EXECUTIVE SUMMARY

TERTIARY COAL RESOURCES IN THE NORTHERN

ROCKY MOUNTAINS AND GREAT PLAINS REGION—A

CLEAN AND COMPLIANT FOSSIL FUEL BEYOND 2000

By R.M. Flores and D.J. Nichols

in U.S. Geological Survey Professional Paper 1625-A
ES-ii

Contents

Introduction...........................................................................................................................ES-1

Coal Included in This Assessment..................................................................................ES-2

Clean Air Act Requirements.............................................................................................ES-5

Clean, Compliant Coal—A Finite Resource .................................................................ES-6

Tertiary Coal Meets Emission Standards.......................................................................ES-6

Tertiary Coal for the Future...............................................................................................ES-7

Contents of these CD-ROM Publications......................................................................ES-8

Figures

ES-1. Coal basins under study in the current resource assessment, by region.

ES-2. The Northern Rocky Mountains and Great Plains assessment region.

ES-3. Composite stratigraphic section of coal-bearing Tertiary rocks in the four

major basins studied in the Northern Rocky Mountains and Great Plains

assessment region.

Table

ES-1. Summaries of coal resources calculated for coal assessed in the Northern

Rocky Mountains and Great Plains assessment region, by basin 
ES-1

INTRODUCTION

The U.S. Geological Survey (USGS) is assessing coal resources in five regions

within the conterminous United States (fig. ES-1) to determine the quantity, quality,

and minability of coal likely to be used within the next 20-30 years. This assessment

is critical because the utilization of coal has been rising in the U.S., primarily

because it is the least expensive fuel for generation of electrical power that is

essential to the goals and infrastructure of the Nation. Previous coal resource

assessments attempted to assess the total amount of coal in the ground in the U.S.,

but those estimates tended to be high and socially irrelevant because they included

coal deposits that are not available (coal that is in beds too thin or too deep

underground to be mined efficiently, or that is too close to urban areas to be mined

practically), or coal that is not of sufficient quality to serve as a fuel resource into the

next century. A new assessment was required that focuses on those coal resources

likely to be utilized in the next 20-30 years, resources that for the most part are

currently being developed in existing mines.

This current National Coal Resource Assessment (NCRA) covers selected coal beds

or zones in each of the five regions (fig. ES-1). Other coal deposits are either

unassessed or have been reviewed in summary fashion rather than in detail. Data on

the selected coal beds or zones that have been assessed include estimates of quantity,

quality, and, in some cases, availability. The assessments of regions other than the

Northern Rocky Mountains and Great Plains may be found in the other sets of CDROM’s that are part of the NCRA series.

The Northern Rocky Mountains and Great Plains region (fig. ES-2) contains

considerable resources of some of the cleanest coal in the U.S. Much of this coal is
ES-2

compliant with emission regulations for trace elements of environmental concern set

by the Clean Air Act and administered by the U.S. Environmental Protection

Agency (EPA). Production of clean and compliant coal from the region, especially

from the Powder River Basin of Wyoming, has been increasing in recent years, a

trend that is expected to continue beyond the year 2000. In this Executive Summary,

(1) the coal included in the current assessment in the Northern Rocky Mountains

and Great Plains region is discussed, including those coal basins that were studied in

detail in the current assessment and those that are only summarized from past

literature (unassessed basins); (2) the provisions of the EPA Clean Air Act are

reviewed; (3) the nature of coal resources in the region is described, with special

reference to its clean and compliant qualities; and (4) the contents and organization

of the CD-ROM publications are outlined.

COAL INCLUDED IN THIS ASSESSMENT

The current coal resource assessment investigations in the Northern Rocky

Mountains and Great Plains region concentrated on selected coal beds and zones in

rocks of Tertiary age in four basins—coal resources that are most likely to be

utilized in the next 20-30 years. These coal deposits are described in detail and

estimates of quantity and quality are made for the Powder River Basin in Wyoming

and Montana, the Williston Basin in North Dakota, the Greater Green River Basin in

Wyoming, and the Hanna-Carbon Basin in Wyoming. Coal availability and

recoverability for selected areas in the Powder River Basin are assessed, as well.

Table ES-1 summarizes the total resources in millions of short tons in each of the

four assessed basins. In other basins in the region, Tertiary coal resources that are

less likely to be utilized in the next 20-30 years are summarized but were not

assessed. These unassessed areas include the Bighorn Basin, Wyoming; Bull
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Mountain Basin, Montana; Wind River Basin, Wyoming; Denver Basin, Colorado;

North Park Basin, Colorado; and Raton Basin, Colorado and New Mexico. Coal of

other geologic ages that may exist within any of these assessed or unassessed

basins, such as coal of Cretaceous age, is not discussed.

Table ES-1. Summaries of coal resources calculated for coal assessed in the

Northern Rocky Mountains and Great Plains assessment region, by basin, and for

deposits in-place. Resources are shown in millions of short tons with two significant

figures for strippable coal. The resource area does not include mine or lease areas.

Resources were not calculated for coal beds less than 2.5 ft thick

Basin State Coalfields Millions of

short tons

 Powder River Wyoming and

 Montana

 Wyodak-Anderson area,

 Ashland, and Colstrip

570,000

 Williston North Dakota Bowman-Dickinson, Beulah, and

 Center-Falkirk

76,000

 Greater Green

 River

 Wyoming Point of Rocks-Black Butte 2,700

 Hanna-Carbon Wyoming Ferris, Hanna, and South Carbon 7,200
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Previous and present USGS and U.S. Bureau of Mines investigations in the central

and northern Appalachian Basin and in the Illinois Basin indicated that of the

original in-place coal resources, only 50-60 percent is available for mining after

land-use restrictions and technological restrictions are applied, and only 11-38

percent is recoverable by modern mining techniques. After application of clean-air

compliance restrictions and mine planning studies, only 4-13 percent of this

recoverable coal can be mined economically. The current coal resource assessment

considers these factors in order to present data of use to National officials, planners,

mining companies, scientists, and the general public.

Data on thickness, lateral extent, nature of continuity, geometry, distribution, quality,

and geochemical properties of coal has been collected and digitally analyzed to

permit classification of in-place coal resources by surface and subsurface ownership

(Federal, State, and private). Resource calculations include categories of measured,

indicated, inferred, and hypothetical resources as defined by the USGS. Each

category is statistically analyzed for levels of uncertainty. In selected areas, the inplace coal resources are analyzed for their availability and recoverability based on

land-use, technologic, and mining restrictions. Land-use restrictions applying to

building sites, infrastructure, streams, and wildlife habitats follow Federal, State, and

local guidelines.

For ease of use, information in this USGS Professional Paper is presented digitally

on two CD-ROM’s. The data are reproduced as running text, bulleted text, graphic

displays, tables, subsurface cross sections, and maps in a geographic information

system (GIS) format.
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The in-depth assessments of the coal that may be used in the next 20-30 years are

necessarily limited by the availability of certain data, such as proprietary data; no

data of a proprietary nature are released in this document. In addition, coal-bearing

areas within National Parks are not subject to mining, and this assessment does not

include coal in Tribal lands.

CLEAN AIR ACT REQUIREMENTS

By the year 2000, in order to mitigate the environmental impact of coal utilization in

the United States, coal-fired power plants are required by the Clean Air Act and

EPA emission standards to use low-sulfur coal, which is defined as coal containing

0.6 pounds or less of sulfur per million Btu, or 1.2 pounds or less of SO2 per

million Btu (lbs/mmBtu). Present SO2 emission standards allow a maximum of 2.5

lbs/mmBtu. In addition, the coal-fired power plants may be required by the EPA to

reduce emissions of trace elements of environmental concern (for example, arsenic,

mercury, and selenium) as defined in the 1990 Clean Air Act Amendments. Thus,

an increased demand for clean, compliant coal (coal low in sulfur, ash or fine

particulates, and trace elements of environmental concern) by power plants will be

driven by these regulations. The resulting increased production of clean, compliant

coal will continue to deplete low cost, minable reserves of this coal. Depletion of

these reserves will lead to intense pressure to develop similar deposits of coal at

greater depths and at greater cost.
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CLEAN, COMPLIANT COAL—A FINITE RESOURCE

Coal containing low amounts of sulfur, ash, and trace elements of environmental

concern is found in many of the coal-bearing rocks of Tertiary age in the Northern

Rocky Mountains and Great Plains region. About a dozen coal beds and zones of

the Fort Union Formation and equivalent Tertiary rocks in this region yielded more

than 38 percent of the 1998 total coal production in the U.S. For the past 25 years,

production of this coal has increased from about 25 to about 383 million short tons,

a more than fifteenfold increase. Production is mostly from surface mines whose

strip ratio (ratio of the amount of waste removed to the amount of coal recovered)

has changed from about 1:1 to as much as 3:1. This high-quality coal has been

increasingly utilized by electric power generating plants in States in the western,

midwestern, southern, and southeastern U.S. and foreign countries. The high

production of this coal has reduced the amount of remaining low-cost, clean, and

compliant coal. Such coal serves as the main combustible fuel, or as a blend with

non-compliant coal, in many of these power plants.

TERTIARY COAL MEETS EMISSION STANDARDS

Most Tertiary coal is considered a clean, low-contaminant, compliant coal resource.

Coal in the Powder River Basin contains less sulfur and less ash than coal from

other regions in the conterminous U.S. For example, coal produced from the

Powder River Basin has one of the lowest mean values of SO2 of any coal in the

U.S. The extensively mined Wyodak-Anderson coal zone has the lowest mean

sulfur and ash yield in the Powder River Basin (arithmetic mean for sulfur is 0.48

percent and ash yield is 6.44 percent, as-received basis, 279 samples). The quantity

of trace elements of environmental concern named in the 1990 Clean Air Act
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Amendments is of increasing importance in meeting compliance standards. These

trace elements include antimony, arsenic, beryllium, cadmium, chromium, cobalt,

lead, manganese, mercury, nickel, selenium, and uranium. Tertiary coal from the

Powder River and Williston Basins has the lowest contents of these elements when

compared to other coal within the Northern Rocky Mountains and Great Plains

region and coal from other coal-producing regions in the conterminous U.S.

TERTIARY COAL FOR THE FUTURE

The Northern Rocky Mountains and Great Plains region of Wyoming, Montana,

and North Dakota contains a vast expanse of coal-bearing rocks of Tertiary age.

These coal-bearing rocks exist from the surface to a depth of about 6,000 ft in

certain basins (the Powder River, Williston, and Greater Green River Basins) and

from the surface to a depth of 12,000 ft in the Hanna-Carbon Basin. The apparent

rank of Tertiary coal ranges from lignite to subbituminous in the shallower strata

and from subbituminous to bituminous in the deeper strata. Major production in the

Powder River Basin is from the Wyodak-Anderson and Rosebud coal zones (fig.

ES-3). In 1998 these coal zones, which range in thickness from 25 to 140 ft,

produced more than 340 million short tons from 25 mines and made up more than

34 percent of the total U.S. coal production in that year. These coal deposits are

projected to produce 416 million short tons per year by 2015, based on the projected

increase per year of U.S. production, as forecast by the U.S. Department of

Energy’s Energy Information Agency in 1996. Coal resources in the Williston

Basin are produced from the Beulah-Zap, Hagel, Harmon, and Hansen coal zones

(fig. ES-3). These coal zones range in thickness from 20 to 40 ft. In the HannaCarbon Basin, coal production is from the Ferris and Hanna Formations (which are

in part stratigraphically equivalent to the Fort Union Formation), from the Ferris
ES-8

Nos. 23, 25, 31, 50, 65, and Hanna Nos. 77, 78, 79, and 81 coal beds (fig. ES-3).

These beds are each as much as 30 ft thick. In the Greater Green River Basin, coal

production is primarily from the Deadman coal zone and the equivalent coal seams

(fig. ES-3). These beds range in thickness from 2 to 25 ft.

CONTENTS OF THE CD-ROM PUBLICATIONS

USGS Professional Paper 1625-A comprises the first and second of a set of three

CD-ROM’s for the Northern Rocky Mountains and Great Plains region. The first

contains text and graphics for this Executive Summary and for 39 separate chapters

of the assessment study (as summarized below). Each chapter is assigned a unique

two-letter code that is used to designate figures and tables throughout each chapter.

Graphics are viewed using Adobe Acrobat software included on this CD-ROM. The

second CD-ROM of Professional Paper 1625-A contains data, maps, and cross

sections produced as GIS coverages; metadata for the GIS coverages are also

included. A read-only version of the ArcView software required is included on that

CD-ROM to enable the user to query the data and to interactively create and print

maps. The third CD-ROM, which is USGS Open-File Report 99-376, contains

Excel files of the non-proprietary stratigraphic data on which the cross

sections are based and the non-proprietary geochemical data for coal quality.

The first chapter on the first CD-ROM of Professional Paper 1625-A is an

Introduction that includes a section entitled Perspectives; it is a series of graphics to

be viewed as a slide show. These graphic displays summarize the rationale for the

assessment study in the Northern Rocky Mountains and Great Plains region, explain

the “why,” “how,” and “where” of the assessment, and note the benefits to society.

Following this is bulleted text that presents some background for the study and lists
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the objectives and strategy. Next, the geologic setting of the region is described, and

then the depositional setting and its influence on the coal resources is discussed.

Finally, coal quality is summarized. Graphic displays accompany each of these

sections.

The second chapter describes database creation and resource evaluation

methodology. Chapters following are grouped into Parts I-V, which contain detailed

descriptions of each of the basins studied.

Part I covers the Powder River Basin, Part II the Williston Basin, Part III the

Hanna-Carbon Basin, and Part IV covers the Greater Green River Basin. Topics

discussed for each of these basins include a synthesis of coal deposits, framework

geology, biostratigraphy, land-use and ownership, coal resources, and coal quality

and geochemistry. Part I on the Powder River Basin also includes chapters on five

individual coalfields and on coal availability and coal recoverability studies in the

basin. Part V groups the summaries of the unassessed basins that include Tertiary

coal deposits in the Bighorn, Bull Mountain, Wind River, Denver, North Park, and

Raton Basins. The final chapter on the first CD-ROM is a slide show with

photographs and Quicktime movies about surface mining and reclamation

operations in the Northern Rocky Mountains and Great Plains region.

The GIS projects on the second CD-ROM of Professional Paper 1625-A and the

non-proprietary stratigraphic and geochemical data in the third CD-ROM, Open-File

Report 99-376, cover the Powder River, Williston, Hanna-Carbon, and Greater

Green River Basins only. The maps, cross sections, and tables are grouped by basin.

Users are urged to refer to the “readme” file on the second CD-ROM to learn how

to navigate within and utilize the GIS projects.
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As noted, letter codes are assigned to each chapter as shown in the Contents for this

CD-ROM, and most illustrations (figures) are numbered using these letter codes as

prefixes for ease of reference. However, some Acrobat graphics (such as those in

the Perspectives section) are not numbered as figures. They are accessed by clicking

on “hot links” (words shown in red in the text) or by clicking on the directional

arrows that appear on these displays. In all chapters included on this CD-ROM, text

that appears in red is hot-linked to a figure or a table. In the Contents sections of

each chapter, pages on which sections within the chapter begin are hot-linked by

page numbers shown in red.

USGS Professional Paper 1625-A and Open File Report 99-376 in CD-ROM

format represent the combined efforts of a team of geologists, computer specialists,

and others, both within USGS and in collaborating agencies, who have compiled

and interpreted the data and prepared the report over a period of five years. Refer to

the credits and authorship in the first CD-ROM for a complete list.
Gulf Coast

Illinois Basin

Appalachian

Basin

Colorado

Plateau

Figure ES-1. Coal basins under study in the current resource assessment, by region.

Northern Rocky Mountains

and Great Plains
Montana North

Dakota

South Dakota

Colorado

Wyoming

New Mexico

Surface Fort Union Formation

and equivalent Paleocene rocks

Subsurface Fort Union 

Formation and equivalent rocks

Coal mine or lease areas 

Strippable Coal beds and zones

0 200 Miles

Figure ES-2. The Northern Rocky Mountains and Great Plains assessment region.

Nebr.
Wyodak-Anderson

Beulah-Zap 

Hagel 

Harmon

Hansen

Knobloch

Rosebud

Deadman seams

}

}

........................................Powder River Basin

...........................................................Williston Basin

.....................................................................Williston Basin

.....................................................Powder River Basin

...............................................................Williston Basin

.................................Greater Green River Basin

Hanna Nos. 77-79, 81

Ferris Nos. 23, 

25, 31, 50, & 65 }.......................................................Hanna Basin

................................................Hanna Basin

Johnson-107 .............................................................Carbon Basin

Figure ES-3. Composite stratigraphic section of coal-bearing Tertiary rocks in the 

four major basins studied in the Northern Rocky Mountains and Great Plains 

assessment region. The coal beds and zones named are those covered in detail in 

this assessment.