U.S. Department of the Interior

U.S. Geological Survey

Open-File Report 2011–1134

Assessment of Coal Geology, Resources, and Reserves in the 

Southwestern Powder River Basin, Wyoming
Cover. Photograph taken east of Buffalo, Wyoming, showing widespread clinker exposures. Photograph by 

Connie Modzelewski, Buffalo Field Office, Bureau of Land Management, Buffalo, Wyoming.
Assessment of Coal Geology, Resources, 

and Reserves in the Southwestern Powder 

River Basin, Wyoming

ByLee M. Osmonson, David C. Scott, Jon E. Haacke, James A. Luppens, and 

Paul E. Pierce

Open-File Report 2011–1134

U.S. Department of the Interior

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

KEN SALAZAR, Secretary

U.S. Geological Survey

Marcia K. McNutt, Director

U.S. Geological Survey, Reston, Virginia: 2011

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Suggested citation: 

Osmonson, L.M., Scott, D.C., Haacke, J.E., Luppens, J.A., and Pierce, P.E., Assessment of coal geology, resources, and 

reserves in the Southwestern Powder River Basin, Wyoming: U.S. Geological Survey Open-File Report 2011–1134, 

135 p.
iii

Contents

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

Introduction and Objectives ........................................................................................................................1

Previous Coal Resource Estimates.............................................................................................................2

Previous and Current Coal Mining .............................................................................................................3

Other Energy Commodities...........................................................................................................................3

Study Methodology........................................................................................................................................4

Data Collection......................................................................................................................................4

Coal Bed Nomenclature ......................................................................................................................4

Coal Bed Correlations ..........................................................................................................................5

Geologic Setting.............................................................................................................................................5

Geologic Modeling.........................................................................................................................................5

Influence of Geology in Coal Bed Correlations ........................................................................................6

Clinker.....................................................................................................................................................6

Dip of Coal Beds....................................................................................................................................6

Coal Bed Geology...........................................................................................................................................6

Upper Healy Coal Bed........................................................................................................................15

Healy Coal Bed....................................................................................................................................16

Murray Coal Bed.................................................................................................................................16

Ucross Coal Bed..................................................................................................................................16

Felix Coal Bed......................................................................................................................................16

Lower Felix Coal Bed..........................................................................................................................16

Roland (Upper Rider) Coal Bed.........................................................................................................16

Roland (Lower Rider) Coal Bed ........................................................................................................17

Roland of Baker (1929) Coal Bed......................................................................................................17

Smith Coal Bed....................................................................................................................................17

Anderson Coal Bed.............................................................................................................................17

Dietz 3 Coal Bed ..................................................................................................................................17

Upper Canyon Coal Bed.....................................................................................................................17

Canyon Coal Bed.................................................................................................................................18

Lower Canyon Coal Bed ....................................................................................................................18

Werner Coal Bed.................................................................................................................................18

Otter Coal Bed .....................................................................................................................................18

Gates Coal Bed....................................................................................................................................18

Pawnee Coal Bed................................................................................................................................18

Deep 1 Coal Bed..................................................................................................................................19

Deep 2 Coal Bed..................................................................................................................................19

Deep 3 Coal Bed..................................................................................................................................19

Roberts Coal Bed ................................................................................................................................19

Resource Allocation Planning ...................................................................................................................19

Factors Affecting Extraction of Coal Resources ....................................................................................20

Federal Land Systems........................................................................................................................21

Railroads...............................................................................................................................................21
iv

Roads ....................................................................................................................................................21

Dwellings and Buildings ....................................................................................................................21

Alluvial Valley Floors ..........................................................................................................................21

Airports.................................................................................................................................................21

Archaeological Areas .......................................................................................................................22

Coalbed Methane................................................................................................................................22

Oil and Oil-Related Gas Wells...........................................................................................................22

Pipelines...............................................................................................................................................22

Power Lines .........................................................................................................................................22

Rivers, Lakes, and Streams...............................................................................................................22

Towns....................................................................................................................................................22

State Lands ..........................................................................................................................................22

Coal Reserve Evaluation Methodology ....................................................................................................23

Coal Quality..........................................................................................................................................23

Mine Model Design ............................................................................................................................28

Economic Analysis Methodology.....................................................................................................28

Underground Mine Model Assumptions.........................................................................................29

Resources Evaluation ........................................................................................................................31

Surface Coal Economic Analyses Results......................................................................................31

Fort Union Formation.................................................................................................................31

Wasatch Formation ...................................................................................................................32

Underground Coal Economic Analysis Results .............................................................................32

Underground Coal Resources .................................................................................................32

Underground Mining Model Analysis ....................................................................................33

Conclusions...................................................................................................................................................33

Acknowledgments.......................................................................................................................................34

References Cited..........................................................................................................................................35

Glossary.........................................................................................................................................................38

Figures

1–4. Maps showing:

 1. Location of Southwestern Powder River Basin assessment area, Northern 

Wyoming Powder River Basin assessment area, and Gillette coal field, 

Wyoming and Montana. .....................................................................................................40

 2. Coal fields in the Southwestern Powder River Basin assessment area....................41

 3. Areas of coal resources in the Stevens Preference Right Lease Applications 

(PRLA’s) in the Southwestern Powder River Basin assessment area........................42

 4. Drill hole locations in the Powder River Basin, Wyoming............................................43

5. Flow chart showing generalized methodology used during coal resource 

and reserve evaluation. .............................................................................................................44

6. Coal bed and coal zone names used in different publications in the Powder 

River Basin...................................................................................................................................45

7. Generalized geology of the Powder River Basin, Wyoming and Montana.......................46
v

8. Generalized stratigraphic column for the Powder River Basin, Wyoming 

and Montana ...............................................................................................................................47

9. Stratigraphy of coal beds in the southwestern Powder River Basin 

assessment area.........................................................................................................................48

10. Map shwoing location of clinker in the southwestern Powder River 

Basin assessment area .............................................................................................................49

11. Stripping ratios for the Roland Baker and Smith coal beds in the 

southwestern Powder River Basin assessment area. .........................................................50

12–20. Cross sections:

 12. West-east cross section A–A’ through the northern part of the 

 southwestern Wyoming Powder River Basin assessment area showing 

 subsurface coal beds ......................................................................................................51

 13. West-east cross section B–B’ through the north-central part of the 

 southwestern Wyoming Powder River Basin assessment area 

 showing subsurface coal beds ......................................................................................52

 14. West-east cross section C–C’ through the central part of the 

 southwestern Wyoming Powder River Basin assessment area 

 showing subsurface coal beds ......................................................................................53

 15. West-east cross section D–D’ through the south-central part of the 

 southwestern Wyoming Powder River Basin assessment area 

 showing subsurface coal beds ......................................................................................54

 16. West-east cross section E–E’ through the southern part of the 

 southwestern Wyoming Powder River Basin assessment area 

 showing subsurface coal beds ......................................................................................55

 17. South-north cross section F–F’ through the central part of the 

 southwestern Wyoming Powder River Basin assessment area 

 showing subsurface coal beds ......................................................................................56

 18. South-north cross section G–G’ through the northern part of the 

 southwestern Wyoming Powder River Basin assessment area 

 showing subsurface coal beds ......................................................................................57

 19. South-north cross section H–H’ through the south-central part of the 

 southwestern Wyoming Powder River Basin assessment area 

 showing subsurface coal beds ......................................................................................58

 20. South-north cross section I–I’ through the south-eastern part of the 

 southwestern Wyoming Powder River Basin assessment area 

 showing subsurface coal beds ......................................................................................59

21–89. Maps showing:

 21. Isopach map of the Upper Healy coal bed showing extent of resources 

 greater than 2.5 ft thick within the southwestern Powder River 

 Basin assessment area. ...................................................................................................60

 22. Depth to the top of the Upper Healy coal bed within the southwestern 

 Powder River Basin assessment area...........................................................................61

 23. Coal resource reliability categories for the Upper Healy coal bed 

 within the southwestern Powder River Basin assessment area. .............................62

 24. Isopach map of the Healy coal bed showing extent of resources 

 greater than 2.5 ft thick within the southwestern Powder River 

 Basin assessment area. ...................................................................................................63

 25. Depth to the top of the Healy coal bed within the southwestern 

 Powder River Basin assessment area...........................................................................64
vi

 26. Coal resource reliability categories for the Healy coal bed within 

 the southwestern Powder River Basin assessment area. .........................................65

 27. Isopach map of the Murray coal bed showing extent of resources 

 greater than 2.5 ft thick within the southwestern Powder River 

 Basin assessment area. ...................................................................................................66

 28. Depth to the top of the Murray coal bed within the southwestern 

 Powder River Basin assessment area...........................................................................67

 29. Coal resource reliability categories for the Murray coal bed 

 within the southwestern Powder River Basin assessment area. .............................68

 30. Isopach map of the Ucross coal bed showing extent of resources 

 greater than 2.5 ft thick within the southwestern Powder River 

 Basin assessment area. ...................................................................................................69

 31. Depth to the top of the Ucross coal bed within the southwestern 

 Powder River Basin assessment area...........................................................................70

 32. Coal resource reliability categories for the Ucross coal bed 

 within the southwestern Powder River Basin assessment area. .............................71

 33. Isopach map of the Felix coal bed showing extent of resources 

 greater than 2.5 ft thick within the southwestern Powder River 

 Basin assessment area. ...................................................................................................72

 34. Depth to the top of the Felix coal bed within the southwestern 

 Powder River Basin assessment area...........................................................................73

 35. Coal resource reliability categories for the Felix coal bed within 

 the southwestern Powder River Basin assessment area. .........................................74

 36. Isopach map of the Lower Felix coal bed showing extent of 

 resources greater than 2.5 ft thick within the southwestern Powder 

 River Basin assessment area..........................................................................................75

 37. Depth to the top of the Lower Felix coal bed within the 

 southwestern Powder River Basin assessment area. ................................................76

 38. Coal resource reliability categories for the Lower Felix coal 

 bed within the southwestern Powder River Basin assessment area.......................77

 39. Isopach map of the Roland (Upper Rider) coal bed showing 

 extent of resources greater than 2.5 ft thick within the 

 southwestern Powder River Basin assessment area. ................................................78

 40. Depth to the top of the Roland (Upper Rider) coal bed within the 

 southwestern Powder River Basin assessment area. ................................................79

 41. Coal resource reliability categories for the Roland (Upper Rider) 

 coal bed within the southwestern Powder River Basin assessment area..............80

 42. Isopach map of the Roland (Upper Rider) coal bed showing 

 extent of resources greater than 2.5 ft thick within the 

 southwestern Powder River Basin assessment area. ................................................81

 43. Depth to the top of the Roland (Lower Rider) coal bed within the 

 southwestern Powder River Basin assessment area. ................................................82

 44. Coal resource reliability categories for the Roland (Lower Rider) 

 coal bed within the southwestern Powder River Basin assessment area..............83

 45. Isopach map of the Roland Baker (1929) coal bed showing extent 

 of resources greater than 2.5 ft thick within the southwestern 

 Powder River Basin assessment area...........................................................................84

 46. Depth to the top of the Roland Baker (1929) coal bed within the 

 southwestern Powder River Basin assessment area....................................................85
vii

 47. Coal resource reliability categories for the Roland Baker (1929) 

 coal bed within the southwestern Powder River Basin assessment area.............86

 48. Isopach map of the Smith coal bed showing extent of resources 

 greater than 2.5 ft thick within the southwestern Powder River 

 Basin assessment area. ...................................................................................................87

 49. Depth to the top of the Smith coal bed within the southwestern 

 Powder River Basin assessment area...........................................................................88

 50. Coal resource reliability categories for the Smith coal bed 

 within the southwestern Powder River Basin assessment area. .............................89

 51. Isopach map of the Anderson coal bed showing extent of 

 resources greater than 2.5 ft thick within the southwestern 

 Powder River Basin assessment area...........................................................................90

 52. Depth to the top of the Anderson coal bed within the 

 southwestern Powder River Basin assessment area .................................................91

 53. Coal resource reliability categories for the Anderson 

 coal bed within the southwestern Powder River Basin assessment area..............92

 54. Isopach map of the Dietz 3 coal bed showing extent of 

 resources greater than 2.5 ft thick within the southwestern 

 Powder River Basin assessment area...........................................................................93

 55. Depth to the top of the Dietz 3 coal bed within the southwestern 

 Powder River Basin assessment area...........................................................................94

 56. Coal resource reliability categories for the Dietz 3 coal bed 

 within the southwestern Powder River Basin assessment area. .............................95

 57. Isopach map of the Upper Canyon coal bed showing extent of 

 resources greater than 2.5 ft thick within the southwestern 

 Powder River Basin assessment area...........................................................................96

 58. Depth to the top of the Upper Canyon coal bed within the 

 southwestern Powder River Basin assessment area. ................................................97

 59. Coal resource reliability categories for the Upper Canyon 

 coal bed within the southwestern Powder River Basin assessment area..............98

 60. Isopach map of the Canyon coal bed showing extent of 

 resources greater than 2.5 ft thick within the southwestern 

 Powder River Basin assessment area...........................................................................99

 61. Depth to the top of the Canyon coal bed within the southwestern 

 Powder River Basin assessment area................................................................................ 100

 62. Coal resource reliability categories for the Canyon coal bed 

 within the southwestern Powder River Basin assessment area. ...........................101

 63. Isopach map of the Lower Canyon coal bed showing extent 

 of resources greater than 2.5 ft thick within the southwestern 

 Powder River Basin assessment area.........................................................................102

 64. Depth to the top of the Lower Canyon coal bed within the 

 southwestern Powder River Basin assessment area. ..............................................103

 65. Coal resource reliability categories for the Lower Canyon 

 coal bed within the southwestern Powder River Basin assessment area............104

 66. Isopach map of the Werner coal bed showing extent of 

 resources greater than 2.5 ft thick within the southwestern 

 Powder River Basin assessment area.........................................................................105

 67. Depth to the top of the Werner coal bed within the southwestern 

 Powder River Basin assessment area.............................................................................106
viii

 68. Coal resource reliability categories for the Werner coal bed 

 within the southwestern Powder River Basin assessment area. ...........................107

 69. Isopach map of the Otter coal bed showing extent of resources 

 greater than 2.5 ft thick within the southwestern Powder River 

 Basin assessment area. .................................................................................................108

 70. Depth to the top of the Otter coal bed within the southwestern 

 Powder River Basin assessment area.........................................................................109

 71. Coal resource reliability categories for the Otter coal bed 

 within the southwestern Powder River Basin assessment area. ...........................110

 72. Isopach map of the Gates coal bed showing extent of resources 

 greater than 2.5 ft thick within the southwestern Powder River 

 Basin assessment area. .................................................................................................111

 73. Depth to the top of the Gates coal bed within the southwestern 

 Powder River Basin assessment area.........................................................................112

 74. Coal resource reliability categories for the Gates coal bed 

 within the southwestern Powder River Basin assessment area. ...........................113

 75. Isopach map of the Pawnee coal bed showing extent of 

 resources greater than 2.5 ft thick within the southwestern 

 Powder River Basin assessment area.........................................................................114

 76. Depth to the top of the Pawnee coal bed within the southwestern 

 Powder River Basin assessment area.........................................................................115

 77. Coal resource reliability categories for the Pawnee coal bed 

 within the southwestern Powder River Basin assessment area. ...........................116

 78. Isopach map of the Deep 1 coal bed showing extent of resources 

 greater than 2.5 ft thick within the southwestern Powder River 

 Basin assessment area. .................................................................................................117

 79. Depth to the top of the Deep 1 coal bed within the southwestern 

 Powder River Basin assessment area.........................................................................118

 80. Coal resource reliability categories for the Deep 1 coal bed 

 within the southwestern Powder River Basin assessment area. ...........................119

 81. Isopach map of the Deep 2 coal bed showing extent of resources 

 greater than 2.5 ft thick within the southwestern Powder River 

 Basin assessment area. .................................................................................................120

 82. Depth to the top of the Deep 2 coal bed within the southwestern 

 Powder River Basin assessment area.........................................................................121

 83. Coal resource reliability categories for the Deep 2 coal bed 

 within the southwestern Powder River Basin assessment area. ...........................122

 84. Isopach map of the Deep 3 coal bed showing extent of resources 

 greater than 2.5 ft thick within the southwestern Powder River 

 Basin assessment area. .................................................................................................123

 85. Depth to the top of the Deep 3 coal bed within the southwestern 

 Powder River Basin assessment area.........................................................................124

 86. Coal resource reliability categories for the Deep 3 coal bed 

 within the southwestern Powder River Basin assessment area. ...........................125

 87. Isopach map of the Roberts coal bed showing extent of resources 

 greater than 2.5 ft thick within the southwestern Powder River 

 Basin assessment area. .................................................................................................126

 88. Depth to the top of the Roberts coal bed within the southwestern 

 Powder River Basin assessment area.........................................................................127
ix

 89. Coal resource reliability categories for the Roberts coal bed 

 within the southwestern Powder River Basin assessment area. ...........................128

90. Illustration showing the effect of coal bed depth upon restricted resource 

due to mine pit highwall setback requirements ..................................................................129

91. Map of land use restrictions in the southwestern Powder River 

Basin assessment area ...........................................................................................................130

92. Map of coal ownership in the southwestern Powder River Basin assessment area...131

93. Estimated variability of as-received and moist, mineral-matter-free heating 

content values versus depth for the Wyodak-Anderson coal beds in the 

southwestern Powder River Basin assessment area ........................................................132

94. Diagram of typical longwall mining operation.....................................................................133

95. Map showing the areal extent for the Upper Healy and Healy coal beds......................134

96. Map showing the areal extent for the Upper Healy and Healy coal beds......................135

Tables

1. Coal resources reported in millions of short tons by reliability category for the 

southwestern Powder River Basin assessment area ............................................................7

2. Coal resources reported in millions of short tons, by coal ownership 

categories for the southwestern Powder River Basin assessment area .........................10

3. Coal resources reported in millions of short tons by overburden depth for 

the southwestern Powder River Basin assessment area....................................................12

4. Available as-received coal quality data from the Fort Union Formation in the 

southwestern Powder River Basin assessment area ..........................................................25

5. Available as-received coal quality data from the Wasatch Formation in the 

Lake DeSmet area in the southwestern Powder River Basin 

assessment area.........................................................................................................................27

6. Costs by underground mining case for the southwestern Powder River 

Basin assessment area based upon a 20-year project life at an annual 

production rate of 6 million tons per year...............................................................................30

7. Costs of underground longwall mining for the southwestern Powder River 

Basin assessment area based on a 20-year project life at an annual 

production rate of 6 million tons.......................................................................................................30

8. Contingency alternatives for estimating costs for longwall mining...................................30

9. Underground excavation dimensions in the longwall mining model for 

a 10-foot mining height ..............................................................................................................30

10. Available resources for beds greater than or equal to 5.0 foot thick, 

overburden less than or equal to 500 feet, and < 10:1 strip ratio, reported 

in millions of short tons by stripping ratio for the southwestern Powder 

River Basin assessment area ...................................................................................................33

11. Underground coal resources for the southwestern Powder River 

Basin assessment area .............................................................................................................34
x

Abbreviations Used in This Report 

Btu/lb British thermal unit per pound

ft feet

mi mile

mi2 square mile

yr year

BST billion short tons

GIS Geographic Information System

MST million short tons

MST/yr million short tons per year

NWPRB Northern Wyoming Powder River Basin (assessment area)

PRB Powder River Basin

PRLA Preference Right Lease Application

PSO lease area in Sheridan County; part of a land-exchange proposal

SWPRB Southwestern Powder River Basin (assessment area) 

ST short ton

BLM Bureau of Land Management

USGS U.S. Geological Survey

UTM Universal Transverse Mercator

Conversion Factors

Multiply By To obtain

Length

foot (ft) 0.3048 meter (m)

mile (mi) 1.609 kilometer (km)

square mile (mi2

) 2.590 square kilometer (km2)

square feet (ft2

) 0.0929 square meters (m2)

Density

pounds (lbs) 0.4536 kilograms (kg)

short tons (2,000 lbs) 0.9072 metric tons (2,204.6 lbs)

millions of short tons (MST) 1,000,000 short tons

billions of short tons (BST) 1,000,000,000 short tons 

trillions of short tons (TST) 1,000,000,000,000 short tons

Area

acre-ft 1,770 short tons of subbituminous coal
Abstract

The availability of abundant new borehole data from 

recent coal bed natural gas development was utilized by the 

U.S. Geological Survey for a comprehensive evaluation of 

coal resources and reserves in the southwestern part of the 

Powder River Basin in Wyoming. This report on the Southwestern Powder River Basin assessment area represents the 

third area within the basin to be assessed, the first being for 

coal resources and reserves in the Gillette coal field in 2008, 

and the second for coal resources and reserves in the northern 

Wyoming area of the basin in 2010. 

There are no active coal mines in the Southwestern 

Powder River Basin assessment area. The only significant 

production is attributed to the Dave Johnston Mine, in the 

extreme southern part of the area, which accounted for some 

104 million short tons of coal from 1959 to 2000. Several 

small mines were developed in the 1950s near the Lake 

DeSmet area in the northwestern part of the area; however, 

less than 25,000 short tons of coal were produced.

Eight coal beds are present at depths between 1,000 and 

2,000 ft in the Southwestern Powder River Basin assessment 

area. Portions of these coal beds might be recovered by underground mining methods in the future; however, the lack of 

sufficient drill data precluded an economic study to assess the 

potential of surface mineable coal resources. Consequently, 

none of the coal resources in the Southwestern Powder River 

Basin assessment area were designated as reserves or recoverable coal.

A total of 37 coal beds were identified during this assessment, 23 of which were modeled and evaluated to determine 

in-place coal resources. The total original coal resource in the 

Southwestern Powder River Basin assessment area for these 

23 coal beds, with no restrictions applied was calculated to be 

369 billion short tons. Available coal resources, which are part 

of the original resource that is accessible for potential mine 

development after subtracting all restrictions, are about 341 

billion short tons (92.4 percent of the total original resource). 

Approximately 61 percent are at depths between 1,000 

Assessment of Coal Geology, Resources, and Reserves in 

the Southwestern Powder River Basin, Wyoming

By Lee M. Osmonson,1 David C. Scott,1 Jon E. Haacke,1 James A. Luppens,2 and Paul E. Pierce2

and 2,000 ft, with a modeled price of about $30 per short 

ton. Therefore, the majority of coal resources in the Southwestern Powder River Basin assessment area are considered 

sub-economic.

Introduction and Objectives 

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

first digital National Coal Resource Assessment of in-place 

coal resources in 2009 for selected coal beds in the United 

States (Pierce and Dennen, 2009). These estimates do not, by 

themselves, provide all the information needed for resource 

planning. Calculations of that portion of the in-place coal 

resources that are economically recoverable (coal reserves) are 

equally important (Luppens and others, 2008). (Note: Technical terms used in this report requiring additional explanation 

are italicized when used for the first time and their definitions 

are given in the Glossary section at the end of the report.) 

Confusion concerning the use of the terms “coal 

resources” and “coal reserves” is relatively common. The two 

terms have been used interchangeably; however, there are 

significant differences. Coal resources include those in-place 

tonnage estimates determined by summing the volumes for 

identified and hypothetical coal resources and coal zones of a 

minimum thickness and within certain depth limits (commonly 

0–2,000 ft deep). Coal reserves, a subset of the coal resources, 

are considered economically producible at the time of classification (Pierce and Dennen, 2009). Luppens and others 

(2009) discuss the terms “coal resources” and “coal reserves” 

and summarize how coal availability and recoverability studies (CARS) are used to determine estimates of economically 

recoverable coal resources.

Previous estimates (see references in “Previous Coal 

Resource Estimates” section) of coal reserves have typically used average mining percentages to obtain volume 

estimates of recoverable coal. Those estimates are general 

and do not take into consideration the amount of coal that 

cannot be mined because of environmental concerns, geological constraints, coal loss owing to mining and preparation 

technology, or economic constraints. More recently, published 

studies by the USGS have indicated that application of sitespecific restrictions to estimates of available coal resources

1

U.S. Geological Survey, Denver, Colorado 80225

2

U.S. Geological Survey, Reston, Virginia 20192
2 Assessment of Coal Geology, Resources, and Reserves in the Southwestern Powder River Basin, Wyoming

significantly reduces the amount of coal that is considered 

recoverable (Ellis and others, 2002).

The current USGS coal assessment project is the Powder River Basin (PRB) located in northeastern Wyoming and 

southeastern Montana (fig. 1). The PRB was subdivided into 

four areas to keep the databases and modeled areas to a more 

manageable size and permit a more timely publication of 

assessment results. Luppens and others (2008) summarized the 

first area that contained coal resource and reserve estimates for 

the Gillette coal field (fig. 1). Scott and others (2010) summarized the second area that contained coal resource and reserve 

estimates for the Northern Wyoming Powder River Basin 

assessment area (NWPRB) (fig. 1). 

This report summarizes the third area within the PRB 

and covers an area of approximately 4,750 square miles (mi2

) 

in the southwestern part of the PRB in portions of Johnson, 

Campbell, Converse, Natrona, and Niobrara Counties, Wyoming. The assessment area extends from the southern boundary of the NWPRB assessment area to the southern margin of 

the PRB, and eastward to the western boundary of the Gillette 

coal field (fig. 1). This part of the PRB is referred to in this 

report as the Southwestern Powder River Basin (SWPRB) 

assessment area. The fourth area to be assessed will be the 

Montana portion of the PRB. 

Reliable coal resource and reserve estimates of these 

areas are essential for use in local, State, and Federal energy 

and land-use policy decisions for the foreseeable future. 

Additionally, this information can aid planners in determining the possible socio-economic effects on the region as coal 

resources are developed and eventually approach depletion 

(Luppens and others, 2008). 

Coal availability and recoverability studies in the United 

States have previously relied on reinterpretation of existing 

data. Because of the recent development of coalbed methane 

in Wyoming and Montana, substantial volumes of new data 

from drill holes are now available. The interpretation of these 

new data provides a more accurate view of the coal resources 

and reserves in the PRB. 

The primary objectives of this assessment were as 

follows:

1. Complete the third regional coal resource and 

reserve assessment in the PRB.

2. Improve geological assurance by updating the current stratigraphic database with information obtained 

from recently completed coalbed methane and oil 

and gas wells.

3. Develop a more comprehensive in-place coal 

resource computer model with the geological assurance to support regional reserve estimates.

4. Complete an economic mining evaluation that was 

customized to the environmental and technological 

restrictions in the SWPRB assessment area and 

derive a regional estimate of coal resources and 

reserves.

5. Complete the coal assessment for the Wyoming 

portion of the PRB.

Previous Coal Resource Estimates

Previous studies contain estimates of coal resources and 

reserves in the SWPRB assessment area as well as the other 

portions of the PRB. These studies have included different 

coal beds, coal zones, and boundaries, and have different 

purposes for which resources and reserves were calculated. 

Differences in criteria, such as variations in coal thickness and 

overburden categories have been used for those calculations 

(Luppens and others, 2008).

1. Mapel (1954) estimated 3 billion short tons (BST) 

of coal reserves in the Buffalo-Lake DeSmet area 

in beds more than 2.5 ft thick and under less than 

1,000 ft of overburden (fig. 2). Several years later, 

Mapel (1959) estimated total coal reserves in the 

Buffalo-Lake DeSmet area in beds more than 2.5 ft 

thick and under less than 1,000 ft of overburden at 

about 6.4 BST. 

2. Remaining strippable subbituminous coal reserves 

in several coal fields in the SWPRB assessment area 

were estimated by Smith (1972) and modified by 

Glass (1976). The Buffalo-Lake DeSmet area was 

estimated to contain about 1 BST; the Dry Cheyenne 

coal field was estimated to contain about 180 million 

short tons (MST); and the Sussex coal field was 

estimated to contain about 13 MST (fig. 2) (Glass, 

1976). 

3. In 1980, Glass estimated remaining strippable coal 

reserves at the Dave Johnston Mine in the Glenrock 

coal field at 91 MST (fig. 2) (Glass, 1980).

4. A report detailing the Final Environmental Assessment of the Belco—Bureau of Land Management 

(BLM) Coal Lease Exchange indicated that the 

Belco area, located just southeast of Buffalo, 

Wyoming contained between 137 and 185 MST of 

minable coal at a stripping ratio of 5:1 or less. The 

minable coal beds in the Belco area are the Healy 

and Ucross (fig. 2) (U.S. Bureau of Land Management, 1999).

5. In 1983, a report was submitted to the BLM for 

the lease acquisition of Preference Right Lease 

Applications (PRLA’s) known as the Stevens North 

(W-12767, W-14390, W-14392), and the Stevens 

South (PRLA W-14355) (Western Fuels Association, 

Inc., 1983). These four PRLA’s form one unit and 

are collectively known as the Stevens Project Area. 

In-place coal resources were estimated to be 625.3 

MST for the entire area (figs. 2 and 3). 
Other Energy Commodities 3

As documented in these various estimates, resource and 

reserve estimates change as more data becomes available 

therefore, it is possible to refine previous resource and reserve 

estimates. These new estimates prove the usefulness of periodically recalculating coal resources and reserves. Because of the 

availability of new data, economic coal recoverability calculations in this report are significant refinements of previous coal 

resource and reserve studies in the SWPRB assessment area. 

Previous and Current Coal Mining 

In 1883, coal mining in the PRB began near the towns 

of Glenrock and Douglas, Wyoming (Ellis and others, 2002) 

(fig. 1). The subsequent development of railroad lines in 1886 

and 1887 significantly influenced the growth of coal mining activity in the area (Ellis and others, 2002). The Barber, 

Buffalo, Dry Cheyenne, Glenrock, Lost Spring, Powder 

River, Pumpkin Buttes, and Sussex coal fields are all within 

the boundary of the SWPRB assessment area (fig. 2) (Glass, 

1976). The first documented coal mining in the SWPRB 

assessment area began in the Buffalo coal field around the 

year 1900 (Mapel, 1959). Mapel (1959) defined a 640 mi2

 area 

and referred to it as the Buffalo-Lake DeSmet area (fig. 2). 

Between 1919 and 1950 several small mines were operated 

in the Lake DeSmet area, but with only minor production 

amounts. Approximately 19,000 short tons (ST) of coal were 

produced from the Kreselok Mine in section 2, T. 53 N., R. 

82 W. (fig. 2). A small strip mine was also operated in 1951 in 

section 3, T. 52 N., R. 82 W. (fig. 2), with recorded production 

of about 4,000 ST (Mapel, 1959). Total production from the 

Buffalo-Lake DeSmet area was less than 25,000 ST.

The only significant production in the SWPRB assessment area came from the Dave Johnston Mine in the Glenrock 

coal field (fig. 2). From 1958 to 2000, 104 MST of coal were 

produced from surface mining operations (Nick Jones, written 

commun., 2010). Reclamation began in 2000 after the mine 

was closed and was completed in 2005. A wind farm now 

occupies much of the reclaimed Dave Johnston Mine site. 

There is no current coal mining or production in the SWPRB 

assessment area.

Other Energy Commodities

Conventional oil and gas, along with coalbed methane 

are currently being developed in the SWPRB assessment area. 

Methane, however, is discussed as a separate gas resource 

because there are potential conflicts and concerns specific to 

its development that do not apply to conventional oil and gas 

development. 

Powder River Basin oil and gas development began in 

1887 with the discovery of an oil and gas field near Moorcroft, 

Wyoming (Ellis and others, 2002; fig. 1). According to the 

Wyoming Oil and Gas Conservation Commission, 1,370 oil 

and gas wells were reported within the SWPRB assessment 

area as of January, 2010 (Wyoming Oil and Gas Conservation 

Commission, 2009) (fig. 4). Generally, there is little conflict 

between coal development and conventional oil and gas 

development in the SWPRB assessment area, as oil and gas 

reservoirs are primarily in stratigraphic units below minable 

coal beds. 

Coalbed methane development in the PRB began in the 

early 1980s and as of January, 2010, 8,273 wells had been 

drilled in the SWPRB assessment area (fig. 4) (Wyoming Oil 

and Gas Conservation Commission, 2009). In 2003, an Environmental Impact Statement contained an analysis of potential 

impacts based on the assumption that by the year 2012 there 

will be about 51,000 producing private, State, and Federal 

coalbed methane wells and associated ancillary facilities in 

an almost 8 million acre area covering all or parts of Campbell, Converse, Johnson, and Sheridan Counties, Wyoming 

(U.S. Bureau of Land Management, 2003). Production life of 

coalbed methane wells is estimated to be about 10 to 12 yr, 

although production from multiple seams can extend the life 

of the well by an additional 10 to 30 yr (De Bruin and others, 

2004).

To produce coalbed methane, groundwater is pumped 

from the coal bed and can be discharged to holding ponds for 

consumption by livestock, discharged to existing drainage 

systems, released into the atmosphere through the use of misting towers, or re-injected into stratigraphic units. Concerns 

regarding possible contamination of existing surface water, 

the quality of water in holding ponds, the production of saline 

crust on the ground surface, the lowering of the water table, 

and possible contamination or depletion of groundwater in 

existing aquifers have all been examined in the PRB by Rice 

and others (2000). 

Conflicts have arisen between coal mining and coalbed 

methane development. One conflict involves the ownership of 

coalbed methane whether it belongs to the owner of the oil and 

gas estate or the owner of the coal estate. The U.S. Supreme 

Court resolved this issue in 1999, when it ruled that coalbed 

methane is part of the oil and gas estate (Supreme Court of 

the United States, Amoco Production Co. vs. Southern Ute 

Tribe (98-830), 526, U.S. 865 (1999)). In addition, the court 

that specified the owner of the coalbed methane leases has the 

right to gain access and to develop its estate, and owners of the 

land surface should be adequately compensated for damage 

to their property resulting from coalbed methane extraction. 

The Bureau of Land Management has established Conflict 

Administration Zones to guide the development of coalbed 

methane leases in the path of near-term coal mining. In these 

zones, standard guidelines offer a process for settling conflicts 

and scheduling development of each resource under a Federal 

mineral estate.
4 Assessment of Coal Geology, Resources, and Reserves in the Southwestern Powder River Basin, Wyoming

Study Methodology

The methodology for calculating coal resources and 

reserves in the SWPRB assessment area is described by the 

three phases shown on the flow chart in figure 5. The first 

phase began with data collection and editing as a result of the 

acquisition of recently acquired geologic information. The 

second phase involved correlating coal beds, geologic modeling of those beds, resource allocation to determine land use, 

and technological restrictions within the SWPRB assessment 

area. The third phase involved completing a mining economics 

evaluation to determine coal reserves. 

Data Collection

This report completes data collection and data interpretation for the Wyoming portion of the PRB. Over 44,750 wells 

have been drilled in the Wyoming portion of the PRB, of 

which, 18,370 drill holes were used to construct the database (fig. 4). This total represents oil and gas wells, coalbed 

methane wells, and coal exploration drill holes. Because of 

the huge volume of data, data not available for use, and data 

that were incomplete, only about 40 percent of the total was 

used. A total of 10,210 data points were used in the Gillette 

coal field report; 4,003 data points were used in the NWPRB 

assessment area report, and 4,157 data points were used in this 

report. 

The database of Luppens and others (2008) was used as 

a basis for coal bed correlations along the eastern boundary of 

the SWPRB assessment area. Correlations from the NWPRB 

assessment area (Scott and others, 2010) were used as a basis 

for coal bed correlations in the northern part of the SWPRB 

assessment area.

 As of September 2009, approximately 1,370 oil and gas 

wells and 8,273 coalbed methane wells had been drilled in 

the SWPRB assessment area. Data within a three-mile-wide 

buffer zone were added around the assessment area’s boundary to extend stratigraphic correlations and to minimize the 

edge effect when the coal beds were modeled. The drill hole 

geophysical logs selected for data entry were downloaded as 

TIFF images from the Wyoming Oil and Gas Conservation 

Commission web site (2009). USGS personnel completed 

data entry for a total of 3,131 new geophysical well logs. In 

addition, the Wyoming State Geological Survey contributed 

519 data points, and the USGS National Coal Resources Data 

System contributed 507 data points. The entire 4,157 data 

points were then entered into the StratiFact® database program 

for use in stratigraphic correlation (GRG Corporation, 1998). 

Because the geophysical logs differ widely in quality 

and resolution, the interpretation of coal thickness is generally 

difficult. Gamma-ray logs were available for most of the wells 

and constituted the basis for most of the lithologic interpretation. Traditionally, oil and gas wells were logged primarily 

for detail in deep formations, and the upper (coal-bearing) 

intervals were either not logged or minimally gamma logged 

through the surface casing. Log data in older wells usually 

consisted only of spontaneous potential, resistivity and conductivity logs, making the identification of coal beds more difficult. The most reliable log suite consisted of natural gamma, 

gamma-gamma density, and resistivity traces. However, many 

coalbed methane wells were logged with gamma only, either 

in open hole or through steel drill pipe or casing. Additionally, 

many of those methane wells were logged with gamma ray 

only to the top of the target coal.

The primary focus of this report was to determine coal 

resources and reserves rather than to conduct a comprehensive geological study; therefore, detailed non-coal lithology 

types were not critical to the results of this evaluation. As a 

result, all lithology was coded as either coal or rock. Parting

intercepts within coal beds and interburden between coal beds 

were also coded as rock. Intervals with no geophysical log 

such as the shallower part of an oil well or coalbed methane 

well that was not logged to the bottom, were entered as “No 

Log.” However, if the methane-producing interval was available from production records, that interval was entered as coal.

Coal Bed Nomenclature

Correlation of individually named coal beds and coal 

zones across the entire PRB has been difficult, because the 

beds commonly split, merge, and pinch out (Flores and others, 

1999). Also, in the past, distances between individual drill 

holes were often large (on the scale of 5–10 mi) increasing the 

uncertainty in correlating coal beds from one drill hole to the 

next. However, with the exploratory drilling and development 

of coalbed methane in the PRB, data from thousands of new 

drill holes are now available, and the distance between drill 

holes is thus reduced (fig. 4). 

Many different names for individual coal beds and coal 

zones in the PRB have been used during the past 30 yr (fig. 6). 

A report by Kent and others (1980), who described the northern part of the Gillette coal field that falls within the Spotted Horse coal field of Olive (1957), established a coal bed 

nomenclature system that has become the standard for much 

of the PRB in Wyoming. Kent and others (1980) retained certain existing coal bed nomenclature and revised other nomenclature by introducing new coal bed names. Molnia and Pierce 

(1992) also described coal bed stratigraphy in the central PRB 

in Wyoming and Montana; their nomenclature follows the 

usage of Culbertson and others (1979), Law and others (1979), 

Kent and others (1980), and Culbertson (1987). Flores and 

others (1999) defined a coal zone in the PRB known as the 

Wyodak-Anderson, which includes many named coal beds in 

the upper part of the Tongue River Member of the Fort Union 

Formation. The bed names used in this report and the equivalent names used in previous reports are found in figure 6. For 

this assessment, resource calculations for individual coal beds 

composing the Wyodak-Anderson zone included the Smith, 

Anderson, Lower Anderson, Dietz 3, Upper Canyon, Canyon, 

Lower Canyon, and Werner. The stratigraphic framework for 
Geologic Modeling 5

coal bed correlations in this report is based on the work of 

Luppens and others (2008), and Scott and others (2010).

Coal Bed Correlations

When all the drill hole data entry was completed, the 

graphical interface of the StratiFact (GRG Corporation, 1998) 

database was a critical tool for managing the interpretation of 

the large volume of information. With the StratiFact program, 

on-screen cross sections were selected, edited, and correlated. 

Both linear and circular cross sections were constructed to correlate coal beds across the SWPRB assessment area. Circular 

cross sections that verify closure were especially valuable 

when coal beds either split or thinned adjacent to sand channels. In this process, the beginning and ending drill holes of 

the cross section are the same, assuring that the coal beds do 

not cross each other. 

Coal bed nomenclature used by Luppens and others 

(2008) in the Gillette coal field report and Scott and others 

(2010) in the Northern Wyoming Powder River Basin assessment report was used as a basis for correlating and naming 

coal beds between those two areas. Guidelines were established regarding which nomenclature would be used when two 

named beds merge into a single bed. The general correlation 

guidelines used for this assessment are as follows:

• Two named beds are considered to have merged into 

a single named bed when the intervening parting was 

less than 2.0 ft thick. The following exceptions have 

been made for modeling purposes:

• In individual holes, coal beds split by partings as 

much as 5 ft thick are considered to be merged if 

surrounding holes indicate the beds have merged 

into a single bed.

• In individual holes, coal beds with no partings or 

partings less than 2.0 ft thick are considered to be 

split into two beds if surrounding holes show the 

coal has split into two beds.

• The upper bed’s name will be used for the merged-bed 

name with one exception:

• A rider name becomes the main bed name; for 

example Roland (Baker, 1929) bed merged with 

Roland (Upper Rider) bed becomes Roland 

(Baker, 1929) bed.

Geologic Setting

The PRB covers about 22,000 mi2 in northeastern 

Wyoming and southeastern Montana (fig. 7). Near the west 

margin of the basin, the axis trends northwest-southeast and is 

distinctly asymmetrical with steep dips on the west side and 

gentle dips on the east (fig. 7). The Eocene Wasatch Formation 

covers about one-third of the PRB, mostly in Wyoming, and 

the underlying Paleocene Fort Union Formation is exposed 

along the basin margins in Wyoming and throughout most 

of the basin in Montana (figs. 7, 8). The Wasatch Formation 

conformably overlies the Fort Union Formation in the center 

of the basin and unconformably overlies it along the basin 

margins (fig. 8). The boundary between the two formations is 

generally placed above the Roland coal bed (fig. 8) (Flores and 

others, 1999). Rocks in the Fort Union Formation lie unconformably on the Upper Cretaceous Lance Formation (fig. 8). 

The Fort Union Formation in Wyoming is made up of three 

members, from upper to lower: the Tongue River Member, 

the Lebo Member, and the Tullock Member (fig. 8) (Ellis and 

others, 2002). The Fort Union Formation contains some of the 

thickest and most extensive deposits of subbituminous coal in 

the world (Molnia and Pierce, 1992). Most of this coal is in 

the Wyodak-Anderson coal zone in the Tongue River Member 

(Flores and others, 1999). The Wyodak-Anderson coal zone is 

equivalent to the following coal beds identified in this report 

(from youngest to oldest): Smith, Anderson, Lower Anderson, 

Dietz 1, Dietz 2, Dietz 3, Dietz 4, Canyon, Lower Canyon, 

Ferry, and Werner (figs. 6 and 9). 

In general, Fort Union Formation coals range from subbituminous C to subbituminous A in apparent rank. The lower 

rank subbituminous C coal is located primarily in the shallower part of the basin (surface to 1,000-ft depth), the subbituminous B ranked coal is at an intermediate depth in the basin 

(1,000–1,400-ft depth), and subbituminous A ranked coal is 

in the deepest part of the basin (greater than 1,400-ft depth) 

(Stricker and others, 2007).

The SWPRB assessment area encompasses an area of 

about 5,585 mi2

 in the western and southern parts of the PRB 

in Wyoming (fig. 7). The eastern boundary of the SWPRB 

assessment area is the western boundary of the Gillette coal 

field as defined by Luppens and others (2008). The northern boundary of this assessment area is part of the southern 

boundary of the NWPRB assessment area defined by Scott 

and others (2010). The western and southern boundaries of 

the SWPRB assessment area are defined by the contact of the 

Tertiary age rocks (fig. 7). Along the western edge of the PRB, 

strata dip between 20° and 25° to the east, whereas strata dip 

only about 2° to 5° to the west along the eastern edge of the 

basin (Flores and others, 1999). Surface coal mining has been 

more prevalent along the eastern margin of the basin because 

of the shallower dip of the coal beds.

Geologic Modeling

The first step of phase two of the assessment (fig. 5) was 

the creation of a digital coal bed model. Following coal bed 

correlations, preliminary coal isopach maps were created using 

the single bed mapping software Surfer® (Golden Software, 

2002) to decide which coal beds would be included in the 

geological model. The basic criterion for inclusion of a coal 

bed was a minimum areal continuity of two or more townships. Twenty-three coal beds were selected and digital models 
6 Assessment of Coal Geology, Resources, and Reserves in the Southwestern Powder River Basin, Wyoming

for each bed were constructed. The integrated, multi-bed 

modeling program PC/Cores® (Mentor Consultants, 2005) was 

used to produce the gridded geologic models. This modeling 

program was designed for coal or mineral evaluations and is 

more effective because of its capability to grid multiple beds at 

one time. The multiple gridding software allows for a considerable reduction in time when compared with other programs 

that grid only one parameter at a time. 

The time required to produce all the required grids using 

a program that generates grids one parameter at a time can be 

large, considering that for each coal bed grids must be made 

for coal thickness, parting thickness, coal thickness (coal plus 

parting), and roof and floor structures. Then, grids must be 

calculated for the overburden and interburden for each seam, 

and then the roof grids for each coal bed must be individually 

subtracted from the surface grid or the floor grid for the next 

stratigraphically higher coal bed.

Most multiple-bed modeling programs are highly automated with a subroutine that uses individual coal bed structure 

grids to check for drill holes too shallow to penetrate a given 

bed. This feature produces more-accurate digital models 

without the need for extensive manual editing. The PC/Cores

program code allows correlations to pass through the sections 

of the drill holes that were not geophysically logged to reduce 

the generation of false zero-thickness values.

The geologic models were gridded at a cell size of 150 m 

(about 500 ft). To verify coal bed correlations and coal bed 

areal distributions, preliminary roof and floor contour maps 

for each modeled bed were generated to check for “bull’s eye” 

anomalies. A routine within the PC/Cores modeling program 

was used to identify suspect locations by comparing collar elevations to the digital elevation model of the Earth’s surface. A 

number of location errors were resolved using this technique.

Once the editing was completed, the final geologic model 

was created and all the grids necessary for determination of 

the in-place coal resource volumes were generated. A copy 

of the in-place coal resources model was modified to generate the grids necessary for the coal reserve evaluation. The 

basic assumption used to qualify coal beds for potential coal 

reserve evaluation was to include coal beds that had a thickness of 2.5 ft or greater. A final set of grids from both the coal 

resources and reserves models (thickness, parting thickness, 

and roof and floor structures) for each coal bed were converted 

in PC/Cores to a generic ASCII grid format. These ASCII 

grids were then exported to the software program ArcView® 

Spatial Analyst (ESRI, 2001) to begin the last step in phase 

two of the assessment which was the modeling of the restrictions to mining. 

Influence of Geology in Coal Bed 

Correlations 

It is important to address the influence of geology as it 

relates to resources, reserves, and potential mining of the coal 

beds. The calculation of recoverable resources and reserves, 

for example, requires the identification of geological constraints that are likely to inhibit mining (Thomas, 2002). Such 

constraints in the SWPRB assessment area include clinker and 

dip of the coal beds. 

Clinker

Coates and Heffern (1999) identified an area of about 

110 mi2 in the Lake DeSmet area that contains clinker (fig. 10) 

formed by the burning of the Lake DeSmet coal zone in the 

Wasatch Formation. The Lake DeSmet coal zone was originally correlated with the Healy coal bed (Mapel, 1959; Culbertson and Mapel, 1976). However, Obernyer (1978) indicated 

that the Lake DeSmet coal zone at Lake DeSmet represents 

the coalescing of five individual coal beds. From oldest to 

youngest, these are the Ucross, Murray, Cameron, Healy, and 

Walters (Glass and Jones, 1992). The depression of Lake DeSmet is thought to have been formed by the natural burning of 

this coal bed, causing subsidence of the land surface (Mapel, 

1959).

Clinker is not considered a technical or land use restriction to mining in this report. However, clinker was included 

in the original resource calculation for each coal bed and later 

subtracted from each coal bed total to calculate the available 

coal resource. 

Dip of Coal Beds

Another important factor in the evaluation of the 

resources and reserves in the SWPRB assessment area is the 

dip of the coal beds. As previously mentioned, the PRB is 

an asymmetrical basin with a northwest trending axis parallel to the western margin of the basin. Coal beds dip between 

20° and 25° to the east along the western margin of the basin, 

whereas strata dip only about 2° to 5° to the west along the 

eastern margin of the basin. Stripping ratios for present surface 

mining along the eastern margin of the basin are between 1:1 

and 3:1. Figure 11 shows the strip ratio for the Roland (Baker, 

1929), Smith, Anderson, Dietz 3, Canyon, Lower Canyon, and 

Werner coal beds. 

In summary, the calculation of recoverable resources 

and extractable reserves is dependent on the identification of 

geological constraints that are likely to inhibit mining. In the 

SWPRB assessment area, these geological constraints include 

the identification and location of clinker, and the dip of the 

coal beds. 

Coal Bed Geology

During this evaluation thirty seven coal beds were identified in the SWPRB assessment area (fig. 9). Of that total, 23 

beds were assessed for resource calculations (tables 1, 2, 3). 
Coal Bed Geology 7

Table 1. Coal resources reported in millions of short tons by reliability category for the Southwestern Powder River Basin 

assessment area. Resource includes coal plus partings. Reliability categories are based on distance from data point. Measured: < 

1/4 mile; Indicated: 1/4-3/4 mile; Inferred: 3/4-3.0 miles; Hypothetical: > 3.0 miles. Totals may not sum exactly due to 

rounding.

Coal 

bed

name

Reliability

category

Original

resources

> 2.5 feet thick

Previously

mined

Land Use

restrictions

Technical

 restrictions

Available

resources

Percent of 

total original 

resource

Healy 

(Upper) 

Measured 461 0 34 13 414 8.5

Indicated 1,661 0 188 47 1,407 28.9

Inferred 2,581 0 624 299 1,658 34.1

Hypothetical 182 0 31 128 23 0.5

Total 4,865 0 877 487 3,502 72.0

Healy Measured 1,002 0 70 17 915 9.8

Indicated 3,331 0 393 55 2,883 30.8

Inferred 4,805 0 1,092 217 3,496 37.3

Hypothetical 234 0 81 60 93 1.0

Total 9,373 0 1,636 350 7,387 78.8

Murray Measured 242 0 2 177 63 4.2

Indicated 498 0 10 328 161 10.9

Inferred 706 0 18 503 184 12.4

Hypothetical 39 0 5 30 0 0.0

Total 1,481 0 35 1,038 408 27.5

Ucross Measured 242 0 22 28 192 3.9

Indicated 1,063 0 100 55 908 18.3

Inferred 3,231 0 661 224 2,346 47.4

Hypothetical 416 0 133 48 235 4.7

Total 4,952 0 916 354 3,381 74.3

 Felix Measured 1,249 0 16 66 1,167 26.0

Indicated 2,208 0 26 134 2,048 45.5

Inferred 939 0 12 207 720 16.0

Hypothetical 102 0 0 76 26 0.6

Total 4,497 0 54 482 3,960 88.1

Felix

(Lower)

Measured 1,288 0 21 435 832 7.8

Indicated 2,956 0 76 844 2,036 19.1

Inferred 5,632 0 568 476 4,589 43.0

Hypothetical 807 0 134 81 591 5.5

Total 10,683 0 798 1,837 8,048 75.3

Roland

(Upper

Rider)

Measured 2,164 0 7 591 1,565 25.6

Indicated 3,052 0 7 962 2,083 34.0

Inferred 885 0 31 378 476 7.8

Hypothetical 18 0 0 18 0 0.0

Total 6,118 0 45 1,949 4,124 67.4

Roland

(Lower

Rider)

Measured 680 0 0 205 475 21.8

Indicated 1,084 0 0 278 807 37.1

Inferred 412 0 0 151 261 12.0

Hypothetical 0 0 0 0 0 0.0

Total 2,177 0 0 634 1,543 70.9
8 Assessment of Coal Geology, Resources, and Reserves in the Southwestern Powder River Basin, Wyoming

Table 1. Coal resources reported in millions of short tons by reliability category for the Southwestern Powder River Basin 

assessment area. Resource includes coal plus partings. Reliability categories are based on distance from data point. Measured: 

< 1/4 mile; Indicated: 1/4-3/4 mile; Inferred: 3/4-3.0 miles; Hypothetical: > 3.0 miles. Totals may not sum exactly due to 

rounding.—Continued 

Coal 

bed

name

Reliability

category

Original

resources

> 2.5 feet thick

Previously

mined

Land Use

restrictions

Technical

 restrictions

Available

resources

Percent of 

total original 

resource

Roland of

Baker

(1929)

Measured 2,122 0 62 416 1,644 16.9

Indicated 4,053 0 50 606 3,397 34.9

Inferred 3,453 0 54 456 2,944 30.3

Hypothetical 98 0 1 92 5 0.1

Total 9,727 0 167 1,570 7,990 82.1

Smith Measured 27,262 12 7 86 27,157 30.9

Indicated 47,532 0 42 299 47,190 53.8

Inferred 12,676 0 309 618 11,749 13.4

Hypothetical 275 0 131 70 75 0.1

Total 87,745 12 490 1,073 86,171 99.2

Anderson Measured 2,596 0 26 129 2,440 26.4

Indicated 4,757 0 15 350 4,391 47.5

Inferred 1,883 0 0 304 1,579 17.1

Hypothetical 17 0 0 0 17 0.2

Total 9,253 0 41 784 8,428 91.1

Dietz 3 Measured 3,643 0 24 52 3,567 29.7

Indicated 5,456 0 15 157 5,284 44.1

Inferred 2,885 0 0 342 2,543 21.2

Hypothetical 7 0 0 7 0 0.0

Total 11,992 0 39 558 11,395 95.0

Canyon 

(Upper)

Measured 807 0 2 26 788 15.0

Indicated 1,834 0 13 71 1,750 33.7

Inferred 2,420 0 80 317 2,024 39.0

Hypothetical 131 0 3 84 44 0.8

Total 5,192 0 98 498 4,596 88.5

Canyon Measured 19,178 0 6 42 19,130 29.0

Indicated 30,919 0 31 131 30,757 46.6

Inferred 14,748 0 278 402 14,067 21.3

Hypothetical 1,105 0 104 64 937 1.4

Total 65,951 0 420 639 64,891 98.4

Canyon 

(Lower)

Measured 7,123 0 20 71 7,032 23.9

Indicated 14,884 0 29 238 14,617 49.8

Inferred 7,052 0 84 421 6,547 22.3

Hypothetical 310 0 2 162 145 0.5

Total 29,368 0 136 892 28,341 96.5

Werner Measured 1,564 0 7 126 1,432 13.0

Indicated 4,295 0 37 427 3,830 34.8

Inferred 4,685 0 253 475 3,958 35.9

Hypothetical 473 0 70 52 351 3.2

Total 11,017 0 367 1,080 9,571 86.9
Coal Bed Geology 9

Table 1. Coal resources reported in millions of short tons by reliability category for the Southwestern Powder River Basin 

assessment area. Resource includes coal plus partings. Reliability categories are based on distance from data point. Measured: 

< 1/4 mile; Indicated: 1/4-3/4 mile; Inferred: 3/4-3.0 miles; Hypothetical: > 3.0 miles. Totals may not sum exactly due to 

rounding.—Continued

Coal 

bed

name

Reliability

category

Original

resources

> 2.5 feet thick

Previously

mined

Land Use

restrictions

Technical

 restrictions

Available

resources

Percent of 

total original 

resource

Otter Measured 6,314 0 43 69 6,202 21.8

Indicated 14,452 0 36 211 14,205 49.8

Inferred 7,686 0 4 499 7,183 25.2

Hypothetical 62 0 0 62 0 0.0

Total 28,514 0 83 841 27,591 96.8

Gates Measured 2,350 0 6 92 2,252 10.8

Indicated 8,388 0 18 294 8,075 38.6

Inferred 9,766 0 128 489 9,148 43.7

Hypothetical 426 0 33 52 341 1.6

Total 20,929 0 185 927 19,817 94.7

Pawnee Measured 219 0 0 47 172 5.6

Indicated 845 0 0 179 665 21.8

Inferred 1,790 0 0 393 1,398 45.8

Hypothetical 194 0 14 65 115 3.8

Total 3,049 0 14 685 2,351 77.1

Deep 1 Measured 1,323 0 2 106 1,215 12.8

Indicated 4,624 0 2 347 4,275 44.9

Inferred 3,574 0 0 373 3,201 33.6

Hypothetical 0 0 0 0 0 0.0

Total 9,521 0 4 826 8,691 91.3

Deep 2 Measured 770 0 0 140 629 8.3

Indicated 2,664 0 2 528 2,133 28.2

Inferred 3,827 0 28 872 2,927 38.7

Hypothetical 297 0 0 47 250 3.3

Total 7,557 0 30 1,587 5,940 78.6

Deep 3 Measured 1,397 0 1 100 1,296 9.3

Indicated 5,462 0 2 414 5,055 36.4

Inferred 6,915 0 2 921 5,992 43.1

Hypothetical 119 0 0 51 69 0.5

Total 13,903 0 6 1,486 12,412 89.3

Roberts Measured 836 0 1 62 772 6.9

Indicated 3,578 0 3 245 3,330 29.7

Inferred 6,683 0 11 654 6,018 53.6

Hypothetical 131 0 0 61 70 0.6

Total 11,229 0 16 1,022 10,191 90.8

Total beds Measured 84,832 12 379 3,099 81,342 22.0

Indicated 169,588 0 1,098 7,201 161,288 43.7

Inferred 109,235 0 4,238 9,988 95,009 25.7

Hypothetical 5,440 0 742 1,310 3,389 0.9

Total 369,095 12 6,458 21,597 341,029 92.4
10 Assessment of Coal Geology, Resources, and Reserves in the Southwestern Powder River Basin, Wyoming

Table 2. Coal resources reported in millions of short tons, by coal ownership categories for the Southwestern Powder River Basin 

assessment area. Resource includes coal plus partings. Totals may not sum exactly due to rounding.

Coal 

bed

name

Coal

ownership

Original

resources

> 2.5 feet thick

Previously

mined

Land Use

restrictions

Technical

restrictions

Available

resources

Percent of 

total original 

resource

Healy (Upper) Federal 3,139 0 268 264 2,607 53.6

State 499 0 76 63 359 7.4

Private 1,228 0 532 160 536 11.0

Total 4,865 0 877 487 3,502 72.0

Healy Federal 5,607 0 490 166 4,951 52.8

State 1,186 0 175 64 847 9.0

Private 2,679 0 971 120 1,589 17.0

Total 9,373 0 1,636 350 7,387 78.8

Murray Federal 977 0 15 695 277 18.7

State 173 0 5 119 39 2.6

Private 331 0 16 224 91 6.1

Total 1,481 0 35 1,038 408 27.5

Ucross Federal 2,227 0 205 218 1,803 36.4

State 650 0 75 53 522 10.5

Private 2,075 0 636 83 1,356 27.4

Total 4,952 0 916 354 3,681 74.3

Felix Federal 4,013 0 54 342 3,617 80.4

State 251 0 0 31 220 4.9

Private 233 0 1 109 123 2.7

Total 4,497 0 54 482 3,960 81.1

Felix (Lower) Federal 7,206 0 147 1,548 5,511 51.6

State 1,063 0 84 114 865 8.1

Private 2,415 0 567 175 1,673 15.7

Total 10,683 0 798 1,837 8,048 75.3

Roland

(Upper Rider)

Federal 5,504 0 33 1,672 3,800 62.1

State 303 0 6 119 179 2.9

Private 311 0 7 159 145 2.4

Total 6,119 0 45 1,949 4,124 67.4

Roland

(Lower Rider)

Federal 1,915 0 0 565 1,350 62.0

State 185 0 0 40 145 6.7

Private 77 0 0 29 47 2.2

Total 2,177 0 0 634 1,543 70.9

Roland of

Baker (1929)

Federal 8,174 0 110 1,208 6,856 70.5

State 694 0 5 114 574 5.9

Private 859 0 52 248 559 5.7

Total 9,727 0 167 1,570 7,990 82.1

Smith Federal 76,994 12 103 774 76,105 86.7

State 4,676 0 51 86 4,539 5.2

Private 6,075 0 335 213 5,526 6.3

Total 87,745 12 490 1,073 86,171 98.2
Coal Bed Geology 11

Table 2. Coal resources reported in millions of short tons, by coal ownership categories for the Southwestern Powder River Basin 

assessment area. Resource includes coal plus partings. Totals may not sum exactly due to rounding.—Continued

Coal 

bed

name

Coal

ownership

Original

resources

> 2.5 feet thick

Previously

mined

Land Use

restrictions

Technical

restrictions

Available

resources

Percent of 

total original 

resource

Anderson Federal 7,776 0 34 642 7,101 76.7

State 554 0 1 49 504 5.4

Private 923 0 7 93 823 8.9

Total 9,253 0 41 784 8,428 91.1

Dietz 3 Federal 11,010 0 34 458 10,518 87.7

State 653 0 1 56 596 5.0

Private 329 0 5 44 280 2.3

Total 11,992 0 39 558 11,395 95.0

Canyon 

(Upper)

Federal 4,290 0 15 343 3,931 75.7

State 333 0 19 48 266 5.1

Private 570 0 65 106 399 7.7

Total 5,192 0 98 498 4,596 88.5

Canyon Federal 57,768 0 58 467 57,243 86.8

State 4,022 0 42 61 3,919 5.9

Private 4,162 0 321 112 3,729 5.7

Total 65,951 0 420 639 64,891 98.4

Canyon

(Lower)

Federal 26,321 0 73 616 25,633 87.3

State 1,620 0 13 110 1,498 5.1

Private 1,427 0 50 166 1,210 4.1

Total 29,638 0 136 892 28,341 96.5

Werner Federal 9,041 0 112 923 8,006 72.7

State 807 0 40 56 712 6.5

Private 1,169 0 215 101 853 7.7

Total 11,017 0 367 1,080 9,571 86.9

Otter Federal 25,999 0 66 627 25,306 88.7

State 1,549 0 1 88 1,461 5.1

Private 966 0 17 125 825 2.9

Total 28,514 0 83 841 27,591 96.8

Gates Federal 18,185 0 61 800 17,325 82.8

State 1,478 0 18 52 1,408 6.7

Private 1,267 0 107 76 1,084 5.2

Total 20,929 0 185 927 19,817 94.7

Pawnee Federal 2,525 0 11 584 1,930 63.3

State 272 0 0 41 230 7.6

Private 252 0 2 60 190 6.2

Total 3,049 0 14 685 2,351 77.1

Deep 1 Federal 8,627 0 3 696 7,928 83.3

State 432 0 0 45 386 4.1

Private 463 0 1 85 378 4.0

Total 9,521 0 4 826 8,691 91.3
12 Assessment of Coal Geology, Resources, and Reserves in the Southwestern Powder River Basin, Wyoming

Table 2. Coal resources reported in millions of short tons, by coal ownership categories for the Southwestern Powder River Basin 

assessment area. Resource includes coal plus partings. Totals may not sum exactly due to rounding.—Continued

Coal 

bed

name

Coal

ownership

Original

resources

> 2.5 feet thick

Previously

mined

Land Use

restrictions

Technical

restrictions

Available

resources

Percent of 

total original 

resource

Deep 2 Federal 6,346 0 26 1,332 4,988 66.0

State 394 0 1 85 308 4.1

Private 816 0 23 170 644 8.5

Total 7,557 0 30 1,587 5,940 78.6

Deep 3 Federal 11,531 0 6 1,253 10,273 73.9

State 834 0 0 83 751 5.4

Private 1,538 0 0 150 1,388 10.0

Total 13,903 0 6 1,486 12,412 89.3

Roberts Federal 9,075 0 14 886 8,175 72.8

State 610 0 1 57 553 4.9

Private 1,544 0 1 80 1,464 13.0

Total 11,229 0 16 1,022 10,191 90.8

Total beds Federal 314,250 12 1,937 17,078 295,223 80.0

State 23,138 0 614 1,631 20,893 5.7

Private 32,707 0 3,907 2,888 24,912 6.7

Total 369,095 12 6,458 21,597 341,029 92.4

Table 3. Coal resources reported in millions of short tons by overburden depth for the Southwestern Powder River Basin 

assessment area. Resource includes coal plus partings. Totals may not sum exactly due to rounding.

Coal 

bed

name

Overburden 

thickness

(feet)

Original

resources

> 2.5 feet thick

Previously

mined

Land Use

restrictions

Technical

 restrictions

Available

resources

Percent of 

total original 

resource

Healy (Upper) 0- 500 4,702 0 824 449 3,428 70.5

500-1,000 157 0 52 31 74 1.5

1,000 -2,000 6 0 0 6 0 0.0

> 2,000 1 0 0 1 0 0.0

Total 4,865 0 877 486 3,502 72.0

Healy 0- 500 7,536 0 1,326 170 6,040 64.4

500-1,000 1,771 0 310 165 1,295 13.8

1,000 -2,000 61 0 0 14 47 0.5

> 2,000 5 0 0 1 4 0.0

Total 9,373 0 1,636 350 7,387 78.8

Murray 0- 500 761 0 18 576 167 11.3

500-1,000 662 0 17 428 217 14.6

1,000 -2,000 54 0 0 30 24 1.6

>2,000 3 0 0 3 0 0.0

Total 1,481 0 35 1,038 408 27.5

Ucross 0- 500 138 0 39 36 63 1.3

500-1,000 4,171 0 781 275 3,115 62.9

1,000 -2,000 615 0 96 43 476 9.6

>2,000 28 0 0 0 28 0.6

Total 4,952 0 916 354 3,681 74.3
Coal Bed Geology 13

Table 3. Coal resources reported in millions of short tons by overburden depth for the Southwestern Powder River Basin assessment 

area. Resource includes coal plus partings. Totals may not sum exactly due to rounding.—Continued

Coal 

bed

name

Overburden 

thickness

(feet)

Original

resources

> 2.5 feet thick

Previously

mined

Land Use

restrictions

Technical

 restrictions

Available

resources

Percent of 

total original 

resource

Felix 0- 500 2,574 0 54 161 2,359 52.5

500-1,000 1,862 0 0 272 1,590 35.4

1,000 -2,000 61 0 0 50 11 0.2

> 2,000 0 0 0 0 0 0.0

Total 4,497 0 54 482 3,960 88.1

Felix (Lower) 0- 500 1,538 0 3 763 772 7.2

500-1,000 6,259 0 494 859 4,906 45.9

1,000 -2,000 2,879 0 302 207 2,370 22.2

> 2,000 8 0 0 8 0 0.0

Total 10,683 0 798 1,837 8,048 75.3

Roland (Upper 

Rider)

0- 500 254 0 11 85 159 2.6

500-1,000 4,254 0 0 1,182 3,072 50.2

1,000 -2,000 1,605 0 34 677 894 14.6

> 2,000 5 0 0 5 0 0.0

Total 6,118 0 45 1,949 4,124 67.4

Roland

(Lower Rider)

0- 500 9 0 0 6 4 0.2

500-1,000 1,086 0 0 377 709 32.6

1,000 -2,000 1,081 0 0 251 830 38.1

>2,000 0 0 0 0 0 0.0

Total 2,177 0 0 634 1,543 70.9

Roland of

Baker (1929)

0- 500 2,316 0 92 139 2,112 21.7

500-1,000 4,074 0 5 498 3,571 36.7

1,000 -2,000 3,320 0 71 942 2,307 23.7

>2,000 18 0 0 18 0 0.0

Total 9,727 0 167 1,570 7,990 82.1

Smith 0- 500 1,695 12 0 291 1,392 1.6

500-1,000 12,563 0 0 417 12,146 13.8

1,000 -2,000 73,115 0 489 316 72,309 82.4

>2,000 373 0 1 49 323 0.4

Total 87,745 12 490 1,073 86,171 98.2

Anderson 0- 500 1,043 0 20 217 805 8.7

500-1,000 1,994 0 21 212 1,761 19.0

1,000 -2,000 6,217 0 0 355 5,862 63.3

>2,000 0 0 0 0 0 0.0

Total 9,253 0 41 784 8,428 91.1

Dietz 3 0- 500 0 0 0 0 0 0.0

500-1,000 2,087 0 39 2 2,045 17.1

1,000 -2,000 9,837 0 0 529 9,309 77.6

>2,000 68 0 0 27 41 0.3

Total 11,992 0 39 558 11,395 95.0
14 Assessment of Coal Geology, Resources, and Reserves in the Southwestern Powder River Basin, Wyoming

Table 3. Coal resources reported in millions of short tons by overburden depth for the Southwestern Powder River Basin assessment 

area. Resource includes coal plus partings. Totals may not sum exactly due to rounding.—Continued

Coal 

bed

name

Overburden 

thickness

(feet)

Original

resources

> 2.5 feet thick

Previously

mined

Land Use

restrictions

Technical

 restrictions

Available

resources

Percent of 

total original 

resource

Canyon 

(Upper)

0- 500 2 0 0 2 0 0.0

500-1,000 8 0 0 5 4 0.1

1,000 -2,000 4,356 0 78 363 3,915 75.4

>2,000 826 0 20 128 677 13.0

Total 5,192 0 98 498 4,596 88.5

Canyon 0- 500 5 0 0 5 0 0.0

500-1,000 401 0 2 16 383 0.6

1,000 -2,000 53,492 0 0 272 53,220 80.7

>2,000 12,053 0 420 346 11,288 17.1

Total 65,951 0 420 639 64,891 98.4

Canyon

(Lower)

0- 500 0 0 0 0 0 0.0

500-1,000 284 0 14 1 270 0.9

1,000 -2,000 26,293 0 19 279 25,895 88.2

>2,000 2,891 0 103 612 2,176 7.4

Total 29,368 0 136 892 28,341 96.5

Werner 0- 500 7 0 0 7 0 0.0

500-1,000 13 0 0 4 9 53.5

1,000 -2,000 6,738 0 5 841 5,892 53.5

>2,000 4,259 0 361 227 3,670 33.3

Total 11,017 0 367 1,080 9,571 86.9

Otter 0- 500 7 0 0 7 0 0.0

500-1,000 1 0 0 1 0 0.0

1,000 -2,000 19,799 0 75 289 19,435 68.2

>2,000 8,708 0 8 544 8,156 18.6

Total 28,514 0 83 840 27,591 96.8

Gates 0- 500 0 0 0 0 0 0.0

500-1,000 14 0 0 13 1 0.0

1,000 -2,000 6,374 0 9 341 6,025 28.8

>2,000 14,540 0 177 573 13,790 65.9

Total 21,929 0 185 927 19,817 94.7

Pawnee 0- 500 0 0 0 0 0 0.0

500-1,000 0 0 0 0 0 0.0

1,000 -2,000 234 0 0 100 135 4.4

>2,000 2,815 0 14 585 2,216 72.7

Total 3,049 0 14 685 2,351 77.1

Deep 1 0- 500 30 0 0 10 0 0.0

500-1,000 18 0 0 17 2 0.0

1,000 -2,000 1,198 0 4 135 1,060 11.1

>2,000 8,295 0 0 664 7,630 80.1

Total 9,521 0 4 826 8,691 91.3
Coal Bed Geology 15

Table 3. Coal resources reported in millions of short tons by overburden depth for the Southwestern Powder River Basin assessment 

area. Resource includes coal plus partings. Totals may not sum exactly due to rounding.—Continued

Coal 

bed

name

Overburden 

thickness

(feet)

Original

resources

> 2.5 feet thick

Previously

mined

Land Use

restrictions

Technical

 restrictions

Available

resources

Percent of 

total original 

resource

Deep 2 0- 500 1,148 0 23 216 908 12.0

500-1,000 1,280 0 6 114 1,160 15.4

1,000 -2,000 1,549 0 0 343 1,205 15.9

>2,000 3,580 0 0 914 2,666 35.3

Total 7,557 0 30 1,587 5,940 78.6

Deep 3 0- 500 589 0 0 281 307 2.2

500-1,000 137 0 2 79 56 0.4

1,000 -2,000 5,617 0 4 394 5,218 37.5

>2,000 7,561 0 0 730 6,831 49.1

Total 13,903 0 6 1,486 12,412 89.3

Roberts 0- 500 837 0 0 231 605 5.4

500-1,000 818 0 7 200 612 5.4

1,000 -2,000 5,756 0 4 116 5,635 50.2

>2,000 3,818 0 5 474 3,339 29.7

Total 11,229 0 16 1,022 10,191 90.8

Total beds 0- 500 25,170 12 2,410 3,625 19,123 5.2

500-1,000 43,916 0 1,750 5,169 36,997 10.0

1,000 -2,000 230,155 0 1,191 6,893 222,072 60.2

>2,000 69,854 0 1,107 5,911 62,837 17.0

Total 369,095 12 6,458 21,597 341,029 92.4

Inclusion of a coal bed for this assessment was based on thickness, areal extent, and stratigraphic position in relation to other 

minable beds. Except for the Upper Healy, Healy, Murray, 

Ucross, Felix, and Lower Felix coal beds, which are in the 

Wasatch Formation, the remaining assessed coal beds are all 

within the Tongue River Member of the Fort Union Formation. Because a typical surface-mining sequence begins at the 

ground surface, the following descriptions of coal beds that 

were assessed are discussed from youngest to oldest. 

Summary data for the coal bed thicknesses and depths 

were derived from statistical summaries based on coal bed 

digital models. Coal resources are classified according to geologic assurances of existence or reliability (Wood and others, 

1983). The degree of assurance increases with higher densities 

of geologic data points. Different reliability categories of measured (0.25 mi from point of measurement), indicated (0.25–

0.75 mi from point of measurement), inferred (0.75–3.0 mi 

from point of measurement), and hypothetical (greater than 

3.0 mi from point of measurement) can be established on the 

basis of distance from a data point (Wood and others, 1983). 

Coal resource reliability maps were constructed from the digital model for each coal bed assessed. Nine cross sections were 

constructed to show the position of coal beds relative to each 

other (figs. 12–20). 

Upper Healy Coal Bed

The Upper Healy coal bed is the uppermost coal bed in 

the Wasatch Formation. It is limited in extent to the northwestern part of the SWPRB assessment area and correlates 

with the Walter coal bed of Mapel (1959). The Upper Healy is 

also the uppermost bed that comprises the Lake DeSmet coal 

zone of Obernyer (1978, 1980). The Lake DeSmet coal is the 

one of the thickest known coal zones in the U.S. and is up to 

250 ft thick (Mapel, 1959; Obernyer, 1978, 1980). Obernyer 

(1978, 1980) suggested that the Lake DeSmet coal zone at 

Lake DeSmet (fig. 2) represents the coalescing of several 

major coal beds, possibly in response to basin-margin faulting 

active in Eocene time. From youngest to oldest, these beds are 

the Walters, Healy, Cameron, Murray, and Ucross (Obernyer, 

1978, 1980). During this assessment, numerous thick partings 

were identified in the Lake DeSmet coal zone. During the 

correlation process in this report, the Lake DeSmet coal zone 
16 Assessment of Coal Geology, Resources, and Reserves in the Southwestern Powder River Basin, Wyoming

was divided into four major coal beds (Upper Healy, Healy, 

Murray, and Ucross).

The Upper Healy coal bed, identified on 161 geophysical 

well logs, has a maximum thickness of 66 ft and an average 

thickness of 10 ft (figs. 9 and 21). Depth ranges from shallow 

subcrop to about 1,000 ft along the axis of the basin (fig 22). 

The coal resource reliability map is shown in figure 23; 

approximately 37 percent of the coal resources are in the 

measured and indicated reliability categories (table 1). As seen 

in figure 10, much of the Upper Healy coal bed is clinker and 

would not be considered a resource. 

Healy Coal Bed

Correlated with the Healy coal bed of Mapel (1959), this 

bed is limited in extent to the northwestern part of the SWPRB 

assessment area. The Healy coal bed was identified on 449 

geophysical well logs, has a maximum thickness of 75 ft, and 

an average thickness of 13 ft (figs. 9 and 24). Over 50 percent 

of the area of the Healy coal bed thickness exceeds 20 ft with 

a small area of thickness over 40 ft. Depth of the bed ranges 

from shallow subcrop to about 1,000 ft along the axis of the 

basin (fig. 25). About 40 percent of the coal resources are in 

the measured and indicated reliability categories (table 1). The 

coal resource reliability map is shown in figure 26. 

Murray Coal Bed

The Murray coal bed is also present only in the northwestern part of the SWPRB assessment area. This coal bed 

correlates with the Murray coal bed of Mapel (1959) and was 

identified on 593 geophysical well logs, has a maximum thickness of 14 ft, and an average thickness of 3 ft (figs. 9 and 27). 

This coal only attains a thickness of 10 ft, south of Buffalo. 

Depth ranges from shallow subcrop to about 1,000 ft along 

the axis of the basin (fig. 28). The resource reliability map is 

shown in figure 29; about 15 percent of the coal resources are 

in the measured and indicated reliability categories (table 1).

Ucross Coal Bed

Correlated with the Ucross of Mapel (1959), the Ucross 

is the bottom coal bed in the Lake DeSmet coal zone of Obernyer (1978, 1980) and is limited to the northern part of the 

SWPRB assessment area. As seen in the isopach maps of the 

Upper Healy, Healy, Murray, and Ucross coal beds, (figs. 21, 

24, 27, and 30) the areal extent of all four beds are very similar, suggesting that they are all part of the coal zone comprising the Lake DeSmet coal zone of Obernyer (1978, 1980). 

The Ucross coal bed was identified in 273 geophysical well 

logs and has a maximum thickness of 38 ft with an average 

thickness of 9 ft (figs. 9 and 30). One area along the extreme 

northwestern corner of the SWPRB assessment area contains 

coal that has a thickness exceeding 20 ft. Depth of the Ucross 

coal bed ranges from shallow subcrop to over 1,000 ft over the 

area of the thickest part of the coal bed (fig. 31). The resource 

reliability map for the Ucross coal bed is shown in figure 32. 

About 22 percent of the coal resources are in the measured and 

indicated reliability categories (table 1).

Felix Coal Bed

The extent of the Felix coal bed is mostly limited to the 

northeastern part of the SWPRB assessment area. This coal 

bed, identified in 1,156 geophysical well logs, has a maximum 

thickness of 48 ft with an average thickness of 7 ft (figs. 9 and 

33). One small area contains coal that exceeds a thickness of 

20 ft. Depth of the Felix coal bed ranges from shallow subcrop 

to about 1,500 ft over the areas of the thickest part of the coal 

bed (fig. 34). The Felix coal bed correlates with the Felix coal 

bed in the NWPRB assessment area (fig. 6). The coal resource 

reliability map for the Felix coal bed is shown in figure 35. 

About 71 percent of the coal resources are in the measured and 

indicated reliability categories (table 1). 

Lower Felix Coal Bed

The Lower Felix is the lowest coal bed identified in the 

Wasatch Formation. The bed was identified on 1,890 geophysical well logs, has a maximum thickness of 35 with an average 

thickness of 7 ft (figs. 9 and 36). The Lower Felix bed is present in a large area in the northern part of the SWPRB assessment area. There are three significant areas where the Lower 

Felix coal exceeds a thickness of 20 ft. Depth of the Lower 

Felix coal bed ranges from shallow outcrop to about 1,500 

ft along the axis of the basin (fig. 37). The Lower Felix coal 

bed correlates with the Lower Felix coal bed in the NWPRB 

assessment area (fig. 6). The coal resource reliability map for 

the Lower Felix bed is shown in figure 38. Over 26 percent of 

the coal resources are within the measured and indicated reliability categories (table 1). 

Roland (Upper Rider) Coal Bed

The Roland (Upper Rider) coal bed is an upper split of 

the Roland (Baker, 1929) coal bed and is most continuous 

throughout the northern half of the SWPRB assessment area, 

where it reaches a maximum thickness of 32 ft. The bed was 

identified on 2,805 geophysical well logs and has an average 

thickness of 4 ft (figs. 9 and 39). This bed, where present, 

marks the contact between the Wasatch and Fort Union Formations. Depth ranges from shallow subcrop to about 1,500 ft 

along the axis of the (fig. 40). The Roland (Upper Rider) coal 

bed correlates with the Roland (Upper Rider) coal bed in the 

NWPRB assessment area (fig. 6). Approximately 60 percent of 

the coal resources are within the measured and indicated reliability categories (table 1). The coal resource reliability map is 

shown in figure 41.
Coal Bed Geology 17

Roland (Lower Rider) Coal Bed

Where the Roland (Upper Rider) coal bed is absent, the 

Roland (Lower Rider) is stratigraphically the highest coal bed 

within the Tongue River Member of the Fort Union Formation. The Roland (Lower Rider) was identified on 1,107 geophysical well logs. With a maximum thickness of 19 ft and an 

average thickness of 4 ft (figs. 9 and 42) it is less continuous 

than the Roland (Upper Rider) and is present in a small area in 

the very northern part of the SWPRB assessment area. Depth 

ranges from shallow subcrop to about 1,500 ft along the axis 

of the basin (fig. 43). The Roland (Lower Rider) coal bed correlates with the Roland (Baker, 1929) coal bed in the NWPRB 

assessment area (fig. 6). Approximately 58 percent of the coal 

resources are within the measured and indicated reliability 

categories (table 1). The coal resource reliability map is shown 

in figure 44.

Roland of Baker (1929) Coal Bed

Where neither the Roland (Upper Rider) nor the Roland 

(Lower Rider) is present, the Roland of Baker (1929) coal 

bed is stratigraphically the highest coal bed within the Tongue 

River Member of the Fort Union Formation. In this case, the 

top of the bed is generally considered to mark the boundary 

between the Fort Union and Wasatch Formations (Flores and 

others, 1999) (fig. 9). Hereafter the Roland of Baker (1929) 

will be referred to as Roland (Baker) coal bed. The bed was 

identified on 2,442 geophysical well logs. With a maximum 

thickness of 36 ft and an average thickness of 7 ft (figs. 9 

and 45), it is present in a large area in the northern part of the 

SWPRB assessment area and a smaller area in the southern 

part of the area. This bed correlates with the Roland coal bed 

of Luppens and others (2008) in the Gillette coal field and 

the Roland (Baker) coal bed of Scott and others (2010). The 

most significant area where the Roland exceeds a thickness 

of 20 ft is in the extreme northern part of the SWPRB assessment area. Depth of the Roland coal bed ranges from shallow 

subcrop to over 1,500 ft along the axis of the basin (fig. 46). 

The Roland of Baker coal bed correlates with the Roland of 

Taff (1909) coal bed in the NWPRB assessment area (fig. 6). 

Approximately 65 percent of the coal resources are within the 

measured and indicated reliability categories (table 1). Coal 

resource reliability categories for the Roland bed are shown in 

figure 47.

Smith Coal Bed

The Smith is the most significant coal bed in the SWPRB 

assessment area. It was identified on 3,666 geophysical well 

logs, has a maximum thickness of 266 ft, and an average 

thickness of 32 ft (figs. 9 and 48). It is continuous throughout 

the northern half of the SWPRB assessment area and correlates to the Smith coal bed of Luppens and others (2008) and 

the Smith coal bed of Scott and others (2010). The Smith bed 

is the thickest coal in the SWPRB assessment area where it 

exceeds 120 ft. The coal bed extends eastward into the Gillette 

coal field where it is one of the more significant coal beds in 

that field. This coal bed is also equivalent to the Big George 

coal bed. Depth of the Smith coal bed ranges from shallow 

subcrop to over 2,500 ft along the axis of the basin (fig. 49). 

Coal resource reliability categories for the Smith bed are 

shown in figure 50. The Smith coal bed correlates with the 

Smith coal bed in the NWPRB assessment area (fig. 6). Over 

84 percent of the coal resources are within the measured and 

indicated reliability categories (table 1).

Anderson Coal Bed

Identified on 1,387 geophysical well logs, the Anderson 

bed has a maximum thickness of 61 ft (figs. 9 and 51). The 

bed averages 10 ft thick and correlates with the Anderson coal 

bed in the Gillette coal field and the Anderson coal bed in the 

NWPRB assessment area (fig. 6). Anderson coal is present in 

several locations of the SWPRB assessment area, the largest in 

the central part of the assessment area. Depth of the Anderson 

coal bed ranges from shallow subcrop to about 2,000 ft along 

the axis of the basin (fig. 52). More than 73 percent of the 

coal resources are within the measured and indicated reliability categories (table 1). The coal reliability map is shown in 

figure 53. 

Dietz 3 Coal Bed

Limited in areal extent to the very northern part of the 

SWPRB assessment area, the Dietz 3 coal bed was identified 

on 1,248 geophysical well logs. The bed has a maximum 

thickness of 119 ft and an average thickness of 14 ft (figs. 9 

and 54). There are two small areas where thickness exceeds 

40 ft. Depth ranges from shallow subcrop to over 2,500 ft 

along the axis of the basin (fig. 55). The Dietz 3 bed correlates 

with the Dietz 3 of Scott and others (2010) in the NWPRB 

assessment area. Depth of the Dietz 3 coal bed ranges from 

shallow subcrop to over 2,000 ft along the axis of the basin 

(fig. 56). The Dietz 3 coal bed correlates with the Dietz 1 and 

Dietz 2 coal beds in the NWPRB assessment area (fig. 6). 

More than 73 percent of the coal resources are within the 

measured and indicated reliability categories (table 1).

Upper Canyon Coal Bed

The Upper Canyon coal bed is an upper split of the 

Canyon coal bed which is discussed below. Figure 57 shows 

that the subsurface extent is limited to the northwestern part 

of the SWPRB assessment area. The coal bed was identified 

on 396 geophysical well logs. Maximum thickness of the bed 

is 31 ft; average thickness is 8 ft (figs. 9 and 57), and depth 

ranges from shallow subcrop to about 2,500 ft (fig. 58). Coal 

resource categories for the bed are shown in figure 59. The 
18 Assessment of Coal Geology, Resources, and Reserves in the Southwestern Powder River Basin, Wyoming

Upper Canyon coal bed correlates with the Dietz 3 and Dietz 

4 coal beds in the NWPRB assessment area (fig. 6). Measured 

and indicated coal resources total more than 48 percent of the 

extent of the coal bed (table 1). 

Canyon Coal Bed

Originally named the Monarch coal bed by Taff in1909, 

this coal bed is equivalent to the Canyon coal bed of Baker 

(1929) (in Law and others, 1979). Since that time it has been 

referred to as both the Canyon and the Monarch. In this report 

it will be referred to as the Canyon coal bed and correlates to 

the Canyon coal bed in the Gillette coal field (Luppens and 

others, 2008) and the Canyon coal bed of Scott and others 

(2010). The Canyon coal bed and the Smith coal bed are the 

two thickest and continuous coal beds in the SWPRB assessment area. Present throughout most of the northern and central 

parts of the SWPRB assessment area, the Canyon coal bed 

was identified in 2,463 geophysical well logs and reaches a 

maximum thickness of 182 ft with an average thickness of 

29 ft (figs. 9 and 60). Depth ranges from shallow subcrop to 

about 2,500 ft along the axis of the basin (fig. 61). More than 

75 percent of the coal resources are within the measured and 

indicated reliability categories (table 1). The Canyon coal bed 

correlates with the Canyon coal bed in the NWPRB assessment area (fig. 6). The coal resource reliability map for the 

Canyon bed is shown in figure 62. Along the eastern edge of 

the areal extent of the Canyon there is an apparent paleochannel where the coal thins and becomes absent (fig. 60). 

Lower Canyon Coal Bed

Present only in the northern part of the SWPRB assessment area, the Lower Canyon is a lower split of the Canyon 

coal bed. This coal bed was identified on 1,729 geophysical 

well logs, has a maximum thickness of 81 ft, and averages 

16 ft thick (figs. 9 and 63). There are three areas along the 

eastern edge of the areal extent that exceed 40 ft in thickness. 

Depth ranges from shallow subcrop to about 3,000 ft along 

the axis of the basin (fig. 64). More than 73 percent of the coal 

resources are within the measured and indicated reliability 

categories (table 1). The Lower Canyon coal bed correlates 

with the Lower Canyon coal bed in the NWPRB assessment 

area (fig. 6). The same paleochannel seen in the Canyon coal 

bed can also be seen in the Lower Canyon coal bed. The coal 

resource reliability map for the Lower Canyon bed is shown in 

figure 65.

Werner Coal Bed

The Werner coal bed, identified in 1,124 geophysical 

well logs, has a maximum thickness of 76 ft and averages 8 ft 

thick (figs. 9 and 66). Only small isolated areas contain coal 

that exceeds 20 ft thick. The Werner coal correlates with the 

Werner of Luppens and others (2008) and the Werner of Scott 

and others (2010). Depth ranges from shallow subcrop to over 

2,500 ft over the areas of greatest coal thickness (fig. 67). 

More than 47 percent of the coal resources are within the measured and indicated reliability categories (table 1). The Werner 

coal bed correlates with the Werner coal bed in the NWPRB 

assessment area (fig. 6). The coal resource reliability map for 

the Werner bed is shown in figure 68.

Otter Coal Bed

Distribution of the Otter coal bed is shown in figure 69. 

Based on 1,040 geophysical well logs, it reaches a maximum 

thickness of 158 ft and has an average thickness of 24 ft 

(figs. 9 and 69). Areas of greatest thickness occur along the 

northeastern edge of the SWPRB assessment area. Depth 

ranges from shallow subcrop to about 4,000 ft along the 

axis of the basin (fig. 70). More than 71 percent of the coal 

resources are within the measured and indicated reliability 

categories (table 1). The Werner coal bed correlates with the 

Werner coal bed in the NWPRB assessment area (fig. 6). The 

coal resource reliability map for the Otter bed is shown in 

figure 71.

Gates Coal Bed

The Gates coal bed is slightly larger than the Otter coal 

bed in areal extent and present only in the northern part of the 

SWPRB assessment area. The Gates coal correlates with the 

Gates of Luppens and others (2008) and the Gates of Scott 

and others (2010). Identified on 819 geophysical well logs, 

the coal has a maximum thickness of 122 ft and averages 13 ft 

thick (figs. 9 and 72). Depth ranges from shallow subcrop to 

about 4,000 ft along the axis of the basin (fig. 73). More than 

49 percent of the coal resources are within the measured and 

indicated reliability categories (table 1). The Gates coal bed 

correlates with the Gates coal bed in the NWPRB assessment 

area (fig. 6). The coal resource reliability map for the Gates 

bed is shown in figure 74.

Pawnee Coal Bed

The Pawnee coal bed is present only in small areas in the 

northern part of the SWPRB assessment area. The coal bed 

was identified on 217 geophysical well logs, has a maximum 

thickness of 19 ft and averages 5 ft (figs. 9 and 75). Depth 

ranges from shallow subcrop to about 4,000 ft along the axis 

of the basin (fig. 76). The Pawnee coal bed correlates with the 

Pawnee of Luppens and others (2008) and Scott and others 

(2010). More than 27 percent of the coal resources are within 

the measured and indicated reliability categories (table 1). The 

Pawnee coal bed correlates with the Pawnee coal bed in the 

NWPRB assessment area (fig. 6). The coal resource reliability 

map for the Pawnee coal bed is shown in figure 77.
Resource Allocation Planning 19

Deep 1 Coal Bed

The Deep 1 coal bed, identified on 738 geophysical well 

logs, has a maximum thickness of 32 ft and averages 9 ft thick 

(figs. 9 and 78). The coal occurs mostly along the eastern edge 

of the northern part of the SWPRB assessment area. The Deep 

1, Deep 2, and Deep 3 coal beds could not be correlated to 

any known coal beds. Depth ranges from shallow subcrop to 

about 4,000 ft (fig. 79). Approximately 57 percent of the coal 

resources are within the measured and indicated reliability 

categories (table 1). The coal resource reliability map for the 

Deep 1 bed is shown in figure 80.

Deep 2 Coal Bed

The Deep 2 coal bed occurs along the eastern part of 

the northern part of the SWPRB assessment area and in a 

large area in the southern part of the area. Identified on 713 

geophysical well logs, the coal has a maximum thickness of 

29 ft and averages 5 ft thick (figs. 9 and 81). Depth ranges 

from shallow subcrop to about 4,000 ft near the axis of the 

basin (fig. 82). Approximately 36 percent of the coal resources 

are within the measured and indicated reliability categories 

(table 1). The coal resource reliability map for the Deep 3 coal 

bed is shown in figure 83.

Deep 3 Coal Bed

The Deep 3 coal bed occurs in about the same areal 

extent as the Deep 2 coal bed. The coal was identified on 796 

geophysical well logs, has a maximum thickness of 32 ft, and 

averages 8 ft thick (figs. 9 and 84). Depth ranges from shallow 

subcrop to about 4,000 ft near the axis of the basin (fig. 85). 

Approximately 45 percent of the coal resources are within the 

measured and indicated reliability categories (table 1). The 

coal resource reliability map for the Deep 3 coal bed is shown 

in figure 86.

Roberts Coal Bed

The Roberts coal was identified in two areas of the 

SWPRB assessment area (fig. 87). The smaller area is located 

in the extreme northeast part of the SWPRB assessment area. 

A larger area is located in the southern part of the SWPRB 

assessment area. The Roberts coal bed was identified on 

465 geophysical well logs, reaches a maximum thickness of 

36 ft, and averages 9 ft thick (figs. 9 and 87). Depth of the 

Roberts coal bed ranges from shallow subcrop to over 4,000 ft 

(fig. 88). Approximately 36 percent of the coal resources 

are within the measured and indicated reliability categories 

(table 1). The coal resource reliability map for the Roberts bed 

is shown in figure 89.

Resource Allocation Planning

The objective in resource planning is to determine the 

available resources. This objective is accomplished by first 

subtracting the resources previously mined from the original 

resources; the result equals the remaining resources. Subtracting the land use and technical restrictions from the remaining 

resources equals the available resources. The following discussion details the methodology used in determining available 

resources.

Geologic digital modeling for the evaluated coal beds 

was done using PC/Cores (Mentor Consultants, 2005). In the 

next step of the coal resource assessment, files were imported 

into a Geographic Information System (GIS). The GIS system 

was used to allocate coal resources by first subtracting areas 

with various restrictions to mining (previous mining, towns, 

railroads, alluvial valley floors, etc.) in order to calculate the 

amount of available coal.

ArcView® and the ArcView Spatial Analyst® extension 

(Environmental Systems Research Institute, Inc., 2000, 2001) 

were used to perform the various GIS analyses and ultimately 

calculate coal resource volumes. In addition, ArcGIS® (Environmental Systems Research Institute, Inc., 2006) was used 

in some cases to project digital coverages, shapefiles, or grids 

to the assessment area’s base map projection. The geographic 

referencing base of the digital data used for the GIS analysis 

is the Universal Transverse Mercator (UTM) map projection, 

using the following parameters: map units= meters; zone=13; 

datum=NAD27; and spheroid = Clarke 1866.

USGS coal resource assessments do not have a standard grid-cell size that is used for all GIS analyses. For this 

GIS assessment, a grid-cell size of 30 m (about 100 ft) on a 

side was chosen. Consequently, all grids used within the GIS 

analysis were either originally created with a grid cell size of 

30 m or resampled from 150 m to 30 m.

The first task in the GIS analysis involved the creation 

of ArcView (Environmental Systems Research Institute, Inc., 

2000) readable grids from the ASCII files of the coal, parting, 

and overburden isopach grids that were created by the digital 

coal models. These ArcView grids were used to create a total 

thickness (coal plus parting) grid and an areal-extent grid for 

each coal bed to be evaluated. The next task involved creating 

a group of grids that categorized the SWPRB assessment area, 

with each grid representing one specific theme. These grid 

themes consisted of mined out areas, overburden-to-coal bed 

ratios, counties, coal ownership, resource reliability categories, coal bed depth, and restrictions to mining (that is, land 

use restrictions and technical restrictions). The grid themes 

for mined out areas, land-use restrictions, and coal ownership 

were derived from digital information obtained from the Wyoming Bureau of Land Management. The grid theme for the 

counties was developed from a digital file of Wyoming county 

lines obtained from the Wyoming Spatial Data Clearinghouse 

(2009) (http://wgiac2.state.wy.us). The other grid themes were 

developed independently for this evaluation.
20 Assessment of Coal Geology, Resources, and Reserves in the Southwestern Powder River Basin, Wyoming

The grid of environmental restrictions includes buffer zones that surround the restricted areas. The location 

and width of these buffers are commonly mandated by State 

or Federal regulations, but specifications presented in the 

Buffalo Resource Management Plan (U.S. Bureau of Land 

Management, 2001), such as additional buffers around the 

town of Buffalo, Wyoming, were also used in this evaluation. 

Each restriction buffer measures hundreds or, in the case of 

the extra-jurisdictional buffer around the town of Buffalo, 

thousands of feet in width at the surface, as discussed in the 

following section on factors affecting coal resources. 

One of the improvements in the assessment methodology 

was revising the technique for defining how surface restrictions affect the development of the underlying resources at 

depth. Previous economic assessments used a simple “cookie 

cutter” approach when they applied regulatory surface buffers 

(such as a 300-ft buffer around an inhabited house) below the 

surface. The surface buffers were simply projected vertically 

downward through the coal beds to be evaluated. However, a 

restricted area actually widens with depth when surface mining operations are considered, owing to the additional setback 

distance required to maintain a safe mining pit highwall 

angle. Consequently, the area that is affected by a restriction 

becomes larger the deeper a coal bed lies beneath the surface. 

For example, a circular restriction at the surface having a 

diameter of 600 ft encompasses an area of about 282,600 ft2

, 

or approximately 6.5 acres. At a depth of 200 ft, however, this 

same restriction has a diameter of 858 ft encompassing an area 

of about 577,900 ft2

, or approximately 13 acres whereas at a 

depth of 500 ft the restriction has a diameter of 2,144 ft and 

encompasses an area of about 3,608,400 ft2

, or approximately 

83 acres. Figure 90 illustrates the effect of depth on overall 

land-use restriction size. 

The technical restrictions grids include those areas where 

coal beds are less than 2.5 ft thick and areas where coal beds 

are less than 5 ft thick. For this evaluation, coal resources of 

less than 2.5 ft in thickness are not considered to represent 

viable resources, whereas coal resources greater than 2.5 ft 

thick but less than 5.0 ft thick are not considered to represent 

currently minable resources or potential available resources.

The grid of mined out areas accounted for all previous 

mining within the SWPRB assessment area, including those 

mines shown in figure 91. The counties grid contained locations of three principal counties within this area (Campbell, 

Converse, and Johnson). The coal mineral ownership grid 

divided the area into Federal, State, and private ownership 

categories (fig. 92). The resource reliability grid divided the 

area into measured, indicated, inferred, and hypothetical coal 

resources whereas the coal bed depth grid divided the area 

into four categories of depth: 0–500 ft; 500–1,000 ft; 1,000–

2,000 ft; and greater than 2,000 ft. 

Once all the individual theme grids were generated, the 

next step was to apply these grids to the coal resources of 

the 23 coal beds to be evaluated. First, the individual theme 

grids were combined into one composite themes grid, which 

was then used with the coal bed areal-extent grids to define 

the SWPRB assessment area resources on a bed-by-bed basis 

according to all the various categories. Next, areas within 

each coal bed that represented previously mined coal and 

restrictions (land-use and technical) were removed from 

consideration. 

Factors Affecting Extraction of Coal 

Resources

Many factors can affect the availability of coal for mining. Almost 85 percent of the coal in the SWPRB assessment 

area is Federally-owned and must be leased in order to be 

mined (table 2). A four-step coal screening process, defined 

in the 43 CFR 3420.1-4 regulations, determines which areas 

of Federal coal are acceptable for leasing. The following list 

shows coal-leasing unsuitability criteria listed in the Code of 

Federal Regulations, Title 43 Subpart 3461.5 (43 CFR 3461.5) 

(Office of the Federal Register, 2003).

Unsuitability Criteria

Federal land systems 

Rights-of-way and easements (for example, railroads) 

Dwellings, roads, cemeteries, and public buildings 

Wilderness study areas

Lands with outstanding scenic quality

Lands used for scientific study

Historic lands and sites

Natural areas

Critical habitat for threatened or endangered plant and 

 animal species

State listed threatened or endangered species

Bald or golden eagle nests

Bald and golden eagle roost and concentration areas

Federal lands containing active falcon cliff nesting site

Habitat for migratory bird species

Fish and wildlife habitat for resident species

Floodplains

Municipal watersheds

National resource waters

Alluvial valley floors 

State or Indian tribe proposed criteria

These 20 specific legal criteria are used to determine if an 

area is unsuitable for leasing and surface mining. The criteria 

were established by the Surface Mining Control and Reclamation Act (SMCRA) of 1977 (Public Law 95-87, 1977). The 

unsuitability criteria require consideration of land use, scenic 

areas, natural areas, historic sites, wildlife habitats, flood 

plains, alluvial valley floors, and other special lands. Although 

the 20 unsuitability criteria were developed for lands owned 
Factors Affecting Extraction of Coal Resources 21

by the Federal government, many of the criteria would also 

be applicable to State-owned and privately-owned lands. For 

example, areas containing threatened or endangered plant or 

animal species are protected from destruction wherever they 

occur. Municipal watersheds are likewise protected from detrimental actions regardless of who owns the land. It is important to understand that not all criteria listed in the above table 

affect development within the SWPRB assessment area.

Other potential restrictions to mining include land use 

restrictions such as; airports, archaeological areas, coalbed 

methane wells, oil and oil-related gas wells, pipelines, power 

lines, rivers, lakes, streams, and towns.

Restrictions to mining vary with location and local landmanagement regulations. Thus, different study areas can have 

different mining restrictions and availability considerations. 

This report reflects assumptions concerning restrictions to 

mining that are based on local practices in the PRB, and specifically to those practices within the SWPRB assessment area. 

In addition, the Bureau of Land Management personnel in 

Casper, Wyoming, provided guidance concerning restrictions 

to mining and the distances to be buffered around specific 

features, and also provided files that delineate many of the 

features and the buffer distances used for the study. A more 

detailed determination of restrictions and other availability 

considerations would be necessary as part of leasing and mineplanning phases of property development.

Figure 91 shows the areas within the SWPRB assessment 

area that were affected by restrictions. In some cases, an area 

that was originally declared unavailable for coal mining could 

have a mitigation measure that would permit mining. The following is a detailed discussion of potential mining restrictions 

for this area. All buffer restrictions refer to distances at the 

surface.

Federal Land Systems

Within the Converse County portion of the SWPRB 

assessment area, there is a part of the Thunder Basin National 

Grassland that includes scattered Federal lands under the 

jurisdiction of the U.S. Forest Service, although it is not part 

of a National Forest. The same unsuitability criteria and landuse conflicts discussed in this report apply to coal mining on 

the Thunder Basin National Grassland. Where the mineral 

ownership there is Federal, the Bureau of Land Management 

develops coal-leasing and mining stipulations in cooperation 

with the U.S. Forest Service. Federal subsurface coal ownership is shown in figure 92.

Railroads

There are three railroad routes through the SWPRB 

assessment area (fig. 91). The southeast-northwest route in 

the northern part of the area is a rail line of the Burlington 

Northern Santa Fe Railway. In the southern part of the area, 

the north-south route consists of a single railroad corridor 

combining rail lines of both the Burlington Northern Santa Fe 

Railway and the Union Pacific Railroad, whereas the generally 

east-west route consists of two separate rail lines of these same 

two companies.

Although it is conceivable that the rail lines of these 

existing routes could be relocated to allow mining to proceed, 

it is assumed that these main rail lines would not be moved 

and are restrictions to mining. The total restricted width for 

each of the railroad lines, including the right-of-way and a 

100-ft buffer along each side, is 600 ft.

Roads

County roads (mostly gravel) cross many areas throughout the SWPRB assessment area. These roads are not considered to restrict mining because it is assumed that they could 

be easily relocated or temporarily blocked off to allow mining 

to proceed. In addition, a number of State and U.S. highways, 

including Interstate Highways 25 and 90, are present within 

the area (fig. 91). For this study, it is assumed that all of these, 

except the interstate highways, could also be relocated to 

allow for mining. For each of the interstate routes, the total 

restricted width is 450 ft, including the highway right-of-way 

and a 100-ft buffer on either side.

Dwellings and Buildings

Individual dwellings and buildings that exist outside 

of incorporated areas (such as Buffalo) are not considered 

restrictions to mining within the SWPRB assessment area. 

These individual structures could probably be purchased by a 

coal company, which could then move or raze them in order to 

proceed with mining.

Alluvial Valley Floors 

All areas identified as alluvial valley floors by the State 

program delegated to enforce the Surface Mining Control and 

Reclamation Act of 1977 (Surface Mining Control and Reclamation, Public Law 95-87)–where mining would interrupt, 

discontinue, or preclude farming–are unsuitable for surface 

coal mining and thus are deemed to be restrictions. In addition, areas outside alluvial valley floors where mining would 

materially damage the quantity or quality of water supplying 

alluvial valley floors are unsuitable; however, this analysis did 

not cover those areas.

Airports

The Johnson County airport is located near the city of 

Buffalo, about two and a quarter miles northwest of the central 

business district and it is included within the Buffalo restriction buffer area.
22 Assessment of Coal Geology, Resources, and Reserves in the Southwestern Powder River Basin, Wyoming

Archaeological Areas 

No major archaeological areas that would prevent mining 

are known in the SWPRB assessment area. There are several 

minor archaeological sites and also several minor historic sites 

within this area. A mitigation plan would be developed before 

coal mining disturbed these areas. Therefore, coal within these 

known sites was not excluded from this resource study.

Coalbed Methane

The rapid growth in coalbed methane production within 

the SWPRB assessment area has resulted in the placement of 

thousands of wells, along with their accompanying pipeline 

infrastructure, throughout the area. Designating all of these 

wells and their extensive gas delivery systems as being restrictive to mining would effectively exclude much of the assessment area from resource consideration. As stated previously, 

the expected lifetime of these wells in this area, producing 

from a single coal bed, is 10 to 12 years. The Bureau of Land 

Management has designated Conflict Administration Zones to 

minimize conflicts between coal mines and coalbed methane wells in the path of projected near-term mining. For the 

purpose of this study, it is assumed that coal within any part of 

the assessment area will be mined after the methane operations 

have ceased operating in that area. Therefore, these facilities 

are not considered a restriction to mining.

Oil and Oil-Related Gas Wells

Hundreds of oil and gas wells are located throughout the 

SWPRB assessment area. Resolution of land-use conflicts 

between coal mining and the oil and gas field development 

will depend on economic conditions, regulations, and negotiations between oil developers and coal developers. An area 

around a major cluster of active wells might be eliminated 

from mining activities until these wells are no longer actively 

producing, or mining activities might proceed around individual active wells that are given a buffer zone. Conversely, 

specific wells might be plugged and then re-established after 

mining. For this study, it was assumed that the wells will no 

longer be actively producing when mining operations reach 

them and thus they are not considered to be restrictions to 

mining.

Pipelines

There is a network of underground oil and gas pipelines 

throughout the SWPRB assessment area. Probably most, if not 

all, of these pipelines would be moved so that surface mining 

could proceed. However, moving and restoring them would 

represent an added economic cost to mining. In any case, 

pipelines were not considered to be restrictions to mining for 

this study.

Power Lines

All power lines within the assessment area could be 

moved to accommodate surface mining operations. Thus, 

power lines are not considered a restriction to mining in this 

area.

Rivers, Lakes, and Streams

The Powder River is the longest body of flowing water 

within the SWPRB assessment area. However, throughout 

its course within the assessment area, it is a shallow, slow 

moving, meandering stream as is the case with all of the 

river’s tributaries and other creeks in the SWPRB assessment 

area. Therefore, surface mining operations could temporarily 

relocate the courses of these streams and then return them to 

their pre-mining locations during mine reclamation assuming 

no protected species of flora or fauna exist. Only the parts of 

these water courses that have been designated by the State 

Land Quality Division as alluvial valley floors significant to 

farming would need to be preserved with no modification. In 

contrast, although the North Platte River only flows through 

a small part of the southern end of the assessment area, this 

prominent water course is considered to be a restriction to 

mining (fig. 91). In addition to the width of the river, the 

restriction includes a 100 ft buffer on each side. Shallow lakes 

and small ponds that do exist could either be temporarily 

moved during mining or simply reformed after the mining 

operations ceased. However, Lake DeSmet, a recreational site 

and water supply source located about six mi north of the city 

of Buffalo is considered to be a restriction to mining for this 

assessment (fig. 91). The restriction includes a 100-ft buffer 

surrounding the lake.

Towns

The entire municipality of Buffalo and parts of the 

municipalities of Douglas and Rolling Hills are located within 

the SWPRB assessment area and are permanent restrictions 

to mining (fig. 91). In addition to the actual incorporated area, 

the mining restriction for each municipality includes a buffer 

that extends well beyond the municipality limits. The boundary of the town buffer for Buffalo is taken from the Buffalo 

Resource Management Plan Update (U.S. Bureau of Land 

Management, 2001) developed by the Bureau of Land Management for potential coal development areas within the PRB 

of Wyoming. The buffers for Douglas and Rolling Hills extend 

out to a distance of 300 ft beyond each town’s limits.

State Lands

There are no State parks or forests within the SWPRB 

assessment area. However, the historic site of Fort Reno, a 

U.S. Cavalry army post constructed in the 1860s along the 
Coal Reserve Evaluation Methodology 23

Bozeman Trail, is located within the SWPRB assessment area 

and is administered by the Wyoming State Parks and Cultural 

Resources Department. The site, listed on the National Register of Historic Places, lies near the Powder River approximately 22 mi northeast of the town of Kaycee. The grounds 

comprising the fort site have mostly returned to a natural cover 

of prairie sod, although a large stone monument and several 

interpretive signs mark the site. As is, the site could potentially 

be a restriction to future mining; however, the site no longer 

contains original structures or ruins and the area involved is 

small. Furthermore, the area of the site could be returned to a 

pre-mining state during remediation and the monument and 

signs restored. Therefore, for this evaluation there are no State 

lands that are considered to be restrictions to mining.

Coal Reserve Evaluation Methodology 

The third and final phase in the resource assessment is the 

economic evaluation of the available resources calculated in 

phase two (fig. 5). This phase begins by selecting the available 

resources information for each evaluated bed and parsing them 

into either surface minable or underground minable resources. 

However, the potential for available coal resources for coal 

beds in the Fort Union Wyodak coal zone recovered by surface 

mining is very limited. On the other hand, significant thick, 

deep coal resources exist in the Roland (Baker, 1929), Smith, 

Anderson, Dietz 3, Canyon, Lower Canyon, Werner, and Otter 

coal beds.

In the extreme southwestern portion of the NWPRB 

assessment area (Scott and others, 2010) and the northwestern 

portion of the SWPRB assessment area, there is also a relatively limited area of potentially mineable Wasatch coal beds 

(Upper Healy and Healy). These coal beds are the northernmost extension of the Buffalo coal field (fig. 2).

Recoverable coal resources are determined through economic analysis. The present value of all mining expenditures 

over a project life at a rate of return or return on investment is 

evaluated in a discounted cash flow calculation that yields a 

discounted cash flow rate of return. A break-even cost per ton 

is calculated using the discounted cash flow and annual production rate. The portion of the recoverable coal that is minable at or below the current sales price of coal is designated 

as reserves. Because of the limited surface minable resources, 

only underground minable resources have been evaluated 

economically in this report.

Coal Quality

Coal quality is one of the major factors in the marketability of coal and is an important parameter in economic 

evaluations as coal is sold based on its calorific value 

expressed in British thermal units per pound of coal (Btu/

lb). Quality parameters such as increased ash content, which 

lowers the calorific value, negatively impact the operating and 

maintenance costs at coal-fired power plants. Therefore, coals 

with lower ash and sulfur content and higher calorific values 

command a premium selling price. 

The Clean Air Act Amendments have enforced emission 

limits to reduce certain air pollutants such as sulfur dioxide. 

The sulfur dioxide emissions limits for all new coal-fired 

power plants built after 1976 were capped at 1.2 pounds of 

sulfur dioxide per million Btu (U.S. Environmental Protection Agency, 1980). Any coal that could be burned and meet 

the sulfur dioxide emission standards for air quality (emit 

less than 0.6 pounds or less sulfur per million Btu, or 1.2 

pounds of sulfur dioxide per million Btu) without the need for 

flue-gas desulfurization was designated “compliance coal”, 

also known as low sulfur coal (U.S. Energy Information 

Administration, 2010). Subsequent phases of the Clean Air 

Act Amendments have further restricted sulfur dioxide emissions. Currently, New Source Performance Standards establish

uniform national Environmental Protection Agency air emission standards that limit the amount of pollution allowed from 

new sources or from modified existing sources (U.S. Environmental Protection Agency, 2005). Under New Source Performance Standards, Best Available Control Technology emission 

limitations are based on the maximum degree of reduction of 

each pollutant subject to regulation under the Clean Air Act

Amendments (U.S. Environmental Protection Agency, 2005). 

The minimum Best Available Control Technology standard for 

sulfur dioxide emissions is 90 percent regardless of the sulfur 

content. The abundance of low sulfur coal in the PRB has been 

a significant factor in the steadily growing demand for coal 

from this region.

There are currently no active mines in the SWPRB 

assessment area, but limited production from coal beds in 

both the Fort Union and Wasatch Formations has occurred. 

Lacking the relatively thick, shallow coal beds found in the 

Gillette coal field on the eastern flank of the Powder River 

Basin, mining has not been widespread. As a result, publically 

available coal quality information from coal exploration coring and mines, except for the now abandoned Dave Johnston 

Mine near Glenrock, WY, is sparse. Additionally, limited coal 

quality data have been generated from a few wells during 

recent coalbed methane exploration. For some coal fields 

within the SWPRB assessment area, only a single proximate 

coal analysis for each coal bed was available. For regions like 

the Gillette coal field where extensive mining with abundant 

coal analytical data exists, assessing the coal quality variations 

is straightforward. However, when dealing with relatively few 

coal analyses, it is especially important to try to assess both 

the accuracy and representativeness of each available data set.

A review of publically available coal quality data during 

the current coal resource assessment of the SWPRB assessment area revealed significant problems and other limitations 

with that data. Problems with accuracy included unaccounted 

moisture loss and cited data that only presented selective data 

or introduced errors from the original reports. Problems associated with representativeness are especially difficult to evaluate. If the sample is not representative of the entire coal bed, 
24 Assessment of Coal Geology, Resources, and Reserves in the Southwestern Powder River Basin, Wyoming

the value of the analytical results on that sample are limited, 

especially if the sample was biased towards lower ash portions 

of the bed. When evaluating coal quality data where information is limited, it is always preferable to research the circumstances regarding the sampling and analytical parameters from 

the original sources. Cited data commonly omits important 

information such as moisture integrity and representativeness 

issues.

Luppens (2011) presented a detailed analysis of the published coal quality data available from the SWPRB assessment 

area. The results of this review for the surface minable portions of coal beds in both the Fort Union and Wasatch Formations are summarized in tables 4 and 5. 

Coal quality for the shallow Fort Union Formation coal 

beds is from the Dry Cheyenne, Glenrock, and Sussex coal 

fields (fig. 2, table 4). With the close proximity of Glenrock 

and Dry Cheyenne coal fields, it would be expected that 

moisture and apparent rank values would be similar. However, 

moisture ranges from about 19.5–28.7 percent and correspondingly moist, mineral matter free calorific values range from 

8,540–9,805 Btu/lb, which results in a relatively large range of 

apparent rank from low Subbituminous C to Subbituminous B 

(American Society for Testing and Materials (ASTM), 2008). 

The published average moisture content of 26.6 percent 

for the produced coal from the Dave Johnston Mine (Glass, 

1997), which is owned by Pacific Power and Light Company 

(PPL), is the most reliable estimate of the moisture content 

(at 12.1 percent ash) in the Glenrock and Dry Cheyenne coal 

fields (table 4). However, Glass and Jones (1992) published 

an average of three analyses from the Dave Johnston Mine 

that was more than 5.0 percent lower than the published value 

of (26.6 percent) from the mining company (table 4). The 

three analyses used by Glass and Jones (1992) were originally 

published by Glass (1975) and consisted of two face channel 

analyses, 74-36 and 74-37, and a typical core hole analysis 

provided by mining company from the Smith bed (table 4). 

The two face channel analyses were obtained from exposed 

highwall faces that had been exposed to drying conditions for 

weeks to months prior to sample collection. In fact, the condition of sample 74-36 was described as “weathered” by Glass 

(1975). The 19.5 percent moisture content of sample 74-37 is 

more than 7.0–10.0 percent lower than the range in average 

moisture contents from the adjacent Gillette coal field (Luppens, 2008).

More realistic estimates of ranges in coal quality from 

thee Glenrock and Dry Cheyenne coal fields would be: 

moisture, 26.0–29.0 percent; ash, 7.5–12.0 percent; sulfur, 

0.4–0.6 percent; and gross calorific values, 7,500–8,000 Btu/lb 

(Luppens, 2011). These coal quality estimates are significantly 

lower than would be projected from the published data. It is 

interesting to note that one of the reasons for closing the Dave 

Johnston Mine in 2000 was deteriorating coal quality (PACIFICORP, 2008).

The only coal quality data for the Sussex coal field is 

from a field investigation by Wegemann (1912) (table 4). A 

few small mines were the source of coal samples for analysis. 

Like the Glenrock and Sussex coal fields, the relatively large 

ranges on the moisture contents and apparent rank are suggestive of effects due to unaccounted moisture loss. Given 

the lack of impervious materials to seal the samples 100 years 

ago, it can be assumed that the samples from Wegemann 

(1912) suffered at least minor moisture loss. The average of 

the 5 analyses for the Sussex coal field was normalized at 30.0 

percent moisture (table 4) to derive a more realistic estimate 

of the expected coal quality of this area. However, the normalized average still falls short of true quality due to the issue of 

representativeness in the Sussex coal field.

All samples from mines in the Sussex coal field were low 

ash benches avoiding higher ash partings in each of the mined 

coal beds (Luppens, 2011). The presence of high ash partings 

is very common in the Sussex coal field (Wegemann, 1912). It 

is estimated that whole bed analyses would have ash contents 

2.0–5.0 percent and calorific values 200–500 Btu/lb lower that 

the normalized average (table 4).

Coal quality information for the deep Wyodak-Anderson 

coal zone resources is especially sparse. An average analysis 

for the Smith coal bed (Big George) bed at a depth exceeding 

1,000 ft is listed in table 4. Additionally, limited quality information from a few coalbed methane wells was summarized 

by Stricker (2007). Those data were reviewed by Luppens in 

2010 to see if a relationship between depth and calorific values 

could be established similar to the trend observed by Testa and 

Pratt (2003). Figure 93 demonstrates that there is a fairly good 

relationship between the estimated variability calorific values 

of the Wyodak zone coal beds with depth. Mining costs generally increase with depth. Figure 94 shows that those increased 

costs at greater depths might be at least partially offset with 

the realization of increased coal quality, hence higher market 

value at greater depths.

Limited coal quality data for coal beds in the Wasatch 

Formation are available. No significant, large-scale mining has 

occurred in the Wasatch coal beds in the PRB, even though 

the Healy bed in the Lake DeSmet area (fig. 2) is the thickest 

known coal bed in the contiguous United States (Jones, 2010). 

A summary of coal quality data for the Wasatch Formation is 

presented in table 5. In general, these coal beds have higher 

ash and sulfur contents and lower calorific values than the Fort 

Union Formation coals currently being produced in the PRB 

(Luppens and others, 2008). Partings are common and fairly 

persistent in many Wasatch coal beds, which probably contribute to the lower quality (Mapel and others, 1953; Jones, 2010).

Limitations with existing published Wasatch Formation 

coal quality information stem from both the accuracy and, in 

particular, the representativeness of the data. Mapel and others (1953) noted that the moisture content for the Bureau of 

Reclamation Core (table 5) was anomalously low (which they 

attributed to unaccounted for moisture loss during shipping 

and handling), yet the analytical results were used in calculating the average coal quality for the Lake DeSmet area cores. 

Given the fact that several face channel samples from mines 

in the Lake DeSmet area had moistures values in excess of 

30.5 percent, all the core samples appear to be at least 1.5 to 
Table 4. Available as-received coal quality data from the Fort Union Formation in the Southwestern Powder River Basin assessment area. (British T(BTU/lb); Moist, mineral-matter free (m,mmf); Subbituminous B (subB); Subbituminous C (subC).

Area name/Coal bed name No. of analyses Moisture % Sulfur % Ash %

Gross 

Calorific

Value 

(Btu/lb)

Pounds of

SO2/million 

Btu

G

Dry Cheyenne coal field-Stevens North area3

Roland of Baker (1929) coal bed 5 28.7 0.51 7.7 7,831 1.30 

Smith coal bed 2 26.1 0.47 7.5 8,247 1.14 

Glenrock coal field-Stevens area3

Roland of Baker (1929) coal bed 1 22.2 0.42 14.7 7,860 1.07 

Smith coal bed 1 23.5 0.38 4.4 9,010 0.84 

Glenrock coal field-Dave Johnston Mine

Roland of Baker (1929) coal bed4 5 27.4 0.45 7.9 7,950 1.13 

Smith bed face channel sample 74-364 1 20.7 0.5 15.7 7,850 1.27 Smith bed face channel sample 74-374 1 19.5 0.7 8.8 8,870 1.58 Typical Smith bed core sample analyses from Dave Johnston Mine4 1 26.4 0.5 9.7 7,830 1.33 Smith coal bed (average of 3 analyses above from Glass/Jones)5,7 3 22.2 0.6 11.4 8,180 1.47 Dave Johnston Mine (produced averages)7 --- 26.6 0.45 12.1 7,581 1.19 

Sussex coal field4,5

Reported Value1,4 1 23.5 0.49 5.2 9,160 1.07 

Basin 21,6 1 28.8 0.56 6.7 7,930 1.41 

Basin 31,6 1 23.6 0.68 7.8 8,450 1.61 Basin 41,6 1 18.8 0.57 7.8 9,160 1.24 
Table 4. Available as-received coal quality data from the Fort Union Formation in the Southwestern Powder River Basin assessment area. (British T(BTU/lb); Moist, mineral-matter free (m,mmf); Subbituminous B (subB); Subbituminous C (subC).—Continued Area name/Coal bed name No. of analyses Moisture % Sulfur % Ash % Gross Calorific Value (Btu/lb) Pounds of SO2/million Btu G

Sussex coal field4,5 Basin 51,6 1 23.5 0.49 5.2 9,050 1.08 

Basin 61,6 1 28.1 0.45 4.6 8,350 1.08 Average of 5 Basin Analyses 24.6 0.6 6.4 8,588 1.28 

Estimated Average of 5 Basin analysis (adjusted to 30% moisture)1 30.0 0.51 6.0 7,969 1.28 

Deep Basin coal bed Smith (Big George) coal bed 2,8 22.6 0.25 3.5 9,750 0.51 

1Partial Bed Sample 2Unweighted average of 30 incremental samples from a 200-ft-thick cored portion of the bed below 1,000 ft 3Western Fuels Association, Inc., 1983 4Glass, 1975 5Glass, G.B., and Jones, R.J.(1992) 6Wegemann, C.H. (1912) 7Glass (1997) 8Jones (2010)
Table 5. Available as-received coal quality data from the Wasatch Formation in the Lake DeSmet area in the Southwestern Powder River Basin assThermal Unit per pound (BTU/lb); Moist, mineral-matter free (m,mmf); Subbituminous B (subB); Subbituminous C (subC); Lignite A (ligA).

Area/Coal bed name

No. of 

analyses

Coal bed 

interval

Analytical 

interval Total interval

cored

Total

feet

analyzed

Recovery 

%

Moisture 

%

Sulfur 

%

Ash 

%

Calorific 

value 

(Btu/lb)

Lbs

SO2 

mill

Bt

From To From To

Lake DeSmet area 15

Healy coal bed1 1 28.5 0.6 7.6 7,880 1.

USGS-1 Core1 59.0 141.7 59.0 141.7 82.7 45.5 55.0 29.1 0.6 5.1 7,970 1.

USGS-2A Core1 66.0 119.0 66.0 119.0 53.0 40.8 77.0 30.5 0.5 6.1 7,845 1.USGS3 Core1 101.0 159.7 118.7 159.7 58.7 37.2 63.4 28.3 0.6 7.7 7,890 1.

USGS-6 Core1 172.0 285.0 172.0 272.0 113.0 68.1 60.3 29.3 0.6 9.2 7,515 1.

Bureau of Reclamation Core1 95.0 224.0 95.0 224.9 129.0 101.6 78.7 23.6 1.0 9.7 8,270 2.

Weighted average of all 5 core 

holes

5 27.0 0.7 8.1 7,940 1.

Estimated average of 5 basin 

analyses (at 30.5 % moisture)

5 30.5 0.7 7.7 7,559 1.

Healy coal bed (face channel 

mine sample)

1 30.7 0.4 5.1 7,900 1.

Bed 120 feet below Healy 

coal bed (face channel mine sample)

1 31.1 1.4 8.8 7,350 3.

1Partial bed sample
28 Assessment of Coal Geology, Resources, and Reserves in the Southwestern Powder River Basin, Wyoming

3.0 percent low. Therefore, the average values for the core 

samples in table 5 were adjusted to a more realistic 30.5 percent (Luppens, 2011). 

Unlike the moisture issue, the representativeness of the 

data is more difficult to evaluate due to a combination of 

incomplete core recovery and, specifically, the exclusion of 

all high ash intervals greater than 3/8 inch in thickness for 

all USGS core samples. U.S. Geological Survey guidelines 

at the time mandated that their samplers strictly followed the 

exclusionary procedure for partings and pyrite of certain thicknesses (Golightly and Simon, 1989). The percent of the coal 

bed analyzed recovery ranged from about 57 to 78 percent 

(table 5). The total amount of shale partings excluded from the 

recovered core ranged from 1.1–33.8 ft and averaged 12.8 ft 

or about 14 percent of the total recovered core. Therefore, the 

core hole analytical results cannot be considered even close 

to being representative, especially with all high ash and pyrite 

partings excluded.

Core hole USGS-1 had a percent of excluded shale to 

total recovered core that was similar to that of the 5 core holes 

(table 5). Luppens (2011) used this core hole to derive an estimate of the weighted composite coal quality of the coal with 

the excluded shale. The results of this compositing effort were 

ash contents that ranged from about 13.0–15.5 percent and 

gross calorific values from 6,700–7,000 Btu/lb. This composite estimate more than doubles the average ash content from 

the original reported for USGS-1 of 5.1 percent (table 5) with 

a corresponding penalty to the gross calorific value. Additionally, the effects on the average sulfur content of the composited estimates were impossible to assess due to a lack of data 

but intuitively, the sulfur content for the whole bed should be 

higher than reported with deliberate exclusion of the black 

shale and pyrite-rich partings.

The thorough review of the original report for the Lake 

DeSmet area resulted in a projected average coal quality that 

was significantly lower than the published data. With the relatively high ash and sulfur contents combined with low gross 

calorific values, the estimated coal quality of the area is not 

competitive with any other coal currently being produced in 

the Powder River Basin.

The previous discussion demonstrates why it is always 

preferable to research and evaluate the circumstances regarding the sampling and analytical results from the original 

source when evaluating coal quality information, especially 

when only limited data are available. Cited data often omit 

important information such as moisture integrity and the 

information needed to evaluate the issue of representativeness. 

Using the available published data at face value would have 

significantly over-estimated the coal quality for all the coal 

fields from both the Fort Union and Wasatch Formations in the 

SWPRB assessment area. However, if sufficient sampling and 

handling information is provided, it is often possible to make 

adjustments to reported data to derive more reasonable coal 

quality estimates.

Mine Model Design

Mine models have been developed to evaluate multiple 

and single coal bed resources in the Powder River Basin for 

their potential as reserves. The model included only a single 

pass longwall underground mining model. Each model is 

developed to produce a conceptual costing estimate that 

includes identification of primary capital expenditures and 

operating costs. The models are integrated with economic 

analyses that identify scheduled expenditures for equipment 

and facilities replacement, depreciation in accordance with 

current Internal Revenue Service guidelines, estimate accuracy 

in terms of cost contingency, and a typical return on investment. The economic model is used to determine the total costs 

for the term of the designated project life and the total mass of 

coal mined during this period and by the methodology through 

which the costs were generated. The calculated result is a 

break-even cost per short ton of mined coal. The breakeven 

cost is the calculated mid-point: values above the mid-point 

denote profitability and values below the mid-point denote 

economic loss. The models are structured to provide instantaneous results from adjustments to key parameters and thereby 

provide a tool for comparisons among operating alternatives.

Economic Analysis Methodology

The breakeven cost per ton is determined through discounted cash flow rate of return analysis. Annual cash flow, 

the difference between income and expense per year, is modified in this analysis to include only the expense component. 

Income is determined from the amount needed to recover 

the total of all yearly expenses at a rate of return for a project life that is expressed in years. The rate of return can vary 

from year to year or over the span of several years, but in this 

analysis the rate of return is set at 8 percent (T.K. Lee, written 

commun., 2004). The project life is set at 20 years, a common term or span over which capital and operating items are 

expended. All expense values are expressed in present worth 

or current dollar values.

Capital expenditures are made prior to the infusion of 

income into a project. The convention used in this report 

combines all expenditures into an initial cost made at project 

year 0. Year 0, whenever it is assigned, is the moment at which 

expenditures are expressed in current dollar values. This report 

is produced in calendar year 2010 and project year 0 is 2010. 

Indirect capital cost and similar expenses are applied as a 

percentage of the initial capital investment for lease acquisition, engineering, home office overhead when applicable, and 

similar expenses. An amount of 9 percent is added as indirect 

cost (engineering, construction management and overhead, 

working capital, and so forth). Amortization and salvage are 

excluded in this evaluation.

Subsequent capital expenditures for equipment and facility replacement are made in various project years (5, 7, 10, 14, 

15, and so forth) to account for wear and obsolescence, and 
Coal Reserve Evaluation Methodology 29

are then discounted using the Single Payment Present Worth 

calculation to project year 0 to show their true present worth. 

This calculation may be expressed as: 1/(1+i)n where “I” is the 

interest rate and “n” is the number of compounding periods. 

As these analyses are performed on an annual basis, “n” 

equals one for each year. This calculation is used to discount 

a single future cost or income value to a single present value. 

Time-value discounting is also applied to annual operating 

costs, which is determined using the Uniform Series Present 

Worth calculation and to depreciation. The Uniform Series 

Present Worth formula is shown as: [(1+i) n

 -1]/I. This calculation is used to discount a series of uniform future values to a 

single present value.

All equipment and facilities have been depreciated as 

per Internal Revenue Service guidelines (Department of the 

Treasury, 2008). The convention used herein is to depreciate capital items as quickly as allowable—that is, 5- and 7-yr 

class life capital items use the 200 percent declining balance 

method, 15- and 20-yr class life capital use the 150 percent 

declining balance method, and 39-yr class life capital uses the 

straight line method. Annual depreciation amounts for each of 

the class life designations are calculated using standard percentages provided in the Modified Accelerated Cost Recovery 

System General Depreciation System and totaled for each year 

of the 20-yr project life (Department of the Treasury, 2008).

Some key equipment items may not be replaced during 

the project life and will continue in service past the designated 

depreciation period. These items in the surface and underground mining models have been depreciated nonetheless 

in accordance with IRS Publication 946 (Department of the 

Treasury, 2008). The amount for each year was discounted to a 

total present value. When the major expenditures have all been 

discounted to present dollar values, the break-even cost per ton 

mined is calculated from the major costs as shown in table 6. 

The costs shown in table 6 represent the Case 1 evaluation 

described later in this report.

Total values shown in table 7 represent the expenditures over an economic project life of 20 years. The total 

capital cost including initial and replacement capital expenditures equals the total cash flow in this calculation and can 

be reversed bottom to top to determine the required capital 

expenditure to support a fixed cost and production level. 

Exclusions to the above calculation are depletion allowance, 

salvage, and working capital. These charges over a long project life are minor and are included within the cost contingency. 

Estimation of expenditures is performed at a high level in this 

report to keep the order-of-magnitude estimates.

Cost estimates performed for this report are conducted at 

a conceptual feasibility level corresponding with a Class IV 

or 4 estimates as defined by the Association for the Advancement of Cost Engineering (AACE, 1997) as shown in table 8. 

A contingency is usually applied to all cost estimating 

practices. The cost contingency is determined by the level of 

project definition, preparatory effort, and whether a judgment, 

stochastic estimating, or definitive estimating method is used. 

Contingency is calculated as a percentage of the estimated 

costs and added to the estimated costs to give the total project 

cost.

The level of contingency is also related to time and type 

of industry. Association for the Advancement of Cost Engineering (AACE, 1997) contingency guidelines for estimate 

accuracy usually pertain to construction and general applications and have been adjusted in table 8, which represents 

values commonly used in the mining industry. Normally, as a 

mining project moves from inception to construction and subsequent production, the accuracy percentage range decreases 

with the inclusion of additional information. 

Underground Mine Model Assumptions

An underground mining model was developed to evaluate 

the potential for extraction from eight deep coal beds including the Roland (Baker), Smith, Anderson, Dietz 3, Canyon, 

Lower Canyon, Werner, and Otter (figs. 45, 48, 51, 54, 60, 63, 

66, and 69). Large areas within all these coal beds are 10–20 ft 

thick with much greater thicknesses of 60–100 ft in the Anderson, Canyon, and Otter coal beds. Locally, the Smith coal bed 

thickens to as much as 150 ft (fig. 48). The resources for the 

eight coal beds are all within the mineable depth of 2,000 ft 

from the surface, and thus all are potential resources.

The underground mining of very thick coal beds has not 

been a practice within the United States although, thick underground coal beds have been mined elsewhere by a variety of 

methods. Conventional longwall mining technology was chosen as the method of choice in this report. Current face shearer 

and roof prop designs are available for mining to a maximum 

thickness of 20 ft.

The underground mine model is based on a typical single 

pass longwall mining methodology that can produce a nominal 

6 MST of coal per year, which is an average size for currently 

operating longwall mines (fig. 94). The model has the flexibility to allow for varying mining thicknesses from 8–20 ft 

and depths of less than 1,000–2,000 ft. The model can be used 

to evaluate a wide range of annual production rates with some 

adjustment to longwall panel access openings and pillar sizes.

The mining model was designed for primary entry to the 

longwall panel through five parallel main drifts. Additional 

excavation included a three entry headgate for incoming 

airway and main access to longwall mining and two entry 

tailgates for return airway and supplies. Both the headgate and 

tailgate openings extend perpendicular from the main entries 

to the full panel length and are separated by the width of the 

longwall panel. An initial longwall face opening is excavated 

at the far end of the longwall panel that connects the headgate 

and tailgate. Excavation dimensions for the mining model are 

shown in table 9.

A longwall unit in the underground mine model includes 

five parallel main drifts, a three entry headgate, a two entry 

tailgate, a longwall face, and a panel. All mains, including headgate and tailgate entries, are the standard 10 ft high 
30 Assessment of Coal Geology, Resources, and Reserves in the Southwestern Powder River Basin, Wyoming

Table 6. Costs by underground mining case for the Southwestern Powder River Basin assessment area based 

upon a 20-year project life at an annual production rate of 6 million tons per year. All major costs are shown in mid 

calendar year 2010 dollar values and breakeven costs in dollars per ton.

Case 1 Case 2 Case 3 Case 4

Mining height 10 ft 20 ft 10 ft 20 ft

Depth 1,000 ft 1,000 ft 2,000 ft 2,000 ft

Capital cost $385,600,000 $375,900,000 $408,600,000 $400,900,000

Depreciation $167,900,000 $164,700,000 $172,700,000 $168,900,000

Operating cost $3,218,500,000 $3,166,800,000 $3,276,200,000 $3,227,300,000

Breakeven cost per ton $30.94 $30.40 $31.69 $31.20

Table 7. Costs of underground longwall mining for the Southwestern Powder River Basin assessment area based 

on a 20-year project life at an annual production rate of 6 million tons. All costs are shown in mid calendar year 2010 

dollar values and breakeven cost in dollars per ton.

Component Cost

Capital cost $385,600,000

Depreciation $167,900,000

Operating cost $3,213,000,000

Breakeven cost per ton $30.94

Table 8. Contingency alternatives for estimating costs for longwall mining.

Type Methodology Level of Detail Accuracy range

Order of Magnitude Judgment or stochastic 0-2% Up to 50%

Conceptual Stochastic 1-15% +30/-15%

Budgetary Mixed stochastic and deterministic 10-40% +15/-10%

Definitive Deterministic 50-100% +10/-5%

Table 9. Underground excavation dimensions in the longwall mining model for a 10-foot mining height.

Number Height (feet) Width (feet) Length (feet)

Main entries 5 10 24 1,945

Main crosscuts 94 10 18 85

Headgate 3 10 18 11,635

Headgate crosscuts 131 10 18 65

Tailgate 2 10 16 11,635

Tailgate crosscuts 66 10 16 65

Longwall entry 1 10 18 1,000
Coal Reserve Evaluation Methodology 31

regardless of the mining height (8–10 ft). Opening widths 

are 24 ft for the mains, 18 ft for the headgate, and 16 ft for 

the tailgate. Crosscuts are 18 ft wide for the mains, headgate, 

and tailgate. Pillars in the mains are 65 by 85 ft and the chain 

pillars in the headgate and tailgate are 65 by 160 ft. The 

panel barrier pillar varies from 160 to 300 ft wide, depending 

on mining height and depth. Only the panel barrier pillar is 

adjusted for depth. Other pillars in the panel development have 

been oversized. A panel width of 1,000 ft is used for coal having a 10 ft mining height and 500 ft for a 20 ft mining height.

Annual production for the underground mine model is 

the sum of coal mined from main access, headgate and tailgate 

excavation, longwall production, and pillar recovery. Physical 

dimensions of the longwall panel and associated mine openings are adjusted to maintain 6 MST per year. The effects of 

increased mining height and depth have been correlated with 

variable panel barrier pillar size and overall pillar recovery. 

The longwall panel width varies only with mining height and 

the panel length is adjusted to provide an overall annual production from entries, panel, and pillars of or near six million 

tons.

Underground mining requires both surface and subsurface support facilities and mining system, which is identified as the longwall unit. Expenditures for surface support 

facilities include land improvements, buildings, other facilities 

(electrical distribution, natural gas service, fuel storage, and 

water treatment), plant site equipment, hoisting plant, ventilation plant, and coal handling. Only costs associated with hoisting, ventilation, and water handling are appreciably changed 

with variable mining depths. Underground support facilities 

include shaft and ramp construction and furnishing, shaft 

and ramp station construction and equipment, underground 

ventilation, and all non-surface coal handling. The main drifts 

excavated from the shaft and ramp stations to the limit of the 

shaft-ramp barrier pillar are considered pre-development and 

expensed as a capital cost. All coal derived from pre-development is disposed at the surface. Variations in mining depth 

affect shaft, ramp, inclined conveyor, ventilation, and electrical distribution costs. A slight adjustment is applied for electrical distribution, chiefly for increased electrical cable size. The 

longwall unit includes all longwall face and entry development equipment needed to excavate and maintain underground 

openings previously described.

Resources Evaluation 

Original resources were calculated for all coal beds more 

than 2.5 ft thick and with no restrictions taken out. Remaining 

resources were calculated using the volume of the original 

resource minus the volume of coal that had been mined. Land 

use (environmental) and technical restrictions were then calculated and subtracted from the remaining resource to determine 

available resources. 

The 23 coal beds evaluated in the SWPRB assessment 

area are calculated to contain 369 BST of original coal 

resources (tables1, 2, and 3). The majority of the available 

resources, 295 BST (80 percent of the total), are on Federal 

lands (table 2). About 12 MST of the total original coal 

resource have already been mined, and approximately 16 BST 

are affected by restrictions (land use, and technical). The 

subtraction of all the restrictions to mining leaves 341 BST 

(92.4 percent) of the total original coal resource available for 

development in the SWPRB assessment area. 

Coal resource reliability categories for the original coal 

resources for the 23 assessed coal beds are summarized in 

table 1. About 65.7 percent of the total original resources can 

be classified as measured and indicated, reflecting the overall 

substantial improvement in geologic confidence provided by 

the additional data included in this assessment.

Surface Coal Economic Analyses Results

Some of the key geological criteria used to evaluate the 

potential for surface mining of a coal bed are: thickness, depth 

(overburden thickness), areal extent, structural complexities, 

data distribution, and coal quality. Since there are differences 

in the coal geology between the Fort Union and Wasatch Formations, each formation is discussed separately.

Fort Union Formation

There are significant changes in the basic coal geology of 

the Wyodak-Anderson coal zone moving from the Gillette coal 

field (Luppens and others, 2008) to the NWPRB assessment 

area (Scott and others, 2010) and to the SWPRB assessment 

area. The most notable change is the thinning and splitting of 

the deep, thick Wyodak zone towards the southern and western 

flanks of the PRB. This thinning can be readily observed in 

the cross sections (figs. 12–20) and the coal bed isopach maps 

(figs. 45, 48, 51, 54, 60, and 63). Additionally, the cross sections (figs. 12–20) illustrate that the Wyodak zone coal beds 

are thin and (or) pinch out throughout much of the SWPRB 

assessment area before the beds reach shallower depths where 

recovery by surface mining would be practicable. Relatively 

steep dips (10°–25°) of any coal beds on the western flank of 

the PRB such as the Sussex coal field are also a limiting factor 

(fig. 2).

The composite stripping ratio map for the Fort Union 

coals is shown in fig. 10. The only shallow resources at less 

than a 10:1 stripping ratio are a narrow band of the Roland 

(Baker) and Smith coal beds in the southern portion of the 

SWPRB assessment area which coincides with the abandoned 

Dave Johnston Mine. Figure 11 illustrates the geographic 

setting for this area with less than 10:1 stripping ratio. This 

area lies on the axis of the PRB with no other Fort Union 

Formation coal beds present. The relationship between the 

Smith coal bed in the Glenrock coal field and the Powder 

River Basin structural axis is shown on overburden depth 

map for the Smith coal bed (fig. 49). The coal reliability maps 

for the Roland (Baker) and Smith coal beds (figs. 47 and 50) 
32 Assessment of Coal Geology, Resources, and Reserves in the Southwestern Powder River Basin, Wyoming

demonstrate the lack of sufficient drilling to adequately assess 

the surface recoverable resources left in the Glenrock coal 

field (fig. 2).

Associated with the thinning and splitting of the coal 

beds is the presence of more numerous high ash partings that 

negatively impacted the coal quality by increasing the ash content and lowering the calorific values. The potential for even 

lower grade coal quality was a factor in the decision to close 

the Dave Johnston Mine, the only large commercial mine in 

the SWPRB assessment area. Closure of this mine reflects the 

trend of decreasing coal quality along the shallow southern 

and western flanks of the SWPRB assessment area. The combined effects of the lack of extensive, thick, and shallow coal 

bed exploration targets with attractive coal quality has resulted 

in a lack of sufficient drilling (both conventional coal exploration holes and coalbed methane development). Sufficient 

drilling is necessary to adequately assess surface recoverable 

coal resources of the SWPRB assessment area on a regional 

basis. Therefore, no economic analysis of the surface recoverable Fort Union Formation coals (Roland of Baker (1929) 

and Smith) was performed for the assessment of the SWPRB 

assessment area. 

Wasatch Formation

The Buffalo-Lake DeSmet area (fig. 2), near Buffalo and 

Lake DeSmet, contains Wasatch Formation coals that have 

been evaluated a number of times in the past for potential 

mining (J.A. Luppens, oral commun., 2010). Despite the fact 

that the Healy coal bed in the Buffalo-Lake DeSmet area is 

the thickest known coal bed in the contiguous United States 

(Jones, 2010), no significant, large-scale mining has occurred 

in the Wasatch coal beds in the PRB. The USGS assessment 

of coal resources within the NWPRB assessment area (Scott 

and others, 2010) and the SWPRB assessment have been used 

to model two potentially minable coal beds, the Upper Healy 

and the Healy. Because these two coal beds occur within both 

the NWPRB and SWPRB assessment areas (fig. 1), a smaller 

area of assessment was created from both of the assessment 

areas that encompass the complete areal extent of these two 

coal beds.

Resources of these two coal beds that are available for 

mining are shown in table 10. The resources are based on coal 

bed thicknesses of at least 5 ft, overburden not greater than 

500 ft, and a composite stripping ratio of not greater than 10:1. 

Figure 95 shows the extent of the two coals where the stripping ratio is up to 5:1; figure 96 shows their extent where the 

ratio exceeds 5:1 and up to 10:1. The figures also show the 

mining restrictions applicable to the cities of Sheridan and 

Buffalo, interstate highways 25 and 90, the Burlington Northern Santa Fe Railway route, and Lake DeSmet.

A comparison of figures 95 and 96 shows that the majority of the two coal beds have composite stripping ratios of 

greater than 5:1 that are less favorable from a recovery standpoint. Furthermore, figures 95 and 96 show that the restrictions for Buffalo, Lake DeSmet, and the interstate highways 

significantly impact the availability of the coal beds for mining, especially where the composite stripping ratios are most 

favorable for mining (less than 5:1). In addition, the upper 

portions of these coal beds have been burned over much of the 

area (Smith and others, 1972; Glass, 1997) and the extent of 

the resulting clinker can be seen in figures 95 and 96.

It is suspected that coal quality issues might also be a 

contributing factor for the lack of significant mine development in the Buffalo-Lake DeSmet area. Luppens (2010) 

reviewed the published coal quality data from the BuffaloLake DeSmet area and significant problems were discovered 

from the standpoint of both representiveness of the samples 

analyzed and anomalous moisture values. The published 

and predicted coal quality data values are shown in table 5. 

As discussed earlier, the USGS cores all had high ash layers greater than 3/8 inch removed. The USGS cores adjusted 

to a more reasonable moisture content of 30.5 percent; ash 

of 8.8 percent; sulfur of 0.9 percent; and a calorific value of 

7,512 Btu/lb. The quality parameters are significantly inferior 

to coals currently being produced from the PRB (Luppens 

and others, 2008; and Scott and others, 2010) and would pose 

a competitive disadvantage for developing the Lake DeSmet 

resources.

Due to the combination of effects within this area–

including limited favorable stripping ratios, restrictions to 

mining, predicted inferior coal quality, and areas of clinker–a 

reserve analysis was performed for neither the Upper Healy 

nor the Healy coal beds. Although small areas of these beds 

could possibly be mined in the future, this scenario was not 

addressed here because of the regional scope of this assessment and the lack of sufficient data necessary to outline 

specific small areas for potential surface mining.

Underground Coal Economic Analysis Results

The Southwestern Powder River Basin assessment area 

has limited shallow resources available for surface mining. 

Although no coal is currently being mined underground, there 

are significant resources in deep, thick coal beds. An assessment was performed to define the volume of these thick coal 

beds and define a threshold where underground mining might 

become a viable alternative to surface mining.

Underground Coal Resources

Eight coal beds within the SWPRB assessment area were 

assessed as potentially minable by underground methods. 

These coal beds, which have favorable thicknesses, depths, 

and areal extents for possible underground extraction in 

the future, are the Roland (Baker, 1929), Smith, Anderson, 

Dietz 3, Canyon, Lower Canyon, Werner, and Otter. Except 

for limited areas under major drainages, such as the Powder 

River, the depths to the Roland (Baker, 1929), Smith, Anderson, and Dietz 3 coal beds exceed 1,000 ft in depth. Essentially all of the Canyon, Lower Canyon, Werner, and Otter 
Conclusions 33

coal beds are found at depths of 1,000 ft or greater. Table 11 

shows the coal resources associated with these eight coal beds, 

with the resources for each bed divided into two thickness 

categories (10–20 ft and > 20 ft) in combination with two 

depth categories (500–1,500 ft and 1,500–2,000 ft). Estimated 

optimal coal bed thicknesses for longwall system applications 

for the PRB are 10–20 ft. However, current longwall cutter 

heights are limited to a maximum of 20 ft.

As can be seen in table 11, the Smith coal bed contains the largest amount of potentially minable underground 

resources (82 BST); the Canyon coal bed contains the next 

largest amount (52 BST), followed by the Lower Canyon coal 

bed (24 BST). Collectively, these three coal beds constitute 

158 BST or 79 percent of the total potentially underground 

minable resources of 201 BST. It must be emphasized that 

these potentially minable resource estimates represent a best 

case scenario, since an inventory of restrictions to underground mining has not been performed. It is certain that 

various restrictions–such as the geotechnical constraints of 

adverse roof and floor conditions, local coal bed thinning, and 

hydrology issues–would reduce the amount of coal resources 

ultimately recovered. Nevertheless, the deep, thick coal beds 

in the Southwestern Powder River Basin assessment area 

represent a significant future resource.

Underground Mining Model Analysis

Four economic mining cases were evaluated for their 

potential breakeven cost per ton. Though the mining height 

varied from 10 to 20 ft, and the depth from 1,000 to 2,000 ft, 

the average breakeven cost per ton was about $31.00 at an 

interest rate of 8 percent for a 20 yr project life. Major mining 

costs are summarized in tables 7 and 8.

The width of the typical longwall panel in the mining 

model is the main parameter affecting the economic results of 

the four cases in table 6. As the mining height was doubled, 

the longwall face width was halved, which resulted in shorter 

cutting time for each exposed longwall face; larger and more 

expensive (but fewer) roof shields; and decreased chain pillar 

recovery. Doubling of the mining depth affected surface and 

underground support systems (increased headframe structures, 

larger diameter hoisting ropes, additional shaft fixtures, surface ventilation fans, increased shaft depths and ramp length, 

and increased inclined conveyor length) and mining recovery.

The average cost of mining coal in the SWPRB assessment area using the longwall method for 10–20 ft thickness 

at 1,000–2,000 ft depth was about $31/ton (tables 7 and 8) 

($0.75/ton range from low to high values). The estimated calorific values of the deep coals range from about 9,300 Btu/lb at 

1,000 ft in depth to 10,000 Btu/lb at 2,000 ft in depth (fig. 93). 

Although the mining costs increase with depth, those higher 

costs might be offset by the realization of progressively higher 

quality coal with depth.

The price for Powder River Basin coal for the week ending October 25, 2010 was $14.10 for coal at 8,800 Btu/lb and 

$11.60 for 8,400 Btu/lb (Platts Coal Outlook, 2010). Because 

the current market price is approximately double the current 

market sales price, none of the coal resources in the eight 

deep coal beds in the SWPRB assessment area can currently 

be classified as reserves. However, longwall model analysis 

demonstrates that as the surface mining depths continue to 

increase in other parts of the PRB, underground exploitation of 

the deep, thick coal resources of the SWPRB assessment area 

may become a more viable alternative as long as the demand 

for coal remains strong.

Conclusions

The assessment of the SWPRB assessment area adds to 

the resource and reserve estimates in the PRB. The extensive 

amount of coalbed methane development in the PRB over the 

last ten years has provided a wealth of new, publicly available 

data, especially in the SWPRB assessment area. An important 

distinction of the SWPRB assessment area compared to the 

other PRB assessments (Luppens and others, 2008; Scott and 

others, 2010) is the absence of the extensive thick, shallow 

Wyodak coal zone. Some of the key results of this assessment 

are as follows:

Table 10. Available resources for beds greater than or equal to 5.0 foot thick, overburden less than or equal 

to 500 feet, and < 10:1 strip ratio, reported in millions of short tons by stripping ratio for the Southwestern 

Powder River Basin assessment area. Resource includes coal plus partings. Columns may not sum exactly 

due to rounding.

Coal 

Bed 

Name

Stripping Ratio Total

1:1-5:1

Total

6:1-10:1

Total

1:1 2:1 3:1 4:1 5:1 6:1 7:1 8:1 9:1 10:1 (1:1-10:1)

Upper 

Healy

0 72 133 343 527 585 555 406 267 204 1,075 2,017 3,092

Healy 194 319 431 502 645 681 581 471 369 325 2,091 2,427 4,518

Total 194 391 564 845 1,172 1,266 1,136 877 636 529 3,166 4,444 7,610
34 Assessment of Coal Geology, Resources, and Reserves in the Southwestern Powder River Basin, Wyoming

• The significant increase in the number of available 

drill holes has increased the resource values for 

measured, indicated, and inferred resources in the 

SWPRB. Of the total original resources, for measured and indicated resources, about 65 percent are 

available. This increase in data also significantly 

improved the geological interpretation, including 

revision of coal bed correlations and definition of 

framework channels that controlled the areal extent, 

thickness, and depth of individual beds. 

• The new geologic coal bed models not only provide a more robust assessment of recoverable coal 

resources but will also facilitate other resource 

planning, such as development of coalbed methane 

resources and evaluating the environmental impacts 

of energy-related production.

• The Wyodak coal interval that is of paramount 

importance in the Gillette coal field is thinning and 

splitting to the west and south in the SWPRB assessment area. This thinning and splitting adversely 

affects strip ratios and hence the economics for any 

particular project. Therefore, no economic modeling 

of Fort Union coals for surface mining was practical.

• In the Wasatch Formation, the Upper Healy and 

Healy coal beds have not been mined because of the 

extensive development of clinker and also the poor 

coal quality compared to deeper coal beds. Therefore, no economic modeling of the Wasatch coals for 

surface mining was practical. 

• Eight coal beds are present at depths from 500–2,000 

ft within the SWPRB assessment area. These eight 

coal beds represent a potential underground resource 

of 201 BST. These resources are sub-economic and 

are not considered as reserves or as recoverable at 

this point in time.

• Fifteen significant coal beds were correlated to 

coal beds in the Gillette coal field and the NWPRB 

assessment area. These correlations show the continuous geologic structure of the coal beds across the 

Powder River Basin. 

• The original coal resource in the SWPRB assessment area for all 23 coal beds assessed, with no 

restrictions applied, was calculated to be 369 BST. 

Available coal resources, which are part of the 

original coal resource that is accessible for potential 

mine development after subtracting all restrictions, 

are about 341 billion short tons (92.4 percent of the 

original coal resource). All coal resources in the 

SWPRB assessment area are considered to be subeconomic at this point in time.

Acknowledgments

We would like to acknowledge the following people 

for helping with this publication. Nicholas Jones and staff 

of the Wyoming State Geological Survey supplied drill-hole 

data. Ed Heffern, of the U.S. Bureau of Land Management 

in Cheyenne, Wyoming, supplied the digital file that shows 

the extent of clinker within the southwestern Powder River 

assessment area. Norman Braz, Bureau of Land Management 

in Casper, Wyoming, supplied the digital data that show the 

extent of mined out areas within the southwestern Powder 

River assessment area. Ron Affolter, Joe East, Dick Keefer, 

and Margaret Ellis, all of the USGS, provided technical 

reviews of the manuscript. Tim Grant of the National Energy 

Technology Laboratory of the U.S. Department of Energy also 

provided a technical edit of the manuscript.

Table 11. Underground coal resources for the Southwestern Powder River Basin assessment area (millions of short tons).

Coal thickness and depth 

Coal Bed Name

Roland 

(Baker) Smith Anderson Dietz 3 Canyon Lower Canyon Werner Otter Totals

10-20 feet thick, 500-1,500 feet depth 2,756 4,842 1,725 1,530 2,350 2,289 626 26 16,144

10-20 feet thick, 1,500-2,000 feet depth 151 2,103 19 1,042 1,271 2,482 1,368 543 8,979

Subtotal 10-20 feet thick 2,907 6,945 1,744 2,572 3,621 4,771 1,994 569 25,123

>20 feet thick, 500-1,500 feet depth 1,431 71,115 4,695 6,773 26,496 8,208 308 1,946 120,972

>20 feet thick, 1,500-2,000 feet depth 7 3,842 34 938 21,496 11,367 1,018 16,053 54,755

Subtotal >20 feet thick 1,438 74,957 4,729 7,711 47,992 19,575 1,326 17,999 175,727

Coal Bed Totals 4,345 81,902 6,473 10,283 51,613 24,346 3,320 18,568 200,850
References Cited 35

References Cited

Association for the Advancement of Cost Engineering International (AACE) 1997, Cost Estimate Classification System—

As applied in engineering, procurement, and construction 

for the process industries, AACE International Recommended Practice No. 18R-97.

American Society for Testing and Materials (ASTM International, 2008): Annual Book of ASTM Standards, V. 05.06, 

Chapter D 388-05, p. 250-256. 

Baker, A.A., 1929, The northward extension of the Sheridan 

Coal Field, Big Horn and Rosebud Counties, Montana: U.S. 

Geological Survey Bulletin 806-B, p. 15-67.

Carter, M.D., and Gardner, N.K., 1989, An assessment of 

coal resources available for development: U.S. Geological 

Survey Open File Report 89–362, 52 p.

Coates, D.A., and Heffern, E.L., 1999, Origin and geomorphology of clinker in the Powder River Basin, Wyoming 

and Montana, in Miller, W.R., ed., Coal bed methane and 

the Tertiary geology of the Powder River Basin: Wyoming 

Geological Association 50th Annual Field Conference 

Guidebook, p. 211-229, 1 plate.

Culbertson, W.C., 1987, Diagrams showing proposed correlation and nomenclature of Eocene and Paleocene coal beds 

in the Birney 30’ X 60’ quadrangle, Big Horn, Rosebud, and 

Powder River Counties, Montana: U.S. Geological Survey 

Coal Investigations Map C-113, scale 1:100,000.

Culbertson, W.C., and Mapel, M.J., 1976, Coal in the Wasatch 

Formation, northwest part of the Powder River Basin near 

Sheridan, Sheridan County, Wyoming: Chapter in Wyoming 

Geological Association Guidebook, 28th Annual Field Conference, Casper, Wyoming. p. 193-201.

Culberston, W.C., Kent, B.H., and, W.J., 1979, Preliminary 

diagrams showing correlation of coal beds in the Fort Union 

and Wasatch Formations across the Northern Powder River 

Basin, north-eastern Wyoming and southeastern Montana: 

U.S. Geological Survey Open-File Report 79–1201, 11 p., 

2 diagrams (no scale).

De Bruin, R.H., Lyman, R.M., Jones, R.W., and Cook, L.W., 

2004, Coal bed methane in Wyoming: Wyoming State 

Geological Survey Information Pamphlet 7, second revision, 24 p.

Department of the Treasury, 2008, IRS Publication 946: available at: http://www.irs.gov/publications/p946, accessed in 

June, 2010.

Eggleston, J.R., Carter, M.D., and Cobb, J.C., 1990, Coal 

resources available for development-A methodology and 

pilot study: U.S. Geological Survey Circular 1055, 15 p.

Ellis, M.S., Molnia, C.L, Osmonson, L.M., Ochs, A.M., 

Rohrbacher, T.J., Mercier, T., and Roberts, N.R., 2002, 

Evaluation of economically extractable coal resources in 

the Gillette coal field, Powder River Basin, Wyoming: U.S. 

Geological Survey Open-File Report 02–180, 48p.

Environmental Systems Research International (ESRI), Incorporated, 2000, ArcView software version 3.2a, Environmental Systems Research International, Incorporated, 380 New 

York Street, Redlands, CA 92373, USA.

Environmental Systems Research International (ESRI), Incorporated, 2001, ArcView Spatial Analyst Extension software 

version 2.0, Environmental Systems Research International, 

Incorporated, 380 New York Street, Redlands, CA 92373, 

USA.

Environmental Systems Research International (ESRI), Incorporated, 2006, ArcGIS software version 9.2, Environmental 

Systems Research International, Incorporated, 380 New 

York Street, Redlands, CA 92373, USA.

Flores, R.M., Ochs, A.M., Bader, L.R., Johnson, R.C., and 

Vogler, D., 1999, Framework geology of the Fort Union 

coal in the Powder River Basin, Chapter PF in 1999 

Resource Assessment of selected Tertiary coal beds and 

zones in the Northern Rocky Mountains and Great Plains 

Region: U.S. Geological Survey Professional Paper 

1625–A, 2 CD-ROMs.

Glass, G.B., 1975, analyses and measured sections of 54 Wyoming coal samples: The Geological Survey of Wyoming, RI 

No. 11, 219 p.

Glass, G. B., 1976, Update on the Powder River Coal Basin: 

Chapter in Wyoming Geological Association Guidebook, 28th Annual Field Conference, Casper, Wyoming. 

p. 209-220.

Glass, G.B., 1980, Coal resources of the Powder River Coal 

Basin in Guidebook to the coal geology of the Powder River 

Coal Basin, Wyoming, Field trip no. 5: American Association of Petroleum Geologists Energy Minerals Division, 

June 12-14, 1980, p. 91-124.

Glass, G.B., and Jones, R.J., 1992, Coal Fields and Coal Beds 

of Wyoming: Wyoming Geological Association Reprint 

No. 47, p. 133-167.

Glass, G.B., 1997, Coal geology of Wyoming: Wyoming State 

Geological Survey Reprint No. 63, 21 p.

Glass, G.B., 1997, Coal geology of Wyoming in Sandra, 

A.P., ed., 1997 Keystone Coal Industry Manual, Intertec 

Publishing, Chicago, Illinois.

Golden Software, Inc. Surfer8 software, 2002, Golden Software, Inc., 809 14th Street, Golden, Colorado, 80401-1866, 

USA.
36 Assessment of Coal Geology, Resources, and Reserves in the Southwestern Powder River Basin, Wyoming

Golightly, D.W. and Simon, F.O., 1989, Methods for sampling 

and inorganic analysis of coal: U.S. Geological Survey 

Bulletin 1823, 72p., http://pubs.usgs.gov/bul/b1823/01.htm, 

accessed September, 2010.

Gallegos Research Group (GRG) Corporation, StratiFact software version 4.57, 1998, GRG Corporation, 4175 Harlan 

Street, Wheatridge, Colorado, 80033-5150, USA.

Jones, N.R., 2010, Coal geology of Wyoming in Johnson, P., 

publisher., 2010 Keystone Coal Industry Manual, Mining 

Media International, Jacksonville, Florida.

Kent, B.H., Berlage, L.J., and Boucher, E.M., 1980, Stratigraphic framework of coal beds underlying the western part 

of the Recluse 1 x 1⁄2-degree quadrangle, Campbell County, 

Wyoming: U.S. Geological Survey Coal Investigations Map 

C–81C, 2 plates, scale, 1:100,000.

Law, B.E., Barnum, B.E., and Wollenzien, T.P., 1979, Coal 

bed correlations in the Tongue River Member of the Fort 

Union Formation, Monarch, Wyoming, and Decker, Montana, areas: U.S. Geological Survey Miscellaneous Investigations Series Map I-1128, scale, 1:24,000.

Luppens, J.A., 2011, A critical review of published coal quality data from the southwestern part of the Powder River 

Basin, Wyoming: U.S. Geological Survey, Open File Report 

2011–1148, 40 p.

Luppens, J.A., Scott, D.C., Haacke, J.E., Osmonson, L.M., 

Rohrbacher, T.J., and Ellis, M.S., 2008, Assessment of Coal 

Geology, Resources, and Reserves in the Gillette coal field, 

Powder River Basin, Wyoming: U.S. Geological Survey 

Open File Report 2008–1202, 127 p.

Luppens, J.A., Rohrbacher, T.J., Osmonson, L.M., and Carter, M.D., 

2009, Coal resource availability, recoverability, and economic 

evaluations in the United States—A Summary, in Pierce, B.S., 

and Dennen, K.O., eds., The National Coal Resource Assessment 

Overview: U.S. Geological Survey Professional Paper 1625–F, 

Chapter D, 17 p.

Mapel, W.J., Schopf, J.M., and Gill, J.R., 1953, A thick coal bed 

near Lake DeSmet, Johnson County, Wyoming: U.S. Geological 

Survey Circular 228, 47 p.

Mapel, W.J., 1954, Geology and coal resources of the Lake 

DeSmet Area, Johnson County, Wyoming: U.S. Geological 

Survey Coal Investigations Map C23, scale, 1:50,000.

Mapel, W.J., 1959, Geology and coal resources of the BuffaloLake DeSmet Area Johnson and Sheridan Counties Wyoming: U.S. Geological Survey Bulletin 1078, 148 p.

Mentor Consultants, 2005, PC/Cores, Post Office Box 3147, 

Glen Ellyn, Illinois, USA, 60137.

Molnia, C.L., and Pierce, F.W., 1992, Cross sections showing coal stratigraphy of the southwestern Wyoming Powder 

River Basin, Wyoming and Montana: U.S. Geological 

Survey Miscellaneous Investigations Series Map I-1959-D, 

scale 1:500,000.

Molnia, C.L., Osmonson, L.M., Wilde, E.M., Biewick, L.R.H., 

Rohrbacher, T.J., and Carter, M.D., 1999, Coal availability and recoverability studies in the Powder River Basin, 

Wyoming and Montana, in Fort Union Coal Assessment 

Team, 1999 resource assessment of selected Tertiary coal 

beds and zones in the Northern Rocky Mountains and Great 

Plains Region: U.S. Geological Survey Professional Paper 

1625–A, 119 p.

Obernyer, S.L., 1978, Basin-margin depositional environments 

of the Wasatch Formation in the Buffalo-Lake DeSmet area, 

Johnson County, Wyoming, in Proceedings of the second 

symposium on the geology of Rocky Mountain coal-1977: 

Colorado Geological Survey Resource Series 4, p. 49-65.

Obernyer, S.L., 1980, The Lake DeSmet coal seam, in Guidebook to the coal geology of the Powder River Coal Basin, 

Wyoming: Geological Survey of Wyoming Public Information Circular 14, p. 31-70.

Office of the Federal Register, 2003, code of federal regulations, title 43, part 3460, subpart 3461.5: National Archives 

and Records Administration, p. 588-593, http://www.

gpoaccess.gov/cfr/retrieve.html, accessed June, 2009.

Olive, W.W., 1957, The Spotted Horse Coal Field, Sheridan 

and Campbell Counties, Wyoming: U. S. Geological Survey 

Bulletin 1050, 83 p. 

PACIFICORP, 2008, Dave Johnston Power Plant 50th anniversary and Glenrock Wind Farm community celebration, 

PACIFICOR, Portland, OR.

Pierce, B.S., and Dennen, K.O., eds., 2009, The National Coal 

Resource Assessment Overview: U.S. Geological Survey 

Professional Paper 1625-F, 402 p.

Platts, 2010, Coal Outlook: Platts, a division of The McGrawHill Companies, New York, NY, Vol. 34, No. 37, September 

13, 2010, 12 p. 

Public Law 95-87, 1977 Surface Mining Control and Reclamation Act of 1977, (30 U.S.C. 1201 et seq.), 115 p. http://

www.osmre.gov/smcra.htm, accessed June 2009.

Rice, C.A., Ellis, M.S., and Bullock, J.H., Jr., 2000, Water coproduced with coal bed methane in the Powder River Basin, 

Wyoming-preliminary compositional data: U.S. Geological 

Survey Open-File Report 00-372, 20 p.
References Cited 37

Scott, D.C., Haacke, J.E., Osmonson L.M., Luppens, J.A., 

Pierce, P.E., and Rohrbacher, T.J., 2010, Assessment of 

Coal Geology, Resources, and Reserves in the Northern 

Wyoming Powder River Basin, Wyoming: U.S. Geological 

Survey Open-File Report OF-2010-1294, 137 p.

Smith, J.B., Ayler, M.F., Knox, C.C., and Pollard, B.C., 1972, 

Strippable coal reserves of Wyoming: U.S. Bureau of Mines 

Information Circular IC 8538, 51 p.

Supreme Court of the United States, 1999, Amoco Production 

Co. v. Southern Ute Tribe (98-830), 526, U.S. 865, available 

at http://www.law.cornell.edu., accessed June 2010.

Stermole, F.J., 1974, Economic evaluation and investment 

decision methods; second edition: Investment Evaluations Corporation, 2000 Goldenvue Dr., Golden, Colorado, 

80401, p. 14.

Stricker, G.D., Flores, R.M., Trippi M.H., Ellis, M.S., Olson, 

C.M., Sullivan, J.E., and Takahashi, K.I., 2007, Coal quality 

and major, minor, and trace elements in the Powder River, 

Green River, and Williston Basins, Wyoming and North 

Dakota: U.S. Geological Survey Open-File Report 2007-

1116, 31 p.

Taff, J.A., 1909, The Sheridan coal field, Wyoming, in Coal 

and lignite, Pt. 2: U.S. Geological Survey Bulletin 341, p. 

123-150.

Testa, S.M., and T.J. Pratt, 2003, Sample preparation for coal 

and shale gas resource assessment; in Proceedings, International Coalbed Methane Symposium, Tuscaloosa, Alabama, 

May 5–9, 2003: University of Alabama, Paper 356, 12 p.

Thomas, Larry, 2002, Coal Geology: Dargo Associates Ltd., 

John Wiley and Sons, LTD., West Sussex, England, 365 p.

U.S. Bureau of Land Management, 1999, Final Environmental 

Impact Assessment WY-070-EA-9-191 for the proposed 

Enron (Belco) – BLM coal lease exchange, Casper, Wyoming Field Office, 187 p.

U.S. Bureau of Land Management, 2001, Buffalo resource 

management plan, Appendix D-coal screening process: 

available at: http://www.blm.gov/rmp/WY, accessed June 

2009.

U.S. Bureau of Land Management, 2003, Final Environmental 

Impact Statement and Proposed Plan Amendment for the 

Powder River Basin Oil and Gas Project (WY-070-02-065) 

Buffalo, Wyoming Field Office, 397 p.

U.S. Energy Information Administration, 2010, Energy 

glossary: http://www.eia.doe.gov/glossary/index.cfm, 

accessed September, 2010.

U.S. Environmental Protection Agency, 1980, Standards of 

performance for new stationary source a compilation as of 

July 1, 1980; U.S. Environmental Protection Agency, Office 

of Enforcement, Office of General Enforcement, Division 

of Stationary Source Enforcement. Washington. D.C., 868 

p., http://nepis.epa.gov/Exe/ZyNET.exe/2000WROU.txt., 

accessed September, 2010.

U.S. Environmental Protection Agency, 2005, AirControl NET Documentation report; Pechan Report No. 

05.09.009/9010.463, H. E, Pechan & Associates, Springfield, VA, 1685 p. http://www.epa.gov/air/ozonepollution/

SIPToolkit/documents/DocumentationReport.pdf., accessed 

September, 2010.

Supreme Court of the United States, 1999, Amoco Production 

Co. v. Southern Ute Tribe (98-830), 526, U.S. 865. 

Wegemann, C.H., 1912, The Sussex coal field, Johnson, 

Natrona, and Converse Counties, Wyoming: U.S. Geological Survey Bulletin 471, p. 441-471.

Western Fuels Association, Inc., 1983, Final Showing Report 

Stevens Properties Prospecting Permits, Converse County, 

Wyoming: Western Fuels Association, Inc., Denver, 

Colorado, 25 p.

Wood, G.H., Jr., Kehn, T.M., Carter, M.D., and Culbertson, 

W.C., 1983, Coal resource classification system of the U.S. 

Geological Survey: U.S. Geological Survey Circular 891, 

65 p.

Wyoming Oil and Gas Conservation Commission (WOGCC), 

2009: available at: http://wogcc.state.wy.us, accessed June 

2009.
38 Assessment of Coal Geology, Resources, and Reserves in the Southwestern Powder River Basin, Wyoming

Glossary

The present study includes determinations of original, available, recoverable, and economically recoverable 

(reserves) resources. This terminology has been used in many 

USGS coal studies (see Wood and others, 1983; Carter and 

Gardner, 1989; Eggleston and others, 1990; and Molnia and 

others, 1999). The following definitions were applied in this 

resource evaluation: 

• Available coal resource is the amount of the original resource that is accessible for mine development 

under current regulatory and land-use constraints. This 

resource is the original coal minus previously mined 

coal and coal that cannot be mined owing to land use 

and technical restrictions. 

• Clinker is rock that is produced where coal beds burn 

naturally beneath the ground (Coates and Heffern, 

1999).

• Coal reserves are virgin or accessed parts of a coal 

reserve base which could be economically extracted 

or produced at the time of determination considering 

environmental, legal, and technologic constraints. The 

term reserves need not signify that extraction facilities 

are in place or operative. Reserves include only recoverable coal; thus, terms such as “extractable reserves” 

are redundant and are not a part of the classification 

system. Reserves can be categorized as “measured” 

and “indicated,” as underground or surface minable, 

by thickness of overburden, by thickness of coal in the 

bed, and by various quality factors (Wood and others, 

1983). 

• Coal resources are naturally occurring concentrations 

or deposits of coal in the Earth’s crust, in such forms 

and amounts that economic extraction is currently or 

potentially feasible (Wood and others, 1983). 

• Deterministic is having a predictable outcome due 

to known causes or equivalence to a previous event 

(AACE, 1997, p. 3).

• Discounted cash flow is the stream of the net after-tax 

cash flows where the cash outlays include all operating 

costs, taxes, and investment costs, and where revenues 

include cash payments of product sales. 

• Hypothetical resources are a class of undiscovered 

resources that are either similar to known coal deposits which may be reasonably expected to exist in the 

same coal field or region under analogous geologic 

conditions or are an extension from inferred resources 

(Wood and others, 1983). 

• Headgate is the primary roadway access and egress 

through which equipment, personnel, and supplies are 

provided to a longwall face, through which coal is conveyed to the surface, and through which fresh air flows 

(Stermole, 1974, p. 14). 

• Identified resources are resources whose locations, 

rank, quality, and quantity are known or estimated 

from specific geologic evidence. Identified coal 

resources include economic, marginally economic, and 

subeconomic components. To reflect varying distances 

from points of control or reliability, these subdivisions 

can be divided into demonstrated and inferred, or preferably into measured, indicated, and inferred (Wood 

and others, 1983). 

• Interburden is noncoal material that lies between two 

coal beds. 

• Original coal resource is the total amount of coal inplace before production. Where mining has occurred, 

the total of original resources is the sum of the identified resources, undiscovered resources, coal produced, 

and coal lost in mining (Wood and others, 1983). 

• Overburden is rock including coal or unconsolidated 

material that overlies a specified coal bed. Overburden 

is reported in feet or meters and used to classify the 

depth to an underlying coal bed (Wood and others, 

1983). 

• Parting is a thin layer of stratum or noncoaly material 

within a coal bed which does not exceed the thickness 

of coal in either the directly underlying or overlying 

benches (Wood and others, 1983). 

• Previously mined coal is coal that has already been 

extracted. 

• Recoverable coal resource is coal that is or can be 

extracted from a coal bed during mining. The term 

“recoverable” should be used in combination with 

“resources” and not with “reserves” (Wood and others, 

1983). 

• Reliability categories are based on the distance from 

points of measurement or sampling. The measured, 

indicated, inferred, and hypothetical resource categories, as defined, indicate the relative reliability of 

tonnage estimates as related to distance from points of 

thickness control of particular parts of a coal deposit. 

The reliability categories are not indicative of the 

reliability of the basic data (that is, the accuracy of 

coal measurements, or the accuracy of location of the 

coal outcrop. It is assumed that all basic data used in 

resource estimation have been judged reliable by the 

estimator and that unreliable data have been discarded 

(Wood and others, 1983). 

• Measured—Tonnage estimates computed by 

extrapolation of thicknesses of coal for a radius of 

0.25 mi (0.4 km) from a point of measurement.
Glossary 39

• Indicated—Tonnage estimates computed by 

extrapolation of thicknesses of coal for a radius of 

0.25 to 0.75 mi (0.4 to 1.2 kilometers (km)) from 

a point of measurement.

• Inferred—Tonnage estimates computed by 

extrapolation of thicknesses of coal for a radius 

of 0.75 to 3.0 mi (1.2 to 4.8 km) from a point of 

measurement.

• Hypothetical—Tonnage estimates computed by 

extrapolation of thicknesses of coal for a radius 

beyond 3.0 mi (4.8 km) from a point of measurement.

• Remaining resources are the original resource minus 

the volume of coal that had been previously mined.

• Restrictions to mining include land use, technical 

limitations, and unsuitability that would prohibit mining:

• Land use restrictions are constraints placed upon 

mining by societal policies to protect those surface 

features or entities that could be harmed by mining. Since laws and regulations can be modified 

or repealed, the restrictions, including industrial 

and environmental restrictions, may change. Land 

use restrictions include railroads, cities and towns, 

airports, and interstate highways. 

• Technical restrictions are constraints, relating to 

economics and safety, placed upon mining by the 

state of technology or prescribed by law. These 

restrictions can change with advances in science 

and technology, or modifications in the law. In this 

report, geologic factors are included as technologic restrictions. Technical restrictions include 

coal between 2.5 ft and 5.0 ft thick and clinker 

areas.

• Unsuitability criteria are constraints used to 

determine if an area can be mined by surface mining methods. These include, but are not limited 

to, Federal land systems, dwellings, and alluvial 

valley floors. 

• Single payment Present Worth is the equivalent present value of an expenditure or investment that is made 

at some future date and valuated by compounding 

interest (Stermole, 1974, p. 14).

• Stochastic is random variables having a probability 

distribution or random variables determined through 

conjecture (AACE, 1997, p. 3)

• Surface (strip) mining is the practice of mining a 

seam of mineral by first removing a long strip of overlying soil and rock. Surface mining is practical only 

when the ore body to be excavated is relatively near 

the surface. When coal seams are near the surface, it 

may be economical to extract the coal using open cut

(also referred to as open cast, open pit, or strip) mining 

methods. Open cast coal mining recovers a greater proportion of the coal deposit than underground methods, 

as more of the coal seams may be recovered. 

• Stripping (mining) ratio is the most influential economic factor in the evaluation and planning of open 

pit coal mines. It represents the ratio of the volume 

of overburden or interburden (waste) that must be 

removed to gain access to a unit amount of coal. For 

this assessment, the ratio is expressed as cubic yards of 

overburden to tons of coal. The stripping ratio can be 

approximated by dividing the total thickness of waste 

by the total thickness of coal. For example, given two 

coal beds each 5.0 ft thick at 50 and 105 ft in depth, 

the total waste and coal thicknesses would be 100 and 

10 ft respectively. A simple ratio would be 10:1, but a 

stripping ratio would be 9.1:1 (in cubic yards to a ton 

of coal).

• Tailgate is the secondary roadway access or egress 

from a longwall face and through which return air 

flows (SME, 1992, SME Mining Engineering Handbook, volume 1). 

• Uniform Series Present Worth is the equivalent present value of multiple, equal amount payments made 

at regular spaced, future intervals and valuated by 

compounding interest (Stermole, 1974, p. 14).
40 Assessment of Coal Geology, Resources, and Reserves in the Southwestern Powder River Basin, Wyoming

Figure 1. Location of Southwestern Powder River Basin assessment area, Northern Wyoming Powder River Basin 

assessment area (Scott and others, 2010), and Gillette coal field, (Luppens and others, 2008) Wyoming and Montana.

106°

Sheridan

Johnson Campbell

Converse

Big Horn

Cook

Niobrara Natrona

Powder River

Rosebud

Weston

Custer

Carter

Fallon

Musselshell

Yellowstone

Treasure

104°

MONTANA

WYOMING

MONTANA

WYOMING

Washakie

Big Horn

Hot Springs

Freemont

Platte

0

0 20 40 MILES

20 40 60 KILOMETERS Glenrock

Sheridan

Bualo

Gillette

Decker

Birney

Miles City

Douglas

Moorcroft

Casper

Tertiary limit of the Powder

 River Basin

EXPLANATION

Gillette coal field boundary

County line

Main railroad lines

Interstate roads

City or town

INDEX MAP

Wyoming

Montana

Powder River Basin

90

90

94

25

25

Northern Wyoming Powder River

Basin assessment area

Southwestern Powder River

Basin assessment area

43°

44°

46°

45°

108°
Figures 41

Figure 2. Coal fields in the Southwestern Powder River Basin assessment area (modified from Glass, 1976).

0

0

5 10 20 MILES

5 10 20 KILOMETERS

Campbell

Johnson

Converse

Natrona Niobrara

Weston

Big Horn

Washakie

Sheridan

Cook

Sheridan

Buffalo

 coal field

Barber

coal field

Powder River

coal field

Sussex coal field

Glenrock

coal field

Dry Cheyenne

coal field

Pumpkin

Buttes

coal

field

Lost Spring

 coal field

Bualo-Lake DeSmet area (Mapel, 1959)

Dave Johnston Mine

 (abandoned)

Belco Lease Area

Stevens North

Stevens South

EXPLANATION

County line

Gillette coal eld

Bualo-Lake

DeSmet area

Dave Johnston Mine

(abandoned)

INDEX MAP

WYOMING

Stevens North

 (approximate

location)

Stevens South

 (approximate

location)

Belco lease area

 (approximate

location)

Lake DeSmet

Southwestern Powder

River Basin

assessment area

Northern Wyoming

Powder River Basin

assessment area

R. 87W. R. 85 W. R. 83 W. R. 81 W. R. 79 W. R. 77 W. R. 75 W. R. 73 W. R. 71 W. R. 69 W. R. 67 W. R. 65 W.

T. 42 N.

T. 40 N.

T. 34 N.

T. 36 N.

T. 38 N.

T. 32 N.

T. 44 N.

T. 46 N.

T. 48 N.

T. 50 N.

T. 52 N.

T. 54 N.

T. 56 N.

T. 58 N.

o

43 00’

o

43 30’

o

44 00’

o

44 30’

o

45 00’

o 107 00’ o 106 00’ o 105 00’ 
42 Assessment of Coal Geology, Resources, and Reserves in the Southwestern Powder River Basin, Wyoming

EXPLANATION

Stevens North

Stevens South

T.37 N.

T.36 N.

T.37 N.

T.38 N.

R. 75 W. R. 74 W.

R. 75 W. R. 74 W.

36 31

25 30 29 28 27 26

32 33 34 35

26

35

23

14

11

2

17

5 4 3 2

19 20 21 22 23

18

24

16 15 14

7 8 9 10 11

6

13

12

1

36 31

25 30 29 28 27 26

32 33 34 35

26

35

19 20 21 22 23

18

23 24

16 15 14

7 8 9 10 11

14

11

13

12

17

5 4 3 2

23 19 20 21 22

18

24

16 15 14

8 9 10 11 7

6

13

12

1

23

14

11

23

22

15

10

17

438.5 Million Short

Tons Resource

186.8 Million Short

Tons Resource

WYOMING

INDEX MAP

Area of map

1 2 KILOMETERS

0 1 2 MILES

0

Figure 3. Areas of coal resources in the Stevens Preference Right Lease Applications (PRLA’s) in the 

Southwestern Powder River Basin assessment area.
Figures 43

0

0

5 10 20 MILES

5 10 20 KILOMETERS

Campbell

Johnson

Converse

Natrona Niobrara

Weston

Big Horn

Washakie

Sheridan

Cook

Sheridan

Bualo

Northern Wyoming

Powder River Basin

assessment area

Gillette coal field

boundary

Drill hole 

Southwestern Powder

River Basin assessment

area

County line

City or town

INDEX MAP

WYOMING

Gillette

EXPLANATION

R. 87W. R. 85 W. R. 83 W. R. 81 W. R. 79 W. R. 77 W. R. 75 W. R. 73 W. R. 71 W. R. 69 W. R. 67 W. R. 65 W.

T. 42 N.

T. 40 N.

T. 34 N.

T. 36 N.

T. 38 N.

T. 32 N.

T. 44 N.

T. 46 N.

T. 48 N.

T. 50 N.

T. 52 N.

T. 54 N.

T. 56 N.

T. 58 N.

o

43 00’

o

43 30’

o

44 00’

o

44 30’

o

45 00’

o 107 00’ o 106 00’ o 105 00’ 

Figure 4. Drill hole locations in the Powder River Basin, Wyoming.
Figure 5. Flow chart showing generalized methodology used during coal resource and reserve evaluation.

 1) Coal bed geology (extent, thickness, partings, structure, overburden) 

 2) Factors affecting extraction (land-use and technical restrictions) 3) Location of preparation plants, roads, and rail facilities 4) State and county jurisdictions and resource ownership 

PHASE (1)–DATA COLLECTION AND EDITING 

1) Calculate available resources by mine model, all costs, and data 2) Calculate mining costs, production rates, and tax rates 3) Calculate recoverable tons for incremental cash costs  and discounted cash cost/rate of return, cost curves, and reserves

PHASE (3)–RESERVE ANALYSIS 

Coal bed correlations and editing

 1) Create digital models for all assessed coal beds 2) Create GIS models of restrictions to mining 3) Calculate tonnages and areas for original, mined

 out, restricted, and available resources 

PHASE (2)–MODELING

 1) Coal quality information  2) Recent coal sales price 

 3) Tax information 
Figure 6. Coal bed and coal zone names used in different publications in the Powder River Basin.

Kent and USGS Fort Union Ellis and Gillette coal Northern Wyoming Formation others Pierce and Coal Assessment others field (Luppens Powder River Basin Assesse

Name (1980) others (1990) Team, (1999) and (2002) and others, 2008) (Scott and others, 2010) for this 

Glass, (1997)

Upper Healy Upper He

Healy Mu

Wasatch Ucross Uc

Felix Upper Felix Felix Fe

Felix Lower Felix Lowe

Roland/ Wyodak Roland (Upper Rider) Roland (U

Roland (Lo

Smith Badger Roland Rider Roland Roland of Baker, 1929 Roland of 

 Roland of Taff, 1909

Smith Smith Sm

Upper Wyodak-Anderson Upper Anderson Rider, Anderson Ande

Wyodak Wyodak or coal zone=Smith Wyodak Anderson Lower Anderson

Upper Wyodak (Swartz), Badger, Dietz 1, Dietz 2, Di

Fort Union (Anderson/ School, Sussex, Big Dietz Dietz 3, Dietz 4 Upper 

(Tongue Canyon Canyon) George, Wyodak, Canyon Canyon Canyon Ca

River Anderson, Dietz, Lower Canyon Lower 

Member) Canyon (Monarch), Lower Ferry

Werner Lower Werner Wyodak Werner Werner We

 Wyodak

Otter O

Gates/ Upper Gates/

Kennedy Kennedy Kennedy Gates Gates Ga

Pawnee Pawnee Paw

Odell

DeDeDe

Roberts Ro

 Bed Names 
46 Assessment of Coal Geology, Resources, and Reserves in the Southwestern Powder River Basin, Wyoming

Tftl

Tft

Tftr

Tfu

Tw

Qal

Gillette coal field boundary

Quaternary alluvium

Tertiary White River Formation

Tertiary Wasatch Formation

Tertiary Tongue River Member of the

Fort Union Formation

Tertiary Tongue River and Lebo Shale

Members of the Fort Union Formation

(undifferentiated)

Tertiary Tullock Member of the 

Fort Union Formation

 Fort Union Formation (undifferentiated)

Basin axis

EXPLANATION

County line

Twr

Northern Wyoming Powder

River Basin assessment area

Southwestern Powder

River Basin assessment area

43°

44°

46°

45°

108° 106°

Sheridan

Johnson Campbell

Converse

Big Horn

Cook

Niobrara

Natrona

Powder River

Rosebud

Weston

Custer

Carter

Fallon

Musselshell

Treasure

104°

Tftl

Tft

Tft

Tftr

Tfu

Tw

Tw

Twr

0

0 20 40 MILES

20 40 60 KILOMETERS Glenrock

Sheridan

Buffalo

Gillette

Decker

Birney

Miles City

Douglas

MONTANA

WYOMING

Moorcroft

City or town

Casper

Platte

Big Horn

Washakie

Hot Springs

Freemont

INDEX MAP

Wyoming

Montana

Powder River Basin

Qal

Qal

Qal

Yellowstone

Figure 7. Generalized geology of the Powder River Basin, Wyoming and Montana (modifed from Flores and 

others, 1999).
Figures 47

STRATIGRAPHIC UNITS IN THE 

POWDER RIVER BASIN

Lakota Formation

Fall River Formation

Thermopolis Shale

Muddy Sandstone

Mowry Shale

Belle Fourche Formation

Greenhorn Formation

Carlile Shale

Frontier Formation

Cody Shale

Pierre Shale

Niobrara Formation

Bearpaw Shale

Fox Hills Sandstone

Surficial deposits

AGE

EOCENE

PALEOCENE

LATE 

CRETACEOUS

EARLY 

CRETACEOUS

Tongue River Member

Lebo Member

Tullock Member

QUATERNARY

TERTIARY CRETACEOUS

PLIOCENEOLIGOCENE

WYOMING MONTANA

Mesaverde

Formation

Hell Creek Formation

Wasatch Formation

Lance Formation

White River Formation

Fort Union

Formation

Figure 8. Generalized stratigraphic column for the Powder River Basin, Wyoming and 

Montana (modified from Ellis and others, 2002).
Coal Bed Names/ Coal Beds Resources Formation identified calculated Maximum Average name in this assessment (see tables 1,2,3) thickness (ft) thickness (ft)

Upper Healy Upper Healy 66 10

Healy Healy 75 13

Wasatch Murray Murray 14 3

Ucross Ucross 38 9

Upper Felix

Felix Felix 48 7

Lower Felix Lower Felix 35 7

Roland (Upper Rider) Roland (Upper Rider) 32 4

Roland (Lower Rider) Roland (Lower Rider) 19 4

Roland of Baker (1929) Roland of Baker (1929) 36 7

Roland of Taff (1909)

Smith Rider

Smith Smith 266 32

Anderson (Upper Rider)

Anderson (Lower Rider) 

Anderson Anderson 61 10

Lower Anderson

Fort Union Dietz 1

(Tongue River Dietz 2

 Member) Dietz 3 Dietz 3 119 14

Dietz 4

Upper Canyon Upper Canyon 31 8

Canyon Canyon 182 29

Lower Canyon Lower Canyon 81 16

Ferry Rider 

Ferry

Werner Werner 76 8

Otter Rider

Otter Otter 158 24

Gates Gates 122 13

Pawnee Pawnee 19 5

Odell

Deep 1 Deep 1 32 9

Deep 2 Deep 2 29 5

Deep 3 Deep 3 32 8

Deep 4

Roberts Roberts 36 9

 Coal Stratigraphy

Figure 9. Stratigraphy of coal beds in the Southwestern Powder River Basin assessment area showing names 

used in this report (maximum and average thickness only shown for coal beds assessed for resources in this 

report).

48 Assessment of Coal Geology, Resources, and Reserves in the Southwestern Powder River Basin, Wyoming
Figures 49

0

0

5 10 20 MILES

5 10 20 KILOMETERS

Campbell Johnson

Converse Natrona Niobrara

Weston

Big Horn

Washakie

Sheridan Campbell

Cook

EXPLANATION

Northern Wyoming

Powder River Basin

assessment area

Gillette coal field

boundary

Southwestern Powder

River Basin assessment

area

County line

Area of clinker

INDEX MAP

WYOMING

R. 87W. R. 85 W. R. 83 W. R. 81 W. R. 79 W. R. 77 W. R. 75 W. R. 73 W. R. 71 W. R. 69 W. R. 67 W. R. 65 W.

T. 42 N.

T. 40 N.

T. 34 N.

T. 36 N.

T. 38 N.

T. 32 N.

T. 44 N.

T. 46 N.

T. 48 N.

T. 50 N.

T. 52 N.

T. 54 N.

T. 56 N.

T. 58 N.

o

43 00’

o

43 30’

o

44 00’

o

44 30’

o

45 00’

o 107 00’ o 106 00’ o 105 00’ 

Figure 10. Location of clinker in the Southwestern Powder River Basin assessment area (modified from 

Heffern, 2010).
50 Assessment of Coal Geology, Resources, and Reserves in the Southwestern Powder River Basin, Wyoming

0

0

5 10 20 MILES

5 10 20 KILOMETERS

Campbell Johnson

Converse Natrona Niobrara

Weston

Big Horn

Washakie

Sheridan Campbell

Cook

Lake

DeSmet

Sheridan

Casper

Douglas

Rolling Hills

Bualo

EXPLANATION

Northern Wyoming

Powder River Basin

assessment area

Gillette coal field

boundary

Southwestern Powder

River Basin assessment

area

Lake DeSmet

County line

Town buffer 

City or town

INDEX MAP

WYOMING

1:1

5:1

10:1 Stripping ratio

Stripping ratio

Stripping ratio

Areas of 10:1 or 

less stripping ratio

R. 87W. R. 85 W. R. 83 W. R. 81 W. R. 79 W. R. 77 W. R. 75 W. R. 73 W. R. 71 W. R. 69 W. R. 67 W. R. 65 W.

T. 42 N.

T. 40 N.

T. 34 N.

T. 36 N.

T. 38 N.

T. 32 N.

T. 44 N.

T. 46 N.

T. 48 N.

T. 50 N.

T. 52 N.

T. 54 N.

T. 56 N.

T. 58 N.

o

43 00’

o

43 30’

o

44 00’

o

44 30’

o

45 00’

o 107 00’ o 106 00’ o 105 00’ 

Figure 11. Stripping ratios for the Roland Baker (1929) and Smith coal beds in the Southwestern Powder 

River Basin assessment area.
Figure 12. West-east cross section A–A’ through the northern part of the southwestern Wyoming Powder River Basin assessment ar

showing subsurface coal beds (vertical exaggeration approximately 5,000 ×).

Upper Healy

Healy

Ucross

Approximate land surface

Lower Felix

Felix

Roland Baker (1929)

Smith

Dietz 3

Canyon

Lower Canyon

Werner

Otter

Gates

Pawnee

Roberts

Deep 2

Deep 3

Deep 1

Ucross

Lower Felix

0 5 10

0 5 10

MILES

KILOMETERS

Deep 1

Vertical scale

1,000 ft

2,000 ft

500 ft

0 ft

1,500 ft

A 

WEST 
Figure 13. West-east cross section B–B’ through the north-central part of the southwestern Wyoming Powder River Basin assessme

area showing subsurface coal beds (vertical exaggeration approximately 5,000 ×).

Healy

Upper Healy

Lower Canyon

Canyon

Deep 1

Deep 2

Otter

Werner

Gates

Lower Felix

Smith

Anderson

0 5 10

0 5 10 MILES

KILOMETERS

Lower Felix

Approximate land surface

Vertical scale

1,000 ft

2,000 ft

500 ft

0 ft

1,500 ft

B 

WEST 
Figure 14. West-east cross section C–C’ through the central part of the southwestern Wyoming Powder River Basin assessment area showing subsurface coal beds (vertical exaggeration approximately 5,000 ×).

Smith

Anderson

Canyon

Lower Canyon Werner

Otter

Gates

Deep 1

Deep 3 Deep 2

Approximate land surface

0 5 10

0 5 10

MILES

KILOMETERS

Vertical scale

1,000 ft

2,000 ft

500 ft

0 ft

1,500 ft

C 

WEST 
Figure 15. West-east cross section D–D’ through the south-central part of the southwestern Wyoming Powder River 

Basin assessment area showing subsurface coal beds (vertical exaggeration approximately 5,000 ×).

Roberts

Canyon

Anderson

Smith

Werner

Deep 2 Deep 3

Deep 1

Roland Baker (1929)

Approximate land surface

0 5 10

0 5 10

MILES

KILOMETERS

Vertical scale

1,000 ft

2,000 ft

500 ft

0 ft

1,500 ft

D 

WEST 
Figure 16. West-east cross section E–E’ through the southern part of the southwestern Wyoming Powder River Basin assessment ar

subsurface coal beds (vertical exaggeration approximately 5,000 ×).

Approximate land surface

Roland Baker (1929)

Smith

Deep 1

Deep 3

Roberts

Deep 2

0 5 10

0 5 10

MILES

KILOMETERS

Vertical scale

1,000 ft

2,000 ft

500 ft

0 ft

1,500 ft

E 

WEST 
Figure 17. South-north cross section F–F’ through the central part of the southwestern Wyoming Powder River Basin assessment are

subsurface coal beds (vertical exaggeration approximately 5,000 ×).

Approximate land surface

0 5 10

0 5 10

MILES

KILOMETERS

20

20

Vertical scale

1,000 ft

2,000 ft

500 ft

0 ft

1,500 ft

F 

SOUTH 
Figure 18. South-north cross section G–G’ through the northern part of the southwestern Wyoming Powder River Basin assessment a

subsurface coal beds (vertical exaggeration approximately 5,000 ×).

L

0 5 10

0 5 10

MILES

KILOMETERS

Approximate land surface

Vertical scale

1,000 ft

2,000 ft

500 ft

0 ft

1,500 ft

G 

SOUTH 
Figure 19. South-north cross section H–H’ through the south-central part of the southwestern Wyoming Powder River Basin assessm

showing subsurface coal beds (vertical exaggeration approximately 5,000 ×).

Smith Anderson

Roland Baker (1929) Approximate land surface

Werner

Roberts

Deep 3 Deep 2 Deep 1

0 5 10

0 5 10

MILES

KILOMETERS

Vertical scale

1,000 ft

2,000 ft

500 ft

0 ft

1,500 ft

H 

SOUTH 
Figure 20. South-north cross section I–I’ through the south-eastern part of the southwestern Wyoming Powder River Basin assessme

subsurface coal beds (vertical exaggeration approximately 5,000 ×).

Deep 1

Deep 2

Deep 3

Roberts

0 5 10

0 5 10

MILES

KILOMETERS

Vertical scale

1,000 ft

2,000 ft

500 ft

0 ft

1,500 ft

I 

SOUTH 
60 Assessment of Coal Geology, Resources, and Reserves in the Southwestern Powder River Basin, Wyoming

Campbell Johnson

Natrona Converse Niobrara

Weston

Big Horn

Washakie

Sheridan

Cook

Sheridan

Bualo

Northern Wyoming

Powder River Basin

assessment area

Gillette coal field

boundary

City or town

Southwestern Powder

River Basin assessment

area

EXPLANATION

2.5

5

10

20

40

60

80

County line

INDEX MAP

WYOMING

Thickness (ft)

0

0

5 10 20 MILES

5 10 20 KILOMETERS

R. 87 W. R. 85 W. R. 83 W. R. 81 W. R. 79 W. R. 77 W. R. 75 W. R. 73 W. R. 71 W. R. 69 W. R. 67 W. R. 65 W.

T. 42 N.

T. 40 N.

T. 34 N.

T. 36 N.

T. 38 N.

T. 32 N.

T. 44 N.

T. 46 N.

T. 48 N.

T. 50 N.

T. 52 N.

T. 54 N.

T. 56 N.

T. 58 N.

o

43 00’

o

43 30’

o

44 00’

o

44 30’

o

45 00’

o 107 00’ o 106 00’ o 105 00’ 

Figure 21. Isopach map of the Upper Healy coal bed showing extent of resources greater than 2.5 ft thick within the 

Southwestern Powder River Basin assessment area.
Figures 61

Campbell Johnson

Converse Natrona Niobrara

Weston

Big Horn

Washakie

Sheridan

Cook

Sheridan

Bualo

EXPLANATION

Northern Wyoming

Powder River Basin

assessment area

Gillette coal eld

boundary

City or town

Southwestern Powder

River Basin assessment

area

County line

Basin axis

(approximate)

Depth to top of coal (ft)

 1

 250

 500

1,000

INDEX MAP

WYOMING

0

0

5 10 20 MILES

5 10 20 KILOMETERS

R. 87 W. R. 85 W. R. 83 W. R. 81 W. R. 79 W. R. 77 W. R. 75 W. R. 73 W. R. 71 W. R. 69 W. R. 67 W. R. 65 W.

T. 42 N.

T. 40 N.

T. 34 N.

T. 36 N.

T. 38 N.

T. 32 N.

T. 44 N.

T. 46 N.

T. 48 N.

T. 50 N.

T. 52 N.

T. 54 N.

T. 56 N.

T. 58 N.

o

43 00’

o

43 30’

o

44 00’

o

44 30’

o

45 00’

o 107 00’ o 106 00’ o 105 00’ 

Figure 22. Depth to the top of the Upper Healy coal bed within the Southwestern Powder River Basin assessment 

area.
62 Assessment of Coal Geology, Resources, and Reserves in the Southwestern Powder River Basin, Wyoming

Campbell Johnson

Converse Natrona Niobrara

Weston

Big Horn

Washakie

Sheridan

Cook

Sheridan

Bualo

Gillette coal eld

boundary

City or town 

Northern Wyoming

Powder River Basin

assessment area

Southwestern Powder

River Basin assessment

area

Inferred

Indicated

Measured

EXPLANATION

INDEX MAP

WYOMING

County line

Hypothetical

0

0

5 10 20 MILES

5 10 20 KILOMETERS

R. 87 W. R. 85 W. R. 83 W. R. 81 W. R. 79 W. R. 77 W. R. 75 W. R. 73 W. R. 71 W. R. 69 W. R. 67 W. R. 65 W.

T. 42 N.

T. 40 N.

T. 34 N.

T. 36 N.

T. 38 N.

T. 32 N.

T. 44 N.

T. 46 N.

T. 48 N.

T. 50 N.

T. 52 N.

T. 54 N.

T. 56 N.

T. 58 N.

o

43 00’

o

43 30’

o

44 00’

o

44 30’

o

45 00’

o 107 00’ o 106 00’ o 105 00’ 

Figure 23. Coal resource reliability categories for the Upper Healy coal bed within the Southwestern Powder River 

Basin assessment area.
Figures 63

Campbell Johnson

Natrona Converse Niobrara

Weston

Big Horn

Washakie

Sheridan

Cook

Sheridan

Bualo

Northern Wyoming

Powder River Basin

assessment area

Gillette coal eld

boundary

City or town

Southwestern Powder

River Basin assessment

area

 Thickness (ft)

EXPLANATION

2.5

5

10

20

40

60

80

County line

INDEX MAP

WYOMING

0

0

5 10 20 MILES

5 10 20 KILOMETERS

R. 87 W. R. 85 W. R. 83 W. R. 81 W. R. 79 W. R. 77 W. R. 75 W. R. 73 W. R. 71 W. R. 69 W. R. 67 W. R. 65 W.

T. 42 N.

T. 40 N.

T. 34 N.

T. 36 N.

T. 38 N.

T. 32 N.

T. 44 N.

T. 46 N.

T. 48 N.

T. 50 N.

T. 52 N.

T. 54 N.

T. 56 N.

T. 58 N.

o

43 00’

o

43 30’

o

44 00’

o

44 30’

o

45 00’

o 107 00’ o 106 00’ o 105 00’ 

Figure 24. Isopach map of the Healy coal bed showing extent of resources greater than 2.5 ft thick within the 

Southwestern Powder River Basin assessment area.
64 Assessment of Coal Geology, Resources, and Reserves in the Southwestern Powder River Basin, Wyoming

Campbell Johnson

Natrona Converse Niobrara

Weston

Big Horn

Washakie

Sheridan

Cook

Sheridan

o

Bualo EXPLANATION

Northern Wyoming

Powder River Basin

assessment area

Gillette coal eld

boundary

City or town

Southwestern Powder

River Basin assessment

area

County line

Basin axis

(approximate)

Depth to top of coal (ft)

 1

 250

 500

1,000

INDEX MAP

WYOMING

R. 87 W. R. 85 W. R. 83 W. R. 81 W. R. 79 W. R. 77 W. R. 75 W. R. 73 W. R. 71 W. R. 69 W. R. 67 W. R. 65 W.

T. 42 N.

T. 40 N.

T. 34 N.

T. 36 N.

T. 38 N.

T. 32 N.

T. 44 N.

T. 46 N.

T. 48 N.

T. 50 N.

T. 52 N.

T. 54 N.

T. 56 N.

T. 58 N.

o

43 00’

o

43 30’

o

44 00’

o

44 30’

o

45 00’

o 107 00’ o 106 00’ o 105 00’ 

0

0

5 10 20 MILES

5 10 20 KILOMETERS

Figure 25. Depth to the top of the Healy coal bed within the Southwestern Powder River Basin assessment 

area.
Figures 65

Campbell Johnson

Natrona Converse Niobrara

Weston

Big Horn

Washakie

Sheridan

Cook

Sheridan

Bualo

Gillette coal eld

boundary

City or town 

Northern Wyoming

Powder River Basin

assessment area

Southwestern Powder

River Basin assessment

area

Inferred

Indicated

Measured

EXPLANATION

INDEX MAP

WYOMING

County line

Hypothetical

R. 87 W. R. 85 W. R. 83 W. R. 81 W. R. 79 W. R. 77 W. R. 75 W. R. 73 W. R. 71 W. R. 69 W. R. 67 W. R. 65 W.

T. 42 N.

T. 40 N.

T. 34 N.

T. 36 N.

T. 38 N.

T. 32 N.

T. 44 N.

T. 46 N.

T. 48 N.

T. 50 N.

T. 52 N.

T. 54 N.

T. 56 N.

T. 58 N.

o

43 00’

o

43 30’

o

44 00’

o

44 30’

o

45 00’

o 107 00’ o 106 00’ o 105 00’ 

0

0

5 10 20 MILES

5 10 20 KILOMETERS

Figure 26. Coal resource reliability categories for the Healy coal bed within the Southwestern Powder River Basin 

assessment area.
66 Assessment of Coal Geology, Resources, and Reserves in the Southwestern Powder River Basin, Wyoming

Campbell Johnson

Natrona Converse Niobrara

Weston

Big Horn

Washakie

Sheridan

Cook

Sheridan

Bualo

Northern Wyoming

Powder River Basin

assessment area

Gillette coal eld

boundary

City or town

Southwestern Powder

River Basin assessment

area

Thickness (ft)

EXPLANATION

2.5

5

10

20

County line

INDEX MAP

WYOMING

R. 87 W. R. 85 W. R. 83 W. R. 81 W. R. 79 W. R. 77 W. R. 75 W. R. 73 W. R. 71 W. R. 69 W. R. 67 W. R. 65 W.

T. 42 N.

T. 40 N.

T. 34 N.

T. 36 N.

T. 38 N.

T. 32 N.

T. 44 N.

T. 46 N.

T. 48 N.

T. 50 N.

T. 52 N.

T. 54 N.

T. 56 N.

T. 58 N.

o

43 00’

o

43 30’

o

44 00’

o

44 30’

o

45 00’

o 107 00’ o 106 00’ o 105 00’ 

0

0

5 10 20 MILES

5 10 20 KILOMETERS

Figure 27. Isopach map of the Murray coal bed showing extent of resources greater than 2.5 ft thick within the 

Southwestern Powder River Basin assessment area.
Figures 67

Campbell Johnson

Converse Natrona Niobrara

Weston

Big Horn

Washakie

Sheridan

Cook

Sheridan

Bualo EXPLANATION

Northern Wyoming

Powder River Basin

assessment area

Gillette coal eld

boundary

City or town

Southwestern Powder

River Basin assessment

area

County line

Basin axis

(approximate)

Depth to top of coal (ft)

 1

 250

 500

1,000

INDEX MAP

WYOMING

R. 87 W. R. 85 W. R. 83 W. R. 81 W. R. 79 W. R. 77 W. R. 75 W. R. 73 W. R. 71 W. R. 69 W. R. 67 W. R. 65 W.

T. 42 N.

T. 40 N.

T. 34 N.

T. 36 N.

T. 38 N.

T. 32 N.

T. 44 N.

T. 46 N.

T. 48 N.

T. 50 N.

T. 52 N.

T. 54 N.

T. 56 N.

T. 58 N.

o

43 00’

o

43 30’

o

44 00’

o

44 30’

o

45 00’

o 107 00’ o 106 00’ o 105 00’ 

0

0

5 10 20 MILES

5 10 20 KILOMETERS

Figure 28. Depth to the top of the Murray coal bed within the Southwestern Powder River Basin assessment area.
68 Assessment of Coal Geology, Resources, and Reserves in the Southwestern Powder River Basin, Wyoming

Campbell Johnson

Natrona Converse Niobrara

Weston

Big Horn

Washakie

Sheridan

Cook

Sheridan

Bualo

Gillette coal eld

boundary

City or town 

Northern Wyoming

Powder River Basin

assessment area

Southwestern Powder

River Basin assessment

area

Inferred

Indicated

Measured

EXPLANATION

INDEX MAP

WYOMING

County line

Hypothetical

R. 87 W. R. 85 W. R. 83 W. R. 81 W. R. 79 W. R. 77 W. R. 75 W. R. 73 W. R. 71 W. R. 69 W. R. 67 W. R. 65 W.

T. 42 N.

T. 40 N.

T. 34 N.

T. 36 N.

T. 38 N.

T. 32 N.

T. 44 N.

T. 46 N.

T. 48 N.

T. 50 N.

T. 52 N.

T. 54 N.

T. 56 N.

T. 58 N.

o

43 00’

o

43 30’

o

44 00’

o

44 30’

o

45 00’

o 107 00’ o 106 00’ o 105 00’ 

0

0

5 10 20 MILES

5 10 20 KILOMETERS

Figure 29. Coal resource reliability categories for the Murray coal bed within the Southwestern Powder River Basin 

assessment area.
Figures 69

R. 87 W. R. 85 W. R. 83 W. R. 81 W. R. 79 W. R. 77 W. R. 75 W. R. 73 W. R. 71 W. R. 69 W. R. 67 W. R. 65 W.

T. 42 N.

T. 40 N.

T. 34 N.

T. 36 N.

T. 38 N.

T. 32 N.

T. 44 N.

T. 46 N.

T. 48 N.

T. 50 N.

T. 52 N.

T. 54 N.

T. 56 N.

T. 58 N.

Campbell Johnson

Natrona Converse Niobrara

Weston

Big Horn

Washakie

Sheridan

Cook

Sheridan

Bualo

o

43 00’

o

43 30’

o

44 00’

o

44 30’

o

45 00’

o 107 00’ o 106 00’ o 105 00’ 

Northern Wyoming

Powder River Basin

assessment area

Gillette coal eld

boundary

City or town

Southwestern Powder

River Basin assessment

area

Thickness (ft)

EXPLANATION

2.5

5

10

20

40

County line

INDEX MAP

WYOMING

0

0

5 10 20 MILES

5 10 20 KILOMETERS

Figure 30. Isopach map of the Ucross coal bed showing extent of resources greater than 2.5 ft thick 

within the Southwestern Powder River Basin assessment area.
70 Assessment of Coal Geology, Resources, and Reserves in the Southwestern Powder River Basin, Wyoming

R. 87 W. R. 85 W. R. 83 W. R. 81 W. R. 79 W. R. 77 W. R. 75 W. R. 73 W. R. 71 W. R. 69 W. R. 67 W. R. 65 W.

T. 42 N.

T. 40 N.

T. 34 N.

T. 36 N.

T. 38 N.

T. 32 N.

T. 44 N.

T. 46 N.

T. 48 N.

T. 50 N.

T. 52 N.

T. 54 N.

T. 56 N.

T. 58 N.

Campbell Johnson

Natrona Converse Niobrara

Weston

Big Horn

Washakie

Sheridan

Cook

Sheridan

o

43 00’

o

43 30’

o

44 00’

o

44 30’

o

45 00’

o 107 00’ o 106 00’ o 105 00’ 

EXPLANATION

Northern Wyoming

Powder River Basin

assessment area

Gillette coal eld

boundary

City or town

Southwestern Powder

River Basin assessment

area

County line

Basin axis

(approximate)

Depth to top of coal (ft)

 1

 250

 500

1,000

1,500

INDEX MAP

WYOMING

Bualo

0

0

5 10 20 MILES

5 10 20 KILOMETERS

Figure 31. Depth to the top of the Ucross coal bed within the Southwestern Powder River Basin assessment area.
Figures 71

R. 87 W. R. 85 W. R. 83 W. R. 81 W. R. 79 W. R. 77 W. R. 75 W. R. 73 W. R. 71 W. R. 69 W. R. 67 W. R. 65 W.

T. 42 N.

T. 40 N.

T. 34 N.

T. 36 N.

T. 38 N.

T. 32 N.

T. 44 N.

T. 46 N.

T. 48 N.

T. 50 N.

T. 52 N.

T. 54 N.

T. 56 N.

T. 58 N.

Campbell Johnson

Natrona Converse Niobrara

Weston

Big Horn

Washakie

Sheridan

Cook

Sheridan

Bualo

o

43 00’

o

43 30’

o

44 00’

o

44 30’

o

45 00’

o 107 00’ o 106 00’ o 105 00’ 

Gillette coal eld

boundary

City or town 

Northern Wyoming

Powder River Basin

assessment area

Southwestern Powder

River Basin assessment

area

Inferred

Indicated

Measured

EXPLANATION

INDEX MAP

WYOMING

County line

Hypothetical

0

0

5 10 20 MILES

5 10 20 KILOMETERS

Figure 32. Coal resource reliability categories for the Ucross coal bed within the Southwestern Powder 

River Basin assessment area.
72 Assessment of Coal Geology, Resources, and Reserves in the Southwestern Powder River Basin, Wyoming

R. 87 W. R. 85 W. R. 83 W. R. 81 W. R. 79 W. R. 77 W. R. 75 W. R. 73 W. R. 71 W. R. 69 W. R. 67 W. R. 65 W.

T. 42 N.

T. 40 N.

T. 34 N.

T. 36 N.

T. 38 N.

T. 32 N.

T. 44 N.

T. 46 N.

T. 48 N.

T. 50 N.

T. 52 N.

T. 54 N.

T. 56 N.

T. 58 N.

Campbell Johnson

Natrona Converse Niobrara

Weston

Big Horn

Washakie

Sheridan

Cook

Sheridan

Bualo

o

43 00’

o

43 30’

o

44 00’

o

44 30’

o

45 00’

o 107 00’ o 106 00’ o 105 00’ 

Northern Wyoming

 Powder River Basin

 assessment area

Gillette coal eld

boundary

City or town

Southwestern Powder

River Basin assessment

area

Thickness (ft)

EXPLANATION

2.5

5

10

20

40

County line

INDEX MAP

WYOMING

60

0

0

5 10 20 MILES

5 10 20 KILOMETERS

Figure 33. Isopach map of the Felix coal bed showing extent of resources greater than 2.5 ft thick within the 

Southwestern Powder River Basin assessment area.
Figures 73

R. 87 W. R. 85 W. R. 83 W. R. 81 W. R. 79 W. R. 77 W. R. 75 W. R. 73 W. R. 71 W. R. 69 W. R. 67 W. R. 65 W.

T. 42 N.

T. 40 N.

T. 34 N.

T. 36 N.

T. 38 N.

T. 32 N.

T. 44 N.

T. 46 N.

T. 48 N.

T. 50 N.

T. 52 N.

T. 54 N.

T. 56 N.

T. 58 N.

Campbell Johnson

Natrona Converse Niobrara

Weston

Big Horn

Washakie

Sheridan

Cook

Sheridan

o

43 00’

o

43 30’

o

44 00’

o

44 30’

o

45 00’

o 107 00’ o 106 00’ o 105 00’ 

Bualo

EXPLANATION

Northern Wyoming

Powder River Basin

assessment area

Gillette coal eld

boundary

City or town

Southwestern Powder

River Basin assessment

area

County line

Basin axis

(approximate)

Depth to top of coal (ft)

 1

 250

 500

1,000

1,500

INDEX MAP

WYOMING

0

0

5 10 20 MILES

5 10 20 KILOMETERS

Figure 34. Depth to the top of the Felix coal bed within the Southwestern Powder River Basin assessment area.
74 Assessment of Coal Geology, Resources, and Reserves in the Southwestern Powder River Basin, Wyoming

R. 87 W. R. 85 W. R. 83 W. R. 81 W. R. 79 W. R. 77 W. R. 75 W. R. 73 W. R. 71 W. R. 69 W. R. 67 W. R. 65 W.

T. 42 N.

T. 40 N.

T. 34 N.

T. 36 N.

T. 38 N.

T. 32 N.

T. 44 N.

T. 46 N.

T. 48 N.

T. 50 N.

T. 52 N.

T. 54 N.

T. 56 N.

T. 58 N.

Campbell Johnson

Natrona Converse Niobrara

Weston

Big Horn

Washakie

Sheridan

Cook

Sheridan

Bualo

o

43 00’

o

43 30’

o

44 00’

o

44 30’

o

45 00’

o 107 00’ o 106 00’ o 105 00’ 

Gillette coal eld

boundary

City or town 

Northern Wyoming

Powder River Basin

assessment area

Southwestern Powder

River Basin assessment

area

Inferred

Indicated

Measured

EXPLANATION

INDEX MAP

WYOMING

County line

Hypothetical

0

0

5 10 20 MILES

5 10 20 KILOMETERS

Figure 35. Coal resource reliability categories for the Felix coal bed within the Southwestern Powder River Basin 

assessment area.
Figures 75

R. 87 W. R. 85 W. R. 83 W. R. 81 W. R. 79 W. R. 77 W. R. 75 W. R. 73 W. R. 71 W. R. 69 W. R. 67 W. R. 65 W.

T. 42 N.

T. 40 N.

T. 34 N.

T. 36 N.

T. 38 N.

T. 32 N.

T. 44 N.

T. 46 N.

T. 48 N.

T. 50 N.

T. 52 N.

T. 54 N.

T. 56 N.

T. 58 N.

Campbell Johnson

Natrona Converse Niobrara

Weston

Big Horn

Washakie

Sheridan

Cook

Sheridan

Bualo

o

43 00’

o

43 30’

o

44 00’

o

44 30’

o

45 00’

o 107 00’ o 106 00’ o 105 00’ 

Northern Wyoming

 Powder River Basin

 assessment area

Gillette coal eld

boundary

City or town

Southwestern Powder

River Basin assessment

area

Thickness (ft)

EXPLANATION

2.5

5

10

20

40

County line

INDEX MAP

WYOMING

0

0

5 10 20 MILES

5 10 20 KILOMETERS

Figure 36. Isopach map of the Lower Felix coal bed showing extent of resources greater than 2.5 ft thick within the 

Southwestern Powder River Basin assessment area.
76 Assessment of Coal Geology, Resources, and Reserves in the Southwestern Powder River Basin, Wyoming

R. 87 W. R. 85 W. R. 83 W. R. 81 W. R. 79 W. R. 77 W. R. 75 W. R. 73 W. R. 71 W. R. 69 W. R. 67 W. R. 65 W.

T. 42 N.

T. 40 N.

T. 34 N.

T. 36 N.

T. 38 N.

T. 32 N.

T. 44 N.

T. 46 N.

T. 48 N.

T. 50 N.

T. 52 N.

T. 54 N.

T. 56 N.

T. 58 N.

Campbell Johnson

Converse Natrona Niobrara

Weston

Big Horn

Washakie

Sheridan

Cook

Sheridan

o

43 00’

o

43 30’

o

44 00’

o

44 30’

o

45 00’

o 107 00’ o 106 00’ o 105 00’ 

Bualo

EXPLANATION

Northern Wyoming

Powder River Basin

assessment area

Gillette coal eld

boundary

City or town

Southwestern Powder

River Basin assessment

area

County line

Basin axis

(approximate)

Depth to top of coal (ft)

 1

 250

 500

1,000

1,500

INDEX MAP

WYOMING

0

0

5 10 20 MILES

5 10 20 KILOMETERS

Figure 37. Depth to the top of the Lower Felix coal bed within the Southwestern Powder River Basin 

assessment area.
Figures 77

R. 87 W. R. 85 W. R. 83 W. R. 81 W. R. 79 W. R. 77 W. R. 75 W. R. 73 W. R. 71 W. R. 69 W. R. 67 W. R. 65 W.

T. 42 N.

T. 40 N.

T. 34 N.

T. 36 N.

T. 38 N.

T. 32 N.

T. 44 N.

T. 46 N.

T. 48 N.

T. 50 N.

T. 52 N.

T. 54 N.

T. 56 N.

T. 58 N.

Campbell Johnson

Natrona Converse Niobrara

Weston

Big Horn

Washakie

Sheridan

Cook

Sheridan

Bualo

o

43 00’

o

43 30’

o

44 00’

o

44 30’

o

45 00’

o 107 00’ o 106 00’ o 105 00’ 

Gillette coal eld

boundary

City or town 

Northern Wyoming

Powder River Basin

assessment area

Southwestern Powder

River Basin assessment

area

Inferred

Indicated

Measured

EXPLANATION

INDEX MAP

WYOMING

County line

Hypothetical

0

0

5 10 20 MILES

5 10 20 KILOMETERS

Figure 38. Coal resource reliability categories for the Lower Felix coal bed within the Southwestern Powder 

River Basin assessment area.
78 Assessment of Coal Geology, Resources, and Reserves in the Southwestern Powder River Basin, Wyoming

R. 87 W. R. 85 W. R. 83 W. R. 81 W. R. 79 W. R. 77 W. R. 75 W. R. 73 W. R. 71 W. R. 69 W. R. 67 W. R. 65 W.

T. 42 N.

T. 40 N.

T. 34 N.

T. 36 N.

T. 38 N.

T. 32 N.

T. 44 N.

T. 46 N.

T. 48 N.

T. 50 N.

T. 52 N.

T. 54 N.

T. 56 N.

T. 58 N.

Campbell Johnson

Natrona Converse Niobrara

Weston

Big Horn

Washakie

Sheridan

Cook

Sheridan

Bualo

o

43 00’

o

43 30’

o

44 00’

o

44 30’

o

45 00’

o 107 00’ o 106 00’ o 105 00’ 

Northern Wyoming

 Powder River Basin

 assessment area

Gillette coal eld

boundary

City or town

Southwestern Powder

River Basin assessment

area

Thickness (ft)

EXPLANATION

2.5

5

10

20

40

County line

INDEX MAP

WYOMING

0

0

5 10 20 MILES

5 10 20 KILOMETERS

Figure 39. Isopach map of the Roland (Upper Rider) coal bed showing extent of resources greater than 2.5 ft 

thick within the Southwestern Powder River Basin assessment area.
Figures 79

R. 87 W. R. 85 W. R. 83 W. R. 81 W. R. 79 W. R. 77 W. R. 75 W. R. 73 W. R. 71 W. R. 69 W. R. 67 W. R. 65 W.

T. 42 N.

T. 40 N.

T. 34 N.

T. 36 N.

T. 38 N.

T. 32 N.

T. 44 N.

T. 46 N.

T. 48 N.

T. 50 N.

T. 52 N.

T. 54 N.

T. 56 N.

T. 58 N.

Campbell Johnson

Natrona Converse Niobrara

Weston

Big Horn

Washakie

Sheridan

Cook

Sheridan

o

43 00’

o

43 30’

o

44 00’

o

44 30’

o

45 00’

o 107 00’ o 106 00’ o 105 00’ 

EXPLANATION

Northern Wyoming

Powder River Basin

assessment area

Gillette coal eld

boundary

City or town

Southwestern Powder

River Basin assessment

area

County line

Basin axis

(approximate)

Depth to top of coal (ft)

 1

 250

 500

1,000

1,500

INDEX MAP

WYOMING

Bualo

0

0

5 10 20 MILES

5 10 20 KILOMETERS

Figure 40. Depth to the top of the Roland (Upper Rider) coal bed within the Southwestern Powder River 

Basin assessment area.
80 Assessment of Coal Geology, Resources, and Reserves in the Southwestern Powder River Basin, Wyoming

R. 87 W. R. 85 W. R. 83 W. R. 81 W. R. 79 W. R. 77 W. R. 75 W. R. 73 W. R. 71 W. R. 69 W. R. 67 W. R. 65 W.

T. 42 N.

T. 40 N.

T. 34 N.

T. 36 N.

T. 38 N.

T. 32 N.

T. 44 N.

T. 46 N.

T. 48 N.

T. 50 N.

T. 52 N.

T. 54 N.

T. 56 N.

T. 58 N.

Campbell Johnson

Natrona Converse Niobrara

Weston

Big Horn

Washakie

Sheridan

Cook

Sheridan

Bualo

o

43 00’

o

43 30’

o

44 00’

o

44 30’

o

45 00’

o 107 00’ o 106 00’ o 105 00’ 

Gillette coal eld

boundary

City or town 

Northern Wyoming

Powder River Basin

assessment area

Southwestern Powder

River Basin assessment

area

Inferred

Indicated

Measured

EXPLANATION

INDEX MAP

WYOMING

County line

Hypothetical

0

0

5 10 20 MILES

5 10 20 KILOMETERS

Figure 41. Coal resource reliability categories for the Roland (Upper Rider) coal bed within the Southwestern 

Powder River Basin assessment area.
Figures 81

R. 87 W. R. 85 W. R. 83 W. R. 81 W. R. 79 W. R. 77 W. R. 75 W. R. 73 W. R. 71 W. R. 69 W. R. 67 W. R. 65 W.

T. 42 N.

T. 40 N.

T. 34 N.

T. 36 N.

T. 38 N.

T. 32 N.

T. 44 N.

T. 46 N.

T. 48 N.

T. 50 N.

T. 52 N.

T. 54 N.

T. 56 N.

T. 58 N.

Johnson Campbell

Natrona Converse Niobrara

Weston

Big Horn

Washakie

Sheridan

Cook

Sheridan

Bualo

o

43 00’

o

43 30’

o

44 00’

o

44 30’

o

45 00’

o 107 00’ o 106 00’ o 105 00’ 

Northern Wyoming

 Powder River Basin

 assessment area

Gillette coal eld

boundary

City or town

Southwestern Powder

River Basin assessment

area

Thickness (ft)

EXPLANATION

2.5

5

10

20

County line

INDEX MAP

WYOMING

0

0

5 10 20 MILES

5 10 20 KILOMETERS

Figure 42. Isopach map of the Roland (Upper Rider) coal bed showing extent of resources greater than 2.5 ft thick 

within the Southwestern Powder River Basin assessment area.
82 Assessment of Coal Geology, Resources, and Reserves in the Southwestern Powder River Basin, Wyoming

R. 87 W. R. 85 W. R. 83 W. R. 81 W. R. 79 W. R. 77 W. R. 75 W. R. 73 W. R. 71 W. R. 69 W. R. 67 W. R. 65 W.

T. 42 N.

T. 40 N.

T. 34 N.

T. 36 N.

T. 38 N.

T. 32 N.

T. 44 N.

T. 46 N.

T. 48 N.

T. 50 N.

T. 52 N.

T. 54 N.

T. 56 N.

T. 58 N.

Campbell Johnson

Natrona Converse Niobrara

Weston

Big Horn

Washakie

Sheridan

Cook

Sheridan

o

43 00’

o

43 30’

o

44 00’

o

44 30’

o

45 00’

o 107 00’ o 106 00’ o 105 00’ 

EXPLANATION

Northern Wyoming

Powder River Basin

assessment area

Gillette coal eld

boundary

City or town

Southwestern Powder

River Basin assessment

area

County line

Basin axis

(approximate)

Depth to top of coal (ft)

 1

 250

 500

1,000

1,500

INDEX MAP

WYOMING

Bualo

0

0

5 10 20 MILES

5 10 20 KILOMETERS

Figure 43. Depth to the top of the Roland (Lower Rider) coal bed within the Southwestern Powder River Basin 

assessment area.
Figures 83

R. 87 W. R. 85 W. R. 83 W. R. 81 W. R. 79 W. R. 77 W. R. 75 W. R. 73 W. R. 71 W. R. 69 W. R. 67 W. R. 65 W.

T. 42 N.

T. 40 N.

T. 34 N.

T. 36 N.

T. 38 N.

T. 32 N.

T. 44 N.

T. 46 N.

T. 48 N.

T. 50 N.

T. 52 N.

T. 54 N.

T. 56 N.

T. 58 N.

Campbell Johnson

Natrona Converse Niobrara

Weston

Big Horn

Washakie

Sheridan

Cook

Sheridan

Bualo

o

43 00’

o

43 30’

o

44 00’

o

44 30’

o

45 00’

o 107 00’ o 106 00’ o 105 00’ 

Gillette coal eld

boundary

City or town 

Northern Wyoming

Powder River Basin

assessment area

Southwestern Powder

River Basin assessment

area

Inferred

Indicated

Measured

EXPLANATION

INDEX MAP

WYOMING

County line

0

0

5 10 20 MILES

5 10 20 KILOMETERS

Figure 44. Coal resource reliability categories for the Roland (Lower Rider) coal bed within the Southwestern 

Powder River Basin assessment area.
84 Assessment of Coal Geology, Resources, and Reserves in the Southwestern Powder River Basin, Wyoming

R. 87 W. R. 85 W. R. 83 W. R. 81 W. R. 79 W. R. 77 W. R. 75 W. R. 73 W. R. 71 W. R. 69 W. R. 67 W. R. 65 W.

T. 42 N.

T. 40 N.

T. 34 N.

T. 36 N.

T. 38 N.

T. 32 N.

T. 44 N.

T. 46 N.

T. 48 N.

T. 50 N.

T. 52 N.

T. 54 N.

T. 56 N.

T. 58 N.

Campbell Johnson

Natrona Converse Niobrara

Weston

Big Horn

Washakie

Sheridan

Cook

Sheridan

Bualo

o

43 00’

o

43 30’

o

44 00’

o

44 30’

o

45 00’

o 107 00’ o 106 00’ o 105 00’ 

Northern Wyoming

 Powder River Basin

 assessment area

Gillette coal eld

boundary

City or town

Southwestern Powder

River Basin assessment

area

Thickness (ft)

EXPLANATION

2.5

5

10

20

40

County line

INDEX MAP

WYOMING

0

0

5 10 20 MILES

5 10 20 KILOMETERS

Figure 45. Isopach map of the Roland Baker (1929) coal bed showing extent of resources greater than 2.5 ft thick 

within the Southwestern Powder River Basin assessment area.
Figures 85

R. 87 W. R. 85 W. R. 83 W. R. 81 W. R. 79 W. R. 77 W. R. 75 W. R. 73 W. R. 71 W. R. 69 W. R. 67 W. R. 65 W.

T. 42 N.

T. 40 N.

T. 34 N.

T. 36 N.

T. 38 N.

T. 32 N.

T. 44 N.

T. 46 N.

T. 48 N.

T. 50 N.

T. 52 N.

T. 54 N.

T. 56 N.

T. 58 N.

Campbell Johnson

Natrona Converse Niobrara

Weston

Big Horn

Washakie

Sheridan

Cook

Sheridan

o

43 00’

o

43 30’

o

44 00’

o

44 30’

o

45 00’

o 107 00’ o 106 00’ o 105 00’ 

EXPLANATION

Northern Wyoming

Powder River Basin

assessment area

Gillette coal eld

boundary

City or town

Southwestern Powder

River Basin assessment

area

County line

Basin axis

(approximate)

Depth to top of coal (ft)

 1

 250

 500

1,000

1,500

2,000

INDEX MAP

WYOMING

Bualo

0

0

5 10 20 MILES

5 10 20 KILOMETERS

Figure 46. Depth to the top of the Roland Baker (1929) coal bed within the Southwestern Powder River 

Basin assessment area.
R. 87 W. R. 85 W. R. 83 W. R. 81 W. R. 79 W. R. 77 W. R. 75 W. R. 73 W. R. 71 W. R. 69 W. R. 67 W. R. 65 W.

T. 42 N.

T. 40 N.

T. 34 N.

T. 36 N.

T. 38 N.

T. 32 N.

T. 44 N.

T. 46 N.

T. 48 N.

T. 50 N.

T. 52 N.

T. 54 N.

T. 56 N.

T. 58 N.

Campbell Johnson

Natrona Converse Niobrara

Weston

Big Horn

Washakie

Sheridan

Cook

Sheridan

Bualo

o

43 00’

o

43 30’

o

44 00’

o

44 30’

o

45 00’

o 107 00’ o 106 00’ o 105 00’ 

Gillette coal eld

boundary

City or town 

Northern Wyoming

Powder River Basin

assessment area

Southwestern Powder

River Basin assessment

area

Inferred

Indicated

Measured

EXPLANATION

INDEX MAP

WYOMING

County line

Hypothetical

0

0

5 10 20 MILES

5 10 20 KILOMETERS

Figure 47. Coal resource reliability categories for the Roland Baker (1929) coal bed within the Southwestern 

Powder River Basin assessment area.

86 Assessment of Coal Geology, Resources, and Reserves in the Southwestern Powder River Basin, Wyoming
Figures 87

R. 87 W. R. 85 W. R. 83 W. R. 81 W. R. 79 W. R. 77 W. R. 75 W. R. 73 W. R. 71 W. R. 69 W. R. 67 W. R. 65 W.

T. 42 N.

T. 40 N.

T. 34 N.

T. 36 N.

T. 38 N.

T. 32 N.

T. 44 N.

T. 46 N.

T. 48 N.

T. 50 N.

T. 52 N.

T. 54 N.

T. 56 N.

T. 58 N.

Campbell Johnson

Natrona Converse Niobrara

Weston

Big Horn

Washakie

Sheridan

Cook

Sheridan

Bualo

o

43 00’

o

43 30’

o

44 00’

o

44 30’

o

45 00’

o 107 00’ o 106 00’ o 105 00’ 

Northern Wyoming

 Powder River Basin

 assessment area

Gillette coal eld

boundary

City or town

Southwestern Powder

River Basin assessment

area

Thickness (ft)

EXPLANATION

2.5

5

10

20

40

60

80

100

120 and >

County line

INDEX MAP

WYOMING

0

0

5 10 20 MILES

5 10 20 KILOMETERS

Figure 48. Isopach map of the Smith coal bed showing extent of resources greater than 2.5 ft thick within the 

Southwestern Powder River Basin assessment area.
88 Assessment of Coal Geology, Resources, and Reserves in the Southwestern Powder River Basin, Wyoming

R. 87 W. R. 85 W. R. 83 W. R. 81 W. R. 79 W. R. 77 W. R. 75 W. R. 73 W. R. 71 W. R. 69 W. R. 67 W. R. 65 W.

T. 42 N.

T. 40 N.

T. 34 N.

T. 36 N.

T. 38 N.

T. 32 N.

T. 44 N.

T. 46 N.

T. 48 N.

T. 50 N.

T. 52 N.

T. 54 N.

T. 56 N.

T. 58 N.

Campbell Johnson

Natrona Converse Niobrara

Weston

Big Horn

Washakie

Sheridan

Cook

Sheridan

o

43 00’

o

43 30’

o

44 00’

o

44 30’

o

45 00’

o 107 00’ o 106 00’ o 105 00’ 

EXPLANATION

Northern Wyoming

Powder River Basin

assessment area

Gillette coal eld

boundary

City or towm

Southwestern Powder

River Basin assessment

area

County line

Basin axis

(approximate)

Depth to top of coal (ft)

 1

 250

 500

1,000

1,500

2,000

2,500

INDEX MAP

WYOMING

Bualo

0

0

5 10 20 MILES

5 10 20 KILOMETERS

Figure 49. Depth to the top of the Smith coal bed within the Southwestern Powder River Basin 

assessment area.
Figures 89

R. 87 W. R. 85 W. R. 83 W. R. 81 W. R. 79 W. R. 77 W. R. 75 W. R. 73 W. R. 71 W. R. 69 W. R. 67 W. R. 65 W.

T. 42 N.

T. 40 N.

T. 34 N.

T. 36 N.

T. 38 N.

T. 32 N.

T. 44 N.

T. 46 N.

T. 48 N.

T. 50 N.

T. 52 N.

T. 54 N.

T. 56 N.

T. 58 N.

Campbell Johnson

Converse Natrona Niobrara

Weston

Big Horn

Washakie

Sheridan

Cook

Sheridan

Bualo

o

43 00’

o

43 30’

o

44 00’

o

44 30’

o

45 00’

o 107 00’ o 106 00’ o 105 00’ 

Gillette coal Ffeld

boundary

City or town 

Northern Wyoming

Powder River Basin

assessment area

Southwestern Powder

River Basin assessment

area

Inferred

Indicated

Measured

EXPLANATION

INDEX MAP

WYOMING

County line

Hypothetical

0

0

5 10 20 MILES

5 10 20 KILOMETERS

Figure 50. Coal resource reliability categories for the Smith coal bed within the Southwestern Powder River 

Basin assessment area.
90 Assessment of Coal Geology, Resources, and Reserves in the Southwestern Powder River Basin, Wyoming

R. 87 W. R. 85 W. R. 83 W. R. 81 W. R. 79 W. R. 77 W. R. 75 W. R. 73 W. R. 71 W. R. 69 W. R. 67 W. R. 65 W.

T. 42 N.

T. 40 N.

T. 34 N.

T. 36 N.

T. 38 N.

T. 32 N.

T. 44 N.

T. 46 N.

T. 48 N.

T. 50 N.

T. 52 N.

T. 54 N.

T. 56 N.

T. 58 N.

Campbell Johnson

Natrona Converse Niobrara

Weston

Big Horn

Washakie

Sheridan

Cook

Sheridan

Bualo

o

43 00’

o

43 30’

o

44 00’

o

44 30’

o

45 00’

o 107 00’ o 106 00’ o 105 00’ 

Northern Wyoming

 Powder River Basin

 assessment area

Gillette coal eld

boundary

City or town

Southwestern Powder

River Basin assessment

area

Thickness (ft)

EXPLANATION

2.5

5

10

20

40

60

80

County line

INDEX MAP

WYOMING

0

0

5 10 20 MILES

5 10 20 KILOMETERS

Figure 51. Isopach map of the Anderson coal bed showing extent of resources greater than 2.5 ft thick within the 

Southwestern Powder River Basin assessment area.
Figures 91

R. 87 W. R. 85 W. R. 83 W. R. 81 W. R. 79 W. R. 77 W. R. 75 W. R. 73 W. R. 71 W. R. 69 W. R. 67 W. R. 65 W.

T. 42 N.

T. 40 N.

T. 34 N.

T. 36 N.

T. 38 N.

T. 32 N.

T. 44 N.

T. 46 N.

T. 48 N.

T. 50 N.

T. 52 N.

T. 54 N.

T. 56 N.

T. 58 N.

Campbell Johnson

Natrona Converse Niobrara

Weston

Big Horn

Washakie

Sheridan

Cook

Sheridan

o

43 00’

o

43 30’

o

44 00’

o

44 30’

o

45 00’

o 107 00’ o 106 00’ o 105 00’ 

EXPLANATION

Northern Wyoming

Powder River Basin

assessment area

Gillette coal eld

boundary

City or town

Southwestern Powder

River Basin assessment

area

County line

Basin axis

(approximate)

Depth to top of coal (ft)

 1

 250

 500

1,000

1,500

2,000

INDEX MAP

WYOMING

Bualo

0

0

5 10 20 MILES

5 10 20 KILOMETERS

Figure 52. Depth to the top of the Anderson coal bed within the Southwestern Powder River Basin 

assessment area.
92 Assessment of Coal Geology, Resources, and Reserves in the Southwestern Powder River Basin, Wyoming

R. 87 W. R. 85 W. R. 83 W. R. 81 W. R. 79 W. R. 77 W. R. 75 W. R. 73 W. R. 71 W. R. 69 W. R. 67 W. R. 65 W.

T. 42 N.

T. 40 N.

T. 34 N.

T. 36 N.

T. 38 N.

T. 32 N.

T. 44 N.

T. 46 N.

T. 48 N.

T. 50 N.

T. 52 N.

T. 54 N.

T. 56 N.

T. 58 N.

Campbell Johnson

Natrona Converse Niobrara

Weston

Big Horn

Washakie

Sheridan

Cook

Sheridan

Bualo Hypothetical

Inferred

Indicated

Measured

EXPLANATION

Northern Wyoming

Powder River Basin

assessment area

Gillette coal eld

boundary

City or town 

Southwestern Powder

River Basin assessment

area

County line

INDEX MAP

WYOMING

o

43 00’

o

43 30’

o

44 00’

o

44 30’

o

45 00’

o 107 00’ o 106 00’ o 105 00’ 

0

0

5 10 20 MILES

5 10 20 KILOMETERS

Figure 53. Coal resource reliability categories for the Anderson coal bed within the Southwestern Powder River 

Basin assessment area.
Figures 93

R. 87 W. R. 85 W. R. 83 W. R. 81 W. R. 79 W. R. 77 W. R. 75 W. R. 73 W. R. 71 W. R. 69 W. R. 67 W. R. 65 W.

T. 42 N.

T. 40 N.

T. 34 N.

T. 36 N.

T. 38 N.

T. 32 N.

T. 44 N.

T. 46 N.

T. 48 N.

T. 50 N.

T. 52 N.

T. 54 N.

T. 56 N.

T. 58 N.

Campbell Johnson

Natrona Converse Niobrara

Weston

Big Horn

Washakie

Sheridan

Cook

Sheridan

Bualo

o

43 00’

o

43 30’

o

44 00’

o

44 30’

o

45 00’

o 107 00’ o 106 00’ o 105 00’ 

Northern Wyoming

 Powder River Basin

 assessment area

Gillette coal eld

boundary

City or town

Southwestern Powder

River Basin assessment

area

Thickness (ft)

EXPLANATION

2.5

5

10

20

40

60

80

100

120

County line

INDEX MAP

WYOMING

0

0

5 10 20 MILES

5 10 20 KILOMETERS

Figure 54. Isopach map of the Dietz 3 coal bed showing extent of resources greater than 2.5 ft thick within the 

Southwestern Powder River Basin assessment area.
94 Assessment of Coal Geology, Resources, and Reserves in the Southwestern Powder River Basin, Wyoming

R. 87 W. R. 85 W. R. 83 W. R. 81 W. R. 79 W. R. 77 W. R. 75 W. R. 73 W. R. 71 W. R. 69 W. R. 67 W. R. 65 W.

T. 42 N.

T. 40 N.

T. 34 N.

T. 36 N.

T. 38 N.

T. 32 N.

T. 44 N.

T. 46 N.

T. 48 N.

T. 50 N.

T. 52 N.

T. 54 N.

T. 56 N.

T. 58 N.

Campbell Johnson

Natrona Converse Niobrara

Weston

Big Horn

Washakie

Sheridan

Cook

Sheridan

o

43 00’

o

43 30’

o

44 00’

o

44 30’

o

45 00’

o 107 00’ o 106 00’ o 105 00’ 

 1

 250

 500

1,000

1,500

2,000

2,500

EXPLANATION

Northern Wyoming

Powder River Basin

assessment area

Gillette coal eld

boundary

City or town

Southwestern Powder

River Basin assessment

area

County line

Basin axis

(approximate)

Depth to top of coal (ft)

INDEX MAP

WYOMING

Bualo

0

0

5 10 20 MILES

5 10 20 KILOMETERS

Figure 55. Depth to the top of the Dietz 3 coal bed within the Southwestern Powder River Basin 

assessment area.
Figures 95

R. 87 W. R. 85 W. R. 83 W. R. 81 W. R. 79 W. R. 77 W. R. 75 W. R. 73 W. R. 71 W. R. 69 W. R. 67 W. R. 65 W.

T. 42 N.

T. 40 N.

T. 34 N.

T. 36 N.

T. 38 N.

T. 32 N.

T. 44 N.

T. 46 N.

T. 48 N.

T. 50 N.

T. 52 N.

T. 54 N.

T. 56 N.

T. 58 N.

Campbell Johnson

Natrona Converse Niobrara

Weston

Big Horn

Washakie

Sheridan

Cook

Sheridan

Bualo

o

43 00’

o

43 30’

o

44 00’

o

44 30’

o

45 00’

o 107 00’ o 106 00’ o 105 00’ 

Gillette coal eld

boundary

City or town 

Northern Wyoming

Powder River Basin

assessment area

Southwestern Powder

River Basin assessment

area

Inferred

Indicated

Measured

EXPLANATION

INDEX MAP

WYOMING

County line

Hypothetical

0

0

5 10 20 MILES

5 10 20 KILOMETERS

Figure 56. Coal resource reliability categories for the Dietz 3 coal bed within the Southwestern Powder River 

Basin assessment area.
96 Assessment of Coal Geology, Resources, and Reserves in the Southwestern Powder River Basin, Wyoming

R. 87 W. R. 85 W. R. 83 W. R. 81 W. R. 79 W. R. 77 W. R. 75 W. R. 73 W. R. 71 W. R. 69 W. R. 67 W. R. 65 W.

T. 42 N.

T. 40 N.

T. 34 N.

T. 36 N.

T. 38 N.

T. 32 N.

T. 44 N.

T. 46 N.

T. 48 N.

T. 50 N.

T. 52 N.

T. 54 N.

T. 56 N.

T. 58 N.

Campbell Johnson

Converse Natrona Niobrara

Weston

Big Horn

Washakie

Sheridan

Cook

Sheridan

Bualo

o

43 00’

o

43 30’

o

44 00’

o

44 30’

o

45 00’

o 107 00’ o 106 00’ o 105 00’ 

Northern Wyoming

 Powder River Basin

 assessment area

Gillette coal eld

boundary

City or town

Southwestern Powder

River Basin assessment

area

Thickness (ft)

EXPLANATION

2.5

5

10

20

40

County line

INDEX MAP

WYOMING

0

0

5 10 20 MILES

5 10 20 KILOMETERS

Figure 57. Isopach map of the Upper Canyon coal bed showing extent of resources greater than 2.5 ft thick within 

the Southwestern Powder River Basin assessment area.
Figures 97

R. 87 W. R. 85 W. R. 83 W. R. 81 W. R. 79 W. R. 77 W. R. 75 W. R. 73 W. R. 71 W. R. 69 W. R. 67 W. R. 65 W.

T. 42 N.

T. 40 N.

T. 34 N.

T. 36 N.

T. 38 N.

T. 32 N.

T. 44 N.

T. 46 N.

T. 48 N.

T. 50 N.

T. 52 N.

T. 54 N.

T. 56 N.

T. 58 N.

Johnson Campbell

Converse Natrona Niobrara

Weston

Big Horn

Washakie

Sheridan

Cook

Sheridan

o

43 00’

o

43 30’

o

44 00’

o

44 30’

o

45 00’

o 107 00’ o 106 00’ o 105 00’ 

EXPLANATION

Northern Wyoming

Powder River Basin

assessment area

Gillette coal eld

boundary

City or town

Southwestern Powder

River Basin assessment

area

County line

Basin axis

(approximate)

Depth to top of coal (ft)

 1

 250

 500

1,000

1,500

2,000

2,500

INDEX MAP

WYOMING

Bualo

0

0

5 10 20 MILES

5 10 20 KILOMETERS

Figure 58. Depth to the top of the Upper Canyon coal bed within the Southwestern Powder River Basin 

assessment area.
98 Assessment of Coal Geology, Resources, and Reserves in the Southwestern Powder River Basin, Wyoming

R. 87 W. R. 85 W. R. 83 W. R. 81 W. R. 79 W. R. 77 W. R. 75 W. R. 73 W. R. 71 W. R. 69 W. R. 67 W. R. 65 W.

T. 42 N.

T. 40 N.

T. 34 N.

T. 36 N.

T. 38 N.

T. 32 N.

T. 44 N.

T. 46 N.

T. 48 N.

T. 50 N.

T. 52 N.

T. 54 N.

T. 56 N.

T. 58 N.

Campbell Johnson

Natrona Converse Niobrara

Weston

Big Horn

Washakie

Sheridan

Cook

Sheridan

Bualo

o

43 00’

o

43 30’

o

44 00’

o

44 30’

o

45 00’

o 107 00’ o 106 00’ o 105 00’ 

Gillette coal eld

boundary

City or town 

Northern Wyoming

Powder River Basin

assessment area

Southwestern Powder

River Basin assessment

area

Inferred

Indicated

Measured

EXPLANATION

INDEX MAP

WYOMING

County line

Hypothetical

0

0

5 10 20 MILES

5 10 20 KILOMETERS

Figure 59. Coal resource reliability categories for the Upper Canyon coal bed within the Southwestern 

Powder River Basin assessment area.
Figures 99

R. 87 W. R. 85 W. R. 83 W. R. 81 W. R. 79 W. R. 77 W. R. 75 W. R. 73 W. R. 71 W. R. 69 W. R. 67 W. R. 65 W.

T. 42 N.

T. 40 N.

T. 34 N.

T. 36 N.

T. 38 N.

T. 32 N.

T. 44 N.

T. 46 N.

T. 48 N.

T. 50 N.

T. 52 N.

T. 54 N.

T. 56 N.

T. 58 N.

Campbell Johnson

Natrona Converse Niobrara

Weston

Big Horn

Washakie

Sheridan

Cook

Sheridan

Bualo

o

43 00’

o

43 30’

o

44 00’

o

44 30’

o

45 00’

o 107 00’ o 106 00’ o 105 00’ 

Northern Wyoming

 Powder River Basin

 assessment area

Gillette coal eld

boundary

City or town

Southwestern Powder

River Basin assessment

area

Thickness (ft)

EXPLANATION

2.5

5

10

20

40

60

80

100

>120

County line

INDEX MAP

WYOMING

0

0

5 10 20 MILES

5 10 20 KILOMETERS

Figure 60. Isopach map of the Canyon coal bed showing extent of resources greater than 2.5 ft thick 

within the Southwestern Powder River Basin assessment area.
R. 87 W. R. 85 W. R. 83 W. R. 81 W. R. 79 W. R. 77 W. R. 75 W. R. 73 W. R. 71 W. R. 69 W. R. 67 W. R. 65 W.

T. 42 N.

T. 40 N.

T. 34 N.

T. 36 N.

T. 38 N.

T. 32 N.

T. 44 N.

T. 46 N.

T. 48 N.

T. 50 N.

T. 52 N.

T. 54 N.

T. 56 N.

T. 58 N.

Campbell Johnson

Converse Natrona Niobrara

Weston

Big Horn

Washakie

Sheridan

Cook

Sheridan

Bualo

o

43 00’

o

43 30’

o

44 00’

o

44 30’

o

45 00’

o 107 00’ o 106 00’ o 105 00’ 

EXPLANATION

Northern Wyoming

Powder River Basin

assessment area

Gillette coal eld

boundary

City or town

Southwestern Powder

River Basin assessment

area

County line

Basin axis

(approximate)

Depth to top of coal (ft)

 1

 250

 500

1,000

1,500

2,000

2,500

3,000

4,000

INDEX MAP

WYOMING

0

0

5 10 20 MILES

5 10 20 KILOMETERS

Figure 61. Depth to the top of the Canyon coal bed within the Southwestern Powder River Basin 

assessment area.

100 Assessment of Coal Geology, Resources, and Reserves in the Southwestern Powder River Basin, Wyoming
Figures 101

R. 87 W. R. 85 W. R. 83 W. R. 81 W. R. 79 W. R. 77 W. R. 75 W. R. 73 W. R. 71 W. R. 69 W. R. 67 W. R. 65 W.

T. 42 N.

T. 40 N.

T. 34 N.

T. 36 N.

T. 38 N.

T. 32 N.

T. 44 N.

T. 46 N.

T. 48 N.

T. 50 N.

T. 52 N.

T. 54 N.

T. 56 N.

T. 58 N.

Campbell Johnson

Natrona Converse Niobrara

Weston

Big Horn

Washakie

Sheridan

Cook

Sheridan

Bualo

o

43 00’

o

43 30’

o

44 00’

o

44 30’

o

45 00’

o 107 00’ o 106 00’ o 105 00’ 

Hypothetical

Inferred

Indicated

Measured

EXPLANATION

Northern Wyoming

Powder River Basin

assessment area

Gillette coal eld

boundary

City or town 

Southwestern Powder

River Basin assessment

area

County line

INDEX MAP

WYOMING

0

0

5 10 20 MILES

5 10 20 KILOMETERS

Figure 62. Coal resource reliability categories for the Canyon coal bed within the Southwestern Powder 

River Basin assessment area.
102 Assessment of Coal Geology, Resources, and Reserves in the Southwestern Powder River Basin, Wyoming

R. 87 W. R. 85 W. R. 83 W. R. 81 W. R. 79 W. R. 77 W. R. 75 W. R. 73 W. R. 71 W. R. 69 W. R. 67 W. R. 65 W.

T. 42 N.

T. 40 N.

T. 34 N.

T. 36 N.

T. 38 N.

T. 32 N.

T. 44 N.

T. 46 N.

T. 48 N.

T. 50 N.

T. 52 N.

T. 54 N.

T. 56 N.

T. 58 N.

Campbell Johnson

Converse Natrona Niobrara

Weston

Big Horn

Washakie

Sheridan

Cook

Sheridan

Bualo

o

43 00’

o

43 30’

o

44 00’

o

44 30’

o

45 00’

o 107 00’ o 106 00’ o 105 00’ 

Thickness (ft)

EXPLANATION

2.5

5

10

20

40

60

80

100

Northern Wyoming

 Powder River Basin

 assessment area

Gillette coal eld

boundary

City or town

Southwestern Powder

River Basin assessment

area

County line

INDEX MAP

WYOMING

0

0

5 10 20 MILES

5 10 20 KILOMETERS

Figure 63. Isopach map of the Lower Canyon coal bed showing extent of resources greater than 2.5 ft 

thick within the Southwestern Powder River Basin assessment area.
Figures 103

R. 87 W. R. 85 W. R. 83 W. R. 81 W. R. 79 W. R. 77 W. R. 75 W. R. 73 W. R. 71 W. R. 69 W. R. 67 W. R. 65 W.

T. 42 N.

T. 40 N.

T. 34 N.

T. 36 N.

T. 38 N.

T. 32 N.

T. 44 N.

T. 46 N.

T. 48 N.

T. 50 N.

T. 52 N.

T. 54 N.

T. 56 N.

T. 58 N.

Campbell Johnson

Converse Natrona Niobrara

Weston

Big Horn

Washakie

Sheridan

Cook

Sheridan

o

43 00’

o

43 30’

o

44 00’

o

44 30’

o

45 00’

o 107 00’ o 106 00’ o 105 00’ 

Bualo

EXPLANATION

Northern Wyoming

Powder River Basin

assessment area

Gillette coal eld

boundary

City or town

Southwestern Powder

River Basin assessment

area

County line

Basin axis

(approximate)

Depth to top of coal (ft)

 1

 250

 500

1,000

1,500

2,000

2,500

3,000

4,000

INDEX MAP

WYOMING

0

0

5 10 20 MILES

5 10 20 KILOMETERS

Figure 64. Depth to the top of the Lower Canyon coal bed within the Southwestern Powder River Basin 

assessment area.
104 Assessment of Coal Geology, Resources, and Reserves in the Southwestern Powder River Basin, Wyoming

R. 87 W. R. 85 W. R. 83 W. R. 81 W. R. 79 W. R. 77 W. R. 75 W. R. 73 W. R. 71 W. R. 69 W. R. 67 W. R. 65 W.

T. 42 N.

T. 40 N.

T. 34 N.

T. 36 N.

T. 38 N.

T. 32 N.

T. 44 N.

T. 46 N.

T. 48 N.

T. 50 N.

T. 52 N.

T. 54 N.

T. 56 N.

T. 58 N.

Campbell Johnson

Natrona Converse Niobrara

Weston

Big Horn

Washakie

Sheridan

Cook

Sheridan

Bualo

o

43 00’

o

43 30’

o

44 00’

o

44 30’

o

45 00’

o 107 00’ o 106 00’ o 105 00’ 

Gillette coal eld

boundary

City or town 

Northern Wyoming

Powder River Basin

assessment area

Southwestern Powder

River Basin assessment

area

Inferred

Indicated

Measured

EXPLANATION

INDEX MAP

WYOMING

County line

Hypothetical

0

0

5 10 20 MILES

5 10 20 KILOMETERS

Figure 65. Coal resource reliability categories for the Lower Canyon coal bed within the Southwestern 

Powder River Basin assessment area.
Figures 105

R. 87 W. R. 85 W. R. 83 W. R. 81 W. R. 79 W. R. 77 W. R. 75 W. R. 73 W. R. 71 W. R. 69 W. R. 67 W. R. 65 W.

T. 42 N.

T. 40 N.

T. 34 N.

T. 36 N.

T. 38 N.

T. 32 N.

T. 44 N.

T. 46 N.

T. 48 N.

T. 50 N.

T. 52 N.

T. 54 N.

T. 56 N.

T. 58 N.

Campbell Johnson

Converse Natrona Niobrara

Weston

Big Horn

Washakie

Sheridan

Cook

Sheridan

Bualo

o

43 00’

o

43 30’

o

44 00’

o

44 30’

o

45 00’

o 107 00’ o 106 00’ o 105 00’ 

Northern Wyoming

Powder River Basin

assessment area

Gillette coal eld

boundary

City or town

Southwestern Powder

River Basin assessment

area

Thickness (ft)

EXPLANATION

2.5

5

10

20

40

60

80

County line

INDEX MAP

WYOMING

0

0

5 10 20 MILES

5 10 20 KILOMETERS

Figure 66. Isopach map of the Werner coal bed showing extent of resources greater than 2.5 ft thick 

within the Southwestern Powder River Basin assessment area.
106 Assessment of Coal Geology, Resources, and Reserves in the Southwestern Powder River Basin, Wyoming

R. 87 W. R. 85 W. R. 83 W. R. 81 W. R. 79 W. R. 77 W. R. 75 W. R. 73 W. R. 71 W. R. 69 W. R. 67 W. R. 65 W.

T. 42 N.

T. 40 N.

T. 34 N.

T. 36 N.

T. 38 N.

T. 32 N.

T. 44 N.

T. 46 N.

T. 48 N.

T. 50 N.

T. 52 N.

T. 54 N.

T. 56 N.

T. 58 N.

Campbell Johnson

Natrona Converse Niobrara

Weston

Big Horn

Washakie

Sheridan

Cook

Sheridan

o

43 00’

o

43 30’

o

44 00’

o

44 30’

o

45 00’

o 107 00’ o 106 00’ o 105 00’ 

EXPLANATION

Northern Wyoming

Powder River Basin

assessment area

Gillette coal eld

boundary

City or town

Southwestern Powder

River Basin assessment

area

County line

Basin axis

(approximate)

Depth to top of coal (ft)

 1

 250

 500

1,000

1,500

2,000

2,500

3,000

4,000

INDEX MAP

WYOMING

Bualo

0

0

5 10 20 MILES

5 10 20 KILOMETERS

Figure 67. Depth to the top of the Werner coal bed within the Southwestern Powder River Basin 

assessment area.
Figures 107

R. 87 W. R. 85 W. R. 83 W. R. 81 W. R. 79 W. R. 77 W. R. 75 W. R. 73 W. R. 71 W. R. 69 W. R. 67 W. R. 65 W.

T. 42 N.

T. 40 N.

T. 34 N.

T. 36 N.

T. 38 N.

T. 32 N.

T. 44 N.

T. 46 N.

T. 48 N.

T. 50 N.

T. 52 N.

T. 54 N.

T. 56 N.

T. 58 N.

Campbell Johnson

Natrona Converse Niobrara

Weston

Big Horn

Washakie

Sheridan

Cook

Sheridan

Bualo

o

43 00’

o

43 30’

o

44 00’

o

44 30’

o

45 00’

o 107 00’ o 106 00’ o 105 00’ 

Gillette coal eld

boundary

City or town 

Northern Wyoming

Powder River Basin

assessment area

Southwestern Powder

River Basin assessment

area

Inferred

Indicated

Measured

EXPLANATION

INDEX MAP

WYOMING

County line

Hypothetical

0

0

5 10 20 MILES

5 10 20 KILOMETERS

Figure 68. Coal resource reliability categories for the Werner coal bed within the Southwestern Powder 

River Basin assessment area.
108 Assessment of Coal Geology, Resources, and Reserves in the Southwestern Powder River Basin, Wyoming

R. 87 W. R. 85 W. R. 83 W. R. 81 W. R. 79 W. R. 77 W. R. 75 W. R. 73 W. R. 71 W. R. 69 W. R. 67 W. R. 65 W.

T. 42 N.

T. 40 N.

T. 34 N.

T. 36 N.

T. 38 N.

T. 32 N.

T. 44 N.

T. 46 N.

T. 48 N.

T. 50 N.

T. 52 N.

T. 54 N.

T. 56 N.

T. 58 N.

Campbell Johnson

Natrona Converse Niobrara

Weston

Big Horn

Washakie

Sheridan

Cook

Sheridan

Bualo

o

43 00’

o

43 30’

o

44 00’

o

44 30’

o

45 00’

o 107 00’ o 106 00’ o 105 00’ 

2.5

5

10

20

40

60

80

Northern Wyoming

Powder River Basin

assessment area

Gillette coal eld

boundary

City or town

Southwestern Powder

River Basin assessment

area

Thickness (ft)

EXPLANATION

100

 120 and >

County line

INDEX MAP

WYOMING

0

0

5 10 20 MILES

5 10 20 KILOMETERS

Figure 69. Isopach map of the Otter coal bed showing extent of resources greater than 2.5 ft thick within 

the Southwestern Powder River Basin assessment area.
Figures 109

R. 87 W. R. 85 W. R. 83 W. R. 81 W. R. 79 W. R. 77 W. R. 75 W. R. 73 W. R. 71 W. R. 69 W. R. 67 W. R. 65 W.

T. 42 N.

T. 40 N.

T. 34 N.

T. 36 N.

T. 38 N.

T. 32 N.

T. 44 N.

T. 46 N.

T. 48 N.

T. 50 N.

T. 52 N.

T. 54 N.

T. 56 N.

T. 58 N.

Campbell Johnson

Natrona Converse Niobrara

Weston

Big Horn

Washakie

Sheridan

Cook

Sheridan

o

43 00’

o

43 30’

o

44 00’

o

44 30’

o

45 00’

o 107 00’ o 106 00’ o 105 00’ 

EXPLANATION

Northern Wyoming

Powder River Basin

assessment area

Gillette coal Ffeld

boundary

City or town

Southwestern Powder

River Basin assessment

area

County line

Basin axis

(approximate)

Depth to top of coal (ft)

 1

 250

 500

1,000

1,500

2,000

2,500

3,000

4,000

INDEX MAP

WYOMING

Bualo

0

0

5 10 20 MILES

5 10 20 KILOMETERS

Figure 70. Depth to the top of the Otter coal bed within the Southwestern Powder River Basin 

assessment area.
110 Assessment of Coal Geology, Resources, and Reserves in the Southwestern Powder River Basin, Wyoming

R. 87 W. R. 85 W. R. 83 W. R. 81 W. R. 79 W. R. 77 W. R. 75 W. R. 73 W. R. 71 W. R. 69 W. R. 67 W. R. 65 W.

T. 42 N.

T. 40 N.

T. 34 N.

T. 36 N.

T. 38 N.

T. 32 N.

T. 44 N.

T. 46 N.

T. 48 N.

T. 50 N.

T. 52 N.

T. 54 N.

T. 56 N.

T. 58 N.

Campbell Johnson

Natrona Converse Niobrara

Weston

Big Horn

Washakie

Sheridan

Cook

Sheridan

Bualo

o

43 00’

o

43 30’

o

44 00’

o

44 30’

o

45 00’

o 107 00’ o 106 00’ o 105 00’ 

Gillette coal eld

boundary

City or town 

Northern Wyoming

Powder River Basin

assessment area

Southwestern Powder

River Basin assessment

area

Inferred

Indicated

Measured

EXPLANATION

INDEX MAP

WYOMING

County line

Hypothetical

0

0

5 10 20 MILES

5 10 20 KILOMETERS

Figure 71. Coal resource reliability categories for the Otter coal bed within the Southwestern Powder 

River Basin assessment area.
Figures 111

R. 87 W. R. 85 W. R. 83 W. R. 81 W. R. 79 W. R. 77 W. R. 75 W. R. 73 W. R. 71 W. R. 69 W. R. 67 W. R. 65 W.

T. 42 N.

T. 40 N.

T. 34 N.

T. 36 N.

T. 38 N.

T. 32 N.

T. 44 N.

T. 46 N.

T. 48 N.

T. 50 N.

T. 52 N.

T. 54 N.

T. 56 N.

T. 58 N.

Campbell Johnson

Natrona Converse Niobrara

Weston

Big Horn

Washakie

Sheridan

Cook

Sheridan

Bualo

o

43 00’

o

43 30’

o

44 00’

o

44 30’

o

45 00’

o 107 00’ o 106 00’ o 105 00’ 

Northern Wyoming

Powder River Basin

assessment area

Gillette coal eld

boundary

City or town

Southwestern Powder

River Basin assessment

area

Thickness (ft)

EXPLANATION

2.5

5

10

20

40

60

80

100

>120

County line

INDEX MAP

WYOMING

0

0

5 10 20 MILES

5 10 20 KILOMETERS

Figure 72. Isopach map of the Gates coal bed showing extent of resources greater than 2.5 ft thick within 

the Southwestern Powder River Basin assessment area.
112 Assessment of Coal Geology, Resources, and Reserves in the Southwestern Powder River Basin, Wyoming

R. 87 W. R. 85 W. R. 83 W. R. 81 W. R. 79 W. R. 77 W. R. 75 W. R. 73 W. R. 71 W. R. 69 W. R. 67 W. R. 65 W.

T. 42 N.

T. 40 N.

T. 34 N.

T. 36 N.

T. 38 N.

T. 32 N.

T. 44 N.

T. 46 N.

T. 48 N.

T. 50 N.

T. 52 N.

T. 54 N.

T. 56 N.

T. 58 N.

Campbell Johnson

Natrona Converse Niobrara

Weston

Big Horn

Washakie

Sheridan

Cook

Sheridan

o

43 00’

o

43 30’

o

44 00’

o

44 30’

o

45 00’

o 107 00’ o 106 00’ o 105 00’ 

EXPLANATION

Northern Wyoming

Powder River Basin

assessment area

Gillette coal eld

boundary

City or town

Southwestern Powder

River Basin assessment

area

County line

Basin axis

(approximate)

Depth to top of coal (ft)

 1

 250

 500

1,000

1,500

2,000

2,500

3,000

4,000

INDEX MAP

WYOMING

Bualo

0

0

5 10 20 MILES

5 10 20 KILOMETERS

Figure 73. Depth to the top of the Gates coal bed within the Southwestern Powder River Basin 

assessment area.
Figures 113

R. 87 W. R. 85 W. R. 83 W. R. 81 W. R. 79 W. R. 77 W. R. 75 W. R. 73 W. R. 71 W. R. 69 W. R. 67 W. R. 65 W.

T. 42 N.

T. 40 N.

T. 34 N.

T. 36 N.

T. 38 N.

T. 32 N.

T. 44 N.

T. 46 N.

T. 48 N.

T. 50 N.

T. 52 N.

T. 54 N.

T. 56 N.

T. 58 N.

Campbell Johnson

Natrona Converse Niobrara

Weston

Big Horn

Washakie

Sheridan

Cook

Sheridan

Bualo

o

43 00’

o

43 30’

o

44 00’

o

44 30’

o

45 00’

o 107 00’ o 106 00’ o 105 00’ 

Gillette coal eld

boundary

City or town 

Northern Wyoming

Powder River Basin

assessment area

Southwestern Powder

River Basin assessment

area

Inferred

Indicated

Measured

EXPLANATION

INDEX MAP

WYOMING

County line

Hypothetical

0

0

5 10 20 MILES

5 10 20 KILOMETERS

Figure 74. Coal resource reliability categories for the Gates coal bed within the Southwestern 

Powder River Basin assessment area.
114 Assessment of Coal Geology, Resources, and Reserves in the Southwestern Powder River Basin, Wyoming

R. 87 W. R. 85 W. R. 83 W. R. 81 W. R. 79 W. R. 77 W. R. 75 W. R. 73 W. R. 71 W. R. 69 W. R. 67 W. R. 65 W.

T. 42 N.

T. 40 N.

T. 34 N.

T. 36 N.

T. 38 N.

T. 32 N.

T. 44 N.

T. 46 N.

T. 48 N.

T. 50 N.

T. 52 N.

T. 54 N.

T. 56 N.

T. 58 N.

Campbell Johnson

Converse Natrona Niobrara

Weston

Big Horn

Washakie

Sheridan

Cook

Sheridan

Bualo

o

43 00’

o

43 30’

o

44 00’

o

44 30’

o

45 00’

o 107 00’ o 106 00’ o 105 00’ 

Northern Wyoming

Powder River Basin

assessment area

Gillette coal eld

boundary

City or town

Southwestern Powder

River Basin assessment

area

Thickness (ft)

EXPLANATION

2.5

5

10

20

County line

INDEX MAP

WYOMING

0

0

5 10 20 MILES

5 10 20 KILOMETERS

Figure 75. Isopach map of the Pawnee coal bed showing extent of resources greater than 2.5 ft 

thick within the Southwestern Powder River Basin assessment area.
Figures 115

R. 87 W. R. 85 W. R. 83 W. R. 81 W. R. 79 W. R. 77 W. R. 75 W. R. 73 W. R. 71 W. R. 69 W. R. 67 W. R. 65 W.

T. 42 N.

T. 40 N.

T. 34 N.

T. 36 N.

T. 38 N.

T. 32 N.

T. 44 N.

T. 46 N.

T. 48 N.

T. 50 N.

T. 52 N.

T. 54 N.

T. 56 N.

T. 58 N.

Johnson Campbell

Natrona Converse Niobrara

Weston

Big Horn

Washakie

Sheridan

Cook

Sheridan

o

43 00’

o

43 30’

o

44 00’

o

44 30’

o

45 00’

o 107 00’ o 106 00’ o 105 00’ 

EXPLANATION

Northern Wyoming

Powder River Basin

assessment area

Gillette coal eld

boundary

City or town

Southwestern Powder

River Basin assessment

area

County line

Basin axis

(approximate)

Depth to top of coal (ft)

 1

 250

 500

1,000

1,500

2,000

2,500

3,000

4,000

INDEX MAP

WYOMING

Bualo

0

0

5 10 20 MILES

5 10 20 KILOMETERS

Figure 76. Depth to the top of the Pawnee coal bed within the Southwestern Powder River Basin 

assessment area.
116 Assessment of Coal Geology, Resources, and Reserves in the Southwestern Powder River Basin, Wyoming

R. 87 W. R. 85 W. R. 83 W. R. 81 W. R. 79 W. R. 77 W. R. 75 W. R. 73 W. R. 71 W. R. 69 W. R. 67 W. R. 65 W.

T. 42 N.

T. 40 N.

T. 34 N.

T. 36 N.

T. 38 N.

T. 32 N.

T. 44 N.

T. 46 N.

T. 48 N.

T. 50 N.

T. 52 N.

T. 54 N.

T. 56 N.

T. 58 N.

Campbell Johnson

Natrona Converse Niobrara

Weston

Big Horn

Washakie

Sheridan

Cook

Sheridan

Bualo

o

43 00’

o

43 30’

o

44 00’

o

44 30’

o

45 00’

o 107 00’ o 106 00’ o 105 00’ 

Gillette coal eld

boundary

City or town 

Northern Wyoming

Powder River Basin

assessment area

Southwestern Powder

River Basin assessment

area

Inferred

Indicated

Measured

EXPLANATION

INDEX MAP

WYOMING

County line

Hypothetical

0

0

5 10 20 MILES

5 10 20 KILOMETERS

Figure 77. Coal resource reliability categories for the Pawnee coal bed within the Southwestern 

Powder River Basin assessment area.
Figures 117

R. 87 W. R. 85 W. R. 83 W. R. 81 W. R. 79 W. R. 77 W. R. 75 W. R. 73 W. R. 71 W. R. 69 W. R. 67 W. R. 65 W.

T. 42 N.

T. 40 N.

T. 34 N.

T. 36 N.

T. 38 N.

T. 32 N.

T. 44 N.

T. 46 N.

T. 48 N.

T. 50 N.

T. 52 N.

T. 54 N.

T. 56 N.

T. 58 N.

Campbell Johnson

Natrona Converse Niobrara

Weston

Big Horn

Washakie

Sheridan

Cook

Sheridan

Bualo

o

43 00’

o

43 30’

o

44 00’

o

44 30’

o

45 00’

o 107 00’ o 106 00’ o 105 00’ 

Northern Wyoming

Powder River Basin

assessment area

Gillette coal eld

boundary

City or town

Southwestern Powder

River Basin assessment

area

Thickness (ft)

EXPLANATION

2.5

5

10

20

40

County line

INDEX MAP

WYOMING

0

0

5 10 20 MILES

5 10 20 KILOMETERS

Figure 78. Isopach map of the Deep 1 coal bed showing extent of resources greater than 2.5 ft thick 

within the Southwestern Powder River Basin assessment area.
118 Assessment of Coal Geology, Resources, and Reserves in the Southwestern Powder River Basin, Wyoming

R. 87 W. R. 85 W. R. 83 W. R. 81 W. R. 79 W. R. 77 W. R. 75 W. R. 73 W. R. 71 W. R. 69 W. R. 67 W. R. 65 W.

T. 42 N.

T. 40 N.

T. 34 N.

T. 36 N.

T. 38 N.

T. 32 N.

T. 44 N.

T. 46 N.

T. 48 N.

T. 50 N.

T. 52 N.

T. 54 N.

T. 56 N.

T. 58 N.

Johnson Campbell

Natrona Converse Niobrara

Weston

Big Horn

Washakie

Sheridan

Cook

Sheridan

o

43 00’

o

43 30’

o

44 00’

o

44 30’

o

45 00’

o 107 00’ o 106 00’ o 105 00’ 

EXPLANATION

Northern Wyoming

Powder River Basin

assessment area

Gillette coal eld

boundary

City or town

Southwestern Powder

River Basin assessment

area

County line

Basin axis

(approximate)

Depth to top of coal (ft)

 1

 250

 500

1,000

1,500

2,000

2,500

3,000

4,000

INDEX MAP

WYOMING

Bualo

0

0

5 10 20 MILES

5 10 20 KILOMETERS

Figure 79. Depth to the top of the Deep 1 coal bed within the Southwestern Powder River Basin 

assessment area.
Figures 119

R. 87 W. R. 85 W. R. 83 W. R. 81 W. R. 79 W. R. 77 W. R. 75 W. R. 73 W. R. 71 W. R. 69 W. R. 67 W. R. 65 W.

T. 42 N.

T. 40 N.

T. 34 N.

T. 36 N.

T. 38 N.

T. 32 N.

T. 44 N.

T. 46 N.

T. 48 N.

T. 50 N.

T. 52 N.

T. 54 N.

T. 56 N.

T. 58 N.

Campbell Johnson

Natrona Converse Niobrara

Weston

Big Horn

Washakie

Sheridan

Cook

Sheridan

Bualo

o

43 00’

o

43 30’

o

44 00’

o

44 30’

o

45 00’

o 107 00’ o 106 00’ o 105 00’ 

Gillette coal eld

boundary

City or town 

Northern Wyoming

Powder River Basin

assessment area

Southwestern Powder

River Basin assessment

area

Inferred

Indicated

Measured

EXPLANATION

INDEX MAP

WYOMING

County line

Hypothetical

0

0

5 10 20 MILES

5 10 20 KILOMETERS

Figure 80. Coal resource reliability categories for the Deep 1 coal bed within the Southwestern 

Powder River Basin assessment area.
120 Assessment of Coal Geology, Resources, and Reserves in the Southwestern Powder River Basin, Wyoming

R. 87 W. R. 85 W. R. 83 W. R. 81 W. R. 79 W. R. 77 W. R. 75 W. R. 73 W. R. 71 W. R. 69 W. R. 67 W. R. 65 W.

T. 42 N.

T. 40 N.

T. 34 N.

T. 36 N.

T. 38 N.

T. 32 N.

T. 44 N.

T. 46 N.

T. 48 N.

T. 50 N.

T. 52 N.

T. 54 N.

T. 56 N.

T. 58 N.

Campbell Johnson

Natrona Converse Niobrara

Weston

Big Horn

Washakie

Sheridan

Cook

Sheridan

Bualo

o

43 00’

o

43 30’

o

44 00’

o

44 30’

o

45 00’

o 107 00’ o 106 00’ o 105 00’ 

Northern Wyoming

Powder River Basin

assessment area

Gillette coal eld

boundary

City or town

Southwestern Powder

River Basin assessment

area

Thickness (ft)

EXPLANATION

2.5

5

10

20

40

County line

INDEX MAP

WYOMING

0

0

5 10 20 MILES

5 10 20 KILOMETERS

Figure 81. Isopach map of the Deep 2 coal bed showing extent of resources greater than 2.5 ft thick 

within the Southwestern Powder River Basin assessment area.
Figures 121

R. 87 W. R. 85 W. R. 83 W. R. 81 W. R. 79 W. R. 77 W. R. 75 W. R. 73 W. R. 71 W. R. 69 W. R. 67 W. R. 65 W.

T. 42 N.

T. 40 N.

T. 34 N.

T. 36 N.

T. 38 N.

T. 32 N.

T. 44 N.

T. 46 N.

T. 48 N.

T. 50 N.

T. 52 N.

T. 54 N.

T. 56 N.

T. 58 N.

Campbell Johnson

Converse Natrona Niobrara

Weston

Big Horn

Washakie

Sheridan

Cook

Sheridan

o

43 00’

o

43 30’

o

44 00’

o

44 30’

o

45 00’

o 107 00’ o 106 00’ o 105 00’ 

EXPLANATION

Northern Wyoming

Powder River Basin

assessment area

Gillette coal eld

boundary

City or town

Southwestern Powder

River Basin assessment

area

County line

Basin axis

(approximate)

Depth to top of coal (ft)

 1

 250

 500

1,000

1,500

2,000

2,500

3,000

4,000

INDEX MAP

WYOMING

Bualo

0

0

5 10 20 MILES

5 10 20 KILOMETERS

Figure 82. Depth to the top of the Deep 2 coal bed within the Southwestern Powder River Basin 

assessment area.
122 Assessment of Coal Geology, Resources, and Reserves in the Southwestern Powder River Basin, Wyoming

R. 87 W. R. 85 W. R. 83 W. R. 81 W. R. 79 W. R. 77 W. R. 75 W. R. 73 W. R. 71 W. R. 69 W. R. 67 W. R. 65 W.

T. 42 N.

T. 40 N.

T. 34 N.

T. 36 N.

T. 38 N.

T. 32 N.

T. 44 N.

T. 46 N.

T. 48 N.

T. 50 N.

T. 52 N.

T. 54 N.

T. 56 N.

T. 58 N.

Campbell Johnson

Natrona Converse Niobrara

Weston

Big Horn

Washakie

Sheridan

Cook

Sheridan

Bualo

o

43 00’

o

43 30’

o

44 00’

o

44 30’

o

45 00’

o 107 00’ o 106 00’ o 105 00’ 

Gillette coal eld

boundary

City or town 

Northern Wyoming

Powder River Basin

assessment area

Southwestern Powder

River Basin assessment

area

Inferred

Indicated

Measured

EXPLANATION

INDEX MAP

WYOMING

County line

Hypothetical

0

0

5 10 20 MILES

5 10 20 KILOMETERS

Figure 83. Coal resource reliability categories for the Deep 2 coal bed within the Southwestern Powder 

River Basin assessment area.
Figures 123

R. 87 W. R. 85 W. R. 83 W. R. 81 W. R. 79 W. R. 77 W. R. 75 W. R. 73 W. R. 71 W. R. 69 W. R. 67 W. R. 65 W.

T. 42 N.

T. 40 N.

T. 34 N.

T. 36 N.

T. 38 N.

T. 32 N.

T. 44 N.

T. 46 N.

T. 48 N.

T. 50 N.

T. 52 N.

T. 54 N.

T. 56 N.

T. 58 N.

Campbell Johnson

Natrona Converse Niobrara

Weston

Big Horn

Washakie

Sheridan

Cook

Sheridan

Bualo

o

43 00’

o

43 30’

o

44 00’

o

44 30’

o

45 00’

o 107 00’ o 106 00’ o 105 00’ 

Northern Wyoming

Powder River Basin

assessment area

Gillette coal eld

boundary

City or town

Southwestern Powder

River Basin assessment

area

Thickness (ft)

EXPLANATION

2.5

5

10

20

40

County line

INDEX MAP

WYOMING

0

0

5 10 20 MILES

5 10 20 KILOMETERS

Figure 84. Isopach map of the Deep 3 coal bed showing extent of resources greater than 2.5 ft thick within 

the Southwestern Powder River Basin assessment area.
124 Assessment of Coal Geology, Resources, and Reserves in the Southwestern Powder River Basin, Wyoming

R. 87 W. R. 85 W. R. 83 W. R. 81 W. R. 79 W. R. 77 W. R. 75 W. R. 73 W. R. 71 W. R. 69 W. R. 67 W. R. 65 W.

T. 42 N.

T. 40 N.

T. 34 N.

T. 36 N.

T. 38 N.

T. 32 N.

T. 44 N.

T. 46 N.

T. 48 N.

T. 50 N.

T. 52 N.

T. 54 N.

T. 56 N.

T. 58 N.

Campbell Johnson

Natrona Converse Niobrara

Weston

Big Horn

Washakie

Sheridan

Cook

Sheridan

o

43 00’

o

43 30’

o

44 00’

o

44 30’

o

45 00’

o 107 00’ o 106 00’ o 105 00’ 

EXPLANATION

Northern Wyoming

Powder River Basin

assessment area

Gillette coal eld

boundary

City or town

Southwestern Powder

River Basin assessment

area

County line

Basin axis

(approximate)

Depth to top of coal (ft)

 1

 250

 500

1,000

1,500

2,000

2,500

3,000

4,000

INDEX MAP

WYOMING

Bualo

0

0

5 10 20 MILES

5 10 20 KILOMETERS

Figure 85. Depth to the top of the Deep 3 coal bed within the Southwestern Powder River Basin 

assessment area.
Figures 125

R. 87 W. R. 85 W. R. 83 W. R. 81 W. R. 79 W. R. 77 W. R. 75 W. R. 73 W. R. 71 W. R. 69 W. R. 67 W. R. 65 W.

T. 42 N.

T. 40 N.

T. 34 N.

T. 36 N.

T. 38 N.

T. 32 N.

T. 44 N.

T. 46 N.

T. 48 N.

T. 50 N.

T. 52 N.

T. 54 N.

T. 56 N.

T. 58 N.

Campbell Johnson

Natrona Converse Niobrara

Weston

Big Horn

Washakie

Sheridan

Cook

Sheridan

Bualo

o

43 00’

o

43 30’

o

44 00’

o

44 30’

o

45 00’

o 107 00’ o 106 00’ o 105 00’ 

Gillette coal eld

boundary

City or town 

Northern Wyoming

Powder River Basin

assessment area

Southwestern Powder

River Basin assessment

area

Inferred

Indicated

Measured

EXPLANATION

INDEX MAP

WYOMING

County line

Hypothetical

0

0

5 10 20 MILES

5 10 20 KILOMETERS

Figure 86. Coal resource reliability categories for the Deep 3 coal bed within the Southwestern Powder 

River Basin assessment area.
126 Assessment of Coal Geology, Resources, and Reserves in the Southwestern Powder River Basin, Wyoming

R. 87 W. R. 85 W. R. 83 W. R. 81 W. R. 79 W. R. 77 W. R. 75 W. R. 73 W. R. 71 W. R. 69 W. R. 67 W. R. 65 W.

T. 42 N.

T. 40 N.

T. 34 N.

T. 36 N.

T. 38 N.

T. 32 N.

T. 44 N.

T. 46 N.

T. 48 N.

T. 50 N.

T. 52 N.

T. 54 N.

T. 56 N.

T. 58 N.

Campbell Johnson

Natrona Converse Niobrara

Weston

Big Horn

Washakie

Sheridan

Cook

Sheridan

Bualo

o

43 00’

o

43 30’

o

44 00’

o

44 30’

o

45 00’

o 107 00’ o 106 00’ o 105 00’ 

Northern Wyoming

 Powder River Basin

 assessment area

Gillette coal eld

boundary

City or town

Southwestern Powder

River Basin assessment

area

Thickness (ft)

EXPLANATION

2.5

5

10

20

40

County line

INDEX MAP

WYOMING

0

0

5 10 20 MILES

5 10 20 KILOMETERS

Figure 87. Isopach map of the Roberts coal bed showing extent of resources greater than 2.5 ft thick within 

the Southwestern Powder River Basin assessment area.
Figures 127

R. 87 W. R. 85 W. R. 83 W. R. 81 W. R. 79 W. R. 77 W. R. 75 W. R. 73 W. R. 71 W. R. 69 W. R. 67 W. R. 65 W.

T. 42 N.

T. 40 N.

T. 34 N.

T. 36 N.

T. 38 N.

T. 32 N.

T. 44 N.

T. 46 N.

T. 48 N.

T. 50 N.

T. 52 N.

T. 54 N.

T. 56 N.

T. 58 N.

Campbell Johnson

Natrona Converse Niobrara

Weston

Big Horn

Washakie

Sheridan

Cook

Sheridan

o

43 00’

o

43 30’

o

44 00’

o

44 30’

o

45 00’

o 107 00’ o 106 00’ o 105 00’ 

EXPLANATION

Northern Wyoming

Powder River Basin

assessment area

Gillette coal eld

boundary

City or town

Southwestern Powder

River Basin assessment

area

County line

Basin axis

(approximate)

Depth to top of coal (ft)

 1

 250

 500

1,000

1,500

2,000

2,500

3,000

4,000

5,000

INDEX MAP

WYOMING

Bualo

0

0

5 10 20 MILES

5 10 20 KILOMETERS

Figure 88. Depth to the top of the Roberts coal bed within the Southwestern Powder River Basin 

assessment area.
128 Assessment of Coal Geology, Resources, and Reserves in the Southwestern Powder River Basin, Wyoming

R. 87 W. R. 85 W. R. 83 W. R. 81 W. R. 79 W. R. 77 W. R. 75 W. R. 73 W. R. 71 W. R. 69 W. R. 67 W. R. 65 W.

T. 42 N.

T. 40 N.

T. 34 N.

T. 36 N.

T. 38 N.

T. 32 N.

T. 44 N.

T. 46 N.

T. 48 N.

T. 50 N.

T. 52 N.

T. 54 N.

T. 56 N.

T. 58 N.

Campbell Johnson

Natrona Converse Niobrara

Weston

Big Horn

Washakie

Sheridan

Cook

Sheridan

Bualo

o

43 00’

o

43 30’

o

44 00’

o

44 30’

o

45 00’

o 107 00’ o 106 00’ o 105 00’ 

Gillette coal eld

boundary

City or town 

Northern Wyoming

Powder River Basin

assessment area

Southwestern Powder

River Basin assessment

area

Inferred

Indicated

Measured

EXPLANATION

INDEX MAP

WYOMING

County line

Hypothetical

0

0

5 10 20 MILES

5 10 20 KILOMETERS

Figure 89. Coal resource reliability categories for the Roberts coal bed within the Southwestern 

Powder River Basin assessment area.
Figure 90. Illustration showing the effect of coal bed depth upon restricted resource due to mine pit highwall setback requirements (not to s

26o 26o

858 ft

2,144 ft

200 ft

500 ft

Horizontal limits of projected surface restriction and buffer

Coal bedMine accessible coal-bearing rock Additional restriction due to required mine pit highwall angle (coal unavailable for mining) Surface restriction and buer projected downward (coal unavailable for mining)Restriction to mining

Mine bench Mine bench

300 ft 300 ft

Surface restriction

Buer distance Buer distance

EXPLANATION
130 Assessment of Coal Geology, Resources, and Reserves in the Southwestern Powder River Basin, Wyoming

R. 87 W. R. 85 W. R. 83 W. R. 81 W. R. 79 W. R. 77 W. R. 75 W. R. 73 W. R. 71 W. R. 69 W. R. 67 W. R. 65 W.

T. 42 N.

T. 40 N.

T. 34 N.

T. 36 N.

T. 38 N.

T. 32 N.

T. 44 N.

T. 46 N.

T. 48 N.

T. 50 N.

T. 52 N.

T. 54 N.

T. 56 N.

T. 58 N.

Campbell Johnson

Converse Natrona Niobrara

Weston

Cook

Big Horn

Washakie

Sheridan Campbell

Cook

Bualo

Lake

DeSmet

Dave Johnston Mine

 (abandoned)

Sheridan

Casper

Douglas

Rolling Hills

EXPLANATION

Northern Wyoming

Powder River Basin

assessment area

Mine area

(abandoned)

Southwestern Powder

River Basin assessment

area

Lake DeSmet

County line

Town buer 

City or town

North Platte River

buer

INDEX MAP

WYOMING

o

43 00’

o

43 30’

o

44 00’

o

44 30’

o

45 00’

o 107 00’ o 106 00’ o 105 00’ 

25

90

90

Gillette coal eld

boundary

Railroad

Interstate

Land Use Restrictions

0

0

5 10 20 MILES

5 10 20 KILOMETERS

Figure 91. Land use restrictions in the Southwestern Powder River Basin assessment area.
Figures 131

R. 87 W. R. 85 W. R. 83 W. R. 81 W. R. 79 W. R. 77 W. R. 75 W. R. 73 W. R. 71 W. R. 69 W. R. 67 W. R. 65 W.

T. 42 N.

T. 40 N.

T. 34 N.

T. 36 N.

T. 38 N.

T. 32 N.

T. 44 N.

T. 46 N.

T. 48 N.

T. 50 N.

T. 52 N.

T. 54 N.

T. 56 N.

T. 58 N.

Campbell Johnson

Converse Natrona Niobrara

Weston

Big Horn

Washakie

Sheridan

Cook

Sheridan

Bualo

EXPLANATION

Northern Wyoming

Powder River Basin

assessment area

Gillette coal eld

boundary

Federal coal

State coal

Private coal

Southwestern Powder

River Basin assessment

area

INDEX MAP

WYOMING

o

43 00’

o

43 30’

o

44 00’

o

44 30’

o

45 00’

o 107 00’ o 106 00’ o 105 00’ 

0

0

5 10 20 MILES

5 10 20 KILOMETERS

Figure 92. Coal ownership in the Southwestern Powder River Basin assessment area.
132 Assessment of Coal Geology, Resources, and Reserves in the Southwestern Powder River Basin, Wyoming

2,000

1,800

1,600

1,400

1,200

1,000

800

600

400

200

0

8,000 8,500 9,000 9,500 10,000 10,500 11,000

Depth (ft)

Calorific value (Btu/lb)

subA

 200 ft core @ 9,750 Btu/lb

 (Smith coal bed) Depth vs A.R. Btu trendline

Testa and Pratt, 2003 Btu (m,mmf) trendline

Depth vs Btu/lb trendline

 (Apparent rank)

 (m,mmf) 

Figure 93. Estimated variability of as-received (AR) and moist, mineral-matter-free (m, mmf) heating content 

values versus depth for the Wyodak-Anderson coal beds (fig. 6) in the Southwestern Powder River Basin 

assessment area. The m, mmf heating content values are used to determine apparent rank and the ranges 

are (1) subbituminous C (sub C) <9,500 Btu/lbm,mmf; (2) subbituminous B (sub B) 9,500–10,500 Btu/lbm,mmf; and (3) 

subbituminous A (sub A) >10,500 Btu/lbm,mmf; (ASTM, 2008).
Figures 133

Tailgate

Pillars

Collapsed area Direction of mining Longwall face

Headgate

Main entry

Longwall panel

Barrier pillar

Figure 94. Diagram of typical longwall mining operation.
134 Assessment of Coal Geology, Resources, and Reserves in the Southwestern Powder River Basin, Wyoming

T. 57 N.

T. 56 N.

T. 55 N.

T. 54 N.

T. 53 N.

T. 52 N.

T. 51 N.

T. 50 N.

T. 49 N.

T. 48 N.

T. 47 N.

T. 46 N.

R. 83 W. R. 82 W. R. 81 W. R. 80 W. R. 79 W. R. 78 W. R. 84 W.

Sheridan

Bualo

90

25 90

90

Northern Wyoming

 Powder River Basin

 assessment area

Southwestern Powder

River Basin assessment area

EXPLANATION

INDEX MAP

WYOMING

Area of enlargement

Upper Healy 0-5 strip ratio

 Healy 0-5 strip ratio

City or town with buer

Lake DeSmet

Interstate roads

Railroads

Clinker 

Figure 95. Areal extent for the Upper Healy and Healy coal beds where the stripping ratios are up to 5:1, 

thickness are equal to at least 5.0 ft, and the overburden is less than or equal to 500 ft thick.
Figures 135

T. 57 N.

T. 56 N.

T. 55 N.

T. 54 N.

T. 53 N.

T. 52 N.

T. 51 N.

T. 50 N.

T. 49 N.

T. 48 N.

T. 47 N.

T. 46 N.

R. 83 W. R. 82 W. R. 81 W. R. 80 W. R. 79 W. R. 78 W. R. 84 W.

Sheridan

(buered) Sheridan

Bualo

25

90

90

Northern Wyoming

 Powder River Basin

 assessment area

Southwestern Powder

River Basin assessment area

EXPLANATION

INDEX MAP

WYOMING

Area of enlargement

Upper Healy 0-5 strip ratio

 Healy 0-5 strip ratio

City or town with buer

Lake DeSmet

Interstate roads

Railroads

Clinker 

Figure 96. Areal extent for the Upper Healy and Healy coal beds where the stripping ratios are from 5:1 to 5:10, 

thickness are equal to at least 5.0 ft, and the overburden is less than or equal to 500 ft thick.