U.S. Department of the Interior

U.S. Geological Survey

Open-File Report 2012–1113

Assessment of Coal Geology, Resources, and Reserves 

in the Montana Powder River Basin
Cover: Photograph taken near Decker, Montana, showing a dragline at a surface coal mine. 

Photograph by David C. Scott, U.S. Geological Survey, Denver, Colorado.
Assessment of Coal Geology, Resources, 

and Reserves in the Montana Powder 

River Basin

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

Pierce, and Jay A. Gunderson

Open-File Report 2012–1113

U.S. Department of the Interior

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

KEN SALAZAR, Secretary

U.S. Geological Survey

Suzette M. Kimball, Acting Director

U.S. Geological Survey, Reston, Virginia: 2013

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Suggested citation:

Haacke, J.E., Scott, D.C., Osmonson, L.M., Luppens, J.A., Pierce, P.E, and Gunderson, J. A., 2013, Assessment of coal 

geology, resources, and reserves in the Montana Powder River Basin: U.S. Geological Survey Open-File Report 

2012–1113, 133 p.

Quotations in this report contain errant and variant spellings that are reproduced as written.
iii

Contents

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

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

Previous and Current Coal Mining.....................................................................................................2

Previous Coal Resource Estimates....................................................................................................3

Methodology...................................................................................................................................................4

Data Collection......................................................................................................................................5

Coalbed Modeling.................................................................................................................................5

Resource Allocation Planning ...................................................................................................5

Factors Affecting Extraction of Coal Resources ....................................................................6

Airports.................................................................................................................................9

Alluvial Valley Floors .........................................................................................................9

Archaeological Areas .......................................................................................................9

Coalbed Methane ...............................................................................................................9

Dwellings and Buildings ..................................................................................................10

Federal Land Systems......................................................................................................10

Historic Lands and Sites..................................................................................................10

Oil and Oil-Related Gas Wells.........................................................................................10

Pipelines.............................................................................................................................14

Power Lines .......................................................................................................................14

Railroads.............................................................................................................................14

Rivers, Lakes, and Streams.............................................................................................14

Roads ..................................................................................................................................14

State Lands and Trusts.....................................................................................................14

Towns..................................................................................................................................14

Coal Quality..........................................................................................................................................15

Mine Model Methodology.................................................................................................................17

Geologic Setting...........................................................................................................................................17

Coal Bed Correlations and Nomenclature...............................................................................................18

Coal Bed Assessment .................................................................................................................................19

Roland (Baker) Coal Bed ...................................................................................................................19

Smith Coal Bed....................................................................................................................................19

Anderson Coal Bed.............................................................................................................................28

Dietz 2 Coal Bed ..................................................................................................................................28

Dietz 3 Coal Bed ..................................................................................................................................28

Canyon Coal Bed.................................................................................................................................28

Lower Canyon Coal Bed ....................................................................................................................28

Ferry Coal Bed.....................................................................................................................................29

Werner/Cook Coal Bed ......................................................................................................................29

Otter Coal Bed .....................................................................................................................................29

Gates/Wall Coal Bed ..........................................................................................................................29

Pawnee Coal Bed................................................................................................................................29

Odell Coal Bed.....................................................................................................................................29

Rosebud/Knobloch Coal Bed ............................................................................................................29
iv

McKay/Nance Coal Bed ....................................................................................................................30

Flowers-Goodale Coal Bed ...............................................................................................................30

Robinson/Witham Coal Bed ..............................................................................................................30

Roberts/Terret Coal Bed ....................................................................................................................30

Assessment of Resources and Reserves ................................................................................................30

Surface Coal Resource Results........................................................................................................31

Surface Coal Reserve Results ..........................................................................................................31

Underground Coal Resource Results ..............................................................................................32

Underground Coal Reserves Results...............................................................................................32

Conclusions...................................................................................................................................................35

Acknowledgments.......................................................................................................................................35

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

Glossary.........................................................................................................................................................39

Appendix........................................................................................................................................................41

Modeling Stratigraphic Sequence for Mining ........................................................................................41

Surface Mine Model Design.............................................................................................................42

Stripping and Coal Mining........................................................................................................42

Mine Plant Facilities..................................................................................................................43

Reclamation................................................................................................................................43

Supplies and Utilities.................................................................................................................43

Underground Mine Model Design ...................................................................................................43

Mine Layout Design...................................................................................................................43

Surface Mine Plant....................................................................................................................44

Underground Mine Plant ..........................................................................................................44

Development Excavation..........................................................................................................45

Production Unit ..........................................................................................................................45

Pillar Recovery ...........................................................................................................................45

Surface Mine Model Economic Evaluation....................................................................................45

Net Present Value and Discounted Cash Flow Rate of Return Analyses.........................46

Capital Cost.................................................................................................................................46

Operating Cost............................................................................................................................47

Breakeven Cost Determination ...............................................................................................47

Figures

 1. Location of the Montana Powder River Basin assessment area, Montana, Northern 

Wyoming Powder River Basin assessment area, Wyoming, Southwestern Powder 

River Basin assessment area, Wyoming, and Gillette coal field, Wyoming .....................48

 2. Map showing coal fields, mines, and lease areas in the Montana Powder River Basin 

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

 3. Flow chart showing generalized methodology used for coal resource and reserve 

evaluation.....................................................................................................................................50

 4. Map showing drill-hole locations in the Montana Powder River Basin assessment area ....51

 5. Illustration showing the effect of coal bed depth upon restricted resource due to 

mine-pit highwall setback requirements ................................................................................52
v

 6. Map showing land-use restrictions in the Montana Powder River Basin assessment 

area ...............................................................................................................................................53

 7. Map showing coal ownership in the Montana Powder River Basin assessment area ..........54

 8. Areal extent for the Roland (Baker), Smith, Anderson, Dietz 2, and Dietz 3 coal beds 

where the stripping ratios are from 1:1 to 1:10, thicknesses are equal to at least 

5.0 ft, and the overburden is less than or equal to 500 ft thick in the Montana 

Powder River Basin assessment area ....................................................................................55

 9. Areal extent for the Canyon coal bed where the stripping ratios are from 1:1 to 1:10, 

thicknesses are equal to at least 5.0 ft, and the overburden is less than or equal 

to 500 ft thick in the Montana Powder River Basin assessment area...............................56

10. Areal extent for the Werner/Cook coal bed where the stripping ratios are from 

1:1 to 1:10, Montana Powder River Basin assessment area ...............................................57

11. Areal extent for the Pawnee coal bed where the stripping ratios are from 1:1 to 1:10, 

thicknesses are equal to at least 5.0 ft, and the overburden is less than or equal 

to 500 ft thick in the Montana Powder River Basin assessment area...............................58

12. Areal extent for the Rosebud/Knobloch coal bed where the stripping ratios are from 

1:1 to 1:10, thicknesses are equal to at least 5.0 ft, and the overburden is less than 

or equal to 500 ft thick in the Montana Powder River Basin assessment area ...............59

13. Areal extent for the Flowers-Goodale coal bed where the stripping ratios are from 

1:1 to 1:10, thicknesses are equal to at least 5.0 ft, and the overburden is less 

than or equal to 500 ft thick in the Montana Powder River Basin assessment area ......60

14. Map showing location of areas of low, moderate, and high coalbed methane potential 

in the Montana Powder River Basin assessment area........................................................61

15. Map showing location of mines and area names for coal quality in the Montana 

Powder River Basin assessment area ....................................................................................62

16. Map showing generalized geology of the Powder River Basin, Wyoming and Montana......63

17. Map showing location of mapped faults in the Montana Powder River Basin 

assessment area.........................................................................................................................64

18. Generalized stratigraphic column for the Powder River Basin, Wyoming and Montana......65

19. Coal bed and coal zone names used in various publications in the Powder River Basin, 

Wyoming and Montana .............................................................................................................66

20. Index map showing locations of cross sections from figures 21-27 in the Montana 

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

21. West-east cross section A-A’ showing subsurface distribution of coal beds through 

the Spring Creek and Decker Mine areas in the Montana Powder River Basin 

assessment area.........................................................................................................................68

22. West-east cross section B-B’ showing subsurface distribution of coal beds north 

of the Spring Creek and Decker Mine areas in the Montana Powder River Basin 

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

23. West-east cross section C-C’ showing subsurface distribution of coal beds through 

the Otter Creek Tracts (Arch Coal, Inc.) in the Montana Powder River Basin 

assessment area.........................................................................................................................70

24. South-north cross section D-D’ showing subsurface distribution of coal beds through 

the eastern part of the Montana Powder River Basin assessment area..........................71

25. South-north cross section E-E’ showing subsurface distribution of coal beds through 

the Spring Creek and Decker Mine areas in the Montana Powder River Basin 

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

26. South-north cross section F-F’ showing subsurface distribution of coal beds through 

the central part of the Montana Powder River Basin assessment area...........................73
vi

27. Northwest-southeast cross section G-G’ showing subsurface distribution of coal beds 

through the Montana Powder River Basin assessment area.............................................74

28. Map showing location of clinker in the Montana Powder River Basin assessment area

showing names used in the report ..........................................................................................75

29. Coal stratigraphy in the Montana Powder River Basin assessment area showing 

names used in this report..........................................................................................................76

30. Isopachs showing extent of resources at least 2.5 ft thick in the Roland (Baker) coal 

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

31. Maps of depth to the top of the Roland (Baker) coal bed within the Montana Powder 

River Basin assessment area ...................................................................................................78

32. Maps of the coal resource reliability categories for the Roland (Baker) coal bed within 

the Montana Powder River Basin assessment area............................................................79

33. Isopachs showing extent of resources at least 2.5 ft thick in the Smith coal bed within 

the Montana Powder River Basin assessment area............................................................80

34. Map showing depth to the top of the Smith coal bed within the Montana Powder River 

Basin assessment area .............................................................................................................81

35. Map showing coal resource reliability categories for the Smith coal bed within the 

Montana Powder River Basin assessment area...................................................................82

36. Isopachs showing extent of resources at least 2.5 ft thick in the Anderson coal bed 

within the Montana Powder River Basin assessment area................................................83

37. Map showing depth to the top of the Anderson coal bed within the Montana Powder 

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

38. Map showing coal resource reliability categories for the Anderson coal bed within the 

Montana Powder River Basin assessment area...................................................................85

39. Isopachs showing extent of resources at least 2.5 ft thick in the Dietz 2 coal bed within 

the Montana Powder River Basin assessment area............................................................86

40. Map showing depth to the top of the Dietz 2 coal bed within the Montana Powder River 

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

41. Map showing coal resource reliability categories for the Dietz 2 coal bed within the 

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

42. Isopachs showing extent of resources at least 2.5 ft thick in the Dietz 3 coal bed 

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

43. Map showing depth to the top of the Dietz 3 coal bed within the Montana Powder 

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

44. Map showing coal resource reliability categories for the Dietz 3 coal bed within the 

Montana Powder River Basin assessment area...................................................................91

45. Isopachs showing extent of resources at least 2.5 ft thick in the Canyon coal bed 

within the Montana Powder River Basin assessment area................................................92

46. Map showing depth to the top of the Canyon coal bed within the Montana Powder 

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

47. Map showing coal resource reliability categories for the Canyon coal bed within the 

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

48. Isopachs showing extent of resources at least 2.5 ft thick in the Lower Canyon coal 

bed within the Montana Powder River Basin assessment area ........................................95

49. Map showing depth to the top of the Lower Canyon coal bed within the Montana 

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

50. Map showing coal resource reliability categories for the Lower Canyon coal bed 

within the Montana Powder River Basin assessment area................................................97
vii

51. Isopachs showing extent of resources at least 2.5 ft thick in the Ferry coal bed 

within the Montana Powder River Basin assessment area................................................98

52. Map showing depth to the top of the Ferry coal bed within the Montana Powder River 

Basin assessment area .............................................................................................................99

53. Map showing coal resource reliability categories for the Ferry coal bed within the 

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

54. Isopachs showing extent of resources at least 2.5 ft thick in the Werner/Cook coal 

bed within the Montana Powder River Basin assessment area ......................................101

55. Map showing depth to the top of the Werner/Cook coal bed within the Montana 

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

56. Map showing coal resource reliability categories for the Werner/Cook coal bed 

within the Montana Powder River Basin assessment area..............................................103

57. Isopachs showing extent of resources at least 2.5 ft thick in the Otter coal bed 

within the Montana Powder River Basin assessment area..............................................104

58. Map showing depth to the top of the Otter coal bed within the Montana Powder 

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

59. Map showing coal resource reliability categories for the Otter coal bed within the 

Montana Powder River Basin assessment area.................................................................106

60. Isopachs showing extent of resources at least 2.5 ft thick in the Gates/Wall coal 

bed within the Montana Powder River Basin assessment area ......................................107

61. Map showing depth to the top of the Gates/Wall coal bed within the Montana 

Powder River Basin assessment area ..................................................................................108

62. Map showing coal resource reliability categories for the Gates/Wall coal bed within 

the Montana Powder River Basin assessment area..........................................................109

63. Isopachs showing extent of resources at least 2.5 ft thick in the Pawnee coal bed 

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

64. Map showing depth to the top of the Pawnee coal bed within the Montana Powder

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

65. Map showing coal resource reliability categories for the Pawnee coal bed within 

the Montana Powder River Basin assessment area..........................................................112

66. Isopachs showing extent of resources at least 2.5 ft thick in the Odell coal bed 

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

67. Map showing depth to the top of the Odell coal bed within the Montana Powder 

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

68. Map showing coal resource reliability categories for the Odell coal bed within 

the Montana Powder River Basin assessment area..........................................................115

69. Isopachs showing extent of resources at least 2.5 ft thick in the Rosebud/Knobloch 

coal bed within the Montana Powder River Basin assessment area..............................116

70. Map showing depth to the top of the Rosebud/Knobloch coal bed within the 

Montana Powder River Basin assessment area.................................................................117

71. Map showing coal resource reliability categories for the Rosebud/Knobloch coal 

bed within the Montana Powder River Basin assessment area ......................................118

72. Isopachs showing extent of resources at least 2.5 ft thick in the McKay/Nance coal 

bed within the Montana Powder River Basin assessment area ......................................119

73. Map showing depth to the top of the McKay/Nance coal bed within the Montana 

Powder River Basin assessment area ..................................................................................120

74. Map showing coal resource reliability categories for the McKay/Nance coal bed 

within the Montana Powder River Basin assessment area..............................................121
viii

75. Isopachs showing extent of resources at least 2.5 ft thick in the Flowers-Goodale 

coal bed within the Montana Powder River Basin assessment area..............................122

76. Map showing depth to the top of the Flowers-Goodale coal bed within the Montana 

Powder River Basin assessment area ..................................................................................123

77. Map showing coal resource reliability categories for the Flowers-Goodale coal bed 

within the Montana Powder River Basin assessment area..............................................124

78. Isopachs showing extent of resources at least 2.5 ft thick in the Robinson/Witham 

coal bed within the Montana Powder River Basin assessment area..............................125

79. Map showing depth to the top of the Robinson/Witham coal bed within the Montana 

Powder River Basin assessment area ..................................................................................126

80. Map showing coal resource reliability categories for the Robinson/Witham coal 

bed within the Montana Powder River Basin assessment area ......................................127

81. Isopachs showing extent of resources at least to 2.5 ft thick in the Roberts/Terret 

coal bed within the Montana Powder River Basin assessment area..............................128

82. Map showing depth to the top of the Roberts/Terret coal bed within the Montana 

Powder River Basin assessment area ..................................................................................129

83. Map showing coal resource reliability categories for the Roberts/Terret coal bed 

within the Montana Powder River Basin assessment area..............................................130

84. Pie chart of 18 beds showing amount and percent of total original coal resources 

(215 BST) by coal bed in the Montana Powder River Basin assessment area..............131

85. Cost curve showing estimated recoverable resources vs. sales price per ton of coal.......132

86. Bar graph showing resources in different resource categories for the ten coal 

beds included in the reserve evaluation of the Montana Powder River Basin 

assessment area, reported in billions of short tons............................................................133

87. Bar graph showing resources in different resource categories for the ten coal beds 

included in the reserve evaluation of the Montana Powder River Basin assessment 

area, reported in percentages................................................................................................133
ix

Tables

 1. Coal production from the Montana Powder River Basin assessment area................................3

 2. Available and recoverable resources of 10 beds at least 5.0 ft thick and less than or 

equal to a 10:1 strip ratio in the Montana Powder River Basin assessment area.............7

 3. Available and recoverable resources for 10 coal beds at least 5.0 ft thick, reported 

by bed, for restrictions, recovery rates, mining losses, and recoverable resources 

for the Montana Powder River Basin assessment area........................................................8

 4. Coal resources and restrictions for 18 beds greater than or equal to 2.5 feet thick, 

reported in millions of short tons by coal ownership categories for the Montana 

Powder River Basin assessment area ....................................................................................11

 5. Available as-received coal-quality data for mines and mine leases in the Montana 

Powder River Basin assessment area ....................................................................................15

 6. Available as-received coal-quality data for coal fields and areas in the Montana 

Powder River Basin assessment area ....................................................................................16

 7. Comparison of proximate analysis of coals from mines in the Wyoming and Montana 

portions of the Montana Powder River Basin assessment area........................................16

 8. Coal resources and restrictions for 18 beds greater than or equal to 2.5 feet thick, 

reported in millions of short tons by coal overburden depth for the Montana 

Powder River Basin assessment area ....................................................................................20

 9. Coal resources and restrictions for 18 beds greater than or equal to 2.5 feet thick, 

reported in millions of short tons by reliability category for the Montana 

Powder River Basin assessment area ....................................................................................24

10. Life-of-mine costs by strip ratio in the Montana Powder River Basin assessment area ......32

11. Underground resources in beds at least 10 feet thick and a strip ratio of >10:1, 

in the Montana Powder River Basin assessment area........................................................33

12. Costs by underground mining case for the Montana Powder River Basin assessment 

area based on a 20-year project life at an annual production rate of 6 million short 

tons per year................................................................................................................................35

13. Regional mining model stratigraphic sequence used in the economic evaluation of the 

Montana Powder River Basin assessment area...................................................................42

14. Underground excavation dimensions in the longwall mining model for a 10-ft mining 

height............................................................................................................................................44
x

Abbreviations Used in This Report

Btu/lb British thermal unit per pound

ft feet

ft2 square feet

hr hour

in inch

mi mile

mi2 square mile

yd3 cubic yards

yr year

BST billion short tons

CARS coal availability and resource studies

CBM coalbed methane

GIS geographic information system

MBMG Montana Bureau of Mines and Geology

MST million short tons

MST/yr million short tons per year

MTPRB Montana Powder River Basin assessment area

NWPRB Northern Wyoming Powder River Basin assessment area

PRB Powder River Basin

ST short ton

SWPRB Southwestern Powder River Basin assessment area

USBLM U.S. Bureau of Land Management

USGS U.S. Geological Survey

UTM Universal Transverse Mercator
xi

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) 0.90718474 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 purpose of this report is to summarize geology, coal 

resources, and coal reserves in the Montana Powder River 

Basin (MTPRB) assessment area in southeastern Montana. 

This report represents the fourth assessment area within the 

Powder River Basin to be evaluated in the continuing U.S. 

Geological Survey regional coal assessment program.

There are four active coal mines in the MTPRB assessment area: the Spring Creek and Decker Mines, both near 

Decker; the Rosebud Mine, near Colstrip; and the Absaloka 

Mine, west of Colstrip. During 2011, coal production from 

these four mines totaled approximately 36 million short tons 

(MST). A fifth mine, the Big Sky, had significant production 

from 1969–2003; however, it is no longer in production and 

has since been reclaimed. Total coal production from all five 

mines in the MTPRB assessment area from 1968 to 2011 was 

approximately 1.4 billion short tons (BST). The Rosebud/

Knobloch coal bed near Colstrip and the Anderson, Dietz 2, 

and Dietz 3 coal beds near Decker contain the largest deposits 

of surface minable, low-sulfur, subbituminous coal currently 

being mined in the assessment area.

A total of 26 coal beds were identified during this assessment, 18 of which were modeled and evaluated to determine 

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

MTPRB assessment area for the 18 coal beds assessed was 

calculated to be 215 BST. Available coal resources, which 

are part of the original coal resource remaining after subtracting restrictions and areas of burned coal, are about 162 BST. 

Restrictions included railroads, Federal interstate highways, 

urban areas, alluvial valley floors, state parks, national forests, 

and mined-out areas.

It was determined that 10 of the 18 coal beds had sufficient areal extent and thickness to be evaluated for recoverable 

surface resources ([Roland (Baker), Smith, Anderson, Dietz 

2, Dietz 3, Canyon, Werner/Cook, Pawnee, Rosebud/Knobloch, and Flowers-Goodale]). These 10 coal beds total about 

151 BST of the 162 BST of available resource; however, after 

applying a strip ratio of 10:1 or less, only 39 BST remains of 

the 151 BST. After mining and processing losses are subtracted from the 39 BST, 35 BST of coal were considered as a 

recoverable resource. Coal reserves (economically recoverable 

coal) are the portion of the recoverable coal resource that can 

be mined, processed, and marketed at a profit at the time of the 

economic evaluation. The surface coal reserve estimate for the 

10 coal beds evaluated for the Montana Powder River assessment area is 13 BST.

It was also determined that about 42 BST of underground 

coal resource exists in the MTPRB assessment area; about 34 

BST (80 percent) are within 500–1,000 ft of the land surface 

and another 8 BST are 1,000–2,000 ft beneath the land surface.

Introduction and Objectives

Coal resource and reserve estimates are essential for use 

in making local, state, and federal energy and land-use policy 

decisions for the foreseeable future. These estimates can also 

aid planners in determining the possible socio-economic 

effects on the region as coal resources are developed and 

approach depletion (Luppens and others, 2008). 

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

digital National Coal Resource Assessment of in-place coal 

resources in 2009 (Pierce and Dennen, 2009); however, the 

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 

are equally important (Luppens and others, 2008).

Assessment of Coal Geology, Resources, and Reserves 

in the Montana Powder River Basin

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

Jay A. Gunderson3

1

U.S. Geological Survey, Denver, Colorado 80225.

2

U.S. Geological Survey, Reston, Virginia 20192.

3

Montana Bureau of Mines and Geology, Billings, Montana 59101.
2 Assessment of Coal Geology, Resources, and Reserves in the Montana Powder River Basin

Confusion concerning the use of the terms coal resources41

and coal reserves is common, and the two terms have been 

used interchangeably. However, there is a major difference: 

(1) coal resources include those in-place tonnage estimates 

determined by summing the volumes for identified resources

and hypothetical resources using coal zones of a minimum 

thickness and within certain depth limits (commonly 0–2,000 

ft deep) (Pierce and Dennen, 2009), whereas (2) coal reserves 

constitute a subset of the coal resources that is considered 

economically producible at the time of classification (Pierce 

and Dennen, 2009). Luppens and others (2009) discussed coal 

resources and coal reserves and summarized how coal availability and resource studies (CARS) are used to determine 

estimates of economically recoverable coal resources.

Previous estimates of coal resources and reserves have 

typically used average mining percentages to obtain volume 

estimates of recoverable coal (see references in “Previous Coal 

Resource Estimates” section). Those estimates are general and 

do not take into consideration the volume of coal that cannot 

be mined because of environmental concerns, geological constraints, coal loss because of mining and preparation technology, or economic constraints. Published studies by the USGS 

have indicated that application of site-specific restrictions to 

estimates of available coal resources significantly reduces the 

amount of coal that is considered recoverable (for example, 

Ellis and others, 2002).

At the time of publication of this report, the USGS 

assessment project is the Powder River Basin (PRB), located 

in southeastern Montana and northeastern Wyoming (fig. 1). 

The PRB project was divided into four assessment areas to 

keep databases and modeled areas to a more manageable size 

and permit more timely publication of assessment results. 

Luppens and others (2008) reported on the first assessment 

area and summarized coal resources and reserves for the 

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

and reserve estimates for the Northern Wyoming Powder 

River Basin assessment area (NWPRB assessment area), and 

Osmonson and others (2011) summarized coal resources in the 

Southwestern Powder River Basin assessment area (SWPRB 

assessment area) (fig. 1).

This report summarizes the fourth assessment area within 

the PRB, which covers an area of approximately 7,765 mi2 in 

the Montana portion of the PRB in parts of Big Horn, Custer, 

Powder River, Rosebud, and Treasure Counties, Montana 

(fig. 1). The assessment area extends south from Miles City, 

Montana to the northern state boundary of Wyoming and from 

the eastern boundaries of the Crow and Northern Cheyenne 

Indian Reservations easterly to a few miles east of Broadus, 

Montana. The assessment area will be referred to in this report 

as the Montana Powder River Basin assessment area (MTPRB 

assessment area). 

4

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.

Coal availability and recoverability studies in the United 

States have previously relied on reinterpretation of existing 

data; however, because of the recent development of coalbed 

methane in the Decker Mine area, new data from drill holes 

are now available. The interpretation of these new data provides a view of the coal resources and reserves in the assessment area. 

The primary objectives of this assessment are as follows:

1. Complete the fourth coal resource and reserve 

assessment in the PRB.

2. Update the current stratigraphic database with information obtained from recently completed coalbed 

methane well and oil and gas well data, thereby 

improving geological modeling in the assessment 

area.

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 MTPRB assessment area and 

derive a regional estimate of coal resources and 

reserves.

Previous and Current Coal Mining

On July 28, 1806, Captain William Clark of the Corps 

of Discovery documented coal beds as he floated down the 

Yellowstone River along the northern margin of the Powder 

River Basin:

“...in the evening I passd. Straters of Coal in the 

banks on either Side. those on the Stard. Bluffs was 

about 30 feet above the water and in 2 vanes from 

4 to 8 feet thick, in a horozontal position. the Coal 

Contained in the Lard Bluffs is in Several vaines of 

different hights and thickness. this Coal or Carbonated wood is like that of the Missouri of an inferior 

quality.” (Moulton, 2001).

Less than a year later, Manuel Lisa built a trading post 

at the confluence of the Bighorn and Yellowstone Rivers and 

used lignite coal from nearby outcrops to heat buildings during 

the winter months (Morgan, 1966). Coal within the MTPRB 

assessment area was not commercially mined until 1923 when 

the first modern-day strip mine in the western United States 

was opened at Colstrip, Montana. The coal was mined by 

Northern Pacific Railroad Company and used to fuel steam 

locomotives. In the mid-1940s, coal production from the Rosebud Mine at Colstrip reached peak production of just more than 

4 million short tons (MST) per year. However, by 1957 the 

mine was closed after a decade-long decrease in coal demand 

as steam locomotives were gradually replaced by diesel locomotives (Morgan, 1966). In 1968, Montana Power Company 
Introduction and Objectives 3

acquired the Rosebud Mine and formed a subsidiary, Western 

Energy Company, to manage and develop the Colstrip properties (U.S. Office of Surface Mining, 1983). Total coal production from 1923–1968 for the MTPRB assessment area was less 

than 45 MST (Department of Labor and Industry, Safety and 

Health Bureau, State of Montana, written commun., 2011).

In 1970, the Environmental Protection Agency Clean Air 

Act created a new and significant demand for low-sulfur coal, 

and consequently, the Powder River Basin emerged as one of 

the nation’s primary coal-producing regions. By the mid-1970s, 

strip mines within the MTPRB assessment area had production 

totaling more than 20 MST per year, and accounted for 98 percent of all Montana coal production (Jay Gunderson, Montana 

Bureau of Mines and Geology, written commun., 2011).

The Ashland, Birney-Broadus, Coalwood, Forsyth, 

Miles City, Mizpah, Moorhead, northward extension of the 

Sheridan coal field, and Rosebud coal fields are all within 

the MTPRB assessment area (fig. 2) (Averitt, 1966; McLellan and others, 1990). There are four active coal mines in 

the MTPRB assessment area: the Spring Creek and Decker 

(West, East, and North) Mines, near Decker; the Rosebud 

Mine, near Colstrip; and the Absaloka Mine, west of Colstrip (fig. 2). Coal production from these four mines in 

2011 totaled approximately 36 MST (table 1) (Department 

of Labor and Industry, Safety and Health Bureau, State of 

Montana, written commun., 2011). The Big Sky Mine also 

had significant production, but ended mining operations in 

2003 (table 1, fig. 2). Total production from all 5 mines from 

1968–2010 was about 1.4 billion short tons (BST) (table 1) 

(Department of Labor and Industry, Safety and Health 

Bureau, State of Montana, written commun., 2011). 

Western Energy Company began mining coal at the Rosebud Mine near Colstrip in 1968. Early production was shipped 

out of state by railroad to coal-fired electrical generating 

plants. Beginning in 1975, onsite electrical generation commenced at Colstrip. Since 1985, coal production from the mine 

has averaged about 12 MST per year. Peabody Coal began 

operations at the Big Sky Mine just south of Colstrip in 1969 

and closed operations in 2003. Coal production from the mine 

averaged about 2 MST per year. The Absaloka Mine, located 

10–12 mi west of the Rosebud Mine, began development in 

1974 and production in 1975. The mine, owned and operated 

by Westmoreland Resources, Inc., produced an average of 

about 5–7 MST per year. The Spring Creek Mine, located near 

Decker, opened in 1979 and had production of about 2 MST in 

1983. The mine is owned and operated by Cloud Peak Energy 

Resources LLC. The Decker East, West, and North Mines, 

located near Decker, began operating in 1970 after development of a 19-mi-long railroad spur from Sheridan, Wyoming. 

The mines are owned by Decker Coal Company and operated 

by Kiewit Mining Group, Inc.

In 2010, Arch Coal Inc. acquired the right to mine 572 

MST of state-owned coal in Otter Creek, south of Ashland 

(fig. 2); Arch Coal Inc. already controlled 731 MST of privately owned coal in the Otter Creek area (Mike Dennison, 

The Billings Gazette, March 16, 2010; accessed at: http//

billingsgazette.com/news/state-and-regional/Montana/article 

dce41c8a-3163-11df-b2). 

Table 1. Coal production from the Montana Powder River Basin assessment area.

[Department of Labor and Industry Safety and Health Bureau, State of Montana, P.O. Box 1728, Helena, MT, 59624 

(Jay Gunderson, personal communication, January, 2011)]

Mine name,

years of production Coal bed name

Coal production

in 2011

(millions of tons)

Total coal

production

(millions of tons)

Absaloka (1975–2011) Rosebud 5.1 178.9

Big Sky (1969–2003) Rosebud --- 97.9

Decker (1970–2011) Anderson, Dietz 1, Dietz 2 3.1 362.3

Rosebud (1968–2011) Rosebud 8.8 440.1

Spring Creek (1983–2011) Anderson, Dietz 1, Dietz 2 19.1 288.9

Total 36.1 1,368.1

Previous Coal Resource Estimates

Previous studies in the MTPRB included different 

coal beds, coal zones, and boundaries, and had different 

purposes for which resources and reserves were calculated. 

Differences in criteria, such as variations in coal thickness, 

overburden depth, and areal extent of coal beds were used 

for calculations of coal tonnages. Nevertheless, the previous 

studies form the foundation for most of the coal resource 

compilations that followed. The following is a chronological list of some of the more significant resource and reserve 

estimates for the MTPRB. 

1. Combo and others (1949) published a detailed report 

summarizing Montana coal resources by county, 

rank, reliability category, and thickness. Their estimate for the total coal resources in Montana was 222 
4 Assessment of Coal Geology, Resources, and Reserves in the Montana Powder River Basin

BST, 126 of which are within the MTPRB assessment area. This included reliability categories of

measured, indicated, inferred, and hypothetical based 

on distance from the drill hole or outcrop and depths 

up to 2,000 ft. The measured and indicated coal 

reserves for the assessment area were estimated to be 

47 BST and included beds 2.5 ft thick and greater.

2. The USGS estimated original coal resources in 

the MTPRB assessment area for five counties (Big 

Horn, Custer, Powder River, Rosebud, and Treasure) 

at 127 BST in beds that were 2.5 ft or more in thickness (Averitt, 1966). 

3. In 1968, Groff estimated 5.3 BST of strippable 

reserves in the MTPRB (Groff, 1968).

4. Ayler and others (1969) estimated strippable coal 

reserves for the MTPRB for several coal fields. 

Strippable coal reserves in the northward extension 

of the Sheridan coal field (Decker and Spring Creek 

Mine areas) were estimated at 2,265 MST for seven 

coal beds with a maximum overburden of 120 ft (fig. 

2). Strippable coal reserves for the Birney-Broadus 

coal field were estimated for 3 coal beds at 996 MST 

with a maximum overburden depth ranging between 

50 and 200 ft (fig. 2). Strippable coal reserves for 

the Ashland and Coalwood coal fields combined 

were estimated to be 3,457 MST for 7 coal beds 

with maximum overburden depth ranging between 

120 and 200 ft (fig. 2). Strippable coal reserves for 

the Forsyth coal field (Rosebud Mine area) were 

estimated to be 711 MST for three coal beds with a 

maximum overburden thickness between 110 and 

130 ft (fig. 2).

5. Matson (1971) estimated strippable subbituminous 

coal reserves in the Moorhead coal field for three 

coal beds beneath less than 150 ft of overburden at 

1,979 MST (fig. 2).

6. Matson and Blumer (1973) estimated strippable 

coal reserves for much of the area in the MTPRB 

that included parts of Big Horn, Custer, Powder 

River, and Rosebud Counties (fig. 2). The strippable coal resources in the deposits discussed in that 

report totaled approximately 32 BST. The coal beds 

are fairly evenly distributed throughout the Tongue 

River Member of the Fort Union Formation.

7. Matson and White (1975) published a report that 

summarized underground coal reserves by first 

assigning reliability categories to those resources 

reported as unclassified as to thickness by Combo 

and others (1949), then subtracting published strippable coal reserve numbers. Matson and White (1975) 

estimated 60 BST of underground coal reserves in 

Big Horn, Powder River, and Rosebud Counties. 

8. Roberts and others (1999a) estimated coal resources 

for a 395-mi2 area defined as the Colstrip coal field, 

which included parts of the Forsyth and Ashland 

coal fields (fig. 2). Resources were estimated based 

on reliability categories of measured, indicated, 

inferred, and hypothetical categories and totaled 

more than 12.6 BST.

9. Roberts and others (1999b) estimated coal 

resources for a 1,100-mi2 area defined as the 

Decker coal field that included parts of the northward extension of the Sheridan coal field, the 

Moorhead coal field, and the Birney-Broadus coal 

field (fig. 2). Resources were estimated based on 

measured, indicated, inferred, and hypothetical 

categories and totaled 45 BST.

10. Roberts and others (1999c) also estimated coal 

resources for a 520-mi2 area defined as the Ashland coal field that includes parts of the northward 

extension of the Sheridan coal field, the Moorhead 

coal field, and the Birney-Broadus coal field (fig. 

2). Resources were estimated based on measured, 

indicated, inferred, and hypothetical categories and 

totaled 6 BST. 

11. Coal availability assessments for several 7.5 minute 

quadrangles in the MTPRB were performed in the 

early 2000s (Wilde, 2000; Wilde and Myers, 2003; 

and Wilde and Sandau, 2004, 2005). 

As documented in these various estimates, resource 

and reserve estimates change as more data become available. These new estimates prove the usefulness of periodically recalculating coal resources and reserves. Because of 

the availability of new data, the coal resources and economic 

coal recoverability calculations presented in this report are a 

significant refinement of previous coal resource and reserve 

studies in the MTPRB assessment area.

Methodology

The methodology for calculating coal resources and 

reserves in the MTPRB assessment area is described in three 

phases shown on the flow chart in figure 3. This methodology 

is the same as was used for the previous three PRB assessments 

(Gillette coalfield by Luppens and others, 2008; NWPRB 

assessment area by Scott and others, 2010; and the SWPRB 

assessment area by Osmonson and others, 2011). The first 

phase involved data collection and editing, as a result of the 

acquisition of recently generated geologic information. The 

second phase consisted of modeling coal beds, creating models 

of restrictions to mining, and calculating tonnages for original, 

mined out, restricted, and available resources. The third phase 

involved completing a mining economics evaluation to determine coal economically recoverable resources (reserves). 
Methodology 5

Data Collection

There are 3,137 publically available drill-hole logs in 

the MTRPB assessment area, of which 2,974 were used to 

construct the database used in this assessment (fig. 4): 520 

oil and gas wells, 290 coalbed methane wells, and 2,164 coal 

exploration drill holes. Data selected for entry were supplied 

by the Montana Bureau of Mines and Geology, the USGS 

National Coal Resource Database System (NCRDS), and MJ 

Systems (2009). USGS personnel entered data from the entire 

2,974 drill-hole logs into the StratiFact® database program 

(GRG Corporation, 1998). Data for all public drill holes in 

the Powder River Basin were published by Haacke and Scott 

(2012).

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 generally 

consisted of spontaneous potential, resistivity, and conductivity logs. The most reliable log suite for distinguishing coal 

beds consisted of natural gamma, gamma-gamma density, and 

resistivity traces; however, many coalbed methane wells were 

logged with gamma-ray only, either in open hole or through 

steel drill pipe or casing. Additionally, some of the coalbed 

methane wells were logged only to the top of the target coal.

Detailed non-coal lithology types were not critical to the 

results of this evaluation. As a result, all lithologies were 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 were entered as “No Log”.

Coalbed Modeling

The first step of phase two of the assessment (fig. 3) 

was the creation of digital coal bed models. Following coal 

bed correlations, preliminary coal isopach thickness maps 

were created using the single- bed modeling program Surfer®

(Golden Software, 2002) to decide which coal beds would 

be included in the geologic coal resource model. The basic 

criterion for inclusion was a minimum areal continuity of 

two or more townships (721 mi2). Twenty-six coal beds were 

identified in this assessment; however, based on thickness 

and areal extent, only eighteen were selected for digital 

modeling to calculate resources. The integrated multi-bed 

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

was used to produce gridded coal bed models. This modeling 

program was designed for coal and mineral evaluations and 

is effective for coal bed modeling because of the capability to grid multiple beds at one time. This program allows 

for a considerable reduction in time when compared with 

other programs that grid only one parameter at a time. Time 

required to produce 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 height (coal plus parting), and roof 

and floor structures. Grids must then be calculated for the 

overburden and interburden thicknesses for each seam. The 

roof grid for each coal bed must be individually subtracted 

from the surface grid or the floor grid for the next stratigraphically higher coal bed. 

The coal bed models were gridded at a cell size of 150 m 

(~500 ft). For this assessment, meters were used when discussing modeling, whereas English units were used for thicknesses 

and depths. 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 anomalies. The PC/

Cores program was used to help identify anomalies by comparing collar elevations to the digital elevation model of the 

Earth’s surface.

Subsequent to completion of editing, final geologic 

models were created and all grids necessary for determination 

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

the in-place coal resource model was modified to generate the 

grids necessary for coal reserve evaluation. The basic assumption used to qualify coal beds for potential coal reserve evaluation was a thickness of at least 2.5 ft. 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 was 

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

ASCII grids were then exported to the program ArcView® 

[Environmental Systems Research International, 2001] to 

begin the last step in phase two of the assessment, which was 

the modeling of the restrictions to mining. 

Resource Allocation Planning

The objective in resource planning is to determine the 

amount of available coal resources. This process is accomplished by first subtracting the amount of previously mined 

coal from the calculated amount of the original resources; the 

result is remaining resources. Subtracting the amount of land 

use and technical restrictions from the amount of remaining 

resources yields available resources. The following discussion details the methodology used in determining available 

resources.

Digital modeling for the evaluated coal beds was done 

using PC/Cores (Mentor Consultants, 2005); files were then 

imported into a geographic information system (GIS). The GIS 

system was used to allocate coal resources by first subtracting 

amounts of various restrictions to mining (previously mined 

coal, towns, national forests, alluvial valley floors, and so on) 

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 the amount of coal resources. In addition, ArcGIS®

(Environmental Systems Research Institute, Inc., 2006) was 

used 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 was 
6 Assessment of Coal Geology, Resources, and Reserves in the Montana Powder River Basin

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 used for all GIS analyses. For this GIS assessment, a grid-cell size of 30 m (~100 ft) was chosen. Consequently, all grids used within the GIS analysis were either 

originally created with a grid-cell size of 30 m or resampled 

to 30 m from another cell size. In the case of the digital coalmodel grids, the cell size was resampled from 150 m to 30 m.

The first task in the GIS process involved the creation of 

ArcView® (Environmental Systems Research Institute, Inc., 

2000) grids from ASCII files of the coal, parting, and overburden isopach grids, that were created by the digital coal 

models. These ArcView® grids were then used to create a total 

thickness (coal plus parting) grid, and areal-extent grid for 

each coal bed to be evaluated. The next step involved creating a group of grids that categorized the MTPRB assessment 

area, with each grid representing one specific theme. These 

grid themes consisted of mined-out areas, burned-coal areas, 

land-use restrictions, technical restrictions, overburden-to-coal 

bed ratios, counties, coal ownership, stripping ratios, resource 

reliability categories, and coal bed depth. The grid theme for 

previously mined coal was derived from digital information 

obtained from the Montana Department of Environmental 

Quality. The grid theme for burned-coal areas was developed 

from digital surface clinker information obtained from the 

Montana Bureau of Mines and Geology Geographic Information Systems Laboratory (http://www.mbmg.mtech.edu/gis/

gis-datalinks.asp). The grid theme for coal ownership was 

obtained from USGS digital information (http://pubs.usgs.gov/

of/1998/ofr-98-0102). The grid themes for land-use restrictions 

and counties were derived from digital information obtained 

from the Natural Resource Information System GIS Data List 

of the Montana government (2011) (the remaining grid themes 

were developed internally within the USGS).

The grid of environmental restrictions includes buffer 

zones that surround each restricted area. The location and 

width of these buffers are typically mandated by State or Federal regulations. Each restriction buffer measures hundreds of 

feet in width at the surface, as discussed in the Factors Affecting Extraction of Coal Resources section of this report.

One of the improvements in the assessment methodology 

was revising the technique for defining surface restrictions 

at depth. Previous economic assessments used a standard 

approach when applying 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, because of 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 having a diameter of 600 

ft at the surface encompasses an area of about 282,600 ft2, or 

approximately 6.5 acres. However, at a depth of 200 ft this 

same restriction has a diameter of 858 ft and encompasses 

an area of about 577,900 ft2, or approximately 13 acres. At a 

depth of 500 ft the same restriction has a diameter of 2,144 ft 

and encompasses an area of about 3,608,400 ft2, or approximately 83 acres. Figure 5 illustrates the effect of depth on 

overall land-use restriction size.

The grid of previously mined coal accounts for all prior 

mining within the MTPRB assessment area, including those 

mines shown in figure 6. The grid of counties contains locations of the five principal counties within this area (Big Horn, 

Custer, Powder River, Rosebud, and Treasure). The coal 

mineral ownership grid was divided into Federal, State, and 

private ownership categories (fig. 7). The resource reliability grid was divided into measured, indicated, inferred, and 

hypothetical coal categories and the coal bed depth grid was 

divided into four categories of depth: 0–500 ft; 500–1,000 ft; 

1,000–2,000 ft; and greater than 2,000 ft.

The next step in the process was the application of these 

grids to the coal resources of the coal beds to be evaluated. 

First, the individual theme grids were combined into one 

composite theme grid, which was then used with the coal 

bed areal-extent grids to define the MTPRB assessment area 

resources on a bed-by-bed basis according to all the categories. Next, areas within each coal bed that represented previously mined coal and restrictions (land-use and technical) 

were removed from consideration.

For this assessment, regarding minable resources or 

potential reserves, coal resources were allocated to separate 

stripping-ratio areas for several coal beds. Figure 8 shows 

the composite stripping ratios for the Roland (Baker), Smith, 

Anderson, Dietz 2, and Dietz 3 coal beds. Figures 9-13 show 

the individual stripping ratio areas for the Canyon, Werner/

Cook, Pawnee, Rosebud/Knobloch, and Flowers-Goodale coal 

beds. These stripping ratios were determined before there was 

any prior mining; therefore, all of these coal beds represent 

potentially surface-minable resources within the foreseeable 

future (table 2). However, areas where these coal beds are less 

than 5 ft thick are considered technically restricted for surface 

mining. Consequently, separate PC/Cores models were produced for these coal beds that excluded areas where the coal 

resources were less than 5 ft thick and no mining potential was 

allocated to them. Table 3 shows recoverable resources based 

on restrictions (mining losses, land use, previously mined 

areas, and technical restrictions).

Factors Affecting Extraction of Coal Resources

Many factors can affect the availability of coal for mining. A four-step screening process, defined in the 43 CFR 

3420.1-4 regulations, is used to determine 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).
Table 2. Available and recoverable resources of 10 beds at least 5.0 ft thick and less than or equal to a 10:1 strip ratio in the Montana assessment area. Resources reported in millions of short tons and include coal plus partings. Columns may not sum exactly because of [<, less than; >, greater than; % percent]

Stripping

ratio

Coal bed name

Roland 

(Baker) Smith Anderson Dietz 2 Dietz 3 Canyon Werner Pawnee Rosebud/ Knobloch Flowers- Goodale 

<1:1 35 24 609 26 76 200 464 439 1,516 249 >1:1-2:1 28 19 688 19 91 162 366 250 1,521 180 >2:1-3:1 35 22 961 24 154 215 489 273 1,681 180 >3:1-4:1 39 26 1,124 27 269 254 667 261 1,402 174 >4:1-5:1 39 27 1,051 30 371 289 676 237 936 201 >5:1-6:1 39 28 1,039 33 367 335 704 231 719 197 >6:1-7:1 32 30 916 42 392 396 749 226 567 200 >7:1-8:1 29 32 832 50 392 489 840 236 636 215 >8:1-9:1 26 38 791 55 515 568 1,190 227 750 236 >9:1-10:1 26 41 690 55 636 571 1,370 237 772 238 Total 328 287 8,701 361 3,263 3,479 7,515 2,617 10,500 2,070 
Table 3. Available and recoverable resources for 10 coal beds at least 5.0 ft thick, reported by bed, for restrictions, recovery rates, mining losses, anfor the Montana Powder River Basin assessment area (reported in millions of tons). Columns may not sum exactly because of rounding. [<, less than; >, greater than; ft, feet; % percent] Coal bed name Original resources Mined out Restrictions Available resources (<10:1 ratio) Recovery rate (%) M

lo

Land use Technical (2.5-5.0 ft thick) >10:1 ratio Roland (Baker) 682 0 0 49 305 328 90 

Smith 1,778 0 19 183 1,289 287 90 Anderson 15,027 472 992 104 4,758 8,701 90 Dietz 2 1,556 41 10 311 833 361 90 Dietz 3 8,757 136 1,036 506 3,816 3,263 90 Canyon 18,895 0 3,189 226 12,001 3,479 90 Werner 24,844 0 3,932 615 12,782 7,515 90 Pawnee 13,563 0 2,494 1,568 6,884 2,617 90 Rosebud/Knobloch 40,873 559 9,611 1,545 18,658 10,500 90 1,Flowers-Goodale 25,518 0 631 610 22,207 2,070 90 Total 151,493 1,208 21,914 5,717 82,533 39,121 90 3,
Methodology 9

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

Flood plains

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 

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 list 

affect development within the MTPRB 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 

land-management regulations. Thus, 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 MTPRB assessment area. In addition, U.S. Bureau of Land Management (BLM) personnel in 

Casper, Wyoming, provided guidance concerning restrictions 

to mining and the distances to be buffered around specific features. Because required buffer distances can change through 

time, distances were selected that were considered to be the 

maximum amount required by future regulations. A more 

detailed determination of restrictions and other availability 

considerations would be necessary as part of leasing and mineplanning phases of property development.

Figure 6 shows the areas within the MTPRB 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.

Airports

The Broadus Airport is located near Broadus, Montana, 

about 2.5 mi northwest of the central business district. For 

this assessment, the airport (including a 300-ft buffer surrounding the airport) is considered to be a restriction to mining. The Colstrip Airport is located about 4 mi southwest of 

the central business district of Colstrip, Montana (fig. 6), on 

reclamation land that is surrounded by adjacent mining areas 

of the Rosebud Mine. Therefore, the current Colstrip Airport 

is not considered to represent a restriction to mining for this 

assessment.

Alluvial Valley Floors 

All areas identified as alluvial valley floors where mining 

would interrupt, discontinue, or preclude farming by the state 

program delegated to enforce the Surface Mining Control 

and Reclamation Act of 1977 (Public Law 95-87, 1977), are 

unsuitable for surface coal mining and thus are deemed to be 

restrictions (fig. 6). 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.

Archaeological Areas 

No major archaeological areas that would prevent mining 

are known in the MTPRB assessment area, but there are several minor archaeological sites and also several minor historic 

sites. A mitigation plan would be developed before coal mining disturbed these areas. Therefore, coal within these known 

sites was not excluded from this resource assessment.

Coalbed Methane

Coalbed methane (CBM) development in Montana began 

in 1991 and has proceeded at a much slower pace than in 

neighboring Wyoming. Just over 1,100 wells have been drilled 

in the MTPRB assessment area near the Decker Mine, along 

the Montana–Wyoming border (Montana Board of Oil and 

Gas, 2011), whereas over 30,000 wells have been drilled in the 

Wyoming portion of the PRB (Wyoming Oil and Gas Conservation Commission, 2011) (fig. 4). Production life of CBM 

wells is estimated to be about 10–12 years, although production from multiple beds can extend the life of the well by an 

additional 10–30 years (De Bruin and others, 2004).

Coalbed methane development in the MTPRB is 

restricted to a relatively small area in Big Horn County that 

includes T. 8–10 S., R. 39–41 E. (fig. 4). CBM production in 
10 Assessment of Coal Geology, Resources, and Reserves in the Montana Powder River Basin

the MTPRB assessment area is from the Smith, Anderson, 

Dietz 2, Dietz 3, Canyon, Werner/Cook, and Gates/Wall coal 

beds. There may be some potential for CBM production from 

deeper coal beds that could extend the CBM area northward. 

Van Voast and Thale (2001) identified areas of high, moderate, and low CBM potential for the Rosebud/Knobloch and 

Anderson-Dietz coal beds in the MTPRB assessment area 

(fig. 14). However, gas from the Rosebud/Knobloch has not 

yet been commercially produced, and the deeper FlowersGoodale coalbed methane has been produced with unimpressive results (Jay Gunderson, Montana Bureau of Mines and 

Geology, written commun., 2011). 

The lack of expansion northward in Montana is because 

of a combination of less favorable coal bed targets, and 

increased distance from existing infrastructure. Coal beds in 

the MTPRB assessment area are not as well suited to CBM 

development as those in Wyoming because they lack the overall depth and thickness of coal beds in the central and southern 

PRB. Coal beds become shallower and eventually crop out to 

the north but, although this may be advantageous for surface 

mining, it is not beneficial for CBM development. Coal beds 

at shallow depths or near outcrop are likely to have lower 

hydrodynamic pressures (the pressures necessary to retain the 

adsorbed methane), which would allow methane gas in coal 

seams to migrate toward the outcrop and eventually escape.

Several conflicts have arisen between coal mining and 

coalbed methane development. One conflict involves the 

ownership of coalbed methane and 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, ruling 

that coalbed methane is part of the oil-and-gas estate (Supreme 

Court of the United States, Amoco Production Co. v. Southern 

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

specified that 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 BLM established Conflict Administration Zones to 

provide guidelines for (1) development of coalbed methane 

leases in the path of near-term coal mining, and (2) settling 

conflicts and scheduling development of each resource under 

a federal mineral estate. Although there are hundreds of CBM 

wells within the MTPRB, most of them are clustered in the 

southwestern part, to the south and east of the Spring Creek 

and Decker Mines (fig. 4). Designating all of these wells and 

their accompanying pipeline infrastructure as being restrictive 

to mining would exclude a significant volume of coal resource 

from mining consideration. For the purpose of this assessment, 

it is assumed that coal within any part of the MTPRB will be 

mined after CBM operations have ceased in that area; therefore, these facilities are not considered a restriction to mining.

Dwellings and Buildings

Individual dwellings and buildings that exist outside 

of incorporated areas (such as Colstrip) are not considered 

restrictions to mining within the MTPRB 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.

Federal Land Systems

About 63 percent of the coal in the MTPRB assessment 

area is owned by the federal government and must be leased in 

order to be mined (table 4). The largest percentage of federally-owned area within the area is the Custer National Forest 

(fig. 6), which covers an area of 783 mi2 in western Powder 

River County and southern Rosebud County and is situated 

about 1–1.5 mi to the east of the Northern Cheyenne Indian 

Reservation (fig. 1). The same unsuitability criteria and landuse conflicts that have been discussed apply to coal mining in 

the Custer National Forest; therefore, it represents a restriction 

to surface coal mining that includes a buffer extending out 

to a distance of 300 ft beyond the forest boundary. However, 

the BLM could develop coal-leasing and mining stipulations 

in cooperation with the U.S. Forest Service for underground 

coal mining. Federal subsurface coal ownership is shown in 

figure 7. With respect to the Fort Keogh National Wildlife 

Refuge, located immediately to the southwest of Miles City, 

Montana, at the northern boundary of the assessment area 

(fig. 6), there are no coals that extend into that area.

Historic Lands and Sites

The site of the “Battle of Wolf Mountains” is about three 

mi southwest of Birney, Montana, along the valley of the 

Tongue Rive (fig. 6). This site is the location of the last major 

battle of the Great Sioux War of 1876–1877 and involves an 

area of hundreds of acres. In 2001, the battle site was added to 

the National Register of Historic Places. In 2008, it became a 

National Historic Landmark. Consequently, the 1,300-acre site 

is a restriction to mining for this assessment.

Oil and Oil-Related Gas Wells

Since the first gas discovery was made in 1913 near Hardin, Montana, nearly 2,000 oil and gas wells have been drilled 

in the Montana portion of the PRB. The Bell Creek field, discovered in 1965, is one of Montana’s most prolific oil fields and 

lies along the southeastern margin of the MTPRB assessment 

area. Cumulative production is reported at over 135 million barrels of oil. Several smaller oil fields (less than 1 million barrels 

cumulative) are also along the eastern and western perimeters 

of the MTPRB (Montana Board of Oil and Gas, 2011).

The two largest gas fields near the MTPRB have cumulative production of about 3 billion cubic ft of gas each. They 

are Bell Creek South, adjacent to the Bell Creek oil field, and 

Liscom Creek, located in the north-central PRB along the 

Tongue River in T.1 N., R.45 E. and T.2 N., R.45 E. (Montana 

Board of Oil and Gas, 2011).

Infrastructure for production and transport of oil and 

gas in the area includes roads, pipelines, pump houses, and 

separators. Generally, there is little conflict between coal 
Table 4. Coal resources and restrictions for 18 beds greater than or equal to 2.5 ft thick, reported in millions of short tons, by coal ownership categories for the Montana Powder River Basin assessment area. Resource includes coal plus partings. Totals may not sum exactly because of rounding.—Continued

Coal bed

name

Coal

ownership

Original

resource

Burned

coal

Remaining

resource

Previously

mined coal

Land use

restrictions

Technical

restrictions

Available

resource

Percent

of total

remaining

Roland (Baker)

Federal 643 11 632 0 0 44 588 86.1State 46 2 44 0 0 4 40 5.9Private 6 0 6 0 0 0 6 0.8

Total 695 12 682 0 0 49 634 92.8

Smith

Federal 1,694 37 1,657 0 18 164 1,474 82.9State 97 1 96 0 0 14 82 4.6Private 26 0 25 0 0 4 20 1.2

Total 1,817 38 1,778 0 18 183 1,577 88.7

Anderson

Federal 15,210 1,373 13,837 378 955 100 12,404 82.5State 892 59 833 71 3 2 758 5.0Private 379 23 356 23 34 2 297 2.0

Total 16,481 1,455 15,027 472 992 104 13,458 89.6

Dietz 2

Federal 1,405 29 1,376 32 2 291 1,052 67.6State 89 4 85 9 0 17 59 3.8Private 95 0 94 0 7 3 83 5.4

Total 1,590 33 1,556 41 10 311 1,194 76.7

Dietz 3

Federal 8,598 716 7,882 106 968 478 6,330 72.3State 559 26 534 27 47 20 440 5.0Private 359 18 342 4 21 8 309 3.5

Total 9,516 759 8,757 136 1,036 506 7,079 80.8

Canyon

Federal 17,930 436 17,494 0 3,093 213 14,188 75.1State 978 15 963 0 66 10 888 4.7Private 449 11 438 0 30 3 405 2.1

Total 19,357 462 18,895 0 3,189 226 15,480 81.9

Lower Canyon

Federal 9,623 235 9,388 0 1,814 933 6,641 65.5State 529 11 518 0 52 42 423 4.2Private 243 2 241 0 9 24 207 2.0

Total 10,395 249 10,146 0 1,875 1,000 7,272 71.7
Table 4. Coal resources and restrictions for 18 beds greater than or equal to 2.5 ft thick, reported in millions of short tons, by coal ownership categories for the Montana Powder River Basin assessment area. Resource includes coal plus partings. Totals may not sum exactly because of rounding.—Continued Coal bed name Coal ownership Original resource Burned coal Remaining resource Previously mined coal Land use restrictions Technical restrictions Available resource Percent of total remaining Ferry Federal 2,205 7 2,199 0 308 476 1,414 57.6 State 156 0 156 0 1 22 134 5.5 Private 100 0 100 0 6 11 82 3.3 Total 2,462 7 2,454 0 315 509 1,630 66.4 Werner/Cook Federal 23,616 704 22,913 0 3,848 558 18,506 74.5 State 1,076 26 1,050 0 49 33 967 3.9 Private 914 32 882 0 35 23 824 3.3 Total 25,606 762 24,844 0 3,932 615 20,297 81.7 Otter Federal 4,163 62 4,101 0 800 1,516 1,785 40.5 State 215 0 215 0 24 104 86 2.0 Private 96 2 94 0 11 29 55 1.2 Total 4,474 64 4,410 0 835 1,649 1,926 43.7 Gates/Wall Federal 7,567 117 7,450 0 790 1,567 5,093 62.6 State 340 1 339 0 7 59 273 3.4 Private 350 2 348 0 6 52 290 3.6 Total 8,257 121 18,137 0 802 1,678 5,656 69.5 Pawnee Federal 12,563 248 12,314 0 2,438 1,438 8,438 62.2 State 596 4 592 0 14 85 492 3.6 Private 676 19 657 0 41 45 571 4.2 Total 13,834 271 13,563 0 2,494 1,568 9,501 70.1

Odell

Federal 1,618 23 1,594 0 297 892 404 22.7State 69 0 68 0 1 43 25 1.4Private 118 2 116 0 0 96 20 1.1

Total 1,803 26 1,778 0 298 1,031 449 25.3

Rosebud/Knobloch

Federal 31,513 744 30,769 243 8,728 1,346 20,452 50.0State 1,353 118 1,235 11 44 88 1,092 2.7Private 9,749 881 8,869 305 839 111 7,614 18.6

Total 42,616 1,743 40,873 559 9,611 1,545 29,158 71.3
Table 4. Coal resources and restrictions for 18 beds greater than or equal to 2.5 ft thick, reported in millions of short tons, by coal ownership categories for the Montana Powder River Basin assessment area. Resource includes coal plus partings. Totals may not sum exactly because of rounding.—Continued

Coal bed

name

Coal

ownership

Original

resource

Burned

coal

Remaining

resource

Previously

mined coal

Land use

restrictions

Technical

restrictions

Available

resource

Percent

of total

remaining

McKay/Nance

Federal 6,867 85 6,782 0 766 1,577 4,439 42.9State 482 11 471 6 9 80 376 3.6Private 3,201 101 3,100 62 128 274 2,635 25.4

Total 10,549 196 10,353 68 903 1,932 7,450 72.0

Flowers-Goodale

Federal 20,619 85 20,535 0 349 461 19,724 77.3State 1,055 10 1,045 0 58 26 961 3.8Private 4,012 74 3,938 0 223 123 3,592 14.1

Total 25,686 169 25,518 0 631 610 24,277 95.1

Robinson/Witham

Federal 5,112 10 5,102 0 4 1,500 3,598 38.3State 387 6 381 0 0 66 315 3.3Private 4,064 144 3,919 0 0 221 3,699 39.3

Total 9,562 160 9,402 0 4 1,786 7,612 81.0

Roberts/Terret

Federal 7,811 60 7,752 0 49 1,748 5,955 56.9State 476 3 473 0 1 120 353 3.4Private 2,311 65 2,246 0 45 588 1,614 15.4

Total 10,599 128 10,471 0 95 2,455 7,921 75.6

Total

Federal 178,758 4,982 173,776 759 25,229 15,303 132,485 63.5State 9,396 297 9,099 123 377 838 7,761 3.7Private 27,145 1,377 25,768 394 1,436 1,616 22,323 10.7

Total 215,300 6,656 208,644 1,277 27,042 17,757 162,568 77.9
14 Assessment of Coal Geology, Resources, and Reserves in the Montana Powder River Basin

development and conventional oil and gas development in the 

MTPRB assessment area, as oil and gas reservoirs are primarily in stratigraphic units below minable coal beds. Where there 

is oil and gas development and coal mining in the same areas, 

mining is confined to areas outside a specific buffer distance 

from wells, pipelines, and other oil- and gas-related facilities.

Resolution of land-use conflicts between coal mining and 

oil and gas field development depends 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 reestablished after mining. For this assessment, 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 are underground oil and gas pipelines within the 

MTPRB assessment area. Presumably most, if not all, could be 

moved to allow surface mining. 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 assessment.

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 the 

MTPRB assessment area.

Railroads

The main railroad route through the MTPRB assessment 

area is an east-west rail section of the Burlington Northern 

Santa Fe Railway that is located in the extreme northern 

part of the assessment area (figs. 1, 6); it is not considered a 

restriction because coal beds do not extend into that part of 

the assessment area. In addition, there are three spur railroad 

lines that do traverse land underlain by coal. Two of these 

are in the northern part of the assessment area connecting the 

main railroad line and extending south to the Absaloka and 

Rosebud Mines. The third connects to a section of the main 

railroad line of the Burlington Northern Santa Fe Railway to 

the south (near Sheridan, Wyoming) and extends north to the 

Decker and Spring Creek Mines (fig. 1). It is assumed that the 

spur railroad lines would be moved as necessary for mining; 

therefore, they are not considered to be restrictions to mining. 

Rivers, Lakes, and Streams

The Powder River and the Tongue River are the longest 

courses of flowing water within the MTPRB assessment area. 

They are shallow, slow moving, meandering streams, as is 

the case with all of the perennial stream tributaries and other 

creeks in the area. Therefore, surface-mining operations could 

temporarily divert the stream channels and then return them 

to their pre-mining locations as part of mine reclamation. The 

parts of these water courses that are designated by the Montana 

State Land Quality Division as alluvial valley floors significant 

to farming, however, would be exempt from mining. The relatively broad valley of the Yellowstone River lies in the extreme 

northern part of the assessment area, but has no restriction 

effect on mining because the coals do not extend into that area.

Shallow lakes and small ponds that do exist within the 

MTPRB could either be temporarily moved during mining or simply reformed after the mining operations ceased. 

However, the Tongue River Reservoir, a recreational site and 

water-supply source located about 2.5 mi northeast of Decker, 

Montana, is considered to be a restriction to mining for this 

assessment (fig. 6). The restriction includes a 100-ft buffer surrounding the lake.

Roads

County roads (mostly gravel) cross many areas throughout the MTPRB assessment area. These roads are not considered to restrict mining because 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 Highway 94, are present within the area (fig. 6). 

For this study, it is assumed that all of these highways would 

also be relocated to allow for mining, except for the interstate 

highway. However, like the main railroad line, the interstate 

highway lies in the extreme northern part of the assessment 

area and has no restriction effect on the coal beds because the 

coals do not extend into that part of the area.

State Lands and Trusts

Two state parks are situated within the MTPRB assessment area: the Rosebud Battlefield State Park and the Tongue 

River Reservoir State Park (fig. 6); both parks are considered 

to be restrictions to mining. The Rosebud Battlefield State 

Park is about 15 mi northwest of Decker, Montana, and the 

Tongue River Reservoir State Park is about 6 mi northeast of 

Decker. The restriction for each park includes a buffer that 

extends out to a distance of 300 ft beyond the park boundaries.

Also within the assessment area are a fishing access 

site (at Twelve Mile Dam) and two conservation easements 

(fig. 6). The fishing access site and one of the easements are 

under the jurisdiction of the Montana Fish, Wildlife & Parks. 

The other conservation easement is overseen by the Montana 

Land Reliance. These lands are considered to be restricted 

from mining; however, they have no restriction effect on the 

coal beds because the coals do not extend into their locations 

within the northern part of the assessment area.

Towns

The municipalities of Colstrip and Broadus are located 

within the MTPRB assessment area and are permanently 
Methodology 15

restricted from mining (fig. 6). In addition to the actual 

incorporated areas, the mining restriction for each municipality includes a buffer that extends out to a distance of 300 ft 

beyond the municipality limits.

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 (Btu/lb). Quality parameters 

such as increased ash content, which lowers the calorific 

value, negatively effects 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 (lbs) 

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 (emits 

less than 0.6 lbs or less sulfur per million Btu or 1.2 lbs 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. Also, new 

Source Performance Standards establish uniform national 

Environmental Protection Agency air-emission standards that 

limit the amount of pollution from new sources or from modified existing sources. Under New Source Performance Standards, Best Available Control Technology emission limitations 

Table 5. Available as-received coal-quality data for mines and mine leases in the Montana 

Powder River Basin assessment area.

[BTU/lb, Thermal Unit/pound]

Mine name Ash

(percent)

Sulfur

(percent)

Moisture

(percent)

Calorific value

(Btu/lb)

Absaloka Mine1 9.1 0.68 24.5 8,687

Big Sky Mine2 8.8 0.75 25.9 8,750

Decker Mines1 4.4 0.38 23.8 9,500

Rosebud Mine1 9.1 0.74 25.9 8,529

Spring Creek Mine1 4.1 0.34 25.4 9,350

Otter Creek (Arch lease)3 5.5 0.15 ------ 8,110

1

From Wilde, 2010.

2

From Wilde, 2001.

3

From Culbertson and Saperstone, 1987.

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.

Coal quality information has been available since the 

early 1970s from five mines in the MTPRB (Absaloka, Big 

Sky, Decker, Rosebud, and Spring Creek). Table 5 summarizes 

coal quality for those five mines and the Otter Creek lease 

area. Coal quality data was summarized by Roberts and 

others [1999a, 1999b, 1999c, after Matson and Blumer (1973)] 

or select areas within the MTPRB assessment area (fig. 15, 

table 6). Results for individual coal beds in coal fields and 

areas were reported in ranges, whereas results for the Absaloka Mine area (table 6) were reported as averages. Within the 

MTPRB assessment area, sulfur ranged from 0.1–7.2 percent, 

ash content ranged from 2.5–12.6 percent, and the Btu/lb values ranged from 6,019–9,850.

In comparison to coal mined in the Wyoming portion 

of the PRB, coal in the MTPRB assessment area is generally 

higher in sodium content (table 7). High sodium content in 

coal can cause excessive slagging in most power plant boilers and therefore is marketed to power plants with specially 

designed boilers. Coal beds (Anderson, Dietz 2, Dietz 3) in 

the Decker and Spring Creek Mine areas have higher sodium 

content than coals (Rosebud/Knobloch coal bed) in the 

Rosebud and Absaloka Mine areas (table 7). Coal within the 

Tongue River Member of the Fort Union Formation is mainly 

classified as subbituminous B to lignite A, based on heatof-combustion values (Gilmour and Dahl, 1967). Although 

there is a general decrease in coal rank from west to east, the 

transition is gradual (fig. 15). Because the MTPRB assessment 

area contains mostly subbituminous B coal, all resources were 

calculated using 1,770 tons per acre-foot. 
16 Assessment of Coal Geology, Resources, and Reserves in the Montana Powder River Basin

Table 6. Available as-received coal-quality data for coal fields and areas in the Montana Powder River 

Basin assessment area (see fig. 15 for locations).

[All data from Roberts and others (1999a, 1999b, 1999c; BTU/lb, British Thermal Unit/pound]

Coal field or area name Bed name Sulfur

(percent) 

Ash

(percent)

Calorific value

(Btu/lb) 

Ashland coal field Knobloch 0.1–0.5 3.7–6.8 7,761–9,070

Foster Creek area Knobloch 0.3–1.6 6.7–8.7 7,380–7,840

Greenleaf Creek-Miller Creek area Knobloch 0.42–0.44 5.5–6.7 8,209–8,935

Absaloka Mine area Robinson 0.79 7.88 8,665

Absaloka Mine area McKay 0.89 8.83 8,642

Absaloka Mine area Rosebud 0.65 8.24 8,767

Colstrip coal field Rosebud 0.53–7.20 7.86–12.58 7,810–9,090

Decker/Spring Creek area Anderson 0.1–0.9 3.0–9.1 6,594–9,850

Decker/Spring Creek area Dietz 2, 3 0.1–2.4 2.5–14.1 6,019–9,561

Decker/Spring Creek area Canyon 0.1–2.5 3.2–10.7 6,646–9,113

Table 7. Comparison of proximate analysis of coals from mines in the Wyoming and Montana portions of 

the Powder River Basin.

[All data from Guide to Coal Mines, April 21, 2010; BTU/lb, British Thermal Unit/pound]

Mine name Sodium as percent of ash Sulfur

(percent) 

Ash

(percent)

Calorific value

(Btu/lb) 

Wyoming mines

Antelope 1.64 0.24 5.25 8,800

Belle Ayr 1.90 0.33 4.50 8,550

Black Thunder 1.30 0.30 5.50 8,800

Buckskin 1.80 0.30 5.00 8,400

Cabbalo 1.40 0.34 5.10 8,500

Codero Rojo 1.40 0.34 5.40 8,400

Eagle Butte 1.90 0.34 4.50 8,400

Rawhide 1.60 0.37 5.40 8,300

Montana mines

Absaloka 2.00 0.60 9.00 8,750

Decker 1.00–8.00 0.40 4.20 9,450

Rosebud 0.30 0.80 8.50 8,750

Spring Creek 8.50 0.38 4.10 9,350
Geologic Setting 17

Mine Model Methodology

Mine models were developed to determine the recoverable potential of coal resources in the MTPRB assessment 

area. Both surface and underground mine models included 

simplified algorithms for determining required equipment 

rates and sizes to cut, load, and convey burden and coal. These 

calculations were embedded in interlocking spreadsheets 

(Microsoft 2007 EXCEL®) which are used to correlate equipment requirements with personnel, supply, and facility physical needs. Unit costs that were available through InfoMine 

USA, Inc. (2010) were applied to these physical parameters 

and adjusted to their time-value for determination of the total 

project net present value on a case-by-case basis. 

Information from four surface coal mines operating in the 

MTPRB assessment area was used to develop a surface-mine 

model to accommodate localized geologic conditions. Each of 

these mines is unique as related to individual corporate policy 

affecting the design of each mine.

Reserves in the Gillette coalfield (Luppens and others, 

2008) and the Northern Wyoming Powder River Basin assessment area (Scott and others, 2010) were evaluated using the 

USGS software program CoalVal (Rohrbacher and McIntosh, 

2010). Both of these areas involved single coal bed modeling for which CoalVal was designed. Modeling for multiple 

coal beds in the MTPRB assessment area was evaluated using 

the approach described in the Appendix of this report. The 

results of both evaluation methodologies are considered to be 

adequate representations of industry practice.

The methodology of parsing out the coal resources by 

composite stripping-ratio increments used in the Gillette coal 

field assessment (Luppens and others, 2008) was also used in 

the MTPRB assessment area. However, with more beds that 

have a thinner average thickness throughout a larger stratigraphic interval, the approach to the coal reserve evaluation 

model for the MTPRB assessment area had to be modified 

from the composited single seam approach used for the Gillette coal field. Further complicating the development of a 

regional mining model for this area is the fact that not all beds 

are everywhere present. Mine models and assumptions for 

both surface and underground reserve analysis are given in the 

Appendix at the end of this report.

Geologic Setting

The Powder River Basin is an elongate, north-northwesttrending sedimentary basin that covers about 22,000 mi2

 of 

northeastern Wyoming and southeastern Montana (fig. 16). It 

forms a broad asymmetric syncline with a gently dipping east 

limb and a more steeply dipping west limb. The synclinal axis 

lies near the basin’s western margin, trending north-northwest 

in the Wyoming portion of the PRB, and gradually turning 

north-northeasterly in the Montana portion (Lopez, 2005). 

The Montana portion of the basin is bounded by structural 

uplifts––the Bighorn Mountains to the west, and the Black 

Hills to the east. The basin becomes shallow to the north 

against the south flank of the Miles City arch. Two systems of 

northeast-trending faults are present in the MTPRB assessment area (fig. 17), and may represent extensions of the Lake 

Basin and Nye-Bowler fault zones (Vuke and others, 2001a, 

2001b; Lopez and Heath, 2007).

Strata exposed at the surface in the MTPRB assessment 

area consist almost entirely of the lower Tertiary (Paleocene) 

Fort Union Formation (fig. 18). The Fort Union Formation 

is composed of three members; from oldest to youngest, the 

Tullock, Lebo (informally referred to as the Lebo shale), and 

Tongue River Members. Together, they form a thick sequence 

of interbedded sandstones, conglomerates, siltstones, shales, 

and coals. The deposition of clastic sediments that produced 

these units was accompanied by tremendous accumulations of 

peat in nearby low-energy environments such as flood plains 

and swamps. In the MTPRB assessment area, the Fort Union 

Formation ranges in thickness from a few hundred feet in the 

north to approximately 4,000 ft at the Montana-Wyoming border (Jay Gunderson, Montana Bureau of Mines and Geology, 

written commun., 2011). 

Underlying the Fort Union Formation, delta-plain sandstones and shales of the Upper Cretaceous Hell Creek Formation (equivalent to the Lance Formation in Wyoming) grade 

upward into the fluvial-dominated strata of the lowermost 

Tullock Member of the Fort Union Formation. The top of the 

Hell Creek Formation is placed at the base of the lowest coal 

bed in the Tullock Member (Brown, 1993), and generally corresponds to an upward change in sedimentary character from 

cross-bedded to planar-bedded sandstones (Vuke and others, 

2001c). The Hell Creek Formation and older marine and nonmarine sedimentary units that underlie the Fort Union Formation are only exposed along the basin margins.

The Eocene Wasatch Formation in some areas unconformably overlies the Fort Union Formation and crops out 

only in the southernmost part of the MTPRB assessment area, 

along topographic highs between stream valleys including the 

Tongue River, Hanging Woman Creek, and Otter Creek (Vuke 

and others, 2001b). The contact between the two formations 

is identified, in part, by the distinctive heavy mineral suites in 

each (Denson and others, 1990). 

Coal beds are present in all three members of the Fort 

Union Formation and in the Wasatch Formation in the 

MTPRB assessment area. The Fort Union Formation contains 

some of the thickest and most extensive deposits of subbituminous coal in the world (Molnia and Pierce, 1992). The 

most important beds are in the Tongue River Member of the 

Fort Union Formation. This unit has as many as 26 coal beds, 

some of which attain thicknesses as much as 80 ft. Progressively older coal beds become exposed at the surface to the 

north because of their south-dips combined with the drop in 

surface elevation to the north. The largest volume of coal is in 

the Wyodak-Anderson coal zone in the Tongue River (Flores 

and others, 1999), which contains the equivalent (in descending order) of the Smith, Anderson, Dietz 2, Dietz 3, Canyon, 

Lower Canyon, Ferry, and Werner/Cook (fig. 19). 
18 Assessment of Coal Geology, Resources, and Reserves in the Montana Powder River Basin

Cross sections A–A’ to G–G’ in figs. 20 to 27 illustrate 

the coal bed geometry and stratigraphic sequence of the lower 

Tongue River Member coal beds. Generally, coal beds below 

the Wyodak-Anderson coal zone that are present in eastern 

Montana tend to be thinner and more discontinuous, with the 

exception of the Pawnee, Rosebud/Knobloch, and FlowersGoodale (fig. 19).

Clinker, which is widespread, and geologic structure, on 

a more local scale, exerts varying effects on resource development. Almost everywhere in the MTPRB, coal beds more than 

5 ft thick have burned. The heat produced brightly colored 

material known as clinker––rocks that overlie a burned coal 

bed and were altered, baked, and fused. The clinker affects a 

thickness of the overlying material that is roughly 2–3 times 

the original thickness and quantity of the coal that has burned. 

Thickness of clinker can therefore be used in exploration as 

an added indication of the thickness of a coal bed. A coal 

bed 5–10 ft thick can produce a clinker zone 10–30 ft thick, 

whereas a coal bed 50 ft thick may produce a clinker zone 

100–200 ft thick (Matson and Blumer, 1973).

Large areas of original near-surface coal resources have 

been destroyed by burning at their outcrop and beneath shallow cover. Approximately 1,000 mi2

 of the surface area in the 

MTPRB is affected by clinker (Coates and Heffern, 1999) 

(fig. 28). Roberts and others (1999c) outlined large areas of 

clinker in the Spring Creek and Decker Mine area affecting 

the Anderson, Dietz 2, and Dietz 3 coal beds. In the Rosebud 

Mine area, where the Rosebud and McKay beds merge to form 

a single bed, clinker deposits have been reported to attain a 

thickness of as much as 120 ft (Tudor, 1975).

The amount of burned coal was subtracted from the 

amount of the original coal resource. To calculate the amount 

of coal that has been burned, it was assumed that there is up to 

a three-to-one ratio of clinker thickness to burned coal thickness (Coates and Heffern, 1999). Consequently, to estimate 

the areas of coal within each bed that had been burned, a 

combination of surface clinker extent, coal overburden thickness, and coal bed thickness was used during the GIS analysis. 

Specifically, wherever surface clinker lies over a coal bed and 

the thickness of the overburden is three times (or less) the 

thickness of the coal, the coal within the bed was considered to 

be completely burned. Nevertheless, this procedure probably 

produces a conservative estimate of the amount of burned coal 

throughout the MTPRB assessment area. The total volume of 

clinker is estimated to be about 7 BST.

The structural dip of coal beds can affect the type of 

mining of those beds. A dip of 5°, for example, has much less 

effect on both surface and underground mining, than does a 

dip of 20° or greater. The dip of coal beds in the Spring Creek, 

Decker, and Rosebud Mine areas is generally less than 5°, 

with dip orientations varying from southeasterly to southwesterly. However, dips are steepened by high-angle normal faults 

that are present in the western half of the MTPRB assessment 

area. Figures 21 and 22 illustrate the gentle dip of coal beds in 

the eastern part of the PRB in contrast to the steeper dip of the 

same beds along the west margin of the basin. 

In the southwestern part of the MTPRB assessment area, 

numerous northeast-trending faults are present in the northward extension of the Sheridan coal field (fig. 17). The faults, 

most of which are downthrown on the east, postdate coalbed 

formation. Faults shown in figure 17 are based on Ellis and 

others (1999a, b) and Roberts and others (1999c), or they 

were identified during the correlation phase of this study from 

observations of stratigraphic offset between drill holes. The 

faults in the western part of the MTPRB range from 0.5–6.0 

mi in length, with displacements of as much as 140 ft (Robinson and Van Gosen, 1986). In most cases, fault displacement is 

not much more than 100 ft. Areas where numerous high-angle 

faults are present are not conducive to either surface or underground mining operations. 

Faults in coal beds also have an important effect on the 

selection of mining methods and on productivity. Major faults 

with vertical displacements greater than 65 ft commonly are 

used to delineate mine plan boundaries. Numerous minor 

faults are generally associated with and trend almost parallel 

to major faults. The adverse effects of faulting are greater on 

underground mining operations. Whereas a fault with a vertical displacement of 3–16 ft may not pose much of a problem 

in a surface mine, it may be a serious impediment in underground mining (Thomas, 2002). 

The method of underground mining affects the amount 

of resources lost to faults. If the method used is longwall 

mining, there will be a larger resource loss because longwall 

operations need hazard-free runs in a designated panel of coal. 

Longwall panels are typically 5,000–10,000 ft in length and 

750–1,500 ft in width; thus, a large, relatively unfaulted block 

of coal is required. Also to be considered is the amount the 

faulted coal bed is displaced out of line with the preset coal 

shearer. If coal panels between faults are too small, then whole 

blocks may be lost to mining (Thomas, 2002).

Coal Bed Correlations and 

Nomenclature

Because coal beds commonly split, merge, and pinch out, 

the correlation of individually named coal beds and coal zones 

across the PRB has been difficult (Flores and others, 1999). 

Also, distances between individual drill holes can be large, 

increasing the uncertainty in correlating coal beds from one 

drill hole to the next. Some reports relied on drill-hole data 

that were 10 or more miles apart. However, with the drilling 

and development of new CBM in the PRB, data from thousands of new drill holes are now available, and the distance 

between drill holes is thus reduced (fig. 4). 

The graphical interface of the StratiFact (GRG Corporation, 1998) database was a critical tool for managing interpretation of the large amount of existing information across the 

MTPRB assessment area. Using StratiFact, on-screen cross 

sections were selected, edited, and correlated. Both linear 

and circular cross sections were constructed to correlate coal 
Coal Bed Assessment 19

beds; the circular cross sections, in which both the beginning 

and ending drill holes are the same, were especially valuable 

in maintaining accuracy in the tracing of individual beds and 

avoid miscorrelation. 

Various names for individual coal beds and coal zones in 

the PRB have been used during the past 30 years (fig. 19). 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 and Montana. 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).

In the area of the Absaloka, Big Sky, and Rosebud Mines, 

coal bed nomenclature for this assessment in the MTPRB is 

generally consistent with the terminology of Dobbin (1929) 

and nomenclature adhered to in subsequent studies by Matson 

and Blumer (1973), Tudor (1975), Robinson and Van Gosen 

(1986), and Derkey (1986). 

Coal bed nomenclature for the Spring Creek and Decker 

Mine areas generally follows that of Roberts and others 

(1999b). Within the Spring Creek and Decker Mine area, Roberts and others (1999b) described the Anderson-Canyon coal 

zone, which is equivalent to the Wyodak-Anderson coal zone 

of Flores and Bader (1999) that contains the Anderson, Dietz 

2, Dietz 3, Cox, and Canyon coal beds. Coal beds of the same 

name in this assessment correlate with the coal bed names in 

the Wyodak-Anderson coal zone; coal bed names used in this 

report and the equivalent names used in previous reports are 

shown in figure 19. The stratigraphic sequence of all 26 beds 

is shown in figure 29. 

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:

1. Two named beds are considered to have merged into 

a single named bed when the intervening parting is 

less than 2 ft thick. The following exceptions were 

made for modeling purposes:

• In individual holes, coal beds split by partings as 

much as 5 ft thick are considered merged if nearby 

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 split 

into two beds if surrounding holes show the coal 

has split into two beds.

2. The upper bed’s name will be used for the mergedbed name.

Coal Bed Assessment

Because a typical surface-mining sequence begins at the 

ground surface, the following descriptions of coal beds that 

were assessed in the MTPRB 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), which are directly dependent on the density of geologic 

data points. The different reliability categories–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. 

Roland (Baker) Coal Bed

The Roland (Baker) is the uppermost coal bed assessed 

for resource calculations in the MTPRB assessment area. It 

was identified in 141 drill holes, has a maximum thickness of 

14 ft, and averages 6 ft thick (fig. 30). The coal bed is present in a small area near the Decker and Spring Creek Mines 

in the southwestern part of the MTPRB assessment area and 

correlates to the Roland (Baker) coal bed in the NWPRB 

assessment area (Scott and others, 2010). Overburden maps 

for all the beds (depth to top of bed) start at 2.5 ft instead of 

the normal 0 ft, so that the overburden isopach maps match the 

thickness isopach maps. Depth of the Roland (Baker) ranges 

from shallow subcrop to about 1,000 ft south of the Decker 

and Spring Creek Mines. Although limited in extent, more 

than 92 percent of the available coal resource is at a depth 

of less than 500 ft (fig. 31, table 8). Coal resource reliability 

categories for the Roland (Baker) are shown in figure 32. 

More than 75 percent of the available coal is considered a 

demonstrated resource, reflecting the overall quantity of data 

(table 9); approximately 86 percent of this coal is owned by 

the federal government (table 4).

Smith Coal Bed

The Smith coal bed, as interpreted from 308 drill holes, has 

a maximum thickness of 20 ft and averages 6 ft thick (fig. 33). 

It has about the same areal extent as the Roland (Baker) coal 

bed in the southwestern part of the MTPRB assessment area 

and correlates to the Smith coal bed in the NWPRB assessment 

area (Scott and others, 2010). For this assessment, the Smith, 

Anderson, Dietz 2, Dietz 3, Canyon, Lower Canyon, Ferry, and 

Werner/Cook coal beds constitute the Wyodak-Anderson coal 
Table 8. Coal resources and restrictions for 18 beds greater than or equal to 2.5 feet thick, reported in millions of short tons by overburden depth for Montana Powder River Basin assessment area. Resource includes coal plus partings. Totals may not sum exactly because of rounding.—Continued Coal bed name Overburden thickness (feet) Original resource Burned coal Remaining resource Previously mined coal Land use restrictions Technical restrictions Available resource Perc

of to

remai

Roland (Baker) 0–500 693 12 680 0 0 49 631 92.6 500–1,000 2 0 2 0 0 0 2 0.3 1,000–2,000 0 0 0 0 0 0 0 0.0 2,000–3,000 0 0 0 0 0 0 0 0.0 Total 695 12 682 0 0 49 634 92.8 Smith 0–500 469 7 462 0 2 28 432 83.4 500–1,000 970 21 949 0 6 82 861 5.3 1,000–2,000 375 10 365 0 11 72 283 0.0 2,000–3,000 2 0 2 0 0 1 0 0.0 Total 1,817 38 1,778 0 19 183 1,577 88.7 Anderson 0–500 15,463 1,455 14,009 472 992 104 12,440 82.8 500–1,000 1,018 0 1,018 0 0 0 1,017 6.8 1,000–2,000 0 0 0 0 0 0 0 0.0 2,000–3,000 0 0 0 0 0 0 0 0.0 Total 16,481 1,455 15,027 472 992 104 13,458 89.6 Dietz 2 0–500 1,356 33 1,323 41 10 226 1,046 67.2 500–1,000 233 0 233 0 0 86 148 9.5 1,000–2,000 0 0 0 0 0 0 0 0.0 2,000–3,000 0 0 0 0 0 0 0 0.0 Total 1,590 33 1,556 41 10 311 1,194 76.7Dietz 3

0–500 8,156 759 7,397 136 1,036 424 5,801 66.2500–1,000 1,352 0 1,352 0 0 82 1,270 14.51,000–2,000 8 0 8 0 0 0 8 0.2,000–3,000 0 0 0 0 0 0 0 0.0

Total 9,516 759 8,757 136 1,036 506 7,079 80.8
Table 8. Coal resources and restrictions for 18 beds greater than or equal to 2.5 feet thick, reported in millions of short tons by overburden depth for Montana Powder River Basin assessment area. Resource includes coal plus partings. Totals may not sum exactly because of rounding.—Continued

Coal bed

name

Overburden

thickness

(feet)

Original 

resource

Burned coal Remaining 

resource

Previously

mined coal

Land use

restrictions

Technical 

restrictions

Available

resource

Perc

of to

remai

Canyon

0–500 14,915 462 14,452 0 3,189 193 11,071 58.6500–1,000 4,372 0 4,372 0 0 33 4,339 23.01,000–2,000 70 0 70 0 0 0 70 0.42,000–3,000 0 0 0 0 0 0 0 0.0

Total 19,357 462 18,895 0 3,189 226 15,480 81.9

Lower Canyon

0–500 6,695 249 6,446 0 1,875 761 3,810 37.6500–1,000 3,537 0 3,537 0 0 236 3,301 32.51,000–2,000 162 0 162 0 0 2 160 1.62,000–3,000 0 0 0 0 0 0 0 0.0

Total 10,395 249 10,146 0 1,875 1,000 7,272 71.7

Ferry

0–500 ft 1,410 7 1,402 0 315 314 773 31.5500–1,000 1,051 0 1,051 0 0 195 857 34.91,000–2,000 0 0 0 0 0 0 0 0.02,000–3,000 0 0 0 0 0 0 0 0.0

Total 2,462 7 2,454 0 315 509 1,630 66.4

Werner/Cook

0–500 14,804 762 14,041 0 3,931 371 9,740 39.2500–1,000 10,427 0 10,427 0 1 210 10,216 41.1,000–2,000 376 0 376 0 0 35 341 1.42,000–3,000 0 0 0 0 0 0 0 0.0

Total 25,606 762 24,844 0 3,932 615 20,297 81.7

Otter

0–500 1,841 64 1,777 0 830 530 417 9.5500–1,000 2,387 0 2,387 0 5 978 1,404 31.81,000–2,000 246 0 246 0 0 141 105 2.42,000–3,000 0 0 0 0 0 0 0 0.0

Total 4,474 64 4,410 0 835 1,649 1,926 43.7
Table 8. Coal resources and restrictions for 18 beds greater than or equal to 2.5 feet thick, reported in millions of short tons by overburden depth for Montana Powder River Basin assessment area. Resource includes coal plus partings. Totals may not sum exactly because of rounding.—Continued Coal bed name Overburden thickness (feet) Original resource Burned coal Remaining resource Previously mined coal Land use restrictions Technical restrictions Available resource Perc

of to

remai

Gates/Wall 0–500 3,165 121 3,045 0 793 651 1,601 19.7 500–1,000 3,769 0 3,769 0 9 780 2,980 36.6 1,000–2,000 1,323 0 1,323 0 0 247 1,076 13.2 2,000–3,000 0 0 0 0 0 0 0 0.0 Total 8,257 121 8,137 0 802 1,678 5,656 69.5 Pawnee 0–500 8,228 271 7,957 0 2,481 337 5,139 37.9 500–1,000 3,267 0 3,267 0 13 534 2,720 20.

1,000–2,000 2,338 0 2,338 0 0 697 1,641 12.2,000–3,000 0 0 0 0 0 0 0 0.0 Total 13,834 271 13,563 0 2,494 1,568 9,501 70.1 Odell 0–500 1,460 26 1,434 0 298 845 291 16.4 500–1,000 340 0 340 0 0 183 157 8.8 1,000–2,000 4 0 4 0 0 4 1 0.0 2,000–3,000 0 0 0 0 0 0 0 0.0 Total 1,803 26 1,778 0 298 1,031 449 25.3 Rosebud/Knobloch 0–500 26,169 1,743 24,425 559 9,611 810 13,445 32.9 500–1,000 12,884 0 12,884 0 0 428 12,456 30.5 1,000–2,000 3,563 0 3,563 0 0 306 3,257 8.0 2,000–3,000 0 0 0 0 0 0 0 0.0 Total 42,616 1,743 40,873 559 9,611 1,545 29,158 71.3

McKay/Nance

0–500 6,732 196 6,536 68 903 935 4,630 44.7500–1,000 2,968 0 2,968 0 0 658 2,310 22.31,000–2,000 849 0 849 0 0 339 510 4.92,000–3,000 0 0 0 0 0 0 0 0.0

Total 10,549 196 10,353 68 903 1,932 7,450 72.0
Table 8. Coal resources and restrictions for 18 beds greater than or equal to 2.5 feet thick, reported in millions of short tons by overburden depth for Montana Powder River Basin assessment area. Resource includes coal plus partings. Totals may not sum exactly because of rounding.—Continued

Coal bed

name

Overburden

thickness

(feet)

Original 

resource

Burned coal Remaining 

resource

Previously

mined coal

Land use

restrictions

Technical 

restrictions

Available

resource

Perc

of to

remai

Flowers-Goodale

0–500 8,315 169 8,146 0 553 264 7,329 28.7500–1,000 8,452 0 8,452 0 0 132 8,319 32.61,000–2,000 8,886 0 8,889 0 78 204 9,604 33.72,000–3,000 34 0 34 0 0 10 24 0.

Total 25,686 169 25,518 0 631 610 24,277 95.1

Robinson/Witham

0–500 5,261 160 5,100 0 4 464 4,632 49.3500–1,000 2,371 0 2,371 0 0 562 1,809 19.21,000–2,000 1,930 0 1,930 0 0 760 1,170 12.42,000–3,000 0 0 0 0 0 0 0 0.0

Total 9,562 160 9,402 0 4 1,786 7,612 81.0

Roberts/Terret

0–500 3,717 128 3,589 0 95 914 2,580 24.6500–1,000 2,135 0 2,135 0 0 644 1,491 14.21,000–2,000 4,285 0 4,285 0 0 872 3,413 32.62,000–3,000 462 0 462 0 0 25 437 4.2

Total 10,599 128 10,471 0 95 2,455 7,921 75.6

Total

0–500 130,101 6,656 123,445 1,277 26,935 8,374 86,859 41.6500–1,000 60,660 0 60,660 0 28 5,741 54,890 26.31,000–2,000 24,042 0 24,042 0 78 3,606 20,358 9.82,000–3,000 497 0 497 0 0 36 461 0.2

Total 215,300 6,656 208,644 1,277 27,042 17,757 162,568 77.9
Table 9. Coal resources and restrictions for 18 beds greater than or equal to 2.5 feet thick, reported in millions of short tons by reliability category for the Montana Powder River Basin assessment area. Resource includes coal plus partings. Reliability categories are based on distance from data point. Measured: less than 0.25 miles; Indicated: 0.25–0.75 miles; Inferred: 0.75-3.0 miles; Hypothetical: more than 3.0 miles. Totals may not sum exactlbecause of rounding.—Continued Coal bed name Reliability category Original resource Burned coal Remaining resource Previously mined coal Land use restrictions Technical restrictions Available resource Percent of total remaining Roland (Baker) Measured 166 3 163 0 0 7 156 22.9 Indicated 353 7 346 0 0 20 325 47.7 Inferred 174 2 173 0 0 21 151 22.2 Hypothetical 1 1 1 0 0 0 1 0.1 Total 695 12 682 0 0 49 634 92.8 Smith Measured 469 7 462 0 2 28 432 24.3 Indicated 971 21 949 0 6 82 861 48.4 Inferred 375 10 365 0 11 72 283 15.9 Hypothetical 2 0 2 0 0 1 0 0.0 Total 1,817 38 1,778 0 19 183 1,577 88.7 Anderson Measured 3,855 164 3,692 402 167 6 3,117 20.7 Indicated 7,608 611 6,997 70 252 25 6,651 44.3 Inferred 4,916 651 4,265 0 530 51 3,683 24.5 Hypothetical 102 29 73 0 43 22 7 0.0 Total 16,481 1,455 15,027 472 992 104 13,458 89.6 Dietz 2 Measured 682 13 669 40 8 59 561 36.0 Indicated 671 13 658 1 2 182 474 30.4 Inferred 225 6 218 0 0 61 158 10.1 Hypothetical 12 0 12 0 0 10 2 0.1

Total 1,590 33 1,556 41 10 311 1,194 76.7

Dietz 3

Measured 2,003 116 1,887 96 64 50 1,678 19.2Indicated 4,710 332 4,378 38 295 196 3,849 44.0Inferred 2,732 306 2,426 3 633 247 1,543 17.6Hypothetical 71 6 65 0 44 12 9 0.1Total 9,516 759 8,757 136 1,036 506 7,079 80.8
Table 9. Coal resources and restrictions for 18 beds greater than or equal to 2.5 feet thick, reported in millions of short tons by reliability category for the Montana Powder River Basin assessment area. Resource includes coal plus partings. Reliability categories are based on distance from data point. Measured: less than 0.25 miles; Indicated: 0.25–0.75 miles; Inferred: 0.75-3.0 miles; Hypothetical: more than 3.0 miles. Totals may not sum exactlbecause of rounding.—Continued

Coal bed

name

Reliability 

category

Original 

resource

Burned

coal

Remaining 

resource

Previously

mined coal

Land use

restrictions

Technical 

restrictions

Available

resource

Percent

of total

remaining

Canyon

Measured 2,408 22 2,385 0 140 17 2,229 11.8Indicated 7,841 148 7,693 0 664 77 6,951 36.8Inferred 8,689 272 8,417 0 2,045 117 6,256 33.1Hypothetical 420 20 400 0 340 15 45 0.2Total 19,357 462 18,895 0 3,189 226 15,480 81.9

Lower Canyon

Measured 1,211 4 1,208 0 99 42 1,067 10.5Indicated 3,805 29 3,776 0 519 259 2,998 29.5Inferred 4,883 173 4,710 0 1,063 644 3,003 29.6Hypothetical 496 43 453 0 194 55 204 2.0Total 10,395 249 10,146 0 1,875 1,000 7,272 71.7

Ferry

Measured 194 0 194 0 9 39 146 5.9Indicated 714 2 712 0 57 156 499 20.3Inferred 1,510 4 1,506 0 243 277 985 40.2Hypothetical 44 0 43 0 6 37 0 0.0Total 2,462 7 2,454 0 315 509 1,630 66.4

Werner/Cook

Measured 1,874 35 1,839 0 110 23 1,707 6.9Indicated 8,747 188 8,559 0 716 132 7,710 31.0Inferred 14,364 505 13,860 0 2,724 437 10,699 43.1Hypothetical 621 35 586 0 382 24 180 0.7Total 25,606 762 24,844 0 3,932 615 20,297 81.7

Otter

Measured 391 2 388 0 39 99 251 5.7Indicated 1,428 19 1,409 0 187 433 789 17.9Inferred 2,578 40 2,538 0 586 1,067 884 20.1Hypothetical 77 2 75 0 23 50 2 0.0Total 4,474 64 4,410 0 835 1,649 1,926 43.7
Table 9. Coal resources and restrictions for 18 beds greater than or equal to 2.5 feet thick, reported in millions of short tons by reliability category for the Montana Powder River Basin assessment area. Resource includes coal plus partings. Reliability categories are based on distance from data point. Measured: less than 0.25 miles; Indicated: 0.25–0.75 miles; Inferred: 0.75-3.0 miles; Hypothetical: more than 3.0 miles. Totals may not sum exactlbecause of rounding.—Continued Coal bed name Reliability category Original resource Burned coal Remaining resource Previously mined coal Land use restrictions Technical restrictions Available resource Percent of total remaining Gates/Wall Measured 374 4 370 0 46 53 271 3.3 Indicated 2,126 32 2,094 0 221 314 1,559 19.2 Inferred 5,576 81 5,495 0 502 1,169 3,824 47.0 Hypothetical 181 4 177 0 33 142 2 0.0 Total 8,257 121 8,136 0 802 1,678 5,656 69.5 Pawnee Measured 607 8 599 0 57 52 489 3.6 Indicated 3,433 66 3,367 0 354 302 2,711 20.0 Inferred 9,310 182 9,128 0 1,855 1,167 6,105 45.0 Hypothetical 483 14 469 0 227 46 196 1.4 Total 13,834 271 13,563 0 2,494 1,568 9,501 70.1 Odell Measured 92 1 92 0 13 43 36 2.0 Indicated 473 8 465 0 82 231 152 8.6 Inferred 1,193 16 1,178 0 203 713 261 14.7 Hypothetical 44 0 44 0 0 44 0 0.0 Total 1,803 26 1,778 0 298 1,031 449 25.3 Rosebud/Knobloch Measured 4,691 175 4,516 489 602 58 3,367 8.2 Indicated 12,056 780 11,276 66 2,905 328 7,977 19.5 Inferred 24,661 678 23,984 4 5,996 1,033 16,950 41.5 Hypothetical 1,207 111 1,097 0 107 126 864 2.1

Total 42,616 1,743 40,873 559 9,611 1,545 29,158 71.3

McKay/Nance

Measured 1,841 52 1,790 68 55 94 1,573 15.2Indicated 3,288 69 3,218 0 270 450 2,498 24.1Inferred 5,268 50 5,218 0 578 1,350 3,291 31.8Hypothetical 152 26 127 0 1 37 89 0.9Total 10,549 196 10,353 68 903 1,932 7,450 72.0
Table 9. Coal resources and restrictions for 18 beds greater than or equal to 2.5 feet thick, reported in millions of short tons by reliability category for the Montana Powder River Basin assessment area. Resource includes coal plus partings. Reliability categories are based on distance from data point. Measured: less than 0.25 miles; Indicated: 0.25–0.75 miles; Inferred: 0.75-3.0 miles; Hypothetical: more than 3.0 miles. Totals may not sum exactlbecause of rounding.—Continued

Coal bed

name

Reliability 

category

Original 

resource

Burned

coal

Remaining 

resource

Previously

mined coal

Land use

restrictions

Technical 

restrictions

Available

resource

Percent

of total

remaining

Flowers-Goodale

Measured 812 6 806 0 20 11 774 3.0Indicated 4,922 38 4,884 0 177 67 4,640 18.2Inferred 18,449 121 18,328 0 432 455 17,441 68.3Hypothetical 1,504 4 1,500 0 2 77 1,421 5.6Total 25,686 169 25,518 0 631 610 24,277 95.1

Robinson/Witham

Measured 1,842 78 1,764 0 2 74 1,688 18.0Indicated 2,615 66 2,549 0 0 385 2,164 23.0Inferred 4,898 16 4,882 0 2 1,240 3,640 38.7Hypothetical 208 0 208 0 0 87 120 1.3Total 9,562 160 9,402 0 4 1,786 7,612 81.0

Roberts/Terret

Measured 384 4 380 0 3 54 323 3.1Indicated 2,081 23 2,059 0 17 338 1,703 16.3Inferred 7,287 74 7,213 0 74 1,778 5,361 51.2Hypothetical 847 27 819 0 2 285 533 5.1Total 10,599 128 10,471 0 95 2,455 7,921 75.6

Total

Measured 23,899 695 23,203 1,096 1,436 807 19,864 9.5Indicated 67,842 2,453 65,389 174 6,725 3,980 54,511 26.1Inferred 117,088 3,184 113,903 7 17,477 11,901 84,518 40.5Hypothetical 6,472 323 6,149 0 1,404 1,069 3,676 1.8Total 215,300 6,656 208,644 1,277 27,042 17,757 162,568 77.9
28 Assessment of Coal Geology, Resources, and Reserves in the Montana Powder River Basin

zone described in both the Gillette coal field report (Luppens 

and others, 2008) and the NWPRB assessment area report 

(Scott and others, 2010) (fig. 19). Depth of the Smith ranges 

from shallow subcrop to about 1,000 ft south of the Decker and 

Spring Creek Mines; more than 83 percent of the available coal 

resource is at a depth of less than 500 (fig. 34, table 8). Coal 

resource reliability categories for the Smith bed are shown in 

figure 35. More than 72 percent of the available coal is considered a demonstrated resource reflecting the overall quantity of 

data (table 9); most of the available coal resource is owned by 

the Federal government (83 percent) (table 4).

Anderson Coal Bed

Identified in 851 drill holes, the Anderson coal bed has a 

maximum thickness of 93 ft near the Decker and Spring Creek 

Mine areas (fig. 36). The coal bed averages 22 ft thick and 

correlates with the Anderson coal bed in the NWPRB assessment area (Scott and others, 2010) and also the Anderson coal 

bed of Roberts and others (1999c). The coal is present in a 

large area in the southwestern part of the MTPRB assessment 

area (fig. 36). The Anderson, along with the Dietz 2 and Dietz 

3 coal beds, is presently mined at the Decker and Spring Creek 

Mines. Depth of the Anderson ranges from shallow subcrop to 

about 1,000 ft near the Decker and Spring Creek Mines; more 

than 82 percent of the available coal resource is at a depth of 

less than 500 ft (fig. 37, table 8). About 65 percent of the available coal is considered a demonstrated resource reflecting the 

overall quantity of data (table 9). The coal reliability map is 

shown in figure 38; approximately 83 percent of the available 

coal resource is owned by the federal government (table 4).

Dietz 2 Coal Bed

The Dietz 2 coal bed was identified in 443 drill holes, 

has a maximum thickness of 32 ft, and averages 6 ft thick 

(fig. 39). It is present in a small area in the southwestern part 

of MTPRB assessment area and correlates to the Dietz 2 

coal bed in the NWPRB assessment area (Scott and others, 

2010) and also the Dietz 2 coal bed of Roberts and others 

(1999c). Depth of the Dietz 2 ranges from shallow subcrop to 

about 1,000 ft near the Decker and Spring Creek Mine areas; 

approximately 67 percent of the available coal resource is 

at a depth of less than 500 ft (fig. 40, table 8). Coal resource 

reliability categories for the Dietz 2 are shown in figure 41. 

More than 66 percent of the available coal is considered a 

demonstrated resource reflecting the overall quantity of data 

(table 9); most of the available coal resource (68 percent) is 

owned by the federal government (table 4).

Dietz 3 Coal Bed

The Dietz 3 coal bed, as interpreted from 741 drill holes, 

has a maximum thickness of 59 ft and an average thickness 

of 11 ft (fig. 42). The coal bed is present in two separate areas 

near the Decker and Spring Creek Mines where it exceeds a 

thickness of over 40 ft. The Dietz 3 bed correlates with the 

Dietz 3 in the NWPRB assessment area (Scott and others, 

2010) and the Dietz 3 coal bed of Roberts and others (1999c). 

Depth ranges from shallow subcrop to about 1,000 ft near the 

Decker and Spring Creek Mines. Approximately 66 percent 

of the available coal resource is at a depth of less than 500 

ft (fig. 43, table 8). About 63 percent of the available coal 

is considered a demonstrated resource reflecting the overall 

quantity of data (fig. 44; table 9); more than 72 percent of the 

available coal resource is owned by the Federal government 

(table 4).

Canyon Coal Bed

Originally named the Monarch coal bed by Taff (1909), 

this coal bed is equivalent to the Canyon coal bed of Baker 

(1929) (Law and others, 1979). Since that time it has been 

referred to as both the Canyon and the Monarch. The Canyon coal bed name is used in this report as it correlates to 

the Canyon coal bed in the NWPRB assessment area (Scott 

and others, 2010). This coal bed also correlates with the 

Canyon coal bed of Roberts and others (1999c). The coal 

bed is present in a large area within the southwestern part 

of the MTPRB assessment area (fig. 45). Canyon coal was 

identified in 762 drill holes and reaches a maximum thickness of 57 ft; average thickness is 14 ft (fig. 45). Depth 

ranges from shallow subcrop to about 1,500 ft near the 

Decker and Spring Creek Mines; more than 58 percent of 

the available coal resource is at a depth of less than 500 ft 

(fig. 46, table 8). About 48 percent of the available coal is 

considered a demonstrated resource reflecting the overall 

quantity of data (table 9). The coal resource reliability map 

for the Canyon bed is shown in figure 47; about 75 percent 

of the available coal resource is owned by the Federal government (table 4). 

Lower Canyon Coal Bed

The Lower Canyon coal bed, a lower split of the Canyon 

coal bed, was identified in 533 drill holes, has a maximum 

thickness of 42 ft, and averages 8 ft thick (fig. 48). It is present in a large area in the Decker and Spring Creek Mines in 

the southwestern part of the assessment area. This bed correlates to the Lower Canyon coal bed in the NWPRB assessment area (Scott and others, 2010) and also to the Lower 

Canyon of Roberts and others (1999c). Depth ranges from 

shallow subcrop to about 1,500 ft near the Decker and Spring 

Creek Mine areas; more than 37 percent of the available coal 

resource is at a depth of less than 500 ft (fig. 49, table 8). 

About 40 percent of the available coal is considered a demonstrated resource (table 9); the coal resource reliability map for 

the Lower Canyon bed is shown in figure 50; more than 65 

percent of the available coal resource is owned by the Federal 

government (table 4).
Coal Bed Assessment 29

Ferry Coal Bed

The Ferry coal bed was identified in 169 drill holes 

and is limited in areal extent to the southwestern part of the 

MTPRB assessment area. The bed has a maximum thickness of 15 ft and an average thickness of 6 ft (fig. 51). Depth 

ranges from shallow subcrop to about 1,500 ft near the Spring 

Creek Mine; about 31 percent of the available coal resource 

is at a depth of less than 500 ft (fig. 52, table 8). This coal bed 

correlates with the Ferry coal bed in the NWPRB assessment 

area (Scott and others, 2010). Only about 25 percent of the 

available coal is considered a demonstrated resource (table 9). 

The coal resource reliability map for the Ferry bed is shown 

in figure 53; about 58 percent of the available coal resource is 

owned by the Federal government (table 4).

Werner/Cook Coal Bed

The Werner/Cook coal bed, identified in 508 drill holes, 

has a maximum thickness of 62 ft and averages 15 ft (fig. 54). 

This is the oldest coal bed in the Wyodak-Anderson coal zone. 

It correlates with the Werner coal bed in the NWPRB assessment area of Scott and others (2010). The coal bed is present 

near the Decker and Spring Creek Mines, where it exceeds a 

thickness of 60 ft. Depth ranges from shallow subcrop to over 

1,500 ft near the Spring Creek Mine; about 39 percent of the 

available coal resource is at a depth of less than 500 ft (fig. 55, 

table 8). More than 37 percent of the available coal is considered a demonstrated resource (table 9). The coal resource 

reliability map for the Werner/Cook bed is shown in figure 56; 

about 74 percent of the available coal resource is owned by the 

federal government (table 4).

Otter Coal Bed

Distribution of the Otter coal bed is shown in figure 57. 

Based on 315 drill holes, it reaches a maximum thickness of 

32 ft and has an average thickness of 4 ft (fig. 57). The Otter 

coal bed correlates with the Otter coal bed in the NWPRB 

assessment area (Scott and others, 2010). Areas of greatest 

thickness are near the Decker and Spring Creek Mine areas in 

the southwestern part of the MTPRB assessment area. Depth 

ranges from shallow subcrop to over 1,500 ft near the Spring 

Creek Mine; about 9 percent of the available coal resource is 

at a depth less than 500 ft (fig. 58, table 8). About 24 percent 

of the available coal is considered a demonstrated resource 

(table 9). The coal resource reliability map for the Otter bed 

is shown in figure 59; about 40 percent of the available coal 

resource is owned by the federal government (table 4).

Gates/Wall Coal Bed

Known as the Wall coal bed in Montana and as the Gates 

coal bed in Wyoming, this bed is present in a large area in the 

southwestern part of the MTPRB assessment area (fig. 60). It 

correlates with the Gates coal bed in the NWPRB assessment 

area (Scott and others, 2010). Identified in 244 drill holes, 

the coal has a maximum thickness of 23 ft and averages 5 ft 

thick (fig. 60). Depth ranges from shallow subcrop to about 

2,000 ft in the Spring Creek Mine area; about 19 percent of the 

available coal resource is at a depth of less than 500 ft (fig. 61, 

table 8). About 22 percent of the available coal is considered 

a demonstrated resource (table 9). The coal resource reliability map for the Gates/Wall bed is shown in figure 62; about 

62 percent of the available coal resource is owned by the 

Federal government (table 4).

Pawnee Coal Bed

The Pawnee coal bed has a large areal extent in the 

southern part of the MTPRB assessment area. The coal bed 

was identified in 278 drill holes, has a maximum thickness 

of 34 ft and averages 8 ft (fig. 63). Depth ranges from shallow subcrop to about 2,000 ft in the Spring Creek Mine area; 

about 37 percent of the available coal resource is at a depth of 

less than 500 ft (fig. 64, table 8). The coal bed correlates with 

the Pawnee coal bed in the NWPRB assessment area (Scott 

and others, 2010). More than 23 percent of the available coal 

is considered a demonstrated resource (table 9). The coal 

resource reliability map for the Pawnee coal bed is shown in 

figure 65; about 62 percent of the available coal resource is 

owned by the Federal government (table 4).

Odell Coal Bed

The Odell coal bed is present in a small area in the southcentral part of the MTPRB assessment area. The coal bed was 

identified in 117 drill holes, has a maximum thickness of 14 ft, 

and averages 3 ft (fig. 66). Depth ranges from shallow subcrop 

to about 2,000 ft in the south-central part of the assessment 

area; about 16 percent of the available coal is at a depth of 

less than 500 ft (fig. 67, table 8). The Odell coal bed correlates with the Odell coal bed in the NWPRB assessment area 

(Scott and others, 2010). Only about 10 percent of the available coal is considered a demonstrated resource (table 9). The 

coal resource reliability map for the Odell coal bed is shown 

in figure 68; about 22 percent of the available coal resource is 

owned by the Federal government (table 4). 

Rosebud/Knobloch Coal Bed

The Rosebud/Knobloch coal bed is known as the Rosebud coal bed west of Rosebud Creek and as the Knobloch east 

of Rosebud Creek (fig. 69); it is one of the most significant 

coal beds in the MTPRB assessment area. Identified in 4,168 

drill holes, this coal is mined in the Rosebud, Absaloka, and 

Big Sky Mine areas where it has a maximum thickness of 72 ft 

and averages 15 ft thick (fig. 69). Some of the thickest coal is 

under the Custer National Forest (fig. 69). The Rosebud/Knobloch coal bed correlates to the Rosebud coal bed of Roberts 
30 Assessment of Coal Geology, Resources, and Reserves in the Montana Powder River Basin

and others (1999c). Depth ranges from shallow subcrop to 

about 2,000 ft along the south-central part of the assessment 

area; about 33 percent of the available coal resource is at a 

depth of less than 500 ft with an additional 30 percent between 

500–1,000 ft deep (fig. 70, table 8). The Rosebud/Knobloch 

coal bed is presently mined at both the Absaloka and Rosebud 

Mines. Approximately 27 percent of the available coal is considered a demonstrated resource (table 9). The coal resource 

reliability map for the Rosebud/Knobloch coal bed is shown 

in figure 71; about 50 percent of the available coal resource is 

owned by the Federal government (table 4). 

McKay/Nance Coal Bed

The McKay/Nance coal bed, known as the McKay coal 

bed west of Rosebud Creek and as the Nance east of Rosebud 

Creek, is present in the Rosebud, Absaloka, and Big Sky Mine 

areas (fig. 72) and merges into the Rosebud/Knobloch coal 

bed east of Ashland. This merging contributes to the greater 

thickness of the Rosebud/Knobloch in that area. As identified 

in 1,697 drill holes, maximum thickness is 30 ft and average 

thickness is 9 ft (fig. 72). It correlates with the McKay coal 

bed of Roberts and others (1999c). Because of a topographic 

high (Little Wolf Mountains), depth to the coal bed ranges 

from shallow subcrop to over 2,000 ft between the Absaloka and Big Sky Mines. About 44 percent of the available 

coal resource is at a depth of less than 500 ft, with an additional 22 percent at a depth of 500–1,000 ft (fig. 73, table 8). 

Approximately 39 percent of the available coal is considered 

a demonstrated resource (table 9). The coal resource reliability map for the McKay/Nance coal bed is shown in figure 74; 

about 43 percent of the available coal resource is owned by the 

Federal government (table 4).

Flowers-Goodale Coal Bed

Identified in 365 drill holes, the Flowers-Goodale coal 

bed underlies a large area in the southern half of the assessment area. Maximum thickness is 35 ft, and average thickness is 9 ft (fig. 75). Depth ranges from shallow subcrop to 

about 2,500 ft in the southwestern part of the assessment area; 

about 28 percent of the available coal resource is at a depth 

of less than 500 ft, with an additional 32 percent at a depth of 

500–1,000 ft deep (fig. 76, table 8). Approximately 21 percent 

of the available coal is considered a demonstrated resource 

(table 9). The coal resource reliability map for the FlowersGoodale coal bed is shown in figure 77; about 77 percent of 

the available coal resource is owned by the Federal government (table 4).

Robinson/Witham Coal Bed

The Robinson/Witham coal bed is known as the Robinson coal bed west of Rosebud Creek and as the Witham coal 

bed east of Rosebud Creek (fig. 78). The coal bed, identified in 

646 drill holes, has a maximum thickness of 37 ft and averages 

6 ft thick (fig. 78). The coal is also in a large area in the southcentral part of the MTPRB assessment area. The Robinson/

Witham correlates with the Robinson of Roberts and others 

(1999c). Because of a topographic high (Little Wolf Mountains), depth to the coal bed ranges from shallow subcrop 

to over 2,000 ft between the Absaloka and Big Sky Mines. 

About 49 percent of the available coal resource is at a depth 

of less than 500 ft with an additional 19 percent at a depth of 

500–1,000 ft deep (fig. 79, table 8). Approximately 41 percent 

of the available coal is considered a demonstrated resource 

(table 9). The coal resource reliability map for the Robinson/

Witham coal bed is shown in figure 80; about 38 percent of the 

available coal resource is owned by the Federal government 

(table 4). 

Roberts/Terret Coal Bed

Identified in 217 drill holes, the Roberts/Terret coal bed 

is present throughout much of the central part of the assessment area. This bed correlates with the Roberts coal bed in the 

NWPRB assessment area of Scott and other (2010), maximum 

thickness is 28 ft and average thickness is 5 ft (fig. 81). Depth 

of the Roberts/Terret coal bed ranges from shallow subcrop to 

over 2,500 ft; about 24 percent of the available coal resource is 

at a depth of less than 500 ft (fig. 82, table 8). Approximately 

19 percent of the available coal is considered a demonstrated 

resource (table 9). The coal resource reliability map for the 

Roberts/Terret bed is shown in figure 83; about 57 percent of 

the available coal resource is owned by the Federal government (table 4).

Assessment of Resources and 

Reserves

This assessment represents the most thorough evaluation 

of coal resources within the MTPRB assessment area in terms 

of both the number of data points interpreted and coal beds 

assessed. As a consequence, the total amount of coal resources 

assigned to the hypothetical reliability category is only about 2 

percent (table 9). 

In summary, a total of 26 coal beds, all in the Fort Union 

Formation were included in this assessment, 18 of which were 

modeled and evaluated to determine in-place coal resources 

(fig. 29). With no restrictions applied, the total original 

resource for these 18 beds was calculated to be about 215 

BST. Available coal resources, which are part of the original 

coal resource remaining after subtracting restrictions and areas 

of burned coal, were then calculated. Restrictions included 

railroads, federal interstate highways, urban areas, alluvial valley floors, state parks, national forests, and mined-out areas.

Figure 84 provides amount and percent of original 

coal resources by individual beds. Tables 4, 8, and 9 provide resource summaries based on ownership, overburden 
Assessment of Resources and Reserves 31

thickness, and reliability categories. About 7 BST (3 percent) 

of the total original coal resource was estimated to be burned 

(clinker) along the outcrop in the MTPRB, leaving a resource 

of 208 BST. Approximately 46 BST (22 percent) of the original resource is affected by restrictions (previously mined, too 

thin, land use, and technical). Subtraction of these restrictions 

from the 208 BST leaves about 162 BST (78 percent) of the 

original resource available for potential development in the 

MTPRB (tables 4, 8, 9).

Surface Coal Resource Results

Strip ratio maps were derived from overburden isopach 

maps of the 18 assessed beds. As displayed in the overburden maps of the Anderson, Dietz 2, and Dietz 3 (figs. 37, 40, 

43), as well as the overburden map of the Rosebud/Knobloch 

(fig. 70), the areas of least overburden thickness are near 

active coal mines. About 42 percent (87 BST) of the original 

resource is less than 500 ft deep; about 26 percent (55 BST) 

is between 500- and 1,000-ft depths; and about 10 percent 

(21 BST) is deeper than 2,000 ft (table 8). Coal resource reliability categories for the 18 beds are summarized in table 9. 

About 76 percent (159 BST) of the total original resources 

can be classified as measured, indicated or inferred, reflecting 

the overall substantial improvement in reliability confidence 

provided by the additional data included in this assessment. 

Coal ownership for the 18 beds is summarized in table 4. The 

majority of available coal resources, 132 BST (64 percent of 

the original), are owned by the federal government (table 4). 

Only about 4 percent (315 MST) is owned by the State of 

Montana, and about 11 percent (22 BST) is owned by private 

entities (table 4). 

It was determined that 10 of the 18 coal beds had sufficient areal extent and thickness to be further evaluated for 

recoverable resources. These are the Roland (Baker), Smith, 

Anderson, Dietz 2, Dietz 3, Canyon, Werner/Cook, Pawnee, 

Rosebud/Knobloch, and Flowers-Goodale, with a calculated total of 151 BST of the 162 BST of available resource 

(table 3). At a strip ratio of 10:1 or less, 39 BST remained 

of this total (table 2), and after mining and processing losses 

were also subtracted, only about 35 BST of coal were considered as a recoverable resource (table 2).

Surface Coal Reserve Results

The third and final phase in the assessment of the 

MTPRB was the economic evaluation of recoverable resources 

for the 10 coal beds listed above. Economically recoverable 

resources (reserves) were determined through economic 

analysis (see Appendix for detailed discussion of surface-mine 

models and assumptions). The present value of all mining 

expenditures over a project life at a rate of return (ROR) on 

investment is evaluated in a discounted cash flow calculation 

that yields a discounted cash flow rate of return. A breakeven 

cost per ton was calculated using the discounted cash flow and 

annual production rate. The portion of the recoverable coal 

that is economically minable at a cost that is at or below the 

current sales price of coal is designated as reserves.

The term “reserves” refers to that portion of the recoverable coal resource that can be mined at a profit at the time of 

the assessment; therefore, it was necessary to determine the 

freight on board (FOB) market price. Because the sale of coal 

is normally based on heating value, the determination of the 

average regional coal heating value for the MTPRB assessment area was required. On the basis of publically available 

data, an average heating value of 8,821 Btu/lb was derived. 

However, it should be emphasized that the large range in 

reported coal quality (tables 5-7) and the lack of specific data 

for every coal bed precluded development of a precise coal 

quality model. The November, 2011 FOB sales price for 8,800 

Btu/lb coal from the PRB was $13.20 per ton (Platts, 2011a).

Once an estimate of the sales price was determined, the 

final step in the economic evaluation was determining what 

portion of the resources could be considered coal reserves 

(total tons at or below the estimated sales price). To derive a 

reserve estimate for the MTPRB assessment area, a composite 

cost curve (fig. 85) was developed for the cumulative total 

recoverable resources from table 10; the breakeven costs utilized an 8 percent ROR. Using the $13.20 per ton FOB sales 

price, the coal reserve estimate for the MTPRB is about 13 

BST (figs. 86, 87). 

Reserve estimates are a constantly moving target, as sales 

prices continually fluctuate, responding to variations in market 

demand. For example, from June to December 2011, the price 

for 8,800 Btu/lb coal from the PRB has fluctuated from a low 

of $12.35 per ton to a high of $15.15 per ton (Platts, 2011b, 

2011c). As seen in the cost curve (fig. 85), the variation in 

price can change the reserve estimate significantly. 

The results of the MTPRB assessment area coal resources 

and reserves assessment by tonnages and percentages for the 

10 coal beds included in the economic evaluation are summarized in figures 86 and 87. The 35 BST of recoverable 

resources, which are only 23 percent of the original resource, 

represent the total estimated amount of coal that can be 

produced by surface-mining technologies (figs. 86, 87). The 

significant amount of coal affected by all the restrictions to 

mining and mining losses precludes recovery of all of the 

original in-place coal resources. Also, the volume of estimated 

coal reserves is a much smaller subset (9 percent) of the original resources than the total recoverable resources (35 percent). 

The relation of original resources to reserves is consistent with 

previous USGS coal assessments, which typically determine 

the reserve fraction to be less than 20 percent (Luppens and 

others, 2009).

As a basin matures through time with respect to the 

level of development, resources become progressively more 

expensive to produce. Sale prices generally increase over 

the long term and operating costs follow accordingly as 

long as demand is steady. Resources once considered to be 

subeconomic, may be elevated to the status of reserves with 

continued favorable sales prices as well as productivity and 
32 Assessment of Coal Geology, Resources, and Reserves in the Montana Powder River Basin Table 10 . Life-of-mine costs by strip ratio in the Montana Powder River Basin assessment area. (Costs based on a 20-year project life at an annual production rate of 10 million short tons per year. Costs reported for mid-calendar year 2010). Stripping ratio 1:1 2:1 3:1 4:1 5:1 6:1 7:1 8:1 9:1 10:1 Capital cost (millions of dollars) 267.8 318.3 346.1 390.0 423.6 455.2 507.0 576.8 685.3 721.3 Operation cost (millions of dollars) 1,076.8 1,288.1 1,818.5 2,259.3 2,687.2 2,875.8 3,660.4 4,129.0 4,430.5 4,942.8 Income (millions of dollars) 1,401.6 1,674.4 2,238.5 2,732.7 3,201.1 3,172.9 4,275.6 4,829.0 5,262.3 5,818.2 Total tons (millions) 200 200 200 200 200 200 200 200 200 200 Breakeven cost (dollars per short ton) $7.01 $8.37 $11.19 $13.66 $16.01 $18.63 $21.38 $24.14 $26.31 $29.09

technological advances in mining. Therefore, reserve studies 

should be considered a cyclic process and models should be 

adjusted periodically using the most recent data and reassessed 

using the most current recovery technology and economics.

Underground Coal Resource Results

A significant volume of coal resources in the MTPRB 

assessment area is contained in beds that are at considerable 

depth; no coal is being recovered by underground mining, nor 

expected to be in the near future. In as much as there may be 

underground recovery in the future, however, an underground 

evaluation was conducted to determine a rough estimate of the 

magnitude of underground resources.

The minable coal bed thickness for longwall systems is 

generally from 5 to 13 ft (Thomas, 2002). Although longwall 

shearers are commonly used for seam thicknesses between 5 

and 20 ft (Myszkowski and Paschedag, 2009), a 10-ft minimum 

was used as a more conservative estimate of potential underground resources for longwall operations. Deeper, in-place 

resource totals are listed in table 11 for coal beds with a 10-ft 

minimum thickness and a stripping ratio greater than 10:1. 

These include the same beds that were evaluated for surface 

minable deposits. No restrictions to mining were applied to the 

coal resources listed in table 11. Of the total of about 42 BST 

of underground tonnage, about 34 BST (80 percent) is within 

500–1,000 ft of the land surface and another 8 BST is 1,000–

2,000 ft beneath the land surface. 

As with other coal basins, only a fraction of the total 

underground resource is typically recoverable. Factors such as 

adverse roof and floor conditions, slope of the coal beds, and 

essential safety barriers between different mining operations, 

typically present restrictions to mining. Although recovery in 

multiple bed areas is generally most efficient by mining from 

the uppermost bed downward, that situation is extremely difficult to control. Additionally, interburden between beds must 

be thick enough to prevent interbed structural effects. None of 

these factors were used to develop the model of underground 

mining described in the Appendix. 

Underground Coal Reserves Results

Breakeven cost analysis was determined for potential 

underground coal reserves in the MTPRB assessment area in 

the same manner as described for surface coal reserves (see 

Appendix for detailed discussion of underground mine models 

and assumptions). The breakeven cost per ton was determined 

using the previously described longwall mine model. Four 

separate mine models were developed using either 10- or 20-ft 

coal thickness and either 1,000-or 2,000-ft depth (table 12). 

The overall capital cost for mining 6 MST of coal for 20 years, 

based on a 10-ft-thick bed at a depth of 1,000 ft, was estimated 

at $386 million, with $3,218 million in operating cost (table 

12, Case 1). The breakeven cost per ton was calculated to be 

$30.94 (table 12). The cost per ton decreases slightly as thickness increases to 20 ft (table 12, Cases 2 and 4).
Table 11. Underground resources in beds at least 10 feet thick and a strip ratio of greater than 10:1, in the Montana Powder River Basin assessment area.—Continued

Coal bed name Depth (feet) Underground tonnage (millions of short tons) Acreage (acres) Average thickness (feet)

Anderson

500–1,000 897 21,239 24

1,000–2,000 0 0 222,000–3,000 0 0 0

>3,000 0 0 0

Total 897 21,239 Not applicable

Dietz 2

500–1,000 123 4,527 15

1,000–2,000 0 0 02,000–3,000 0 0 0

>3,000 0 0 0

Total 123 4,527 Not applicable

Dietz 3

500–1,000 754 23,992 18

1,000–2,000 6 271 132,000–3,000 0 0 0

>3,000 0 0 0

Total 760 24,263 Not applicable

Canyon

500–1,000 4,163 134,495 17

1,000–2,000 70 2,463 162,000–3,000 0 0 0

>3,000 0 0 0

Total 4,233 136,958 Not applicable
Table 11. Underground resources in beds at least 10 feet thick and a strip ratio of greater than 10:1, in the Montana Powder River Basin assessment area.—Continued Coal bed name Depth (feet) Underground tonnage (millions of short tons) Acreage (acres) Average thickness (feet) Lower Canyon 500–1,000 2,408 98,199 14 1,000–2,000 119 5,427 12 2,000–3,000 0 0 0 >3,000 0 0 0 Total 2,527 103,626 Not applicable Werner/Cook 500–1,000 6,963 147,873 27 1,000–2,000 39 1,538 14 2,000–3,000 0 0 0 >3,000 0 0 0 Total 7,002 149,411 Not applicable Pawnee 500–1,000 1,855 66,247 16 1,000–2,000 639 29,981 12 2,000–3,000 0 0 0 >3,000 0 0 0 Total 2,494 96,228 Not applicable Rosebud/Knobloch 500–1,000 10,271 279,220 21 1,000–2,000 1,251 42,354 17 2,000–3,000 0 0 0 >3,000 0 0 0 Total 11,522 321,574 Not applicable Flowers-Goodale 500–1,000 6,468 225,224 16 1,000–2,000 5,854 225,587 15 2,000–3,000 3 145 0 >3,000 0 0 0

Total 12,325 450,956 Not applicable

Total

500–1,000 33,902 1,001,016 Not applicable

1,000–2,000 7,978 307,621 Not applicable2,000–3,000 3 145 Not applicable

>3,000 0 0 Not applicable

Total 41,882 1,405,010 Not applicable
References Cited 35

Table 12. Costs by underground mining case for the Montana Powder River Basin assessment area based on 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.

Case 1 Case 2 Case 3 Case 4

Mining height (feet) 10 20 10 20

Depth (feet) 1,000 1,000 2,000 2,000

Capital cost (millions of dollars) 385.6 375.9 408.6 400.9

Depreciation (millions of dollars) 167.9 164.7 172.7 168.9

Operation cost (millions of dollars) 3,218.5 3,166.8 3,276.2 3,227.3

Breakeven cost (dollars per short ton) $30.94 $30.40 $31.69 $31.20

Conclusions

The MTPRB is the last of four coal resource and reserve 

assessment reports within the Powder River Basin, Wyoming 

and Montana. A total of 26 coal beds were identified during 

this assessment, 18 of which were modeled and evaluated 

to determine in-place coal resources. The total original coal 

resource in the Montana Powder River Basin assessment area 

for the 18 coal beds assessed, with no restrictions applied, 

was calculated to be 215 BST. Available coal resources, which 

are part of the original coal resource remaining after subtracting restrictions and areas of burned coal, are about 162 BST. 

Restrictions included railroads, federal interstate highways, 

urban areas, alluvial valley floors, state parks, national forests, 

and previously mined areas.

Ten of the 18 coal beds each had sufficient areal extent 

and thickness to be evaluated for recoverable resources 

(Roland (Baker), Smith, Anderson, Dietz 2, Dietz 3, Canyon, 

Werner/Cook, Pawnee, Rosebud/Knobloch, and FlowersGoodale). These beds totaled about 151 BST of the 162 BST of 

available resource. At a strip ratio of 10:1 or less, only 39 BST 

remained of the available resource of 151 BST. After mining 

and processing losses were subtracted from the 39 BST, 35 

BST of coal were considered as a recoverable resource. Coal 

reserves (economically recoverable coal) are the portion of the 

recoverable coal resource that can be mined, processed, and 

marketed at a profit at the time of the economic evaluation. The 

coal reserves estimate for the 10 coal beds evaluated for the 

Montana Powder River assessment area is 13 BST.

About 42 BST of underground resource exists in the 

assessment area; about 34 BST (80 percent) are at depths 500–

1,000 ft and another 8 BST are at depths 1,000–2,000 ft. Breakeven cost analysis was determined for potential underground 

coal reserves in the MTPRB assessment area, using a longwall 

mine model. Four separate mine models were developed using 

both 10- and 20-ft coal thicknesses and either 1,000- or 2,000-ft 

depths. The overall capital cost for mining 6 MST of coal for 20 

years, based on a 10-ft-thick bed at a depth of 1,000 ft, was estimated at $386 million, with $3,218 million in operating cost. 

The breakeven cost per ton was calculated to be $30.94. The 

cost per ton decreases slightly as thickness increases to 20 ft.

Acknowledgments

This report was produced as a result of the efforts 

and cooperation of many people. Ed Heffern, U.S. Bureau 

of Land Management in Cheyenne, Wyoming, supplied 

the digital files that show the extent of clinker within the 

Montana Powder River Basin assessment area. Tim Grant, 

National Energy Technology Laboratory, U.S. Department 

of Energy; and Carol Molnia, Dick Keefer, and Margaret 

Ellis, all of the USGS, provided technical reviews of the 

manuscript.

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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 resources are remaining coal resources 

that are thick and shallow enough to be mined by either 

surface or underground methods and that are unencumbered by land use, environmental, societal, regulatory, 

or technologic restrictions as they may apply in a specific State or region (Carter and Gardner, 1989). 

• Clinker material 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 
40 Assessment of Coal Geology, Resources, and Reserves in the Montana Powder River Basin

and amounts that economic extraction is currently or 

potentially feasible (Wood and others, 1983). 

• Demonstrated resource is a term commonly used for 

the sum of coal classified as measured and indicated 

resources (Wood and others, 1983).

• Dip (dipping) is the angle at which a bed, stratum, or 

vein is inclined from the horizontal (Thrush, and the 

staff of the Bureau of Mines, 1968). 

• Discounted cash flow is the stream of the net aftertax cash flows where the cash outlays include all 

operating costs, taxes, and investment costs, and 

where revenues include cash payments of product 

sales (Association for the Advancement of Cost Engineering, 1997).

• Freight on Board (FOB) is a reference to the place 

where purchased goods will be shipped without transportation charge.

• 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). 

• 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 (Wood 

and others, 1983).

• 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). 

• 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). 

• 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 (Wood and others, 1983).

• 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 (Wood 

and others, 1983).

• Interburden is the rock between two coal beds. When 

two potentially minable coal beds occur within a minimum acceptable distance above or below on another, 

one will not be mined–often the thinner of the two 

(Carter and Gardner, 1989). 

• 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 (Wood and 

others, 1983).

• Original coal resource is the total amount of coal 

in-place 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 is used to classify the 

depth to an underlying coal bed (Wood and others, 

1983). 

• Outcrop is that part of a rock formation (coal bed) that 

appears at the surface of the ground (Thrush, 1968).

• Parting is a thin layer of stratum or noncoaly material 

within a coal bed that 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 from a deposit. 

• Rate of return (ROR) is the ratio of money gained or 

lost relative to the amount of money invested (Association for the Advancement of Cost Engineering, 

1999).

• 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). 
Modeling Stratigraphic Sequence for Mining 41

• Remaining resources represent resources in the 

ground after subtracting coal that has been previously 

mined from the original resource (Carter and Gardner, 

1989).

• Restrictions to mining include land use restrictions, 

technical limitations, and unsuitability criteria that 

would prohibit mining, as defined below:

• 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, some 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 specific legal 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.

• Strip (stripping) ratio 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) (Thrush, 

1968).

• Surface (strip) mining is mining at or near the 

ground surface and is generally done where the overburden can be removed economically. A strip mine is 

a surface mine in which the overburden is removed 

from a coalbed before the coal is removed (Thrush, 

1968).

• Tailgate is the secondary roadway access or egress 

from a longwall face and through which return air 

flows (SME, 1992). 

Appendix

Modeling Stratigraphic Sequence for 

Mining

Mine models in the MTPRB assessment area differ 

from those used in the Wyoming Powder River Basin in 

two respects. First, the coal bed thicknesses in the MTPRB 

assessment area are more variable than in the NWPRB 

assessment area of Wyoming (Scott and others, 2010). 

Also, areas of thicker coal (greater than 20 ft thick) are 

more pod-like as illustrated by the isopach maps of the 

Dietz 3, Canyon, Lower Canyon, Werner/Cook, Pawnee, 

and Flowers-Goodale coal beds (figs. 42, 45, 48, 54, 63, 

75). Second, deeply-dissected drainages limit the areal 

extent of shallow surface minable coal beds in the MTPRB 

assessment area. Cross sections A–A’ and B–B’ (figs. 21 

and 22) as well as the overburden map for the Werner/

Cook coal bed (fig. 55) illustrate the impacts of the surface 

morphology. Areas where these coal beds are less than 

250 ft deep are in many places limited to relatively narrow 

bands along the drainages.

To simplify the development of a MTPRB assessment 

area regional mining model and keep it as realistic as possible, a representative model-bed section was developed 

based on approximate average thicknesses of 5 coal beds: 

Roland (Baker), Smith, Anderson, Dietz 2, and Dietz 3 

(table 13). The first coal bed is modeled at the 1:1strip 

ratio; additional coal beds are added for ratios from 2:1 

through the 4:1. To help simplify the models, interburden thicknesses remain relatively constant and additional 

overburden is increased for the 5:1+ ratio models. The 

combined stripping ratio map for the regional mining 

model stratigraphic sequence was performed on stripping 

ratios from 1:1 to 10: 1. The coal bed and overburden 

thicknesses used in the model are based on average values 

in the southwestern portion of the MTPRB. An additional 

coal bed is added to each stripping ratio increment up to 

the 5:1 ratio. From stripping ratios of 6:1 to 10:1, the coal 

bed and interburden thicknesses are fixed and overburden 

was added above the uppermost coal bed to arrive at higher 

ratio increments. Three key parameters––coal production, 

stripping ratio, and rate of return (ROR)––were evaluated 

as to their effect on the breakeven price per ton for mining 

coal. The breakeven cost per ton at an 8 percent ROR and 

resource volume for 1:1 to 10:1 stripping ratios are shown 

in table 10. The costs per ton vary from $7.01 at a 1:1 ratio 

to $29.09 at a 10:1 ratio (table 10).

In addition to the regional mining model sequence, the 

Canyon, Werner/Cook, Pawnee, Rosebud/Knobloch, and 

Flowers-Goodale coal beds were evaluated for reserve potential. The stripping ratio maps for these coal beds are shown 

in figures 9-13. The individual coal bed stripping ratio maps 

demonstrate the relation between the deeply-dissected surface 
42 Assessment of Coal Geology, Resources, and Reserves in the Montana Powder River Basin

morphology and coal thickness. A comparison of the isopach 

map and stripping ratio map for a given bed illustrates this 

relation. For example, the more extensive area of less than 

a 10:1 ratio in R. 39 E. to R. 41 E. for the Werner/Cook bed 

(fig. 10) corresponds to the thickest portion of the Werner/

Cook bed (fig. 54). Elsewhere, the less than 10:1 ratio areas 

for the thinner portions of the Werner/Cook bed are confined 

to narrow bands along drainages.

Surface Mine Model Design

The surface mine model is based on a minimal level 

of project definition, which is indicative of a pre-feasibility level of cost estimation. Thicknesses of overburden, 

coal, and interburden are known through geologic modeling of the basin resources. Variations in coal quality, minor 

disruptions in continuity, groundwater characteristics, and 

overburden characteristics, among other localized factors, 

are less well known. The surface mine model represents a 

simplified multiple coal-bed sequence that is continuously 

excavated in a top-to-bottom and lengthwise configuration 

at an overall rate that attains an annual rate of coal production. All strata are assumed to be near horizontal in this 

mine model.

Stripping and Coal Mining

The surface mine model includes an elongated strip pit 

with highwall, spoil piles, and multiple coal beds. Overburden 

is drilled and blasted before loading and is deposited in spoil 

piles. The top of the coal is cleared of remaining overburden 

debris and is ripped and stockpiled for loading. Stockpiled 

coal in the pit is hauled to a dump facility in the mine plant 

area.

Equipment for overburden and interburden stripping 

and coal loading and hauling is sized for a 10-millionshort-ton-per-year coal mining operation lasting 20 years, 

which is consistent with previous assessments in the PRB. 

Shovel loading and rear dump-truck haulage is used to provide a common basis for the comparative modeling results 

produced in this assessment. Stripping shovels are sized 

for operating 24 hours per day and 365 days per year, and 

coal-loading shovels are designed for operating 20 hours 

per day and 350 days per year. An equipment availability 

of 89 percent is applied to both functions, whereas stripping is allowed 95 percent equipment use, and coal loading 

85 percent equipment use. Stripping and coal loading 

shovels range from 15 to 60 cubic yards in bucket capacity, 

and the production rate of each unit yields 10 million tons 

of coal annually. Mining support equipment is included 

for haul-road maintenance, night illumination, in-pit water 

handling, and transportation for production supervisors and 

associated personnel. The total mining and direct support 

equipment cost is estimated at $62.7 million for the 1:1 

stripping ratio case and $206.5 million for the 10:1 stripTable 13.

ping ratio case.

Regional mining model stratigraphic sequence used in the economic evaluation of the Montana Powder River Basin assessment area.

Coal bed Burden and average thickness totals (feet) Stripping ratio 1:1 2:1 3:1 4:1 5:1 6:1 7:1 8:1 9:1 10:1

Roland (Baker) Average burden thickness 93 183 272 360 450 540

Average thickness 9 9 9 9 9 9

Smith Average burden thickness 115 149 149 149 149 149 149

Average thickness 11 11 11 11 11 11 11

Anderson Average burden thickness 112 112 112 112 112 112 112 112

Average thickness 29 29 29 29 29 29 29 29

Dietz 2 Average burden thickness 41 60 60 60 60 60 60 60 69

Average thickness 15 15 15 15 15 15 15 15 15

Dietz 3 Average burden thickness 21 32 32 32 32 32 32 32 32 32

Average thickness 19 19 19 19 19 19 19 19 19 19

Totals

Total coal 19 34 63 74 83 83 83 83 83 83Total burden 21 73 204 319 446 536 625 713 803 893
Modeling Stratigraphic Sequence for Mining 43

Calculations for the Rosebud/Knobloch single coal bed are 

greatly simplified. Only a single overburden and a single coal 

bed are considered whereas the removal of each burden and coal 

stratum in the multiple coal bed sequence must be at individual 

rates that provide for the overall removal at the predetermined 

production rate of 10 million tons per year in this assessment.

Mine Plant Facilities

The mine plant contains those facilities essential for supporting mining, such as buildings, coal-handling equipment 

and structures, truck dump facility, rail-loading facilities, and 

mobile and stationary equipment. The mine model contains 

several functions, such as providing for administration building, change house, maintenance shop, warehouse, laboratory 

building, emergency building, utility building, guard house 

and tool sheds.

This assessment includes several mining cases (stripping 

ratios of 1:1 to 10:1) for which different space requirements 

are anticipated, and the buildings are sized accordingly. Coal 

handling at the mine plant includes truck scales, inclined and 

horizontal belt conveyors, stacking tubes, scalping screen, coal 

breaker, coal silo, belt sampler, belt scales, railcar mover, and 

associated equipment. The mine plant also includes multiple 

elevated steel structures, enclosures, and concrete foundations. 

Preliminary designs for a truck dump to accommodate a wide 

range of large rear-dump truck capacities and a railroad loop 

were prepared, from which unit costing was performed. The 

typical model mine plant cost of $20 million was calculated 

for all case studies, which included estimated costs for the following items:

• $5 million for land improvements

• $1 million for buildings 

• $5 million for coal handling equipment and structures

• $1 million for truck dump

• $2 million for railroad loop and access 

• $2 million for miscellaneous structures

• $4 million for mobile and stationary equipment

Reclamation

Reclamation is an additional ongoing function and a 

major costing center in the surface mine model. A fleet of 

earthmoving and farm-type equipment perform a variety of 

activities from removal of brush and topsoil through contouring spoil piles, seed bed preparation, and planting. 

Supplies and Utilities

Additional costing items in the surface mine model 

include equipment operating items, personnel wages, supplies (explosives, mulch, and seed) and utilities (electricity 

and natural gas/propane). The total annual operating cost is 

estimated at $54 million for the 1:1 strip ratio case and $247 

million for the 10:1 case.

Underground Mine Model Design

Thick, deep, coal beds throughout the MTPRB provide 

potential mining targets for which surface mining may not be 

economic. No underground mines are operating in the PRB as 

discussed in the NWPRB assessment area (Scott and others, 

2010) and the SWPRB assessment area (Osmonson and others, 2011). For each assessment, a separate underground mine 

model was developed; the NWPRB model was based on a 

production rate of 11 MST per year, and the SWPRB assessment area model was based on a production rate of 6 MST 

per year. The SWPRB assessment expanded the scope of the 

NWPRB assessment by considering the effects of thickness 

and depth. This assessment further refines economic analysis 

of the MTPRB assessment area by including potential overall 

coal recovery with thickness and depth.

The preliminary underground mine model provides a 

reasonable estimate of the economic tipping point where 

underground mining might be a more viable alternative to surface mining, which, in turn, establishes a limit on recoverable 

resources by surface mining.

Potential underground coal reserves in the MTPRB 

assessment area were evaluated using a conventional, single 

pass, continuous, longwall methodology. Face shearer and roof 

support design are available for mining a bed up to 20 ft thick, 

which is not an uncommon thickness in portions of the PRB. A 

mining model that was developed for the SWPRB assessment 

area was used in the MTPRB assessment area to determine 

potential reserves.

Mine Layout Design

The underground mine model incorporates longwall technology that includes four distinct primary components: surface 

mine plant, underground mine plant, development excavation, 

and longwall panel. All openings, support pillars, and longwall 

panel dimensions are sized to provide an annual production 

level of about 6 MST of coal per year, which is an average size 

for operating longwall mines. This average annual production 

is acquired through development, production, and pillar recovery operations. The model can be used to evaluate mining 

thicknesses that vary from 8–20 ft and depths from 500 ft to 

as much as 3,000 ft. The model can also 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 
44 Assessment of Coal Geology, Resources, and Reserves in the Montana Powder River Basin

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 14.

All mains, headgate, and tailgate entries are 10-ft high 

in the base case. 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 and headgate and 16-ft wide for the tailgate. Pillars in the mains are 65 ft by 85 ft and the chain pillars 

in the headgate and tailgate are 65 ft 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 of production 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; the panel length is adjusted to provide the overall annual production from entries, panel, and pillars. 

Surface Mine Plant

Coal handling facilities are the primary purpose of the 

surface mine plant. The surface mine plant for the underground mine are those facilities essential for supporting 

mining, including buildings, coal handling equipment, rail 

loading facilities, and mobile and stationary equipment. The 

mine-model surface plant includes an administration building, 

change house, maintenance shop, warehouse, laboratory building, emergency building, utility building, guard house and 

tool sheds, and hoisting and ventilation facilities to support 

underground operations. 

Other facilities include a stacking tube, horizontal and 

inclined belt conveyors, scalping screens, coal breaker, 

coal silo, waste bin, rail loadout structure, rail loop, various 

elevated steel structures and housings, preparation plant, and 

concrete foundations. The inclined belt conveyor is included 

with the surface mine plant whereas the excavation for the 

incline is included with the underground mine plant. All stationary coal handling facilities are oversized to move in excess 

of the 6 MST annual production rate.

Hoisting facilities are included in the surface mine 

plant and shaft excavation and furnishing are included in 

the underground mine plant component of the mine model. 

Hoisting facilities are detailed for a single, vertical, 24-ftdiameter men-and-materials shaft. The primary mine hoist is 

sized to lower and raise about 317 mining, mining support, 

and technical support personnel working on a two-shift-perday basis. The hoisting plant might typically include a 110-ft 

high open steel headframe with a 12-ft-diameter head sheave, 

a 10-ft-diameter double-drum, single-clutch hoist, 15⁄8-inchdiameter steel hoisting ropes, a 70-man-capacity double-deck 

mancage, and a 12-ton counterweight. An additional 80-inchdiameter emergency hoist with 3⁄4-inch-diameter steel 

hoisting rope, head sheave, and escape capsule are included 

in the hoisting plant as well. One dedicated ventilation shaft 

is included in the mine plant but hoisting facilities for it are 

not provided.

Ventilation facilities include two 10 ft-diameter, 

800-horsepower surface mine fans, ducting, concrete foundation, electrical controls and switchgear, and appropriate 

enclosures. These facilities are provided for a 24-ft-diameter 

vertical shaft.

Underground Mine Plant

Three excavations (men-and-materials shaft, ventilation 

shaft, and ramp) connect surface and underground mine plants 

at the surface to the underground. A nominal depth of 1,000 ft 

has been used for shafts and an inclined length of 2,280 ft for 

a ramp. Both shafts are excavated with large-diameter drilling equipment and lined with 2 ft of concrete. Both shafts are 

equipped with wall brackets to support one 4-inch-diameter 

and one 8-inch-diameter steel pipeline, one 15kV/500MCM 

insulated electrical power cable, and a small communications 

Table 14. Underground excavation dimensions in the longwall mining model for a 10 feet 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
Modeling Stratigraphic Sequence for Mining 45

cable. The men-and-materials shaft also includes steel buntons 

with landings, steel ladders, and timber mancage guides. The 

ramp is excavated with a continuous mining machine and 

lined with rock bolts, wire mesh, and shotcrete.

Primary excavations at the bottom of the underground 

mine plant at the men-and-materials shaft include a warehouse, 

shop, lunchroom, refuge chambers, water sump, electrical 

substation, and connecting runaround access way. The bottom 

of the ramp is located some distance away and has excavations 

for refuge chambers, electrical substation, and runabout access 

way. Both the shaft and ramp stations are lighted with 100-, 

400-, and 1,000-watt fixtures. Stationary equipment in the shaft 

station includes four 100psi/490cfm air compressors and ten 

500gpm/200 ft head centrifugal water pumps. Both the shaft 

and ramp stations include concrete flooring, steel equipment 

bases, and 5kV/4/0 electrical cable distribution.

Fresh air provided by surface fans supplies the secondary 

air distribution using 36-inch-diameter, rigid ventilation ducts, 

which are boosted with 14,000 cfm ventilation fans. This secondary system is used throughout the underground mine.

Development Excavation

Underground excavation that extends some distance 

beyond the shaft and ramp stations is completed prior to 

production mining as described for the production unit section 

of this assessment and is performed as a construction activity. 

Coal removed during this project phase is transported to the 

surface and disposed as a waste product. 

Development excavation includes five parallel headings 

with connecting crosscut openings. These headings extend 

approximately 1,300 ft to the edge of the mine plant barrier 

pillar. This barrier pillar is sufficiently sized in order for underground mine plant facilities to be protected from structural 

instability because of mining production. About 15,000 ft of 

equivalent primary openings are excavated during this phase, 

including 6,500 ft of main access way, 6,800 ft of crosscuts, 

and 1,700 ft of other equivalent openings. All excavation 

during this phase is performed by a continuous miner and supporting mobile equipment.

Production Unit

The production unit is generally centered near the longwall panel. All pre-longwall mining following development 

excavation is considered production and not development. The 

production unit includes the main access way extending from 

the initial development excavation, gateway excavation, longwall opening, and longwall panel. The normalized production 

unit includes 1,836 ft of main access-way development. Each 

opening is 24-ft wide with 18-ft-wide crosscuts located on 

103-ft center- lines. Five access-way headings are excavated 

on 109-ft center-lines. 

Gateway excavation starts at the main access way and 

extends to the full length of the longwall panel. A three-entry 

arrangement is developed for the headgate and two entries for 

the tailgate. Headgate openings are 18 ft wide with 18-ft-wide 

crosscut connections, which are placed on 178-ft center lines. 

Tailgate openings are designed as 16-ft openings with 16-ftcrosscut connections on 176-ft center lines. A single longwall 

opening is excavated to connect the ends of the gateways. This 

opening is 18 ft wide and exposes the initial longwall face. 

A longwall panel that is 1,000 ft wide and 14,571 ft long is 

included in the underground mine-model design. This panel 

size is estimated to provide sufficient coal for a continuous year 

of operation without moving to a new area. A complete suite of 

standard equipment is included in the model (face shearer, roof 

supports, armored face conveyor, and supporting systems).

Pillar Recovery

Pillar recovery provides substantial coal production as 

a final activity in the typical production unit. This operation 

involves enough removal of a single pillar mass to provide 

a sufficient amount of coal production without collapsing 

the immediate roof area during the activity. Pillar recovery 

is included in the underground coal mining model for chain 

pillars, panel barrier, and main access pillars for the typical 

longwall unit.

High vertical stresses are applied to the lateral edges of 

the longwall panel as the shearer cuts across the face of the 

longwall and progresses toward the end of the panel. These 

stresses tend to concentrate over the rib line of the opening 

adjacent to the panel. The forward edge of the first row of 

support pillars in the gateways on either side of the panel, are 

expected to partially collapse. This collapse is likely to cause 

a yield zone that extends some distance into the pillar interior. 

The remaining portion of the pillar not collapsed is expected 

to be competent enough to allow significant recovery by a continuous miner. The vertical stress concentration over the outer 

pillar line in the headgate should be less than the stress over 

the longwall panel periphery, and a higher pillar extraction rate 

can be expected. 

All the material on the panel side of the barrier pillar 

is expected to be coal waste. Pillar recovery will need to be 

conducted from the main access way. Excavation of the barrier 

pillar will be conducted together with main access-way pillar 

recovery. Recovery will be partial, in order to leave sufficient 

natural support for retreating from the area.

Surface Mine Model Economic Evaluation

Economic analysis was performed on near-surface 

coal resources as shown in table 10 to determine the reserve 

potential in the MTPRB assessment area. The surface mine 

model was used to demonstrate how coal delineated in the 

generalized model in table 10 can be mined. The surface 

mine model has also been used to calculate the breakeven 

cost per ton, which is the total mining cost divided by the 

total number of tons mined. A cost estimate for mining that 

is below the breakeven cost is potentially profitable, and a 
46 Assessment of Coal Geology, Resources, and Reserves in the Montana Powder River Basin

mining cost above the breakeven cost is not. The breakeven 

cost is calculated from the total expenditures for a 20-year 

time period. A net present value analysis based on discounted 

capital and operating expenditures is used to calculate the 

breakeven cost, as explained in the Net Present Value and 

discounted Cash Flow Rate of Return Analyses section of 

this report.

Preliminary economic modeling of single seam scenarios indicated results that were closely similar to that of 

the regional mining model. Therefore, the breakeven costs 

in table 10 for the regional mining model were also applied 

to the single bed models. This simplification facilitated the 

reserve analysis by requiring the development of only one 

cost curve. 

Net Present Value and Discounted Cash Flow 

Rate of Return Analyses

Discounted Cash Flow Rate of Return (DCFROR) is 

most commonly used in industry to determine the profitability 

of an investment. Cash flow (the difference between price 

and cost or income and investment) is calculated for each 

economic period throughout a project life. For a coal-minemodel economic evaluation, cash flows are determined for 

each year of a 20-year mine life. The present values of these 

cash flows are calculated for both the surface and underground mine models. Future values may also be calculated 

without any apparent advantage but present value analysis 

is the convention adopted for this assessment. As relatively 

large expenditures are incurred throughout a typical mine 

life, the effect of these expenditures directly affect the overall 

mine cost by the value of those expenditures in terms of 

current or present dollar values. A dollar spent tomorrow is 

assumed to be less in value than one spent today. The future 

expenditures are, thereby, discounted to 2012 dollar values. 

DCFROR calculations include the original cost to bring a 

mine into operation, discounted expenditures made during the 

mine life, discounted cash flows for each productive year, and 

the salvage cost at the end of the project. Known parameters 

in DCFROR calculations are expenditures for capital items, 

ongoing costs to produce coal, an interest rate, and the mine 

life. The rate of return, which is unknown and determined by 

the calculation, is the measure of profitability.

DCFROR calculations may include either constant or 

escalated dollar values but not both. Escalated dollar values 

were used for the economic evaluations. Equipment, various major supply items, and utilities are known to increase 

and decrease in cost at different rates with time. Escalated or 

current dollar values are actual revenues or costs that will be 

incurred at specific points in time and more applicable with the 

method of analysis used for the coal mine model. 

Net Present Value (NPV) analysis is used in determining 

the potential reserves for the MTPRB, as income (sales price 

times tons mined) is not known or fixed. An arbitrary interest 

rate of 8 percent is used as the annual compounding rate (T.K. 

Lee, written commun., 2004) for a 20-year time period. NPV 

analysis provides a means by which a profit or loss sales price 

(equivalent to the breakeven cost) can be determined. This 

calculation is possible as the rate of return in the DCFROR 

calculation is set at zero and all capital expenditures and 

income from salvage are discounted to present values; the 

net present value is the sum of these discounted amounts. 

The capital cost NPV is set equal to the unknown cash flow 

NPV, so that overall capital cost is equal to the overall cash 

flow. The calculated tax is removed from the NPV cash flow 

and the NPV operating costs are added to produce the desired 

income to pay for all the expense and yield a desired rate of 

return (8 percent).

Capital Cost

The purchase and replacement costs for capital items are 

determined for each stripping ratio case. Capital items include 

mining and process equipment; engineering, laboratory, and 

other technical equipment; light and medium trucks; land 

improvements; buildings; reclamation; and other mobile and 

stationary equipment.

The total direct capital investment for equipment and 

facilities is applied as a single expense at the initial point in 

time (project year 0), which for this evaluation is calendar 

year 2011. Additional capital investments are made during 

the 5th, 7th, 10th, and 14th year for a 15-year project life to 

replace obsolete and worn-out equipment. Additional multiples of 5, 7, and 10-year equipment replacements are added 

as appropriate for project or mine lives extending to 20-year 

duration. Capital reinvestment is generally performed for 

equipment as certain land improvements are not replaced 

until the 15th year, and buildings continue service for the life 

of the mine.

Salvage value has been determined for this economic 

evaluation. Salvage adds income as the unused value of a 

capital asset less a market adjustment is deducted from the NPV 

of capital expenditure. The value of salvage is generally discounted in overview calculations such as this, because of to its 

lessened effect for long project lives. A dollar spent and returned 

today will be worth a dollar, whereas it will only have a value of 

21¢ after 20 years (calculated at 8 percent interest rate). 

Capital depreciation is determined by placing appropriate costs in the class life designations specified for tax 

calculations that are based on Internal Revenue Service (IRS) 

guidelines as set forth in Publication 946 of the Department 

of the Treasury (2008). The tax class life designations are 

3, 5, 7, 15, 20, and 39 years for mining-related activities. 

Depreciation options are available. Capital items are depreciated as quickly as possible in this evaluation. The first 

three designations (costs specified for 3, 5, and 7 years) are 

depreciated using the 200 percent declining balance method. 

Other class life designations use a 150 percent declining balance method for 15 and 20 years and straight-line method for 

39 years. Annual depreciation amounts for each of the class 

life designations are calculated using standard percentages 

provided in the Modified Accelerated Cost Recovery System 
Modeling Stratigraphic Sequence for Mining 47

(MACRS) General Depreciation System (GDS) for each year 

of the 20-year mine life (Department of the Treasury, 2008). 

The depreciable amount for each year of the project life is 

discounted to a net present value.

Other initial expenditures are made for capital items that 

do not fall within the direct capital cost category. These are 

indirect capital costs. These initial expenditures can include 

lease acquisition, engineering, home office overhead when 

applicable, licenses, fees, patents, and miscellaneous items. 

Both tangible and non-tangible items may be included. Tangible indirect costs are depreciable and non-tangible items are 

amortized in accordance with IRS guidelines (Department of 

the Treasury, 2008). An amount of 8 percent of direct capital 

costs has been included in this evaluation; amortization and 

working capital are excluded.

Operating Cost

Operating costs including personnel, equipment maintenance and fluids, supplies, and utilities are calculated as 

annual expenses. Supplies include explosive and accessory use 

in stripping, and seed mixture in reclamation. Utilities include 

the local power charge for electricity and natural gas/propane 

for heating buildings.

Breakeven Cost Determination

Breakeven cost calculation is performed upon the 

total capital cost discounted to present value as previously 

described, depreciation, and operating costs to yield the 

required income to produce these values. This income, which 

is determined at net present value, is divided by the total calculated production throughout the mine life to give the average cost per ton or the pivot point for potential profitability. 

This breakeven cost per ton has been calculated for stripping 

ratio cases from 1:1 to 10:1 as shown in table 10.
48 Assessment of Coal Geology, Resources, and Reserves in the Montana Powder River Basin

106o 104o

MONTANA

WYOMING

Broadus

Washakie

Johnson

Natrona

Converse

Niobrara

Weston

Crook Campbell

Sheridan

Big Horn

Powder River

Carter

Fallon Rosebud

Treasure

Custer

Big Horn

Musselshell

Yellowstone

Fremont

Hot Springs

Glenrock

Sheridan

Buffalo

Gillette

Decker

Birney

Miles City

Douglas

Moorcroft

Forsyth

43o

44o

46o

45o

o

108

Lame

Deer

90

90

94

25

Powder River Basin

(Tertiary limit)

EXPLANATION

Main railroad lines

County line

Northern Wyoming Powder

River Basin assessment area

Gillette coal field

Southwestern Powder

River Basin assessment area

Montana Powder River

Basin assessment area

Interstate highways

INDEX MAP

Wyoming

Montana

Powder River Basin

Indian reservations

City or town

90

Colstrip

Ashland

Custer

MILES

KILOMETERS

0 20 40

0 20 40 60

Platte

Figure 1. Locations of the Montana Powder River Basin assessment area, Montana, Northern Wyoming Powder River Basin 

assessment area, Wyoming, (Scott and others, 2010), Southwestern Powder River Basin assessment area, Wyoming, (Osmonson and 

others, 2011), and the Gillette coal field, Wyoming (Luppens and others, 2008).
T

TT

TTT

T

T

T

R. 35 E. R. 36 E. R. 37 E. R. 38 E. R. 39 E. R. 40 E. R. 41 E. R. 42 E. R. 43 E. R. 44 E. R. 45 E. R. 46 E. R. 47 E. R. 48 E. R. 49 E. R. 50 E. R. 51 E. R. 52 E. R. 53 E. R. 54 E. R. 55 E. R. 56 E. R. 57 E.

Custer County

Rosebud County

Treasure County

Big Horn County

Powder River County

Fallon County

Carter County

Lame Deer

Miles City

Forsyth

Broadus

Decker

Birney

Colstrip

Crow Agency

Lodge Grass

Northward Extension of

Big Sky Mine

Spring Creek Mine

Absaloka Mine

Decker Mines(east, west, and north)

Rosebud Mine

45 30’ o

45 00’ o

46 00’ o

o 107 00’ o 106 00’ o 105 00’

Ashland

20 MILES

KILOMETERS

00 5

5

10

10

20 30 

Figure 2. Map showing coal fields, mines, and lease areas in the Montana Powder River Basin assessment area. (Modifed from Averitt, 1966, and Mc
Figure 3. Flow chart showing generalized methodology used for coal resource and reserve evaluation.

 1) Coal bed geology (extent, thickness, partings, structure, overburden, etc.) 

 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 reserve

PHASE (3)--RESERVE ANALYSIS 

Coal bed correlations and editing

 1) Create digital models for all assessed coal beds 2) Create Geographic Information System 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(s) 

 3) Tax information 
Figure 4. Map showing drill-hole locations in the Montana Powder River Basin assessment area.

R. 35 E. R. 36 E. R. 37 E. R. 38 E. R. 39 E. R. 40 E. R. 41 E. R. 42 E. R. 43 E. R. 44 E. R. 45 E. R. 46 E. R. 47 E. R. 48 E. R. 49 E. R. 50 E. R. 51 E. R. 52 E. R. 53 E. R. 54 E. R. 55 E. R. 56 E. R. 57 E.

Custer County

Rosebud County

Treasure County

Big Horn County

Powder River County

Fallon County

Carter County

45°30’

45°00’

46°00’

107°00’ 106°00’ 105°00’

20 MILES

KILOMETERS

00 5

5

10

10

20 30 
Figure 5. Illustration showing the effect of coal bed depth upon restricted resource due to mine-pit highwall setback requirements (not to scale).

26o 26o

858 ft

Horizontal limits of projected surface restriction and buffer

Coal bedMine accessible coal-bearing rock Additional restriction because of required mine pit highwall angle (coal unavailable for mining

Surface restriction and bu er projected downward (coal unavailable for mining)

Restriction to mining

Mine bench Mine bench

300 ft 300 ft

Surface restriction

Bu er distance Bu er distance

EXPLANATION

2,144 ft
Figure 6. Map showing land-use restrictions in the Montana Powder River Basin assessment area.

T. 6 

T. 7 

T. 8 T. 5 

T. 4 T. 3 T. 2 

T. 1 

T. 1 

T. 2 

T. 3 S

T. 4 

T. 5 S

T. 6 T. 7 T. 8 T. 9 

R. 35 E. R. 36 E. R. 37 E. R. 38 E. R. 39 E. R. 40 E. R. 41 E. R. 42 E. R. 43 E. R. 44 E. R. 45 E. R. 46 E. R. 47 E. R. 48 E. R. 49 E. R. 50 E. R. 51 E. R. 52 E. R. 53 E. R. 54 E. R. 55 E. R. 56 E. R. 57 E.

Custer County

Rosebud County Treasure County

Big Horn County

Powder River County

Fallon County

Carter County

Yellowstone River

State Park

Montana Land Reliance

Conservation Easement

Tongue River Reservoir

 and State Park

Custer National Forest

 Broadus airport

945

945

Yellowstone River

Big Sky Mine

Spring Creek

Mine

Absaloka Mine

Decker Mines (east, west, and north)

Rosebud Mine

Custer National Forest

Twelve Mile Dam-MontanaFish, Wildlife, and Parks

Montana Fish, Wildlife, andParks Conservation Easement

Fort Keogh NationalWildlife Refuge

45 30’ o

45 00’ o

46 00’ o

o 107 00’ o 106 00’ o 105 00’

Wolf Mountains Battlesite

 National Historic Landmark

20 MILES

KILOMETERS

00 5

5

10

10

20 30 
Figure 7. Map showing coal ownership in the Montana Powder River Basin assessment area.

T

T

T. T. 

TTT

T. 

T

T

T. 

T

T. 

TTTT

R. 35 E. R. 36 E. R. 37 E. R. 38 E. R. 39 E. R. 40 E. R. 41 E. R. 42 E. R. 43 E. R. 44 E. R. 45 E. R. 46 E. R. 47 E. R. 48 E. R. 49 E. R. 50 E. R. 51 E. R. 52 E. R. 53 E. R. 54 E. R. 55 E. R. 56 E. R. 57 E.

Custer County

Rosebud County

Treasure County

Big Horn County

PowderRiver County

Fallon County

Carter County 

45 30’ o

45 00’ o

46 00’ o

o 107 00’ o 106 00’ o 105 00’

20 MILES

KILOMETERS

00 5

5

10

10

20 30 
Figure 8. Areal extent for the Roland (Baker), Smith, Anderson, Dietz 2, and Dietz 3 coal beds where the stripping ratios are from 1:1 to 10:1, thicknessefeet, and the overburden is less than or equal to 500 feet thick in the Montana Powder River Basin assessment area.

T. 

T

T. T. 

T. T. T. 

T. 

T

T. 

T. 

T. 

T. 

T. T. T. T. 

R. 35 E. R. 36 E. R. 37 E. R. 38 E. R. 39 E. R. 40 E. R. 41 E. R. 42 E. R. 43 E. R. 44 E. R. 45 E. R. 46 E. R. 47 E. R. 48 E. R. 49 E. R. 50 E. R. 51 E. R. 52 E. R. 53 E. R. 54 E. R. 55 E. R. 56 E. R. 57 E.

Custer County

Rosebud County

Treasure County

Big Horn County

Powder River County

Fallon County

Carter County

Miles City

Forsyth

Lame Deer

Colstrip

Crow Agency

Lodge Grass

45 30’ o

45 00’ o

46 00’ o

o 107 00’ o 106 00’ o 105 00’

20 MILES

KILOMETERS

00 5

5

10

10

20 30 
Figure 9. Areal extent for the Canyon coal bed where the stripping ratios are from 1:1 to 10:1, thicknesses are equal to at least 5.0 feet, and the overbu500 feet thick in the Montana Powder River Basin assessment area.

R. 35 E. R. 36 E. R. 37 E. R. 38 E. R. 39 E. R. 40 E. R. 41 E. R. 42 E. R. 43 E. R. 44 E. R. 45 E. R. 46 E. R. 47 E. R. 48 E. R. 49 E. R. 50 E. R. 51 E. R. 52 E. R. 53 E. R. 54 E. R. 55 E. R. 56 E. R. 57 E.

Custer County

Rosebud County

Treasure County

Big Horn County

Powder River County

Fallon County

Carter County

45 30’ o

45 00’ o

46 00’ o

o 107 00’ o 106 00’ o 105 00’

20 MILES

KILOMETERS

00 5

5

10

10

20 30 
Figure 10. Areal extent for the Werner/Cook coal bed where the stripping ratios are from 1:1 to 10:1, thicknesses are equal to at least 5.0 feet, and the oequal to 500 feet thick in the Montana Powder River Basin assessment area.

T

T

TT

TTT

T

T

T

T

T

T

TTTT

R. 35 E. R. 36 E. R. 37 E. R. 38 E. R. 39 E. R. 40 E. R. 41 E. R. 42 E. R. 43 E. R. 44 E. R. 45 E. R. 46 E. R. 47 E. R. 48 E. R. 49 E. R. 50 E. R. 51 E. R. 52 E. R. 53 E. R. 54 E. R. 55 E. R. 56 E. R. 57 E.

Custer County

Rosebud County

Treasure County

Big Horn County

Powder River County

Fallon County

Carter County

45 30’ o

45 00’ o

46 00’ o

o 107 00’ o 106 00’ o 105 00’

20 MILES

KILOMETERS

00 5

5

10

10

20 30 
Figure 11. Areal extent for the Pawnee coal bed where the stripping ratios are from 1:1 to 10:1, thicknesses are equal to at least 5.0 feet, and the overbto 500 feet thick in the Montana Powder River Basin assessment area.

T

TT

TTT

T

T

T

R. 35 E. R. 36 E. R. 37 E. R. 38 E. R. 39 E. R. 40 E. R. 41 E. R. 42 E. R. 43 E. R. 44 E. R. 45 E. R. 46 E. R. 47 E. R. 48 E. R. 49 E. R. 50 E. R. 51 E. R. 52 E. R. 53 E. R. 54 E. R. 55 E. R. 56 E. R. 57 E.

Custer County

Rosebud County

Treasure County

Big Horn County

Powder River County

Fallon County

Carter County

45 30’ o

45 00’ o

46 00’ o

o 107 00’ o 106 00’ o 105 00’

20 Miles

Kilometers

00 5

5

10

10

20 30 
Figure 12. Areal extent for the Rosebud/Knobloch coal bed where the stripping ratios are from 1:1 to 10:1, thicknesses are equal to at least 5.0 feet, and than or equal to 500 feet thick in the Montana Powder River Basin assessment area.

TTT

T

T

R. 35 E. R. 36 E. R. 37 E. R. 38 E. R. 39 E. R. 40 E. R. 41 E. R. 42 E. R. 43 E. R. 44 E. R. 45 E. R. 46 E. R. 47 E. R. 48 E. R. 49 E. R. 50 E. R. 51 E. R. 52 E. R. 53 E. R. 54 E. R. 55 E. R. 56 E. R. 57 E.

Custer County

Rosebud County

Treasure County

Big Horn County

Powder River County

Fallon County

Carter County

Colstrip

45 30’ o

45 00’ o

46 00’ o

o 107 00’ o 106 00’ o 105 00’

20 MILES

KILOMETERS

00 5

5

10

10

20 30 
Figure 13. Areal extent for the Flowers-Goodale coal bed where the stripping ratios are from 1:1 to 10:1, thicknesses are equal to at least 5.0 feet, and tor equal to 500 feet thick in the Montana Powder River Basin assessment area.

T

T

TT

TTT

T

T

T

T

T

T

TTTT

R. 35 E. R. 36 E. R. 37 E. R. 38 E. R. 39 E. R. 40 E. R. 41 E. R. 42 E. R. 43 E. R. 44 E. R. 45 E. R. 46 E. R. 47 E. R. 48 E. R. 49 E. R. 50 E. R. 51 E. R. 52 E. R. 53 E. R. 54 E. R. 55 E. R. 56 E. R. 57 E.

Custer County

Rosebud County

Treasure County

Big Horn County

Powder River County

Fallon County

Carter County

45 30’ o

45 00’ o

46 00’ o

o 107 00’ o 106 00’ o 105 00’

20 MILES

KILOMETERS

00 5

5

10

10

20 30 
Figure 14. Map showing location of areas of low, moderate, and high coalbed methane potential in the Montana Powder River Basin assessment area 

R. 35 E. R. 36 E. R. 37 E. R. 38 E. R. 39 E. R. 40 E. R. 41 E. R. 42 E. R. 43 E. R. 44 E. R. 45 E. R. 46 E. R. 47 E. R. 48 E. R. 49 E. R. 50 E. R. 51 E. R. 52 E. R. 53 E. R. 54 E. R. 55 E. R. 56 E. R. 57 E.

Custer County

Rosebud County

Treasure County

Big Horn County

Powder River County

Fallon County

Carter County

45 30’ o

45 00’ o

46 00’ o

o 107 00’ o 106 00’ o 105 00’

R. 35 E. R. 36 E. R. 37 E. R. 38 E. R. 39 E. R. 40 E. R. 41 E. R. 42 E. R. 43 E. R. 44 E. R. 45 E. R. 46 E. R. 47 E. R. 48 E. R. 49 E. R. 50 E. R. 51 E. R. 52 E. R. 53 E. R. 54 E. R. 55 E. R. 56 E. R. 57 E.

Custer County

Rosebud County

Treasure County

Big Horn County

Powder River County

Fallon County

Carter County

Area of Low estimated coalbed methane potential

Area of Moderate estimated coalbed methane potential

Area of High estimated coalbed methane potential

20 MILES

KILOMETERS

00 5

5

10

10

20 30 
Figure 15. Map showing location of mines and area names for coal quality in the Montana Powder River Basin assessment area (see tables 5 and 6 fo(Modified from Roberts and others, 1999a, 1999b, 1999c).

R. 35 E. R. 36 E. R. 37 E. R. 38 E. R. 39 E. R. 40 E. R. 41 E. R. 42 E. R. 43 E. R. 44 E. R. 45 E. R. 46 E. R. 47 E. R. 48 E. R. 49 E. R. 50 E. R. 51 E. R. 52 E. R. 53 E. R. 54 E. R. 55 E. R. 56 E. R. 57 E.

Custer County

Rosebud County

Treasure County

Big Horn County

Powder River County

Fallon County

Carter County

Big Sky Mine

Spring Creek Mine

Absaloka Mine

Decker Mines

Rosebud Mine

Ashland coaland others1999a)

Foster Creek area (Robertsand others, 1999a)

Greenleaf CreekMiller Creek area(Roberts and others1999a)

(Roberts and others1999b)

Decker/Spring Creek area(Roberts and others, 1999c)

Subbituminous Lignite coalcoal

45 30’ o

45 00’ o

46 00’ o

o 107 00’ o 106 00’ o 105 00’

20 MILES

KILOMETERS

00 5

5

10

10

20 30 
Figures 63

Figure 16. Map showing generalized geology of the Powder River Basin, Wyoming and Montana. (Modified from Flores and others, 

1999, and Ellis and Colton, 1994).

Tftrl

Tft

Tft

Tftr

Tw

Tw

Qal

Twr

Tftr

Tft

43o

44

o

46o

45

o

108° 106° 104°

Washakie

Musselshell

Johnson

Natrona

Niobrara

Platte

Weston

Crook

Campbell

Sheridan

Big Horn

Carter

Fallon

Yellowstone

Treasure

MILES

KILOMETERS

0 20 40

0 20 40 60

Custer

Rosebud

Powder River MONTANA

WYOMING

Hot

Springs

Fremont

Converse

Big Horn

Basin axis

Northern Wyoming Powder

River Basin assessment area

Southwestern Powder

River Basin assessment area

Montana Powder River

Basin assessment area

Faults (approximate) 

Tftr

Quaternary alluvium

Tertiary White River Formation

Tertiary Wasatch Formation

 Tongue River Member 

 Tullock Member 

Tertiary Fort Union Formation

(undifferentiated)

EXPLANATION

INDEX MAP

Wyoming

Montana

Powder River Basin

 Lebo Shale Member

Qal

Twr

Tw

 Tongue River and Lebo Shale

 Members Tftrl

Tft

Tfu

Qal

County line
Figure 17. Map showing location of mapped faults in the Montana Powder River Basin assessment area. (Modified from Roberts and others, 

T

T

TT

TTT

T

T

T

T

T

T

TTTT

R. 35 E. R. 36 E. R. 37 E. R. 38 E. R. 39 E. R. 40 E. R. 41 E. R. 42 E. R. 43 E. R. 44 E. R. 45 E. R. 46 E. R. 47 E. R. 48 E. R. 49 E. R. 50 E. R. 51 E. R. 52 E. R. 53 E. R. 54 E. R. 55 E. R. 56 E. R. 57 E.

Custer County

Rosebud County

Treasure County

Big Horn County

Powder River County

Fallon County

Carter County

o

45 30’ o

45 00’ o

46 00’ o

107 00’ o 106 00’ o 105 00’

20 MILES

KILOMETERS

00 5

5

10

10

20 30 
Figures 65

Figure 18. Generalized stratigraphic column for the Powder River Basin, Wyoming and Montana. (Modified from 

Ellis and others, 2002).

Carlile Shale

Frontier Formation

Pierre Shale

Niobrara Formation

AGE

LATE

CRETACEOUS

EARLY

CRETACEOUS

Lance Formation Hell Creek Formation

White River Formation

Fort Union

Formation

Thermopolis Shale

Muddy Sandstone

Wasatch Formation

Bell Fourche Formation

Greenhorn Formation

Mowry Shale

Fox Hills Sandstone

Bearpaw Shale

Mesaverde

Formation

QUATERNARY

Lebo Member

Cody Shale

Tullock Member

Surficial deposits

Tongue River Member

Lakota Formation

Fall River Formation

PLIOCENEOLIGOCENE

EOCENE

TE

PALEOCENE

R

TIA

RY CR

E

TACEO

U

S

WYOMING MONTANA

STRATIGRAPHIC UNITS IN THE

 POWDER RIVER BASIN
Figure 19. Coal bed and coal zone names used in different publications in the Powder River Basin, Wyoming and Montana.

Kent and Pierce and Flores and Ellis and Luppens and Sco and Osmonson and 

others (1980) others (1990) others, (1999) others (2002) others (2008) others (2010) others (2011) 

Upper Healy Upper Healy, Healy

Healy Murray

WASATCH Ucross Ucross

FM Felix Upper Felix Felix Felix

Felix Lower Felix Lower Felix

Roland/ Wyodak Roland (Upper Rider) Roland (Upper Rider)

Roland (Lower Rider)

Smith Badger Roland Rider Roland Roland (Baker) Roland (Baker) 

Roland (Taff)

Smith Smith Smith 

Upper Wyodak-Anderson Upper Anderson Rider, Anderson Anderson 

Wyodak Wyodak or coal zone=Smith Wyodak Anderson Lower Anderson 

Upper Wyodak (Swartz), Badger, Dietz 1, Dietz 2, Dietz 3 

FORT UNION (Anderson/ School, Sussex, Big Dietz Dietz 3, Dietz 4 Upper Canyon

FM Canyon Canyon) George, Wyodak, Canyon Canyon Canyon Canyon 

(Tongue Anderson, Dietz, Lower Canyon Lower Canyon 

River Canyon (Monarch), Lower Ferry 

Member) Werner Lower Werner Wyodak Werner Werner Werner 

Wyodak

O er O er 

Gates/ Upper Gates/

Kennedy Kennedy Kennedy Gates Gates Gates 

Pawnee Pawnee Pawnee 

Odell 

Rosebud Deep 1 

McKay Deep 2 

Deep 3 

Robinson 

Roberts Roberts 

Bed Names
Figure 20. Index map showing locations of cross sections in figures 21-27 in the Montana Powder River Basin assessment area.

R. 35 E. R. 36 E. R. 37 E. R. 38 E. R. 39 E. R. 40 E. R. 41 E. R. 42 E. R. 43 E. R. 44 E. R. 45 E. R. 46 E. R. 47 E. R. 48 E. R. 49 E. R. 50 E. R. 51 E. R. 52 E. R. 53 E. R. 54 E. R. 55 E. R. 56 E. R. 57 E.

A A’

B B’

C C’

D

D’

E

E’

F

F’

G’

G

20 MILES

KILOMETERS

00 5

5

10

10

20 30 
Roland (Baker) Smith Lower Can

Anderson Canyon Dietz 3 Dietz 2 Lower Canyon Ferry Werner/Cook Otter Gates/Wall Pawnee Odell Rosebud/Knobloch Flowers-Goodale Roberts/Terret Robinson/Witham McKay/Nance 

Gates/Wall Approximate land surface A 

A 

Montana Powder RivBasin AsseArea 0 5 10 20 MILES 0 5 10 20 KILOMETERS Vertical Scale: 1 Inch = 833 Feet 0 1,000 3,000 Vertical scale in feet Wyodak Anderson coal zone 2,000

Figure 21. West-east cross section A-A’ showing subsurface distribution of coal beds through the Spring Creek and Decker Mine areas in the Montanassessment area. (Vertical exaggeration approximately 63 X).
Figure 22. West-east cross section B-B’ showing subsurface distribution of coal beds north of the Spring Creek and Decker Mine areas in the Montanassessment area. (Vertical exaggeration approximately 63 X).

Anderson

Dietz 2

Dietz 3

Canyon

Pawnee

Rosebud/Knobloch

Werner/Cook

McKay/Nance Flowers-Goodale

Robinson/Witham

Lower Canyon

Approximate land surface

B 

MontaPowdeBasin Area

Custer National Forest

0 5 10 20 MILES

0 5 10 20 KILOMETERS

Vertical Scale: 1 Inch = 833 Feet

0 

1,0002,000

3,000

Vertical scale

in feet

Wyodak

Anderson

coal zone 
Figure 23. West-east cross section C-C’ showing subsurface distribution of coal beds through the Otter Creek Tracts (Arch Coal, Inc.) in the Montana Passessment area. (Vertical exaggeration approximately 32 X).

C 

Gates/Wall Pawnee

McKay/Nance

Flowers-Goodale Rosebud/Knobloch

Robert/Terret Robinson/Witham

Approximate land surface

MontanaPowder RiveBasin AssesArea

Custer National Forest

0 5 10 MILES

0 5 10 KILOMETERS

0 

1,000

2,0003,000

Vertical scale

in feet

Vertical Scale: 1 Inch = 833 Feet
Figure 24. South-north cross section D-D’ showing subsurface distribution of coal beds through the eastern part of the Montana Powder River Basin exaggeration approximately 63 X).

D 

Canyon

Lower Canyon

Werner/Cook

Rosebud/Knobloch

McKay/Nance

Flowers-Goodale

Robinson/Witham

Approximate land surface

MontanaPowder RivBasin AsseArea

Pawnee

0

0 5 10 20 MILES

5 10 20 KILOMETERS

0 

1,000

2,0003,000

Vertical scale

in feet

Vertical Scale: 1 Inch = 833 Feet
Figure 25. South-north cross section E-E’ showing subsurface distribution of coal beds through the Spring Creek and Decker Mine areas, Montana Poassessment area. (Vertical exaggeration approximately 16 X).

E 

0 

1,000

2,0003,000

Vertical scale

in feet

Vertical Scale: 1 Inch = 833 Feet

Roland (Baker)

Anderson

Smith

Approximate land surface

Dietz 2

Dietz 3

Canyon

Lower Canyon

Werner/Cook

Pawnee

Flowers-Goodale

MontanaPowder RivBasin AssesArea

0

0 5

5 10 MILES

10 KILOMETERS
Figure 26. South-north cross section F-F’ showing subsurface distribution of coal beds through the central part of the Montana Powder River Basin a(Vertical exaggeration approximately 70 X).

F 

Vertical Scale: 1 Inch = 833 Feet

Approximate land surface

Roland (Baker)

Smith

Anderson

Dietz 2

Canyon

Lower

Canyon Werner/Cook

Pawnee

Rosebud/Knobloch NcKay/Nance

Flowers-Goodale

Robinson/Witham

Location 

MontanaPowder RivBasin AsseArea

Custer National Forest

0 5 10 20 MILES

0 5 10 20 KILOMETERS

0 

1,000

2,0003,000

Vertical scale

in feet

Wyodak

Anderson

coal zone 
Figure 27. Northwest-southeast cross section G-G’ showing subsurface distribution of coal beds through the Montana Powder River Basin assessmeexaggeration approximately 76 X).

G

Approximate land surface

Dietz 2

Canyon Lower Canyon

Werner/Cook

Pawnee

Rosebud/Knobloch McKay/Nance Flowers-Goo

Robinson/Witham

MontanaPowder RiveBasin AssesArea

Custer National Forest

0 5 10 20 MILES

0 5 10 20 KILOMETERS

0 

1,000

2,0003,000

Vertical scale

in feet

Vertical Scale: 1 Inch = 833 Feet
Figure 28. Map showing location of clinker in the Montana Powder River Basin assessment area. (Modified from Heffern and others, 1993).

R. 35 E. R. 36 E. R. 37 E. R. 38 E. R. 39 E. R. 40 E. R. 41 E. R. 42 E. R. 43 E. R. 44 E. R. 45 E. R. 46 E. R. 47 E. R. 48 E. R. 49 E. R. 50 E. R. 51 E. R. 52 E. R. 53 E. R. 54 E. R. 55 E. R. 56 E. R. 57 E.

Custer County

Rosebud County

Treasure County

Big Horn County

Powder RiverCounty

Fallon County

Carter County

Lame Deer

Northern Cheyenne Indian Reservation

45 30’ o

45 00’ o

46 00’ o

o 107 00’ o 106 00’ o 105 00’

20 MILES

KILOMETERS

00 5

5

10

10

20 30 
76 Assessment of Coal Geology, Resources, and Reserves in the Montana Powder River Basin

Figure 29. Coal stratigraphy in the Montana Powder River Basin assessment area, showing names used in this report. Maximum and 

average thickness shown for 18 coal beds assessed for resources and reserves in this report.

Coal Bed Names/

Coal Beds Resources Coal Bed Names/ Maximum Average

identified in this calculated (18) Reserves thickness thickness

assessment (26) (see tables 4,8,9) calculated (feet) (feet)

Roland (Baker) Roland (Baker) Roland (Baker) 14 6

Roland (Taff)

Smith Smith Smith 20 6

Anderson Anderson Anderson 93 22

Dietz 1

Dietz 2 Dietz 2 Dietz 2 32 6

Dietz 3 Dietz 3 Dietz 3 59 11

Dietz 4

Cox

Canyon Canyon Canyon 57 14

Lower Canyon Lower Canyon 42 8

FORT UNION Ferry Ferry 15 6

Formation Werner/Cook Werner/Cook Werner/Cook 62 15

(Tongue River Otter Otter 32 4

Member) Gates/Wall Gates/Wall 23 5

Pawnee Pawnee Pawnee 34 8

Brewster-Arnold

Odell Odell 14 3

Cache

Rosebud/Knobloch Rosebud/Knobloch Rosebud/Knobloch 72 15

Calvert

McKay/Nance McKay/Nance 30 9

Flowers-Goodale Flowers-Goodale Flowers-Goodale 35 9

Upper Witham

Robinson/Witham Robinson/Witham 37 6

Roberts/Terret Roberts/Terret 28 5

Coal Stratigraphy
Figure 30. Isopachs showing extent of resources at least 2.5 feet thick in the Roland (Baker) coal bed within the Montana Powder River Basin assess

R. 35 E. R. 36 E. R. 37 E. R. 38 E. R. 39 E. R. 40 E. R. 41 E. R. 42 E. R. 43 E. R. 44 E. R. 45 E. R. 46 E. R. 47 E. R. 48 E. R. 49 E. R. 50 E. R. 51 E. R. 52 E. R. 53 E. R. 54 E. R. 55 E. R. 56 E. R. 57 E.

Custer County

Rosebud County

Treasure County

Big Horn County

Powder River County

Fallon County

Carter County

45 30’ o

45 00’ o

46 00’ o

o 107 00’ o 106 00’ o 105 00’

20 MILES

KILOMETERS

00 5

5

10

10

20 30 
Figure 31. Map showing depth to the top of the Roland (Baker) coal bed within the Montana Powder River Basin assessment area.

R. 35 E. R. 36 E. R. 37 E. R. 38 E. R. 39 E. R. 40 E. R. 41 E. R. 42 E. R. 43 E. R. 44 E. R. 45 E. R. 46 E. R. 47 E. R. 48 E. R. 49 E. R. 50 E. R. 51 E. R. 52 E. R. 53 E. R. 54 E. R. 55 E. R. 56 E. R. 57 E.

Custer County

Rosebud County

Treasure County

Big Horn County

Powder River County

Fallon County

Carter County

45 30’ o

45 00’ o

46 00’ o

o 107 00’ o 106 00’ o 105 00’

20 MILES

KILOMETERS

00 5

5

10

10

20 30 
Figure 32. Map showing coal resource reliability categories for the Roland (Baker) coal bed within the Montana Powder River Basin assessment area

R. 35 E. R. 36 E. R. 37 E. R. 38 E. R. 39 E. R. 40 E. R. 41 E. R. 42 E. R. 43 E. R. 44 E. R. 45 E. R. 46 E. R. 47 E. R. 48 E. R. 49 E. R. 50 E. R. 51 E. R. 52 E. R. 53 E. R. 54 E. R. 55 E. R. 56 E. R. 57 E.

Custer County

Rosebud County

Treasure County

Big Horn County

Powder RiverCounty

Fallon County

Carter County

45 30’ o

45 00’ o

46 00’ o

o 107 00’ o 106 00’ o 105 00’

20 MILES

KILOMETERS

00 5

5

10

10

20 30 
Figure 33. Isopachs showing extent of resources at least 2.5 feet thick in the Smith coal bed within the Montana Powder River Basin assessment area

R. 35 E. R. 36 E. R. 37 E. R. 38 E. R. 39 E. R. 40 E. R. 41 E. R. 42 E. R. 43 E. R. 44 E. R. 45 E. R. 46 E. R. 47 E. R. 48 E. R. 49 E. R. 50 E. R. 51 E. R. 52 E. R. 53 E. R. 54 E. R. 55 E. R. 56 E. R. 57 E.

Custer County

Rosebud County

Treasure County

Big Horn County

Powder River County

Fallon County

Carter County

45 30’ o

45 00’ o

46 00’ o

o 107 00’ o 106 00’ o 105 00’

20 MILES

KILOMETERS

00 5

5

10

10

20 30 
Figure 34. Map showing depth to the top of the Smith coal bed within the Montana Powder River Basin assessment area.

R. 35 E. R. 36 E. R. 37 E. R. 38 E. R. 39 E. R. 40 E. R. 41 E. R. 42 E. R. 43 E. R. 44 E. R. 45 E. R. 46 E. R. 47 E. R. 48 E. R. 49 E. R. 50 E. R. 51 E. R. 52 E. R. 53 E. R. 54 E. R. 55 E. R. 56 E. R. 57 E.

Custer County

Rosebud County

Treasure County

Big Horn County

Powder River County

Fallon County

Carter County

45 30’ o

45 00’ o

46 00’ o

o 107 00’ o 106 00’ o 105 00’

20 MILES

KILOMETERS

00 5

5

10

10

20 30 
Figure 35. Map showing coal resource reliability categories for the Smith coal bed within the Montana Powder River Basin assessment area.

R. 35 E. R. 36 E. R. 37 E. R. 38 E. R. 39 E. R. 40 E. R. 41 E. R. 42 E. R. 43 E. R. 44 E. R. 45 E. R. 46 E. R. 47 E. R. 48 E. R. 49 E. R. 50 E. R. 51 E. R. 52 E. R. 53 E. R. 54 E. R. 55 E. R. 56 E. R. 57 E.

Custer County

Rosebud County

Treasure County

Big Horn County

Powder RiverCounty

Fallon County

Carter County

45 30’ o

45 00’ o

46 00’ o

o 107 00’ o 106 00’ o 105 00’

20 MILES

KILOMETERS

00 5

5

10

10

20 30 
Figure 36. Isopachs showing extent of resources at least 2.5 feet thick in the Anderson coal bed within the Montana Powder River Basin assessment 

R. 35 E. R. 36 E. R. 37 E. R. 38 E. R. 39 E. R. 40 E. R. 41 E. R. 42 E. R. 43 E. R. 44 E. R. 45 E. R. 46 E. R. 47 E. R. 48 E. R. 49 E. R. 50 E. R. 51 E. R. 52 E. R. 53 E. R. 54 E. R. 55 E. R. 56 E. R. 57 E.

Custer County

Rosebud County

Treasure County

Big Horn County

Powder River County

Fallon County

Carter County

45 30’ o

45 00’ o

46 00’ o

o 107 00’ o 106 00’ o 105 00’

20 MILES

KILOMETERS

00 5

5

10

10

20 30 
Figure 37. Map showing depth to the top of the Anderson coal bed within the Montana Powder River Basin assessment area.

R. 35 E. R. 36 E. R. 37 E. R. 38 E. R. 39 E. R. 40 E. R. 41 E. R. 42 E. R. 43 E. R. 44 E. R. 45 E. R. 46 E. R. 47 E. R. 48 E. R. 49 E. R. 50 E. R. 51 E. R. 52 E. R. 53 E. R. 54 E. R. 55 E. R. 56 E. R. 57 E.

Custer County

Rosebud County

Treasure County

Big Horn County

Powder River County

Fallon County

Carter County

45 30’ o

45 00’ o

46 00’ o

o 107 00’ o 106 00’ o 105 00’

20 MILES

KILOMETERS

00 5

5

10

10

20 30 
Figure 38. Map showing coal resource reliability categories for the Anderson coal bed within the Montana Powder River Basin assessment area.

R. 35 E. R. 36 E. R. 37 E. R. 38 E. R. 39 E. R. 40 E. R. 41 E. R. 42 E. R. 43 E. R. 44 E. R. 45 E. R. 46 E. R. 47 E. R. 48 E. R. 49 E. R. 50 E. R. 51 E. R. 52 E. R. 53 E. R. 54 E. R. 55 E. R. 56 E. R. 57 E.

Custer County

Rosebud County

Treasure County

Big Horn County

Powder RiverCounty

Fallon County

Carter County

45 30’ o

45 00’ o

46 00’ o

o 107 00’ o 106 00’ o 105 00’

20 MILES

KILOMETERS

00 5

5

10

10

20 30 
Figure 39. Isopachs showing extent of resources at least 2.5 feet thick in the Dietz 2 coal bed within the Montana Powder River Basin assessment are

R. 35 E. R. 36 E. R. 37 E. R. 38 E. R. 39 E. R. 40 E. R. 41 E. R. 42 E. R. 43 E. R. 44 E. R. 45 E. R. 46 E. R. 47 E. R. 48 E. R. 49 E. R. 50 E. R. 51 E. R. 52 E. R. 53 E. R. 54 E. R. 55 E. R. 56 E. R. 57 E.

Custer County

Rosebud County

Treasure County

Big Horn County

Powder River County

Fallon County

Carter County

45°30’

45°00’

46°00’

107°00’ 106°00’ 105°00’

20 MILES

KILOMETERS

00 5

5

10

10

20 30 
Figure 40. Map showing depth to the top of the Dietz 2 coal bed within the Montana Powder River Basin assessment area.

R. 35 E. R. 36 E. R. 37 E. R. 38 E. R. 39 E. R. 40 E. R. 41 E. R. 42 E. R. 43 E. R. 44 E. R. 45 E. R. 46 E. R. 47 E. R. 48 E. R. 49 E. R. 50 E. R. 51 E. R. 52 E. R. 53 E. R. 54 E. R. 55 E. R. 56 E. R. 57 E.

Custer County

Rosebud County

Treasure County

Big Horn County

Powder River County

Fallon County

Carter County

45°30’

45°00’

46°00’

107°00’ 106°00’ 105°00’

20 MILES

KILOMETERS

00 5

5

10

10

20 30 
Figure 41. Map showing coal resource reliability categories for the Dietz 2 coal bed within the Montana Powder River Basin assessment area.

R. 35 E. R. 36 E. R. 37 E. R. 38 E. R. 39 E. R. 40 E. R. 41 E. R. 42 E. R. 43 E. R. 44 E. R. 45 E. R. 46 E. R. 47 E. R. 48 E. R. 49 E. R. 50 E. R. 51 E. R. 52 E. R. 53 E. R. 54 E. R. 55 E. R. 56 E. R. 57 

Custer County

Rosebud County

Treasure County

Big Horn County

Powder RiverCounty

Fallon Coun

Carter County

45 30’ o

45 00’ o

46 00’ o

o 107 00’ o 106 00’ o 105 00’

20 MILES

KILOMETERS

00 5

5

10

10

20 30 
Figure 42. Isopachs showing extent of resources at least 2.5 feet thick in the Dietz 3 coal bed within the Montana Powder River Basin assessment are

R. 35 E. R. 36 E. R. 37 E. R. 38 E. R. 39 E. R. 40 E. R. 41 E. R. 42 E. R. 43 E. R. 44 E. R. 45 E. R. 46 E. R. 47 E. R. 48 E. R. 49 E. R. 50 E. R. 51 E. R. 52 E. R. 53 E. R. 54 E. R. 55 E. R. 56 E. R. 57 E.

Custer County

Rosebud County

Treasure County

Big Horn County

Powder River County

Fallon County

Carter County

45 30’ o

45 00’ o

46 00’ o

o 107 00’ o 106 00’ o 105 00’

20 MILES

KILOMETERS

00 5

5

10

10

20 30 
Figure 43. Map showing depth to the top of the Dietz 3 coal bed within the Montana Powder River Basin assessment area.

R. 35 E. R. 36 E. R. 37 E. R. 38 E. R. 39 E. R. 40 E. R. 41 E. R. 42 E. R. 43 E. R. 44 E. R. 45 E. R. 46 E. R. 47 E. R. 48 E. R. 49 E. R. 50 E. R. 51 E. R. 52 E. R. 53 E. R. 54 E. R. 55 E. R. 56 E. R. 57 E.

Custer County

Rosebud County

Treasure County

Big Horn County

Powder River County

Fallon County

Carter County

45 30’ o

45 00’ o

46 00’ o

o 107 00’ o 106 00’ o 105 00’

20 MILES

KILOMETERS

00 5

5

10

10

20 30 
Figure 44. Map showing coal resource reliability categories for the Dietz 3 coal bed within the Montana Powder River Basin assessment area.

R. 35 E. R. 36 E. R. 37 E. R. 38 E. R. 39 E. R. 40 E. R. 41 E. R. 42 E. R. 43 E. R. 44 E. R. 45 E. R. 46 E. R. 47 E. R. 48 E. R. 49 E. R. 50 E. R. 51 E. R. 52 E. R. 53 E. R. 54 E. R. 55 E. R. 56 E. R. 57 E.

Custer County

Rosebud County

Treasure County

Big Horn County

Powder RiverCounty

Fallon County

Carter County

45 30’ o

45 00’ o

46 00’ o

o 107 00’ o 106 00’ o 105 00’

20 MILES

KILOMETERS

00 5

5

10

10

20 30 
Figure 45. Isopachs showing extent of resources at least 2.5 feet thick in the Canyon coal bed within the Montana Powder River Basin assessment ar

R. 35 E. R. 36 E. R. 37 E. R. 38 E. R. 39 E. R. 40 E. R. 41 E. R. 42 E. R. 43 E. R. 44 E. R. 45 E. R. 46 E. R. 47 E. R. 48 E. R. 49 E. R. 50 E. R. 51 E. R. 52 E. R. 53 E. R. 54 E. R. 55 E. R. 56 E. R. 57 E.

Custer County

Rosebud County

Treasure County

Big Horn County

Powder River County

Fallon County

Carter County

45 30’ o

45 00’ o

46 00’ o

o 107 00’ o 106 00’ o 105 00’

20 MILES

KILOMETERS

00 5

5

10

10

20 30 
Figure 46. Map showing depth to the top of the Canyon coal bed within the Montana Powder River Basin assessment area.

R. 35 E. R. 36 E. R. 37 E. R. 38 E. R. 39 E. R. 40 E. R. 41 E. R. 42 E. R. 43 E. R. 44 E. R. 45 E. R. 46 E. R. 47 E. R. 48 E. R. 49 E. R. 50 E. R. 51 E. R. 52 E. R. 53 E. R. 54 E. R. 55 E. R. 56 E. R. 57 E.

Custer County

Rosebud County

Treasure County

Big Horn County

Powder River County

Fallon County

Carter County

45 30’ o

45 00’ o

46 00’ o

o 107 00’ o 106 00’ o 105 00’

20 MILES

KILOMETERS

00 5

5

10

10

20 30 
Figure 47. Map showing coal resource reliability categories for the Canyon coal bed within the Montana Powder River Basin assessment area.

T

TTT

T

T

R. 35 E. R. 36 E. R. 37 E. R. 38 E. R. 39 E. R. 40 E. R. 41 E. R. 42 E. R. 43 E. R. 44 E. R. 45 E. R. 46 E. R. 47 E. R. 48 E. R. 49 E. R. 50 E. R. 51 E. R. 52 E. R. 53 E. R. 54 E. R. 55 E. R. 56 E. R. 57 E.

Custer County

Rosebud County

Treasure County

Big Horn County

Powder RiverCounty

Fallon County

Carter County

45 30’ o

45 00’ o

46 00’ o

o 107 00’ o 106 00’ o 105 00’

20 MILES

KILOMETERS

00 5

5

10

10

20 30 
Figure 48. Isopachs showing extent of resources at least 2.5 feet thick in the Lower Canyon coal bed within the Montana Powder River Basin assessm

R. 35 E. R. 36 E. R. 37 E. R. 38 E. R. 39 E. R. 40 E. R. 41 E. R. 42 E. R. 43 E. R. 44 E. R. 45 E. R. 46 E. R. 47 E. R. 48 E. R. 49 E. R. 50 E. R. 51 E. R. 52 E. R. 53 E. R. 54 E. R. 55 E. R. 56 E. R. 57 E.

Custer County

Rosebud County

Treasure County

Big Horn County

Powder River County

Fallon County

Carter County

45°30’

45°00’

46°00’

107°00’ 106°00’ 105°00’

20 MILES

KILOMETERS

00 5

5

10

10

20 30 
Figure 49. Map showing depth to the top of the Lower Canyon coal bed within the Montana Powder River Basin assessment area.

R. 35 E. R. 36 E. R. 37 E. R. 38 E. R. 39 E. R. 40 E. R. 41 E. R. 42 E. R. 43 E. R. 44 E. R. 45 E. R. 46 E. R. 47 E. R. 48 E. R. 49 E. R. 50 E. R. 51 E. R. 52 E. R. 53 E. R. 54 E. R. 55 E. R. 56 E. R. 57 E.

Custer County

Rosebud County

Treasure County

Big Horn County

Powder River County

Fallon County

Carter County

45 30’ o

45 00’ o

46 00’ o

o 107 00’ o 106 00’ o 105 00’

20 MILES

KILOMETERS

00 5

5

10

10

20 30 
Figure 50. Map showing coal resource reliability categories for the Lower Canyon coal bed within the Montana Powder River Basin assessment area

R. 35 E. R. 36 E. R. 37 E. R. 38 E. R. 39 E. R. 40 E. R. 41 E. R. 42 E. R. 43 E. R. 44 E. R. 45 E. R. 46 E. R. 47 E. R. 48 E. R. 49 E. R. 50 E. R. 51 E. R. 52 E. R. 53 E. R. 54 E. R. 55 E. R. 56 E. R. 57 E.

Custer County

Rosebud County

Treasure County

Big Horn County

Powder RiverCounty

Fallon County

Carter County

45 30’ o

45 00’ o

46 00’ o

o 107 00’ o 106 00’ o 105 00’

20 MILES

KILOMETERS

00 5

5

10

10

20 30 
Figure 51. Isopachs showing extent of resources at least 2.5 feet thick in the Ferry coal bed within the Montana Powder River Basin assessment area

R. 35 E. R. 36 E. R. 37 E. R. 38 E. R. 39 E. R. 40 E. R. 41 E. R. 42 E. R. 43 E. R. 44 E. R. 45 E. R. 46 E. R. 47 E. R. 48 E. R. 49 E. R. 50 E. R. 51 E. R. 52 E. R. 53 E. R. 54 E. R. 55 E. R. 56 E. R. 57 E.

Custer County

Rosebud County

Treasure County

Big Horn County

Powder River County

Fallon County

Carter County

45 30’ o

45 00’ o

46 00’ o

o 107 00’ o 106 00’ o 105 00’

20 MILES

KILOMETERS

00 5

5

10

10

20 30 
Figure 52. Map showing depth to the top of the Ferry coal bed within the Montana Powder River Basin assessment area.

R. 35 E. R. 36 E. R. 37 E. R. 38 E. R. 39 E. R. 40 E. R. 41 E. R. 42 E. R. 43 E. R. 44 E. R. 45 E. R. 46 E. R. 47 E. R. 48 E. R. 49 E. R. 50 E. R. 51 E. R. 52 E. R. 53 E. R. 54 E. R. 55 E. R. 56 E. R. 57 E.

Custer County

Rosebud County

Treasure County

Big Horn County

Powder River County

Fallon County

Carter County

45 30’ o

45 00’ o

46 00’ o

o 107 00’ o 106 00’ o 105 00’

20 MILES

KILOMETERS

00 5

5

10

10

20 30 
Figure 53. Map showing coal resource reliability categories for the Ferry coal bed within the Montana Powder River Basin assessment area.

R. 35 E. R. 36 E. R. 37 E. R. 38 E. R. 39 E. R. 40 E. R. 41 E. R. 42 E. R. 43 E. R. 44 E. R. 45 E. R. 46 E. R. 47 E. R. 48 E. R. 49 E. R. 50 E. R. 51 E. R. 52 E. R. 53 E. R. 54 E. R. 55 E. R. 56 E. R. 57 E.

Custer County

Rosebud County

Treasure County

Big Horn County

Powder RiverCounty

Fallon County

Carter County

45 30’ o

45 00’ o

46 00’ o

o 107 00’ o 106 00’ o 105 00’

20 MILES

KILOMETERS

00 5

5

10

10

20 30 
Figure 54. Isopachs showing extent of resources at least 2.5 feet thick in the Werner/Cook coal bed within the Montana Powder River Basin assessme

R. 35 E. R. 36 E. R. 37 E. R. 38 E. R. 39 E. R. 40 E. R. 41 E. R. 42 E. R. 43 E. R. 44 E. R. 45 E. R. 46 E. R. 47 E. R. 48 E. R. 49 E. R. 50 E. R. 51 E. R. 52 E. R. 53 E. R. 54 E. R. 55 E. R. 56 E. R. 57 E.

Custer County

Rosebud County

Treasure County

Big Horn County

Powder River County

Fallon County

Carter County

45 30’ o

45 00’ o

46 00’ o

o 107 00’ o 106 00’ o 105 00’

20 MILES

KILOMETERS

00 5

5

10

10

20 30 
Figure 55. Map showing depth to the top of the Werner/Cook coal bed within the Montana Powder River Basin assessment area.

R. 35 E. R. 36 E. R. 37 E. R. 38 E. R. 39 E. R. 40 E. R. 41 E. R. 42 E. R. 43 E. R. 44 E. R. 45 E. R. 46 E. R. 47 E. R. 48 E. R. 49 E. R. 50 E. R. 51 E. R. 52 E. R. 53 E. R. 54 E. R. 55 E. R. 56 E. R. 57 E.

Custer County

Rosebud County

Treasure County

Big Horn County

Powder River County

Fallon County

Carter County

45 30’ o

45 00’ o

46 00’ o

o 107 00’ o 106 00’ o 105 00’

20 MILES

KILOMETERS

00 5

5

10

10

20 30 
Figure 56. Map showing coal resource reliability categories for the Werner/Cook coal bed within the Montana Powder River Basin assessment area.

R. 35 E. R. 36 E. R. 37 E. R. 38 E. R. 39 E. R. 40 E. R. 41 E. R. 42 E. R. 43 E. R. 44 E. R. 45 E. R. 46 E. R. 47 E. R. 48 E. R. 49 E. R. 50 E. R. 51 E. R. 52 E. R. 53 E. R. 54 E. R. 55 E. R. 56 E. R. 57 E.

Custer County

Rosebud County

Treasure County

Big Horn County

Powder RiverCounty

Fallon County

Carter County

45 30’ o

45 00’ o

46 00’ o

o 107 00’ o 106 00’ o 105 00’

20 MILES

KILOMETERS

00 5

5

10

10

20 30 
Figure 57. Isopachs showing extent of resources at least 2.5 feet thick in the Otter coal bed within the Montana Powder River Basin assessment area

R. 35 E. R. 36 E. R. 37 E. R. 38 E. R. 39 E. R. 40 E. R. 41 E. R. 42 E. R. 43 E. R. 44 E. R. 45 E. R. 46 E. R. 47 E. R. 48 E. R. 49 E. R. 50 E. R. 51 E. R. 52 E. R. 53 E. R. 54 E. R. 55 E. R. 56 E. R. 57 E.

Custer County

Rosebud County

Treasure County

Big Horn County

Powder River County

Fallon County

Carter County

45 30’ o

45 00’ o

46 00’ o

o 107 00’ o 106 00’ o 105 00’

20 MILES

KILOMETERS

00 5

5

10

10

20 30 
Figure 58. Map showing depth to the top of the Otter coal bed within the Montana Powder River Basin assessment area.

R. 35 E. R. 36 E. R. 37 E. R. 38 E. R. 39 E. R. 40 E. R. 41 E. R. 42 E. R. 43 E. R. 44 E. R. 45 E. R. 46 E. R. 47 E. R. 48 E. R. 49 E. R. 50 E. R. 51 E. R. 52 E. R. 53 E. R. 54 E. R. 55 E. R. 56 E. R. 57 E.

Custer County

Rosebud County

Treasure County

Big Horn County

Powder River County

Fallon County

Carter County

45 30’ o

45 00’ o

46 00’ o

o 107 00’ o 106 00’ o 105 00’

20 MILES

KILOMETERS

00 5

5

10

10

20 30 
Figure 59. Map showing coal resource reliability categories for the Otter coal bed within the Montana Powder River Basin assessment area.

R. 35 E. R. 36 E. R. 37 E. R. 38 E. R. 39 E. R. 40 E. R. 41 E. R. 42 E. R. 43 E. R. 44 E. R. 45 E. R. 46 E. R. 47 E. R. 48 E. R. 49 E. R. 50 E. R. 51 E. R. 52 E. R. 53 E. R. 54 E. R. 55 E. R. 56 E. R. 57 E.

Custer County

Rosebud County

Treasure County

Big Horn County

Powder RiverCounty

Fallon County

Carter County

45 30’ o

45 00’ o

46 00’ o

o 107 00’ o 106 00’ o 105 00’

20 MILES

KILOMETERS

00 5

5

10

10

20 30 
Figure 60. Isopachs showing extent of resources at least 2.5 feet thick in the Gates/Wall coal bed within the Montana Powder River Basin assessmen

R. 35 E. R. 36 E. R. 37 E. R. 38 E. R. 39 E. R. 40 E. R. 41 E. R. 42 E. R. 43 E. R. 44 E. R. 45 E. R. 46 E. R. 47 E. R. 48 E. R. 49 E. R. 50 E. R. 51 E. R. 52 E. R. 53 E. R. 54 E. R. 55 E. R. 56 E. R. 57 E.

Custer County

Rosebud County

Treasure County

Big Horn County

Powder River County

Fallon County

Carter County

45 30’ o

45 00’ o

46 00’ o

o 107 00’ o 106 00’ o 105 00’

20 MILES

KILOMETERS

00 5

5

10

10

20 30 
Figure 61. Map showing depth to the top of the Gates/Wall coal bed within the Montana Powder River Basin assessment area.

R. 35 E. R. 36 E. R. 37 E. R. 38 E. R. 39 E. R. 40 E. R. 41 E. R. 42 E. R. 43 E. R. 44 E. R. 45 E. R. 46 E. R. 47 E. R. 48 E. R. 49 E. R. 50 E. R. 51 E. R. 52 E. R. 53 E. R. 54 E. R. 55 E. R. 56 E. R. 57 E.

Custer County

Rosebud County

Treasure County

Big Horn County

Powder River County

Fallon County

Carter County

45 30’ o

45 00’ o

46 00’ o

o 107 00’ o 106 00’ o 105 00’

20 MILES

KILOMETERS

00 5

5

10

10

20 30 
Figure 62. Map showing coal resource reliability categories for the Gates/Wall coal bed within the Montana Powder River Basin assessment area.

R. 35 E. R. 36 E. R. 37 E. R. 38 E. R. 39 E. R. 40 E. R. 41 E. R. 42 E. R. 43 E. R. 44 E. R. 45 E. R. 46 E. R. 47 E. R. 48 E. R. 49 E. R. 50 E. R. 51 E. R. 52 E. R. 53 E. R. 54 E. R. 55 E. R. 56 E. R. 57 E.

Custer County

Rosebud County

Treasure County

Big Horn County

Powder RiverCounty

Fallon County

Carter County

45 30’ o

45 00’ o

46 00’ o

o 107 00’ o 106 00’ o 105 00’

20 MILES

KILOMETERS

00 5

5

10

10

20 30 
Figure 63. Isopachs showing extent of resources at least 2.5 feet thick in the Pawnee coal bed within the Montana Powder River Basin assessment a

R. 35 E. R. 36 E. R. 37 E. R. 38 E. R. 39 E. R. 40 E. R. 41 E. R. 42 E. R. 43 E. R. 44 E. R. 45 E. R. 46 E. R. 47 E. R. 48 E. R. 49 E. R. 50 E. R. 51 E. R. 52 E. R. 53 E. R. 54 E. R. 55 E. R. 56 E. R. 57 E.

Custer County

Rosebud County

Treasure County

Big Horn County

Powder River County

Fallon County

Carter County

45 30’ o

45 00’ o

46 00’ o

o 107 00’ o 106 00’ o 105 00’

20 MILES

KILOMETERS

00 5

5

10

10

20 30 
Figure 64. Map showing depth to the top of the Pawnee coal bed within the Montana Powder River Basin assessment area.

R. 35 E. R. 36 E. R. 37 E. R. 38 E. R. 39 E. R. 40 E. R. 41 E. R. 42 E. R. 43 E. R. 44 E. R. 45 E. R. 46 E. R. 47 E. R. 48 E. R. 49 E. R. 50 E. R. 51 E. R. 52 E. R. 53 E. R. 54 E. R. 55 E. R. 56 E. R. 57 E.

Custer County

Rosebud County

Treasure County

Big Horn County

Powder River County

Fallon County

Carter County

45 30’ o

45 00’ o

46 00’ o

o 107 00’ o 106 00’ o 105 00’

20 MILES

KILOMETERS

00 5

5

10

10

20 30 
Figure 65. Map showing coal resource reliability categories for the Pawnee coal bed within the Montana Powder River Basin assessment area.

R. 35 E. R. 36 E. R. 37 E. R. 38 E. R. 39 E. R. 40 E. R. 41 E. R. 42 E. R. 43 E. R. 44 E. R. 45 E. R. 46 E. R. 47 E. R. 48 E. R. 49 E. R. 50 E. R. 51 E. R. 52 E. R. 53 E. R. 54 E. R. 55 E. R. 56 E. R. 57 E.

Custer County

Rosebud County

Treasure County

Big Horn County

Powder RiverCounty

Fallon County

Carter County

45 30’ o

45 00’ o

46 00’ o

o 107 00’ o 106 00’ o 105 00’

20 MILES

KILOMETERS

00 5

5

10

10

20 30 
Figure 66. Isopachs showing extent of resources at least 2.5 feet thick in the Odell coal bed within the Montana Powder River Basin assessment area

R. 35 E. R. 36 E. R. 37 E. R. 38 E. R. 39 E. R. 40 E. R. 41 E. R. 42 E. R. 43 E. R. 44 E. R. 45 E. R. 46 E. R. 47 E. R. 48 E. R. 49 E. R. 50 E. R. 51 E. R. 52 E. R. 53 E. R. 54 E. R. 55 E. R. 56 E. R. 57 E.

Custer County

Rosebud County

Treasure County

Big Horn County

Powder River County

Fallon County

Carter County

45 30’ o

45 00’ o

46 00’ o

o 107 00’ o 106 00’ o 105 00’

20 MILES

KILOMETERS

00 5

5

10

10

20 30 
Figure 67. Map showing depth to the top of the Odell coal bed within the Montana Powder River Basin assessment area.

R. 35 E. R. 36 E. R. 37 E. R. 38 E. R. 39 E. R. 40 E. R. 41 E. R. 42 E. R. 43 E. R. 44 E. R. 45 E. R. 46 E. R. 47 E. R. 48 E. R. 49 E. R. 50 E. R. 51 E. R. 52 E. R. 53 E. R. 54 E. R. 55 E. R. 56 E. R. 57 E.

Custer County

Rosebud County

Treasure County

Big Horn County

Powder River County

Fallon County

Carter County

45 30’ o

45 00’ o

46 00’ o

o 107 00’ o 106 00’ o 105 00’

20 MILES

KILOMETERS

00 5

5

10

10

20 30 
Figure 68. Map showing coal resource reliability categories for the Odell coal bed within the Montana Powder River Basin assessment area.

R. 35 E. R. 36 E. R. 37 E. R. 38 E. R. 39 E. R. 40 E. R. 41 E. R. 42 E. R. 43 E. R. 44 E. R. 45 E. R. 46 E. R. 47 E. R. 48 E. R. 49 E. R. 50 E. R. 51 E. R. 52 E. R. 53 E. R. 54 E. R. 55 E. R. 56 E. R. 57 E.

Custer County

Rosebud County

Treasure County

Big Horn County

Powder RiverCounty

Fallon County

Carter County

45 30’ o

45 00’ o

46 00’ o

o 107 00’ o 106 00’ o 105 00’

20 MILES

KILOMETERS

00 5

5

10

10

20 30 
Figure 69. Isopachs showing extent of resources at least 2.5 feet thick in the Rosebud/Knobloch coal beds within the Montana Powder River Basin as

R. 35 E. R. 36 E. R. 37 E. R. 38 E. R. 39 E. R. 40 E. R. 41 E. R. 42 E. R. 43 E. R. 44 E. R. 45 E. R. 46 E. R. 47 E. R. 48 E. R. 49 E. R. 50 E. R. 51 E. R. 52 E. R. 53 E. R. 54 E. R. 55 E. R. 56 E. R. 57 E.

Custer County

Rosebud County

Treasure County

Big Horn County

Powder RiverCounty

Fallon County

Carter County

Rosebud coal bed Knobloch coal bed

Rosebud Creek

45 30’ o

45 00’ o

46 00’ o

o 107 00’ o 106 00’ o 105 00’

20 MILES

KILOMETERS

00 5

5

10

10

20 30 
Figure 70. Map showing depth to the top of the Rosebud/Knobloch coal beds within the Montana Powder River Basin assessment area.

R. 35 E. R. 36 E. R. 37 E. R. 38 E. R. 39 E. R. 40 E. R. 41 E. R. 42 E. R. 43 E. R. 44 E. R. 45 E. R. 46 E. R. 47 E. R. 48 E. R. 49 E. R. 50 E. R. 51 E. R. 52 E. R. 53 E. R. 54 E. R. 55 E. R. 56 E. R. 57 E.

Custer County

Rosebud County

Treasure County

Big Horn County

Powder RiverCounty

Fallon County

Carter County

Rosebud coal bed Knobloch coal bed

Rosebud Creek

45 30’ o

45 00’ o

46 00’ o

o 107 00’ o 106 00’ o 105 00’

20 MILES

KILOMETERS

00 5

5

10

10

20 30 
Figure 71. Map showing coal resource reliability categories for the Rosebud/Knobloch coal beds within the Montana Powder River Basin assessment 

T

TT

TTT

T

T

T

R. 35 E. R. 36 E. R. 37 E. R. 38 E. R. 39 E. R. 40 E. R. 41 E. R. 42 E. R. 43 E. R. 44 E. R. 45 E. R. 46 E. R. 47 E. R. 48 E. R. 49 E. R. 50 E. R. 51 E. R. 52 E. R. 53 E. R. 54 E. R. 55 E. R. 56 E. R. 57 E.

Custer County

Rosebud County

Treasure County

Big Horn County

Powder RiverCounty

Fallon County

Carter County

Rosebud coal bed Knobloch coal bed

Rosebud Creek

45 30’ o

45 00’ o

46 00’ o

o 107 00’ o 106 00’ o 105 00’

20 MILES

KILOMETERS

00 5

5

10

10

20 30 
Figure 72. Isopachs showing extent of resources at least 2.5 feet thick in the McKay/Nance coal beds within the Montana Powder River Basin assess

R. 35 E. R. 36 E. R. 37 E. R. 38 E. R. 39 E. R. 40 E. R. 41 E. R. 42 E. R. 43 E. R. 44 E. R. 45 E. R. 46 E. R. 47 E. R. 48 E. R. 49 E. R. 50 E. R. 51 E. R. 52 E. R. 53 E. R. 54 E. R. 55 E. R. 56 E. R. 57 E.

Custer County

Rosebud County

Treasure County

Big Horn County

Powder River County

Fallon County

Carter County

Rosebud Creek

McKay coal bed Nance coal bed

45 30’ o

45 00’ o

46 00’ o

o 107 00’ o 106 00’ o 105 00’

20 MILES

KILOMETERS

00 5

5

10

10

20 30 
Figure 73. Map showing depth to the top of the McKay/Nance coal beds within the Montana Powder River Basin assessment area.

R. 35 E. R. 36 E. R. 37 E. R. 38 E. R. 39 E. R. 40 E. R. 41 E. R. 42 E. R. 43 E. R. 44 E. R. 45 E. R. 46 E. R. 47 E. R. 48 E. R. 49 E. R. 50 E. R. 51 E. R. 52 E. R. 53 E. R. 54 E. R. 55 E. R. 56 E. R. 57 E.

Custer County

Rosebud County

Treasure County

Big Horn County

Powder River County

Fallon County

Carter County

Rosebud Creek

McKay coal bed Nance coal bed 

45 30’ o

45 00’ o

46 00’ o

o 107 00’ o 106 00’ o 105 00’

20 MILES

KILOMETERS

00 5

5

10

10

20 30 
Figure 74. Map showing coal resource reliability categories for the McKay/Nance coal beds within the Montana Powder River Basin assessment are

TTT

T

T

R. 35 E. R. 36 E. R. 37 E. R. 38 E. R. 39 E. R. 40 E. R. 41 E. R. 42 E. R. 43 E. R. 44 E. R. 45 E. R. 46 E. R. 47 E. R. 48 E. R. 49 E. R. 50 E. R. 51 E. R. 52 E. R. 53 E. R. 54 E. R. 55 E. R. 56 E. R. 57 E.

Custer County

Rosebud County

Treasure County

Big Horn County

Powder RiverCounty

Fallon County

Carter County

McKay coal bed Nance coal bed

45 30’ o

45 00’ o

46 00’ o

o 107 00’ o 106 00’ o 105 00’

20 MILES

KILOMETERS

00 5

5

10

10

20 30 
Figure 75. Isopachs showing extent of resources at least 2.5 feet thick in the Flowers-Goodale coal bed within the Montana Powder River Basin asses

R. 35 E. R. 36 E. R. 37 E. R. 38 E. R. 39 E. R. 40 E. R. 41 E. R. 42 E. R. 43 E. R. 44 E. R. 45 E. R. 46 E. R. 47 E. R. 48 E. R. 49 E. R. 50 E. R. 51 E. R. 52 E. R. 53 E. R. 54 E. R. 55 E. R. 56 E. R. 57 E.

Custer County

Rosebud County

Treasure County

Big Horn County

Powder River County

Fallon County

Carter County

45 30’ o

45 00’ o

46 00’ o

o 107 00’ o 106 00’ o 105 00’

20 MILES

KILOMETERS

00 5

5

10

10

20 30 
Figure 76. Map showing depth to the top of the Flowers-Goodale coal bed within the Montana Powder River Basin assessment area.

R. 35 E. R. 36 E. R. 37 E. R. 38 E. R. 39 E. R. 40 E. R. 41 E. R. 42 E. R. 43 E. R. 44 E. R. 45 E. R. 46 E. R. 47 E. R. 48 E. R. 49 E. R. 50 E. R. 51 E. R. 52 E. R. 53 E. R. 54 E. R. 55 E. R. 56 E. R. 57 E.

Custer County

Rosebud County

Treasure County

Big Horn County

Powder RiverCounty

Fallon County

Carter County

45 30’ o

45 00’ o

46 00’ o

o 107 00’ o 106 00’ o 105 00’

20 MILES

KILOMETERS

00 5

5

10

10

20 30 
Figure 77. Map showing coal resource reliability categories for the Flowers-Goodale coal bed within the Montana Powder River Basin assessment ar

R. 35 E. R. 36 E. R. 37 E. R. 38 E. R. 39 E. R. 40 E. R. 41 E. R. 42 E. R. 43 E. R. 44 E. R. 45 E. R. 46 E. R. 47 E. R. 48 E. R. 49 E. R. 50 E. R. 51 E. R. 52 E. R. 53 E. R. 54 E. R. 55 E. R. 56 E. R. 57 E.

Custer County

Rosebud County

Treasure County

Big Horn County

Powder RiverCounty

Fallon County

Carter County

45 30’ o

45 00’ o

46 00’ o

o 107 00’ o 106 00’ o 105 00’

20 MILES

KILOMETERS

00 5

5

10

10

20 30 
Figure 78. Isopachs showing extent of resources at least 2.5 feet thick in the Robinson/Witham coal beds within the Montana Powder River Basin ass

R. 35 E. R. 36 E. R. 37 E. R. 38 E. R. 39 E. R. 40 E. R. 41 E. R. 42 E. R. 43 E. R. 44 E. R. 45 E. R. 46 E. R. 47 E. R. 48 E. R. 49 E. R. 50 E. R. 51 E. R. 52 E. R. 53 E. R. 54 E. R. 55 E. R. 56 E. R. 57 E.

Custer County

Rosebud County

Treasure County

Big Horn County

Powder River County

Fallon County

Carter County

Robinson coal bed Witham coal bed

Rosebud Creek

45 30’ o

45 00’ o

46 00’ o

o 107 00’ o 106 00’ o 105 00’

20 MILES

KILOMETERS

00 5

5

10

10

20 30 
Figure 79. Map showing depth to the top of the Robinson/Witham coal beds within the Montana Powder River Basin assessment area.

R. 35 E. R. 36 E. R. 37 E. R. 38 E. R. 39 E. R. 40 E. R. 41 E. R. 42 E. R. 43 E. R. 44 E. R. 45 E. R. 46 E. R. 47 E. R. 48 E. R. 49 E. R. 50 E. R. 51 E. R. 52 E. R. 53 E. R. 54 E. R. 55 E. R. 56 E. R. 57 E.

Custer County

Rosebud County

Treasure County

Big Horn County

Powder River County

Fallon County

Carter County

Robinson coal bed Witham coal bed

Rosebud Creek 

45 30’ o

45 00’ o

46 00’ o

o 107 00’ o 106 00’ o 105 00’

20 MILES

KILOMETERS

00 5

5

10

10

20 30 
Figure 80. Map showing coal resource reliability categories for the Robinson/Witham coal beds within the Montana Powder River Basin assessment a

R. 35 E. R. 36 E. R. 37 E. R. 38 E. R. 39 E. R. 40 E. R. 41 E. R. 42 E. R. 43 E. R. 44 E. R. 45 E. R. 46 E. R. 47 E. R. 48 E. R. 49 E. R. 50 E. R. 51 E. R. 52 E. R. 53 E. R. 54 E. R. 55 E. R. 56 E. R. 57 E.

Custer County

Rosebud County

Treasure County

Big Horn County

Powder RiverCounty

Fallon County

Carter County

Robinson coal bed Witham coal bed

Rosebud Creek

45 30’ o

45 00’ o

46 00’ o

o 107 00’ o 106 00’ o 105 00’

20 MILES

KILOMETERS

00 5

5

10

10

20 30 
Figure 81. Isopachs showing extent of resources at least 2.5 feet thick in the Roberts/Terret coal beds within the Montana Powder River Basin assess

R. 35 E. R. 36 E. R. 37 E. R. 38 E. R. 39 E. R. 40 E. R. 41 E. R. 42 E. R. 43 E. R. 44 E. R. 45 E. R. 46 E. R. 47 E. R. 48 E. R. 49 E. R. 50 E. R. 51 E. R. 52 E. R. 53 E. R. 54 E. R. 55 E. R. 56 E. R. 57 E.

Custer County

Rosebud County

Treasure County

Big Horn County

Powder River County

Fallon County

Carter County

45 30’ o

45 00’ o

46 00’ o

o 107 00’ o 106 00’ o 105 00’

20 MILES

KILOMETERS

00 5

5

10

10

20 30 
Figure 82. Map showing depth to the top of the Roberts/Terret coal beds within the Montana Powder River Basin assessment area.

R. 35 E. R. 36 E. R. 37 E. R. 38 E. R. 39 E. R. 40 E. R. 41 E. R. 42 E. R. 43 E. R. 44 E. R. 45 E. R. 46 E. R. 47 E. R. 48 E. R. 49 E. R. 50 E. R. 51 E. R. 52 E. R. 53 E. R. 54 E. R. 55 E. R. 56 E. R. 57 E.

Custer County

Rosebud County

Treasure County

Big Horn County

Powder River County

Fallon County

Carter County

45 30’ o

45 00’ o

46 00’ o

o 107 00’ o 106 00’ o 105 00’

20 MILES

KILOMETERS

00 5

5

10

10

20 30 
R. 35 E. R. 36 E. R. 37 E. R. 38 E. R. 39 E. R. 40 E. R. 41 E. R. 42 E. R. 43 E. R. 44 E. R. 45 E. R. 46 E. R. 47 E. R. 48 E. R. 49 E. R. 50 E. R. 51 E. R. 52 E. R. 53 E. R. 54 E. R. 55 E. R. 56 E. R. 57 E.

Custer County

Rosebud County

Treasure County

Big Horn County

Powder RiverCounty

Fallon County

Carter County

45 30’ o

45 00’ o

46 00’ o

o 107 00’ o 106 00’ o 105 00’

20 MILES

KILOMETERS

00 5

5

10

10

20 30 

Figure 83. Map showing coal resource reliability categories for the Roberts/Terret coal beds within the Montana Powder River Basin assessment are
Figure 84. Pie chart of 18 coal beds showing amount and percent of total original coal resources (215 Billion Short Tons (BST )) in individual beds in thPowder River Basin assessment area.

Anderson

16.4 BST (7.7 %)

Dietz 2

1.6 BST (0.7 %)

Dietz 3

9.5 BST (4.4 %)

Canyon

19.4 BST (9.0 %

Lower Can

10.4 BST (4.8 

Ferry

2.5 BST (1.1 %

Werner/Cook

25.6 BST (11.9 %)

Otter

4.5 BST (2.1%)

Gates/Wall

8.2 BST (3.8 %) Pawnee 13.8 BST (6.4 %)

Odell

1.8 BST (0.8 %)

Rosebud/Knobloch

42.6 BST (19.8 %)

McKay/Nance

10.6 BST (4.9 %)

Flowers-Goodale

25.7 BST (11.9 %)

Robinson/Witham9.6 BST (4.4 %)

Roberts/Terret

10.6 BST (4.9 %)

Roland (Baker)0.7 BST (0.3 %) Smith 1.8 BST (0.8 %)
Figure 85. Cost curve showing estimated recoverable resources vs. sales price per ton of coal. Example shows that at the November, 2011 price of $13.20, 12.8 billion short tons (BST ) of coal in assessment area are in the reserve category.

$0.00$5.00

$10.00$15.00$20.00$25.00$30.00$35.00

0 5 10 15 20 25 30 35 

BILLIONS OF TONS

Recoverable Resources

$13.20

12.8 bst

COST PER TON
Figures 133

RESOURCE IN BILLIONS OF SHORT TONS (bst)

 0

Economic Resource

Original Resource -- 151 

Available Resource -- 39 

Recoverable Resource -- 35 

Remaining Resource -- 150 

13

C

OAL RESOURCE 

C

ATEGORY

25 50 75 100 125 150

Coal

resource

ORIGINAL

REMAINING

AVAILABLE

RECOVERABLE

ECONOMIC

 Exclusions

None

Coal already mined

Restricted

Future mining losses

Uneconomic

99

26

23

1

73

 3

0 10 20 30 40 50 60 70 80 90 100

100 

9 14

Figure 86. Bar graph showing resources in different resource categories for the ten coal beds included 

in the reserve evaluation (5.0 feet thick or greater, 10:1 stripping ratio or less) of the Montana Powder River 

Basin, reported in billions of short tons (at a sales price of $13.20 as of November 14, 2011).

Figure 87. Bar graph showing resources in different resource categories for the ten coal beds included in the 

reserve evaluation (5.0 feet thick or greater, 10:1 stripping ratio or less) of the Montana Powder River Basin, 

reported in percentages (at a sales price of $13.20 as of November 14, 2011). Percent of remaining resources are 

shown in colored bars; excluded resources from the previous category are shown in white bars.
Haacke and others—Assessment of Coal Geology, Resources, and Reserves in the Montana Powder River Basin—Open-File Report 2012–1113