.5° N.

North American Datum of 1983.
Leasable Minerals 35

Figure 12. Map showing Federal oil and gas leases and oil 

and gas provinces within the Southwestern and South-Central 

Wyoming and Bear River Watershed study areas, Wyoming and 

Utah. USGS, U.S. Geological Survey.

BIG SANDY

BLOCK

USK

K

CONTINENTAL

DIVIDE BLOCK

SOUTH PASS

BLOCK

Green River

Rock

Springs

G

TER COUNTY

SUBLETTE COUNTY

FREMONT COUNTY

80

287

191

191

109°0'

IDAHO

MONTANA

OREGON

WYOMING

NEVADA UTAH

WASHINGTON

CO

CA

Map

area

Study areas

County boundaries

State boundaries

Proposed withdrawal areas

USGS study area boundary

Base data

Southwestern Wyoming oil and gas province

Wyoming Thrust Belt oil and gas province

Oil and gas provinces

Oil and gas

Gas

Oil

Oil and gas field type

Closed lease

Authorized simultaneous oil and gas lease on public land

Authorized noncompetetive oil and gas lease on public land

Authorized competetive oil and gas lease on public land

Oil and gas leases by section

EXPLANATION

Oil and gas provinces from USGS SW WY Oil and Gas Assessment Team (2005a).

Oil and gas field data from Wyoming State Geological Survey (2012).

Dicken and San Juan (2016).
36 Geology and Mineral Resources of the Southwestern and South-Central Wyoming and Bear River Watershed Sagebrush Focal Areas

Table 5. Assessed oil and gas potential in the Wyoming Thrust Belt and Southwestern Wyoming Provinces (U.S. 

Geological Survey, 2004; U.S. Geological Survey Southwestern Wyoming Province Assessment Team, 2005a).

[AU, assessment unit; MMBO, million barrels of oil; BCFG, billion cubic feet of gas; MMBNGL, million barrels natural gas liquids]

Resource type Mean oil (MMBO) Mean gas (BCFG) Mean natural gas 

liquids (MMBNGL)

Wyoming Thrust Belt Province

Conventional

Thrust Belt Conventional AU 38.83 556.92 57.27

Coalbed gas

Frontier-Adaville-Evanston Coalbed Gas AU 361.1 0

Southwestern Wyoming Province

Conventional 27.83 2,420.8 73.93

Coalbed gas 0 1,528.92 0

Tight gas 0 80,577.67 2,500.28

Conventional oil 103.64 62.18 3.73

Geothermal Energy

Geothermal energy constitutes one of the Nation’s largest sources of renewable electric power. Its potential is an 

important consideration, given that current projections indicate 

the United States will need to increase its electrical power 

generating capacity by approximately 25 percent over the next 

25 years (Energy Information Administration, 2015). Although 

the installed capacity of geothermal (approximately 3,000 

megawatts electric, MWe) falls short of meeting the Nation’s 

power needs, it constitutes a fraction of the estimated available resources based on recent assessments. With potential 

advances in exploration and development technologies, 

geothermal resources could provide a significant source of 

baseload electric power. Because of government mandates and 

incentives for renewable energy, it is expected that the demand 

for geothermal energy will continue to grow, and, given the 

concentration of geothermal resources in the Western United 

States, a significant part of this growth could occur on public 

lands. This section, which provides a review of the geothermal 

resource potential of the study areas, is based on the results 

of the USGS 2008 assessment of the Nation’s moderate- and 

high-temperature geothermal resources (Williams and others, 

2008) that includes a provisional assessment for enhanced 

geothermal systems (EGS), as well as earlier USGS and statelevel inventories and assessments.

Mineral Description

Geothermal resources can be divided into two categories—conventional and unconventional. Conventional 

resources are those geothermal systems defined by Muffler 

(1979) as “any regionally localized geological setting where 

naturally occurring parts of the Earth’s thermal energy are 

transported close enough to the Earth’s surface by circulating 

steam or hot water to be readily harnessed for use.” These 

geothermal (or alternatively, hydrothermal) systems involve 

the natural vertical movement of water through either free or 

forced convection (for example, Duffield and Sass, 2003). All 

of the geothermal systems developed for commercial electric 

power generation in the United States fall in this category. 

Within this framework, identified hydrothermal systems are 

divided into three temperature classes: low-temperature (<90 

degrees Celsius, °C), moderate-temperature (90 to 150 °C), 

and high-temperature (>150 °C). High-temperature systems 

include both liquid- and vapor-dominated resources. Moderate-temperature systems are almost exclusively liquid-dominated, and all low-temperature systems are liquid-dominated. 

All three temperature classes are suitable for direct use applications, but in general, only moderate- and high-temperature 

systems are viable for electric power generation. The heat 

source of a hydrothermal system can be characterized as either 

magmatic or amagmatic. Magmatic geothermal reservoirs, 

which derive their heat from shallow-crustal magma bodies, 

are typically larger and higher in temperature than amagmatic 

systems, which owe their heat to deep circulating fluids within 

the background geothermal gradient of the upper crust (Coolbaugh and others, 2006).

Unconventional geothermal resources may have the 

technical potential for electric power generation, reductions 

in demand for other nonrenewable sources of energy, or 

direct-use applications, but have not yet been adopted on a 

commercial basis. These resources include deep, high-temperature sedimentary basins, especially geothermal resources 

collocated with oil and gas accumulations or zones of geopressured fluids, and enhanced geothermal systems (EGS). 

EGS constitute the part of a geothermal resource for which a 

measureable increase in production over its natural state is or 

can be attained through mechanical, thermal, and (or) chemical stimulation of the reservoir rock (Williams and DeAngelo, 

2011).
Leasable Minerals 37

Geology and Occurrence

Compilations of geothermal occurrences in Wyoming 

and Utah (Breckenridge and Hinckley, 1978; Reed and others, 1983; Lienau and Ross, 1996; Blackett and Wakefield, 

2004) do not identify any thermal springs or wells within the 

boundaries of the Southwestern and South-Central Wyoming 

and Bear River Watershed study areas (fig. 13). This absence 

of geothermal manifestations is consistent with the relatively 

low values of favorability for the occurrence of moderateand high-temperature geothermal systems across the region 

spanned by the study areas, with the exception of the part of 

the Bear River Watershed study area that extends into eastern 

Cache County in Utah (fig. 14). This low favorability reflects 

the relative absence of factors associated with the formation of 

moderate- and high-temperature geothermal systems, such as 

seismicity, Quaternary faulting, Quaternary magmatic activity, 

a dominantly extensional crustal stress regime, or high crustal 

heat flow (Williams and DeAngelo, 2008).

Low-temperature thermal springs and wells outside of the 

study areas in Wyoming, southeastern Idaho, and northeastern 

Utah (figs. 13 and 14) occur in diverse settings. Those in the 

thrust belt to the west and northwest of the Bear River Watershed study area are the result of fluid circulation in permeable 

faults and fractures driven by differences in topography. Those 

to the north and northeast in Sublette and Fremont Counties 

of Wyoming correlate with shallow thermal aquifers formed 

due to flow along permeability contrasts in sedimentary 

units (Breckenridge and Hinckley, 1978). Low-temperature 

resources can be exploited for direct-use applications (for 

example, greenhouses, aquaculture, district heating, drying for 

industrial and agricultural applications), provided the infrastructure for those applications is located on site.

Exploration and Development

Southwestern and South-Central Wyoming Sagebrush 

Study Area

Exploration for hydrothermal systems within and near 

the Southwestern and South-Central Wyoming study area has 

been limited to four crustal heat flow measurements (Williams and DeAngelo, 2011). These range from an average 

of approximately 50 milliwatts per square meter (mW m-2) 

at the southwestern boundary of the Wind River Range to 

approximately 70 mW m-2 south of the study area within the 

greater Green River Basin. The values of heat flow near the 

Wind River Mountains are elevated in comparison with other 

Archean terranes, most likely because of thinning of the lithosphere during the Laramide orogeny (Lenardic, 1997), but are 

still relatively low in comparison to the average crustal heat 

flow in the Western United States. 

Higher heat flow in the greater Green River Basin, 

although not indicative of favorability for the occurrence of 

moderate- and high-temperature hydrothermal systems due 

to the absence of other contributing factors such as seismicity, Quaternary faulting, Quaternary magmatic activity, or a 

dominantly extensional crustal stress regime, is consistent 

with conductive geothermal resources in the deeper permeable 

units of the basin. Temperature gradient mapping based on 

the bottom hole temperature (BHT) records from oil and gas 

exploration wells indicates that formations in the Green River 

Basin can reach or exceed temperatures of 93 °C (200 Fahrenheit, °F) at depth (Finn, 2002). Although the lowest temperature commercial geothermal development in the conterminous 

United States is a 107 °C resource at Wabuska, California, 

a recent Department of Energy-funded project at the Rocky 

Mountain Oilfield Testing Center in the Powder River Basin 

demonstrated the technical capability of generating electric 

power from produced oil field waters with in situ temperatures 

that range from 90 to 95 °C (Anderson, 2010).

Bear River Watershed Study Area

As noted above, the Bear River Watershed study area 

extends from the greater Green River Basin westward across 

the Wyoming thrust belt to the eastern edge of the Great Basin, 

from a region of relatively low hydrothermal favorability in 

the eastern part of the study area (fig. 13) to a region of higher 

favorability in the west. Higher heat flow, as well as seismicity 

and Quaternary faulting, are indications of crustal permeability (Williams and Deangelo, 2008). As a result, the western 

reaches of the study area carry the highest potential for this 

region, even though there are no identified low or moderateto-high-temperature geothermal systems within the Bear River 

Watershed study area. There is a geothermal development site 

located just west of the Bear Lake Plateau block (fig. 2) in 

Cache County, Utah—the Renaissance geothermal prospect 

(Austin and others, 2006). This prospect may be related to 

a permeable fault zone that was penetrated by a petroleum 

exploration well at a depth of 2,500 m in 1974 and which 

yielded hot water at a temperature of approximately 140 °C.

Results of Previous USGS Assessments

The 2008 USGS geothermal resource assessment (Williams and others, 2008) did not identify any moderate- or 

high-temperature geothermal systems within the Utah-Wyoming study areas. The assessment of undiscovered resources 

was based, in part, on a series of geographic information 

systems (GIS) logistic regression analyses through which 

geothermal potential was modeled using a weighted combination of evidence layers derived from mappable geologic and 

tectonic features available in digital databases (Williams and 

DeAngelo, 2008; Williams and others, 2009). Figure 13 illustrates the distribution of relative geothermal potential from 

these analyses across the region encompassing the Southwestern and South-Central Wyoming and Bear River Watershed 

study areas. Mean favorability for conventional resources in 

the Bear River Watershed is approximately 50 percent of the 

average for the entire Western United States, whereas that for 
38 Geology and Mineral Resources of the Southwestern and South-Central Wyoming and Bear River Watershed Sagebrush Focal Areas

Bear

Lake

Evanston

WYOMI

UTAH

IDAHO

BEAR LAKE PLATEAU

BLOCK

FOSSIL BASIN

BLOCK

FONTENELLE

BLOCK

BIG SANDY

BLOCK

SWEETW

LINCOLN COUNTY

UINTA COUNTY

RICH

COUNTY

BEAR LAKE

COUNTY

CARIBOU COUNTY

CACHE

COUNTY

FRANKLIN

COUNTY

WEBER

COUNTY

MORGAN

COUNTY

80

189

30 89

30

89

189

30

1

111°0' 110°0' 

42°30'

42°0'

41°30'

0 10 20 30 40 

0 10 20 30 40 50 KILOMETERS

Base modified from U.S. Geological Survey DEM data, 2016.

Roads and political data © 2014 Esri and its licensors.

Boundary data from San Juan and others (2016).

USA Contiguous Albers Equal Area Conic Projection.

Central meridian, 110° W., latitude of origin, 37.5° N.

North American Datum of 1983.
Leasable Minerals 39

Figure 13. Map showing the locations of low-, moderate-, and high-temperature 

geothermal systems and geothermal development sites, as well as hydrothermal 

favorability from the 2008 U.S. Geological Survey (USGS) geothermal assessment for 

an area encompassing the Southwestern and South-Central Wyoming and Bear River 

Watershed study areas, Wyoming and Utah (Williams and DeAngelo, 2008).

Green River

Rock

Springs

ING

BOARS TUSK

BLOCK

CONTINENTAL

DIVIDE BLOCK

SOUTH PASS

BLOCK

WATER COUNTY

SUBLETTE COUNTY

FREMONT COUNTY

80

287

191

191

91

109°0'

IDAHO

MONTANA

OREGON

WYOMING

NEVADA UTAH

WASHINGTON

CO

CA

Study areas

Map

area

County boundaries

State boundaries

Proposed withdrawal areas

USGS study area boundary

Base data

Geothermal developing sites (as of September 2, 2014)

Maple Grove Hot Springs

Moderate and high temperature geothermal systems

Well

Spring

Low-temperature geothermal springs and wells

Low

Medium

High

Geothermal favorability

EXPLANATION

50 MILES

Geothermal data from DeAngelo and Williams (2016a, b).
40 Geology and Mineral Resources of the Southwestern and South-Central Wyoming and Bear River Watershed Sagebrush Focal Areas

Bear

Lake

BEAR LAKE PLATEAU

BLOCK

FOSSIL BASIN

BLOCK

FONTENELLE

BLOCK

BIG SANDY

BLOCK

Evanston

WYOMING

UTAH

IDAHO

SWEETWATE

LINCOLN COUNTY

SUB

UINTA COUNTY

RICH

COUNTY

BEAR LAKE

COUNTY

CARIBOU COUNTY

CACHE

COUNTY

FRANKLIN

COUNTY

WEBER

COUNTY

MORGAN

COUNTY

80

189

30 89

30

89

189

30

191

111°0' 110°0' 

42°30'

42°0'

41°30'

0 10 20 30 40 

0 10 20 30 40 50 KILOMETERS

Base modified from U.S. Geological Survey DEM data, 2016.

Roads and political data © 2014 Esri and its licensors.

Boundary data from San Juan and others (2016).

USA Contiguous Albers Equal Area Conic Projection.

Central meridian, 110° W., latitude of origin, 37.5° N.

North American Datum of 1983.
Leasable Minerals 41

Figure 14. Map showing the locations of low-, moderate-, 

and high-temperature geothermal systems and geothermal 

development sites, as well as the estimated temperature at 6 

km depth, for an area encompassing the Southwestern and 

South-Central Wyoming and Bear River Watershed study areas, 

Wyoming and Utah. USGS, U.S. Geological Survey; °C, degrees 

Celsius.

BOARS TUSK

BLOCK

CONTINENTAL

DIVIDE BLOCK

SOUTH PASS

BLOCK

Green River

Rock

Springs

G

ER COUNTY

BLETTE COUNTY

FREMONT COUNTY

80

287

191

191

109°0'

Map

area

Study areas

IDAHO

MONTANA

OREGON

WYOMING

NEVADA UTAH

WASHINGTON

CO

CA

County boundaries

State boundaries

Proposed withdrawal areas

USGS study area boundary

Base data

Geothermal developing sites (as of September 2, 2014)

Maple Grove Hot Springs

Moderate and high temperature geothermal systems

Well

Spring

Low-temperature geothermal springs and wells

<100

100.1 - 125

125.1 - 150

150.1 - 175

175.1 - 200

200.1 - 225

225.1 - 250

>250

Temperature (°C) at 6-kilometers depth

EXPLANATION

50 MILES

Geothermal data from DeAngelo and Williams (2010a, b).
42 Geology and Mineral Resources of the Southwestern and South-Central Wyoming and Bear River Watershed Sagebrush Focal Areas

the Southwestern and South-Central Wyoming is approximately 5 percent that of the Western U.S. average. As noted 

above, the western margin of the Bear River Watershed has 

elevated geothermal potential and drilling indicates water hot 

enough for electric power generation at the Renaissance site 

just to the west. However, the western boundary of the Bear 

River Watershed and the Renaissance site are separated by the 

Wellsville Mountains, and, as the permeable fault penetrated at 

Renaissance is most likely confined to the western margin of 

the Wellsville Mountains, it is not clear that the presence of a 

potential geothermal resource at Renaissance has significance 

for the presence or absence of geothermal resources in Bear 

River Watershed.

Low-temperature geothermal resources of this region 

were assessed by Reed (1983), with subsequent inventories of 

low-temperature springs and wells published by Breckenridge 

and Hinckley (1978), Reed and others (1983), and Lienau 

and Ross (1996). No springs and wells from these inventories 

are located within the Utah-Wyoming study areas, although 

Reed (1983) did note the low-temperature potential associated 

with thermal aquifers in the greater Green River Basin. These 

aquifers could be exploited locally for direct-use applications, 

and it is conceivable that under more favorable commercial 

conditions, geothermal power demonstration projects similar 

to the Department of Energy’s Rocky Mountain Oilfield Testing Center (RMOTC) Powder River Basin project (described 

by Anderson, 2010) could be established in the greater Green 

River Basin. However, no site-specific assessment has been 

conducted in the greater Green River Basin to quantify the 

geothermal-resource potential from oil and gas production for 

which the produced waters are delivered in sufficient quantity 

and temperature to produce electric power.

In the provisional assessment of EGS resource potential 

(Williams and others, 2008), the threshhold for EGS viability was established as a minimum temperature of 150 °C at 

a depth of 6 km (see also Williams and DeAngelo, 2011). 

Any region below that temperature-depth threshold was not 

included in the assessment. The region covered by the Southwestern and South-Central Wyoming study area is at or just 

below that cut-off, and, consequently, cannot be considered 

as having significant EGS potential. Temperatures at a depth 

of 6 km across the Bear River Watershed study area range 

from approximately 150 to 225 °C, which is equivalent to the 

average for the entire Western United States (fig. 14). Consequently, the Bear River Watershed study area could become a 

target for EGS development if geothermal production technology becomes commercially viable, but it should be noted that 

large regions of the Western United States, including northern 

Nevada, northwestern Utah, and southern Oregon and Idaho, 

have temperatures at 6 km depth that are well in excess of 

250 °C, making them more attractive for first generation EGS 

development (Williams and DeAngelo, 2011).

Coal

Coal supplies 33 percent of electrical power in the United 

States (Energy Information Administration, 2015). Although 

its percentage of total electrical generation has declined, it 

will likely continue to be a major source of electrical power in 

the years to come. Coal on Federal lands is managed by BLM 

as a leasable solid mineral under the Mineral Leasing Act of 

1920. BLM manages coal leasing, as well as other administrative duties related to coal production from Federal coal lands 

throughout the United States. 

Mineral Description

Coal is a black or dark-brown combustible rock that 

consists of compressed and carbonized vegetable matter and is 

used as a fuel.

Geology and Occurrence in the Study Area

The USGS report of coal fields in the conterminous 

United States (East, 2013) shows that parts of the Southwestern and South-Central Wyoming and Bear River Watershed 

study areas are within the Green River and Hams Fork coal 

regions (fig. 15). These coal regions are both known to have 

subbituminous to bituminous Tertiary and Cretaceous coal.

The Green River coal region includes the Tertiary and 

Upper Cretaceous rocks (fig. 16) of the greater Green River 

Basin (fig. 3). Coal-bearing formations include, from oldest 

to youngest, the Upper Cretaceous Rock Springs and Almond 

Formations of the Mesaverde Group; the Upper Cretaceous 

Lance Formation; the Paleocene Fort Union Formation; and 

the Eocene Wasatch Formation. These formations have been 

mined for coal around the Rock Springs Uplift since the mid1880s (Gardner and Flores, 1989). Currently (2016) the Jim 

Bridger and Black Butte Mines are active on the eastern side 

of the uplift and another inactive mine (Stansbury) is on the 

west side (fig. 15; mine status from Wyoming Department of 

Environmental Quality, 2015).

The Hams Fork coal region occurs within the thrust 

belt area. This is an area of very complex geology due to the 

extreme faulting and steeply dipping beds. Coal-bearing rocks 

trend north-south, and are bounded by the fault-controlled 

structure. Four coal fields have been named in the region—

Evanston, Greys River, Kemmerer, and McDougal Coal Fields 

(Glass, 1977). Coal-bearing formations include, from oldest 

to youngest, the Lower Cretaceous Bear River and Cokeville 

Formations; the Upper Cretaceous Sage Junction1

, Frontier, 

Blind Bull, and Adaville Formations; the Cretaceous to Paleocene Evanston Formation; and the Eocene Wasatch Formation 

(fig. 16). Historically, coal has been mined in the area since 

1

Earlier publications place the Sage Junction Formation at the top of the 

Lower Cretaceous (Rubey, 1973), but here we follow the Wyoming State 

Geological Survey’s placement in the lowermost part of the Upper Cretaceous 

section (see Jones and others, 2011) and, thus, an early Late Cretaceous age. 
Leasable Minerals 43

1869 (Glass, 1977). The Adaville and Frontier Formations 

have produced the most coal. Prospects and mines, mostly 

concentrated in the Adaville and Frontier Formations, dot 

the region (Jones and others, 2011). Currently the Kemmerer 

Mine, working in the Adaville Formation, is the only active 

mine in the Hams Fork coal region (Wyoming Department of 

Environmental Quality, 2015).

The USGS has not done a formal quantitative assessment 

of coal resources within the Southwestern and South-Central 

Wyoming or Bear River Watershed study areas, but Berryhill 

and others (1950) estimated resources of 15.96 billion short 

tons for the Green River coal region and 4.87 billion short tons 

for the Hams Fork coal region.

Recent Exploration and Mining Activity

Southwestern and South-Central Wyoming Study Area

Most of the Southwestern and South-Central Wyoming 

study area is within the northern part of the Green River coal 

region (fig. 16) with the exception of the South Pass block, 

which is underlain by Precambrian rocks of the Wind River 

Range. As mentioned, those parts of the study area that are 

within the coal region have never been quantitatively assessed 

by the USGS for coal resources or coal reserves. Figure 17 is 

provided for ease of finding the areas mentioned in the following section.

Exploratory drilling for coal occurred in T. 22 N., R. 

104 W. (fig. 17) in the early 1970s. Coal was observed in the 

Paleocene Fort Union and the Cretaceous Almond and Rock 

Springs Formations of the Mesaverde Group. The Fort Union 

coal beds are few and mostly 0.9 m (3 ft) thick or less. The 

Almond coal beds are more numerous and range up to about 

1.5 m (5 ft) thick. The Rock Springs Formation has numerous 

coal beds with thicknesses up to 4.5 m (15 ft). None of the 

drill holes were within the proposed withdrawal area. Three 

sections within that township were leased for coal, but the 

leases have since been closed (Dicken and San Juan, 2016b). 

The nearest holes to the proposed withdrawal area were drilled 

in the Fort Union and Almond Formations.

Several prospect pits were also observed in T. 22 N., R. 

104 W. (fig. 17) (Jones and others, 2011). These pits were in 

the Eocene Wasatch Formation, which has no mapped coal in 

that area. Although the pits are in the study area, they are not 

within the proposed withdrawal areas.

The National Coal Resource Assessment (Ellis and 

others, 1999) studied the greater Green River Basin, but the 

assessed area of that report is south of the Southwestern and 

South-Central Wyoming study area, and it only assessed the 

Deadman coal of the Paleocene Fort Union Formation, which 

is currently being mined on the eastern side of the Rock 

Springs Uplift (fig. 4).

Bear River Watershed Study Area

The Bear River Watershed study area is partially within 

two coal regions (fig. 16). As mentioned above, none of the 

area has been quantitatively assessed by the USGS for coal 

resources, although some of the townships within the study 

area have coal-bearing rocks. For purposes of this discussion, 

the Bear River Watershed study area can be divided into three 

blocks—Bear Lake Plateau, Fossil Basin, and Fontenelle (fig. 

2).

The Bear Lake Plateau block is not within any coal 

region. Geologic formations range in age from Paleozoic to 

Quaternary. None of the formations present is coal bearing.

The Fossil Basin block overlies parts of three coal fields 

(Kemmerer, Greys River, and Evanston) within the Hams 

Fork coal region. However, most of the proposed withdrawal 

areas do not directly overlie coal-bearing rocks because of the 

geometry of the thrust belt (fig. 4).

The Kemmerer coal field is partially within T. 20 and 

21 N., R. 117 W. (fig. 17). The Kemmerer Mine is partially 

located in those townships (Jones and others, 2011), however, 

the nearest proposed withdrawal areas are more than 2.8 km 

(1.75 mi) west of the mine permit area (Wyoming Department of Environmental Quality, 2015). The Federal coal 

leases extend 0.8 km (0.5 mi) further west than the permit area 

(Bureau of Land Management, 2016) but are still 1.6 km (1 

mi) from the nearest proposed withdrawal areas. As the coal 

beds at the mine dip steeply to the west, the mine activities are 

very unlikely to expand westward. From 1983 through 2015, 

132,452,275 short tons of coal were produced, and 4,470,864 

short tons of coal were produced in 2015 (Mine Safety and 

Health Administration, 2016).

The Greys River Coal Field is partially within five PLSS 

townships: T. 22 N., R. 118 W.; T. 22 N., R. 119 W.; T. 23 N., 

R. 118 W.; T. 23 N., R. 119 W.; and T. 24 N., R. 118 W. (fig. 

15, 17). No mining has been documented in this coal field 

(Glass, 1977).

The northern tip of the Evanston Coal Field barely protrudes into the Fossil Basin block in T. 20 N., R. 118 W. (figs. 

15, 17). Although a number of old mines exist in the southern 

part of the coal field, no mining is known to have occurred 

within the block (Glass, 1977, Jones and others, 2011).

The Fontenelle block straddles the Green River and 

Hams Fork coal regions (fig. 15). Several small old mines are 

reported in T. 22 N., R. 115 W. (Jones and others, 2011). There 

are no known coal reserves within the PLSS townships and 

none within the proposed withdrawal areas in this block.

Results of Previous USGS Assessments

A previous assessment has not been undertaken in the 

study area.
44 Geology and Mineral Resources of the Southwestern and South-Central Wyoming and Bear River Watershed Sagebrush Focal Areas

BEAR LAKE

PLATEAU

BLOCK

FOSSIL BASIN

BLOCK

FONTENELLE

BLOCK

BIG SANDY

BLOCK

Grey's River

Coal Field

Kemmerer

Coal Field

Evanston

Coal Field

Grey's River

Coal Field

McDougal

Coal Field

Bear

Lake

Evanston

Green R

Kemmerer

WYOMIN

UTAH

IDAHO

SWEETWATER COUN

LINCOLN COUNTY

SUBLETTE COUNTY

UINTA COUNTY

RICH

COUNTY

BEAR LAKE

COUNTY

CARIBOU COUNTY

CACHE

COUNTY

FRANKLIN

COUNTY

WEBER

COUNTY

MORGAN

COUNTY

80

189

30 89

30

89

189

30

19

KEMMERER

HAYSTACK

111°0' 110°0' 

42°30'

42°0'

41°30'

100 20 30 40 50 KILOMETERS

0 10 20 30 40 

Base modified from U.S. Geological Survey DEM data, 2016.

Roads and political data © 2014 Esri and its licensors.

Boundary data from San Juan and others (2016).

USA Contiguous Albers Equal Area Conic Projection.

Central meridian, 110° W., latitude of origin, 37.5° N.

North American Datum of 1983.
Leasable Minerals 45

BOARS TUSK

BLOCK

CONTINENTAL

DIVIDE BLOCK

SOUTH PASS

BLOCK

River

Rock Springs

NG

NTY

FREMONT COUNTY

80

287

191

191

1

BLACK BUTTE

JIM BRIDGER

LEUCITE HILLS

STANSBURY

109°0'

IDAHO

MONTANA

OREGON

WYOMING

NEVADA UTAH

WASHINGTON

CO

CA

Map

area

Study areas

County boundaries

State boundaries

Proposed withdrawal areas

USGS study area boundary

Base data

Closed logical mining unit

Closed coal lease

Authorized logical mining unit

Authorized preferential right coal lease

Authorized coal lease

Federal coal leases aggregated by lease serial number

Mine permit boundaries

Hams Fork coal region

Green River coal region

EXPLANATION

MILES50

Permit locations from Wyoming Department of Environmental Quality (2015).

Coal region data from East (2013).

Figure 15. Map showing the coal regions (in turquoise and 

lavender) and mine-permit boundaries (outlined in red) in and near 

the Southwestern and South-Central Wyoming and Bear River 

Watershed study areas. USGS, U.S. Geological Survey.
46 Geology and Mineral Resources of the Southwestern and South-Central Wyoming and Bear River Watershed Sagebrush Focal Areas

Green River coal field

Epoch

Approx.

Age

Period (Ma) Hams Fork

coal field

North and West

(Hogback and

Green River Basins)

Central

(Rock Springs Uplift)

East

(Great Divide and

Washakie Basins)

Eocene

Paleocene

Tertiary

Cretaceous

Lower

Upper

Fowkes

Formation

Bridger Formation

Laney Member Laney Member

Conglomerate of Sublette Range

Evanston

Formation

Hogback

Formation Wasatch Formation

Pass Peak Formation

Wilkins Peak

Member Wilkins Peak

Member

Washakie

Fm

Fort Union Formation

Main body of

Wasatch Formation

Niland Tongue

Intrusive igneous rocks Diamicite and Sandstone Green River

Formation

Conglomerate

Alkali Creek Tongue

Godiva Rim MemberBattle Spring Fm

Cathedral

Bluffs

Tongue

Cathedral

Bluffs

T.

Harebell

Formation

Lance

Formation Lance Formation

Fox Hills Sandstone

Lewis Shale

Ericson

Sandstone

Mesaverde

Formation

Mesaverde Group

Mesaverde Group

Rock Springs

Formation

Almond Formation Almond Formation

Meeteetse Formation

Pine Ridge

Sandstone

Allen Ridge

Formation

Haystack

Mountains

Formation

Blair Formation

Baxter Shale

Cody

Shale

Cody Shale

Steele

Shale

Frontier Formation Frontier

Formation

Frontier

Formation

Niobrara

Formation

Mowry Shale

Muddy Sandstone

Thermopolis Shale

Cloverly Formation

Bear River Formation

Aspen Shale

Blind Bull Formation

Green

Wasatch Wasatch Fm

 Fm

River Fm

Tipton Shale

Member

Tipton Sh

 Mbr

Luman Tongue

Farson Sandstone Member

Chappo

Member

Main body

of

Wasatch

Formation

Sohare

Formation Adaville

Formation

Hilliard

Shale

Bacon

Ridge

Sandstone

Quealy

Formation

Thomas

Fork Fm

Cokeville

Formation

Smiths Formation Wayan Formation

Sage Junction

Formation Gannett Group

Smoot Formation

Draney Limestone

Bechler Conglomerate

Ephraim

Conglomerate

Peterson Limestone

43

55

65

100

138

Figure 16. Illustration showing 

stratigraphic column for southwest 

Wyoming. Formations named in red 

are coal bearing (after Wyoming 

State Geological Survey, 2011). Ma, 

mega-annum or millions of years 

ago; Fm, Formation, Sh, Shale; Ss, 

Sandstone; Ls, Limestone; Cgl, 

Conglomerate.
Leasable Minerals 47

Phosphate

Phosphate is classified as a non-energy, solid, leasable 

mineral by the BLM, which manages it on Federal lands under 

the Mineral Leasing Act of 1920, as amended (Bureau of Land 

Management, 2012).

Mineral Description

Phosphate rock is the primary global source for phosphorus, which is an essential nutrient for all living organisms 

(Ruttenberg, 2005). Sedimentary phosphate (phosphorite) 

of marine origin constitutes the majority of phosphate rock 

used worldwide (Cathcart, 1978). Phosphate rock is initially 

processed into phosphoric acid or converted into elemental 

phosphorus (P4) for use in the manufacture of agricultural 

products such fertilizers, pesticides, and animal feeds (Jasinski and others, 2004; Zhang and others, 2006; Ragheb and 

Khasawneh, 2010). To a lesser degree, phosphate is used in 

the manufacture of insecticides, herbicides, flame retardants, 

semiconductors, fireworks, matches, household cleaning products, and food additives. The principal phosphate mineral in 

phosphorite is carbonate fluorapatite (Ca5

 (PO4, CO3OH)3 (F)), 

commonly referred to as francolite (Filippelli and Delaney, 

1992). The phosphorus content in phosphate rock and in fertilizer is expressed as phosphorus pentoxide (P2

O5) (Kauwenbergh, 2010). Typically, mined phosphate has a minimum 

grade of 24 percent P2O5, has a minimum bed width of 1 m, 

is laterally extensive, and has minimal overburden (Rogers, 

1995). The largest current domestic phosphate production is 

from phosphorite of Miocene to Pliocene age in Florida and 

North Carolina, with less production from the extensive area 

of Permian deposits referred to as the “Western Phosphate 

Field,”which extends into parts of Idaho, Montana, Wyoming, 

and Utah (Jasinski, 2016).

Geology and Occurrence in the Study Area

The two most phosphate-rich rock units in the Western 

Phosphate Field are the Meade Peak Member and Retort 

Tongue (fig. 18) of the Permian Phosphoria Formation (Mansfield, 1940; Sheldon, 1957; McKelvey and others, 1959; 

Gulbrandsen and Krier, 1980; Maughan, 1994). Phosphate 

in the Phosphoria Formation occurs as pelletal phosphorite 

that is interbedded with organic matter-enriched mudstone 

and siltstone, limestone, dolomite, and chert (Piper and Link, 

2002). Also recognized in parts of the Western Phosphate 

Field are phosphorites of the Mississippian Deseret Limestone 

and Woodman Formation in Utah and eastern Nevada (Jewell 

and others, 2000). These Mississippian deposits, referred to 

as the Delle-event phosphorites, consist of pelletal phosphatic 

crusts, pisolitic phosphates, and detrital aggregates of ooidal 

and other types of phosphate grains (Nichols and Silberling, 

1991a, b). Concentrations of P2O5 in sampled phosphorite beds 

of the Deseret Limestone range from 23 to 36 percent and, in 

the Woodman Formation, from 25 to 30 percent (Jewell and 

others, 2000).

The phosphorites of the Western Phosphate Field 

differ from the relatively flat-lying, unconsolidated “landpebble” phosphate of the southeastern coastal region of the 

United States, as the Western U.S. host lithologies are older, 

well-indurated, are cross-cut by veins reflecting multiple 

episodes of injection by heated fluids, contain a series of 

diagenetic, epigenetic, and supergene mineral assemblages, 

show evidence of deep burial to the point of catagenesis, 

were deformed by intense folding and thrust faulting from 

Late Jurassic or Cretaceous to early Eocene time and later by 

extensional faulting from Neogene to Holocene time, and were 

affected by Neogene to Quaternary volcanism associated with 

the passage of the Yellowstone Hot Spot (Grauch and others, 

2004). Such a dynamic history resulted in exposures that tend 

to follow narrow ridges, consist of steeply dipping beds, and 

are truncated and offset by extensional faults.

Within the Southwestern and South-Central Wyoming 

and Bear River Watershed study areas, Permian and Mississippian phosphorites and phosphatic shales transect parts of 

southwestern Wyoming and northeastern Utah (fig. 19). In 

Wyoming, the principal source for phosphate is the Meade 

Peak Member of the Phosphoria Formation, which crops out 

along much of the northern half of the Tunp Range and over 

a restricted area near Rock Creek at the southern end of the 

range (Rubey and others, 1980; Love and Christiansen, 1985). 

At the southern end of the Tunp Range, near Rock Creek, the 

exposures of the Phosphoria Formation are approximately 34 

m thick (Kivi, 1940). As in the Sublette Range, the Phosphoria 

Formation in the Tunp Range consists of the Meade Peak, Rex 

Chert, and Retort Shale Members, with the Tosi Chert absent 

(McKelvey and others, 1953; Sheldon and others, 1954). 

McKelvey and others (1953) provide measured sections of 

the Phosphoria Formation in the middle part of the Tunp 

Range. At the Rock Creek exposure, Kivi (1940) identified a 

2.13-m-thick bed of phosphate rock that averaged 35 percent 

P2O5 (Carnes, 2015).

To the north and east of the South Pass block (figs. 2 and 

19) of the Southwestern and South-Central Wyoming study 

area, and southeast of Lander in Fremont County, low- to 

medium-grade phosphate deposits of the Meade Peak Member 

and the Retort Tongue of the Phosphoria Formation crop out 

(fig. 19) along the northeastern flank of the Wind River Range 

(Carnes, 2015).

Past production in the Wyoming part of the study area 

was from the Leefe, Cokeville, and South Mountain Mines in 

Lincoln County (fig. 19). The Leefe Mine, located approximately 48 km west of Kemmerer, produced phosphate rock 

from the Meade Peak Member of the Phosphoria Formation from 1947 to 1977 (Wyoming Board of Equalization, 

1948–1972; Wyoming Department of Revenue, 1973–1978; 

Jasinski and others, 2004). Productive beds at the Leefe Mine 

ranged in grade from 25 to 35 percent P2O5 (McKelvey and 

others, 1953). The mine included two open pits (Dover, 1995) 

and yielded more than 4,725,000 tons of phosphate rock 
48 Geology and Mineral Resources of the Southwestern and South-Central Wyoming and Bear River Watershed Sagebrush Focal Areas

Bear

Lake

Evanston

Green R

WYOM

UTAH

IDAHO

LINCOLN COUNTY

SUBLETTE COUNTY

UINTA COUNTY

RICH COUNTY

BEAR LAKE

COUNTY

CARIBOU COUNTY

CACHE

COUNTY

FRANKLIN

COUNTY

WEBER

COUNTY

MORGAN

COUNTY

80

189

30 89

30

89

189

30

191

10S

44E

14S

43E

13S

43E

11S

44E

13S

44E

11S

43E

12S

44E

14S

44E

14S

45E

13S

41E

10S

42E

08S

44E

12S

41E

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45E

11S

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09S

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42E

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45E

11S

42E

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42E

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12S

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43E

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42E

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40E

12S

43E

10S

43E

14S

41E

14S

42E

08S

41E

08S

42E

11N

03E

12N

03E

10N

03E

11N

07E

10N

07E

09N

07E

08N

07E

12N

05E

12N

06E

13N

07E

09N

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06N

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08N

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03E

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02E 09N

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02E

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07E

10N

06E

11N

06E

12N

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02E

10N

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11N

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14N

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06N

04E 06N

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07E

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04E

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08N

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10N

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13N

06E

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02E

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05E

24N

115W

23N

115W

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117W

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119W

28N

119W

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113W

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119W

22N

117W

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112W

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114W

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120W

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117W

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114W

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118W

28N

112W

25N

119W

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117W

26N

115W

26N

119W

28N

113W

27N

113W

16N

116W

18N

114W

22N

112W

15N

114W

23N

114W

16N

114W

19N

115W

31N

109W

19N

114W

17N

114W

23N

109W

24N

110W

19N

116W

17N

110W

18N

115W

22N

111W

30N

113W

17N

113W

30N

114W

26N

117W

31N

107W

27N

117W

17N

116W

17N

111W

29N

109W

25N

110W

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108W

17N

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111W

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1

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114W

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116W

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115W

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118W

18N

113W

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117W

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110W

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26N

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110W

26N

111W

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119W

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110W

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120W

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116W

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119W

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115W

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116W

29N

108W

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113W

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118W

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113W

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109W

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115W

18N

111W

26N

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109W

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112W

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117W

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112W

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111W

30N

117W

29N

112W

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108W

32N

108W

30N

116W

29N

118W

28N

117W

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109W

31N

117W

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108W

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109W

20N

110W

28N

116W

31N

116W

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114W

20N

113W

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110W

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115W

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27N

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115W

111°0' 110°0' 

42°30'

42°0'

41°30'

100 20 30 40 50 KILOMETERS

0 10 20 30 40 MILES50

Base modified from U.S. Geological Survey DEM data, 2016. 

Roads and political data © 2014 Esri and its licensors.

Boundary data from San Juan and others (2016).

PLSS boundaries from respective state governments, 2016.

USA Contiguous Albers Equal Area Conic Projection.

Central meridian, 110° W., latitude of origin, 37.5° N.

North American Datum of 1983.
Leasable Minerals 49

Figure 17. Map showing the Public Land Survey System (PLSS) 

township and range grid for the entire region of the Southwestern 

and South-Central Wyoming and Bear River Watershed study 

areas. USGS, U.S. Geological Survey.

River

Rock Springs

MING

SWEETWATER COUNTY

FREMONT COUNTY

80

287

191

191

30N

98W

31N

98W

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102W

19N

107W

26N

101W

15N

103W

27N

105W

N

W

26N

103W

23N

106W

22N

101W

27N

102W

22N

103W

17N

104W

18N

101W

17N

100W

23N

100W

25N

103W

22N

102W

18N

102W

27N

104W

15N

105W

18N

103W

15N

101W

32N

102W

26N

104W

27N

100W

18N

106W

25N

100W

15N

102W

17N

106W

21N

104W

23N

103W

19N

100W

17N

103W

17N

102W

24N

101W

19N

103W

21N

102W

15N

106W

27N

103W

15N

107W

18N

105W

19N

106W

23N

101W

23N

105W

22N

104W

15N

100W

19N

102W

26N

100W

21N

103W

31N

105W

18N

104W

23N

102W

19N

101W

W

31N

103W

24N

103W

30N

105W

30N

106W

31N

100W

24N

100W

19N

104W

23N

104W

32N

104W

24N

102W

28N

100W

24N

104W

16N

106W

32N

100W

28N

101W

16N

104W

16N

105W

N

W

16N

107W

16N

103W

28N

102W

31N

101W

16N

102W

16N

101W

28N

103W

24N

106W

20N

100W

20N

101W

24N

107W

20N

105W

24N

105W

20N

103W

20N

102W

28N

104W

20N

104W

N

W

20N

106W

20N

107W

28N

106W

28N

105W

24N

98W

23N

98W

22N

98W

21N

98W

33N

106W

33N

105W

33N

104W

33N

102W

33N

100W

33N

101W

33N

103W

32N

99W

22N

107W

33N

98W

14N

99W

14N

101W

14N

102W

14N

103W

14N

104W

14N

105W

14N

106W

14N

107W

N

W

14N

100W

109°0'

IDAHO

MONTANA

OREGON

WYOMING

NEVADA UTAH

WASHINGTON

CO

CA

Map

area

Study areas

County boundaries

State boundaries

Proposed withdrawal areas

USGS study area boundary

Base data

PLSS townships of Utah (Salt Lake meridian)

PLSS townships of Idaho (Boise meridian)

PLSS townships of Wyoming (6th principal meridian)

EXPLANATION
50 Geology and Mineral Resources of the Southwestern and South-Central Wyoming and Bear River Watershed Sagebrush Focal Areas

Northeastern

Great Basin Wyoming Shelf

Wasatch Range,

Utah

Southeastern Idaho,

Western and Central

Wyoming

Central

Wyoming

PeriodEpoch Lower Permian Upper Permian

Permian

PARK CITY FORMATION

PARK CITY FORMATION

PHOSPHORIA FORMATION

PHOSPHORIA FORMATION

PHOSPHORIA FORMATION

Grandeur

Member

Grandeur

Member

Grandeur

Member

Lower chert member

Meade Peak

Member

Meade Peak

Member

Meade Peak

Member

Rex Chert

Member

Rex Chert

Member Rex Chert

Member

Franson

Member Franson

Member

Franson Member

Ervay

Limestone

Member

Retort

Phosphatic Shale

Member

Ervay Ls. Member

Tongue of

PHOSPHORIA

FORMATION

Tosi Chert

Member Tosi Chert

Member

Ervay

Limestone

Member

Retort

Phosphatic Shale

Member

Figure 18. Correlation chart of Permian Phosphoria and Park City Formations from the northeastern Great Basin 

to the Wyoming shelf (from Maughan, 1994).
Leasable Minerals 51

(Wyoming Board of Equalization, 1948–1972). The Leefe 

Mine was the last active phosphate mine in Wyoming and 

closed because of the depletion of phosphate rock resources at 

the site. After mining operations ceased, phosphate processing 

continued at the Leefe plant using raw material mined from 

the Phosphoria Formation in Idaho and Utah into the 1980s 

(Harris and Hausel, 1984; Carnes, 2015). The Cokeville Mine 

was an underground mine that operated from 1906 to 1931 

(Jasinski and others, 2004). The South Mountain Mine was 

both underground and open pit and was operated from 1946 

to 1951 (Jasinski and others, 2004). Production figures from 

Cokeville and South Mountain Mines are not available.

In Utah, the principal phosphate deposits are the Permian 

phosphatic shales of the Phosphoria and intertonguing Park 

City Formations, which have past and current production, and 

the Mississippian phosphatic shales of the Delle Phosphatic 

Member of the Deseret Limestone and equivalent units, which 

have not been exploited (Tooker, 1992). Early phosphate 

mines located in the Crawford Mountains in the Utah part of 

the Bear River Watershed study area include (1) the Arickaree 

Mine in the Phosphoria Formation that operated from 1907 to 

1920 and reopened in 1953; (2) six underground mines that 

operated from 1960 to 1977; and (3) several other mines that 

were active from the late 1950s to the mid-1960s (Jasinski and 

others, 2004). 

The only currently active phosphate operation in Utah is 

outside the study area at the Little Brush Creek Mine (about 

113 km south of Rock Springs, Wyoming, and is therefore 

not shown on figures in this report), which has been operating 

since 1961 as a surface mine on the south flank of the Uinta 

Mountains (figs. 3 and 4) in the Permian Phosphoria and Park 

City Formations (Jasinski and others, 2004). Within the Bear 

River Watershed study area, past interest in phosphate exploration is indicated by two sections in Rich County just south 

of the Lake Town phosphate deposits in the Mississippian 

Humbug Formation and Deseret Limestone that have closed 

phosphate-prospecting permits (fig. 19).

Exploration and Mining Activity

Currently, mining in the Western Phosphate Field occurs 

only in Idaho and Utah in areas outside the Southwestern and 

South-Central Wyoming and Bear River Watershed study 

areas. In 2015, production from the entire field was 5.52 million metric tons (Jasinski, 2016). Utah production from Little 

Brush Creek mine (about 70 mi south of Rock Springs) (Rabchevsky, 1995; Jasinski and others, 2004) was approximately 

3.7 million metric tons (Mt) of ore in 2014 (Boden and others, 

2015). Production ceased in Wyoming in 1978 owing to depletion of reserves (Jasinski and others, 2004).

Results of Previous USGS Assessments

The USGS Western U.S. Phosphate project (completed in 

2004) was entirely focused on areas outside the Southwestern 

and South-Central Wyoming and Bear River Watershed 

study areas. Carnes (2015) provides a comprehensive report 

on phosphate resources in Wyoming that highlights previously reported medium- to high-grade phosphate rock beds 

of greater than 0.9 m (3 ft) in thickness and includes analysis 

of new data points. One of these new data points falls along 

the margin of the Southwestern and South-Central Wyoming 

and Bear River Watershed study area. This point is just east 

of the Middle Fork of Pine Creek in the Tunp Range, Lincoln 

County, and has a P2

O5 content of >30 percent (Carnes, 2015).

Trace Elements as Potential Byproducts of 

Elemental Phosphorus and Phosphoric Acid 

Production

Arsenic, cadmium, chromium, copper, molybdenum, 

nickel, rare earth elements, selenium, silver, uranium, vanadium, and zinc are found in trace amounts in the Phosphoria 

Formation (Piper, 2001).

Vanadium

Within the francolite crystal lattice, VO4 is among the 

ions that may substitute for PO4 (Cathcart, 1991; Kolodny 

and Luz, 1992; Jarvis and others, 1994). Vanadium in carbonaceous shales and phosphorite beds of the Phosphoria 

Formation occurs in trace amounts that exceed the average for 

marine shales (Fischer, 1962; Maughan, 1994). On average, 

the vanadium pentoxide (V2O5) content of phosphate rock of 

the Phosphoria Formation is about 0.05 percent (500 ppm) 

(Cathcart and Gulbrandsen, 1973). Maughan (1994) showed 

that vanadium in the Meade Peak Member ranged from 100 

to 1,000 parts per million (ppm) with highest concentration 

in southeastern Idaho; in the Retort Tongue, vanadium ranged 

from 100 to 400 ppm with highest concentration in southwestern Montana. Bauer and Dunning (1979) analyzed samples 

from three measured sections in the Phosphoria Formation at 

Conda, Idaho; Coal Canyon, Wyoming; and Brazer Canyon, 

Utah (fig. 19), and found that the highest-grade vanadium 

occurred in a 1.143-m-thick bed that contained 0.67 percent 

(6,700 ppm) V2

O5, 2.4 percent P2O5 and 10 ppm uranium.

In the Afton area in western Wyoming, outside the study 

area, Love and others (2003) describe vanadium reserves of 

about 30 million tons of “indicated” vanadium ore that averages 1.1 percent (11,000 ppm) V2

O5, estimated for the shale 

and mudstone beds in the Meade Peak Member of the Phosphoria Formation. The richest central 0.64 m of the vanadiferous zone is black shale, oolite, and dark-gray mudstone. The 

vanadiferous zone is remarkably consistent in character, grade, 

thickness, and lateral continuity throughout the Afton and 

adjacent 2,590-km2 mountainous area (Love and others, 2003).

Vanadium has been recovered as a by-product of elemental phosphorus and phosphoric acid production (Coleman 

and Clevenger, 1967). In 1941, Anaconda Copper Mining 

Company began recovering vanadium as a by-product from 

phosphate rock in their processing plant at Conda, Idaho 
52 Geology and Mineral Resources of the Southwestern and South-Central Wyoming and Bear River Watershed Sagebrush Focal Areas

BEAR LAKE

PLATEAU

BLOCK

FOSSIL BASIN

BLOCK

FONTENELLE

BLOCK

BIG SANDY

BLOCK

Bear

Lake Rock

Creek

WYOMING

UTAH

IDAHO

LINCOLN COUNTY

RICH COUNTY

UINTA COUNTY

CACHE

COUNTY

BEAR LAKE

COUNTY

FRANKLIN

COUNTY

WEBER

COUNTY

SWEETWATE

COUNTY

80

30

189

89

89

189

30

TUNP RANGE

SUBLETTE RANGE

Brazier Canyon

CRAWFORD

MTS.

Green R

Afton

Conda

Kemmerer

Rock Creek

Middle Fork

Pine Creek

Leefe Mine

Arickaree Mine

South

Mountain

Mine

Lake Town

Phosphate

Deposits

Coal Canyon

Cokeville

Mine

111°0' 110°0' 

42°30'

42°0'

41°30'

0 10 20 30 40 5

0 10 20 30 40 50 KILOMETERS

Base modified from U.S. Geological Survey DEM data, 2016.

Roads and political data © 2014 Esri and its licensors.

Boundary data from San Juan and others (2016).

USA Contiguous Albers Equal Area Conic Projection.

Central meridian, 110° W., latitude of origin, 37.5° N.

North American Datum of 1983.
Leasable Minerals 53

Figure 19. Map of the surface extent of Permian and 

Mississippian phosphorite and phosphatic shale in the 

Southwestern and South-Central Wyoming and Bear River 

Watershed study areas (Stoeser and others, 2007; Ludington and 

others, 2007), showing study area boundaries and U.S. Geological 

Survey (USGS) Mineral Resources Database (MRDS) past 

producing phosphate mines, prospects, and sites.

BOARS TUSK

BLOCK

CONTINENTAL

DIVIDE BLOCK

SOUTH PASS

BLOCK

ER

River

Rock Springs

Lander

109°0'

Map

area

Study areas

IDAHO

MONTANA

WYOMING

OREGON

NEVADA UTAH

WASHINGTON

CO

County boundaries

State boundaries

Proposed withdrawal areas

USGS study area boundary

Base data

Phosphate location

Phosphate prospect permit, closed

Non-energy solid mineral permits

Phosphorite; Phosphatic-shale

 (Two locations south of Bear Lake Plateau block)

Phosphatic-shale

Phosphorite

Phosphate lithology

EXPLANATION

50 MILES

Permit data from Dicken and and San Juan (2016).
54 Geology and Mineral Resources of the Southwestern and South-Central Wyoming and Bear River Watershed Sagebrush Focal Areas

(Love and others, 2003). At a nearby plant near Soda Springs, 

Idaho, vanadium has been recovered from vanadium-rich ferrophosphorus, a product of the electric reductor furnaces used 

to manufacture elemental phosphorus (Bauer and Dunning, 

1979). Several companies have developed processes by which 

vanadium is recovered as a by-product from phosphoric acid 

(Fisher, 1962; Bauer and Dunning, 1979; Guirguis, 1985). In 

1985 and 1986, the Phosphoria Formation was the chief U.S. 

domestic source of vanadium (Kuck, 1985; Goldberg and 

others, 1992). By 2003, domestic vanadium production was 

solely from recovery from various industrial waste materials such as fly ash, petroleum residues, spent catalysts, and 

vanadium-bearing iron slag (Magyar, 2003).

Uranium

Uranium is among the ions that can substitute for calcium 

in the francolite crystal lattice (Cathcart, 1991; Kolodny and 

Luz, 1992; Jarvis and others, 1994). Marine phosphorite 

deposits contain 6 to 120 ppm uranium, and organic phosphorites have as much as 600 ppm (Ragheb and Khasawneh, 

2010). In the past, when demand was high, uranium was commercially recovered as a by-product from phosphoric acid, an 

intermediate product of processing phosphatic rock (Kouloheris, 1979; Botella and Gasós, 1989; Ragheb and Khasawneh, 

2010; Ulrich and others, 2014). There is renewed interest in 

uranium recovery from phosphorite (Ulrich and others, 2014).

Uranium content of the Permian Phosphoria phosphorites 

from Idaho, Montana, Utah, and Wyoming ranges from 0.002 

to 0.021 percent (20 to 210 ppm), averaging 0.009 percent (90 

ppm) (Gulbrandsen, 1966; Cathcart, 1978).

Rare Earth Elements

Rare earth elements (REEs) are among the ions that can 

substitute for Ca in the francolite crystal lattice (Cathcart, 

1991; Kolodny and Luz, 1992; Jarvis and others, 1994). Lanthanum occurs in trace amounts in the Phosphoria Formation. 

In the Meade Peak Member, lanthanum concentrations range 

from 50 to 300 ppm, with highest concentrations in southeastern Idaho. In the Retort Member, lanthanum concentrations 

range from 50 to 350 ppm, with the highest concentrations in 

southwestern Montana (Maughan, 1994).

Altschuler and others (1967) recognized the potential to 

recover REEs as a by-product from phosphoric acid processed 

from phosphate rock from sedimentary deposits. Subsequent 

research maintains that extraction of REEs from sedimentary 

phosphate rock could be as high as 100 percent (Emsbo and 

others, 2015).

Potash

Potash is a water-soluble compound of potassium (K) 

formed by geologic and hydrologic processes. Along with 

phosphorous and nitrogen, potash is an essential nutrient necessary to sustain plant life. In addition to fertilizer, potash has 

been used for the bleaching of textiles, glass manufacture, and 

soap production.

Mineral Description

The major potash resources of the world are evaporiterelated deposits that principally occur as potash salts such 

as sylvite (KCl), and sylvinite (KCl+NaCl) (Garrett, 1996). 

They generally co-occur with chlorides, sulfates, and halite in 

evaporite sequences (Orris and others, 2014). Potash derived 

from groundwater- and lake-brine can also be harvested at the 

surface from man-made solar evaporation ponds. Industrial 

phrases used to describe potash varieties are muriate of potash 

(MOP) and sulfate of potash (SOP). MOP is composed of 

potassium chloride (KCl), whereas SOP is composed of potassium sulfate (K2

SO4).

Non-evaporite sources of potash, which are often not 

economical to mine today for use as fertilizer, include potassium-bearing silicate minerals that occur in igneous rocks. 

Alkalic igneous rocks that are high in sodium and potassium 

and contain minerals such as leucite (K(AlSi2O6)) and nepheline (Na3

KAl4Si4O16) were investigated in the early 1900s 

as a possible source for potash when it was in short supply in 

the United States (Schulz and Cross, 1912). Another source of 

SOP is the mineral alunite (KAl3(SO4)2(OH)6), which occurs 

in veins and hydrothermally altered rocks and in sedimentary 

deposits (Hall, 1978). Alunite is a relatively minor source of 

SOP and commonly not economical to mine, and so it was not 

included as part of the global potash assessment described in 

Orris and others (2014).

Geology and Occurrence

An important source of potash salt production in the 

Western United States is derived from brine that has formed in 

intracontinental, closed basins (Orris, 2011). Closed basins are 

those having restricted surface-water inflow and outflow. The 

Basin and Range physiographic province, characterized by 

lowland basins and surrounding adjacent mountain ranges, has 

a geography in which closed-basin lakes form and brines can 

subsequently evolve. During the Pleistocene, large, closedbasin lakes formed in the Western United States in the Basin 

and Range—the former Lake Bonneville is an example of one 

such lake. In the case of Lake Bonneville, water became saline 

and concentrated in potash during evaporation as lake levels 

declined from about 15,000 years before present (B.P.) to the 

Holocene. Today, groundwater that is a remnant of the former 

Lake Bonneville is pumped from shallow wells near Wendover, Utah. The groundwater is transferred to solar evaporation ponds where it is evaporated at the surface, and potash is 

recovered through a series of industrial processing and refining 

techniques.

No closed-basin brine-type potash occurrences are known 

within the Southwestern and South-Central Wyoming or Bear 

River Watershed study areas, but a potash tract identified in 
Locatable Minerals 55

Orris and others (2014) does occur within the Basin and Range 

Province. The eastern edge of the tract is approximately 10 km 

(6 mi) west of the westernmost part of the Bear River Watershed study area. This possible potash occurrence is classified 

as a closed-basin brine type and coincides with the potash tract 

defined by the maximum extent of the former Lake Bonneville 

shoreline (Orris, 2014).

Nontraditional and commonly non-economic potash 

sources can be derived from silicate rocks and minerals that 

occur at or near the Earth’s surface. Alkalic igneous rocks that 

have high potassium concentrations are exposed in the Leucite 

Hills northeast of Rock Springs, Wyoming. A potash prospect that contains the silicate mineral leucite is located near 

the Leucite Hills within the Southwestern and South-Central 

Wyoming study area in Sweetwater County, Wyoming. The 

prospect is about 5 km (3 mi) north of the Boars Tusk block 

(fig. 2) at 109.192 longitude, 41.964 latitude (Fernette and others, 2016a; U.S. Geological Survey, 2016; Harris and others, 

1985). No other occurrences of potash derived from alkalic 

igneous rocks are known in the study area.

Exploration, Development, or Mining and Results 

of Previous USGS Assessments

There is no known exploration, development, mining, or 

assessments of potash in the study area.

Locatable Minerals

Locatable minerals include both metallic minerals and 

nonmetallic minerals administered by BLM on Federal lands 

under the Mining Law. The law provides for the filing of mining claims to explore for and produce these minerals (Bureau 

of Land Management, 2012).

For the Southwestern and South-Central Wyoming and 

Bear River Watershed study areas, metallic locatable minerals include gold (and silver), copper (and silver), uranium, 

titanium, and iron. The first three were assessed in detail. 

Titanium and iron potential are discussed, but no tract for 

potential and certainty rating is given. Likewise, diamonds 

and dolomite, nonmetallic locatable resources, are discussed, 

and a tract for potential and certainty rating is presented for 

diamonds.

Table 6 lists how many active and closed claims and what 

type of claims are within the proposed withdrawal area. In 

the proposed withdrawal areas within the Southwestern and 

South-Central Wyoming study area there are no active lode 

claims, but there are 13 active placer claims. Most of those 

are presumed to be in the Dickie-Spring–Oregon Gulch area, 

although there are no geographic descriptions detailed enough 

to pinpoint the exact location (table 6, fig. 20). There are no 

active claims in the Bear River Watershed study area for either 

lode or placer deposits (fig. 20).

Table 7 shows surface management permits for the 

proposed withdrawal area within the study area. There are two 

types of permits. One is a plan of operations, and the other 

is a notice of intent. The unique number of cases is a summary of all permits within the proposed withdrawal area. The 

specific status (authorized, pending, closed, cancelled, expired, 

rejected, or withdrawn) further explains how many of each 

type of permit are within the proposed withdrawal area. Only 

one plan of operations for locatable minerals is pending for the 

entire study area: in the South Pass block of the Southwestern 

and South-Central Wyoming study area, where there are also 

two closed plans (table 7; fig. 21). There are no locatable mineral operations in the Bear River Watershed study area (table 

7; fig. 21).

Surface-management authorizations are tallied in more 

detail by commodity type in table 8. Active permits are those 

that have a status of authorized or pending. In the entire study 

area, there is just one active surface-management authorization (table 8, fig. 21). It is for a placer gold operation on the 

Table 6. Summary of mining claims for locatable minerals in sections containing the proposed withdrawal area within the (A) 

Southwestern and South-Central Wyoming study area, Wyoming, and (B) Bear River Watershed study area, Wyoming and Utah.

[Source: Bureau of Land Management LR2000 database, March 6, 2016. The number of cases is for the complete section that includes a proposed withdrawal 

area] 

A. Southwestern and South-Central Wyoming study area, Wyoming.

Area Active lode 

claims

Closed lode 

claims

Active placer 

claims

Closed placer 

claims

Active 

millsites

Closed 

millsites

Sections containing proposed 

withdrawal area

0 2,321 13 621 0 0

B. Bear River Watershed study area, Wyoming and Utah.

Area Active lode 

claims

Closed lode 

claims

Active placer 

claims

Closed placer 

claims

Active 

millsites

Closed 

millsites

Sections containing proposed 

withdrawal area

0 38 0 56 0 12
56 Geology and Mineral Resources of the Southwestern and South-Central Wyoming and Bear River Watershed Sagebrush Focal Areas

Sweetwater River near South Pass in Fremont County, Wyoming, although it is not known if the site is on the main river 

or a tributary stream.

Locatable minerals are present in scattered areas across 

the study area (table 9, fig. 22). Within the proposed withdrawal areas, few deposits have produced. Within the greater 

study area, there have been a few productive mines (table 9). 

Production for many producing properties is aggregated so as 

to not release proprietary corporate data.

Mineral Potential

This report uses the BLM mineral-potential classification 

system, which categorically ranks areas according to potential 

and certainty (appendix 1). For example, areas can be assigned 

high, moderate, and low mineral resource potential according 

to the degree of likelihood that geologic processes operated in 

an area in such a way as to permit accumulation of resources. 

Level of certainty is ranked A through D, least confident to 

most confident, based on indirect or direct evidence about the 

existence of mineral resources. The definitions of these levels 

of resource potential are given in a companion report (Hammarstrom and Zientek, 2016). In this classification, potential 

refers the presence (occurrence) of a concentration of one 

or more energy and (or) mineral resource. It does not imply 

potential for profitable development and (or) extraction of the 

mineral resource(s).

A geologically based approach is used to assess mineral 

resource potential in the study areas. The science behind the 

USGS assessment approach relies on the concept that mineral 

Table 7. Summary of status and number of 43 CFR 3809 surface-management authorizations for locatable minerals in the proposed 

withdrawal area within the (A) Southwestern and South-Central Wyoming study area, Wyoming, and (B) Bear River Watershed study 

area, Wyoming and Utah.

[Source: Bureau of Land Management LR2000 database, accessed March 6, 2016. The number of cases is for the complete section that includes a proposed 

withdrawal area. ND, no data]

A. Southwestern and South-Central Wyoming study area, Wyoming.

Permit type Number of unique 

cases

Active Authorized Pending Closed Cancelled Expired Rejected Withdrawn

Plan of operations 3 ND ND 1 2 ND ND ND ND

Notice of intent 15 ND ND ND 15 ND ND ND ND

B. Bear River Watershed study area, Wyoming and Utah.

Permit type Number of unique 

cases

Active Authorized Pending Closed Cancelled Expired Rejected Withdrawn

Plan of operations ND ND ND ND ND ND ND ND ND

Notice of intent ND ND ND ND ND ND ND ND ND

Table 8. Active 43 CFR 3809 surface-management authorizations summarized by 

commodity in the proposed withdrawal area within the (A) Southwestern and SouthCentral Wyoming study area, Wyoming, and (B) Bear River Watershed study area, 

Wyoming and Utah.

[Source: Bureau of Land Management database, March 6, 2016. The number of cases is for the 

complete section that includes a proposed withdrawal area. ND, no data]

A. Southwestern and South-Central Wyoming study area, Wyoming.

Commodity Number of active 

notices Number of active plans of operations

Gold, placer 0 1

B. Bear River Watershed study area, Wyoming and Utah.

Commodity Number of active 

notices Number of active plans of operations

ND ND ND
Locatable Minerals 57

Table 9. Mineral deposits, mines, and important exploration prospects that occur in or near (within 500 meters of) the Southwest and 

South-Central Wyoming study area, Wyoming.

[Name, (alternate name); Au, gold; O, orogenic low-sulfide gold-quartz vein type; PlP, paleoplacer; P, placer; PP, past producer; R, resource]

Site name Site type Latitude Longitude Commodities Deposit 

type

Active in 

past 10 

years

Resource and 

production 

information

Caribou Mine −108.72 42.51 Au O N PP

Carissa Mine −108.79 42.47 Au O N PP, R

Carrie Shields Mine −108.78 42.46 Au O N PP

Diana Mine −108.73 42.50 Au O N PP

Dickie Springs-Oregon Gulch Exploration −108.83 42.30 Au PlP ? Potential resource

Doc Barr Mine −108.76 42.47 Au O N PP

Duncan Mine −108.75 42.48 Au O N PP

Empire State (B&H) Mine −108.76 42.47 Au O N PP

Franklin Mine −108.81 42.46 Au O N PP

Garfield (Buckeye) Mine −108.74 42.51 Au O N PP

Ground Hog Mine −108.75 42.49 Ag O N PP

Mary Ellen Mine −108.74 42.48 Au O Y PP

Midas Mine −108.73 42.50 Au O N PP

Rock Creek Placers Placer Mine −108.74 42.51 Au P N PP

Rose Mine −109.28 42.38 Au O N PP

Soules and Perkins Mine −108.73 42.50 Au O N PP

St. Louis Mine −108.73 42.48 Au O N PP

deposits can be classified into groups or types based on common characteristics and associations (Skinner and Barton, 

1973). A given mineral deposit type will have characteristic 

ore body geometries, tonnage and grade distribution, and rock 

and mineral properties that determine if the occurrence or 

deposit fits a deposit type or model. Deposits of a given type 

are expected to have a common mode of genesis (Eckstrand, 

1984). The genetic foundation of deposit types informs the 

assignment of mineral resource potential categories. The 

companion report (Hammarstrom and Zientek, 2016) includes 

short descriptive models for the deposit types assessed in the 

SaMiRA reports.

Mineral deposit types can be grouped into larger mineral 

systems. Mineral systems models organize ideas about how 

different mineral deposit types relate to regional-scale movements of energy and mass in the Earth, allowing deposit types 

to be related to geology and tectonics at many scales. The 

discussion of mineral potential in this report is organized by 

mineral systems and their related deposit types (Hammarstrom 

and Zientek, 2016, table H1). In each section, the mineral 

system is briefly described, followed by a summary of the 

geology and occurrence of deposit types related to the mineral 

system in the study area, a description of exploration and mining history, and discussion of the potential for the occurrence 

of undiscovered deposits. Each section is organized by deposit 

type.

Metallic Locatable Minerals

Of the seven blocks in Wyoming and northeastern Utah 

that contain proposed withdrawal areas (fig. 2), only the 

South Pass, Fossil Basin, and Bear Lake Plateau blocks have 

potential for any locatable metallic deposits that can be rated 

for moderate or high potential within specific tracts. Tracts are 

presented for three types of gold (Au) deposits and for a single 

type of copper deposit.

No tract is presented for iron deposits in Algoma-type 

banded iron formations because, though the large Atlantic City 

iron mine is immediately north of the South Pass block, and a 

resource of some 331 million short tons of 22 to 35 percent Fe 

remained when the mine closed in 1983 (Anonymous, 1960; 

Bayley, 1963, p. C10–C1; Hausel, 1991, p. 28–29), the iron 

formation is not known to extend into the land proposed for 

withdrawal (Bayley, 1963, plate 1; Hausel, 1991, plate 1).

Deposits of heavy-mineral sands that formed in coastal 

environments almost certainly underlie parts of the proposed 

withdrawal area of both study areas. However, these deposits are not considered to be economically viable at this time, 

because they are in lithified Upper Cretaceous sandstones and 

would require crushing and other processing to liberate the 

heavy minerals. It serves no purpose to conduct an assessment 

of those deposits at this time.
58 Geology and Mineral Resources of the Southwestern and South-Central Wyoming and Bear River Watershed Sagebrush Focal Areas

BEAR LAKE

PLATEAU

BLOCK

FOSSIL BASIN

BLOCK

FONTENELLE

BLOCK

BIG SANDY

BLOCK

Bear

Lake

Evanston

Green R

WYOMIN

UTAH

IDAHO

LINCOLN COUNTY

SUBLETTE COUNTY

UINTA COUNTY

RICH

COUNTY

BEAR LAKE

COUNTY

CARIBOU COUNTY

CACHE

COUNTY

FRANKLIN

COUNTY

WEBER

COUNTY

MORGAN

COUNTY

80

189

30 89

30

89

189

30

191

111°0' 110°0' 

42°30'

42°0'

41°30'

100 20 30 40 50 KILOMETERS

0 10 20 30 40 

Base modified from U.S. Geological Survey DEM data, 2016.

Roads and political data © 2014 Esri and its licensors.

Boundary data from San Juan and others (2016).

USA Contiguous Albers Equal Area Conic Projection.

Central meridian, 110° W., latitude of origin, 37.5° N.

North American Datum of 1983.
Locatable Minerals 59

Figure 20. Map showing active and pending mine claims for 

locatable commodities in the Southwestern and South-Central 

Wyoming and Bear River Watershed study areas, Wyoming and 

Utah. USGS, U.S. Geological Survey.

BOARS TUSK

BLOCK

CONTINENTAL

DIVIDE BLOCK

SOUTH PASS

BLOCK

River

Rock Springs

NG

SWEETWATER COUNTY

FREMONT COUNTY

80

287

191

191

1

109°0'

Map

area

Study areas

IDAHO

MONTANA

OREGON

WYOMING

NEVADA UTAH

WASHINGTON

CO

CA

County boundaries

State boundaries

Proposed withdrawal areas

USGS study area boundary

Base data

Closed mine claims

11 - 15

6 - 10

3 - 5

1 - 2

Active lode and placer mine claims per section

EXPLANATION

MILES50

Claim data from Dicken and San Juan (2016).
60 Geology and Mineral Resources of the Southwestern and South-Central Wyoming and Bear River Watershed Sagebrush Focal Areas

BEAR LAKE

PLATEAU

BLOCK

FOSSIL BASIN

BLOCK

FONTENELLE

BLOCK

BIG SANDY

BLOCK

Evanston

Green R

Bear

Lake

WYOMIN

UTAH

IDAHO

LINCOLN COUNTY

SUBLETTE COUNTY

UINTA COUNTY

RICH

COUNTY

BEAR LAKE

COUNTY

CARIBOU COUNTY

CACHE

COUNTY

FRANKLIN

COUNTY

WEBER

COUNTY

MORGAN

COUNTY

80

189

89 30

30

89

189

30

191

111°0' 110°0' 

42°30'

42°0'

41°30'

100 20 30 40 50 KILOMETERS

0 10 20 30 40 

Base modified from U.S. Geological Survey DEM data, 2016.

Roads and political data © 2014 Esri and its licensors.

Boundary data from San Juan and others (2016).

USA Contiguous Albers Equal Area Conic Projection.

Central meridian, 110° W., latitude of origin, 37.5° N.

North American Datum of 1983.
Locatable Minerals 61

Figure 21. Map showing 43 CFR 3809 surface-management 

authorizations for locatable commodities in the Southwestern and 

South-Central Wyoming and Bear River Watershed study areas, 

Wyoming and Utah. USGS, U.S. Geological Survey.

BOARS TUSK

BLOCK

CONTINENTAL

DIVIDE BLOCK

SOUTH PASS

BLOCK

River

Rock Springs

NG

SWEETWATER COUNTY

FREMONT COUNTY

80

287

191

191

109°0'

Map

area

Study areas

IDAHO

MONTANA

OREGON

WYOMING

NEVADA UTAH

WASHINGTON

CO

CA

County boundaries

State boundaries

Proposed withdrawal areas

USGS study area boundary

Base data

Uranium

Stone

Precious metals

Locatable minerals (undefined commodity)

Closed or expired permits

Authorized and pending permits

EXPLANATION

MILES50

Permit data from Dicken and San Juan (2016).
62 Geology and Mineral Resources of the Southwestern and South-Central Wyoming and Bear River Watershed Sagebrush Focal Areas

BEAR LAKE

PLATEAU

BLOCK

FOSSIL BASIN BLOCK

FONTENELLE

BLOCK

BIG SANDY

BLOCK

BOAR

BL

Bear

Lake

Evanston

Green 

WYOMING

UTAH

IDAHO

LINCOLN COUNTY

SUBLETTE COUNTY

UINTA COUNTY

RICH

COUNTY

BEAR LAKE

COUNTY

CARIBOU

COUNTY

CACHE

COUNTY

FRANKLIN

COUNTY

WEBER

COUNTY

MORGAN

COUNTY

80

189

30 89

30

89

189

30

191

Paradise

Montpelier

Lake Alice District

Swan Peak

Richmond

111°0' 110°0' 

42°30'

42°0'

41°30'

100 20 30 40 50 KILOMETERS

0 10 20 30 40 

Base modified from U.S. Geological Survey DEM data, 2016.

Roads and political data © 2014 Esri and its licensors.

Boundary data from San Juan and others (2016).

USA Contiguous Albers Equal Area Conic Projection.

Central meridian, 110° W., latitude of origin, 37.5° N.

North American Datum of 1983.
Locatable Minerals 63

Figure 22. Map showing mineral deposits, mines, and 

important exploration prospects for locatable commodities in 

the Southwestern and South-Central Wyoming and Bear River 

Watershed study areas, Wyoming, and Utah. USMIN, U.S. 

Geological Survey (USGS) Mineral Deposit Database.

S TUSK

OCK

CONTINENTAL

DIVIDE BLOCK

SOUTH PASS BLOCK

 River

Rock Springs

SWEETWATER COUNTY

FREMONT COUNTY

80

287

191

191

1

Great Divide Basin

South Pass–

Atlantic City

District

Lewiston Gold District

109°0'

Map

area

Study areas

IDAHO

MONTANA

OREGON

WYOMING

NEVADA UTAH

WASHINGTON

CO

CA

County boundaries

State boundaries

Proposed withdrawal areas

USGS study area boundary

Base data

USMIN mining districts

tungsten

titanium

silver

manganese

lead

iron

garnet

beryllium; tourmaline

Other USMIN commodity occurrences

uranium

gold

dolomite

copper

USMIN commodity occurrences assessed in this report

EXPLANATION

MILES50

Commodity and mining district data from Fernette and others (2016a).
64 Geology and Mineral Resources of the Southwestern and South-Central Wyoming and Bear River Watershed Sagebrush Focal Areas

Hydrothermal-Metamorphic Mineral System

Mineral deposits that form from hydrothermal fluids 

generated by thermal events associated with major fault zones 

occur in orogens formed by large-scale processes related to 

convergence of tectonic plates (Hageman and Cassidy, 2000). 

The fault zones may cut regionally metamorphosed rocks of 

all ages, can be as much as several kilometers wide and more 

than 100 km long, and are nearly vertical. Such deposits are 

most commonly enriched in gold with lesser silver, and some 

are also enriched in copper, lead, tungsten, and zinc.

Orogenic Low-Sulfide Gold-Quartz Veins (Orogenic Gold 

Veins)

Mineral Description

In deposits of this type, gold mineralization is primarily 

found in hydrothermal quartz veins in shear zones that occur 

near major fault zones in metamorphic rocks. Gold deposition 

occurred in and near fault zones at depths ranging from 3 to 20 

km from fluids that were apparently generated from prograde 

metamorphic devolatilization reactions (reactions that give 

off water (H2O), carbon dioxide (CO2), methane (CH4), and 

possibly other compounds, as heat and pressure are increased) 

in eugeosynclinal sedimentary and volcanic rock sequences. 

In such fluids, the gold is probably complexed with bisulfide anions, and the metal precipitates where the complex is 

destabilized, probably by the precipitation of sulfides. In some 

systems of this kind, mineralization in the veins can be traced 

to more than 2 km in depth. The veins are mainly composed 

of quartz (silicon dioxide, SiO2), with less abundant carbonate minerals, such as ankerite (Ca(Fe,Mg,Mn)(CO3

)2), siderite 

(FeCO3), and calcite (CaCO3). Pyrite (FeS2) and arsenopyrite 

(FeAsS) constitute less than 5 percent of the veins. The main 

ore mineral in most deposits is native gold. Orogenic lowsulfide gold-quartz veins are found in continental metamorphic 

belts of almost every geologic age, from Archean to Miocene. 

Hammarstrom and Zientek (2016) provide an overview of the 

methodology, and appendix 3 in Day and others (2016) provides a synopsis of the orogenic low-sulfide gold-quartz veins 

deposit model.

Geology and Occurrence in the Study Area

Orogenic low-sulfide gold-quartz veins have been known 

within the South Pass block of the Southwestern and SouthCentral Wyoming study area since 1864, when soldiers from 

Fort Bridger discovered a lode north of present day Atlantic 

City, Wyoming, and located a claim on it, naming it the Buckeye lode (Coutant, 1899, p. 639–640). In the next summer, 

1865, a second group of Fort Bridger soldiers was in the area, 

and a soldier named Tom Ryan discovered the gold-bearing 

Carissa lode (Layman, 2012). In spring of 1867, the H.S. 

Reedall party of 5 to 10 men left Salt Lake City with intent to 

locate Ryan’s discovery, claim it, and work it. They located the 

“Cariso” lode and established the Shoshonie Mining District. 

Within a year they had recovered $15,000 in gold (about 750 

troy oz) using only hand methods of mining and recovery. In 

the summer of 1867, Lewis Robison, a mountain man, arrived 

in Salt Lake City carrying 40 oz of gold reportedly recovered 

in 2 days in the South Pass-Atlantic City area (Bagley, 2011). 

The results of Robison’s and the Reedall party’s efforts set off 

a gold rush to South Pass City and Atlantic City over the next 

couple of years. By 1869, there were more than 300 structures 

and 1,900 people in South Pass City, but a bust soon followed and the 1880 census registered fewer than 200 people. 

However, like many of the districts that were discovered in the 

second half of the 19th century, the South Pass-Atlantic City 

district has seen renewed activity in nearly every time of high 

gold prices, a trend that continued into the 1990s.

The gold-bearing quartz veins in shear zones mined in the 

South Pass-Atlantic City district are hosted by, and deformed 

within, shear zones, most of which cut the Miners Delight 

Formation (fig. 23), a sequence of metagraywacke intruded 

by sills and fewer dikes of metadacite and orthoamphibolite 

(metadiabase). The Miners Delight apparently overlies the 

Roundtop Mountain Greenstone, which itself overlies the 

Goldman Meadows Formation, and the informal Diamond 

Springs formation, in order. The Roundtop Mountain Greenstone consists mostly of basalt, some of it pillowed, whereas 

the Diamond Springs consists of mostly serpentinized ultramafic volcanic rocks. The Goldman Meadows is composed of 

pelitic schist that alternates with magnetite facies banded iron 

formation, the rock type that was mined for 20 years by U.S. 

Steel in their Atlantic City open pit, about three miles north 

of Atlantic City. All of the rocks in the metasedimentary and 

metavolcanic package are tightly folded into a large syncline 

with many smaller-scale steep folds enclosed in it: bedding 

dips steeply inward from the South Pass-Atlantic City district 

on the northwest side, and from the Lewiston district on the 

southeast side. In general, the most productive shear zones 

strike and dip nearly parallel with bedding and foliation, most 

dipping near-vertical. However, in the middle of the syncline, 

the Miners Delight Formation contains only sparse shear zones 

and essentially no evidence of gold mineralization. Productive shear zones are found preferentially along and within 

metadacite and metadiabase sills, and those dikes and sills 

are nearly absent from the center of the syncline. Preference 

of the gold mineralization for shear zones, rather than thick, 

undeformed quartz veins, was observed by Hausel (1991, p. 

32 and p. 40). Relatively thick and continuous quartz veins, at 

the Alpine and Tornado Mines in the South Pass-Atlantic City 

district and the Lone Pine Mine in the Lewiston district, have 

had only small production whereas nearby shear zones are 

among the most successful mines of the districts, including the 

Franklin, Carissa, and Miners Delight Mines (fig. 24). Another 

10 mapped veins of massive quartz (Hausel, 1991) have no 

recorded production.

Both sides of the syncline were later intruded by granitic batholiths. The Louis Lake granodiorite intrudes on the 

northwest, and an unnamed granodiorite intrudes southeast of 
Locatable Minerals 65

Lewiston. The youngest Precambrian magmatism in the area 

occurs west of South Pass City where granite dikes and plugs, 

accompanied by numerous granitic pegmatites, intruded the 

Miners Delight Formation (Bayley and others, 1973).

The productive shear zones of the South Pass-Atlantic 

City district have envelopes of altered (sericitized) rock that 

are typically narrow, rarely thicker than a couple of meters, but 

have impressively thick zones of gold mineralization at a few 

places (for example, Hausel, 1991, p. 45). The shear zones and 

veins contain the expected carbonate gangue minerals along 

with quartz, arsenopyrite, and pyrite. A few of the veins and 

shear zones also contain up to several percent chalcopyrite 

(copper iron sulfide, CuFeS2) with at least two of the copperrich veins occurring near the contacts of the supracrustal rocks 

with the Louis Lake granodiorite (the Anderson Ridge and 

Tornado Mines; fig. 24).

Like in other gold districts of this type, fluid inclusions in 

quartz homogenize at around 275 °C, which, when corrected 

for the pressure at the time of trapping, is about 350 °C on the 

basis of their carbon dioxide and methane contents. The fluids 

are relatively dilute, averaging about 12.24 NaCl equivalent 

weight percent, and contain high CO2 concentrations and some 

methane. The average bulk fluid composition was 83.09 mole 

percent water, 16.15 mole percent CO2, and 3.46 mole percent 

NaCl. The fluids and the gold are believed to have been 

released from the sedimentary and volcanic rocks during highgrade metamorphism at depth (McGowan, 1990).

Exploration and Mining Activity

The South Pass-Atlantic City district had some 33 patented lode gold claims or groups of claims, many of those patented more than 100 years ago (Bureau of Land Management, 

2016). Mining activity has continued sporadically even to the 

present day. In the part of the district within the South Pass 

block (8 of the district’s 14 total sections) there are 38 active 

lode claims (mostly unpatented) and 7 active placer claims. 

There are no known pending actions regarding lode gold mining in the eight sections of the district within the South Pass 

block. (There are two authorized surface management plans 

for lode gold operations in those same eight sections within 

the district.) Examination of a Bureau of Land Management 

map from 1972 (Layman, 2012) indicates that, at that time, 

around 40 patented lode claims, were still in private ownership 

in the district. The Lewiston district has a similar history; it 

had 11 patented lode claims or groups of claims. Historically, 

lode gold mining has produced in excess of 224,823 troy oz 

of gold from South Pass-Atlantic City district and more than 

21,000 troy oz of gold from the Lewiston district (Hausel, 

1991, table 1, p. 30–31.) The largest producing mines in South 

Pass-Atlantic City district, listed in order of total ounces 

produced, were the Miners Delight (60,000 troy oz), Carissa, 

Caribou, Soules and Perkins, and Garfield (Buckeye) (21,000 

troy oz) (fig. 24). (Note that the Miners Delight Mine is well 

outside the study area and is therefore not included in table 2.)

A notable recent cycle of exploration activity took place 

in the South Pass-Atlantic City district from the mid-1970s 

into the 1990s, spurred when the U.S. Government abandoned 

the gold standard in 1971, which released the price of gold 

from a fixed $35 per troy oz to rise to its free-market value. 

In the decade following, the price of gold rose briefly to 

more than $1,800 per troy oz before settling slowly to around 

$1,300 per troy oz, near where it remains today.

Anaconda Copper was among the first companies to 

reexamine South Pass-Atlantic City district after the gold price 

was released, and they drilled several holes near the Carissa 

mine in 1974 (Hausel, 1991. p. 45). One hole intersected the 

Carissa shear zone at 198 to 213 m (650 to 700 ft) depth, 

where the zone was 4.9 m (16.1 ft) thick grading 4.4 grams per 

metric ton (g/t) of gold (Hausel, 1991. p. 45). Additional mineralized rock was encountered at depths between 213 and 284 

m (700 and 930 ft) below surface. Carissa underground workings consist of five levels. The primary shaft reaches the 4th 

level at 107 m (350 ft) below the surface and a winze connects 

with the 5th level at 122 m (400 ft) depth. The four upper levels support stopes; the nearly 700 m (2,300 ft) of drifts in the 

old workings extend as much as 232 m (760 ft) along strike. 

There appears to be considerable rock of good grade between 

107 and 284 m (350 and 930 ft) below surface along the shear 

zone, which averages 1.8 m (6 ft) wide at the surface (Hausel, 

1991). Hausel (1989) showed that a zone 30 m (97 ft)-wide 

containing the shear zone is mineralized to 0.8 g/t (0.0223 oz 

per short ton). Even ignoring the deeper mineralization, there 

is considerable unmined rock of good grade within the first 

four levels. In the second half of the 1980s into the 1990s, 

Consolidated McKinney Resources, a Canadian junior mining 

company from Vancouver, explored the Carissa and drilled 

eight holes. Reporting to Consolidated McKinney, de Quadros 

(1989) stated that H.S. MacFarlane with Carissa Gold (who 

operated the mine between October, 1949, and January 1955; 

Layman, 2012), calculated that remaining resources from levels 1 through 4 totaled 229,500 metric tons at 13.5 g/t at a 9.34 

g/t cutoff (252,400 short tons at 0.432 troy oz per short ton at a 

cutoff grade of 0.274 troy oz per short ton) (Hausel, 1991).

In 1967, the State of Wyoming purchased all of the property and structures of South Pass City and designated them as 

an official state historic site. In 2003, the State of Wyoming 

bought the Carissa Mine, mill, and patented claims, adding 

them to the South Pass City Historic Site (Layman, 2012). The 

State has since cleaned out and restored the mill building and 

rebuilt an ore pass platform from the head of the shaft into the 

mill. Both are now suitable for tourists to visit.

Potential for Occurrence

Tracts for undiscovered orogenic low-sulfide gold-quartz 

veins in and near the South Pass-Atlantic City district and the 

Lewiston district are based on the most important mappable 

feature of the known deposits, the mineralized shear zones. 

Hausel’s (1991) geologic map at 1:48,000-scale was used 

to delineate the mineralized zones. Each of the shear zones, 
66 Geology and Mineral Resources of the Southwestern and South-Central Wyoming and Bear River Watershed Sagebrush Focal Areas

SOUTH PASS BLOCK

SWEETWATER COUNTY

SUBLETTE

COUNTY

Wgd

Tmu

Ws

Tmu

Tmu

Wg

Wg

Wg

Wmu

Wg

Tmu

Wmu

Ws

Ws

Tmu

Wg

Ws

Tmu

Wg

Tmu

Wg

Ws

Tmu

Wg

Wg

Ws

Tmu

Ws

Tmu

Tmu

Tmu

Ws

Tmu

Ws

Ws

Ws

Carrie Shields Mine

Ground Hog Group

Gold Dol

Miners Delight

Anderson Ridge

Franklin Mine

Carissa Mine

Tornado Mine

Caribou Mine

Duncan Mine

Alpine Mine

Mary Ellen

Diana Mine

Rose Mine

St Louis 

Atlantic City Iron Mine

Garfield (Buckeye) Min

Soules and Perkins

109°0' 108°50' 108°40' 

42°30'

42°20'

1086420 KILOMETERS

Base modified from U.S. Geological Survey DEM data, 2016. 0 2 4 6 8 

Political boundaries and roads from Esri (2013).

Roads and political data © 2014 Esri and its licensors.

USA Contiguous Albers Equal Area Conic Projection.

Central meridian, 110° W., latitude of origin, 37.5° N.

North American Datum of 1983.

A

B
Locatable Minerals 67

LEWISTON

OROGENIC GOLD

H/D

Continental Fault

SOUTH PASS

OROGENIC GOLD

H/D

FREMONT COUNTY

Ws

Tmu

Wg

Wg

Tmu

Wmu

Wg

Wg

Ws

Ws

Wg

Wg

Tmu

Tmu

Ws

lar Mine

Wolf Mine

Burr

Lewiston townsite

e

Lone Pine Mine

108°30'

Map

area

Study areas

IDAHO

MONTANA

OREGON

WYOMING

NEVADA UTAH

WASHINGTON

County boundaries

USGS study area boundary

Base data

Other mine site

USMIN gold occurrence location

Continental Fault

Shear zones

Shear zone 500-m buffer

High-potential (H) tract with high (D) certainty

Atlantic City Iron Mine

Ws Archean metasedimentary rocks

Wmu Archean metamorphosed mafic and ultramafic rocks

Wgd Archean granodiorite of the Louis Lake pluton

Wg Granitic rocks of 2,600-Ma age group

Tmu Upper Miocene rocks

Simplified geology

EXPLANATION

10 MILES

Geology after Stoeser and others (2005 [revised 2007]).

Shear zones and Atlantic City Mine after Hausel (1991).

Fault data from Sutherland and Hausel (2006).

USMIN gold locations from Fernette and others (2016).

Figure 23. Map showing the geology of the South Pass block, 

Southwestern and South-Central Wyoming study area, Wyoming. 

USMIN, U.S. Geological Survey (USGS) Mineral Deposit Database. 

Ma, mega-annum or millions of years ago; m, meters.
68 Geology and Mineral Resources of the Southwestern and South-Central Wyoming and Bear River Watershed Sagebrush Focal Areas

SOUTH PASS BLOCK

SWEETWATER COUNTY

SUBLETTE

COUNTY

Carrie Shields Mine

Ground Hog Group

Gold Dol

Miners Delight

Anderson Ridge

Franklin Mine

Carissa Mine

Tornado Mine

Caribou Mine

Duncan Mine

Alpine Mine

Mary Ellen

Diana Mine

Rose Mine

St Louis 

Garfield (Buckeye) Min

Soules and Perkins

109°0' 108°50' 108°40' 

42°30'

42°20'

1086420 KILOMETERS

Base modified from U.S. Geological Survey DEM data, 2016. 0 2 4 6 8 

Roads and political data © 2014 Esri and its licensors.

Boundary data from San Juan and others (2016).

USA Contiguous Albers Equal Area Conic Projection.

Central meridian, 110° W., latitude of origin, 37.5° N.

North American Datum of 1983.
Locatable Minerals 69

Figure 24. Map showing location of orogenic-gold mines and 

claims, with geology and resource potential tracts, in the South 

Pass block, Southwestern and South-Central Wyoming study 

area, Wyoming. BLM, Bureau of Land Management; USMIN, U.S. 

Geological Survey (USGS) Mineral Deposit Database.

SOUTH PASS

OROGENIC GOLD

H/D

LEWISTON

OROGENIC GOLD

H/D

Continental Fault

FREMONT COUNTY

lar Mine

Wolf Mine

Burr

Lewiston townsite

e

Lone Pine Mine

108°30'

Map

area

Study areas

IDAHO

MONTANA

OREGON

WYOMING

NEVADA UTAH

WASHINGTON

County boundaries

Proposed withdrawal areas

USGS study area boundary

Base Data

USMIN gold locations

Fault

High-potential (H) tract with high (D) certainty

Assessment tract types – low-sulfide orogenic gold veins

Closed lode claim

Closed tunnel site

Active lode claim

Townships containing BLM mining claims

Pending surface management plan for gold

Authorized surface management plan for gold lode

Townships containing BLM mining plans and notices

EXPLANATION

10 MILES

Other mine site

Claim and plans/notices data from Dicken (2016).

Fault data from Sutherland and Hausel (2006).

USMIN gold locations from Fernette and others (2016).
70 Geology and Mineral Resources of the Southwestern and South-Central Wyoming and Bear River Watershed Sagebrush Focal Areas

which in this district are zones of high strain that range to as 

large as 5 km long and 10 m wide, were buffered by 500 m on 

the sides and ends (fig. 23). All of the mineralized shear zones 

and their buffer zones were then enclosed in smoothly curving 

boundaries. Indications of mineralizing processes on the shear 

zones were any kind of exploration or mining activity as symbolized by Hausel (1991), including shafts, adits, trenches, and 

prospect pits. Five hundred meter buffer zones were chosen 

after attempting the same exercise with one-mile and onekilometer buffers. The larger buffers included almost the entire 

syncline. Hausel’s mapping was at the same detail, across the 

central area of the syncline, yet he recorded almost no indication of any gold-exploration or mining across the central part 

of the syncline. Using the smaller buffer zones, there are eight 

shear zones excluded from the tract, all eight mapped near the 

middle of the syncline, and seven of those have no signs of 

mining activity (Hausel, 1991, plate 1). Furthermore, three of 

the eight cut at high angles across the layering in the Miners 

Delight Formation, unlike nearly all of the mineralized shears 

which are parallel to layering. Last, none of the eight shears 

near the middle of the syncline are associated with any metadacite or metadiabase sills or dikes. Of the 106 mapped shear 

zones or veins, only 17 are not also within 500 m of a mapped 

metadacite or metadiabase sill or dike, including those eight 

shear zones excluded from the smooth outline.

The tract ends on the northeast where the Cambrian Flathead Sandstone contact is reached, and, northeastward from 

there, the Flathead rocks overlie the favorable Archean rocks. 

In fact, however, resource potential actually continues beneath 

the Flathead Sandstone and other rocks to the northeast. 

However, the covered Archean rocks with mineral resource 

potential for orogenic gold-quartz veins are, in that direction, 

farther and farther away from the boundaries of the proposed 

withdrawal area at South Pass.

The tract containing all the mineralized shear zones of 

the South Pass-Atlantic City district is labeled South Pass (fig. 

25). The corresponding tract that covers the Lewiston district is labeled Lewiston. These tracts are rated with high (H) 

potential at certainty level D. That there is remaining potential 

in the district is amply proven by Anaconda’s drilling at the 

Carissa mine where the mineralized shear zone was found to a 

depth below surface of 283 m (930 ft). It is expected that other 

of the district’s near-vertical mineralized shear zones also continue to considerable depth, and to our knowledge, none of the 

others has been drill tested. Additional potential in the South 

Pass Orogenic Gold tract lies in areas where the Archean rocks 

are covered by Tertiary sediments between the Franklin and 

Anderson Ridge Mines (fig. 23). No less than 2.4 km of the 

total distance of 7.2 km is covered by the Tertiary and Quaternary sediments, and the area between extends subparallel 

to the elongation direction of shear zones in areas of outcrop 

both to the east and west. Drilling targets might be established 

in covered areas using combinations of magnetic surveys to 

estimate depth to the top of Precambrian crystalline rocks and 

electromagnetic or induced polarization surveys to identify 

electrically conductive rock types. Though this type of deposit 

does not have a lot of sulfides, even a small amount should 

still contrast with the probably high-resistivity Miners Delight 

greywacke and late granites. 

No tract is drawn for the Archean rocks of the center of 

the syncline (either where they are exposed or where they are 

covered by Tertiary sediments). There appears to be no indication of gold mineralizing processes through the middle of the 

syncline, although it is possible that geologic conditions like 

those at the northwest and southeast boundaries of the syncline 

might be present as well near the bottom boundary of the 

syncline, at great depth.

The Lewiston Shear Zone Extension tract extends to the 

southwest from the southern end of the Lewiston Orogenic 

Gold tract. The tract is delineated by extending from the southernmost of the mapped shear zones of the Lewiston district 

by a distance equal to the largest gap between collinear shear 

zones mapped anywhere in either the Lewiston or South PassAtlantic City district. That largest gap distance is interpreted 

as a measure within which prospectivity still exists—the 

measure derived from geometry of shear zones in the mining 

district, itself. The largest gap between the ends of mapped 

collinear shears is 4,734 m (labeled A and B on fig. 23). Therefore, 7,734-m extensions were added to the southernmost 

shear zones in the Lewiston Orogenic Gold tract and buffered 

by 500 m. The southwest end of the tract is constructed by 

connecting the end of the buffer zones by straight lines from 

one shear zone extension end to the next. The result, overall, is 

that the tract is shaped like a segment of a fan (fig. 25).

Because the potential is considered to be high in the 

Lewiston Orogenic Gold tract to the north, the potential in the 

continuation to the south in the Lewiston Shear Zone Extension tract is also considered high (H), yet the certainty is considered to be lower than the tract to the north and east and is 

rated at level B because there is no direct evidence of mineralized rock in the parts of the tract where the Precambrian rocks 

are under Tertiary rocks.

An additional tract, the Lewiston Extension Under 

Tertiary Cover tract, extends permissive rocks farther to the 

southwest beneath younger cover rocks. In USGS mineral 

resource assessments, mineral potential is typically estimated 

to a depth of 1 km. The Archean Miners Delight Formation 

hosts the orogenic low-sulfide gold-quartz vein deposit-type in 

the Lewiston area. North of the Sweetwater River (fig. 3) the 

top of the gold-bearing Archean basement gently dips to the 

south and is covered by the northern extent of a vast expanse 

of Tertiary sediment, thus burying the rocks that have potential 

for orogenic low-sulfide gold-quartz vein deposits. The potential for the occurrence of orogenic low-sulfide gold-quartz 

veins clearly continues south and southwest of the known 

Lewiston district under Tertiary (and Quaternary) cover. In the 

Willow Creek drainage area the Tertiary/Archean erosional 

surface dips gently to the south from 1 to 6 degrees, and that 

surface has a rugged paleotopography developed on it with 

local relief of several hundred feet. Nonetheless, assuming an 

overall gentle southward regional dip of 5 degrees, the southward extent to which the Archean rocks would be buried to a 
Locatable Minerals 71

depth of 1 km or less would be over 11.5 km. Thus the tract, 

entirely beneath Tertiary cover, extends from the contact of 

Tertiary sediments onto Archean rocks and continues for 11.5 

km in the direction of the mapped shear zones to the north or 

northeast. The 500-m buffers on the sides of the outermost 

shear zones are continued south or southwestward. Again, a 

southern or southwestern end for the extension is provided 

by connecting the buffered end of the shear zone extensions 

with straight lines, producing a tract with a shape like another 

segment of a fan, this one opened wider than the shear zone 

extension tract. The tract thus extends 11.5 km from the edge 

of exposed Precambrian rocks near Lewiston.

The southern extent of the Lewiston Extension Under 

Tertiary Cover tract is terminated at the Continental Fault, 

although it is possible that mineralization could extend beyond 

the fault (fig. 25). The Continental Fault is a normal fault 

upthrown on the south, such that the Archean/Tertiary contact 

would be displaced to higher elevation on the south side of the 

fault. As a result, Archean rocks permissive for undiscovered 

orogenic low-sulfide gold-quartz vein deposits could extend 

on the south side of the Continental Fault.

The extent and location of Archean rocks south of the 

fault, however, is highly uncertain. There is an intimate 

relationship between the location of the Continental Fault and 

the location of the underlying Wind River thrust (Berg, 1983). 

According to seismic stratigraphy and petroleum exploration 

drill holes, the Continental Fault nearly overlies the top of the 

sharp edge of the wedge of Precambrian rock that was thrust 

southwestward late in the Laramide orogeny (Berg, 1983). In 

areas to the northwest of the South Pass proposed withdrawal 

area, the vertically projected thrust edge—the sharp edge of 

the wedge of Precambrian rock projected vertically to the 

land surface—lies 1.6 km or less to the southwest from the 

trace of the Continental Fault locally, and at other places, the 

Continental Fault lies 1.6 km or less to the southwest of the 

vertically project thrust edge. The thrust edge marks the place 

where the Archean/Tertiary contact would fall dramatically in 

elevation from perhaps 1,830 to 1,980 m in elevation (at the 

leading edge of the hanging wall), to more than 6,100 m below 

sea level vertically below on the footwall block (Berg, 1983, 

figure 4, p. 260). Thus, locally, the Lewiston Extension Under 

Tertiary Cover tract would continue to the south of the Continental Fault, but at other places, that surface will have dropped 

very abruptly to more than 20 km (12 mi) below the surface 

before reaching the Continental Fault. Without both seismic 

surveys and drill-hole information that provides ground truth 

for the seismic results, the location of the vertical projection 

of the thrust edge cannot be accurately located, and we cannot 

know where the tract should end before the Continental Fault 

(at the vertical projection of the edge of the wedge of thrusted 

Precambrian rock) versus where a relatively small amount of 

additional land should be added to the tract south of the Continental Fault. Therefore, we chose to end the Lewiston Extension Under Tertiary Cover tract at the Continental Fault, a 

place that is typically marked on the ground by sharp changes 

in topography and rock types (figs. 23 and 25).

The Lewiston Extension Under Tertiary Cover tract, 

either at the start of cover over the prospective Precambrian 

rocks or where the Precambrian rocks are covered by substantial thicknesses of Tertiary rock, cannot, with any certainty, 

be asserted to contain gold-bearing shear zones. Continuity of 

the Archean metasedimentary and metavolcanic host rocks is 

reasonably assured, but not the continuity of the mineralized 

shear zones; therefore, the tract is rated with moderate (M) 

potential at a level of certainty of A. A geologic environment 

for these Precambrian rocks (metamorphosed eugeosynclinal 

package with metavolcanics, metapelites, and metagraywacke) 

is known to potentially host orogenic low-sulfide gold-quartz 

veins, but no more is known except that gold-bearing shear 

zones are present several kilometers to the north and northeast. Without further evidence, the distance is too great to 

assume continuity of any single shear zone or even a section 

containing shear zones at all, so high potential is not indicated. 

Geophysical surveys indicating rock with low resistivity in the 

Precambrian wedge might be taken as indication of sulfidebearing shear zones, but no “electrical” geophysical surveys 

exist for the tract area. With no exposure of any kind and no 

geophysical surveys, the available data are insufficient and 

cannot be considered as evidence either for or against resource 

potential for orogenic low-sulfide gold-quartz veins.

Economic Analysis

Gold deposits on the margins of the study area have 

been economically viable in the past and may be so again 

in the future in the tracts delineated as South Pass Orogenic 

Gold and Lewiston Orogenic Gold. Deposits in the Lewiston 

Shear Zone Extension tract would be at depth, and thus more 

expensive to locate and develop. Any deposits in the Lewiston 

Extension Under Tertiary Cover tract are purely speculative at 

this time.

Discussion of where gold is being produced in the Western United States can be found in Bleiwas (2016). None of the 

current gold production from Utah is within the study area, 

and there is currently no gold production in Wyoming.

Sedimentary Mineral System

A variety of mineral deposits are formed within sedimentary rocks by processes themselves restricted to the enclosing 

sedimentary basin. Processes of diagenesis, using only water 

that is trapped with the sediments, can result in the conversion of volcanic ash into bentonite clay or ashy sediments into 

valuable zeolite minerals. Epigenetic deposits of base metals 

with or without barite can be deposited by mixing groundwaters that permeate from distances of tens or hundreds of 

miles away with the connate water trapped with the original 

sediment. Alternatively, far-traveled groundwater can deposit 

zinc, lead, barite, and silver by discharging into the seawater 

immediately above the seafloor where it mixes and reacts with 

the seawater. Sandstone-hosted deposits of uranium, vanadium, and copper can be precipitated from waters recharging 
72 Geology and Mineral Resources of the Southwestern and South-Central Wyoming and Bear River Watershed Sagebrush Focal Areas

LEWISTON EXTENSION

UNDER TERTIARY COVER

M/A

SOUTH PASS BLOCK

SWEETWATER COUNTY

SUBLETTE

COUNTY

Carrie Shields Mine

Ground Hog Group

Gold Dol

Miners Delight

Anderson Ridge

Franklin Mine

Carissa Mine

Tornado Mine

Caribou Mine

Duncan Mine

Alpine Mine

Mary Ellen

Diana Mine

Rose Mine

St Louis 

Garfield (Buckeye) Min

Soules and Perkins

109°0' 108°50' 108°40' 

42°30'

42°20'

1086420 KILOMETERS

Base modified from U.S. Geological Survey DEM data, 2016. 0 2 4 6 8 

Roads and political data © 2014 Esri and its licensors.

Boundary data from San Juan and others (2016).

USA Contiguous Albers Equal Area Conic Projection.

Central meridian, 110° W., latitude of origin, 37.5° N.

North American Datum of 1983.
Locatable Minerals 73

Figure 25. Map showing the mineral-potential tracts for orogenic 

low-sulfide gold veins in the South Pass block, Southwestern 

and South-Central Wyoming study area, Wyoming. USMIN, U.S. 

Geological Survey (USGS) Mineral Deposit Database.

LEWISTON

H/D

LEWISTON

SHEAR ZONE

EXTENSION

H/B

Continental Fault

SOUTH PASS

H/D

FREMONT COUNTY

lar Mine

Wolf Mine

Burr

Lewiston townsite

e

Lone Pine Mine

108°30'

Map

area

Study areas

IDAHO

MONTANA

OREGON

WYOMING

NEVADA UTAH

WASHINGTON

County boundaries

Proposed withdrawal areas

USGS study area boundary

Base data

USMIN gold locations

Fault

Moderate-potential (M) tract with unknown (A) certainty

High-potential (H) tract with high (D) or low (B) certainty

Assessment tract types – orogenic gold vein

EXPLANATION

10 MILES

Other mine site

USMIN gold locations from Fernette and others (2016).

Fault data from Sutherland and Hausel (2006).
74 Geology and Mineral Resources of the Southwestern and South-Central Wyoming and Bear River Watershed Sagebrush Focal Areas

from the surface, where those waters mix and react with the 

connate water and with constituents of the diagenetically 

changed sandstone. A far-traveled epigenetic groundwater can 

precipitate copper and possibly silver or cobalt by discharging 

from a red-bed package into carbonaceous rocks or into a sour 

gas reservoir.

Sediment-Hosted Stratabound Copper Deposits

Mineral Description

Sediment-hosted stratabound copper deposits consist of 

fine-grained, copper- and copper-iron-sulfide minerals that 

form stratabound to stratiform disseminations in siliciclastic 

or dolomitic sedimentary rocks. Chalcocite (Cu2S) and bornite 

(Cu5FeS4) typically cement the host rocks and replace certain 

detrital grains and earlier cements. Sulfide minerals occur less 

commonly as veinlets. The concentration of sulfide minerals 

generally conforms closely with stratification of the host rocks, 

but, in detail, may cross the stratification. Deposits are characterized by zoning of ore minerals laterally along and across 

bedding from pyrite to chalcopyrite to bornite to chalcocite 

to hematite (Fe2O3) (Hayes and others, 2015; see appendix 3 

in Day and others, 2016). Fringes of ore bodies distal from 

the source of ore solutions may contain sphalerite ((Zn,Fe)S), 

galena (PbS), and pyrite coexisting with chalcopyrite and may 

grade farther yet from the source to rock, whose only sulfide 

is pyrite. The gentle cross-through beds of epigenetic zones of 

hematite (with Fe3+) grading to copper sulfides grading across 

the zonation to pyrite (with Fe2+) are evidence that oxidation/

reduction processes were involved in ore precipitation.

Sediment-hosted stratabound copper deposits are formed 

in sedimentary basins that contain relatively thick (>300 m 

and commonly >1 km) successions of red (hematitic) clastic 

sedimentary rocks with or without evaporites, or in basins that 

have thick subaerially erupted (continental) basalt sequences. 

Based on ore and gangue mineral zoning and alteration, 

mineral paragenesis, fluid inclusion studies, and stable isotope 

geochemistry, the metal-bearing fluids were low temperature (75–220 °C), hematite stable (oxidized), sulfate- and 

chloride-rich, subsurface brines generated during compaction 

and lithification of the sediments in the basin (Zientek and 

others, 2013a; Hayes and others, 2015). The primary cause of 

base-metal sulfide precipitation is reaction of the ore fluid (the 

cupriferous brine) with rocks or fluids that either provide sulfide, or form sulfide from ore fluid sulfate by reduction (Hayes 

and others, 2015).

Three subtypes of sediment-hosted stratabound copper 

deposits are recognized based on the processes responsible for 

precipitation of copper sulfides. In the reduced facies subtype, 

amorphous solid carbonaceous material in dark gray to black 

shale or siltstone serves as the reductant of ore fluid sulfate to 

form sulfide. Resulting deposits are sheet-like, following the 

beds of organic-rich shale or siltstone. Though they may be 

just a few meters to about 10 m thick, reduced facies deposits 

have areas commonly in the tens of square kilometers, and in 

the case of the Kupferschiefer deposit in Poland, more than 

100 km2

. In the sandstone subtype, hydrogen sulfide within a 

reservoir of natural gas reacts directly with dissolved copper 

in the ore fluid to precipitate copper sulfides, and methane of 

the natural gas acts as a reductant to form further sulfide by 

reaction with ore fluid sulfate. The newly formed sulfide can 

also react to precipitate copper sulfides. Sandstone deposits 

tend to be thicker than reduced facies, but are not as extensive in area and are tabular to lens-like in shape (thicknesses 

around 20 m and areas of 5 km2 are common). Finally, in the 

red-bed subtype deposits, carbonized plant fossils within gray 

fluvial sandstones isolated within the clastic sequence of red 

sedimentary rocks serve as the reductant for ore fluid sulfate. 

Red-bed deposits are typically only meters thick, are elongate 

within the ribbon-like host sandstone, and have areas generally less than 1 km2

 (Hayes and others, 2015). Red-bed copper deposits are commonly too small to be profitably mined in 

today’s global copper market.

Geology and Occurrence in the Study Area

There is potential for sandstone-type sediment-hosted 

stratabound copper deposits in the Fossil Basin and Bear 

Lake Plateau blocks of the Bear River Watershed study area. 

There is also potential for red-bed-type deposits, and there 

is conceptually a chance for reduced facies deposits, though 

no reduced facies-type occurrences are known. Both red-bed 

and sandstone types occur to the north or northwest of the 

proposed withdrawal area. 

The Griggs Mine in Lake Alice district, Wyoming, is 

37 km (23 mi) north from the northern boundary of the 

Fossil Basin block and 40 km (25 mi) north of the northern 

boundary of proposed withdrawal area in that block. It was 

discovered in 1895, operated 1915–1920, and was examined 

and reexamined during World War II and later in the 20th 

century before being reclaimed as a private summer cabin 

site on patented land (U.S. Geological Survey, 2016). The 

Griggs Mine is on a thrust sheet that is continuous into the 

proposed withdrawal area (fig. 26). The Griggs Mine and five 

other copper occurrences in the Lake Alice district are hosted 

by the upper part of the Nugget Sandstone of latest Triassic 

and earliest Jurassic age (fig. 6) (Love and Antweiler, 1973). 

The Nugget Sandstone is composed mostly of wind deposited 

dune sands like the correlative Navajo Sandstone of the Glen 

Canyon Group on the Colorado Plateau, and the Nugget is 

almost everywhere red, except for the places that host copper 

mineralization and places where the Nugget produces petroleum (fig. 26). The Nugget is the most important reservoir 

rock for thrust belt oil and gas in Wyoming, Utah, and Idaho 

(Powers, 1983). The Griggs Mine is a sandstone-type copper 

deposit and has cap rocks of dolomitic breccia impregnated 

with pyrobitumen, a hard black organic substance like solidified tar that occupies former pores and fractures. The cap 

rock is part of the Gypsum Spring Formation (or Member of 

the Twin Creek Limestone). The original seal rocks for a gas 

reservoir may have been evaporitic rocks, perhaps anhydrite, 
Locatable Minerals 75

which would have been consumed by reaction with the 

natural gas. The average grade from five samples of ore from 

the Griggs Mine analyzed by Love and Antweiler (1973) was 

2.66 percent copper, 280 g/t silver, and 1.43 percent zinc, but 

two of the five were labeled “selected high-grade samples.” 

Osterwald and others (1966, p. 56) state that in 1919, 15 

[short] tons of Griggs ore brought $1,180. At a price of 

18.18 cents per pound of copper that year (Inflation Monkey, 

2012), that calculates to a grade of 21.63 percent copper in 

the shipment, an astronomical grade for sandstone copper ore 

that probably records that the shipment was carefully handsorted to include nothing but almost pure copper-carbonates. 

Osterwald and others (1966) later report that in 1942, Griggs 

ore averaged $18.00 per short ton [in value of its contained 

copper]. At an average price of 12.27 cents per pound from 

that year (Inflation Monkey, 2012), the produced grade for 

the year calculates to 7.33 percent copper, still far too high a 

grade to be run-of-the-mine ore, still reflecting selective hand 

sorting of the ore that was shipped. Worldwide, the median 

grade of mined sandstone-type copper deposits is 1.2 percent and the median silver grade is 19.5 g/t (0.51 troy oz per 

short ton) (Zientek and others, 2013b, p. 44). The worldwide 

median tonnage of mined sandstone-type copper deposits is 

10 million metric tons (Mt), while the mean tonnage is 77 Mt 

(Zientek and others, 2013b). The largest sandstone copper 

deposit in the United States is Rock Creek, Montana, which 

contains 137 Mt of 0.72 percent copper and 54 g/t silver 

(Couture and Tanaka, 2005).

Three red-bed-type copper occurrences, the Bonanza 

Mine, the Bonneville Mine, and the Evening Star claims, lie 

west of the Fossil Basin block and north of the Bear Lake 

Plateau block (figs. 26 and 27) (Gale, 1909). These three 

occurrences are hosted by the Triassic Ankareh Formation 

red-bed sequence (fig. 6) in gray sandstone beds containing carbonized plant fossils. A fourth red-bed-type copper 

occurrence, the Cockscomb (figs. 26 and 27), is hosted by the 

Lower Cretaceous Gannett Group and also in gray sandstones 

within that red-bed sequence. The Cockscomb occurrence 

is south of the Fossil Basin block and east of the Bear Lake 

Plateau block (fig. 27). The Rock Creek Valley copper occurrence, within the proposed Fossil Basin withdrawal area (fig. 

27), is hosted by the Pennsylvanian Weber Sandstone (fig. 6) 

and is probably a sandstone type occurrence.

Exploration and Mining Activity

Since the time of operation of the Griggs Mine during 

World War II, there has apparently been little or no mining or 

exploration for sediment-hosted stratabound copper deposits 

in the area of the Fossil Basin and Bear Lake Plateau blocks. 

Based on BLM data (see Dicken and San Juan, 2016b), the 

only claims for copper near the study area are the patented 

lode claim group at the Griggs Mine itself. There are no pending and no authorized surface management plans for copper 

mining within or near the proposed withdrawal areas.

Potential for Occurrence

The presence of the Griggs Mine and other sedimenthosted copper occurrences demonstrates that a copper mineralizing system was present in the thrust belt. The best host 

rocks are mapped sufficiently to predict their location within 

the study area, even beneath cover. The sites of localization of 

mineralization are predictable—they were formerly petroleum 

traps. In addition, although the known copper occurrences are 

not densely distributed, there are red-bed-type copper occurrences several kilometers to the west and south of the Fossil 

Basin block, and there is a single sandstone-type copper occurrence, Rock Creek Valley (fig. 27), within the Fossil Basin 

proposed withdrawal area.

A tract consisting of a number of north-trending elongate 

strips of land has been constructed, consistent with earlier 

USGS assessments for sediment-hosted stratabound copper deposits (for example, Zientek and others, 2014). Earlier 

assessments for sediment-hosted stratabound copper deposits 

identified whole basins as permissive for this type of copper 

mineralization (Parks and others, 2016). The whole depositional basin of the Nugget Sandstone is inappropriate to 

consider for this assessment. Earlier assessments for sedimenthosted stratabound copper deposits identified lands that had 

prospective host rocks at the surface or in the subsurface and 

then assessed those lands to a depth appropriate for the kind 

of mining that would be needed and with the expected value 

of the ore. In this assessment, the potential for deposits of 

this type is estimated to a depth of 1 km (3,281 ft) below the 

surface. Permissive tracts were identified as follows.

Geologic maps of excellent quality at 1:62,500-scale are 

available for the Sage and Kemmerer 15-minute quadrangles 

(Rubey and others, 1975) and the Cokeville 30-minute quadrangle (Rubey and others, 1980). These geologic maps are 

accompanied by east-west geologic cross sections constructed 

at 4.6 km intervals north to south. Eleven of these cross-sections cover the Fossil Basin block.

The cross sections, together with their corresponding 

geologic maps, were used to identify all areas where the Nugget Sandstone is known to be, or projects to be, present at less 

than 1 km depth within both the Fossil Basin and the Bear 

Lake Plateau blocks. The separated strips of the tract are each 

controlled by some particular relation between the Nugget 

Sandstone, the major thrust faults, the accompanying folds, 

and the erosion surface. Each relation continues parallel to a 

particular thrust fault for several kilometers up to several tens 

of kilometers.

The area of the Bear Lake block is almost entirely 

covered by the Logan 30’×60’ quadrangle mapped at scale 

of 100,000 by Dover (1995). This geologic map covers a 

north-south extent larger than the combination of the Sage and 

Kemmerer, and Cokeville quadrangles by Rubey and others 

(1975; 1980). Three cross sections across the Logan quadrangle (Dover, 1995) are spaced approximately 18 km apart. 

Therefore, the precision of the tract defined using the Logan 

map (Dover, 1995) is considerably less than that attained using 
76 Geology and Mineral Resources of the Southwestern and South-Central Wyoming and Bear River Watershed Sagebrush Focal Areas

JACKSON

Pinedale

Logan

Coalville

Evanston

SALT LAKE CITY

Alpine

Jackson

IDAHO

UTAH

WYOMING

UTAH

IDAHO

WYOMING

Hoback

Basin

Snake

River

Plain

Teton Range

Bear Lake

LAKE ALICE

DISTRICT

EVENING STAR

CLAIMS

BONNEVILLE

MINE

BONANZA

MINE

COCKSCOMB

ROCK

CREEK

VALLEY DARBY

CACHE CREEK

PROSPECT

WILLARD-PARIS

DARBY (HOGS BACK)

ABSAROKA

CRAWFORD

TUNP

Uinta Mountains

112° 111° 110°

44°

43°

42°

41°

20

GRIGGS

MINE Big Piney-LaBarge

Producing Complex

LAKEVIEW-MEADE

EXPLANATION

Oil and gas fields with Nugget

 Sandstone as major reservoir

Quaternary and Tertiary volcanic rocks

Precambrian rocks

Thrust fault (sawtooth on overthrust 

 block), dashed where inferred

Producing oil and gas fields and

 indicated new discoveries

0 10 20 30 MILES

0 10 20 30 KILOMETERS

Copper mine or prospect

Figure 26. Map showing sediment-hosted stratabound copper locations relative to thrust faults and oil and gas 

fields in the thrust belt. Traces of major thrusts, adjacent basement uplifts, and oil and gas fields are from Powers 

(1983). Sediment-hosted stratabound copper occurrences are from the Mineral Resources Data System (MRDS; U.S. 

Geological Survey, 2016) and Love and Antweiler (1973).
Locatable Minerals 77

11 cross-sections from the Sage, Kemmerer, and Cokeville 

(Rubey and others, 1975, 1980) quadrangles.

The areas in which the Nugget Sandstone is within a 

kilometer of the surface in Utah are not geologically different 

than those in Wyoming. There is no reason to judge those in 

Wyoming with greater potential based only upon the one or 

two copper occurrences. As a result, we have included all of 

the strips of land with the Nugget within 1 km of the surface 

into a single tract for potential and certainty rating.

There are no known copper occurrences in the Nugget Sandstone in the Logan quadrangle. Results from USGS 

stream sediment and soil sampling were examined for the 

entire Bear Lake Plateau and Fossil Basin PLSS blocks, and 

there are no anomalous areas, nor even anomalous single 

samples. Also, there are no surveys by geophysical methods 

appropriate for exploring for this deposit type. However, given 

that (1) the Alice Lake district, to the north, is on a thrust sheet 

that extends continuously southward into the Fossil Basin 

block and contains the Rock Creek Valley copper occurrence, 

and (2) the copper mineralizing system extended at least from 

the red-bed-type occurrences in Idaho to as far south as the 

Cockscomb occurrence (fig. 26), we estimate the mineral 

resource potential as moderate (M). Evidence for potential is 

direct in the form of the sandstone-type Rock Creek Valley 

copper occurrence, yet the single occurrence is quantitatively 

minimal, which requires a certainty assignment of C.

Economic Analysis of the Deposit Types

Sediment-hosted stratabound copper deposits are typically higher grade than porphyry copper deposits, the world’s 

largest-producing copper deposit type. Sediment-hosted 

stratabound copper deposits also commonly have byproduct or 

coproduct silver (Hayes and others, 2015). There are insufficient numbers of known occurrences in the assessment region 

to permit a prediction of deposit tonnages. Although sandstone-type copper deposits can have large tonnage (median of 

10 Mt and mean of 77 Mt), the only example in the area, the 

Griggs Mine, was a shallow mine operated along just 305 m 

(1,000 ft) of length. Production and resource information for 

the Griggs Mine is not available. Another deposit like Griggs 

is unlikely to be economically viable in this area in the foreseeable future. However, potential for undiscovered copper 

resources in deposits of 10 Mt and perhaps more is considered 

possible.

Most of U.S. the copper production is from large, openpit porphyry-type deposits, not from sediment-hosted stratabound deposits. It has been only 2 years since the last U.S. 

mine in a sandstone-type copper deposit closed after mining 

more than 90 Mt. Mining is currently proposed at two new 

sites, the Rock Creek deposit and the Montanore deposit, both 

in Montana. The Lisbon Valley, Utah, sandstone-type copper 

deposit continues to produce from three separated ore bodies totaling 48 Mt or 0.47 percent copper (Hahn and Thorson, 

2005).

Discussion of the economics of copper can be found in 

Bleiwas (2016). None of the current copper production attributed to Utah is from the study area. 

Banded-Iron Formation

Mineral Description

Banded-iron formation is sedimentary rock characterized 

by alternating iron-rich and silica-rich layers. The thickness of 

individual layers is typically a few millimeters to a few centimeters. Overall, an iron formation may be meters to hundreds 

of meters thick. The principal iron minerals are hematite, 

magnetite (Fe3O4), siderite or another iron-carbonate, or pyrite, 

or less commonly, an iron silicate such as stilpnomelane 

((K,Ca,Na)(Fe2+,Mg,Fe3+)8(Si,Al)12(O,OH)27·nH2O). The iron 

formation is designated as carbonate facies, hematite-facies, 

or the like, dependent on the most important iron mineral. The 

iron minerals present today are not those that were chemically 

precipitated from seawater but are those that formed during 

diagenesis after burial and during metamorphism of the rocks. 

Algoma-type iron formations are those in Archean rocks. They 

are generally found in relatively thin units (meters to tens of 

meters) within sections dominated by volcanic rocks, pelitic 

rocks, and chert. See appendix 3 in Day and others (2016) for 

a more detailed discussion of the banded-iron (Algoma-type) 

mineral-deposit model.

Geology and Occurrence in the Study Area

In the Archean rock section that hosts the South PassAtlantic City district, the Miner’s Delight Formation graywackes are interpreted to be stratigraphically underlain by 

the Roundtop Mountain Greenstone, which is comprised of 

mafic metavolcanic rocks, originally pillow basalts at places. 

Stratigraphically below the Roundtop Mountain Greenstone 

is the Goldman Meadows Formation, which consists of pelitic 

schists, intercalated magnetite-facies banded iron formation, and, near the bottom, a single 6- to 12-m thick unit of 

quartzite. In detail, Bayley (1963) recognized and mapped two 

intervals of magnetite-facies banded iron formation. The lower 

is 6 to 18 m thick, and the upper or main iron formation is 43 

to 49 m thick. The iron formations are exposed on both flanks 

and around the nose of a complex, isoclinal syncline, overturned to the east, which has been faulted and deformed by 

extreme compression. Without the extreme compression during the Archean, there would be no Atlantic City iron ore body 

because, on the northwestern limb of the syncline, the extreme 

compression and faulting has thickened the iron formation by 

repetition on reverse faults from about 46 to 183 m. The Atlantic City iron mine, immediately north of the northern boundary of the South Pass block, operated in the area of thickened 

iron formation, removing 82 Mt (90 million short tons) of ore 

between 1962 and 1983 (Hausel, 1991, p. 28–29). The original 

resource announced by U.S. Steel Corporation was 110 Mt 

(121 million short tons) of proven reserves at 25 to 32 percent 
78 Geology and Mineral Resources of the Southwestern and South-Central Wyoming and Bear River Watershed Sagebrush Focal Areas

BEAR LAKE

PLATEAU

BLOCK

NUGGET

SANDSTONE COPPER

M/C

FOSS

B

FON

B

Bear

Lake

Bear River

Bear River

UTAH

IDAHO

LINCOLN COUNTY

RICH

COUNTY

UINTA COU

CACHE COUNTY

BEAR LAKE

COUNTY

FRANKLIN COUNTY

30

89

89

189

Montpelier

District

Lake Alice District

Cockscomb

Duke

Mine

Griggs Mine

Evening Star

Bonanza

Shaft Bonneville

Group

Rock Creek Valley

? ?

111°0' 

42°30'

42°0'

41°30'

20151050 KILOMETERS

Base modified from U.S. Geological Survey DEM data, 2016. 0 5 10 15 MILES20

Roads and political data © 2014 Esri and its licensors.

Boundary data from San Juan and others (2016).

USA Contiguous Albers Equal Area Conic Projection.

Central meridian, 110° W., latitude of origin, 37.5° N.

North American Datum of 1983.
Locatable Minerals 79

Figure 27. Map showing the mineral-potential tracts for 

sedimentary-hosted copper deposits in the Bear River Watershed 

study area, Wyoming and Utah. USGS, U.S. Geological Survey. 

MRDS, USGS Mineral Resources Data System. USMIN, USGS 

Mineral Deposit Database.

SIL BASIN

BLOCK

TENELLE

BLOCK

Fontenelle

Res.

WYOMING

NTY

SWEETWATER

COUNTY

SUBLETTE COUNTY

80

189

30

110°0'

Map

area

Study areas

IDAHO

MONTANA

WYOMING

OREGON

NEVADA UTAH

WASHINGTON

County boundaries

State boundaries

Proposed withdrawal areas

USGS study area boundary

Base Data

Copper location

MRDS locatable minerals

Moderate-potential (M) tract with moderate (C) certainty

Assessment tract types – sediment-hosted stratabound copper

Mineral data from USGS (2016).

Mining districts from Fernette and others (2016a).

EXPLANATION

USMIN mining districts
80 Geology and Mineral Resources of the Southwestern and South-Central Wyoming and Bear River Watershed Sagebrush Focal Areas

iron, and 273 Mt (300 million short tons) of indicated ore at 

22 to 35 percent iron (Anonymous, 1960, p. 27). There are ten 

smaller concentrations of iron ore northeast and southwest of 

the Iron Mountain Mine. (Bayley, 1963, p. C22). Resources in 

those smaller deposits are not known.

Bayley and others (1973, plate 1) show the main iron 

formation in the Goldman Meadows Formation pinching out 

entirely, in outcrop, in T. 29 N, R. 100 W., sec. 8 (fig. 17), 

6,280 m south-southwest from the center of the ore body of 

the mine (which he labels “U.S. Steel Corp. iron mine”). Hausel (1991, plate 1) depicts the southwestern end of the Goldman Meadows Formation differently than Bayley and others 

(1973). He places the southwestern-most outcrops of the main 

iron formation about 6,920 m south-southwest from the center 

of the pit lake. There, Hausel (1991) shows the iron formation, 

about 30 m thick (or a little less), descending beneath Tertiary and Quaternary cover. Although the overlying Roundtop 

Mountain Greenstone re-emerges to the southwest from below 

the younger sediments, the Goldman Meadows Formation and 

underlying Diamond Spring ultramafic rocks do not. In either 

case, the iron formation disappearance from outcrop, though 

it is inside the northern-most PLSS township in the block, is 

at least 3 km northeast of any proposed withdrawal area in the 

South Pass block. There does not appear to be any signature 

on airborne magnetic surveys that could be interpreted as 

magnetite-facies banded iron formation. For that reason, we 

made no assessment of the potential for banded iron formation-hosted iron deposits.

Economic Analysis

The relatively low grade (about 30 percent iron) of the 

Atlantic City ore would make reopening that mine difficult at 

this time. Currently, “direct shipping” hematite ore that has in 

excess of 56 percent iron is produced from large deposits in 

Australia and Brazil, and, except in China, that hematite ore 

dominates world production (Tuck, 2016; Geoscience Australia, 2014). At the Atlantic City mill, ore was crushed, ground, 

and magnetically separated, then pelletized to form taconite 

pellets, which were roasted, and then shipped by rail to a steel 

mill in the Salt Lake City area (Bayley, 1963). 

Discussion of where iron is being produced in the Western United States can be found in Bleiwas (2016). None of the 

current production of iron is from the study area.

Sandstone Roll-Front Uranium

Mineral Description

Sandstone roll-front uranium deposits are formed by 

reduction precipitation of the uranium minerals uraninite 

(UO2) and, in places, coffinite (U(SiO4,(OH)4)). Typically, 

oxygenated uranium-bearing paleo-groundwater moved 

downdip by gravity within gently dipping permeable fluvial 

sandstone beds (Fischer, 1974; Boberg, 2010). Reducing conditions are encountered along the groundwater flow path due 

to the presence of organic carbon buried within the original 

sediments or by seepage of hydrocarbons into the sediments 

(Boberg, 2010), and ore minerals precipitate near the transition 

between oxidized and reduced sedimentary rocks (Fischer, 

1974; Boberg, 2010). Uranium in the paleo-groundwater is 

derived from uranium-enriched surficial water resulting from 

the leaching of ash-fall tuffs and deeply weathered Precambian 

rocks (Boberg, 2010; Dahlkamp, 2010). Sandstone roll-front 

uranium ore bodies are variably crescent-shaped in cross section, with the tails pointing updip, and are irregularly linear in 

plan view (Dahlkamp, 2010). The richest ore tends to be concentrated along the concave edge of the reduced (unaltered) 

zone within the crescent (Fischer, 1974; Dahlkamp, 2010). A 

large sandstone roll-front uranium deposit may be a few tens 

of meters in stratigraphic thickness and in lateral width, and it 

may extend hundreds of meters along the oxidation-reduction 

front (Fischer, 1974).

Across a typical sandstone roll-front uranium ore body, 

variations in the uranium content are detected by gamma logs, 

and mineralogical zonations reflect processes of alteration due 

to oxidation and precipitation by reduction (fig. 28) (Boberg, 

2010). Within the ore zone, uraninite and coffinite are finely 

disseminated as cements in gray, pyritic sandstone. The sandstone ore also contains carbonized plant fragments and patches 

of calcite cements. The gray, pyritic ore lies immediately 

adjacent to a change laterally (towards the interior) in the same 

sandstone beds to ferric-iron minerals like earthy hematite and 

earthy orange goethite (Dahlkamp, 2010). With the exception 

of calcite and some of the pyrite, all of the authigenic minerals 

in the system are very fine-grained. Uraninite and coffinite are 

commonly “sooty.” 

The typical reduction/oxidation (redox) “front” is a 

sharply defined color boundary visible in the sediments that 

has a crescent shape in cross section, crossing through bedding and lamination, concave towards the ferric-iron mineral 

(oxidized, altered) side (fig. 28, row D; Rubin, 1970; Fisher, 

1974; Boberg, 2010; Dahlkamp, 2010). Uranium ore, as much 

as 7.5 m thick, but typically less, lies immediately adjacent 

to the roll front and extends laterally from the redox boundary within gray sandstone for several tens to, at rare places, 

600 m into a basinward “seepage zone” (Rubin, 1970) before 

thinning to the bottom of the sandstone and grading out (fig. 

28, rows B and D). Farther into unaltered gray sandstone, the 

rock has a small background amount of pyrite and calcite. 

Both pyrite and calcite are most abundant near the redox 

front on the unoxidized side. Oxidized sandstone with colors 

of grayish pink or grayish yellow, colored by hematite grain 

coatings or limonite grain coatings respectively, in the same 

stratigraphic unit, may extend for miles or even tens of miles, 

typically toward basin margins. Sandstone within the altered 

tongue may have goethite pseudomorphs after pyrite for a few 

hundred feet or less from the front or even a small amount 

of very fine-grained pyrite. Carbonized plant fragments also 

disappear with distance from the front into altered sandstone, 

but uncommon relicts of reduced rocks within the altered 

tongue have been found at places, even kilometers into the 
Locatable Minerals 81

altered sandstone, and some contained high concentrations of 

uranium. Calcite cements are generally absent from the altered 

tongue. In map view, the roll-front in a single sand body is 

irregular, but it is common for lobes of alteration to be kilometers across and convex towards the center of a basin. 

Ore grades and thicknesses are not developed along all 

of the length of a roll-front, but rather, the ore bodies in map 

view are like “widely spaced elongate beads on a string” 

(Fischer, 1974, p. 364). Radiometric equilibrium refers to the 

ratio of measured chemical uranium grade to the calculated 

equivalent grade from the natural gamma logs (radiometric 

equivalent grade). If the ore’s radioactive decay products 

were consistent with the age of the ore, the ore would be 

considered at equilibrium. If the decay products were greater 

than expected for the age of the ore, the equivalent grade was 

higher than the chemical grade and the equilibrium would be 

considered negative. Generally, the equivalent radiometric 

grade changes from negative to positive at the redox front. 

Natural-gamma logging tools were calibrated at pits operated 

by the Atomic Energy Commission in Casper, Wyoming, such 

that (radiometric) equivalent U3

O8 grades (e U3O8) could be 

calculated in the field. Across most sandstone roll-front uranium deposits, the equivalent grade changed from negative in 

the altered tongue to positive in ore and farther basinward.

For decades before the late 1970s, Wyoming was the 

second-leading uranium-producing State in the United States 

(Boberg, 2010), and all the major production came from 

sandstone roll-front uranium deposits within lower Eocene or 

upper Paleocene sandstones. Most of the remaining produced 

uranium came from roll-front deposits in the Lower Cretaceous Inyan Kara Group on the western flanks of the Black 

Hills. Only a very small fraction of the production came from 

deposits of any other deposit type, even though traces of uranium mineralization are found scattered through virtually the 

entire stratigraphic section in Wyoming, from Precambrian to 

Quaternary rocks (Boberg, 2010).

In central Wyoming, sandstone roll-front uranium 

deposits occur in sandstones in four different basins separated 

by Laramide uplifted, Precambrian-cored mountain ranges. 

Sedimentation patterns demonstrate that the ranges contributed 

enormous volumes of feldspathic to arkosic sand to the Wind 

River, Powder River, Shirley, and Great Divide Basins (listed 

in clockwise order starting in the northwest).

After the earliest post-World War II flurry of discoveries 

of outcropping uranium ore bodies using Geiger counters and 

scintillometers on the ground, most exploration for sandstone 

roll-front uranium deposits in Wyoming employed “interpolative” drilling without prior geochemical or geophysical 

surveys. Companies explored claim blocks that had quickly 

blanketed all of the edges and into the middle of basins using 

relatively inexpensive rotary drilling with light muds. A geologist logged the drill cuttings, and a contract well logger logged 

the holes using a combination of resistivity, self-potential, and 

natural-gamma downhole logs. The geologist in the field was 

responsible for recognizing lithologies, interpreting altered 

versus unaltered rocks in tens of different sandstone intervals 

penetrated by the drill, and then placing the next hole. Where a 

first hole penetrated altered sandstone, and a second penetrated 

unaltered rock in a same sandstone unit, a third hole would 

be placed midway between the first two; then a fourth midway in the shortest gap between altered and unaltered; and so 

forth until a next hole cut the actual roll-front mineralization. 

Recognition of the tongue of altered sandstone was critical, 

and gamma log signatures of “remote barren” (also called 

“tails”), of “limb ore,” of “near seepage,” and of “remote 

seepage” zones were used together with cuttings logs in the 

interpolation process. Applying a broadly similar exploration 

method would be the best approach to evaluate the potential 

for sandstone roll-front uranium deposits in the Big Sandy 

and Continental Divide blocks. Drill hole data are crucial to 

evaluating those proposed withdrawal areas.

Geology and Occurrence in the Study Area

Neither the Big Sandy nor the Continental Divide 

blocks contains any known uranium occurrences. However, 

both these blocks are down-dip and basin-ward from places 

where there are occurrences and documented radiometric 

anomalies. Specifically, there are known occurrences and 

radiometric anomalies in the Wasatch Formation (fig. 29). 

Wasatch sandstones that underlie younger formations to the 

south or southwest might, therefore, also host sandstone rollfront uranium deposits beneath the Big Sandy or Continental 

Divide blocks. Areas that are the roots of alteration tongues 

typically contain widely scattered uranium mineralization that 

is focused in mudstones, rather than sandstones, or mineralization that is found in relict carbonized plant fragments. In 

a few places, relict mineralization of roll-front tails or limbs 

contained enough uranium to support a short-lived, smallscale mining operation. Occurrences found in the Wasatch 

Formation west of Oregon Buttes and south of the Continental 

Fault were short-lived operations, but further details are not 

available. There is more detail available about the rocks that 

host radiometric anomalies described by Winterhalder (1954). 

Anomalies that Winterhalder found on the northwest flank of 

Oregon Buttes (fig. 29, area labeled 1) were in both the top of 

the Tipton Tongue of the Green River Formation mudstones 

and in sandstones at the base of the Cathedral Bluffs Tongue 

of the Wasatch Formation sandstones. Radioactivity was as 

much as 20 times background (Winterhalder, 1954). Two additional anomalies to the northwest were both in coarse-grained, 

arkosic, conglomeratic sandstones. In the anomaly just southeast of Wyoming State Highway 28 (fig. 29, area labeled 2), 

radioactivity was 13 times background, and in the one farther 

northwest (fig. 29, area labeled 3), radioactivity was 10 times 

background. The small past-producing mines and radiometric 

anomalies are good evidence for the presence of uranium and 

its mobility in a recharge zone that could be the root for alteration tongues of roll-fronts in the Wasatch that might underlie 

the Big Sandy and (or) the Continental Divide blocks.

National Uranium Resources Evaluation (NURE) airborne gamma-ray spectrometry coverage was examined above 
82 Geology and Mineral Resources of the Southwestern and South-Central Wyoming and Bear River Watershed Sagebrush Focal Areas

Feldspar altering to kaolinite Feldspar alteration

Hematite staining Hematite staining

Limonite staining Limonite staining

Increasing pitting and tarnishing Pyrite content

Fragments dull and flaky Carbon content fragments shiny and firm

Uranium and Vanadium

Selenium

Molybdenum

F. Metals

E. Mineralogy

D. Visible

 alteration

C. Natural

 gamma log

 character

B. Roll-front

 geometry

A. Uranium

 disequilibrium – – +/– + + +

Remote barren

“Limb ore”

Near barren interior Interface zone Ore zone

“Roll-front ore”

Near seepage zone Remote seepage zone

Shale/clay

Shale/clay

Grayish orange to

grayish yellow sandstone Medium to dark

gray sandstone

Light to medium

gray fresh sandstone

0

10

20

30

40

50

0

10

20

30

40

50

0

10

20

30

40

50

60

0

10

20

30

40

50

60 1 2 3 4 5 6 2 3 4 5 6 1 1 2 3 4 5 6 21 3 4 5 6 1 2 3 4 5 6 1 2 3 4

Light red to reddish

orange sandstone

Figure 28. Schematic cross section of a sandstone roll-front uranium deposit (redrawn from Boberg, 2010, with permission). Row A, 

“Uranium disequilibrium,” indicates whether chemical uranium will generally be less (–) or more (+) than that calculated from a gamma 

log of a drill hole. Row B, “Roll-front geometry,” introduces commonly used zonation terms. Row C, “Natural gamma log character,” 

shows schematic graphs of downhole gamma logs. (Where the natural gamma log is squared off to the right, it indicates that the first 

run through the zone went off the scale. A second, or third, run is shown inside that, showing the counts per second at a scale 10 times 

or 100 times the original scale.) Row D, “Visible alteration,” highlights the characteristics, commonly demonstrated by color, of host 

rocks. Row E, “Mineralogy,” plots the presence or absence of common minerals that are subject to alteration and (or) oxidation and 

precipitation by reduction. Row F, “Metals,” plots metal ores commonly associated sandstone roll-front uranium deposit.

the hypothetical recharge zone. No notable anomalies were 

present for any of the elemental parameters or the elemental 

ratios (Geometrics, 1978; Geodata International, Inc., 1980; 

Hill and others, 2009). The airborne gamma-ray spectrometry 

was flown at 3-mile (4.8 km) line spacing, so small targets 

could easily have been missed.

USGS stream-sediment and soil sampling geochemical 

results were examined particularly for uranium (Goodknight 

and others, 1982; Shannon and others, 1979; Morgan and 

others, 1981). The USGS National Geochemical Database 

includes all NURE samples (Smith and others, 2016). The 

northern part of the hypothetical recharge area (T. 28 N., R. 

103 W.; fig 17) was identified as the fifth-best anomaly in the 

Lander 1-degree by 2-degree quadrangle (Goodknight and 

others, 1982, p. A-42). Goodnight and others’ identification 

of this area was on the basis of a stream sediment sample that 

contained more than 6.6 ppm uranium and a second stream 

sediment sample that had residual uranium greater than 1.15 

ppm. Mineralized rock bodies in such a recharge zone are typically small and widely scattered; other sedimentary uranium 

occurrences were known nearby, but not in the drainage that 

yielded the anomalous NURE samples. 

Probably far more important would be an examination for ferric iron oxide alteration in Wasatch Formation 

sandstone(s) in the hypothesized recharge zone. Figure 30 

shows an outstanding example of what such ferric alteration 

looks like on images from remote sensing data. The area, 

known as Red Rim, is the outcropping recharge zone for 

sandstone roll-front uranium deposits within the Fort Union 

Formation that underlie the west-central part of the map area. 

The namesake rim of altered sandstone (labeled “Red Rim” on 

fig. 30) intersects Interstate Highway 80 about 12 km west of 
Locatable Minerals 83

central Rawlins, Wyoming (fig. 3). The surface areas displayed 

in bright pink are characterized by strong spectral absorption 

features related to ferric-iron minerals in Landsat 7 imagery 

(Rockwell and others, 2015; Rockwell, 2013) and indicate the 

presence of abundant hematite in altered sandstone. The 10- 

to 15-degree dip of the Fort Union beds is steep enough that 

erosion-resistant sandstone beds each form discrete hogbacks 

separated from the next sandstone both up- and down-section. 

The strong ferric-iron signal is stratabound—that is, confined 

to certain beds. Identification of the strike and dip of bedding, 

together with the strong ferric-iron alteration signal, lead to 

the ability to recognize additional altered sandstone beds to 

the west-northwest even though those beds to the west do 

not form prominent ridges. The sandstones to the west are at 

a lesser dip, 5 degrees or less, and the area of major ferriciron signal for those is wider than for Red Rim. The major 

ferric-iron signal for those sandstones is, nonetheless, still 

stratabound.

Another example of remote sensing of sandstone rollfront alteration is illustrated in the central Great Divide Basin, 

which is about 75 km east of the Continental Divide block (fig. 

2). The remote sensing signature of ferric iron mineralization 

in the area around the Sweetwater Mine, a roll-front uranium 

mine that was open from 1980 to 1983, is shown in figure 31. 

The Sweetwater district was described by Sherborne and others (1980).

The Sweetwater open-pit mine is about 1 km wide and 

is incompletely ringed with anomalous iron signatures. It 

lies between three MRDS locations, the southeasternmost of 

which is labeled “Sweetwater Mill.” There is a combination 

of altered and unaltered sandstone on the dumps, as well as 

some additional mineral signals from fresh pyrite weathering 

to sulfate minerals (green pixels denote “clay, sulfate, mica, 

marble, and (or) dry vegetation”). Unaltered sandstone there is 

from the sandstone interval at the ENQ Solution prospect, the 

next sandstone interval above the sandstone beds in the Battle 

Spring arkose host rocks at the Sweetwater Mine. (Unaltered 

ENQ sandstone is from the overburden lying above ore in the 

Sweetwater sandstone beds.) In figure 31, the network of roads 

shows in pink, the strong ferric-iron minerals signal, though 

there are places where the roads don’t have that signal. This 

is not a false signal, however, because these roads were built 

using the local material, spreading it from its source with a 

road-grader. The grader spread friable altered sandstone in the 

directions that the grader traveled. Other studies have found 

that certain grasses—cheatgrass for example—are characterized by absorptions in the ultraviolet and blue wavelengths 

similar to those of ferric-iron minerals at Landsat 7 spectral 

resolution because of their yellow-brown color when they are 

dry (Rockwell, 2013). These grasses and other dry and (or) 

dead plant material, may also mimic the spectral characteristics of clay, sulfate, mica, and some pure carbonate rocks 

at Landsat 7 spectral resolution (Elvidge and Lyon, 1985). 

However, this area has grasses only within the draws and near 

the playa lakes. The tops of the low ridges have only sagebrush and some low mound-like plants, similar to some plants 

in alpine tundra. The ground is about 50 percent bare along the 

low ridgelines. Slightly above the center of the image in figure 

31 the ferric-iron signal is present in several draws, but there 

still remain some large areas of strong ferric-iron minerals 

signal that are arrayed in bands running east-northeast. These 

are the signatures in Landsat 7 images of sandstone roll-front 

alteration; however these are in broad, rounded outcrops of 

nearly unconsolidated sandstones, and the beds dip shallowly 

so that the outcrops are bands up to several hundred meters 

wide. The beds dip northwest at about 1.7 degrees (calculated 

from drilling data from 1976). The ENQ sandstone body that 

forms the overburden at the Sweetwater pit lies at a vertical 

depth of about 189 m below surface at the northwestern edge 

of the map area in figure 31. Four discrete sandstone layers 

each about 15 m thick are exposed and form low rises crossed 

by the Jeffrey City-Wamsutter road. These four sandstone beds 

are the next four sandstones up-section from the ENQ sandstone beds, ascending stratigraphically to the northwest.

Figure 31 indicates that the roll-front alteration is 

stratabound, but at gentle dips, and also shows that grading 

dirt roads can spread the alteration along their paths. Caution 

must be exercised when interpreting alteration in this region 

because of the spectral similarities between dry vegetation and 

ferric iron, phyllosilicate, sulfate, and carbonate minerals at 

Landsat 7 spectral resolution.

The same type of processed Landsat 7 imagery as in 

figures 30 and 31 is shown figure 29, for the Big Sandy and 

Continental Divide blocks. In the area of exposed Wasatch 

Formation northeast from outcrop of the Laney Member of 

the Green River Formation and southwest of the Continental 

Fault, there are disconnected patches aligned west-northwestward showing the signal of major ferric-iron minerals (shown 

in pink on fig. 29). In the area between Oregon Buttes (area of 

healthy vegetation, in dark green, at center right) and Wyoming Highway 28, the Wasatch Formation is involved in the 

Reds Cabin monocline (Zeller and Stephens, 1969, plate 1) 

striking northwest and dipping 20 to 50 degrees to the southwest. North of the monocline, the rocks dip gently toward 

the north; south of it, they dip gently to the south. There are a 

few patches of likely alteration—two of those are near to and 

partly overlap the radioactive anomalies from Winterhalder 

(1954). Thus, the patches of major ferric-iron minerals (pink 

on fig. 29, areas labeled 2 and 3) signal are stratabound, or 

nearly so. Winterhalder noted iron staining in the patch to 

the northwest (fig. 29, area labeled 3). Taken together, the 

disconnected patches of major ferric-iron mineral signal, the 

ground radioactive anomalies, and the small past-producing 

mine (adjacent to 3, fig. 29) constitute permissive evidence for 

sandstone roll-front uranium-system alteration in that area and 

also indicate that the altered rocks dip into the subsurface to 

the southwest and south. 

Farther west in the area near the Juel Creek, a past-producing uranium mine, the strike of beds runs broadly parallel 

to the Continental Fault. To the southeast of the abandoned 

mine, pink patches (fig. 29) possibly recording major ferriciron minerals do not run parallel to the fault, and instead, run 
84 Geology and Mineral Resources of the Southwestern and South-Central Wyoming and Bear River Watershed Sagebrush Focal Areas

BIG SANDY

BLOCK

SOUTH PASS

BLOCK

Unknown

Rainbow

Unknow

Juel Creek

Sandy Cal No. 2

WASATCH FORMATION LANEY MEMBER

Elk Mountain

28

CONTINENTAL

109°30' 109

42°20'

42°10'

0 5 10 

0 5 10 15 KILOMETERS

Base adapted from National Geographic Society and i-cubed, 2013.

Roads and political data © 2014 Esri and its licensors.

Boundary data from San Juan and others (2016).

USA Contiguous Albers Equal Area Conic Projection.

Central meridian, 110° W., latitude of origin, 37.5° N.

North American Datum of 1983.
Locatable Minerals 85

Figure 29. Map addressing potential for sandstone roll-front uranium deposits in the Big Sandy and Continental Divide blocks of the 

Southwestern and South-Central Wyoming study area. The map shows geology from Zeller and Stephens (1969), Landsat 7 spectral 

mineral signature from remote sensing from Rockwell (2013) and Rockwell and others (2015), past-producing small uranium mines from 

the Mineral Resources Data System (MRDS; U.S. Geological Survey, 2016), and ground radiometric anomalies from Winterhalder (1954) 

of the area in the recharge zone to the Wasatch Formation. USGS, U.S. Geological Survey.

CONTINENTAL

DIVIDE BLOCK

wn

Sand Creek

Oregon Buttes

1

2

3

FAULT

Reds Cabin

Monocline

A

S

9°0'

Map

area Study areas

IDAHO

MONTANA

OREGON

WYOMING

NEVADA UTAH

WASHINGTON

County boundaries

Proposed withdrawal areas

USGS study area boundary

Base data

MRDS uranium location

Reds Cabin Monocline (A on anticlinal axis, S on synclinal axis)

Ground radiometric anomaly (numbered according to text)

Continental Fault

Laney Member of the Green River Formation—

 dashed where uncertain

Minor ferric iron (high redness)

Major ferric iron

Ferrous or coarse-grained ferric iron (may include

 oxidized basalts, fire ash, some moist soils, and

 any blue/green rocks)

Ferric ± ferric iron

Dense, green vegetation

+ moderate to major ferric iron

+ minor ferric iron

+ major ferric iron

+ ferrous or coarse-grained ferric iron

Clay, sulfate, mica, marble and (or) dry vegetation

 (dry grasses abundant in northern Great Basin)

Landsat 7 mineral data (July 9, 2013 - reduced vegetation suppression)

EXPLANATION

15 MILES

Geology after Sutherland and Hausel (2007),

and Sutherland and Luhr (2011).

Landsat 7 data from Rockwell (2013).

Mine locations from USGS (2016).

Radiometric anomaly data from Winterhalder (1954).

Monocline data from Zeller and Stephens (1969).
86 Geology and Mineral Resources of the Southwestern and South-Central Wyoming and Bear River Watershed Sagebrush Focal Areas

8

To Wamsutter

107°30' 

41°48'

41°46'

41°44'

41°42'

0 1 2 3 MILES

0 1 2 3 KILOMETERS

Base modified from National Geographic Society and i-cubed, 2016.

Political data © 2014 Esri and its licensors.

USA Contiguous Albers Equal Area Conic Projection.

Central meridian, 110° W., latitude of origin, 37.5° N.

North American Datum of 1983.
Locatable Minerals 87

Figure 30. Map showing Landsat 7 spectral mineral signature of sandstone 

roll-front uranium system alteration at the Red Rim area, 11 to 16 kilometers west 

of Rawlins, Wyoming. Red Rim is about 125 kilometers east-southeast from the 

Continental Divide block of the Southwestern and South-Central Wyoming study 

area. Paleocene Fort Union Formation sandstones are altered by sandstone 

roll-front uranium system processes, producing hematite in the altered tongues 

in several different sandstones, some of which are also resistant to erosion so 

that they each stand in elevated outcrops that dip 10 to 15 degrees to the westnorthwest. Note major ferric-iron mineral signatures in the sandstones. Sandstone 

roll-front uranium deposits in the same sandstones down-dip in the subsurface to 

the west occur within 5 to 11 kilometers. Strong ferric-iron mineral signals to the 

east are from Jurassic and Triassic red beds.

80 To Rawlins

107°20'

Map area

Study areas

IDAHO

MONTANA

OREGON

WYOMING

NEVADA UTAH

WASHINGTON

CO

CA

Minor ferric iron (high redness)

Major ferric iron

Dense, green vegetation

Clay, sulfate, mica, marble and (or) dry vegetation +

 minor ferric iron

Clay, sulfate, mica, marble and (or) dry vegetation +

 major ferric iron

Clay, sulfate, mica, marble and (or) dry vegetation

 (dry grasses abundant in northern Great Basin)

Landsat 7 mineral data (July 9, 2013 - reduced vegetation suppression)

EXPLANATION

County boundaries

Landsat data from Rockwell (2013).
88 Geology and Mineral Resources of the Southwestern and South-Central Wyoming and Bear River Watershed Sagebrush Focal Areas

Lone Wolf

Sourdough Gulch

State School #1

Red Desert Project

ENQ Solution Mine Site

11

05 

12

26

16

05

25

14

23

33 35

03

13

04

24 21

28

34

09

15

17

10

22

02

32

20

27

08

33

29

32

21

28

16

08

17

09

20

29

04

30

04

19

18

07

02 05 05 04 03

33 34 35

32 33 34 

31

30

19

06

18

07

06

32

R. 94 W. R. 93 W. 

To Jeffrey City

To Wamsutter

Wamsutter Crooks Gap Road

108°0' 107

42°5'

42°0'

0 1 2 3 4 KILOMETERS

0 1 2 3 

Base from National Geographic Society and i-cubed Inc. map data (2016).

MRDS data from USGS (2016).

Landsat 7 data from Rockwell (2013).

USA Contiguous Albers Equal Area Conic Projection.

Central meridian, 110° W., latitude of origin, 37.5° N.

North American Datum of 1983.
Locatable Minerals 89

Figure 31. Map showing Landsat-7 spectral mineral signatures 

of sandstone roll-front uranium system alteration in the 

Sweetwater district, central Great Divide Basin, Wyoming, 

72 kilometers east of the Continental Divide block of the 

Southwestern and South-Central Wyoming study area. MRDS, 

U.S. Geological Survey (USGS) Mineral Resources Data System.

Sweetwater Mill

Sweetwater Open Pit

11

02

02

03

34

25

35

27

23 24

26

22 

13

15

14

12

10

03

35

06

07

18

19

30

31

06

32

12 07

T. 25 N.

T. 24 N.

T. 24 N.

T. 23 N.

R. 93 W. R. 92 W.

To Separation Flats

To Rawlins

via I-80

Mineral Exploration Road

BLM Road 3203

7°55'

Map

area

Study areas

IDAHO

MONTANA

WYOMING

OREGON

NEVADA UTAH

WASHINGTON

MRDS locations

Minor ferric iron (high redness)

Major ferric iron

Dense, green vegetation

Clay, sulfate, mica, marble and (or) dry vegetation +

 minor ferric iron

Clay, sulfate, mica, marble and (or) dry vegetation +

 major ferric iron

Clay, sulfate, mica, marble and (or) dry vegetation

 (dry grasses abundant in northern Great Basin)

Landsat 7 mineral data (July 9, 2013 - reduced vegetation suppression)

EXPLANATION

4 MILES 
90 Geology and Mineral Resources of the Southwestern and South-Central Wyoming and Bear River Watershed Sagebrush Focal Areas

nearly perpendicular to it, approximately parallel to drainage. The patches are, therefore, interpreted as dry vegetation. 

Compared with Red Rim, there is little suggestion of possible 

sandstone roll-front alteration in the Wasatch Formation in this 

area to the west.

Though the spectral data from satellite imagery can aid 

the mineral exploration of large areas, data from drill holes is 

better for the direct assessment of the possibility of sandstone 

roll-front uranium deposits in the subsurface of the Big Sandy 

and Continental Divide blocks. Examination of the electronic 

files of the Wyoming Oil and Gas Commission revealed a few 

tens of petroleum tests in the area, both within the boundaries 

of the Big Sandy block and to its north and northeast. About 

20 of those were examined by Jim Rogers of the Wyoming 

State Geological Survey, and about 10 were examined by one 

of us (Hayes). No logs were recorded for the shallow parts of 

any of these petroleum tests. Electric logs were available typically starting at 1,830 or 2,440 m (6,000 or 8,000 feet) below 

surface, far below where the holes penetrated the Wasatch 

Formation.

H.W. Roehler of the USGS conducted work over several 

years in the northern Green River Basin and provided measured sections in areas to the south of the Big Sandy and Continental Divide blocks and both within and at the south edge 

of the Fontenelle block (Roehler, 1990, 1991). His revised 

nomenclature for the intertongued part of the Green River and 

Wasatch Formation made the nomenclature of the Fontenelle 

area conform with the remainder of the basin, which made 

correlation with the work of Zeller and Stephens (1969, plate 

2) possible. As a result, Roehler effectively eliminated all of 

the main body of the Wasatch Formation in all three of the 

blocks—Big Sandy, Continental Divide, and Fontenelle—

from consideration for sandstone roll-front uranium deposits. 

In addition, he named two new units of the intertongued 

Wasatch and Green River Formations in these areas, and these 

two, the Farson Sandstone Member of the Green River Formation and the Alkali Creek Member of the Wasatch Formation, 

are units that are considered prospective sandstone intervals 

for uranium.

On a fence diagram of measured sections and drill hole 

logs that extends east-west from the proposed withdrawal area 

in the Fontenelle block to a location just west of the Boars 

Tusk block, Roehler (1990) correlated rocks of the intertongued Wasatch and Green River interval. He showed that the 

main body of the Wasatch Formation consists of fluvial, thinbedded, red mudstone with only minor sandstone intervals. 

This is a facies of the Wasatch earlier identified by Childers 

(1974) in the Great Divide part of the basin to the northwest 

of the Sweetwater district and lying between two paleochannel trends, between Oregon Buttes and the Cyclone Rim area 

near Bison Basin. This facies, where it consists of red beds 

representing mudflats (Childers, 1974), cannot be mineralized by a redox roll-front because it is already oxidized, and 

thus is not reactive with oxidizing uraniferous groundwater. 

Zeller and Stephens (1969, p. 12) observed that, south of the 

hypothesized recharge zone, the main body of the Wasatch is 

characterized by pastel red and purple claystone and mudstone 

and thick lenticular dusky-yellow coarse-grained sandstone. 

Thus, the main body of the Wasatch is anticipated to contain 

no suitable host rocks for uranium mineralization anywhere in 

the area of the Big Sandy, Continental Divide, and Fontenelle 

blocks. 

Roehler (1990) correlated units throughout the northwestern part of the greater Green River Basin on the basis 

of his identification of the Shegg’s bed of the Tipton Shale 

Member of the Green River. This correlation placed the Farson 

Sandstone Member of the Green River Formation (fig. 16) 

(Roehler, 1991, p. B19–B26) above the Shegg’s bed and below 

any of the oil shales of the Wilkins Peak or Laney Members 

of the Green River Formation. In its type section on the flanks 

of White Mountain in section 13, T. 23 N., R. 105 W. (fig 17), 

at the west edge of the Boars Tusk block, Roehler (1991, p. 

B25–B26) describes only drab-colored sandstones: gray, tan, 

or brown, some with calcareous cement. It is doubtful that any 

of these sandstones, so described, have been altered by rollfront processes. Altered sandstones are pervasively colored 

pink, orange, or locally, pinkish or orangish gray; they are not 

mottled with iron oxide concentrations, and the iron oxides do 

not mineralize strongly along joints or bedding planes. They 

contain goethitic pseudomorphs of pyrite only where they are 

within tens of meters to about 300 m of a roll front; otherwise 

all vestiges of former pyrite are absent. They do not have 

calcareous cements, nor do they contain carbonized plant fragments. Similar to the White Mountain section, Roehler (1991) 

describes only drab-colored sandstones in the Farson Sandstone Member in the Alkali Creek section just south of the 

Fontenelle proposed withdrawal area. Thus, though the Farson 

Sandstone Member appears to be a suitable host for sandstone 

roll-front uranium deposits, the best available information 

suggests that there is no alteration tongue anywhere cutting 

the fence of holes and measured sections extending from the 

Fontenelle to the Boars Tusk block. However, similar information is not available for the Farson Sandstone Member to the 

north, in the hypothesized recharge area for roll-front altered 

tongues, and the Farson is notably present. Roehler (1991) 

shows a picture of its bold outcrops in the south-central part 

of section 21, T. 27 N., R. 101 W. (fig. 17) on the west flanks 

of Oregon Buttes, where the Farson is north of the axis of 

the Reds Cabin monocline (fig. 29) and dipping gently to the 

north. From plate 2 of Zeller and Stephens (1969), the Farson 

is correlatable with sandstones totaling 68 m thick including 

21 m of arkose at its top, lying above the main body of the 

Wasatch Formation and the recognizable, limestone-bearing 

Schegg’s bed. It underlies the Cathedral Bluffs Tongue of the 

Wasatch Formation in that area (and is shown that way on 

plate 2 of Zeller and Stephens, 1969). In 55 m of Cathedral 

Bluffs section shown on their plate 2, Zeller and Stephens 

indicate three sandstone units, in ascending order: 8.0 m thick, 

6.7 m thick, and 3.0 m thick. In their text they indicate that 

shades of red characterize the lower half of the Cathedral 

Bluffs Tongue but that shades of green characterize the upper 

half. No more detailed information is given. It is nonetheless 
Locatable Minerals 91

clear that radioactive rocks, a small past-producing mine, and 

possible roll-front altered sandstones between Oregon Buttes 

and Elk Mountain (north of the Continental Divide block, 

and to the northeast of the Big Sandy block, respectively, fig. 

29) are near, in section, to the top of the Farson Sandstone 

Member and to the immediately overlying lower part of the 

Cathedral Bluffs. That follows from Winterhalder’s (1954, 

p. 7) identification of the Hiawatha Member of the Wasatch 

Formation in the same place that Roehler (1991) photographed 

the Farson Sandstone Member. From there, structure contours 

on the bottom of the Laney Tongue of the Green River Formation from Zeller and Stephens (1969, plate 1) and attitudes of 

bedding show that all of the different radiometric anomalies, 

uranium occurrences, and the small past-producing mine 

(labeled “Unknown”) lie within about 150 m of section from 

approximately the bottom of the Farson Member to the upper 

part of the Cathedral Bluffs Tongue (Zeller and Stephen, 1969, 

plates 1 and 2; and figure 29, this report). Once more, subsurface information from drill holes in this area and extending 

south in a fence into the Big Sandy block are needed to better 

measure the potential for sandstone roll-front uranium deposits 

beneath the proposed withdrawal area. 

The Fontenelle block has more strong signals of major 

ferric-iron minerals in outcrops than any of the other examples 

(fig. 32). Although there is strong evidence for the presence 

of ferric-iron minerals from Landsat 7 data in the Fontenelle 

block, there is no reason to suggest that any of it is from sandstone uranium roll-front alteration. In the north-central part 

of the block, narrow bands of pixels showing the signature 

of abundant ferric-iron minerals run directly along the easttrending valleys; but these patterns conform with the drainage, 

not the bedding of the rocks, suggesting that this signal is from 

dry cheatgrass or other vegetation. In most places the major 

ferric-iron minerals signature is stratabound, but its strongest 

expression is in the Laney Member of the Green River Formation, which is mostly composed of oil shale and is an unsuitable host for sandstone-hosted roll-front uranium deposits. 

Additional stratabound anomalies are within the Wilkins Peak 

Member of the Green River Formation, in basal parts of that 

section that consist of oil shale. The stratigraphically lowest 

part of the Wasatch and Green River Formations is a basal 

conglomerate (unit Twco on fig. 32) followed upward by the 

La Barge Member of the Wasatch Formation, which would 

now be correlated with the main body of the Wasatch to the 

east and north. Both the basal conglomerate and the main 

body of the Wasatch are red beds, and the hematite that colors 

the red beds is the source of their patchy strong ferric-iron 

minerals signature in the spectral data from Landsat 7 imagery. 

Between the main body of the Green River Formation and the 

base of the Wilkins Peak, Roehler (1991) has described the 

Farson Sandstone Member of the Green River Formation and 

the overlying Alkali Creek Tongue of the Wasatch Formation, both sandy intervals, and both apparently unaltered with 

only drab-colored sandstones, some of them calcareous. The 

Cathedral Bluffs Tongue of the Wasatch was the other interval 

with some potential to the north, and it must correlate with the 

upper part of the Wasatch, unit Twu of M’Gonigle and Dover 

(2004). In that interval, as well, Roehler (1991) describes 

only drab-colored sandstones until near the top of the interval, 

where, instead, he describes rocks of the red muddy facies that 

cannot be mineralized because they are already oxidized.

In the Fontenelle block (fig. 32), the Wasatch Formation 

crops out in hogback ridges near the western boundary of the 

block, parallel to the underlying Hogback thrust fault, and 

the rocks dip eastward into the subsurface, with dips flattening to the east. To the east, like the area north of the Big 

Sandy block, the Laney Shale Member of the Green River 

Formation appears above the Wasatch Formation. There are 

no past-producing uranium mines in the study area, nor to 

the west in recharge zones for Wasatch aquifers. There are no 

uranium mineral occurrences in the proposed withdrawal area 

or the recharge areas. There is no pattern of airborne gammaray spectrometry anomalies from NURE data. There are no 

uranium anomalous geochemical samples for this area in 

USGS archives. There are no active claims for uranium. There 

are closed lode claims in sections 2 and 3, T. 24 N., R. 114 W. 

(fig.17), but these are not in the proposed withdrawal area.

Exploration and Mining Activity

The nearest known sandstone roll-front uranium deposit 

to the Continental Divide block lies about 56 km east-northeast and is called Bison Basin (Dahlkamp, 2010, p. 182 and p. 

192–193). Additional small roll-front deposits lie to the west 

of that and as near as 40 km east of the Continental Divide 

block. Drilling may have penetrated roll fronts nearly as far 

west as Oregon Buttes (Bill Boberg, oral commun., April 29, 

2016); an occurrence also indicated, but not fully documented, 

by Childers (1974, p. 138).

At present, there are no active uranium claims and no 

pending or authorized plans for surface disturbance related 

to uranium mining or exploration in any of the Big Sandy, 

Continental Divide, Fontenelle, or Boars Tusk blocks. There 

are closed lode claims in section 26, T. 27 N., R. 105 W., and 

in section 29, T. 26 N., R. 106 W., of the Big Sandy block 

(fig. 17). It is not known if uranium was the intended target of 

those claims.

Potential for Occurrence

A tract for evaluation of potential for sandstone rollfront uranium deposits in the South Pass, Big Sandy, and 

Continental Divide blocks was constructed as follows. The 

north boundary of the tract is the Continental Fault across the 

northeastern corner of the Big Sandy block (fig. 33). (Wasatch 

Formation rocks probably exist north of the Continental Fault, 

but sandstone roll-front uranium deposits are not known to 

occupy such a position at any other place in the State, relative to a thrust fault bounding a Wyoming range.) South of 

the fault, the Wasatch Formation crops out between the fault 

and the places where, farther south, the Wasatch is overlain 

by the Laney Shale Member of the Green River Formation. 

Rocks prospective for sandstone roll-front uranium deposits 
92 Geology and Mineral Resources of the Southwestern and South-Central Wyoming and Bear River Watershed Sagebrush Focal Areas

Fonten

 

30

189

30

LINC

COU

Tgl

Tgl

Tgw

Twu

Tgw Twco

Twu

Twu

Tgl

Twu

Twu

Tgl

Twn

Twu

Tgw

Tgw

Tgl

Twn

Twlb

Twlb

Tgl

Twlb

Twlb

Tgl

Twu

Tgl

Twlb

Tgll

Twn

Twlb

Twlb

Twn

Tgl

Roehler (1990) Measured

Sections 1586 and 1686

Fontenelle Creek

Roehler Measured Section

(1991, p. B15–B19)

FONTENELL

42°0'

0 5 10 15 KILOMETERS

Base modified from U.S. Geological Survey DEM data, 2016. 0 5 10 15 MILE

Roads and political data © 2014 Esri and its licensors.

Boundary data from San Juan and others (2016).

USA Contiguous Albers Equal Area Conic Projection.

Central meridian, 110° W., latitude of origin, 37.5° N.

North American Datum of 1983.
Locatable Minerals 93

Figure 32. Map showing Landsat 7 spectral mineral signatures from the intertongued Wasatch and Green River Formations in the 

Fontenelle block, Bear River Watershed study area, Wyoming, and their relation to sandstone roll-front uranium system alteration. 

Formation contacts are from M’Gonigle and Dover (2004). Correlations of their units with those of Roehler (1991) are as follows from the 

base of the Wasatch Formation on the west: Twco—Wasatch Formation basal conglomerate; Twlb— La Barge Member of the Wasatch 

Formation, which is equivalent to Roehler’s main body of the Wasatch; Twn—New Fork Tongue of the Wasatch Formation, which is 

equivalent to, in ascending stratigraphic order, Schegg’s bed of the Green River Formation of Roehler (1991), Farson Sandstone Member 

of the Green River Formation, and Alkali Creek Tongue of the Wasatch Formation; Tgw—Wilkins Peak Member of the Green River 

Formation; Twu—upper Wasatch Formation, which is equivalent to Cathedral Bluffs Member of the Wasatch; Tgl—Laney Member of 

the Green River Formation.

nelle

Res.

SWEETWATER

COUNTY

COLN

UNTY

LE BLOCK

110°0'

Map

area

Study areas

IDAHO

MONTANA

WYOMING

OREGON

NEVADA UTAH

WASHINGTON

County boundaries

Proposed withdrawal areas

USGS study area boundary

Base data

Measured sections (dotted at gap in section)

Geologic units discussed in text

Minor ferric iron (high redness)

Major ferric iron

Ferrous or coarse-grained ferric iron (may include

 oxidized basalts, fire ash, some moist soils, and

 any blue/green rocks)

Ferric ± ferric iron

Dense, green vegetation

Clay, sulfate, mica, marble and (or) dry vegetation +

 moderate to major ferric iron

Clay, sulfate, mica, marble and (or) dry vegetation +

 minor ferric iron

Clay, sulfate, mica, marble and (or) dry vegetation +

 major ferric iron

Clay, sulfate, mica, marble and (or) dry vegetation +

 ferrous or coarse-grained ferric iron

Clay, sulfate, mica, marble and (or) dry vegetation

 (dry grasses abundant in northern Great Basin)

Landsat 7 mineral data (July 9, 2013 - reduced vegetation suppression)

EXPLANATION

ES

Geology after M’Gonigle and Dover (2004).

Landsat 7 data from Rockwell (2013).
94 Geology and Mineral Resources of the Southwestern and South-Central Wyoming and Bear River Watershed Sagebrush Focal Areas

are sandstones down section from the Laney within the upper, 

Cathedral Bluffs Tongue of the Wasatch and, underlying those, 

the sandstones of the Farson Sandstone Member of the Green 

River Formation. Sandstones in both those intervals should be 

present in the subsurface below both the Continental Divide 

and the Big Sandy PLSS blocks. That is, to the best of our 

knowledge, potentially favorable host rocks underlie both 

proposed withdrawal areas.

The tract has been artificially confined to the west and 

east, as follows. From the northwestern corner of the Big 

Sandy block and the southeastern corner of the Continental 

Divide block, lines were drawn perpendicular to the trace of 

the Continental Fault about 8 km to the west of the line on 

the west edge of the Big Sandy block and about 8 km to the 

east of the line on the east of the Continental Divide block to 

the South Pass block. Those lines were extended far enough 

southward to enclose the entirety of the Big Sandy and Continental Divide PLSS blocks, and a line parallel to the Continental Fault was then extended from west to east from the 

southeast end of the Continental Divide block to meet the end 

of the eastern boundary (fig. 33).

The potential for sandstone roll-front uranium deposits 

in the South Pass, Continental Divide and Big Sandy blocks 

must be greater than “low,” because there is evidence of uranium mobility in the assumed recharge areas of the Wasatch 

and Green River Formation sandstones up gradient from the 

proposed withdrawal area. Evidence for uranium deposits is 

in the form of radioactive anomalies identified on the ground 

by Winterhalder (1954), the small past-producing uranium 

mine, and possible sandstone roll-front-system alteration (fig. 

29). However, through most of the area of this hypothesized 

recharge area, there is no suggestion of sandstone roll-front 

uranium system alteration particularly in comparison to areas 

that have known altered rocks in outcrop. Possible outcrops 

of altered rock occur near Winterhalder’s (1954) radiometric 

anomalies numbers 3 and 2, respectively (fig. 29). These are in 

what probably was the recharge area for Cathedral Bluffs and 

Farson Member sandstones that then extended south beneath 

the Big Sandy block. However, because of the vagaries of 

groundwater movement directions in the subsurface and our 

lack of knowledge of the paleo-geography during the (geologic) time when mineralizing processes might have occurred, 

the Continental Divide block might have equal or higher 

potential than the Big Sandy block. The potential rating for 

this tract (fig. 33) is considered to be moderate (M), given the 

evidence for uranium mobility (fig. 29). The certainty level 

is B, because we currently have no drill hole data from the 

study area, and the evidence is indirect, based only from the 

hypothesized recharge area to the north near the Continental 

Fault (fig. 29). With further drill hole data, the potential and 

certainty levels potentially would be modified.

The Boars Tusk block appears to have no potential for 

sandstone roll-front uranium deposits because the Farson 

Sandstone Member crops out west of the two PLSS townships 

containing proposed withdrawal areas, and crops out at higher 

elevation than either township, and dips westward away from 

the proposed withdrawal areas. Therefore, Farson Member 

host rocks aren’t present beneath the Boars Tusk block. The 

Cathedral Bluffs Member, if present, lies above the Farson so 

also is not present beneath the study area. The only Wasatch 

rocks that may underlie the Boars Tusk block, itself, is the 

main body of the Wasatch Formation, and it is likely to be the 

muddy, red-bed facies at the bottom of Roehler’s (1990) measured section and thus not prospective for sandstone roll-front 

uranium deposits.

Potential for sandstone roll-front uranium deposits in 

the subsurface of the Fontenelle block is rated low (L). There 

is no evidence for any mobility of uranium in this area, nor, 

particularly, in the recharge areas for Wasatch or Green River 

sandstones on the western edge of the block. However, there 

are suitable host rocks—for example, the Farson Sandstone 

Member of the Green River Formation as measured by 

Roehler (1990) and described by Roehler (1991, p. B16–B19). 

Roehler described all of the sandstones of his Alkali Creek 

section, from both the Farson Member and the Alkali Creek 

Member, as being brown, gray-green, or gray. These descriptions suggest that there are no outcrops of roll-front alteration 

within the section. Given that suitable host rocks are present, 

but that there is no evidence for any uranium mineralizing 

process in the area, the potential is judged to be low (L). This 

potential rating is applied at certainty level C (fig. 33). The 

sandstones that are suitable host rocks can be observed in 

outcrop, and they appear to be unaltered, which is a piece of 

direct evidence that appears to refute the possible existence of 

uranium resources. Otherwise, there is simply an absence of 

any indications of mineralization processes for uranium.

Economic Analysis

Any sandstone roll-front uranium deposits found in 

the subsurface below the Big Sandy, Continental Divide, or 

Fontenelle blocks are most likely to be produced by mining. 

There are operating mines of that type at the Crow Butte Mine 

near Crawford in western Nebraska and at the Highland Mine 

within the southern Powder River Basin, Wyoming, north of 

Douglas. In such mining, the surface disturbance is relatively 

small. There is no company activity to indicate any current 

interest in the area.

Further discussion of where uranium is being produced in 

the Western United States can be found in Bleiwas (2016).

Surficial Mineral Deposits System, Including 

Placers

Ore depositing systems from the Earth’s surface include 

chemical and mechanical types. The most familiar chemical types are deposits formed as soils such as laterites and 

bauxites, for iron and aluminum, respectively. The mechanical 

types include placer deposits, that is, concentrations of valuable heavy minerals that fell from suspension in a transporting 

medium, typically moving water. 
Locatable Minerals 95

A placer deposit is a concentration of valuable detrital 

minerals formed by a process of sedimentation in which the 

relatively high specific gravity of the valuable minerals causes 

them to drop from suspension by the transporting medium and 

thereby separate from minerals of lower specific gravity that 

remain in suspension, or causes them to stop moving in a traction flow while the minerals of lower specific gravity continue 

with the flow.

Alluvial placers form in rivers and streams and represent the initial downstream concentration of heavy minerals 

relative to source rocks, within a watershed. Heavy minerals 

deposit and concentrate where gradients flatten and (or) where 

water flow velocity decreases (Yeend, 1986). “Heavy mineral grains are most concentrated at the base of gravel where 

natural traps such as riffles, fractures, bedding planes, or other 

features are oriented transverse to the water flow such as at the 

inside of meanders, below rapids and falls, beneath boulders, 

and in vegetation mats” (Jones and others, 2015, p. 25).

Minerals concentrated by this placer-forming process 

include native gold (Au) and other native metals, ilmenite 

(FeTiO3

), cassiterite (SnO2), rutile (TiO2), zircon (ZrSiO4), 

monazite ((Ce,La,Th,Nd)PO4), xenotime (YPO4), and many 

others.

Mineral Description

In placer deposits, the action of moving water or wind 

creates segregations of minerals of high density that are resistant to abrasion and resistant to breakdown by chemical and 

mechanical action. Concentration occurs in gravity traps such 

as depressions into bedrock on the bottoms of stream channels, or downstream from any feature that might be centimeters higher on the bed of a stream and lying transverse to the 

flow direction. A second potential setting of concentration is 

on beaches within the intertidal zone, referred to as the swash 

zone or the upper foreshore. There, the crashing waves wash 

all the sand grains up the slope of the beach, but the return of 

the water down the slope (the backwash) carries lighter minerals high in a millimeters- to rarely centimeters-thick sedimentcharged flow while the denser minerals are left behind, the 

densest at the top of the wave’s reach and incrementally 

lighter minerals in their order towards the bottom of the beach. 

Each backwashing wave thus produces a lamination that has 

denser and typically finer-grained minerals at the bottom and 

lighter and coarser grained minerals at the top (Clifton, 1969). 

Because many of the dense minerals are dark colored, these 

placer deposits are sometimes referred to as black-sand deposits. Houston and Murphy (1977) determined that many of the 

heavy-mineral sand deposits from coastal environments in 

Wyoming formed in beach swash-zone environments. However, Force and Rich (1989) concluded that the Trail Ridge, 

Florida, heavy-mineral sand deposit formed in a back-beach 

eolian (wind-deposited) environment. Yet other black-sand 

deposits are believed to represent other depositional environments at or near a coastline (Roehler, 1989). A variety of 

near-the-coast depositional environments appear to be able to 

concentrate heavy minerals into economic concentrations.

Geology and Occurrence in the Study Area

Stream placer-gold concentrations of two (or more) ages 

occur in and near the South Pass proposed withdrawal area. 

The older placer deposits are of early Eocene age within the 

Wasatch Formation. They occur partly within the South Pass 

block but outside of the proposed withdrawal area. The placer 

occurrences are just 1.1 km (0.67 mi) south of the proposed 

withdrawal area at the nearest point (fig. 34). A younger group 

of placer deposits occurs within Quaternary gravels, mostly 

in the alluvium along the modern streams. However, any 

Quaternary terrace gravels are also included in the tract for 

Quaternary placers.

In addition, heavy-mineral sands that formed in coastal 

environments may occur in the study area. One such deposit, 

near Cumberland Gap (Houston and Murphy, 1962), is 26 km 

(16 mi) south of the southeastern corner of the Fossil Basin 

block. Given their stratabound and stratiform nature, their relatively large areal extents (the best exposed of any of them in 

Wyoming is an elongated lens at least 4 km (2.5 mi) long, 180 

m (600 ft) wide, and 3.7 m (12 ft) thick in the center; Houston 

and Murphy, 1977, p. A24), and with the continuity of the 

hosting sandstones across the study areas in the subsurface, 

heavy-mineral sand deposits are likely underlying a number of 

places in the Fossil Basin, Fontenelle, and Big Sandy blocks. 

Such deposits may also underlie the Boars Tusk and Continental Divide blocks. If the proposed withdrawal areas were larger 

in the Boars Tusk and Continental Divide blocks, they would 

certainly also contain heavy-mineral sand deposits locally.

Each of these three types of placer deposits is addressed 

below, and tracts are evaluated for the first two types.

Paleoplacer Gold Deposits in the Study Area

Geology and Occurrence in the Study Area.—Placer gold 

concentrations of early Eocene age within the Wasatch Formation are partly within the South Pass block though outside of 

the proposed withdrawal area. The placer occurrences are 1.1 

km (0.67 mi) south of the proposed withdrawal areas at their 

nearest points (fig. 34).

The Dickie Springs-Oregon Gulch area (fig. 34) has been 

mined in very small operations since 1863—even before the 

opening of the South Pass-Atlantic City district to its north—

yet it has never supported anything but hand operations. 

Mining in this district has been difficult since the outset. The 

gold appears to be disseminated finely through large thicknesses of the conglomeratic facies of the Wasatch Formation, 

and, except seasonally, there is no supply of water for washing out the gold. Hausel (1980, p. 6) estimated that the Dickie 

Springs-Oregon Gulch “district” had produced 310,000 troy 

oz of gold by about 1926.

Gold in the Dickie Springs-Oregon Gulch paleoplacer 

district is hosted by cobble- to boulder-facies conglomerate of 

the lower Eocene Wasatch Formation, south of the Continental 
96 Geology and Mineral Resources of the Southwestern and South-Central Wyoming and Bear River Watershed Sagebrush Focal Areas

FONTENELLE

L/C

BIG SA

M/B

BIG SANDY BLOCK

FONTENELLE BLOCK

C o n t i n e n t a l

F a u l t

Rock Springs

WYOMING

SWEETWATER COUNTY

LINCOLN COUNTY

SUBLETTE COUNTY

189

191

30

191

Juel Creek

110°0' 

42°30'

42°0'

0 10 20 30 KILOMETERS

Base modified from U.S. Geological Survey DEM data, 2016. 0 10 20 MILES30

Roads and political data © 2014 Esri and its licensors.

Boundary data from San Juan and others (2016).

USA Contiguous Albers Equal Area Conic Projection.

Central meridian, 110° W., latitude of origin, 37.5° N.

North American Datum of 1983.
Locatable Minerals 97

Figure 33. Map showing mineral-potential tracts for sandstone 

roll-front uranium deposits in the Southwestern and South-Central 

Wyoming and Bear River Watershed study areas, Wyoming 

and Utah. USGS, U.S. Geological Survey. MRDS, USGS Mineral 

Resources Data System.

ANDY

B

SOUTH PASS BLOCK

CONTINENTAL

DIVIDE BLOCK

BOARS TUSK BLOCK

FREMONT COUNTY

80

109°0'

Map

area

Study areas

IDAHO

MONTANA

OREGON

WYOMING

NEVADA UTAH

WASHINGTON

County boundaries

Proposed withdrawal areas

USGS study area boundary

Base data

Uranium location

MRDS locatable minerals

Continental Fault (ball and bar on downthrown plate)

Geologic structure

Low-potential (L) tract with moderate (C) certainty

Moderate-potential (M) tract with low (B) certainty

Assessment tract types – sandstone roll-front uranium

EXPLANATION

Fault data from Sutherland and Hausel (2006), and Sutherland and Luhr (2011).

MRDS mine locations from USGS (2016).
98 Geology and Mineral Resources of the Southwestern and South-Central Wyoming and Bear River Watershed Sagebrush Focal Areas

DICKIE SPRINGS—OREGON GULCH

PALEOPLACER

H/D

SWEETWATER RIVER 

PLACERS

M/C

PACIFIC BUTTES LOBE

DICKIE SPRINGS LOBE

SWEETWATER COUNTY

SUBLETTE

COUNTY

Sweetwater River

Willow

Creek

Slough

Creek

Sand Creek

Rock Creek

Meadow

Oregon

C

Rock

Slaughterhouse

Gulch

Pine Creek

Fish Creek

Dickie

Springs

Carsissa

Placer

Rock

Creek

Placers

Meadow 

Hermit

Gulch

Placer

Yankee 

Spri

Promise

Gulch

Placer

Dickie

Springs

Placer

Big Atlantic

Gulch Placer

Smith

Gulch

Placer

109°0' 108°50' 108°40' 

42°30'

42°20'

1086420 KILOMETERS

Base modified from U.S. Geological Survey DEM data, 2016. 0 2 4 6 8 

10

Roads and political data © 2014 Esri and its licensors.

Boundary data from San Juan and others (2016).

USA Contiguous Albers Equal Area Conic Projection.

Central meridian, 110° W., latitude of origin, 37.5° N.

North American Datum of 1983.
Locatable Minerals 99

Figure 34. Map showing mineral-potential tracts for paleoplacer gold and placer gold in the South 

Pass block of the Southwestern and South-Central Wyoming study area, Wyoming. BLM, Bureau of 

Land Management; USGS, U.S. Geological Survey; USMIN, USGS Mineral Deposit Database.

SOUTH PASS BLOCK

SAND CREEK PALEOPLACER

L/A

SWEETWATER RIVER 

PLACERS

M/C

SOUTH PASS PLACERS

H/D

SAND CREEK LOBE

FREMONT COUNTY

k

Creek

Wilson Bar

Unnamed

Placer

Lancaster Placer

Crows Nest Placer

 Gulch Placer

e Gulch Placer

ng Gulch Placer

Dutch

Tom Flats

Placer

Beaver Creek Placer

Littler Beaver Creek Placer

108°30'

Map

area

Study areas

IDAHO

MONTANA

OREGON

WYOMING

NEVADA UTAH

WASHINGTON

County boundaries

Proposed withdrawal areas

USGS study area boundary

Base Data

0.6 - 1,000 ppm Au (>99th percentile)

0.1 - 0.5 ppm Au (97.5-99th percentile)

Not detected

Gold, concentrates, parts per million (median = 2 ppm)

0.063 - 458.200 ppm Au (>16x background)

Not detected

Gold, rocks, parts per million (crustal avg = 0.004 ppm)

0.063 - 32.000 ppm Au (>16x background)

Gold, SedSoils, parts per million (soil avg = 0.004 ppm)

USMIN placer-gold locations

Closed placer claim

Active placer claim

Pending surface management plan for gold placer

Authorized surface management plan for gold placer

Authorized surface management notice for gold placer

BLM mining notices, plans, and claims present in section

Permissive (L) tract with unknown (A) certainty

 (Pacific Butte Lobe not assessed in this report)

Moderate-potential (M) tract with moderate (C) certainty

High-potential (H) tract with high (D) certainty

Assessment tract types – placer and paleoplacer gold

EXPLANATION

0 MILES

Mining claim data from Dicken (2016).

Deposit type and tract data from USGS (2016).

Mine locations from Fernette and others (2016).

Sweetwater placers in Sand Creek Lobe from Patterson and others (1987).

Paleoplacers from Love and others (1978).
100 Geology and Mineral Resources of the Southwestern and South-Central Wyoming and Bear River Watershed Sagebrush Focal Areas

Fault. The productive area’s south boundary is formed where 

the Bridger Formation overlies the Wasatch on the south. The 

Wasatch conglomerate facies occurs in three or more lobes. 

These are the Pacific Butte lobe on the west (not shown on 

figure 34 as it is west of the study area, but still in Fremont 

County), the Dickie Springs lobe in the middle (Love and 

others, 1978), and the Sand Creek lobe on the east (Patterson 

and others, 1987) (fig. 34). The Dickie Springs lobe represents 

no less than 400 m (1,300 ft) in thickness of Wasatch section (Love and others, 1978), and the other lobes must also 

represent substantial thicknesses. Largely random sampling 

of the Pacific Butte and Dickie Springs lobes has yielded gold 

grades from below the level of detection up to 660 milligrams 

of gold per cubic meter of gravel (mg/m3). However, that high 

end of the grades is subject to question because Love and others (1978) may not have ensured the validity of their results by 

processing bulk samples. Sample sizes in such sediment must 

be very large—on the order of a backhoe bucketful, rather 

than a 4.5-kilogram (10-pound) sample bag full—because the 

boulders must be mined along with the black sand.

If water were readily available, a dredging operation 

would require an average grade of no less than 500 mg/m3 for 

profitable operation (J.F. Hayes, placer mining engineer with 

more than 25 years of experience, written commun., February, 

2016). Only 1 of the 31 samples analyzed by Love and others 

(1978) from the Dickie Springs lobe contained greater than 

500 mg/m3 of gold, and only 5 of 31 samples even exceeded 

100 mg/m3 of gold.

Exploration and Mining Activity.—Placer claims continue to 

be held in the Dickie Springs conglomerate lobe, but none are 

found within either the Pacific Butte or the Sand Creek lobes. 

The Dickie Springs conglomerate lobe includes parts of 17 

sections, and just 4 of those sections have active claims within 

them. The four sections directly overlie the Dickie Springs 

proper in Oregon Gulch. Mining in both areas may be focused 

on Quaternary sediments that overlie the Wasatch Formation 

rather than deposits in the Wasatch Formation. There is an 

authorized surface-management plan for placer gold mining 

within sections 19, 29, and 30, T. 27 N., R. 100 W. (fig. 17), 

covering three of the same sections that contain active placer 

claims along upper Oregon Gulch. These sections lie just 

south of the southern-most part of the proposed withdrawal 

area, and do not overlap it.

Fremont Gold U.S. LLC proposed and conducted placer 

gold exploration between 2005 and 2012 (Kirk Rentmeister, 

oral communication, June 7, 2016), in an area that they and the 

BLM referred to as the Dickie Springs project, but the actual 

work areas all lay north of the Continental Fault, thus involving no rock of the Wasatch Formation conglomerate lobes 

(Bureau of Land Management, 2005).

Potential for Occurrence.—As demonstrated by the many 

years of sporadic small-scale mining and the sampling results 

of Love and others (1978), there is certainly some demonstrable level of placer gold concentration in the Dickie Springs 

lobe of the Wasatch Formation conglomerate facies. The 

results of Love and others (1978) constitute a valid geochemical anomaly. Love and others (1978) even showed a picture of 

gold recovered by panning, thereby providing direct evidence 

for the presence of gold. Thus, although the grades cannot be 

interpreted to indicate a deposit with clear economic potential, 

the BLM classification of levels of potential requires this area 

to be classified with high (H) mineral resource potential for 

placer gold (fig. 34). A reminder is given that this does not 

imply that the potential concentration is or may be economic. 

Historically, the Dickie Springs lobe did produce gold. For 

that reason only, its certainty is rated at level D.

In contrast to the Dickie Springs lobe of Wasatch conglomerate facies, in the Pacific Butte conglomerate lobe to the 

west, all 11 samples analyzed contained less than 100 mg/m3

of gold. Love and others (1978) describe the detrital composition of the Pacific Butte lobe, and it clearly had a different source area or areas than the Dickie Springs lobe. There 

appears to be no reason to consider the Pacific Butte lobe as a 

permissive tract at all, so we have not.

The Sand Creek lobe of Wasatch conglomerate facies was 

mapped and sampled by Patterson and others (1987). They 

state that the conglomerates there are gold bearing and show 

locations of eight samples from which native gold was found 

in panned concentrates (Patterson and others, 1987, plate 1). 

However, their text (Patterson and others, 1987, p. 11) states 

that 10 samples had native gold in the panned concentrates. 

A later section (Patterson and others, 1987, p. 17) states that, 

“Additional sampling of Quaternary alluvium and of conglomerate of Tertiary age showed that 5 of 28 samples of alluvium 

contained one or more gold flakes, but none of the 7 samples 

of Tertiary conglomerate yielded any gold.” No gold geochemical analyses were provided for the whole rocks of any 

of these samples. They rated the lower Eocene conglomerates 

as having low resource potential at certainty level C (Patterson and others, 1987, plate 1) but rated seven tiny drainages 

with Quaternary sediments in them that drain the Sand Creek 

lobe as moderate (M) potential at level C certainty. There 

are no active claims in the area of the Sand Creek lobe, and 

there is no history of claims in that area. There are seemingly 

contradictory statements in Patterson and others (1987) about 

sampling results in the Sand Creek lobe of Wasatch conglomerate facies, so it is left to the reader to interpret what data are 

accurate and what are not. The rating applied by Patterson and 

others (1987) is consistent only with the descriptions that follow the early reconnaissance given on page 11. There, it stated 

that (after finding gold in panned concentrates in the reconnaissance phase), “. . . 5 of 28 [new] samples of Quaternary 

alluvium had flakes of gold in panned concentrates, but none 

of seven samples of Eocene conglomerates yielded gold in 

panned concentrates.” They then rated the Quaternary alluvium to have moderate potential and the Eocene conglomerate 

to have low potential. We arrive at the same conclusion—that 

potential within the Sand Creek lobe of Wasatch conglomerate facies is low (L). The data are very sparse, but the most 

significant indicate that these conglomerates are along-strike 

equivalents of the Dickie Springs lobe—an indirect criterion. 
Locatable Minerals 101

Actual sampling results that can be reliably placed in time 

and space were all negative for the Tertiary conglomerates, 

as in the quotation above. The indicated certainty level really 

appears to be A: simply insufficient.

Economic Analysis.—Dickie Springs lobe of Wasatch conglomerate facies has a long history of producing small 

amounts of gold. To date, however, there appears to have been 

no valid test of the potential for economic mining in these 

rocks. Gold prices have been relatively stable for several years 

at a level that cannot be viewed as lucrative. The results of 

Love and others (1978) do not serve well as a valid test of 

the potential, as they did not take bulk samples; their samples 

were instead taken in 25- by 40-cm bags, each weighing about 

11 pounds (p. 385). A valid test of this deposit remains to be 

completed.

Discussion of where gold is being produced in the Western United States can be found in Bleiwas (2016). No gold is 

currently produced in Wyoming, and none of the current gold 

production attributed to Utah is from the study area.

Quaternary Placer Gold

Numerous placer claims continue to be held in the greater 

South Pass Quaternary placer area, and there are patented 

placer claims in many drainages. Some of the drainages are 

considered to be “mined out,” but there may still be “colors” 

remaining. For the purpose of this report, we refer to all the 

Quaternary placer deposits in this area as the Sweetwater 

River placers (appendix 2).

Geology and Occurrence in the Study Area.—With somewhat 

greater reliability than his statements about production from 

the Dickie Springs-Oregon Gulch paleoplacers, Hausel (1991, 

p. 30–31) tabulated placer production of the South PassAtlantic City district, totaling 101,250 troy oz of gold from 

8 placer mines. Hausel further gave his opinion (p. 64) that 

production for the dredging of Rock Creek between 1933 and 

1941 is considerably underreported. There is little doubt that 

placer production from the earliest years of the district went 

entirely unreported. Among the areas having the largest placer 

production are Meadow Gulch (50,000 troy oz), Yankee Gulch 

(25,000 troy oz), and Rock Creek (at least 11,500 troy oz) (fig. 

34).

There is a single pending surface management plan for 

placer gold in section 28, T. 28 N., R. 100 W. (fig. 17), at the 

confluence of Pine Creek with the Sweetwater River. Most of 

this section is included within the South Pass proposed withdrawal area, but the land immediately adjacent to the Sweetwater River that is probably an east-west line of four placer 

claims, is not. In that section there is a single active placer 

claim. There are also 8 closed placer claims and 38 closed lode 

gold claims in the section.

There is a single surface-management plan for placer 

gold mining that is authorized within the heart of the lode 

mining area in sections 2 and 11, T. 29 N., R. 100 W. (fig. 17). 

This is within the study area but is 8 km (5 mi) from proposed 

withdrawal area. Another surface management plan for placer 

gold mining is authorized on lower Rock Creek for the 3.2 km 

(2 mi) above its confluence with the Sweetwater River. This 

area is within the study area and lies 1.6 km (1 mi) northeast 

of the southeastern part of the proposed withdrawal area. Rock 

Creek above this area was all dredged between 1933 and 1941.

In the 8-section area that lies within the study area but 

outside of any proposed withdrawal area, and which constitutes 

somewhat more than half of the area with most of the lode gold 

mining, there are 7 active placer claims and 47 closed placer 

claims. That count does not include the area immediately surrounding South Pass City where many patented placer claims 

were apparently purchased and “segregated from mining” 

(Layman, 2012, p. 38). Conservatively estimated, as of a 1972 

map (Bureau of Land Management, 1972), it appears that there 

were no fewer than 26 other patented placer claims or claim 

blocks or other once-private properties that have been “segregated from mining” across the principal area of lode mining in 

the South Pass-Atlantic City district.

Potential for Occurrence.—Considerable placer mining has 

taken place along drainages in Quaternary alluvium and other 

sediments within and downstream from the South PassAtlantic City gold district. Nonetheless there are large areas of 

drainages in the area remaining unmined. A notable one, for 

example, is Willow Creek below South Pass City. Examination 

of production records suggests that placer gold mining prospects can be divided into two levels of potential. Streams that 

directly drain the area of lode mines and have not been previously mined can all be considered direct extrapolations of those 

drainages already profitably mined. These are shown in bright 

pink on figure 34 as the South Pass placers. They are considered to have high (H) potential with a D level of certainty. Just 

as for the Dickie Springs lobe of lower Eocene conglomerate, 

the Quaternary gravels along the stream courses produced gold, 

and thus automatically get the certainty rating D.

Among the additional streams that drain lands without any 

lode gold mining, there are a number that nonetheless did support some placer mining. Included are Oregon Gulch-Meadow 

Creek and Dickie Springs Creek, which drain the Dickie 

Springs lobe of Wasatch conglomerate facies. Also included 

are drainages like Slaughterhouse Gulch, Pine Creek, and Fish 

Creek whose courses are marked by lines of patented placer 

claims. Together, all of these drainages are shown on figure 34 

as the Sweetwater River placers. Historical production from 

these was minor, but some gold was recovered, leading to a 

rating of moderate (M) potential at certainty level C. The lines 

of patented placer claims along several streams rated in this 

category are direct evidence that a mineral resource probably exists, but the lack of production records and the lack of 

dredge tailings along the stream courses makes the presence of 

the claims only quantitatively minimal. Patterson and others 

(1987) assigned M/C to both these and the Quaternary alluvial 

placers, apparently assuming that the placer resource had been 

mostly exhausted.

Economic Analysis.—Discussion of where gold is being produced in the Western United States can be found in Bleiwas 

(2016). No gold is produced in Wyoming, and none of the 
102 Geology and Mineral Resources of the Southwestern and South-Central Wyoming and Bear River Watershed Sagebrush Focal Areas

current gold production attributed to Utah is from the study 

area. 

Coastal Titanium Placer Deposits

Geology and Occurrence in the Study Area and Exploration.—Coastal placer titanium (±zircon, ±rare-earth element) 

deposits, also called heavy-mineral sand deposits from coastal 

environments (VanGosen and others, 2014), almost certainly 

exist in the subsurface of the Big Sandy, Fontenelle, and Fossil Basin blocks. The same would be true of the Continental 

Divide and Boars Tusk blocks if they were larger, but those 

are relatively small areas. Within the Bear Lake Plateau block, 

it has not been demonstrated that Upper Cretaceous sandstone 

is present in the subsurface in thrust plates deep beneath the 

Lakeview-Meade Plate.

Heavy-mineral sand deposits are well known and widespread in Upper Cretaceous sandstones in Wyoming (Houston and Murphy, 1962) and elsewhere throughout the Rocky 

Mountain States (Houston and Murphy 1970; 1977; Force and 

Creely, 2000; Force and others, 2001). The Frontier Formation of earliest Late Cretaceous age, is host to a coastal placer 

titanium occurrence near Cumberland Gap about 26 km south 

of the nearest proposed withdrawal area in the southeast part 

of the Fossil Basin block.

In the Cumberland Gap area, the Frontier Formation 

represents the deposits of two progradations. In a progradation, sand is deposited and preserved beneath younger deposits 

as the beach and related deposits shift episodically seaward 

over thousands to tens of thousands of years. Bodies of coastal 

sand are overlain by estuarine coal, which is overlain by 

fluviatile sandstones and mudstones; progradation sequences 

contain sediment from continental environments over sediment that is marine. The two intervals of coastal and fluviatile 

rocks in the Frontier Formation are separated from one another 

by an interval of marine shale known as the Allan Hollow 

shale member (Hale, 1960). The shale was deposited during 

a westward transgression of the Late Cretaceous inland sea 

when the inland sea probably widened and became deeper. 

Transgression is the opposite of the beach prograding. During 

transgression, the beach and related deposits shift episodically 

continent-ward over thousands to tens of thousands of years. 

That entire cycle was apparently repeated a second time, with 

the top of the formation marked at the bottom of the transgressive beds of the second cycle, at the base of the Hilliard Shale. 

For a single place through all of Frontier depositional time, 

the coastal environments capable of creating a coastal titanium 

placer deposit passed over four times, first migrating eastward 

(by prograding coastal and fluviatile deposition), next moving 

westward (by marine transgression), then the same depositional environments repeated for the second progradation and 

transgression. However, Houston and Murphy (1970) observed 

that the black-sand deposits were associated only with the prograding parts of cycles, not with the transgressing parts, so for 

each place in western Wyoming when the Frontier Formation 

was being deposited there were two times within which heavy 

mineral sandstone deposits might form, namely the two times 

that beaches prograded across that place. At every time during 

the two progradations of the Frontier beaches, there was the 

chance, somewhere along the coastline, to produce a heavymineral sand deposit as part of the formation’s sandstones. 

Although the exact position within the stratigraphy is not 

known, the likelihood of there being a coastal placer titanium 

deposit somewhere beneath an area as large as the Fossil Basin 

proposed withdrawal area is very high.

Beneath the Fontenelle, the Big Sandy, the Boars Tusk, 

and the Continental Divide blocks, everywhere at depths of 

at least one hundred meters (a few hundred feet), and at some 

places at depths of more than 1 km, the Rock Springs Formation of the Mesaverde Group may also contain heavy-mineral 

sand occurrences. In the Rock Springs Formation, there was 

first a transgression of the Cretaceous interior sea where it 

overrode and eroded a small amount of previously deposited 

rocks in what later became the Green River Basin, then progradation took the coastal sand-depositing environments back 

eastward across the same area. So for Rock Springs time, each 

location had one chance for a coastal placer titanium deposit 

to form.

Given a large enough area, the probability that there is a 

heavy-mineral sand deposit within the Rock Springs Formation somewhere beneath the study area in the Green River 

Basin is very high. The spacing to be expected at any given 

time is shown, for example, by Roehler (1989). Over the time 

of deposition of the McCourt Sandstone Tongue of the Rock 

Springs Formation of the Mesaverde Group, typically about 

21 m thick, no fewer than six heavy-mineral sand occurrences 

formed along a 64-km long stretch of coastline (Roehler, 

1989, p. 3). All together the six heavy mineral sand deposits 

occupied a minimum of 1,811 m of the McCourt coastline 

(Roehler, 1989, plate 1), which accounts for at least 2.8 percent of the total length of coastline and probably considerably 

more. Lengths of black-sandstone outcrop could be measured 

only in the direction along outcrop, probably only rarely in the 

actual direction of elongation of the black sandstone deposit; 

thus 1,811 m cumulatively along outcrop is a minimum total 

length of black sandstone deposits. The certainty that heavymineral sand deposits are present in the subsurface within 

any given large area is best understood with the analogy of 

crossing an area with a discrete groups of points along a line, 

as follows. The McCourt Sandstone coastline with 1,811 m of 

black sand being deposited in six groups of points per 64.4-km 

reach of coastline is viewed as crossing eastward across all of 

the southwestern quarter of Wyoming over perhaps 100,000 

years of prograding and depositing the sand. During the crossing (progradation), each of the six segments that total 1,811 m 

in length, in each instant of time, shift slightly north or south 

along the coastline. The overall crossing produces an area of 

heavy mineral sand deposition by the combination of moving 

eastward across (progradation) and migration of a black-sand 

depositing environment along the line (coastline). The only 

uncertainty is whether each particular area and thickness of 

black sand is preserved, not eroded away just days or weeks 
Locatable Minerals 103

later along the shifting coastline. Otherwise, every place 

where the McCourt sandstone is present would have greater 

than a 2.8-percent chance to have a coastal environment heavy 

mineral-sandstone deposit present; any vertical plane along 

the 64.4-km paleo-coastline is likely to have six black sand 

deposits present even after some were eroded away along the 

shifting coastline.

Looked at differently, if the McCourt Sandstone was 

everywhere at the surface, it should be a rare case to be able to 

move more than 12.45 km in any direction without encountering a McCourt-hosted black sandstone deposit. That 12.45 km 

distance is 64,390 m minus 1,814 m divided by 5—the 64 km 

length along outcrop minus the length of exposed (outcropping) black sandstone divided by the 5 intervals between the 

6 black-sand deposits. Thus, 12.45 km is a very conservative 

figure because not all of the McCourt is outcropping along 

the entire 64 km—probably much less than 50 percent is 

outcropping—and, as before, where black sandstone is at the 

surface, the outcrop probably does not run along the direction 

of elongation of the body of black sandstone. With that result, 

it is clear why any land area of a township (6 miles by 6 miles, 

or 9.6 km by 9.6 km) is likely to have at least one McCourthosted black-sandstone body underlying it, and a block totaling 10 townships like the Fontenelle block is all but certain to 

have at least one.

However, modern heavy-mineral sand deposits from 

coastal environments are mined from sediment that has not yet 

lithified; the deposit is still a weak aggregate of nearly loose 

detrital grains, or the sediment has not even aggregated at all. 

Also, these deposits are at and immediately below the surface, 

accessible to open-pit mining. They can be mined without 

blasting, and the ore (sediment) fed directly into a gravity 

separation circuit—they do not need to be crushed or ground. 

Therefore, lithified sandstones of Wyoming’s Late Cretaceous 

coastal placer titanium deposits cannot currently compete 

economically with the deposits along modern coastlines, nor 

will they be able to compete until almost all the heavy-mineral 

sands along the modern coasts are mined out. Furthermore, 

most of Wyoming’s coastal placer titanium deposits are buried, requiring underground mining, and mining and extraction 

costs are far greater than in the loose sand deposits along modern or Pleistocene coastlines. Therefore, although the coastal 

placer titanium occurrences and deposits must almost certainly 

be present, they can be considered resources only for the 

long-term future, because they are not economically competitive with deposits along the modern coastlines that require no 

underground access, no drilling, no blasting, no crushing, and 

no grinding.

Potential for Occurrence.—Subsurface data is inadequate 

to try to further quantify the numbers of this type of deposit 

anywhere beneath the study area. However, with knowledge 

of the stratigraphic intervals that contain black-sand deposits, 

an oil well natural gamma log of an oil test has occasionally 

identified such a deposit in Wyoming. Anomalous concentration of, for example, monazite in the black sandstone produces 

a high-gamma zone within the known host sandstone interval. 

Petroleum tests, almost nowhere drilled any closer to one 

another than the next quarter-quarter of a section even within a 

producing field (660-ft grid spacing), never really test continuity of an accidently penetrated black sandstone deposit. It is 

beyond the scope of this work to check for natural gamma log 

anomalies within the Frontier Formation and the Rock Springs 

Formation in every petroleum test hole in every proposed 

withdrawal area. Therefore, no tract for assessment for coastal 

placer titanium deposits is drawn, and no assessments of 

resource potential are given for the Southwestern and SouthCentral Wyoming and Bear River Watershed study areas.

Economic Analysis.—As discussed above, heavy-mineral sand 

deposits in Upper Cretaceous sandstones in the study areas are 

not now economic, and they will not become economic until 

the heavy-mineral sand deposits along the world’s modern 

coastlines are all exhausted or nearly so.

Discussion of where titanium is being produced in the 

United States can be found in Bleiwas (2016). There has been 

no production of titanium from the study area.

Nonmetallic Locatable Minerals

No nonmetallic locatable minerals are found in the study 

area. Nevertheless, there may be potential for diatreme-hosted 

diamond deposits associated with lamproites of the Leucite 

Hills volcanic field and for high-purity dolomite principally in 

the Bear Lake Plateau block. Each is discussed briefly, below.

Diatreme-Hosted Diamond (Diamonds in 

Lamproite)

Mineral Description

Diamond is a crystalline form of elemental carbon that 

forms at extremely high temperature and pressure conditions 

that are possible only deep in the Earth’s upper mantle. Large 

diamonds, particularly large diamonds without flaws, are 

extremely rare and are very valuable as gemstones. The vast 

majority of diamonds, however, are small, flawed, and colored 

by various impurities. These small impure diamonds have a 

variety of industrial uses, particularly as abrasives to embed 

in saw blades for cutting stone and concrete, and are similarly 

used for core-drilling bits.

Geology and Occurrence in the Study Area

The Southwestern and South-Central Wyoming study 

area includes a single area with some potential for diamonds, 

namely the Leucite Hills volcanic field. The Leucite Hills are 

22 occurrences of intrusive and extrusive lamproite scattered 

across about 960 km2 (375 mi2) of the northern part of the 

Rock Springs Uplift (fig. 35). Lamproites are rare, strongly 

alkaline, mafic to ultramafic, igneous rocks. Those of the 

Leucite Hills are ultrapotassic, containing major proportions 
104 Geology and Mineral Resources of the Southwestern and South-Central Wyoming and Bear River Watershed Sagebrush Focal Areas

of either leucite or sanidine together with phlogopite and 

diopsidic pyroxene.

Boars Tusk itself, a well-known landmark, is a two-spired 

volcanic neck that stands nearly 122 m (400 ft) high above 

the flood plain of Killpecker Creek. It is about 42 km (26 mi) 

north of Rock Springs. It is an erosional remnant of wyomingite; that is, phlogopite-diopside-leucite lamproite.

Lamproites are one of two types of igneous rocks that 

are known host rocks to diamonds. The other, more familiar 

igneous rock type associated with diamonds is kimberlite, and 

some igneous rock classifications divide a third rock type, 

orangeite, apart from kimberlites. Both lamproites and kimberlites are typically found in areas of thick crust and subcrustal 

lithosphere, commonly greater than 75 km (46 mi) thick. Both 

kimberlites and lamproites occur in fields or swarms that 

contain tens of individual small pipes or dikes of igneous rock, 

and the Leucite Hills are typical of such a field (fig. 35). Thick 

subcrustal lithosphere is typically present under old, Archean 

cratons, like the Wyoming craton. Lamproitic and kimberlitic 

magmatism requires such thick lithosphere because the temperatures at which such magmas form are greater than 1,200 

°C and the pressures are 60 to 75 kilobars, corresponding to 

depths of 160 to 200 km below surface (Eggler and others, 

1979). In addition, diamonds are only stable at depths greater 

than 150 km (Haggerty, 1999). The instability of diamonds 

from 150 km to perhaps 50 km depth has led geologists to 

conclude that they must move through that zone rapidly—

perhaps even explosively—in small batches of kimberlite or 

lamproite magma, consistent with the abundant xenolith and 

xenocryst fragments in such rocks.

The igneous rocks of the Leucite Hills include a variety of lamproites but no kimberlites. They include several 

volcanic necks and a number of restricted-area (less than a few 

tens of square kilometers) volcanic flows, now expressed as 

erosion resistant cap rocks for small mesas. Boars Tusk and 

another lamproite occur north of proposed withdrwal areas in 

the northeast corner of the Boars Tusk block. The other intrusive body is the Matthews Hill dike. The next nearest known 

lamproite is at Twin Rocks, which is more than 11 km (7 mi) 

from the nearest proposed withdrawal area (fig. 35). Lange 

and others (2000) give a range of ages for the Leucite Hills of 

3.0 to 0.89 Ma.

To date, all lamproites that are known to contain diamonds also (1) contain (forsteritic) olivine, (2) contain chromite (both of the above are xenocrytic or xenolithic, as are the 

diamonds themselves), (3) have greater than 20 percent MgO, 

(4) have less than 45 percent SiO2

, and (5) contain greater 

than or equal to 7 percent K2O (Scott-Smith, 1996). Where 

diamonds have been found in lamproites, they are restricted 

to volcaniclastic facies olivine lamproites and have not been 

found in intrusive olivine lamproites, even in the same igneous 

complex. Diamonds are not restricted to volcaniclastic facies 

of kimberlites.

In the Leucite Hills volcanic field, olivine has been found 

in 6 of the 22 lamproites—Endlich Hill, Hague Hill, South 

Table Mountain, Emmons Mesa, Hatcher Mesa, and Black 

Rock (Hausel, 2006, appendix 1). All six of those are in the 

eastern half of the volcanic field, not nearer than 12 km (9 mi) 

from any proposed withdrawal area. Chromite has not been 

reported in any lamproite in the field, to date. None of the 59 

single-locality samples reported by Hausel (2006, appendix 

2) contains more than 20 percent MgO. The highest MgO 

reported is 12.75 percent from Kuehner (1980), but the source 

of that sample is not available to us. The second-highest MgO 

is 11.75 percent (Kuehner and others, 1981, p. 671) in a madupite (diopside-bearing lamproite with high barium, strontium, 

thorium, and light rare earth elements, and low nickel; they 

may be differentiates of wyomingites or orendites [diopsidesanidine-phlogopite lamproite] but cannot be a differentiation parent to those others) from Pilot Butte. Eight of the 59 

single-locality samples reported by Hausel (2006, appendix 

2) had less than 45 percent SiO2

. Seven of those were madupites, and they came from a variety of places around the 

volcanic field, although several were from Pilot Butte and 

one was from Twin Rocks. One sample was a “transitional 

rock” (rock having some of the petrographic characteristics of 

both wyomingite and madupite and that contain analcime and 

other zeolites; probably they have been secondarily altered) 

from Twin Rocks. Seven of the 59 single-locality samples 

reported by Hausel (2006, appendix 2) contained less than or 

equal to 7 percent K2O. All but one of those also had less than 

45 percent SiO2. All of the lower potassic rocks were either 

madupites or were aphanitic volcanics, and one was the same 

“transitional” (secondarily altered) rock as had the high SiO2. 

Of the four poorly potassic rocks that were located, two were 

from Pilot Butte, and 2 were from Twin Rocks. In summary, a 

total of only 8 of the 59 sample analyses compiled by Hausel (2006, appendix 2) met even one of Scott-Smith’s (1996) 

petrologic or chemical criteria for diamond favorability. Five 

of those were from Pilot Butte and Twin Rocks, and did not 

also have olivine or green omphacitic pyroxene. Locations of 

the remaining three are not known. Thus, both mineralogical 

and chemical studies suggest the chances for diamonds in the 

known lamproites of the Leucite Hills are low at best. Only 

lamproites that are not yet breached by erosion can be considered prospective.

Exploration and Mining Activity

Boars Tusk and the other lamproites of the Leucite Hills 

have been cursorily explored for diamonds. Both studies that 

have been published (Hausel, 2006; Chesner and others, 1998) 

mainly used the method of indicator minerals, which continues to be the industry standard. The method, developed first 

from kimberlites, takes a very large sample of soil or alluvial 

sediment, separates its heavy minerals, and searches them 

optically (typically with a binocular microscope) for minerals that have mantle origins. Indicators include pyrope garnet, 

pyrope-almandine, chromium-rich diopside, omphacitic 

(grass-green, aluminous) diopside, chromium-rich enstatite, 

chromite, and picroilmenite (Mg-rich) (Fipke and others, 

1995). Hausel (2006) focused on indicator minerals in the 
Locatable Minerals 105

BIG SANDY

BLOCK

BOARS TUSK

BLOCK

CONTINENTAL

DIVIDE BLOCK

SOUTH PASS

BLOCK

SWEETWATER COUNTY

SUBLETTE COUNTY

FREMONT COUNTY

191

80

Green River

Rock Springs

Steamboat Mountain North Table Mountain

South Table Mountain

Endich Hill Hague Hill

Boars Tusk

Matthews Hill

Deer Butte

Cabin Butte

Twin Rocks

Pilot Butte

Zirkel Mesa

Emmons Mesa

Spring Butte

Black Rock

Iddings, Weed, and Hallock Buttes; Wortman Dike

Hatcher Mesa

LEUCITE HILLS 1

L/D

LEUCITE HILLS 2

L/C

LEUCITE HILLS 3

L/B

108°30' 109°0' 109°30'

42°30'

42°0'

41°30'

IDAHO

MONTANA

OREGON

WYOMING

NEVADA UTAH

WASHINGTON

Maparea

USGS study area boundaryProposed withdrawal areas

County boundaries

Base data

Lamproite—Some intrusions too small to see at this scale

Geologic formations

High (D) certaintyModerate (C) certainty

Low (B) certainty

Lamproite tracts with low (L) potential

EXPLANATION

KILOMETERS 20151050

MILES20 15 10 5 0 Base modified from U.S. Geological Survey DEM data, 2016.

Roads and political data © 2014 Esri and its licensors.Boundary data from San Juan and others (2016).USA Contiguous Albers Equal Area Conic Projection.Central meridian, 110° W., latitude of origin, 37.5° N.North American Datum of 1983.

Geologic data from Jones and Scott (2010).

and Stoeser and others (2005 [revised 2007]).

Figure 35. Map showing mineral-potential tracts for diamonds in lamproites, Leucite Hills, Southwestern and South-Central Wyoming study area, Wyoming. USGS, U.S. Geological Survey.
106 Geology and Mineral Resources of the Southwestern and South-Central Wyoming and Bear River Watershed Sagebrush Focal Areas

eastern part of the Leucite Hills, where olivine had been found 

as a xenocryst in six of the lamproite plugs and flows and 

where omphacitic diopside had been described earlier from 

the Hatcher Mesa flows (Barton and van Bergen, 1981). Thus, 

Hausel’s work provided no test of the Boars Tusk or Matthews 

Hill volcanic necks for diamond. There was an assumption, 

probably a reasonable one, that none was justified. The other 

exploration using indicator minerals was reported in Chesner 

and others (1998). They started by documenting olivine in 10 

of the 22 exposures of Leucite Hills lamproites, then focused 

on only those 10 for further work, again leaving out Boars 

Tusk and Matthews Hill (the 10 that have olivine are not 

named, and Hausel [2006], documents only 6 with olivine). 

These are such volumetrically tiny batches of magma that it 

may be reasonable to assume that the rock exposed is the only 

kind of igneous rock present near any one locality. Yet abandoning Boars Tusk and the Matthews Hill dike may not have 

been fully justifiable, because Fipke and others (1995) state 

clearly that the method is “not as successful when applied to 

lamproites [as opposed to kimberlites].” That is true, in part, 

because kimberlites can have orders of magnitude greater 

concentrations of the indicator minerals than lamproites. In the 

Argyle lamproite deposit in Australia, the largest and richest 

diamond deposit in the world to date, it has been observed that 

garnet is replaced by aluminous spinel and pyroxenes in what 

may equate to a retrograde reaction on the fall in pressure and 

temperature from mantle depths (Fipke and others, 1995, p. 

60). If true generally for lamproites as opposed to kimberlites, 

the great difference in concentrations of indicator minerals 

could be explained. However, aluminous spinel has not been 

described from anywhere in the Leucite Hills.

It is not clear that indicator-mineral studies conducted by 

Hausel (2006) and by Chesner and others (1998) meet industry 

standards. Industry investigations typically collect samples 

of 40 kg (88 lb) or more and separate heavy minerals from 

the entirety of the large samples, commonly using a Wilfley 

shaking table. Only samples that large are considered sufficiently representative. Shipping such samples can be a major 

expense, so it is common to do the Wilfley table separations in 

the field so that only the separates of heavy minerals need to 

be shipped. Where possible, it is even a common practice to 

examine the heavy mineral separates in the field (Karl Smithson and James Austin of Southern Era Resources, Ltd., oral 

commun., July 7, 1998, near Mogoto, South Africa). It would 

be typical for exploration geologists using indicator minerals 

to specify in reporting that samples of 40 kg were collected 

and processed for heavy minerals. Neither Hausel (2006) nor 

Chesner and others (1998) reported the size of their samples, 

and Hausel reported conducting the separation of heavy minerals using a grease table rather than a Wilfley table (Hausel, 

2006, p. 40).

Potential for Occurrence

Fipke and others (1995, p. 2) states that “less than 1 

percent of kimberlite pipes are sufficiently diamondiferous 

to be economic.” A similar number probably applies also to 

lamproites. That fact, along with results from the five tests 

from mineralogy and geochemistry, suggest that it is unlikely 

that any buried intrusive bodies in the Leucite Hills volcanic 

field would contain diamonds, particularly at commercial 

grades.

Tract delineation is based on the tendency of lamproite/

kimberlite intrusions (diatremes) and related rocks to occur in 

clusters. We used the distances between intrusions and intrusion density to create mineral potential tracts. Two Esri ArcGIS tools were used to construct the lamproite tracts (fig. 35): 

(1) the “Generate Near Table” tool (to compute the “maximum 

near distance”), and (2) the “Kernel Density” tool (Hammarstrom and Zientek, 2016). 

First, the distance between the center (centroid) of every 

lamproite (pipe or neck, not including flows) was determined 

using ArcMap’s “Generate Near Table” tool. The maximum 

near-distance is 26.4 km for the Leucite Hills lamproites (from 

Twin Rocks to Pilot Butte). We use this value as the radius

from which to draw a boundary (buffer) around all the known 

lamproites. This boundary forms the outer extent of the tract 

with the lowest level of confidence (B). Second, in order to 

map areas with certainty levels C and D (see appendix 1), the 

kernel density surface (a raster file) was created in ArcGIS 

and classified into three groups using a geometrical interval 

classification scheme. For the Leucite Hills lamproites, the 

boundary between the D and C certainty levels ranges from 

2,919 m to 4,093 m to the center of the nearest lamproite, and 

the boundary between the C and B certainty levels ranges 

from 4,417 m to 4,878 m to the center of the nearest lamproite. 

Only in the extreme southeast corner of the Boars Tusk block 

does the certainty reach level D.

Most of the lands of the Boars Tusk block are considered to have low (L) potential for diatreme-hosted diamond 

deposits with a B level of certainty. All of the Continental 

Divide block is also rated with the same level of potential 

and certainty (L/B). A relatively small part of the Big Sandy 

block is also considered to have low potential with B-level 

certainty. These large areas reflect a lack of knowledge on why 

the lamproites have intruded where they did and a lack of data 

to predict where more might be found. In known kimberlite 

fields, closely spaced lines of magnetic geophysical surveys 

have been effective in locating additional covered kimberlites. 

Lines spaced that closely serve only the purpose of exploration, and public-sector magnetic geophysical surveys are never 

so closely spaced.

Within the study area, a small part along the northern 

edge and another in the southeastern corner of the Boars Tusk 

block are the only areas considered to have any different level 

of certainty, although still at only a low level of potential. 

Those segments are rated with low (L) potential and level C 

certainty (fig. 35). Being as close to Boars Tusk and Matthews 

Hill lamproites as the northern segment is, the evidence is 

considered direct rather than indirect for there being some low 

level of potential for a diamond deposit in a lamproite that 

is not yet exposed by erosion. However, the evidence is still 

rather minimal. Moving closer yet to those lamproites, there is 
Salable Minerals 107

still not even moderate potential for a diamond deposit. After 

all, the various mineralogic and geochemical studies and the 

indicator minerals exploration efforts have given little evidence that these lamproites contain diamonds, yet the certainty 

increases nearer to a known lamproite. At the extreme southeast corner of the Boars Tusk block the potential barely skims 

the area rated Low (L) with certainty level (D).

Economic Analysis

Once a diamond-bearing lamproite is found, there is still 

only a small possibility that there will be an economic concentration of diamonds in the lamproite, with the economics 

strongly affected by the number of gem quality diamonds as 

opposed to industrial diamonds. For the Leucite Hills, it probably is not appropriate to discuss economics unless or until a 

diamond is found.

Dolomite

Dolostone is a sedimentary rock consisting of calciummagnesium-carbonate that is more than 50 percent dolomite—CaMg(CO3

)2. Carbonate rocks are used in gold mining 

operations, cement making, nutrition, agricultural, and other 

industrial applications (U.S. Geological Survey, 2004). Dolomite is generally less suitable than other industrial carbonates 

for most applications. Most dolomite that is mined is simply 

crushed and sieved for use as aggregate in concrete or asphalt 

(Bliss and others, 2008).

Mineral Description

Dolostone, the sedimentary rock, is composed of calcium-magnesium carbonate, the mineral dolomite.

Geology and Occurrence in the Study Area

Few dolomitic units are exposed in the western part of 

the Bear Lake Plateau block (fig. 6). The units include Jurassic Twin Creek Limestone at the extreme southern end of the 

block where there is a Utah Department of Highways potential 

gravel pit (Utah Mineral Occurrence System, UMOS, 1027; 

MRDS 10276517; USMIN 5351). No other pits or prospects 

are within this rock unit.

Little Creek Limestone Pit (UMOS 191; MRDS 

10227074 and 10011446), also known as the Randolf Limestone Pit (USMIN), is a fossiliferous limestone of possible 

Permian age, described in the UMOS database as a coquina. 

It is a small nonproducing pit, claimed for dimension stone. 

There are no production records.

Exploration and Mining Activity

The extent of mining activity is unknown. Minor surface 

disturbances can be seen on satellite imagery (Esri, base imagery) at each of the three sites within the study area. Imagery 

for Sage Creek shows abundant white sediment covering a 

little more than an acre. There does not appear to be any recent 

activity. Little Creek and Randolf Limestone Pits may be the 

same site or very close together (about 100 m apart): each scar 

is about 0.2 acres.

Potential for Occurrence and Economic Analysis

Occurrences of dolomite in the study area have not 

proven to be productive. Dolomite (and related limestone) 

is commonly marketed as a salable mineral in the form of 

crushed stone. Much less common are the pure dolomites 

needed for specialty uses, such as pharmaceuticals, which 

would be ranked as a locatable mineral.

Strategic and Critical Materials

No strategic or critical mineral materials are known to 

occur in the study area.

Salable Minerals

Salable minerals include common varieties of sand, 

gravel, decorative stone, dimension stone, pumice, clay, and 

rock. These mineral materials are typically used in construction, agriculture, decorative building, and landscaping 

applications. Salable minerals are managed according to the 

Material Sales Act of 1947 and all other relevant State and 

Federal laws. The BLM’s Mineral Materials Program manages 

the exploration, development, and disposal of salable minerals 

either by sales contracts or free use permit. Recreational collecting of small quantities of these materials is allowed (generally about one cubic yard), whereas larger volumes require a 

mineral materials sale. Salable mineral permit applications, as 

well as internal BLM proposals to establish free-use collection 

areas, are reviewed on a case-by-case basis (Bureau of Land 

Management, 2012).

Properties that produce salable minerals within 25 km of 

the Southwestern and South-Central Wyoming and Bear River 

Watershed study areas are listed in appendix 5. Only sand and 

gravel mining is currently authorized or pending in the study 

area, and only in the Bear River Plateau (fig. 2) part of the 

Bear River Watershed study area. Closed sand and gravel and 

stone quarries—riprap, specialty stone, and weathered granite 

(also known as grus)—are present in all subdivisions of the 

study area except the Continental Divide block).

Sand and Gravel

Both the Southwestern and South-Central Wyoming and 

Bear River Watershed study area contain rock types that host 

naturally occurring sand and gravel, a form of construction 

aggregate. Sand and gravel deposits, that is, deposits that can 

be mined without blasting or crushing, are commonly found in 
108 Geology and Mineral Resources of the Southwestern and South-Central Wyoming and Bear River Watershed Sagebrush Focal Areas

Table 10. Active Bureau of Land Management mineral material authorizations 

in the proposed withdrawal area within the (A) Southwestern and South-Central 

Wyoming study area, Wyoming, and (B) Bear River Watershed study area, Wyoming 

and Utah.

[Source: Bureau of Land Management LR2000 database, March 6, 2016. The number of cases is for 

the complete section that includes a proposed withdrawal area. ND, no data]

A. Southwestern and South-Central Wyoming study area, Wyoming.

Commodity Number of approved sites Number of pending sites

ND ND ND

B. Bear River Watershed study area, Wyoming and Utah.

Commodity Number of approved sites Number of pending sites

Sand and gravel 2 0

Sand and gravel, sand 0 1

Sand and gravel, shale 1 0

unconsolidated or loosely consolidated Quaternary deposits. 

Other, more lithified units can be quarried and crushed to produce aggregate or crushed stone. If the rock is crushed finely 

enough, it may also be used as sand and gravel.

The March 6, 2016, BLM LR2000 database shows three 

approved sites for sand and gravel, all in the Bear River Plateau area (table 10). Two of these sites are for sand and gravel, 

and the other site is for shale (which indicates that this is not 

an unconsolidated deposit). In addition, there is one pending 

site for sand. The sand and shale sites are on the east side of 

the Bear River Valley.

Following examination of imagery available in Google 

Earth, we conclude that the expired gravel permit, as well as 

one of the authorizations for sand and gravel, appear to be at 

the Birch Creek Reservoir and may have been used for construction of the dam. Another permit for sand and gravel may 

be for extraction of the deposit along the creek.

Within the study area, statistical data on production 

have not been reported to the USGS (Robert Callaghan and 

Elizabeth Scott Sangine, USGS National Minerals Information Center, written commun., March 7 and May 10, 2016, 

respectively). One commercial sand-and-gravel operation is 

within the study area. The U.S. Forest Service has 12 inservice sand-and-gravel pits in the study area; three of these 

are within the proposed withdrawal area in the Bear Lake 

Plateau block (Roger Kesterson, U.S. Forest Service, written commun., March 11, 2016). Because transport costs are 

typically the most significant expense in the production of 

aggregate, the source of the materials must be close to where 

they are needed. Sand and gravel in the study area is primarily 

in unconsolidated alluvial and glacial deposits, where harder 

rocks and minerals are selectively preserved and deleterious 

clay minerals are winnowed out.

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Appendixes
Appendix 1 123

Appendix 1. Mineral Potential Classification System

The approach to classification of the qualitative mineral-resource potential for locatable minerals followed that 

prescribed in Bureau of Land Management (BLM) Manual 

Sections 3031 and 3060 defined originally by Goudarzi (1984) 

(fig. 1–1).

Level of Potential

N. The geologic environment, the inferred geologic processes, and the lack of mineral occurrences do not indicate potential for accumulation of mineral resources.

L. The geologic environment and the inferred geologic 

processes indicate low potential for accumulation of 

mineral resources.

M. The geologic environment, the inferred geologic processes, and the reported mineral occurrences or valid 

geochemical/geophysical anomaly indicate moderate 

potential for accumulation of mineral resources.

H. The geologic environment, the inferred geologic processes, the reported mineral occurrences and (or) valid 

geochemical/geophysical anomaly, and the known 

mines or deposits indicate high potential for accumulation of mineral resources. The “known mines and 

deposits” do not have to be within the area that is being 

classified, but have to be within the same type of geologic environment.

ND. Minerals potential not determined due to lack of useful 

data. This does not require a level of certainty qualifier.

Level of Certainty

A. The available data are insufficient and (or) cannot be considered as direct or indirect evidence to support or refute 

the possible existence of mineral resources within the 

respective area.

B. The available data provide indirect evidence to support or 

refute the possible existence of mineral resources.

C. The available data provide direct but quantitatively minimal 

evidence to support or refute the possible existence of 

mineral resources.

D. The available data provide abundant direct and indirect 

evidence to support or refute the possible existence of 

mineral resources.

For the determination of “no potential” use N/D. This 

class shall be seldom used, and when used it should be for a 

specific commodity only. For example, if the available data 

show that the surface and subsurface types of rock in the 

respective area are batholithic (igneous intrusive), one can 

conclude, with reasonable certainty, that the area does not 

have potential for coal.

As used in this classification, potential refers to potential 

for the presence (occurrence) of a concentration of one or 

more energy and (or) mineral resources. It does not refer to 

or imply potential for development and (or) extraction of the 

mineral resource(s). It does not imply that the potential concentration is or may be economic, that is, could be extracted 

profitably.

Reference Cited

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

Open-File Report 84–787, 41 p., accessed December 9, 

2015, at https://pubs.er.usgs.gov/publication/ofr84787.
124 Geology and Mineral Resources of the Southwestern and South-Central Wyoming and Bear River Watershed Sagebrush Focal Areas

Level of certainty

A B C D

N

L

M

H

Level of resource potential

H/A

M/A

L/A

H/B

M/B

L/B

H/C

M/C

L/C

H/D

M/D

L/D

N/D

High potential with 

insufficient evidence

Moderate potential 

 with insufficient 

evidence

Low potential with 

insufficient evidence

High potential with 

indirect evidence

Moderate potential 

 with indirect evidence

Low potential with 

indirect evidence

High potential with 

direct evidence

Moderate potential

with direct evidence

Low potential with 

direct evidence

High potential with 

abundant direct and

indirect evidence

Moderate potential with 

abundant direct and

indirect evidence

Low potential with 

abundant direct and

indirect evidence

No potential

Current production/significant inventor.

Significant past production.

Active or pending notices or mine plans.

Numerous active claims.

USMIN active exploration.

Prospects, geochemical anomaly,

geophysical anomaly, and (or) 

related deposit type.

Historical mining.

Historical claims.

No active notices or mine plans.

No active exploration. 

No claims.

No other applicable data.

Permissive host rocks +/- previous assessment 

Permissive host rocks +/- previous assessment

Permissive host rocks +/- previous assessment 

Few active claims.

Historical mining. 

No USMIN active exploration. 

No active notices or mine plans.

Minor past production.

Attractive exploration targets.

Active or pending notices or mine plans.

Numerous active claims.

USMIN active exploration.

Attractive exploration targets.

Active or pending notices or mine plans.

Numerous active claims.

USMIN active exploration.

Contains 2 or more of the following:

Current production/significant inventory.

Significant past production.

Active or pending notices or mine plans.

Numerous active claims.

USMIN active exploration.

Contains 1 or more of the following:

Minor past production.

Attractive exploration targets.

Active or pending notices or mine plans.

Numerous active claims.

USMIN active exploration.

Attractive exploration targets.

Active or pending notices or mine plans.

Numerous active claims.

USMIN active exploration.

Chapter A Figure H3 (Appendix fig. for all other chapters)

Contains 2 or more of the following: Contains 2 or more of the following:

Contains 1 or more of the following: Contains 1 or more of the following:

Prospects, geochemical anomaly,

geophysical anomaly, and (or) 

related deposit type.

Prospects, geochemical anomaly,

geophysical anomaly, and (or) 

related deposit type.

Prospects, geochemical anomaly,

geophysical anomaly, and (or) 

related deposit type.

Prospects, geochemical anomaly,

geophysical anomaly, and (or) 

related deposit type.

Prospects, geochemical anomaly,

geophysical anomaly, and (or) 

related deposit type.

Prospects, geochemical anomaly,

geophysical anomaly, and (or) 

related deposit type.

Prospects, geochemical anomaly,

geophysical anomaly, and (or) 

related deposit type.

Reserved for a specific type of 

resource in a well-defined area. For 

example, it is appropriate to say that 

there is no oil potential in an area 

where the only rocks present are 

unfractured Precambrian granite, 

but the term ”low” is appropriate if 

there is a slight possibility for the 

presence of resources.

Figure 1–1. Matrix showing the classification system used for qualitative mineral-resource potential for locatable minerals 

in the Sagebrush Mineral-Resource Assessment (see text for abbreviations). USMIN, U.S. Geological Survey Mineral 

Deposit Database.
Appendix 2 125

Appendix 2. Table of Mineral-Potential Assessment Tracts for Locatable 

Minerals in the Southwestern and South-Central Wyoming Study Area, 

Wyoming, and Bear River Watershed Study Area, Wyoming and Utah

This appendix is available online only as an Excel (.xlsx) 

table at http://dx.doi.org/10.3133/sir20165089E. The table lists 

and summarizes characteristics of the mineral-potential assessment tracts for locatable minerals in the Southwestern and 

South-Central Wyoming study area, Wyoming, and Bear River 

Watershed study area, Wyoming and Utah.
126 Geology and Mineral Resources of the Southwestern and South-Central Wyoming and Bear River Watershed Sagebrush Focal Areas

Appendix 3. Geochemical Samples for the Southwestern and South-Central 

Wyoming Study Area, Wyoming, and Bear River Watershed Study Area, 

Wyoming and Utah

[Of the 395 rock, 1,690 sediment, and 262 concentrate samples taken in the entire 25-kilometer buffered area around the USGS study areas, this table shows the 

number of samples within each subdivision (block),and those within the actual proposed withdrawal areas, and those within the greater PLSS study area]

Southwestern and South-Central Wyoming Study Area, Wyoming Bear River Watershed Study Area, Wyoming and Utah

Subdivision (block) Samples in 

study areas

Samples within 

proposed withdrawal areaSubdivision (block) Samples in 

study areas

Samples within 

proposed withdrawal area

Concentrate samples

South Pass, Wyoming 92 1 Fontenelle, Wyoming 0 0

Big Sandy, Wyoming 0 0 Fossil Basin, Wyoming 0 0

Continental Divide, Wyoming 0 0 Bear Lake Plateau, Utah 0 0

Boars Tusk, Wyoming 0 0

Total 92 1 0 0

Rock samples

South Pass, Wyoming 24 0 Fontenelle, Wyoming 1 1

Big Sandy, Wyoming 5 0 Fossil Basin, Wyoming 1 0

Continental Divide, Wyoming 0 0 Bear Lake Plateau, Utah 5 0

Boars Tusk, Wyoming 0 0

Total 29 0 7 1

Sediment samples

South Pass, Wyoming 48 11 Fontenelle, Wyoming 75 20

Big Sandy, Wyoming 63 20 Fossil Basin, Wyoming 88 7

Continental Divide, Wyoming 5 1 Bear Lake Plateau, Utah 18 1

Boars Tusk, Wyoming 18 2

Total 134 34 181 28
Appendix 4 127

Appendix 4. Table of Oil and Gas Plays and Assessment Units in the 

Southwestern and South-Central Wyoming Study Area, Wyoming, and Bear 

River Watershed Study Area, Wyoming and Utah

This appendix is available online only as an Excel (.xlsx) 

table at http://dx.doi.org/10.3133/sir20165089E. The table 

relates Public Land Survey System (PLSS) townships to U.S. 

Geological Survey (USGS) reports on oil and gas resource 

assessments for assessment units or plays in the Southwestern 

and South-Central Wyoming Sagebrush study area, Wyoming, 

and Bear River Watershed Sagebrush study area, Wyoming 

and Utah. If an assessment was conducted in 1995, then the 

terminology used was “play.” After 1995, the terminology 

became “assessment unit” (AU). In many cases, more than one 

play or AU may be present within a given PLSS township. The 

table lists each PLSS township and the associated play or AU, 

the name of the play or AU, the related USGS publication title, 

and a link to the published USGS geologic assessment report. 

The USGS reports include many additional details regarding 

the source rocks, reservoir rocks, type of trap, reservoir properties, and resource potential.
128 Geology and Mineral Resources of the Southwestern and South-Central Wyoming and Bear River Watershed Sagebrush Focal Areas

Appendix 5. Table of Producing Properties in Southwestern Wyoming and 

Northeastern Utah

This appendix is available online only as an Excel (.xlsx) 

table at http://dx.doi.org/10.3133/sir20165089E. The table 

lists all producing properties in the counties that contain parts 

of the Southwestern and South-Central Wyoming study area, 

Wyoming, and Bear River Watershed study area, Wyoming 

and Utah. This list is derived from a 2011 database of producing properties in the western U.S. from the National Minerals Information Center (Robert Callaghan, written commun., 

March 7, 2016) and supplemented with data from the U.S. 

Forest Service (Roger Kesterson, U.S. Forest Service, written 

commun., March 11, 2016) for properties that are in the Bear 

Lake Plateau block. Only 13 of the 63 properties are within the 

study areas, and 3 of those are within the proposed withdrawal 

area.
Menlo Park Publishing Service Center, California

Manuscript approved on June 27, 2016

Design and layout by Vivian Nguyen
Wilson and others

—Geology and Mineral Resources of the Southwestern and South-Central Wyoming and the Bear River Watershed Sagebrush Focal Area

—Scientific Investigations Report 2016–5089–E, ver. 1.1

ISSN 2328-0328 (online)

http://dx.doi.org/10.3133/sir20165089E