WYOMING

MONTANA

Powder River Basin

0 20 40 KILOMETERS

0 20 40 MILES

44°

45°

46°

43°

107° 106° 105°

Gillette

Miles City

Birney

Sheridan

Buffalo

Glenrock

Glenrock Douglas

Moorcroft

Decker

Colstrip

Ashland

Forsyth

Lame

Deer

Broadus

MONTANA

WYOMING

TREASURE

COUNTY

ROSEBUD

COUNTY

CARTER

COUNTY

CROOK

COUNTY

CAMPBELL

COUNTY

WESTON

COUNTYNIOBRARA COUNTY

NATRONA

COUNTY WASHAKIE COUNTY

JOHNSON

COUNTY

SHERIDAN

COUNTY

CONVERSE COUNTY

BIG

HORN

COUNTY

BIG HORN

COUNTY

POWDER RIVER

COUNTY

CUSTER

COUNTY

FALLON

COUNTY

East Gillette coal field

extension

Indian

Reservations

Montana Powder

River Basin

(USGS Open-File

Report 2012–1113)

Northern Wyoming

Powder River Basin

(USGS Open-File 

Report 2010−1294)

Gillette coal field

(USGS Open-File 

Report 2008–1202)

Southwestern Wyoming

Powder River Basin

(USGS Open-File 

Report 2011–1134)

The Powder River Basin

U.S. Department of the Interior

U.S. Geological Survey

Fact Sheet 2012–3143

February 2013

Introduction

The U.S. Geological Survey (USGS) is responsible for 

providing objective scientific information to support decisions regarding land management, environmental quality, 

and economic, energy, and strategic policy. To accomplish 

this goal, the USGS periodically assesses the Nation’s 

endowment of various energy resources, including coal. 

Because the amount of economically recoverable coal 

resource is substantially less than the total original volume of coal in place, coal reserve base estimates provide 

essential information for energy-related decisions (Luppens 

and others, 2009). To be classified as “reserves,” the coal 

must be considered economically producible at the time 

of classification.

Regional-scale reserve estimates are based on prefeasibility scoping-level studies in turn based on conceptual 

mine designs. Prefeasibility studies have a higher degree of 

uncertainty than feasibility studies developed for commercialization of a specific property. Conceptual mine designs 

do not have sufficient detail to support a final decision by a 

financial institution to support development of a coal deposit 

to the production stage.

The goal of the current USGS United States Coal 

Resources and Reserves Assessment Project is to conduct 

regional-scale, coal resource and reserve assessments of 

the significant coal beds in all major U.S. coal basins. 

The Powder River Basin (PRB) in northeastern Wyoming 

and southeastern Montana (fig. 1) was the first basin to be 

assessed under this effort. It contains the largest deposits of 

low-sulfur subbituminous coal in the world. In 2011, coal 

production from 16 mines in the basin totaled 462 million 

short tons (MST), some 42 percent of the total coal production in the United States, making the PRB the single 

most important coal-producing basin in the Nation. About 

426 MST (92 percent of total PRB coal production) came 

from the Gillette coal field, which is located along the 

eastern margin of the Wyoming PRB (fig. 1). The results 

presented here update coal resource and reserve estimates 

for the PRB and represent the first completed regional-scale 

assessment intended to revise the Nation’s coal reserve base.

Figure 1. Location of individual coal assessment areas in the Powder 

River Basin, Wyoming and Montana. From Haacke and others (2013).

Assessment of Coal Geology, Resources, and Reserve Base 

in the Powder River Basin, Wyoming and Montana

Using a geology-based assessment methodology, the U.S. Geological Survey estimated in-place resources of 1.07 trillion 

short tons of coal in the Powder River Basin, Wyoming and Montana. Of that total, with a maximum stripping ratio of 10:1, 

recoverable coal was 162 billion tons. The estimate of economically recoverable resources was 25 billion tons.

Printed on recycled paper
0 20 40 KILOMETERS

0 20 40 MILES

Quaternary alluvium and 

 terrace deposits

Tertiary White River Formation

Tertiary Wasatch Formation

Tongue River Member 

Tullock Member 

Tertiary Fort Union Formation 

 (undifferentiated)

EXPLANATION

WYOMING

MONTANA

Powder River

Basin

Lebo Shale Member

Tongue River and Lebo 

 Shale Members 

Basin axis

107° 106° 105°

46°

45°

44°

43°

BIG HORN COUNTY

TREASURE

COUNTY

ROSEBUD

COUNTY CUSTER

COUNTY

FALLON

COUNTY

CARTER

COUNTY

POWDER RIVER

COUNTY

CROOK

COUNTY

CAMPBELL

COUNTY

WESTON

COUNTY

WASHAKIE

COUNTY

JOHNSON

COUNTY

SHERIDAN

COUNTY

BIG

HORN

COUNTY

NIOBRARA

COUNTY

NATRONA

COUNTY

CONVERSE

COUNTY

MONTANA

WYOMING

Tftr

Tw

Tftrl

Tfu

Tft

Qal

Twr

Tfl

Tft

Tfl

Tftrl

Tftr

Tfu

Tw

Twr

Qal

The Powder River Basin, 

an elongate, north-northwesttrending basin, covers about 

19,500 mi2 (see fig. 1), exclusive 

of the part of the basin within the 

Crow and Northern Cheyenne 

Indian Reservations in Montana. 

The PRB forms a broad asymmetric syncline with gentle westward 

dips along the eastern flank and 

steep eastward dips along the 

western flank. The synclinal axis 

lies nearer the basin’s western 

margin, trending north-northwest 

in the Wyoming part of the PRB 

and gradually turning northnortheasterly in the Montana part 

(fig. 2). Because the coal beds are 

thick, shallow, and gently dipping 

along the eastern margin of the 

Wyoming part of the basin, large 

open-pit mines have been developed there to extract near-surface 

coal resources (fig. 3).

Four assessment subdivisions in the Powder River Basin 

are based on geography, geology, 

mining conditions, and topography, which resulted in differences in the sizes of databases 

among these areas and facilitated 

a more timely release of assessment results. The four assessed 

areas (fig. 1) were the Gillette 

coal field, Wyoming (Luppens 

and others, 2008); the Northern 

Wyoming Powder River Basin 

(Scott and others, 2010); the 

Southwestern Wyoming Powder 

River Basin (Osmonson and 

others, 2011); and the Montana 

Powder River Basin (Haacke and 

others, 2013).

The primary objectives of the PRB assessment were to:

•	 Improve geological assurance by updating the stratigraphic database using information obtained from recently completed 

coal bed methane (CBM) and oil and gas wells;

•	 Develop more-comprehensive in-place coal resource computer models that also support regional reserve base estimates; and

•	 Complete a surface-mining economic evaluation customized to the environmental and technological restrictions of each 

assessed area and thereby derive regional estimates of the coal reserve base.

Figure 2. Generalized 

geology of the Powder 

River Basin, Wyoming and 

Montana. Modified from 

Flores and Bader (1999).
T. 3 N.

T. 5 N.

T. 7 N.

T. 53N.

T. 55 N.

T. 57 N.

T. 9 S.

T. 7 S.

T. 5 S.

T. 3 S.

T. 1 N.

T. 1 S.

46°

107° 106° 105°

R. 35 W. R. 37 W. R. 39 W. R. 41 W. R. 43 W. R. 45 W. R. 47 W. R. 49 W. R. 51 W. R. 53 W. R. 55 W. R. 57 W.

R. 87 W. R. 85 W. R. 83 W. R. 81 W. R. 79 W. R. 77 W. R. 75 W. R. 73 W. R. 71 W. R. 69 W. R. 67 W. R. 65 W.

T. 33 N.

T. 35 N.

T. 37 N.

T. 39 N.

T. 41 N.

T. 43N.

T. 45 N.

T. 47 N.

T. 49 N.

T. 51 N.

45°

44°

43°

Powder River Basin

MONTANA

WYOMING

CROOK

CAMPBELL COUNTY

COUNTY

WESTON

COUNTY

NIOBRARA

COUNTY

NATRONA

COUNTY

WASHAKIE

COUNTY

JOHNSON

COUNTY

SHERIDAN

COUNTY

CONVERSE

COUNTY

BIG

HORN

COUNTY

BIG HORN

COUNTY

TREASURE

COUNTY

ROSEBUD

COUNTY

CUSTER

COUNTY FALLON

COUNTY

CARTER

COUNTY

POWDER RIVER

COUNTY

EXPLANATION

Thickness (feet)

5

25

50

75

100

125

150

200

250 

300 and >

Mine area

WYOMING

MONTANA

Powder

River

Basin

0 20 40 KILOMETERS

0 20 40 MILES

Study Methodology

Earlier assessments of the Powder 

River Basin were based on correlations of 

coal zones, which included stratigraphic 

intervals that were as much as 800 ft thick 

and included as many as six or more beds 

with combined coal thickness of 100 ft or 

more (Flores, 1999). To evaluate mining 

economics, assessment of economically 

recoverable resources must be based on the 

thickness and extent of individual coal beds. 

The tremendous growth of CBM well development in the PRB has facilitated a unique 

view of subsurface geology. With completion of more than 25,000 drill holes, including corresponding geophysical logs which 

facilitate coal bed correlations, coal beds 

have been more accurately defined and correlated. For the Gillette coal field assessment 

alone, approximately 8,000 new drill holes 

were added to the geologic database for a 

total of 10,210 data points. Interpretation of 

these new data provided an unprecedented 

assessment of the coal resources and the 

reserve base in the PRB. A total of 29,928 

drill holes (of which 21,393 holes were 

non-proprietary) were used in the overall 

PRB assessment (Haacke and Scott, 2013).

The assessment consisted of three 

phases, with the first being data collection, 

editing, and correlation of individual coal 

beds. Both the Wyoming State Geological 

Survey andthe Montana Bureau of Mines 

and Geology facilitated data acquisition. The 

second phase involved modeling the coal 

beds using a digital multibed geologic modeling program to generate coal isopach, structure, and overburden maps for each assessed 

coal bed. Separate models were generated 

for the resource and reserve base evaluations 

using minimum coal thicknesses of 2.5 ft and 

5.0 ft, respectively. To calculate unrestricted 

coal resources potentially available for mining, the coal data were imported into a Geographic Information System (GIS) in which 

coal resources affected by mining restrictions 

were subtracted from the resource base. 

Mining restrictions included towns, railroads, 

environmentally sensitive areas, and coal too 

thin or too deep to mine economically.

The last assessment phase was a 

prefeasibility-level economic mining 

evaluation (± 25 percent) to determine 

economically recoverable coal resources 

(the reserve base). Ten hypothetical mine 

Figure 3. Isopach 

map of the combined 

Smith, Anderson, 

and Canyon coal 

beds (almost 40 

percent of the 

in-place resources) 

showing extent of 

resources in beds at 

least 5 ft thick within 

the Powder River 

Basin, Wyoming and 

Montana.

models were created, one for each stripping 

ratio (thickness of overburden to total thickness of coal) from 1:1 to 10:1. Geologic and 

mining conditions for each assessment area 

were used to customize the mine size and 

costing, and a discounted cash flow (DCF) 

analysis at a given rate of return (ROR) was 

used. Finally, GIS programs were used to 

calculate the volume of available coal for each 

of the 10 stripping ratios.

Once the available resource volumes and 

estimated cost to mine by stripping-ratio interval were completed, a cost curve was generated 

relating sales price to resources (fig. 4). The 

amount of coal at or below the current sales 

price was designated as “reserve base.” The 

cost curve for the Gillette coal field demonstrates that a reserve base estimate is not a 

single value and that the amount of reserve base 

fluctuates as changes occur in the market price.
Remaining 37 coal beds: 

255 BST 23.8%

Rosebud/Knobloch: 

52 BST 4.9%

Gates/Wall:

62 BST 5.8%

Canyon:

150 BST 14%

Lower Canyon:

59 BST 5.5%

Otter:

65 BST 6.1%

Werner/Cook:

73 BST 6.8%

Dietz 3:

50 BST 4.7%

Anderson:

130 BST 12.1%

Smith:

126 BST 11.8%

Roland (Baker):

49 BST 4.6%

$14.00

$10.47

77 BST

18.5 BST

10.1 BST

DCF cost/ton

(dollars)

$10

$20

$30

$40

$50

$60

$70

0 10 20 30 40 50 60 70 80

Billions of tons

(BST)

Figure 4. Cost curve showing reserve estimates at $10.47/ton (as of January 2007) and 

$14.00/ton (as of March 2008) for the Gillette coal field, Powder River Basin, Wyoming 

(Luppens and others, 2008). [Abbreviation: DCF, discounted cash flow]

Figure 5. Pie diagram showing percentages and tonnages of individual coal beds 

in relation to the total 1.1 trillion short tons of coal resources in the Powder River 

Basin, Wyoming and Montana. [Abbreviation: BST, billion short tons; %, percent]

Resource Assessment Results

Based on methodology outlined above, the USGS assessed coal resources 

for 47 coal beds in the Powder River Basin. The most significant coal resources 

lie within the Roland (Baker), Smith, Anderson, Dietz 3, Canyon, Lower 

Canyon, Werner/Cook, Otter, Gates/Wall, and Rosebud/Knobloch coal beds of 

the Tongue River Member of the Paleocene Fort Union Formation. Although 

there are seven coal beds in the Eocene Wasatch Formation, they are of minor 

importance in terms of recoverable coal. These beds generally are thinner and 

of poorer quality than beds in the Fort Union Formation.

The USGS calculated an original in-place coal resource of 1.07 trillion 

short tons (TST) for the 47 coal beds in the PRB, with just ten individual 

coal beds representing more than 75 percent (fig. 5) of the total resources 

(816 billion short tons, BST). Three cross sections (figs. 6–8) and one combined isopach map of the Canyon, Anderson, and Smith beds from the Wyodak 

coal zone (fig. 3) display coal bed geometry in the PRB. Figure 6 illustrates the structural asymmetry of the basin whereas 

figure 7 shows that nearly all of the thick, shallow coal beds on 

the eastern side of the basin are thinner toward the southwestern 

side of the basin. Figure 8 illustrates the thinning and splitting 

of beds within the Wyodak-Anderson coal from the Gillette 

coal field northward into Montana. The combined isopach of 

the three most prominent coal beds (that is, Smith, Anderson, 

and Canyon; fig. 3) shows how these beds have influenced 

coal development in the PRB. Essentially all of the significant 

mining to date in the PRB is limited to shallow depths of these 

thick coal beds, with the exception of the Rosebud-Knobloch 

and Flowers-Goodale coal beds, which are mined in the northern part of the Montana PRB (fig. 3 and fig. 8).

Not all coal beds were included in evaluating mining economics for each assessment area. Only those beds with substantial areal extent, exceeding 5 ft in thickness, and with stripping 

ratios less than 10:1 were included. A summary of reserve base 

assessments for the PRB is shown in table 1. An estimated total 

of 25 billion short tons of coal resources met the definition of 

economically recoverable resources (the reserve base). 

Most of the beds assessed for recoverable resources were 

those with in-place resources of 50 BST or more (fig. 5).

That 25 BST of coal resources classified as the 

reserve base, however, does not mean that the total 

amount of coal left in the Powder River Basin could 

be produced by surface mining technologies. Mining 

costs and coal sales prices are not static, as both tend to 

increase over time. If market prices exceed mining costs, 

the reserve base will grow (the converse is also true). For 

example, coal being mined today would not have been 

classified as reserve base in 1990. The cost curve from 

the Gillette coal field assessment (fig. 4) illustrates the 

dynamic nature of reserve assessments. For example, a 

sales price increase of only $3.43 per ton nearly doubled 

the estimate of the reserve base.

For longer-term energy planning, total estimated 

recoverable resources of 162 BST (table 1) represent a 

more important value than current reserve base estimates. 

In 1990, for example, resources with a stripping ratio 

greater than 2:1 were not classified as reserve base. Yet 

today, coal being mined at stripping ratios of 3:1 to 4:1 

obviously now would be classified as reserve base.

There are no current underground mining operations in the Powder River Basin, nor are any anticipated 

in the foreseeable future. There is a significant deep coal 

resource base in the basin, however, and preliminary 

assessments of deep coal with thicknesses amenable for 

longwall mining were completed for the Southwestern 

Wyoming Powder River Basin (Osmonson and others, 

2011), the northern Wyoming PRB (Scott and others, 

2010), and the Montana PRB (Haacke and others, 2013). 

The combined underground resource for those three 

areas, in beds 10–20 ft thick (the optimal mining height 

for longwall mining systems), was estimated at 302 BST.
Figure 8. North—south cross section C—C’ showing subsurface distribution of coal beds through the central part of the Powder River Basin, Wyoming 

and Montana.

Figure 7. West—east cross section B—B’ showing subsurface distribution of coal beds through the southern part of the Powder River Basin, 

Wyoming and Montana. (Beds dip more steeply along the western margin of the basin in contrast to gently dipping beds along the eastern margin.)

Figure 6. West—east cross section A—A’ showing subsurface distribution of coal beds through the central part of the Powder River Basin, Wyoming 

and Montana. (Beds dip steeply along the western margin of the basin in contrast to gently dipping beds along the eastern margin.)

MONTANA

B

B Powder

River

Basin

B’

WYOMING

0 10 20 MILES

0 10 20 KILOMETERS

2,000 ft

3,000 ft

4,000 ft

5,000 ft

Felix

1,000 ft

Elevation above sea level

Roland (Baker)

Smith

Anderson

Werner/Cook

Gates/Wall

Pawnee

Rosebud/Knobloch

Flowers-Goodale

Roberts/Terret

Approximate land surface

Wyodak-Anderson coal zone

(Flores and Bader, 1999)

Wyodak-Anderson coal zone

(Flores and Bader, 1999)

Dietz 3

Canyon

Lower Canyon

EXPLANATION

Coal beds

B B’

C

C’

Powder

River

Basin

MONTANA

WYOMING

0 20 40 MILES

0 20 40 KILOMETERS

Elevation above sea level

2,000 ft

3,000 ft

4,000 ft

5,000 ft

1,000 ft

Roland (Baker)

Smith

Anderson

Werner/Cook

Gates/Wall

Pawnee

Rosebud/Knobloch

Flowers-Goodale

Roberts/Terret

Approximate land surface

Wyodak-Anderson coal zone

(Flores and Bader, 1999)

Wyodak-Anderson coal zone

(Flores and Bader, 1999)

Dietz 3

Canyon

Lower Canyon

EXPLANATION

Felix

C C’

Coal beds

A A’

Powder

River

Basin

WYOMING

MONTANA

0 10 20 MILES

0 10 20 KILOMETERS

0 ft

1,000 ft

2,000 ft

3,000 ft

4,000 ft

Elevation above sea level

Roland (Baker)

Smith

Anderson

Werner/Cook

Gates/Wall

Pawnee

Rosebud/Knobloch

Flowers-Goodale

Roberts/Terret

Approximate land surface

Wyodak-Anderson coal zone

(Flores and Bader, 1999)

Dietz 3

Canyon

Lower Canyon

EXPLANATION

Coal beds

A A’
Table 1. Powder River Basin coal resources and reserve base, Wyoming and Montana, reported by assessment area, including Gillette coal field, 

Wyoming; NWPRB (Northern Wyoming Powder River Basin); SWPRB (Southwestern Wyoming Powder River Basin); MTPRB (Montana Powder 

River Basin); and PRB (Powder River Basin). (Amounts reported in billions of short tons.)

Coal beds assessed

for reserve base

Gillette coal field NWPRB SWPRB MTPRB PRB

Roland (Baker),

Smith, Anderson 

Rider, Anderson, 

Dietz 3, Canyon

Roland (Baker), 

Smith, Anderson, Dietz 3, 

Canyon, Lower Canyon, 

Werner/Cook

Roland (Baker), Smith, 

Anderson, Dietz 2, 

Dietz 3, Canyon, 

Rosebud/Knobloch, 

Flowers-Goodale

Roland (Baker), Smith, 

Anderson Rider, Anderson, 

Dietz 2, Dietz 3, Canyon, 

Lower Canyon, Werner/Cook, 

Rosebud/Knobloch,

Flowers-Goodale

Total resources 201 285 369 215 1,070

Total Economic Evaluation 165 158 165 488

Recoverable 77 50 35 162

Economic 10 2 13 25

References Cited

Flores, R.M., 1999, Database creation and resource evaluation methodology, chap. DB of Fort Union Coal Assessment Team, 1999 Resource assessment of 

selected Tertiary coal beds and zones in the Northern Rocky Mountains and Great Plains Region: U.S. Geological Survey Professional Paper 1625–A, 

2 CD-ROMs.

 Flores, R.M., and Bader, L.R., 1999, Fort Union coal in the Powder River Basin, Wyoming and Montana—A synthesis, chap. PS of Fort Union Coal 

Assessment Team, 1999 Resource assessment of selected Tertiary coal beds and zones in the Northern Rocky Mountains and Great Plains Region: 

U.S. Geological Survey Professional Paper 1625–A, 2 CD-ROMs.

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

reserves in the Montana Powder River Basin: U.S. Geological Survey Open-File Report 2012–1113, 133 p.

Haacke, J.E., and Scott, D.C., 2013, Drillhole data for coal beds in the Powder River Basin, Montana and Wyoming: U.S. Geological Survey Data Series 

DS 713, 15 p.

Luppens, J.A., Scott, D.C., Haacke, J.E., Osmonson, L.M., Rohrbacher, T.J., and Ellis, M.S., 2008, Assessment of coal geology, resources, and reserve base 

in the Gillette coal field, Powder River Basin, Wyoming: U.S. Geological Survey Open-File Report 2008–1202, 127 p.

Luppens, J.A., Rohrbacher, T.J., Osmonson, L.M., and Carter, M.D., 2009, Coal resource availability, recoverability, and economic evaluations in the 

United States—A summary, chap. D of Pierce, B.S., and Dennen, K.O., eds., The national coal resource assessment overview: U.S. Geological Survey 

Professional Paper 1625–F, 17 p.

Osmonson, L.M., Scott, D.C., Haacke, J.E., Luppens, J.A., and Pierce, P.E., 2011, Assessment of coal geology, resources, and reserve base in the Southwestern 

Powder River Basin, Wyoming: U.S. Geological Survey Open-File Report 2011–1134, 135 p.

Scott, D.C., Haacke, J.E., Osmonson, L.M., Luppens, J.A., Pierce, P.E., and Rohrbacher, T.J., 2010, Assessment of coal geology, resources, and reserve base 

in the Northern Powder River Basin, Wyoming: U.S. Geological Survey Open-File Report 2010–1294, 136 p.

For Further Information

Supporting assessment reports are 

available at the USGS Energy program 

website, at http://energy.usgs.gov.

Coal Assessment Team

James A. Luppens, David C. Scott, 

Lee M. Osmonson, Jon E. Haacke, 

and Paul E. Pierce.

Contact Information James A. Luppens (jluppens@usgs.gov)

David C. Scott (dscott@usgs.gov)

View of a surface coal mine in the Powder River Basin near the town of Gillette, northeastern Wyoming. Photograph by J.A. Luppens, U.S. Geological Survey.