Chapter F

Coal Availability, Recoverability, and Economic 

Evaluations of Coal Resources in the Colorado Plateau:

Colorado, New Mexico, and Utah

By Timothy J. Rohrbacher,1 Carol L. Molnia,1 Lee M. Osmonson,1

M. Devereux Carter,2

 Wynn Eakins,3 Gretchen K. Hoffman,4

David E. Tabet,5

 Janet E. Schultz,3 David C. Scott,6 Dale D. Teeters,6

Glen E. Jones,4

 Jeffrey C. Quick,5 Brigitte P. Hucka,5 and John A. Hanson5

U.S. Geological Survey Professional Paper 1625–B*

U.S. Department of the Interior

U.S. Geological Survey

Chapter F of

Geologic Assessment of Coal in the Colorado Plateau:

Arizona, Colorado, New Mexico, and Utah

Edited by M.A. Kirschbaum, L.N.R. Roberts, and L.R.H. Biewick

1

 U.S. Geological Survey, Denver, Colorado 80225

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

3

 Colorado Geological Survey, Denver, Colorado 80203

4

 New Mexico Bureau of Mines and Mineral Resources, 

Socorro, New Mexico 87801

5

 Utah Geological Survey, Salt Lake City, Utah 84114

6 DST and Associates, Lakewood, Colorado 80228

* This report, although in the USGS Professional Paper series,

is available only on CD-ROM and is not available separately

National Coal

Resource

Assessment

Click here to return to Disc 1 

Volume Table of Contents
Contents

Introduction ................................................................................................................................................. F1

The National and Regional Perspective .......................................................................................... 1

Concepts of Economic Evaluation for Coal Resources ................................................................. 1

Purpose ................................................................................................................................................. 2

Coal Availability and Recoverability Studies: Early Studies to Present Studies ....................... 3

Methodology......................................................................................................................................... 5

Coal Availability, Recoverability, and Economic Evaluation Terminology ......................... 5

Restrictions to Mining................................................................................................................ 6

Calculating Reserves from Resources.................................................................................... 6

Mine Planning .................................................................................................................... 6

Resource Recovery ........................................................................................................... 7

Mining Costs and Reserve Calculations ........................................................................ 8

Acknowledgments........................................................................................................................................ 9

Colorado Plateau Studies............................................................................................................................ 9

Introduction .......................................................................................................................................... 9

State Geological Survey Cooperative Programs.......................................................................... 10

Colorado Studies....................................................................................................................... 10

New Mexico Studies................................................................................................................ 11

Utah Studies .............................................................................................................................. 13

The Availability of Coal Resources in the Somerset 7.5’ Quadrangle, 

West-Central Colorado................................................................................................................. 14

Introduction ........................................................................................................................................ 14

Coal Availability Evaluation Methodology ..................................................................................... 15

Factors Affecting the Availability of Coal Resources ......................................................... 15

Unsuitability Criteria Determinations ........................................................................... 16

Other Land-Use Issues ................................................................................................... 16

Technologic Factors ........................................................................................................ 16

Overview of the Study Area ............................................................................................................. 17

Location and Physiographic Setting...................................................................................... 17

General Geology of the Somerset Quadrangle and Vicinity.............................................. 19

Principal Coal Beds .................................................................................................................. 20

Correlation of Coal Beds.......................................................................................................... 20

Coal Mining History .................................................................................................................. 20

Results: Coal Resources and Coal Available for Mining in the 

Somerset Quadrangle, Colorado ....................................................................................... 20

Coal Resource Categories....................................................................................................... 25

Summary ............................................................................................................................................. 25

Original Coal Resources .......................................................................................................... 25

Mined-Out and Remaining Coal Resources ......................................................................... 25
Restrictions and Available Coal Resources ......................................................................... 25

Availability of Coal Resources in the Fruitland Formation, San Juan Basin, 

Bisti Study Area, Northwest New Mexico................................................................................ 29

Introduction ........................................................................................................................................ 29

Geologic Setting................................................................................................................................. 29

Coal Geology.............................................................................................................................. 29

Coal Quality................................................................................................................................ 30

Available Data ........................................................................................................................... 34

Coal Availability Studies in New Mexico ....................................................................................... 35

Detailed Methodology.............................................................................................................. 35

Review of Restrictions ............................................................................................................. 36

Technological Restrictions............................................................................................. 37

Land-Use Restrictions..................................................................................................... 38

Previous Mining ............................................................................................................... 40

Bisti Study Area Resources ............................................................................................................. 41

Restrictions with Potential for Mitigation............................................................................. 41

Other Coal-Resource Studies ................................................................................................. 42

Summary ............................................................................................................................................. 42

Coal Availability in the Northern Wasatch Plateau Coal Field, Utah.................................................. 43

Abstract............................................................................................................................................... 43

Introduction ........................................................................................................................................ 43

Location and Mining History................................................................................................... 43

Geology....................................................................................................................................... 43

Methodology....................................................................................................................................... 43

Past Mining................................................................................................................................ 46

Technical Restrictions.............................................................................................................. 46

Land-Use Restrictions.............................................................................................................. 47

Resource Categories......................................................................................................................... 49

Reliability.................................................................................................................................... 49

Thickness ................................................................................................................................... 49

Overburden ................................................................................................................................ 50

Results ................................................................................................................................................. 50

Available Coal Resources........................................................................................................ 50

Recovery Factors...................................................................................................................... 52

Future Production ..................................................................................................................... 52

Summary ............................................................................................................................................. 55

Resource Recovery, Economic Evaluation of Minable Coal Resources 

and Project Summary ................................................................................................................... 55

Introduction ........................................................................................................................................ 55

Past Mining Methods............................................................................................................... 55

Present Mining Methods—Somerset and Northern Wasatch Plateau Coal Fields...... 55

Present Mining Methods—Bisti Study Area ....................................................................... 56
Resource Evaluations ....................................................................................................................... 57

The Somerset Quadrangle Study Area ................................................................................. 57

The Bisti Coal Field Study Area .............................................................................................. 58

The Northern Wasatch Plateau Study Area......................................................................... 59

Conclusion .......................................................................................................................................... 59

Selected References.................................................................................................................................. 60

Figures

 1. The Rocky Mountains and Colorado Plateau region and its relationship 

to other coal regions in the National Coal Resource Assessment Project ...................... F2

 2. Process steps and factors considered for the calculation of available coal 

and economically recoverable coal resources....................................................................... 3

 3. Diagram depicting the growth in size of coal availability and 

recoverability resource evaluation study areas, 1986 to present ........................................ 4

 4. Coal availability and recoverability study areas in the Colorado Plateau: 

Arizona, Colorado, New Mexico, and Utah............................................................................ 10

 5. Coal mine locations in the Colorado Plateau......................................................................... 11

 6. The Somerset coal field area location map showing active mines, and inset map 

showing the Somerset quadrangle study area within the Uinta coal region................... 12

 7. Bisti coal field area location map and inset map of study area and active mines.......... 13

 8. The Northern Wasatch Plateau coal field area location map with local mines 

and accompanying relief map delineating the nine-7.5-minute-quadrangle 

study area and its relation to the Wasatch Plateau and Book Cliffs 

coal fields, central Utah ............................................................................................................ 14

 9. Simplified topographic map of the Somerset quadrangle with land ownership 

and mine locations ..................................................................................................................... 18

 10. Generalized composite stratigraphic section showing coal beds and 

adjacent strata of the Somerset quadrangle, Colorado....................................................... 19

 11. Data points and cross-section locations in the Somerset study area, Colorado ............ 21

 12. Coal correlation cross section A-A’, drawn generally E.-W., parallel to the 

North Fork of the Gunnison River............................................................................................. 22

 13. Coal correlation cross section B-B’, drawn generally N.-S., perpendicular 

to the North Fork of the Gunnison River ................................................................................. 23

 14. Pie charts showing total original coal resources and available coal resources 

for the six major coal beds in the Somerset quadrangle..................................................... 24

 15. Tectonic map of the San Juan Basin, New Mexico.............................................................. 30

 16. Photograph taken near Bisti Trading Post, looking to the northeast ................................. 30

 17. Photograph taken south of Bisti Trading Post, looking to the north................................... 30

 18. Geologic map of Bisti study area showing the location of 

drill-hole data, cross-section locations, and the Upper Cretaceous 

and lower Tertiary surficial geology........................................................................................ 31
 19. Generalized stratigraphic column of Fruitland Formation showing coal seams 

in the Bisti study area, San Juan Basin, New Mexico......................................................... 32

 20. Isopach map of total coal in the Red coal seam in the Bisti study area, 

northwest New Mexico............................................................................................................. 32

 21. Isopach map of total coal in the Green coal seam in the Bisti study area, 

northwest New Mexico............................................................................................................. 32

 22. Histograms comparing thickness and parting characteristics for 

each coal seam, northwest New Mexico .............................................................................. 33

 23. Cross section along structural strike in Bisti study area..................................................... 33

 24. Cross section down structural dip in western part of the Bisti study area ...................... 34

 25. Cross section down structural dip in eastern part of the Bisti study area ....................... 35

 26. Histograms comparing weighted average analyses of ash, sulfur, and 

lb sulfur per million Btu’s for the Fruitland Formation coal by seam in the 

study area and in the entire Bisti coal field ........................................................................... 36

 27. Map showing the thickness of overburden above the Red coal seam, 

Bisti study area, New Mexico .................................................................................................. 37

 28. Map showing the thickness of overburden above the Green coal seam, 

Bisti study area, New Mexico .................................................................................................. 38

 29. Mined-out areas and land-use restrictions in Bisti study area.......................................... 40

 30. Histograms summarizing the calculated coal resources by seam in the 

Bisti study area, New Mexico .................................................................................................. 41

 31. Pie diagrams illustrating coal resources excluded by likely restrictions to mining,

Bisti study area ........................................................................................................................... 42

 32. Quadrangle index map of the Northern Wasatch Plateau study area with 

locations of active and abandoned mine portals.................................................................. 44

 33. Coal mining areas and major grabens in the northern Wasatch Plateau, Utah .............. 45

 34. Annual coal production from 1980 to 1997 for mines in the northern half of 

the Wasatch Plateau coal field, Utah...................................................................................... 46

 35. Idealized stratigraphic section showing named coal beds in the 

Blackhawk Formation, northern Wasatch Plateau, Utah .................................................... 46

 36. Pie chart showing the amount of original minable coal by coal bed, 

Northern Wasatch Plateau study area, Utah......................................................................... 47

 37. Location of drill holes and measured sections used to calculate coal resources 

in the Blackhawk Formation, northern Wasatch Plateau, Utah ......................................... 48

 38. Bar graph showing the amount of coal no longer available due to 

past mining (through December 1997), northern Wasatch Plateau, Utah ........................ 49

 39. Pie chart showing technical restrictions that exclude 490 million short tons 

of coal from the available coal resources of the Northern Wasatch 

Plateau study area, Utah........................................................................................................... 49

 40. Pie chart showing land-use restrictions that exclude 146 million short tons 

of coal from the available coal resources of the Northern Wasatch Plateau 

study area, Utah.......................................................................................................................... 49

 41. Data reliability of original minable coal bed tonnage estimates for nine coal beds, 

Northern Wasatch Plateau study area, Utah......................................................................... 49
 42. Bar graph comparing coal bed thickness of the nine minable coal beds 

in the Northern Wasatch Plateau study area, Utah.............................................................. 50

 43. Bar graph comparing the burial depth of the nine minable coal beds in the 

Northern Wasatch Plateau study area, Utah......................................................................... 50

 44. Overburden thickness maps showing depth to the top of major coal beds, 

Blackhawk Formation, Northern Wasatch Plateau study area, Utah................................ 51

 45. Pie charts summarizing the availability of coal resources for nine coal beds, 

northern Wasatch Plateau, Utah ............................................................................................. 52

 46. Map showing the distribution of available coal for the Acord Lakes, Axel Anderson, 

Cottonwood, and Blind Canyon coal beds, northern Wasatch Plateau, Utah.................. 53

 47. Map showing the distribution of available coal for the Wattis, Gordon, 

Castlegate A, and Castlegate D coal beds, northern Wasatch Plateau, Utah ................. 54

 48. Bar graph showing the distribution of original minable coal by bed thickness 

compared to the percent of coal in each thickness interval that has been mined, 

northern Wasatch Plateau, Utah ............................................................................................. 55

Tables

 1 Listing of possible environmental, societal, and technological 

restrictions to mining ................................................................................................................. F7

 2. Mining methods considered in the Colorado Plateau region and their 

associated mining models and recovery rates ....................................................................... 8

 3. Listing of possible restrictions to coal mining, Somerset quadrangle, Colorado ............ 15

 4. Restrictions to Mining, Colorado 34-33-101, et. seq. ............................................................ 17

 5. Common bed names and thickness ranges of principal coal beds, 

Somerset quadrangle, Colorado .............................................................................................. 19

 6. Summary of original, restricted, and available coal resources of the 

Somerset quadrangle, Colorado, by bed ................................................................................ 24

 7. Summary of restricted coal resources of the Somerset quadrangle, 

Colorado, by bed ......................................................................................................................... 24

 8. Summary of estimated original, remaining, and available coal resources of the 

“B” coal bed in the Somerset 7.5-minute quadrangle, Colorado ....................................... 26

 9. Summary of estimated original, remaining, and available coal resources of the 

“D” coal bed in the Somerset 7.5-minute quadrangle, Colorado ....................................... 27

 10. Summary of estimated original, remaining, and available coal resources of the 

“E” coal bed in the Somerset 7.5-minute quadrangle, Colorado........................................ 28

 11. Summary of surface- and underground-minable and available coal resources, 

reported by seam, for the Bisti study area, New Mexico.................................................... 39

 12. Summary of original and available coal resources and restrictions to mining, 

reported by seam, for the Bisti study area, New Mexico.................................................... 39

 13. Restrictions, and their associated buffers and factors that prevent mining, 

in the Northern Wasatch Plateau coal field........................................................................... 47

 14. Total, minable, and available coal resources, northern Wasatch Plateau, Utah ........... 56
 15. Wasatch Plateau study area, Utah: as-received coal quality by bed................................ 56

 16. Somerset study area, Colorado: as-received coal quality by bed .................................... 56

 17. Bisti study area, New Mexico: as-received coal quality by bed........................................ 57

 18. Results of Colorado Plateau coal availability studies in Colorado, 

New Mexico, and Utah.............................................................................................................. 57

 19. Results of Colorado Plateau coal recoverability and economic evaluation 

studies in Colorado, New Mexico and Utah .......................................................................... 58

 20. Recoverable coal resources, as planned by mining method, for the 

Bisti study area, New Mexico .................................................................................................. 59

 21. Recoverable coal resources, as planned by mining method, for the 

Northern Wasatch Plateau study area, Utah......................................................................... 60
Introduction

The National and Regional Perspective

The National Coal Resource Assessment (NCRA) project, begun by the U.S. Geological Survey (USGS) in 1994, 

is studying fi ve major coal-producing areas in the conterminous United States (fi g. 1): the Appalachian Basin, the Illinois 

Basin, the Gulf Coast region, the Northern Rocky Mountains 

and Northern Great Plains region, and the Colorado Plateau 

region (U.S. Geological Survey, 1996). Although USGS sitespecifi c coal availability studies and coal recoverability studies 

predate the NCRA project, the collation and interpretation of 

geological, geographical, environmental, and social information in Geographic Information Systems (GIS) databases as 

part of the NCRA will ultimately save thousands of man-hours 

of data assimilation for subsequent detailed resource examinations within the fi ve coal regions. Computer systems and software have improved, and, as a result, NCRA project databases 

will provide the opportunity to evaluate the coal resources 

for geographical areas composed of multiple 7.5-minute quadrangles. Coal resource examinations in this chapter will report 

on areas ranging from one quadrangle (approximately 57 mi2) 

to as many as nine quadrangles (more than 500 mi2) in size. 

Concepts of Economic Evaluation 

for Coal Resources

Within the context of Coal Availability Studies, the available coal resources are defi ned as that part of the original 

coal resource that is accessible for mine development after 

subtraction of resources restricted by environmental, societal 

and technological constraints (fi g. 2) (Eggleston and Carter, 

1987). Alluvial valley fl oors and producing oil and gas wells 

are examples of constraints that may restrict coal mining in 

their immediate vicinities (Carter and Gardner, 1989; Eggleston and others, 1990; Molnia and others, 1997; Osmonson 

and others, 2000). Recoverable resources (fi g. 2) (Rohrbacher 

and others, 1993a) is that part of the available coal resource 

that is left after normal mining losses and cleaning losses 

are subtracted. Coal seam geometry, geologic hazards, mining 

methods, mine design, and preparation plant recoveries are 

considerations in determining recoverable coal. Coal quality 

and the cost of coal extraction and cleaning are not considered 

restrictions at this point. Calculations of the economically 

extractable coal resource (that part of the recoverable coal that 

can be mined, cleaned, and marketed at a profi t) take into 

account the marketability of the processed coal product; that 

is, coal quality, the cost to produce the coal and deliver it 

to the rail car or over-the-road truck, and its transport to the 

market (Rohrbacher and others, 1993a). We calculate mining 

and processing costs for all recoverable resources, including 

those profi table in today’s market and those that are not profi table today but, as energy resources are depleted, may become 

economic to produce in a future market.

The project methodology (fi g. 2) of coal availability, 

recoverability, and economic evaluation of coal resources 

involves the collection and collation of coal-bed information 

and, ultimately, the determination of the total coal resources 

and reserves of major coal beds. Required information 

includes the location; lithologic description; thickness of coal 

beds, overburden, interburden, and parting; quality of coal 

beds; chemical analysis of overburden, interburden, and partings; rock-mechanics characteristics and structural geologic 

data; the locations of active and abandoned mines; social 

and industrial constraints (towns, highways, powerlines, gas 

and oil wells and pipelines, and railroads); and environmental 

restrictions, such as endangered animal and plant species 

habitat or elk and deer winter range, rivers, alluvial valley 

fl oors, wetlands; and, fi nally, surface and subsurface land 

ownership.

Coal Availability, Recoverability, and 

Economic Evaluations of Coal Resources in the 

Colorado Plateau, Colorado, New Mexico, and Utah

By Timothy J. Rohrbacher, Carol L. Molnia, Lee M. Osmonson, M. Devereux Carter, Wynn Eakins, 

Gretchen K. Hoffman, David E. Tabet, Janet E. Schultz, David C. Scott, Dale D. Teeters, Glen E. Jones, 

Jeffrey C. Quick, Brigitte P. Hucka, and John A. Hanson

F1
Purpose

Coal availability and recoverability studies (CARS) and 

the economic evaluation of coal resources in the Colorado 

Plateau region were completed in order to:

 1. Produce estimates of the amount of coal that may be 

mined at a profi t from Colorado Plateau coal fi elds;

 2. Exchange and share information with industry and 

Government agencies involved with gas (particularly 

coal-bed gas) and oil research and exploration;

 3. Provide regional details and targets for future profi table 

coal extraction;

 4. Provide Government agencies with scientifi cally based, 

sound engineering information for land-use planning;

 5. Provide a means to construct better models to forecast 

future air emissions; 

 6. Produce sound, nonbiased, defensible coal-resourceavailability and economics information for future 

energy plans of the Nation; and

 7. Supplement existing databases through data collection 

from the Bureau of Land Management, Offi ce of Surface Mining, U.S. Forest Service, Environmental Protection Agency, State geological surveys, State departments of taxation and planning, and from the mining 

industry.

The ability to produce estimates of coal mining economics in specifi c areas and to integrate this information with 

supply/demand models in a digital decision-support system 

will allow planners and policy makers in Department of the 

Interior and Department of Energy to make educated, informed 

decisions concerning the environment, industry, and socioeconomic well-being of the Nation. For example, when the 

economically extractable resources from a coal fi eld are compared to the present rates of mining (resource depletion) and 

the socio-economic base of the local and surrounding areas is 

examined, an estimate of local mining industry longevity may 

be derived. This allows local governments and industry energy 

planners to anticipate and to plan for alternative industry and 

services growth. Also, the evaluation models and methodologies forged during these studies will assist in the development 

of other energy availability studies (uranium, oil and gas, coalbed methane).

It is important to note that other programs in the U.S. 

Illinois Basin

Region

Appalachian

Basin

Region

Northern Rocky Mountains

and Northern Great Plains Region

Rocky

 Mountains

and Colorado

Plateau Region

Unassessed Area

Gulf Coast Region

Figure 1. The Rocky Mountains and Colorado Plateau region and its relationship to other coal regions in the National Coal Resource 

Assessment Project.

F2 Geologic Assessment of Coal in the Colorado Plateau: Arizona, Colorado, New Mexico, and Utah
Geological Survey use the data gleaned from these studies. 

For example, the Earthquake Hazards and Global Seismograph Network Programs monitor seismic events that are 

coal-mine related, such as blasting and longwall and pillarextraction caving operations, to check the time, location, and 

amplitude of natural seismic events and to explain seismic 

events in relatively stable areas. Mine-location databases used 

and refi ned by the project, and knowledge of the mining 

methods employed at those locations, assist in explaining 

unknown seismic events. Additionally, environmental health 

issues related to coal-fi red emissions have, and will, benefi t 

from this information because coal quality may be more 

accurately predicted, and thus long-term emissions may be 

better estimated.

Federal and State agencies, mining operators, and coalbed methane developers in all of the major coal-producing 

basins have voiced their support for these detailed geologic 

and mining-economics models, supply/demand models, and 

for the development of decision-support systems. In addition 

to the U.S. Geological Survey and other Department of 

the Interior agencies, the U.S. Forest Service, Department 

of Labor, Department of Defense, Environmental Protection 

Agency, State and local agencies and the coal mining and 

electric power industry have expressed interest in the results. 

Perhaps the most interest in the coal availability-recoverability 

and National Coal Resource Assessment Projects, however, 

comes from the Department of Energy/Energy Information 

Administration, where these studies are used to improve and 

update the national demonstrated reserve base and to assist in 

the development of a national energy policy. 

Coal Availability and Recoverability Studies: 

Early Studies to Present Studies

The U.S. Geological Survey and the Kentucky Geological 

Survey started coal availability studies in 1986 in the Matewan 

COAL AVAILABILITY STUDIES

ORIGINAL COAL

- minus -

 AREAS ALREADY MINED

- minus -

ENVIRONMENTAL

- minus -

TECHNOLOGIC CONSIDERATIONS

AVAILABLE COAL

COAL RECOVERABILITY STUDIES

- minus -

MINING LOSSES

- minus -

WASHING LOSSES

- equals -

RECOVERABLE RESOURCES

- minus -

MINABLE RESOURCES TOO COSTLY TO EXTRACT

- equals -

ECONOMICALLY RECOVERABLE RESOURCE

(Reserve)

- equals -

+ Pillars

SOCIETAL

- minus -

AVAILABLE COAL

Original Minable Coal

Resource

Remaining

Resource

Resource 

Available

for Mining

Recoverable

Resource

Restricted Resource

Economic Resource

Compliant Non Compliant

Mined out

Mining losses Washing losses

Coal + Parting

Surface Mining 12" >_

Underground Mining 24" >_

Produced Tons

Technologic Restrictions

to Mining

Pillars, unreclamable lands, transport

and crushing losses, etc.

Parting in the coal seam ( up to 50% )

Resources lost during Mining

Environmental and Societal

Restrictions to Mining

Resources lost during washing

(Beneficiation)

Sales price production cost >_

< 1.2# SO /MM Btu >1.2# SO /MM Btu 2 2

(Reserve)

Process Steps for Calculation 

of Available Coal and 

Economically Recoverable 

Coal Resources

Flow chart showing factors to be

considered for calculation of

economically recoverable coal resources.

minus

minus

Figure 2. Process steps and factors considered for the calculation of available coal and economically recoverable coal resources.

Coal Availability, Recovery, Economic Evaluations of Coal Resources, Colorado Plateau: Colo., N. Mex., and Utah F3
7.5-minute quadrangle (fi g. 3) in eastern Kentucky (Eggleston 

and Carter, 1987; Eggleston and others, 1990). Upon successful development of a program methodology to determine 

coal resources available for mining (Eggleston and Carter, 

1987) and realistic results of the pilot study, the program 

was expanded to the other coal States in the central and northern Appalachian Basins (Carter and Gardner, 1989), then to 

the coal States in the Illinois Basin, and then to the western 

coal basins. More than 100 cooperative studies by State geological surveys and the U.S. Geological Survey have been 

completed in the Appalachian, Illinois, Powder River, and San 

Juan Basins, and Colorado Plateau (Carter and others, 1999). 

Coal availability and recoverability studies historically 

have restricted the area of study to key 7.5-minute quadrangles 

in order to determine the amount of coal available for mining 

(Carter, 1996; Carter and Gardner, 1989, 1994; Carter and 

Rohrbacher, 1996, 1997; Carter and others, 1999a; Cetin and 

others, 1996; Eggleston and others, 1990; Fedorko, 1996; 

Rohrbacher and others, 1993a, 1993b; Scott, 1995; DST and 

Associates, written commun., 1997, 1998; and U.S. Bureau of 

Mines, 1995). The logic was that if a representative sampling 

of quadrangles could be made, then those results could be 

applied statistically to larger areas to describe the remaining 

coal resources and the restrictions to mining. This logic was 

predicated on the limited data handling and computing capabilities available at that time. However, the Kentucky Geological Survey and others found that, because of geological, 

geographical, and topographic differences between the quadrangles, results from one quadrangle could not be accurately 

projected to another quadrangle (Weisenfl uh and others, 1997). 

The results from more than 30 quadrangles indicated that, in 

most cases, the percentage of resources available for mining 

and recoverable during mining did not vary greatly; however, 

the amount of economically recoverable resources varied and 

the projection of results was not possible. Because of this, we 

began to study areas larger than single 7.5-minute quadrangles 

(fi g. 3), such as coal fi elds, coal basins, and multi-quadrangle 

areas, for coal availability and recoverability. Three of 

these larger studies examined Colorado Plateau coal fi elds: 

the Bisti coal fi eld in the San Juan Basin, New Mexico (Hoffman and Jones, 1999, 2000; DST and Associates, written 

commun., 1999); the northern Wasatch Plateau coal fi eld in 

Utah (Tabet and others, 1999, 2000; DST and Associates, 

written commun., 1999); and the Somerset coal fi eld, Colorado (Schultz and others, 2000; DST and Associates, written 

commun., 2000). Other large-area availability and (or) recoverability studies include the Gillette coal fi eld in Wyoming 

(Osmonson and others, 2000); the Springfi eld coal in the Illinois Basin (Conolly and Zlotkin, 1999; DST and Associates, 

written commun., 2000; Treworgy and others, 1999, 2000; 

Weisenfl uh and others, 1999) and individual coal beds in the 

northern and central Appalachian Basin (Rupert and others, 

1999, 2000). 

The time required for collection of information for these 

types of studies increases as the study area size increases; 

however, because many geographic, environmental, social, and 

geologic databases are now in digital form within the public 

domain, much of the information can be acquired through 

Geographic Information Systems—GIS (Biewick and others, 

1997, 1998; Ferderer, 1996; D.A. Ferderer, U.S. Geological 

Survey, written and oral commun., 1996, 1999). As a result, 

construction of geologic and mining models and calculations 

of recoverable resources and mining economics require far less 

time today than 5 years ago because of advances in computing 

and database organization.

Many databases containing scientifi c and societal information now reside on the Internet. Federal agencies, such 

as the Census Bureau and Department of Labor publish staFigure 3. Diagram depicting the growth in size of coal availability and recoverability resource evaluation study areas, 1986 to present. Small 

rectangles in right-hand part of illustration represent 71⁄2-minute quadrangles.

F4 Geologic Assessment of Coal in the Colorado Plateau: Arizona, Colorado, New Mexico, and Utah
tistics related to population density and surface expressions 

(highways, roads, buildings, industrial sites, etc.). These can be 

supplemented with databases from the USGS database library, 

the ERDAS library, privately marketed databases, and research 

databases from colleges and universities. For more information concerning the USGS Database Library, contact D.A. 

Ferderer at dferdere@usgs.gov or visit the USGS web site 

at: http://www.usgs.gov. Additional information may be found 

at the USGS’s decision support system, called GEODE, at 

www:dss1.er.usgs.gov. 

Methodology

Coal Availability, Recoverability, and 

Economic Evaluation Terminology

Coal availability and recoverability studies and economic 

evaluations of coal resources have been largely dependent on 

the State geological surveys to gather and build the required 

databases (Rohrbacher and others, 1993, 1994, 1995). Those 

databases typically contain:

 1. Detailed geologic information and correlation of coal 

beds, and

 2. Environmental, technical, and social restrictions.

Those databases have been supplemented by information 

gathered from the Bureau of Land Management, Offi ce of 

Surface Mining, U.S. Forest Service, Environmental Protection 

Agency, State departments of taxation and planning, and from 

the mining industry.

The coal availability and recoverability study methodology (Rohrbacher and others, 1993a) is summarized in fi gure 2. 

In this paper, the term reserve refers to any coal resource that 

can be legally extracted at a profi t (Abbott, 1990; U.S. Bureau 

of Mines, 1968). Legally extractable coal resources are determined through a thorough research of land ownership, understanding the geology and the restrictions applied to mining, 

and developing a best-alternative mine plan for resource recovery (in essence, coal availability and coal recoverability). The 

term profi t in this report is defi ned as the point where the 

income from sales of the coal is equal to or greater than the 

cost to produce the coal (economic analysis of coal resources). 

Income taxes and corporate rates of return were not included 

in this analysis but have been addressed in the coal resource 

economics chapter of the NCRA.

In coal availability studies, the net-coal thickness in coal 

beds was measured and summed. Partings greater than 0.25 

inch thick were excluded from the resource calculation (Wood, 

and others, 1983; Eggleston and Carter, 1987; Eggleston and 

Others, 1990). It is very important to note that in recoverability studies, the entire coal seam—coal plus parting plus 

dilution—is measured in the resource calculations (Rohrbacher 

and others, 1993a). 

The term coal seam refers to the coal bed, beds, or 

benches and their associated parting material that must be 

extracted together during the mining. Coal is a solid, more 

or less stratifi ed, combustible carbonaceous rock formed by 

partial to complete decomposition of vegetation. Coal, when 

dried at 100°C, should contain at least 50 percent combustible 

material. Parting material may be composed of combustible 

material, ash material, or other inorganic material in the form 

of carbonaceous shale, bone coal, shale, siltstone, sandstone, 

etc. The ash and parting composition are dependent on the type 

of material from which the coal was formed, the sediments 

carried into the coal while it was forming, ancient volcanic 

eruptions, and the dissolved matter brought in at the time of 

deposition or introduced later (U.S. Bureau of Mines, 1968; 

Stefanko, 1983).

The best-alternative mine plan is developed by employing practical mining schemes that fi t the geology of the 

resource and the restrictions of the environment. Variables 

include the depth to the coal seam; the thickness of the coal 

seam; the structural complexity of the deposit; the environmental, social, and technical restrictions to mining; and the 

coal quality. Subsequently, the economic evaluation of this 

best-alternative plan and its associated coal resources is dependent on the effects of these variables to increase (or decrease) 

the cost of mining. Considering all of the variables, the quality 

of coal produced from the mine may be the single most important one. Depending on the depositional environments of the 

coal and the introduction of fl uids at some time after deposition of the strata, the coal may contain sulfur and other 

undesirable elements, and the parting material may contain 

combustible material, a high amount of noncombustible material (ash and other inorganic material), and higher amounts 

of sulfur and other undesirable elements than the coal. The 

coal may be benefi ciated (washed) to remove as much ash and 

hazardous elements as possible. Washing is successful when 

the ash material has a different density than the coal and the 

sulfur—generally contained as pyrite—is in a form that will 

wash out with the ash material. If the ash has nearly the same 

density as the coal and the sulfur is associated with organic 

constituents in the parting or coal, the coal seam may not able 

to be benefi ciated (Leonard, 1979) and therefore may not be 

economic to mine.

In underground mines, all of the in-seam material (coal 

and partings) must be mined together. During the mining process, some out-of-seam material (dilution) is produced with 

the coal seam. Occasionally, the coal quality of the underground-mined coal (particularly in the thick coal seams of the 

Colorado Plateau) is good enough to be sold directly from 

the mine rather than go through the costly process of coal 

washing. Parting material occurring in a surface-mined coal 

seam may be removed from the coal seam by mining the top 

coal bench, removing the parting bench, then mining the lower 

coal bench. 

Washing increases the cost per short ton of produced 

coal and reduces the included parting and dilution material 

by 88–96 percent, on average, and the coal material by 4–8 

percent, on average. For example, if a mine produced 5 million 

raw short tons per year and the product contained 20 percent 

Coal Availability, Recovery, Economic Evaluations of Coal Resources, Colorado Plateau: Colo., N. Mex., and Utah F5
(1 million short tons) parting plus dilution material and 80 percent (4 million short tons) coal, the resulting recovered saleable tonnage after washing would be a mixture of 80,000 short 

tons of parting and dilution material and 3,760,000 short tons 

of coal, a total of 3,840,000 short tons of washed product. 

If, in the worst case, the parting is 100 percent ash and inorganic material, 4.5 percent sulfur (80 percent of the sulfur as 

pyrite) and 0 Btu’s/lb (no combustible material), and the coal 

contained 5 percent ash, 3.5 percent sulfur (25 percent of the 

sulfur as pyrite) and 13,400 Btu’s/lb heating value (assume 

the moisture of the raw product and the washed product are 

the same), then the raw product from the mine would have 

a quality of 24 percent ash, 3.7 percent sulfur and 10,720 

Btu’s—an unsaleable product in the U.S. market regardless of 

mining costs. However, if the raw product is washed using 

the above recovery rates, the 3,840,000 short tons of washed 

coal will have a product coal quality of 7.3 percent ash, 2.6 

percent sulfur, and 13,120 Btu’s, a saleable product worth 

$23 to $25/short ton in the northern Appalachian coal market 

(depending on the distance from the mine to the power plant). 

For this reason it is imperative that channel and core samples 

collected for chemical and physical property analysis, always 

include parting and potential dilution material, as well as coal. 

The Colorado Plateau coal availability evaluations 

assumed that only coal was available for mining (Eggleston 

and Carter, 1987 and Eggleston and others, 1990; Wood and 

others, 1983). Colorado Plateau coal recoverability evaluations 

assumed that a maximum mix of 50 percent coal and 50 

percent parting plus out-of-seam dilution could be mined. By 

this defi nition, it is possible that the total original resource of 

coal (including parting and dilution) might be as much as 100 

percent greater than the total original coal resource calculated 

with no parting included. The recoverability methodology is 

coal-industry-oriented and allows more coal seams to meet the 

minimum-mining-thickness requirements. This concept forces 

the technology and economics of coal extraction and coal 

cleaning (washing) to be the determining factors for reserve 

calculation. The reasoning for this difference is that the 

availability method is looking for geological explanations 

and understanding the mode of occurrence and extent of 

the deposit, whereas the recoverability method calculates the 

minability, product quality, salability, and economics of the 

deposit.

Restrictions to Mining

Figure 2 shows the general process steps used in coal 

availability and recoverability studies. After the total coal 

resources are modeled and calculated based on mining 

schemes, coal (and parting) resources that had been present 

within mined-out areas are determined. Environmental, societal, and technologic restrictions to mining are outlined and 

the resources affected by these restrictions are calculated. 

These restrictions may vary signifi cantly from coal basin to 

coal basin. Table 1 is a partial listing of possible restrictions 

to mining. Some restrictions are controlled by Federal law (43 

CFR 3461.5), whereas others are determined on a site-by-site 

basis by State and Federal regulatory agencies. Coal resources 

in mined-out and restricted areas are then subtracted from the 

original resources yielding the resources available for mining. 

Computerized prefeasibility mine planning (Rohrbacher, 1997; 

and Rohrbacher and others, 1993a, 1993b) is then applied to 

the available resources, and the potentially minable coal tonnage is determined for each mining method. The mine-planning program, MINEPLAN (see Mining Costs and Reserve 

Calculations section) yields recoverable tonnages and mining 

losses assigned to each mining method. Dilution, based on 

mining method, and wash plant loss is then calculated. The 

total mining losses and washing losses are then subtracted 

from the available resources to calculate the estimated recoverable resource. The minable resource estimates are then analyzed using COALVAL (see Mining Costs and Reserve Calculations section), a coal resource recoverability/mine costing 

program (Suffredini and others, 1994). Results are summarized 

in tables containing estimates of total original in-place short 

tons, tons lost during past mining and washing operations, tons 

lost to mining restrictions, and recoverable tons yielded by 

each mining method. The costs are summarized in increments 

from less than $4/short ton to costs greater than $50/short ton 

(called cost curves) and include a break-even cost to determine 

reserves at a set point in time. A coal reserve as defi ned 

here is a recoverable coal resource that can be mined and 

sold at a profi t in today’s market (Abbott, 1990). All reserves 

are divided into compliance quality, that is less than 1.2 

lb SO2/million Btu’s of heating value, and non-compliance 

quality, greater than 1.2 lb SO2/million Btu’s of heating 

value (fi gure 2). The conversion formula for percent sulfur 

to pounds SO2/million Btu’s may be stated: (percent sulfur 

× 2,000,000)/Btu’s = lb SO2/1,000,000 Btu’s, where percent 

sulfur is in decimals—for example, 2 percent sulfur = 0.02.

Potential restrictions are evaluated for each specifi c 

mining project. In some cases the potential restriction might 

be mitigated.

To make resource recovery and economic evaluations of 

potentially minable coal, individual coal seams must be correlated. This detailed geological work usually takes place at 

the same time as databases containing potential mining restrictions are compiled by the team conducting the availability, 

recoverability, and mining-economics study. 

Calculating Reserves from Resources

Mine Planning

During the early 1990’s the former U.S. Bureau of Mines 

developed a mine planning program, MINEPLAN (see Mining 

Costs and Reserve Calculations section), using GRASS GIS 

scripts to plan the potential mining of available coal resources 

(Rohrbacher and others, 1993). Five surface-mining methods 

and two underground-mining methods were examined for the 

F6 Geologic Assessment of Coal in the Colorado Plateau: Arizona, Colorado, New Mexico, and Utah
mining of Colorado Plateau resources. Those mining methods 

and their production models are listed in table 2. Contour 

stripping was found to be an inapplicable surface method in 

the Colorado Plateau due to environmental restrictions and 

was not considered in the mine planning. The underground 

methods of room and pillar mining and longwall mining were 

chosen because of their high productivity and widespread 

use. We considered local and practical mining methods and 

employed prefeasibility-type mine planning in this study. 

MINEPLAN programming priorities were set to default from 

one mining method to another. For example, if the topography 

was a gentle slope and the coal beds cropped out, then dragline, truck and shovel, or area stripping methods were fi rst 

applied. These surface methods were generally planned to a 

stripping ratio of 10:1 for the fi nal highwall (maximum stripping depth); then, entry sites for underground mine access 

were planned; room and pillar patterns or longwall panels were 

modeled; and the remaining highwall was planned for auger 

mining, prior to planning for reclamation. 

The MINE PLAN program does not require a particular 

map scale for planning. Most of the prefeasibility-type mine 

planning is done at a scale of 1 inch = 2000 ft (1:24,000). 

For that reason, the information that goes into the geo-model 

building, and from which the GIS layers are created, must be 

obtained from information compiled at this scale. Coal availability GIS data collected by the State geological surveys are 

normally prepared at 1 inch = 2000 ft scale.

The methodology of Eggleston and others (1990) 

and Wood and others (1983) assumes that the minimum 

underground-minable coal bed will comprise 28 inches of coal 

(no parting material is included in the minimum seam thickness) and the minimum surface minable coal bed will comprise 

14 inches of coal (again, no parting material was included 

in the minimum seam thickness). In recoverability studies the 

minimum mining thickness (hence seam thickness) used for 

underground mining is 24 inches, and, for surface mining, the 

minimum mining thickness used is 12 inches. These minimum 

thicknesses were agreed upon in consultation with the mining 

industry. The 14-inch and 28-inch minimum bed thicknesses 

used in previous resource assessments will be used in this 

report only for comparison.

Resource Recovery

The mining of a thin seam of coal, whether by surface or 

underground methods, requires more time per ton than mining 

a thick seam (economies of scale), and the equipment used 

to mine thin seams is different than equipment used in thickseam mining. The production models (table 2) are based on 

equipment suitable for mining within the seam thickness. The 

thickness categories are based on present-day mining practices 

(U.S. Bureau of Mines, 1984–1994) as observed by engineers 

who evaluated the mining methods, resource recovery, staffi ng 

and wage rates, productivity, capital equipment, taxation, and 

owning and operating costs. As part of those mine evaluations, 

recovery rates were examined and mine maps digitized to 

document the coal tonnage extracted and the tonnage left in 

the mine as support pillars, pillars between adjacent mines, 

and barrier pillars between the mine and the outcrop. Table 2 

shows the mining methods, production-model categories, and 

associated recovery rates.

The underground mining production models also account 

Table 1. Listing of possible environmental (env), societal (soc), and 

technological restrictions to mining. 

A. Coal-leasing unsuitability criteria from 

Federal Coal Management Regulations (43CFR 3461.5) 

 1. Federal lands (soc) 

 2. Rights of way and easements [i.e., railroad] (soc) 

 3. Dwellings, roads, cemeteries, and public buildings (soc) 

 4. Wilderness Study Areas (env) 

 5. Lands with outstanding scenic quality (env) 

 6. Lands used for scientific study (env) 

 7. Historic lands and sites (soc) 

 8. Natural areas (env) 

 9. Critical habitat for threatened or endangered species (env) 

 10. State listed threatened/endangered species (env) 

 11. Bald or golden eagle nests (env) 

 12. Bald and golden eagle roost and concentration areas (env) 

 13. Federal lands containing active falcon cliff nesting sites (env) 

 14. Habitat for migratory bird species (env) 

 15. Fish and wildlife habitat for resident species (env) 

 16. Flood plains (env) 

 17. Municipal watersheds (soc) 

 18. National resource waters (env) 

 19. Alluvial valley floors (env) 

 20. State or Indian Tribe criteria (soc)

B. Other applicable land-use restrictions 

 1. Towns (soc) 

 2. Pipelines and power lines (soc) 

 3. Industrial sites (soc) 

 4. Archaeological areas (soc) 

 5. Ownership issues (soc) 

 6. Wetlands (env) 

 7. Streams, lakes, and reservoirs (env) 

C. Technological restrictions considered 

 1. Burned or oxidized coal 

 2. Coal beds too thin to mine 

 3. Coal-bed discontinuities 

 4. Coal beds <40 ft apart (too close) 

 5. Coal beds dip too steeply to mine 

 6. Roof or floor problems 

 7. Minimum and maximum depth limitations on 

underground mining 

 8. Too close to intrusives or faults 

 9. Active mines/barrier pillars 

 10. Mined-out/abandoned mine areas 

 11. Subsidence over abandoned mines 

 12. Slopes too steep to reclaim 

 13. Oil and gas development 

 14. Resource block size 

Coal Availability, Recovery, Economic Evaluations of Coal Resources, Colorado Plateau: Colo., N. Mex., and Utah F7
for material excavated from above and below the coal seam 

(dilution) while the seam is being removed. This dilution is 

added to the produced tonnage of coal plus parting material.

Mining Costs and Reserve Calculations

After the geologic and restriction information has been 

compiled, the resulting spatial data are then stored in digital 

databases accessible to Geographic Information System (GIS) 

programs that can produce three-dimensional geologic models, 

coal-quality models, and layers depicting mining-restriction 

information. The restrictions can be registered to the geologic 

model and can individually be subtracted, one layer at a time, 

from the geologic model. The results of these calculations 

are (1) an estimate of the total original coal resource; (2) an 

estimate of coal tonnage for each resource restriction; and (3) 

an estimate of tonnage remaining after restrictions to mining 

have been addressed.

The geologic and restriction data can be manipulated and 

analyzed through three different GIS computer methods. One 

uses a raster-based GIS program named GRASS (Geographical Resources Analysis Support System), developed by the 

U.S. Army Corps of Engineers. GRASS is used to generate 

contour and isopach maps and to produce volumetric analysis 

of the coal beds; it also allows integration of various resource 

characterization and distribution coverages as previously mentioned. The second method is the vector-based ARC/INFO 

program developed by Environmental Systems Research Institute, Inc. (ESRI). As part of this method, isopach and 

contour maps are processed using Interactive Surface Modeling (“Earth Vision”) software developed by Dynamics Graphics, Inc. (Hettinger and others, 1996), and these maps are then 

converted to ARC/ INFO coverages to allow integration of 

geologic and geographical spatial data. The third GIS method 

uses the Spatial Analyst extension of ArcView (ESRI) to analyze both raster- and vector-based data. These three methods 

produce comparable results.

Logical mine planning evaluations are made with the 

MINEPLAN program. MINEPLAN was written for GRASS 

using UNIX shell scripts. Assumptions concerning maximum 

stripping ratios, maximum depth to the coal seam, coal seams 

above (superjacent) and below (subjacent) the seam of interest, 

minimum underground and surface mining areas needed for 

production, restrictions to mining, best-alternative mine layout 

for the 18 mine models (table 2), and surface coal transportation from the mine portal to the wash plant or rail loadout were 

incorporated into the MINEPLAN modeling program. Then 

a logical progression of mine development was designed; for 

example, surface mining would precede underground mining. 

When the maximum economic depth was reached in the surface mine, the program enables us to plan the extraction 

of underground-minable resources. Underground resources 

are fi rst planned with longwall mining methods where the 

resources are thick enough and extensive enough to support 

a longwall operation. The remaining resources are planned 

for room and pillar mining, with pillar extraction and retreat 

Table 2. Mining methods considered in the Colorado Plateau region and their associated mining models 

and recovery rates. 

[MM, million; CY, cubic yard; tpy, short tons per year; *, most common methods in region] 

 Surface methods Production model Recovery factor 

Contour strip (1) 12–36 in seam thickness 78% 

 (2) > 36 in seam thickness 93% 

Area mining (1) > 12 in seam thickness 93% 

Auger mining (1) 12–36 in seam thickness 30% 

 (2) > 36 in seam thickness 30% 

*Truck/shovel mining (T/S) (1) Small T/S operation (< 2MM tpy production) 78–93% 

 (2) Medium T/S operation (2MM–10MM tpy production) 85–95% 

 (3) Large T/S operation (>10MM tpy production) 85–95% 

*Dragline (DL) (1) Small DL operation (< 50 CY bucket size) 80–93% 

 (2) Medium DL operation (50-100 CY bucket size) 85–95% 

 (3) Large DL operation (>100 CY bucket size) 85–95% 

 Underground methods Production model Recovery factor 

*Room and pillar (1) 24–42 in seam thickness 57–62% 

 (2) 42–72 in seam thickness 58–65% 

 (3) 72–96 in seam thickness 60–67% 

 (4) > 96 in seam thickness 62–67% 

*Longwall (1) 42–72 in seam thickness 78–82% 

 (2) 72–96 in seam thickness 78–84% 

 (3) > 96 in seam thickness 78–84% 

F8 Geologic Assessment of Coal in the Colorado Plateau: Arizona, Colorado, New Mexico, and Utah
caving operations where applicable. The MINEPLAN program enables us to identify the minable resource, plan the 

logical mining sequence for the 18 different mine models, and 

calculate the minable tonnage by mine model. The graphic 

output may be checked during the mine planning simulation, 

or the program may be run without interruption. The calculated output from MINEPLAN is exported via ASCII fi les 

directly into the mine costing and recoverability-summarizing 

program, COALVAL. 

COALVAL is an interactive, macro-based, program written for LOTUS software (Lotus Development Corporation), or 

Excel software (Microsoft, Inc.). COALVAL/Lotus was written by Plis and others (1993) and updated by Suffredini and 

others (1994) of the U.S. Bureau of Mines. More recently 

Coghlan (U.S. Geological Survey, written commun., 1999) and 

Rohrbacher (U.S. Geological Survey, written commun., 1999) 

rewrote and updated COALVAL in Excel. The program 

was designed to factor in production rates, optimized equipment and manpower requirements, and engineering cost analyses for typical mining methods and mine sizes. Data from 

U.S. Bureau of Mines economic analyses of more than 100 

U.S. mining operations were categorized by geographic area, 

mining method, and mining confi guration. These data were 

then validated by comparing to mining cost estimates from 

the SME Mining Engineering Handbook (1973), Mining 

Cost Service (1999), and Western Coal Basin Supply and 

Demand Analysis (1988). Then, the costs and production rates 

were incorporated into the COALVAL program models. The 

COALVAL/Lotus models contain cost-of-living and Department of Labor indicators that may be updated on a regular 

basis. The basic output of COALVAL is estimates of recoverable short tons of clean coal by mining method. COALVAL 

also produces a series of cost curves showing how many of 

those recoverable short tons are profi table to mine in today’s 

coal market. 

Acknowledgments

This chapter of the Colorado Plateau Resource Assessment was jointly researched and written by the coal geologists 

of the State geological surveys of Colorado, New Mexico, 

and Utah and the coal availability-recoverability staff at the 

U.S. Geological Survey. The research and published reports 

have been co-funded by the USGS and each cooperating 

State geological survey. Many State and Federal staff not mentioned herein assisted the primary researchers. Their work is 

acknowledged in the State geological survey publications. The 

authors are also deeply indebted to many State and Federal 

agencies and coal mines that provided informational data, such 

as drill holes, mine recovery rates, and coal mine costs for 

these studies.

Wynn Eakins and Carol M. Tremain Ambrose, formerly 

of the Colorado Geological Survey (CGS), and David C. Scott 

and Dale D. Teeters, of DST and Associates, authored Colorado Resource Series Report No. 36 (Eakins and others, 1998) 

on the availability of coal resources in the Somerset quadrangle, Colorado. Wynn Eakins and Janet E. Schultz coauthored the Somerset quadrangle discussion in this chapter.

New Mexico Bureau of Mines and Mineral Resources 

Open-File Report 438, concerning the available coal resources 

of the Bisti coal fi eld, was coauthored by Gretchen K. Hoffman 

and Glen E. Jones (2000). Gretchen K. Hoffman wrote the Bisti 

coal fi eld discussion in this chapter.

David E. Tabet, Jeffrey C. Quick, Brigitte P. Hucka, and 

John A. Hanson of the Utah Geological Survey wrote the coal 

availability paper entitled “The available coal resources for 

nine 7.5-minute quadrangles in the Northern Wasatch Plateau 

coal fi eld, Carbon and Emery Counties, Utah” (UGS Circular 

100, 1999) and the Wasatch Plateau discussion in this chapter.

Finally, the senior author would like to express his gratitude and thanks to Steve Roberts for his observations, suggestions, and detailed review of the manuscript and to Brenda 

Pierce for her organizational concepts concerning the manuscript. Both are research geologists for the U.S. Geological 

Survey. David Tabet of the Utah Geological Survey also critically reviewed the manuscript and suggested changes that 

enabled the author to more closely compare coal availability 

results derived by different methodologies. Their help, guidance, and insistence on writing standards have helped produce 

this report.

Colorado Plateau Studies

Introduction

In 1996 and 1997 U.S. Geological Survey scientists 

became involved in availability and recoverability studies with 

the Colorado Plateau State geological surveys. Coal-fi eld areas 

have been selected for coal availability-recoverability study 

evaluations (fi g. 4) based on the high amount of resources 

they contain, the past and present mining activity (fi g. 5), geologic and cultural characteristics, resource management issues, 

demand for the coal, and data accessibility. Lists of restrictions 

to mining, generally provided by the State geological surveys, 

were reviewed and updated to keep current with new research, 

public opinion, and political agendas.

Coal availability and recoverability studies in the Colorado Plateau began with a recoverability study by the U.S. 

Bureau of Mines (Osmonson) in 1994. The purpose of that 

study was to assist the U.S. Forest Service (USFS) and the 

Bureau of Land Management (BLM) in the evaluation of coal 

resources that would be affected if longwall mining was prohibited near cliff-forming sandstone outcrops in the Manti-La 

Sal National Forest on the Wasatch Plateau, Utah. The coal 

geology data came from the Utah Geological Survey and 

the U.S. Forest Service, and coal informational databases—

maps and digital databases showing mined-out areas and other 

Coal Availability, Recovery, Economic Evaluations of Coal Resources, Colorado Plateau: Colo., N. Mex., and Utah F9
restrictions to coal mining—came from the Utah offi ce of the 

Bureau of Land Management. The spatial databases for the 

Manti-La Sal National Forest study contained geologic and 

mining information such as lithologic descriptions, coal-seam 

thickness, coal quality, geologic structure information, active 

and abandoned mine areas, social and industrial constraints 

(such as private dwellings and buildings, highways, power 

lines, gas and oil wells, and pipelines) and environmentally 

restrictive areas (such as endangered animal and plant species 

habitats, rivers, alluvial valley fl oors, wetlands, National Forest 

surface ownership, raptor habitat, and elk and deer winter 

range).

Once the databases were constructed, the three-dimensional geologic models prepared, and the geographical areas 

(polygons) of restrictions determined, the coal resources were 

calculated by computer and applicable mine plans were developed for the Manti-La Sal National Forest (L.M. Osmonson, 

U.S. Bureau of Mines, written commun., 1994; Rohrbacher, 

1997). The purpose of this study was not only to model and 

study a multi-7.5-minute-quadrangle area and to determine the 

available and recoverable resources and potential reserves but 

also to determine the minable coal resource that would be 

affected if the U.S. Forest Service prohibited mining-induced 

caving within the area of infl uence of rim-rock habitat (cliff 

faces). The results indicated that this regulation could potentially restrict the recovery of more than 500 million short 

tons of 0.6 percent sulfur, 12,700 Btu/lb. coal (sold quality, 

as-received basis).

State Geological Survey Cooperative Programs

Colorado Studies

In 1997 the USGS began a cooperative funding program 

with the Colorado Geological Survey to conduct a coal availability study of the Somerset quadrangle, located on the southCoal-bearing strata

Coal

 Availability/

Recoverability

Studies

Completed

In Progress

(1999)

Planned

Interstates

Railroads 

N. Wasatch

 Plateau Study

N. Book 

Cliffs Study

Somerset Study

Bisti Study

Menefee Study

S. Wasatch

 Plateau Study

Gallup

Farmington 

Durango

Cedar City

Moab

Price

Albuquerque 

Socorro 

Flagstaff

Grand Junction

40

15

15

70

10

113°

113°

34° 34°

40° 40°

106°

106°

0 100 Miles

Colorado Plateau study area

AZ

UT

NM

CO

Henry Mountains

Study

S. Book 

Cliffs Study

Yampa Study

La Ventana Study

Figure 4. Coal availability and recoverability study areas in the Colorado Plateau: Arizona, Colorado, New Mexico, and Utah.

F10 Geologic Assessment of Coal in the Colorado Plateau: Arizona, Colorado, New Mexico, and Utah
ern fl ank of the Piceance Basin in west-central Colorado (fi g. 

6). The study was completed in 1998 and published by the 

Colorado Geological Survey (Eakins and others, 1998). This 

work was followed by an availability study of a fi ve 7.5-minute-quadrangle area containing the Somerset quadrangle and 

four adjoining quadrangles (fi g. 6). The minable coal fi eld is 

restricted by depth considerations (the coal seams are in excess 

of 3,000 ft below the surface) on the north and south sides of 

the fi ve-quadrangle study area, and by outcrops to the west and 

pinch-out of the coal seams to the east.

Coal availability studies were conducted on six major 

coal beds in the Somerset quadrangle and on four of those 

six major beds within the surrounding area of the coal fi eld. 

Data for the two unstudied coal beds outside the Somerset 

quadrangle were too sparse to make accurate correlations or to 

model the beds for mine planning. A modifi ed summary of the 

Somerset quadrangle report is included in this chapter.

Mining began in the Somerset coal fi eld in the late 

1880’s and continues today. Steep ground slopes and Gunnison 

National Forest property preclude surface mining of the coal. 

Most of the present-day production comes from thick-seam 

longwall mining. Coal produced in Somerset coal fi eld mines 

is transported to the utility market, fi rst on the North Fork 

Branch, and then the main line of the Union Pacifi c Railroad. 

The most recent environmental and societal information for 

the Somerset area is contained in an Environmental Impact 

Study completed by the BLM and USFS (U.S. Bureau of Land 

Management, 1999). The recoverability study and economic 

evaluation of the Somerset coal fi eld is being completed (DST 

and Associates, written commun., 2000).

New Mexico Studies

Ths USGS began cooperatively funded coal availability 

studies in 1997 with the New Mexico Bureau of Mines and 

Mineral Resources (NMBMMR). A joint agreement was made 

to investigate the large unmined portions of the San Juan Basin 

Gallup

Farmington 

Durango

Cedar City

Moab

Price

Albuquerque 

Socorro 

Flagstaff

Santa Fe 

Grand Junction

Salt Lake City 

Denver

Tucson 

Phoenix

70

25

40

25

40

15

70

80

10

19

10

 8

Cretaceous

Coal-bearing strata

Colorado Plateau

Region

113°

113°

106°

34° 34°

40°

106°

0 100 Miles

Utah

Colorado

New Mexico

Arizona

AZ

UT

NM

CO

(e.g. loadouts, blending

plants, etc.)

Figure 5. Coal mine locations in the Colorado Plateau.

Coal Availability, Recovery, Economic Evaluations of Coal Resources, Colorado Plateau: Colo., N. Mex., and Utah F11
rather than evaluate current mining areas. Coal availability and 

recoverability studies in the Bisti area (fi g. 4) cover a fourquadrangle area and contain coal resources restricted by the 

Bisti and De-Na-Zin Wilderness Areas. The area of study is 

bounded on the north by the 3,000-ft mining depth limitation, 

on the south by the coal-bed outcrops, on the west by the 

Navajo Indian Reservation, and on the east by the De-Na-Zin 

Wilderness Area (fi g. 7). Coal availability results for the Bisti 

study area were published by the New Mexico Bureau of 

Mines and Mineral Resources (Hoffman and Jones, 1999). 

That report is summarized in this chapter. 

Coal availability studies in this area were conducted on 

four coal zones containing as many as four minable coal seams 

per zone. Coal recoverability studies and economic analysis 

for the coal resources were completed by DST and Associates 

in 1999 (Carter and others, 2000; DST and Associates, written 

commun., 1999). Results are in the Resource Evaluation part 

of this chapter. The New Mexico Bureau of Mines and Mineral 

Resources is conducting coal availability investigations in two 

more multi-quadrangle areas (fi g. 4) in the San Juan Basin: the 

Menefee area (southern San Juan Basin) and the La Ventana 

area (eastern San Juan Basin).

The Bisti area contains a large coal resource and was, 

at one time, the proposed site of a major electrical power 

generation station and on-site coal mine. During the 1980’s 

several small surface operations mined Fruitland Formation 

coals near the Bisti Trading Post (fi g. 7). No rail haulage was 

available to the San Juan Power Plant, so the produced coal 

was transported by truck northward through Farmington, N. 

Mex., then westward to the power plant. During the late 1980’s 

development of the Federal lands in the area was slowed by 

litigation from the Hopi and Navajo Indian Nations, and in the 

early and mid-1990’s much of the area along the outcrop of the 

Fruitland coal beds was declared a Wilderness Area. 

Gallup

Farmington 

Durango

Cedar City

Moab

Price

Albuquerque 

Socorro 

Flagstaff

Santa Fe 

Grand Junction

Salt Lake City 

Denver

Tucson 

Phoenix

70

25

40

25

40

15

70

80

10

19

10

 8

Coal-bearing strata Study area

113°

113°

106°

34° 34°

40°

106°

0 100 Miles

Utah

Colorado

New Mexico

Arizona

AZ

UT

NM

CO

PITK I N

DELTA

GUNNISON

MESA

QUAD

GARF IELD

R I O BLANCO

UINTA

COAL

REGION

SAN JUAN

RIVER COAL

REGION

SOMERSET

UTAH

COLO RADO

Piceance

Basin 139

64

13

141

65

133

92

70

70

50

50

135

82

Glenwood

Springs

Parachute

Grand

Junction

Montrose

Meeker

Gunnison

Delta

Carbondale

Aspen

Eagle

Crested

Butte

Paonia

Colbran

Rifle

0 10 20 30 Mi

0 10 20 30 40 50 Km

N Scale

Rangely

Somerset Study Area Location

Figure 6. The Somerset coal fi eld area location map showing active mines, and inset map (after Eakins and others, 1998) showing the Somerset 

quadrangle study area within the Uinta coal region.

F12 Geologic Assessment of Coal in the Colorado Plateau: Arizona, Colorado, New Mexico, and Utah
Utah Studies

In 1997, the Utah Geological Survey (UGS) began working on a coal availability study encompassing nine 7.5-minute 

quadrangles in the northern Wasatch Plateau. The results of that 

study (Tabet and others, 1999) are summarized in this chapter.

Coal mining in the Northern Wasatch Plateau coal fi eld 

(fi g. 8) is restricted by large fault zones associated with 

grabens of the Basin and Range Province on the west, crossfault systems and lack of drilling information on the south, 

seam outcrops on the east, and faults and lack of coal deposition on the north. Most of the coal resources in the Wasatch 

Plateau and Book Cliffs occur on National Forest lands and 

in areas with high topographic relief. These locations limit 

mining to underground methods, particularly longwall mining 

techniques, and to areas where the coal seams are relatively 

thick. Coal availability studies by the Utah Geological Survey 

in multi-7.5-minute-quadrangle areas continue in the Book 

Cliffs. The USGS has completed the coal recoverability and 

economic evaluation of the northern Wasatch Plateau coal 

resources (fi g. 4) and is currently working on the coal availability, recoverability, and economic evaluation of the southern Wasatch Plateau coal resources. Results of the coal recoverability and the economic evaluation of coal resources are 

found in the Resource Recovery section of this chapter.

Mining began in 1875 in the Huntington Canyon area 

of the Northern Wasatch Plateau study area. Transportation of 

the mined coal to market has been diffi cult because the northsouth-trending mountains form barriers to accessing power 

plants in the eastern or western population centers. Coal must 

be shipped northward across Soldier Summit or south and 

eastward toward Grand Junction, Colo., or must be trucked to 

rail spurs near Levan, (20 mi south of Nephi) in the Sevier 

Valley to the west. Regardless, the biggest cost of this coal is 

not in the mining operations but in the transportation from the 

mine to the user.

Gallup

Farmington 

Durango

Moab

Price

Albuquerque 

Socorro 

Flagstaff

Santa Fe 

Grand Junction

Denver

Tucson 

Phoenix

70

25

40

25

40

15

70

80

10

19

10

 8

Cretaceous

coal-bearing strata Study area

113°

113°

106°

34° 34°

40°

106°

0 100 Miles

Utah

Colorado

New Mexico

Arizona

AZ

UT

NM

CO

T 

23 

N

T 

25 

N

R16W R14W R12W

Study Area

New

Mexico

Kf

Kf

Kf

0 5 10 miles

R iver

Chaco

Outcrops of older rock

Outcrops of younger rock

DE-NA-ZIN 

WA

Bisti

WA

Fossil 

Forest 

RNA De-Na-Zin Was h

(Coal Creek)

BISTI

TRADING

POST

Hunte r Wash

Burnham

Consolidation Coal Co.

& El Paso Natural Gas 

Co.

Lease-inactive

Eastern boundary,

Navajo Reservation

Chaco River

BHP

Minerals

Navajo Mine

1996

Addition

Sunbelt’s

Gateway

Mine

Sunbelt’s

De-Na-Zin

Kf Mine

Geologic contact

Fruitland Formation

Wilderness area

Mine area

Bisti Coal Field Study Area

Figure 7. Bisti coal fi eld area index map and inset map (after Hoffman and Jones, 1999) of study area and active mines. RNA, Research 

Natural Area; WA, Wilderness Area.

Coal Availability, Recovery, Economic Evaluations of Coal Resources, Colorado Plateau: Colo., N. Mex., and Utah F13
The Availability of Coal Resources 

in the Somerset 7.5’ Quadrangle, 

West-Central Colorado

Introduction

The Colorado Geological Survey (CGS), in cooperation 

with the U.S. Geological Survey, produced an estimate of the 

amount of available coal in an area of historical and active 

mining in west-central Colorado. This coal availability study of 

the Somerset quadrangle was delivered to the USGS in August 

of 1998 and published by the CGS as Resource Series 36.

The coal availability study of the Somerset quadrangle 

(fi g. 6) indicates that approximately 75.3 percent of the total 

3.09 billion short tons of coal in-place in the Somerset quadrangle is available for development. Approximately 75 million 

short tons of coal within the quadrangle have been produced 

through 1997, and more than 200 million additional short tons 

were lost or sterilized from mining (Eakins and others, 1998). 

It is diffi cult to compare coal resource estimates from this 

report to previous coal resource reports because previous studies reported coal resources on a much larger scale—a county 

or township basis. These estimates might indicate, in general 

percentages, the amount of available coal in other parts of 

the Uinta Basin that have similar geologic and land-use conditions. 

This coal availability study indicates that more than 75 

percent of the original coal resources in the quadrangle are 

available for mining. Studies in the Appalachian coal region 

indicate that only 50 to 55 percent of the original coal resource 

in most areas of that region is available for development 

(Carter and Gardner, 1994; Carter, Rohrbacher and others, 

2000). Of the remaining Appalachian coal resources, no more 

than 60 percent is considered available for future development 

because of restrictions to mining (Carter and Gardner, 1994; 

Gallup

Farmington 

Durango

Moab

Price

Albuquerque 

Socorro 

Flagstaff

Santa Fe 

Grand Junction

Denver

Tucson 

Phoenix

70

25

40

25

40

15

70

80

10

19

10

 8

Cretaceous

Coal-bearing strata

Colorado Plateau

Study area

113°

113°

106°

34° 34°

40°

106°

0 100 Miles

Utah

Colorado

New Mexico

Arizona

AZ

UT

NM

CO

Northern Wasatch Plateau 

Coal Field Location

Study Area

Figure 8. The Northern Wasatch Plateau coal fi eld area map with local mines and accompanying relief map delineating the nine-7.5-minutequadrangle study area (after Tabet and others, 1999) and its relation to the Wasatch Plateau and Book Cliffs coal fi elds, central Utah.

F14 Geologic Assessment of Coal in the Colorado Plateau: Arizona, Colorado, New Mexico, and Utah
Carter, Rohrbacher and others, 2000).

The effect of land-use and technological factors on the 

availability of the remaining coal in other Colorado coal fi elds 

is not well known. It is important, however, to calculate the 

amount of the remaining coal resources available to mining in 

order to aid decision-makers in addressing issues pertaining to 

future coal development in Colorado.

Coal Availability Evaluation Methodology

Factors Affecting the Availability of Coal Resources

There are many factors that could affect the availability 

of coal for mining. The three general groups of factors to 

consider for coal development are legal unsuitability criteria, 

potential land-use restrictions, and technological factors. Table 

3 provides a complete listing of all factors considered within 

these three groups. Many of the factors given are either not 

applicable to the Somerset quadrangle or, after analysis, were 

not considered to be restrictions. Applicability of restrictions 

was evaluated based on input from mining engineers from 

coal companies that have mines in and near the Somerset 

quadrangle, staff members of the Colorado Division of Minerals and Geology (CDMG), and individuals with the USGS who 

are familiar with other coal availability studies.

A hierarchy was established for land-use and technological restrictions to prevent double-counting of restrictions when 

they overlap. The hierarchy for resolving overlapping applicable land-use restrictions was (1) streams, (2) highways, and 

then (3) railroads. Technological restrictions were considered 

in this order: (1) mined-out areas, (2) minimum coal-bed thickness, (3) proximity to another coal bed, and (4) burned coal 

beds (clinker).

Unsuitability criteria and land-owner restrictions that 

might hinder coal development in the Somerset quadrangle 

include railroads, highways, rivers and lakes, cemeteries, 

towns, critical habitat for threatened and endangered species, 

bald or golden eagle nests, and alluvial valley fl oors. Some of 

these considerations might be mitigated so that coal mining 

could proceed. Other considerations might not be mitigated 

and could prevent mining in their specifi c areas. Technological 

constraints that affect the availability of coal include minedout areas, overburden thickness greater than 3,000 ft, interburden between minable seams less than 40 ft, and coal seams less 

than 24 inches thick.

To identify the factors affecting the availability of coal 

for future mining in the Somerset quadrangle, interviews were 

conducted with mining engineers and geologists with four coal 

companies that have mines in geologic and physiographic settings similar to those found in the quadrangle. Two of the 

coal companies have mines currently operating within the 

quadrangle. Staff members from the CDMG, the State agency 

responsible for permitting and inspecting mines, were also 

interviewed. The information from these interviews was used to 

develop criteria for defi ning available coal in the quadrangle.

Availability of coal must be evaluated based on the 

mining method that will most likely be used to recover the 

coal. In the Somerset coal fi eld, all pre-1980’s mining had 

been conducted by room and pillar underground mining methods. However, since the early 1990’s, new mines and plans 

for expansion within existing mines have involved longwall 

mining exclusively (U.S. Bureau of Land Management, 1999).

Table 3. Listing of possible restrictions to coal mining. 

[After Eakins and others, 1998. Printed in bold, applicable to the Somerset 

quadrangle; Italicized, criteria to consider (those which were considered to 

possibly be applicable). The potential restriction would be evaluated for a 

specific development project. In some cases the potential restriction might be 

mitigated] 

3A. Coal-leasing unsuitability criteria from 

Federal Coal Management Regulations (43CFR 3461.5) 

 1. Federal land systems 

 2. Rights of way and easements [i.e., railroads]

 3. Dwellings, roads, cemeteries, and public buildings

 4. Wilderness Study Areas 

 5. Lands with outstanding scenic quality 

 6. Lands used for scientific study 

7. Historic lands and sites 

 8. Natural areas 

 9. Critical habitat for threatened or endangered species 

 10. State-listed threatened or endangered species 

 11. Bald or golden eagle nests 

 12. Bald and golden eagle roost and concentration areas 

 13. Federal lands containing active falcon cliff nesting site 

 14. Habitat for migratory bird species 

 15. Fish and wildlife habitat for resident species 

 16. Flood plains 

 17. Municipal watersheds 

 18. National resource waters 

 19. Alluvial valley floors

 20. State or Indian Tribe criteria 

3B. Other applicable land-use restrictions 

 1. Towns

 2. Pipelines and powerlines 

 3. Archaeological areas and wetlands 

 4. Streams, lakes, and reservoirs

 5. Surface- and coal-ownership issues

3C. Technological restrictions considered 

 1. Mined-out areas / coal beds too thin

 2. Coal depth (<100 ft overburden or >3,000 ft overburden for 

underground mining)

 3. Coal beds too close together (<40 ft)

 4. Limit of coal (including areas of burned coal)

 5. Oil and gas development 

 6. Active mines and abandoned mines

 7. Subsidence over abandoned mines 

 8. Subsidence is projected to cause material damage 

 9. Roof or floor problems / barrier pillars 

 10. Coal-bed discontinuities 

 11. Steep surface slopes / steeply dipping beds 

 12. Proximity to intrusives or faults 

 13. Insufficient resources to mine / coal quality 

Coal Availability, Recovery, Economic Evaluations of Coal Resources, Colorado Plateau: Colo., N. Mex., and Utah F15
Unsuitability Criteria Determinations

Coal unsuitability criteria are listed in the Federal Regulations, Title 43, Subpart 3461 (43 CFR 3461). These 20 

specifi c legal criteria are used to determine if an area can 

be mined by surface-mining methods. Underground mining 

on Federal lands can be exempted from these criteria, except 

where the mining will include surface operations and have 

surface impacts on Federal lands that cannot be otherwise 

exempted (43 CFR 3461.1).

The unsuitability criteria that were evaluated to be restrictions to mining in the Somerset quadrangle are rights of way 

and easements (applicable to the railroad), roads (applicable to 

Colorado Highway 133) and cemeteries (the miner’s cemetery 

north of Somerset). Dwellings and public buildings within the 

town of Somerset are also restrictions, although the entire town 

of Somerset is restricted under other land-use restrictions. It 

is conceivable that the cemetery, highway, and railroad could 

be relocated, if necessary, to allow mining to proceed once 

the necessary agreements and permits are acquired. For the 

purposes of this study, however, they are considered restrictions to mining. No restriction was applied to highways for 

coal more than 200 ft below the surface.

Other unsuitability criteria that are potential restrictions 

in the quadrangle are critical habitat for threatened or endangered species, bald or golden eagle nests, and alluvial valley 

fl oors. These criteria should be considerations in mine planning. The Colorado Division of Wildlife has not identifi ed any 

bald eagle nests within the quadrangle. Underground mining 

may be permitted beneath alluvial valley fl oors in some cases; 

therefore alluvial valley fl oors were not considered a restriction. These criteria could cause areas to be declared unsuitable 

for coal mining. Detailed studies to determine unsuitability or 

proposing mitigation measures would be made if an expression 

of interest for coal development was submitted to the Government.

Other Land-Use Issues

Coal mining beneath the town of Somerset is considered 

to be restricted. Coal mining beneath streams, lakes, and reservoirs is restricted as well. The North Fork of the Gunnison 

River and Minnesota Reservoir are both considered land-use 

restrictions; however, no restriction was applied to streams 

where the coal is more than 200 ft below the surface.

Other potential land-use restrictions were considered; 

however, none were evaluated to be applicable to the Somerset 

quadrangle. There are no major powerlines or pipelines that 

transect the quadrangle. The Colorado Historical Society has 

identifi ed no signifi cant archaeological sites in the study area 

and no wetlands were identifi ed by the BLM (U.S. Bureau of 

Land Management, 1999). Surface- and coal-ownership issues 

are restrictions only in rare instances.

Technologic Factors

Technologic factors considered to be restrictions to 

mining were depth to coal greater than 3,000 ft, overburden 

less than 100 ft thick, areas of no coal (mined-out areas—both 

active and abandoned mines—and areas of no coal deposition), 

interburden less than 40 ft thick, coal seams less than 28 inches 

thick, and areas of burned coal (clinker). 

No oil and gas development has taken place within the 

quadrangle. A single test hole, drilled in 1981, was not completed as a well. Coal quality is not considered to be a restriction to mining, although it could infl uence the specifi c areas 

of a bed that are selected to be mined. Underground mining 

above or below a mined-out seam is done on a regular basis 

if there has been prior experience or if rock mechanic-studies 

have demonstrated that the new mining area will be stable. 

However, it is likely that subsidence over an abandoned mine 

may preclude mining in the overlying coal seams until the 

subsidence has stabilized. Data to identify areas affected by 

such subsidence is not readily available. Areas with roof or 

fl oor problems that would preclude mining, steep slopes and 

igneous intrusions, and faults, although present, were not considered to be signifi cant enough to be a restriction. Potential 

restrictions identifi ed in other study areas were not present in 

the Somerset quadrangle.

The Colorado Geological Survey, with assistance from 

the U.S. Geological Survey, established a digital database of 

the mined-out areas for the Somerset coal fi eld. Information 

on the extent of mining was obtained from individual mine 

maps or previously compiled 1:24,000-scale maps available 

at the CGS, from maps within mine permit documents at the 

Colorado Division of Minerals and Geology, or from mine 

operators. Boundaries of active mines were updated to January 

1, 1998, based in part on mine plans through the end of 1997.

Depleted reserves consist of that part of the coal seam 

where coal extraction has been completed and the mine abandoned from further production. These abandoned mines contain support pillars that were not extracted at the end of the 

mining operations and barrier pillars that separate one mine 

from another. Barrier pillars are necessary to control water 

infl ow into new mines and to control the natural gases that are 

present in coal (protection for the miners). The Federal Mine 

Safety and Health Administration (MSHA) requires that an 

undisturbed 50-ft barrier pillar of coal be left between active 

and abandoned mines. These barrier pillars have been excluded 

from the available resources as barrier restrictions. Colorado 

law (table 4) goes a step further and requires that the barrier 

pillar be a minimum of 500 ft wide around active mines; 

however, once a mine or mining area becomes inactive, a new 

mining operation may be permitted to mine within 50 ft of the 

abandoned workings. 

The Colorado Surface Coal Mining Reclamation Act 

also includes a number of potential exclusions or restrictions 

F16 Geologic Assessment of Coal in the Colorado Plateau: Arizona, Colorado, New Mexico, and Utah
to underground coal mining, within Title 34, Article 33, as 

indicated in table 4. Many of these exclusions and restrictions 

overlap with Federal restrictions to mining. All were considered for inclusion in the factors affecting availability of coal.

Overview of the Study Area

This overview includes summaries from the Colorado Geological Survey, Resource Series 36, concerning the quadrangle’s 

location and physiographic setting, general geology, principal 

coal beds, correlation of beds, and the history of coal mining.

Location and Physiographic Setting

The Somerset 7.5-minute quadrangle is located in westcentral Colorado in the southeastern part of the Uinta Coal 

region’s Piceance Basin (fi g. 6). The quadrangle is within 

the Somerset coal fi eld in the northwestern part of Gunnison 

County. The town of Somerset, located in the west-central 

part of the quadrangle, is the only population center. A single 

major highway, a section of Colorado Highway 133 between 

the towns of Redstone and Paonia, crosses the quadrangle.

Elevations within the quadrangle range from about 5,900 

to 9,836 ft above sea level (fi g. 9). The lowest elevation is 

along the river at the western boundary of the quadrangle, 

while the highest elevation (9,836 ft.) is in the north-central 

part. Mt. Gunnison, at 12,719 ft, is about 4 mi south-southeast 

of the quadrangle.

Land use in the Somerset quadrangle includes surface 

facilities for two relatively large operating underground mines, 

the town of Somerset, and a few dwellings along the North 

Fork valley. Over half of the quadrangle is within the Gunnison National Forest, and the Bureau of Land Management 

administers a large part of the remainder. Coal mining is the 

primary industry within the quadrangle.

Table 4. Restrictions to Mining, Colorado 34-33-101 et. seq. 

[E, exclusion; R, restriction] 

Restriction/exclusion Explanation of 

restriction or exclusion 

Rule no. 

E Lands within National Park system, National Wildlife Refuges, National system 

of trails, National Wilderness Preservation system, Wild and Scenic Rivers, 

and National Recreation Areas 

2.07.6(2)(d)(iii)(A) 

E Within 300 ft of public building (school, church, hospital, courthouse, 

government building ...) community or institutional building or any public 

park 

2.07.6(2)(d)(iii)(B) 

E Within 100 ft of a cemetery 2.07.6(2)(d)(iii)© 

E Lands designated unsuitable for mining 

(None have been designated in Colorado) 

2.07.6(2)(d)(i) 

E Operations which affect the continued existence of threatened and endangered 

species 

2.07.6(2)(n) 

R Mining on steep slopes (has to meet specific performance standards) 2.06.4 

R Lands within National Forest 2.07.6(2)(d)(iii)(D) 

R Will not adversely affect publicly owned park or place eligible to be included in 

the National Register of Historic Places 

2.07.6(2)(e)(i) 

R Within 100 ft of public road right-of-way 2.07.6(2)(d)(iv) 

R Within 300 ft of an occupied dwelling (unless owner waives) 2.07.6(2)(d)(v) 

R 500 ft, measured horizontally, from active or abandoned underground mines 4.19(1) 

R Beneath or adjacent to any perennial stream, or impoundment or other body of 

water >20 acre-ft 

4.20.4 

R Mining in alluvial valley floors (AV F) and prime farm land 

(AV F’s are identified during permitting process; prime farmland is 

identified by the Office of Surface Mining) 

2.07.6(2)(K) 

R Operations where subsidence is projected to cause material damage 

(Essentially the mine must avoid subsidence or leave support pillars to 

protect aquifers, agricultural land and occupied residential dwellings and 

noncommercial buildings) 

2.05.6(6)(b)(iii) 

4.20 

R Blasting within 1,000 ft of schools, churches, hospitals, and nursing facilities 

and within 500 ft of wells, pipelines, and storage tanks for oil, gas or water 

4.08.4(7) 

R Surface disturbance within 100 ft of perennial streams with biological 

communities in them 

4.05.18 

Coal Availability, Recovery, Economic Evaluations of Coal Resources, Colorado Plateau: Colo., N. Mex., and Utah F17
38 52' 30"

39 

107 30' 107 22' 30"

IIIIIIIIIIIII IIIIIIII IIII IIIIIIIII II II II II II III IIII

IIIIIIIIIIIIIIIIIIIIIIIIIIII II II II IIIII II III

133

Somerset

Railroad

Minnesota•

Reservoir

0 .5 1 Mi

0 .5 1 Km

5

5

4

3

2

1

6

West Elk mine

(Mountain Coal)

x

Sanborn mine

(Oxbow Mining)

7

x Sanborn mine

(Oxbow Mining)

West Elk mine

(Mountain Coal)

Active Mines Inactive Mines

1

2

3

4

5

6

7

Oliver No. 1

Oliver No. 2

Bear No. 1 & 2

Bear No. 3

U.S. Steel

Hawksnest

Edwards

X8522

8500

8000

7500

7000

8500

9000

7500

7000

8500

8000

7500

9000

9500

8000

7500

7000

8000

7500

7000

8000 6500

6500

6000

6500

7000

7500

X8052

7500

7000

6500

6500

7000

7500

8000

7500

7000

6500

7000

7500

8000

8000

8000

7500

7500

6500

7000

7500

8000

X9517

GUNNISON NATIONAL FOREST

Thousand Acre

Flats

Bear

Creek

Thompso

Creek

Fire 

Mountain 

Elk

Creek

Buck

Mesa

Bear

X8169

Cree

X7526

6500

Sanborn

Creek

X8084

X8263

Creek

Gulch

Deep

Gulch

Sylvester

8500 X8548

8000

7500

7000

Flatiron 

East 

Flatiron 

West 

NORTH FORK

GUNNISON

RIVER

Raven

Pine Gl.

Lone

GUNNISON NATIONAL FOREST

Contour interval = 500'

X5953

6222

X

X9836

Minnesota Ck.

Fork

Dry

BLM

BLM

Figure 9. Simplifi ed topographic map of the Somerset quadrangle with land ownership and mine locations.

F18 Geologic Assessment of Coal in the Colorado Plateau: Arizona, Colorado, New Mexico, and Utah
Upper Cretaceous

Rollins

Sandstone

Mbr.

Paonia

Shale

Mbr.

Barren

Mbr.

Bowie

Shale

Mbr.

F 0–4

5–8

D:8–20

6–8

0–5

20-70

90-190

120-210

25-70

15-60

0-20

TYPICAL

 THICKNESS

 (in feet)

SERIES

COAL 

BED

STRATIGRAPHIC

UNIT

LD: 6–15

C

D

LD

E

A

B

LB

B:15–25

LB: 5–10

Mesaverde Fm.

DESIGNATION

 

RANGES

Figure 10. Generalized composite stratigraphic section showing coal 

beds and adjacent strata of the Somerset quadrangle, Colorado (after 

Eakins and others, 1998).

General Geology of the 

Somerset Quadrangle and Vicinity

The Somerset coal fi eld in Delta and Gunnison Counties 

lies in and near a valley cut by the North Fork of the Gunnison 

River and its tributaries. Strata dip generally to the northnortheast at an average of about 3 to 5 degrees. 

The coal in this area occurs in the lower part of the 

Williams Fork Formation (fi g. 10). The coal seams are highvolatile B and C bituminous, and reach up to 25 ft or more 

in thickness. Six major coal seams have been identifi ed in the 

Williams Fork Formation (Johnson, 1948). Many of the coal 

seams are either partially intruded or replaced by intrusives 

and locally may be upgraded in rank because of the intrusives. 

The eastern part of the coal fi eld, near the town of Somerset, 

has coking coal of relatively good quality that may also contain moderately high levels of methane (Tremain and others, 

1995). 

Subsurface geologic information is available for 99 drill 

holes within the quadrangle and a 3-mi zone surrounding 

the quadrangle. Forty-eight of the drill holes are within the 

quadrangle itself. The deepest drill holes, which are located to 

the northeast of the quadrangle, are oil and gas test holes. 

Bedrock units exposed within the Somerset quadrangle 

range from the Upper Cretaceous Mancos Shale to the Tertiary 

Wasatch Formation. The Mancos Shale, the oldest exposed 

formation in the study area, is present in the west-central part 

of the quadrangle along the North Fork of the Gunnison River 

and in the extreme southwestern part.

The overlying Mesaverde Formation has been subdivided 

into four members (ascending order) by Dunrud (1989), Johnson and May (1980), Nowak (1990), and Wellborn (1982a, 

1980b) in the area—the Rollins Sandstone Member, the Bowie 

Shale (or lower coal) Member, the Paonia Shale (or upper 

coal) Member, and the Barren Member (fi g. 10). Johnson and 

May (1980) and Dunrud (1989) include a fi fth member, the 

Ohio Creek Member, in the uppermost part of the Mesaverde 

Table 5. Common bed names and thickness ranges of principal coal beds, Somerset quadrangle. 

[After Eakins and others, 1998] 

Bed name 

(letter designation) 

Common name 

of bed 

Thickness range 

(ft) 

Typical thickness 

(ft) 

Lower B B-1 1.6–20 5–10 

B Somerset; B-1 / B-2 1.2–29 15–25 

C Bear 0–16 6–8 

Lower D Lower Oliver; D-1 2.6–21 6–15 

D Oliver; Upper Oliver; D-2 0–25 8–20 

E Hawksnest 0–15 5–8 

Coal Availability, Recovery, Economic Evaluations of Coal Resources, Colorado Plateau: Colo., N. Mex., and Utah F19
Formation. The signifi cant coal seams in the Somerset quadrangle are within the Bowie Shale (lower coal) and Paonia 

Shale (upper coal) Members of the Mesaverde Formation 

(Dunrud, 1989). 

The Tertiary Wasatch Formation is the youngest bedrock 

unit exposed in the quadrangle. 

Principal Coal Beds

The principal coal seams of the Somerset quadrangle are 

designated, from bottom to top, as the A through F seams. 

Table 5 provides commonly used alternative bed names and 

overall and typical thickness ranges of the B, C, D, and E coal 

seams in the quadrangle. These seams are generally continuous 

but may have signifi cant splits or areas of non-deposition. 

Thinner coal beds between the principal seams, and the A and 

F beds, are not of minable thickness within the quadrangle. 

The B, C, D, and E seams have all been mined, but signifi cant 

areas of potentially minable coal in these beds and in the 

accompanying lower splits of the B and D seams remain. Mapping and resource calculations have been completed for the 

A–F seams and their associated splits. 

Split seams (lower B and D coal beds) are designated 

where the parting thickness exceeds the coal thickness of the 

overlying or underlying coal bed. For example, if the B seam 

consists of 12 ft of coal, 5 ft of shale parting, and 6 ft of 

coal, the seam is considered to be unsplit, with a net seam 

thickness of 18 ft. However, the seam would be considered 

split into two seams if the 12-ft interval of coal was underlain 

by 6 ft of parting and 5 ft of coal. The B seam would be 

12 ft thick and the Lower B seam would be 5 ft thick. The 

thicker seam is normally mined and the thinner seam is a 

lost resource. 

Correlation of Coal Beds

Cretaceous coal beds of Colorado are highly lenticular 

and their minable thicknesses frequently extend laterally for 

relatively short distances. Because of this lenticularity, correlation of coal beds is diffi cult. Coal-seam correlations by 

Dunrud (1976, 1989), Johnson and May (1980), and Nowak 

(1990) utilized closely spaced, proprietary data from mining 

companies. Although no proprietary data was used in the present study, we benefi ted from the previous correlations based 

on proprietary data. The Colorado Geological Survey was able 

to acquire 14 drill holes from Mountain Coal Company to 

fi ll in gaps in data spacing. Data points used in this study 

and cross-section locations are shown in fi gure 11. Several 

previous studies, particularly Dunrud (1989), Johnson (1948), 

and Landis (1949) have covered the entire Somerset coal fi eld 

and surrounding areas, including both north and south of the 

North Fork of the Gunnison River. A combination of their 

coal-seam correlations and newly acquired data were used 

for coal-seam correlations in this study. In this report, as in 

Dunrud (1989), the Hawksnest bed is correlated as the E coal 

seam both north and south of the North Fork of the Gunnison 

River. The seam designated as the F seam by Mountain Coal 

Company’s Mt. Gunnison mine is designated as the E seam in 

this report. Two cross sections showing coal-seam correlations 

(fi gs. 12 and 13) have been included in this report. These 

cross sections not only show the coal-seam correlations, but 

also show the coal seams, major parting and interburden thicknesses, and bed splits.

Coal Mining History

More than 15 million short tons of coal were produced 

in the Uinta Coal region (fi g. 6) in 1997, or 55 percent of 

Colorado’s total coal production. The two operating mines in 

the Somerset quadrangle, the Sanborn Creek and West Elk 

mines, produced 27 percent of Colorado’s coal in 1997: these 

two mines produced a combined 7,322,766 short tons of coal, 

all from the B coal seam. The West Elk mine is a longwall 

operation and the Sanborn Creek mine is a room and pillar 

mine; the mining company is planning to add a longwall 

operation after they have acquired new Federal leases (U.S. 

Bureau of Land Management, 1999) and permits.

Approximately 7.5 percent of Colorado’s cumulative production through 1997 has come from the Somerset quadrangle. 

All mines operating in the quadrangle have been underground 

mines. Thirty-seven coal mines have operated in the Somerset 

coal fi eld during the period from 1903 to the present (Boreck 

and Murray, 1979). Fourteen mines, all of which produced 

more than 100,000 short tons, have operated in the Somerset 

quadrangle. 

Total production for the Somerset quadrangle is approximately 75 million short tons through 1997. About 80 percent 

of the coal mined from the Somerset quadrangle was produced 

from either the B or C bed. The remainder came from the D 

and E beds.

Results: Coal Resources and Coal 

Available for Mining in the 

Somerset Quadrangle, Colorado

The Somerset quadrangle contains almost 3.1 billion 

short tons of total original coal resources. Approximately 275 

million short tons have been removed by mining or lost in 

the mining process, leaving about 2.8 billion short tons of 

remaining coal resources. Because of land-use and technological restrictions, about 2.3 billion short tons (74 percent of 

the original coal resources) are available for mining. The coal 

resources of the Somerset quadrangle are summarized in tables 

6 and 7 and fi gure 14. 

All restricted tonnages, regardless of whether they overlap with other restrictions, are presented. Calculated coal tonnages in table 7 may not necessarily be consistent with those 

F20 Geologic Assessment of Coal in the Colorado Plateau: Arizona, Colorado, New Mexico, and Utah
N

Data point within Somerset 

quadrangle and 3 mile 

surrounding area

Data point used for coal 

correlation diagram 

E-25-A

0 .5 1 Mi

0 .5 1 Km

38 52' 30"

39 

107 30' 107 22' 30"

A

BOW-10

BOW-11

G-9 WSC-4 B

O-1

SMT-6

B'

SMT-8

MNP-1

A'

DH-24

WSC-22

Figure 11. Data points and cross-section locations in the Somerset study area, Colorado (from Eakins and others, 1998).

Coal Availability, Recovery, Economic Evaluations of Coal Resources, Colorado Plateau: Colo., N. Mex., and Utah F21
1

6700

6600

6500

6400

6300

6200

6100

6000

5900

5800

5700

5600 Kr

Elev.6266

(1947)

B

(365)

(60)

To elev.7945

WSC-22 DH-24

Kr

Kr

Kr

E-25-A

To elev.7356

G-9

Elev. 6632

BOW-11

5500

To elev.6894

Elev. 6469

BOW-10

(140)

ELEV

EAST WEST

A = A coal bed

LB = Lower B coal bed

B = B coal bed

C = C coal bed

LD = Lower D coal bed

D = D coal bed

E = E coal bed

F = F coal bed

Kr = Rollins Sandstone 

( ) = Interburden/Parting

thickness

Mbr.

Thickness and depths are in feet. Horizontal distance not to scale.

Numbers to right of column are thicknesses.

EXPLANATION

D 2

D

5

3 6

7

E

F 3

4

LD

(109)

(65)

(199)

7

7

13(9)

(13)

A 1

B

LB

C 6

15

(6)

(13)

A 1

B

LD

(102)

B 24

(64)

A C 3

(65)

(220)

9

(19) D (5) 2

2

(124)

9

4

(28)

(2)

E

F

(1259)

D

E

F

(147)

(49)

14

6

2

1

4 (6)

(5)

4

(61)

10

7

(123)

6 (10)

(12)

LB 5

(77)

B 25 (7)

C

18 (4)

18

(17)

4

3 (16)

A

B

C

(73)

(76)

LD

E

F 3

(197)

(125)

D

5 LD (3)

(99)

(326)

(31)

(425)

(24)

A A'

D

4

(2) 9

(41)

(5)

LD

C

(56)

(2)

7

4

3

3

2

Figure 12. Coal correlation cross section A-A’, drawn generally E.-W., parallel to the North Fork of the Gunnison River (from Eakins 

and others, 1998).

F22 Geologic Assessment of Coal in the Colorado Plateau: Arizona, Colorado, New Mexico, and Utah
7100

7000

6900

6800

6700

6600

6500

6400

6300

6200

6100

6000

5900

5800

5700

5600

5500

NORTH SOUTH

8

(2)

(10)

E

D

3 (23)

(76)

A

1

(2)

(129)

D

E

(180)

8 (10)

(28)

(5)

(6)

6

(2)

3

F

(71)

F

(182)

(1963)

(1259))

To elev.7597

SMT-8

MNP-1

To elev.7356

E-25-A

To elev.7940

WSC-4

Kr

(190)

Kr

(216)

To elev.8051

5

14

(25)

(12)

3 (5)

(9) 2

6

20

D (15)

(76)

8

9

E

F 3

(115)

9

7

4

(98)

C 2

2 A

(26)

(59)

E 9

D

LD

(199)

5

23

3 10

(196)

A

C

C 4

11

9 (3) B

9

2

9

(124)

B

(56)

15

9

B

C

1 (21)

7

(5)

(55)

14

9

(272)

E

D

LD

D

LD

5 (9)

6 (1) 3 (13) 4

3 (7)

O-1 Elev. 6415

Elev. 6765

SMT-6

(610)

C

21 19

Kr

Kr

4

2

B B'

LD

LD

A

(23)

(4)

(56)

(27)

C

A

B

4

B

B

E

(918)

ELEV

A = A coal bed

LB = Lower B coal bed

B = B coal bed

C = C coal bed

LD = Lower D coal bed

D = D coal bed

E = E coal bed

F = F coal bed

Kr = Rollins Sandstone 

( ) = Interburden/Parting

thickness

Thickness and depths are in feet. Horizontal distance not to scale.

Numbers to right of column are thicknesses.

EXPLANATION

Mbr.

Figure 13. Coal correlation cross section B-B’, drawn generally N.-S., perpendicular to the North Fork of the Gunnison River 

(from Eakins and others, 1998).

Coal Availability, Recovery, Economic Evaluations of Coal Resources, Colorado Plateau: Colo., N. Mex., and Utah F23
3%

Lower B

(95)

9%

Lower D

(281)

13%

C

(418)

14%

E

(425)

39%

B

(1,202)

22%

D

(666)

25%

D

(588)

3%

Lower B

(59)

4%

Lower D

(104) 17%

C

(391)

17%

E

(403)

34%

B

(782)

75% Available

(2.3 billion tons)

25% Unavailable

(0.8 billion tons)

A. Original Coal Resources

B. Available Coal Resources

Figure 14. Pie charts showing total original coal resources (A) and available coal resources (B) for 

the six major coal beds (after Eakins and others, 1998) in the Somerset quadrangle (unlabled numbers 

are in millions of short tons).

Table 6. Summary of original, restricted, and available coal resources of the Somerset quadrangle by bed. 

[After Eakins and others, 1998. Figures in millions of short tons] 

Resource category Lower B B C Lower D D E Total 

Original coal resources 95.2 1202.5 417.6 280.7 666.4 425.4 3087.8 

Coal mined or lost during mining 0.0 222.6 25.6 0.0 5.3 21.9 275.4 

Remaining coal 95.2 979.9 392.0 280.7 661.1 403.5 2812.4 

Land-use restrictions 0.0 0.1 0.2 0.9 0.4 0.3 1.9 

Technological restrictions 36.4 198.3 0.9 175.9 72.8 0.3 484.6 

Available coal resources 58.8 781.5 390.9 103.9 587.9 402.9 2325.9 

Table 7. Summary of restricted coal resources of the Somerset quadrangle by bed. 

[After Eakins and others,1998. Figures in millions of short tons] 

Resource category Lower B B C Lower D D E Total 

Land-use restrictions 

Railroads 0.0 20.0 61.0 0.0 0.0 0.0 81.0 

Streams 0.0 50.0 157.0 950.0 430.0 275.0 1,862.0 

Roads 0.0. 8.0 51.0 132.0 90.0 0.0 281.0 

Total land-use restrictions 0.0 78.0 269.0 1,082.0 520.0 275.0 2,224.0 

Technologic restrictions 

Interburden < 40 ft 36,351.0 193,844.0 0.0 175,855.0 72,564.0 0.0 478,614.0 

Burn 0.0 6,533.0 0.0 0.0 0.0 0.0 6,533.0 

Too thin (< 28 in) 230.0 0.0 1,102.0 0.0 268.0 317.0 1,917.0 

Total technologic restrictions 36,581.0 200,377.0 1,102.0 175,855.0 72,832.0 317.0 487,064.0 

F24 Geologic Assessment of Coal in the Colorado Plateau: Arizona, Colorado, New Mexico, and Utah
in table 6 because adjustments have been made for overlapping restrictions in the overall summary totals presented in 

table 6. 

Coal Resource Categories

Original, remaining, and available coal resource estimates 

were subdivided into categories of overburden thickness 

(depth), coal thickness, and reliability of estimate. Overburden 

categories used were: 0–200 ft, 200–1,000 ft, and >1,000 ft. 

Two coal-thickness categories were used: 1.2–2.3 ft (14–28 

inches) and >2.3 ft. Reliability categories for coal resource 

calculation were: measured, indicated, inferred, and hypothetical, as reported in Wood and others (1983). Tables 8, 9 and 

10 provide detailed information on the original, remaining, and 

available coal resources of the B, D, and E beds.

Summary

Original Coal Resources

More than 1.2 billion short tons, or approximately 39 

percent of the original resource of 3.1 billion short tons in 

the Somerset quadrangle, are contained in the B coal seam. 

The D bed contains about 660 million short tons, which 

constitutes 22 percent of the original resource. The C and E 

coal seams each contain more than 400 million short tons of 

coal resource. Together they represent 28 percent of the total 

coal resource.

Approximately 55 percent of the original coal resources 

for all seams is within 1,000 ft of the ground surface. Almost 

all of the original coal resource is greater than 2.3 ft thick; only 

0.05 percent or less of the original coal resource for all beds 

represents coal between 1.2 and 2.3 ft thick. 

Almost all the original coal resource falls within a reliability category of either measured, indicated, or inferred. Less 

than 0.5 percent of the original coal is farther than 3 mi from 

a data point and, therefore, falls within the hypothetical reliability category. Thirteen percent of the original coal resource 

is in the measured category, 38 percent of the original coal 

resource is within the indicated category, and 48 percent is in 

the inferred category.

Mined-Out and Remaining Coal Resources

The B, C, D, and E seams have all been mined within 

the quadrangle. Of the approximately 275 million short tons of 

coal mined or lost in mining, 81 percent is from the B seam, 

9 percent is from the C seam, 8 percent from the E seam, and 

about 2 percent from the D seam. The amount of coal resource 

mined or lost in mining represents about 9 percent of the 

original resource. Remaining resources are about 91 percent of 

the original resource, or 2.8 billion short tons.

Restrictions and Available Coal Resources

Land-use restrictions in the Somerset quadrangle limit the 

availability of only 1.9 million short tons of coal, or much less 

than 0.1 percent of the original coal resource. Technological 

restrictions, however, limit the availability of almost 500 million 

short tons—about 16 percent of the original resource. In cases 

where both land-use and technological restrictions might apply, 

the technological restrictions have been applied, based on the 

established hierarchy. The primary technological restriction is 

interburden that is too thin to support mining of superjacent of 

subjacent seams. When the interburden is less than 40 ft thick, 

the thinner coal seam is presumed to be restricted from mining. 

This restriction would impact the E bed for subjacent seams only 

because it has no overlying coal seam. The entire technological 

restriction for the E seam (about 300,000 short tons) is due to the 

thinness (< 2.3 ft) of the seam. Thin seams account for about 0.3 

percent of the total technological restrictions.

More than 780 million short tons, or approximately 34 

percent of the available resource of 2.3 billion short tons in 

the quadrangle, is coal from the B seam. The D seam contains 

almost 590 million short tons, which represent 25 percent of 

the available coal resource. The E seam has more than 400 

million short tons of available coal resource, or 17 percent of 

the total. The other three seams account for about 24 percent 

of the available coal resource as follows: C seam (17 percent), 

Lower D seam (4 percent), and Lower B seam (3 percent). 

Approximately 51 percent of the available resource for 

all seams is less than 1,000 ft below the surface. Almost all 

the available coal resource falls within a reliability category of 

either measured, indicated, or inferred. The measured category 

contains 10 percent of the available coal resource, 35 percent 

of the available coal resource is within the indicated category, 

and 54 percent is in the inferred category.

Text continues on page 29

Coal Availability, Recovery, Economic Evaluations of Coal Resources, Colorado Plateau: Colo., N. Mex., and Utah F25
Table 8. Summary of estimated original, remaining, and available coal resources of the “B” coal bed in the Somerset 7.5-minute quadrangle, Colorado.

[After Eakins and others, 1998. Figures in thousands of short tons. Resources are subdivided into categories of overburden thickness (0–200 ft, 200–1000 ft, and > 1000 ft), coal thicand reliability of estimate (measured, indicated, inferred, and hypothetical)]

MEASURED INDICATED INFERRED HYPOTHETICAL 

1.2–2.3ft >2.3ft TOTAL 1.2–2.3ft >2.3ft TOTAL 1.2–2.3ft >2.3ft TOTAL 1.2–2.3ft >2.3ft TOTAL 1.2

ORIGINAL

0–200 0 2130 2130 0 0 0 0 0 0 0 0 0 200–1000 0 102285 102285 0 328532 328532 0 191587 191587 0 0 0 >1000 0 50734 50734 0 124515 124515 0 395794 395794 0 6903 6903 TOTAL 0 155149 155149 0 453047 453047 0 587381 587381 0 6903 6903 

MINED OUT**

SURFACE 0–200 0 0 0 0 0 0 0 0 0 0 0 0 

200–1000 0 0 0 0 0 0 0 0 0 0 0 0 TOTAL 0 0 0 0 0 0 0 0 0 0 0 0 

DEEP 0–200 0 870 870 0 0 0 0 0 0 0 0 0 

200–1000 0 53316 53316 0 107812 107812 0 19490 19490 0 0 0 >1000 0 19404 19404 0 21711 21711 0 0 0 0 0 0 TOTAL 0 73590 73590 0 129523 129523 0 19490 19490 0 0 0 

TOTAL 0–200 0 870 870 0 0 0 0 0 0 0 0 0 

200–1000 0 53316 53316 0 107812 107812 0 19490 19490 0 0 0 >1000 0 19404 19404 0 21711 21711 0 0 0 0 0 0 TOTAL 0 73590 73590 0 129523 129523 0 19490 19490 0 0 0 

REMAINING

0–200 0 1260 1260 0 0 0 0 0 0 0 0 0 

200–1000 0 48969 48969 0 220720 220720 0 172097 172097 0 0 0 >1000 0 31330 31330 0 102804 102804 0 395794 395794 0 6903 6903 TOTAL 0 81559 81559 0 323524 323524 0 567891 567891 0 6903 6903 

RESTRICTIONS

LAND-USE 0–200 0 50 50 0 0 0 0 0 0 0 0 0 

200–1000 0 0 0 0 0 0 0 0 0 0 00 

>1000 0 0 0 0 0 0 0 0 0 000 TOTAL 0 50 50 0 0 0 0 0 0 0 0 0 

TECHNOLOGIC 0–200 0 0 0 0 0 0 0 0 0 000 

200–1000 0 17003 17003 0 84697 84697 0 25202 25202 0 0 0 

>1000 0 15509 15509 0 26562 26562 0 29228 29228 0 0 0 TOTAL 0 32512 32512 0 111259 111259 0 54430 54430 0 0 0 

TOTAL 0–200 0 50 50 0 0 0 0 0 0 0 0 0 

200–1000 0 17003 17003 0 84697 84697 0 25202 25202 0 0 0 

>1000 0 15509 15509 0 26562 26562 0 29228 29228 0 0 0 TOTAL 0 32562 32562 0 111259 111259 0 54430 54430 0 0 0 

AVAILABLE

0–200 0 1210 1210 0 0 0 0 0 0 0 0 0 

200–1000 0 31966 31966 0 136023 136023 0 146895 146895 0 0 0 >1000 0 15821 15821 0 76242 76242 0 366567 366567 0 6903 6903 

TOTAL 0 48997 48997 0 212265 212265 0 513462 513462 0 6903 6903 

**Mined and lost-in-mining, by surface and deep mining methods.Note: Totals may not equal sum of components because of independent rounding.
Table 9. Summary of estimated original, remaining, and available coal resources of the “D” coal bed in the Somerset 7.5-minute quadrangle, Colorado.

[After Eakins and others, 1998. Figures in thousands of short tons. Resources are subdivided into categories of overburden thickness (0–200 ft, 200–1000 ft, and > 1000 ft), coal >2.3 ft), and reliability of estimate (measured, indicated, inferred, and hypothetical)]

MEASURED INDICATED INFERRED HYPOTHETICAL 

1.2–2.3ft >2.3ft TOTAL 1.2–2.3ft >2.3ft TOTAL 1.2–2.3ft >2.3ft TOTAL 1.2–2.3ft >2.3ft TOTAL 1.2

ORIGINAL

0–200 108 16623 16731 0 24483 24483 0 94 94 0 0 0 200–1000 30 59059 59089 0 203777 203777 0 130506 130506 0 0 0 >1000 268 16339 16607 0 47558 47558 0 165212 165212 0 2362 2362 2TOTAL 406 92021 92427 0 275818 275818 0 295812 295812 0 2362 2362 4

MINED OUT**

SURFACE 0–200 0 0 0 0 0 0 0 0 0 0 0 0 

200–1000 0 0 0 0 0 0 0 0 0 0 0 0 TOTAL 0 0 0 0 0 0 0 0 0 0 0 0 

DEEP 0–200 48 14 62 0 0 0 0 0 0 0 0 0 

200–1000 29 2368 2397 0 2872 2872 0 0 0 0 0 0 >1000 0 0 0 0 0 0 0 0 0 0 0 0 TOTAL 77 2382 2459 0 2872 2872 0 0 0 0 0 0 

TOTAL 0–200 48 14 62 0 0 0 0 0 0 0 0 0 

200–1000 29 2368 2397 0 2872 2872 0 0 0 0 0 0 >1000 0 0 0 0 0 0 0 0 0 0 0 0 TOTAL 77 2382 2459 0 2872 2872 0 0 0 0 0 0 

REMAINING

0–200 60 16609 16669 0 24483 24483 0 94 94 0 0 0 

200–1000 1 56691 56692 0 200905 200905 0 130506 130506 0 0 0 >1000 268 16339 16607 0 47558 47558 0 165212 165212 0 2362 2362 2TOTAL 329 89639 89968 0 272946 272946 0 295812 295812 0 2362 2362 3

RESTRICTIONS

LAND-USE 0–200 61 370 431 0 0 0 0 0 0 0 0 0 

200–1000 0 0 0 0 0 0 0 0 0 0 0 0 >1000 0 0 0 0 0 0 0 0 0 0 0 0 TOTAL 61 370 431 0 0 0 0 0 0 0 0 0 

TECHNOLOGIC 0–200 0 0 0 0 0 0 0 0 0 0 0 0 

200–1000 0 376 376 0 723 723 0 44357 44357 0 0 0 >1000 268 0 268 0 27067 27067 0 41 41 0 0 0 2TOTAL 268 376 644 0 27790 27790 0 44398 44398 0 0 0 2

TOTAL 0–200 61 370 431 0 0 0 0 0 0 0 0 0 

200–1000 0 376 376 0 723 723 0 44357 44357 0 0 0 >1000 268 0 268 0 27067 27067 0 41 41 0 0 0 2TOTAL 329 746 1075 0 27790 27790 0 44398 44398 0 0 0 3

AVAILABLE

0–200 0 16239 16239 0 24483 24483 0 94 94 0 0 0 

200–1000 0 56315 56315 0 200182 200182 0 86149 86149 0 0 0 

>1000 0 16339 16339 0 20491 20491 0 165171 165171 0 2362 2362 TOTAL 0 88893 88893 0 245156 245156 0 251414 251414 0 2362 2362 

**Mined and lost-in-mining, by surface and deep mining methods.Note: Totals may not equal sum of components because of independent rounding.
Table 10. Summary of estimated original, remaining and available coal resources of the “E” coal bed in the Somerset 7.5-minute quadrangle, Colorado. 

[After Eakins and others, 1998. Figures in thousands of short tons. Resources are subdivided into categories of overburden thickness (0–200 ft, 200–1000 ft, and > 1000 ft), coal >2.3 ft), and reliability of estimate (measured, indicated, inferred, and hypothetical)]

MEASURED INDICATED INFERRED HYPOTHETICAL 

1.2–2.3ft >2.3ft TOTAL 1.2–2.3ft >2.3ft TOTAL 1.2–2.3ft >2.3ft TOTAL 1.2–2.3ft >2.3ft TOTAL 1.2

ORIGINAL

0–200 0 4619 4619 0 37 37 0 0 0 0 0 0 200–1000 270 25239 25509 47 111801 111848 0 91754 91754 0 0 0 3>1000 0 13617 13617 0 41869 41869 0 135839 135839 0 323 323 TOTAL 270 43475 43745 47 153707 153754 0 227593 227593 0 323 323 3

MINED OUT**

SURFACE 0–200 0 0 0 0 0 0 0 0 0 0 0 0 

200–1000 0 0 0 0 0 0 0 0 0 0 0 0 TOTAL 0 0 0 0 0 0 0 0 0 0 0 0 

DEEP 0–200 0 247 247 0 0 0 0 0 0 0 0 0 

200–1000 0 4328 4328 0 9389 9389 0 263 263 0 0 0 >1000 0 2365 2365 0 5275 5275 0 18 18 0 0 0 TOTAL 0 6940 6940 0 14664 14664 0 281 281 0 0 0 

TOTAL 0–200 0 247 247 0 0 0 0 0 0 0 0 0 

200–1000 0 4328 4328 0 9389 9389 0 263 263 0 0 0 >1000 0 2365 2365 0 5275 5275 0 18 18 0 0 0 TOTAL 0 6940 6940 0 14664 14664 0 281 281 0 0 0 

REMAINING

0–200 0 4372 4372 0 37 37 0 0 0 0 0 0 

200–1000 270 20911 21181 47 102412 102459 0 91491 91491 0 0 0 3>1000 0 11252 11252 0 36594 36594 0 135821 135821 0 323 323 TOTAL 270 36535 36805 47 139043 139090 0 227312 227312 0 323 323 3

RESTRICTIONS

LAND-USE 0–200 0 275 275 0 0 0 0 0 0 0 0 0 

200–1000 0 0 0 0 0 0 0 0 0 0 0 0 >1000 0 00 0 0 0 0 0 0 0 0 0 TOTAL 0 275 275 0 0 0 0 0 0 0 0 0 

TECHNOLOGIC 0–200 0 0 0 0 0 0 0 0 0 0 0 0 

200–1000 270 0 270 47 0 47 0 0 0 0 0 0 3>1000 0 00 0 0 0 0 0 0 0 0 0 TOTAL 270 0 270 47 0 47 0 0 0 0 0 0 3

TOTAL 0–200 0 275 275 0 0 0 0 0 0 0 0 0 

200–1000 270 0 270 47 0 47 0 0 0 0 0 0 3>1000 0 0 0 0 0 0 0 0 0 0 0 0 TOTAL 270 275 545 47 0 47 0 0 0 0 0 0 3

AVAILABLE

0–200 0 4097 4097 0 37 37 0 0 0 0 0 0 200–1000 0 20911 20911 0 102412 102412 0 91491 91491 0 0 0 

>1000 0 11252 11252 0 36594 36594 0 135821 135821 0 323 323 TOTAL 0 36260 36260 0 139043 139043 0 227312 227312 0 323 323 

**Mined and lost-in-mining, by surface and deep mining methods.Note: Totals may not equal sum of components because of independent rounding.
Availability of Coal Resources 

in the Fruitland Formation, 

San Juan Basin, Bisti Study Area, 

Northwest New Mexico

Introduction

Coal is an important part of New Mexico’s economy 

and contributes substantially to the State’s educational funds 

through royalties and taxes. The State ranked 8th in the Nation 

in coal sales with approximately 26.9 million short tons sold 

in 1999 (Keystone Coal Industry Manual, 1999; Resource Data 

International, Inc., 2000). Coal is produced from two basins 

in New Mexico—the San Juan Basin located in the northwest 

part of the State and the Raton Basin located in the northeast 

part of the State. Four surface mines in the San Juan Basin 

produced 98 percent of New Mexico’s coal tonnage in 1999; 

one mine in the Raton Basin produced the remaining 2 percent 

of the 1999 tonnage. At least 97 percent of this production was 

used for electrical generation. In the San Juan Basin, coal-fi red 

power plants are close to the mines because of the high cost of 

mining and transportation (average price = $22.23/ sold short 

ton in 1999—Resource Data International, Inc., 2000) of New 

Mexico coal. Production costs are high because the coal seams 

are lenticular and relatively thin (less than 20 ft); however, 

many San Juan Basin coal deposits contain several minable 

seams. These multiple-seam mining operations can be very 

competitive early in the mine’s life when the mining ratios are 

low. However, as the low-ratio coal resources are depleted, the 

mining costs rise (if technical factors remain the same). When 

compared to Powder River Basin (PRB) mines in Wyoming, 

New Mexico coal is expensive to mine because the ratio of 

overburden to coal-seam thickness, ranging from 5:1 to 15:1, is 

higher than mining ratios in the PRB, where the average stripping ratio is 2:1. The high operating costs in San Juan Basin 

mines prohibit transporting the product over long distances, 

but the lack of adequate rail transportation into or out of the 

San Juan Basin (SJB) tends to protect the mines from outside 

competition. Economics dictate transmitting electricity from 

the SJB to other Western and Pacifi c Coast States rather than 

shipping coal to these States. Approximately 60 percent of 

New Mexico’s coal production is from the Upper Cretaceous 

Fruitland Formation (Hoffman and Jones, 1999). This formation has some of the thickest coal seams mined in the SJB 

and they are more continuous (over short distances) than coal 

seams within the Menefee and Crevasse Canyon Formations.

BHP Minerals operates two of the fi ve New Mexico 

mines (fi g. 7): (1) one mine complex that consists of the San 

Juan and La Plata mines, and (2) the Navajo mine. Both mines 

produce coal from the Fruitland Formation. The Navajo mine 

was the 15th largest mine (8.5 million sold short tons) and 

the San Juan/La Plata mine was the 21st largest mine (6.6 

million sold short tons) in the Nation in 1999 (Resource Data 

International, 2000). The Navajo mine has been operating for 

35 years, with total production of more than 241 million short 

tons. Operators of the San Juan mine complex are studying 

the potential of underground mining using longwall methods 

to extend the mine life.

Four quadrangles located approximately 35 mi south of 

Farmington, N. Mex., on the western edge of the Bisti coal 

fi eld were chosen for the present study—Alamo Mesa West, 

Bisti Trading Post, Tanner Lake, and the Pillar 3 NE quadrangles (fi g. 7). The four-quadrangle study area encompasses 

nearly 238 mi2 of coal resource area. The southern extent of 

the BHP Minerals Navajo mine is approximately 16 mi northwest of the study area, and the San Juan power plant is less 

than 60 mi from the study area. Recently relinquished leases 

of the Conpaso mine (El Paso Natural Gas/Navajo Lease) are 

immediately west of the study area (fi g. 7). Within the study 

area, two small mines, the De-Na-Zin and Gateway mines, 

produced coal during the 1980’s.

Geologic Setting

The Bisti coal fi eld is about 37 mi long, beginning 

approximately 7 mi west of the eastern boundary of the Navajo 

Indian Reservation and arbitrarily separated from the Star Lake 

coal fi eld (in the east) at the N.-S. boundary between R. 

9 W. and R. 8 W. Only the western part of the Bisti coal 

fi eld (containing the study area) is shown on fi gure 7. The 

entire coal fi eld is within San Juan County and is included in 

part of the Toadlena and the Chaco Canyon 1:100,000-scale 

topographic quadrangles. Four 7.5-minute quadrangles defi ne 

the study area at the western edge of the Bisti coal fi eld 

and all of these 1:24,000-scale quadrangles are within the 

1:100,000-scale Toadlena topographic quadrangle. Fruitland 

Formation exposures (fi g. 7) within the Bisti coal fi eld trend 

northwest-southeast (N.55°W.), more or less parallel to the 

Late Cretaceous shoreline.

The Bisti coal fi eld lies within the Chaco slope physiographic area (fi g. 15). Coal beds dip 3 to 5 degreesto the northnortheast. Lack of signifi cant faulting and high-angle dips have 

allowed economical surface mining in the Bisti coal fi eld. 

Erosion of the Fruitland Formation and overlying Kirtland 

Shale lithologies results in a badlands topography (fi gs. 16, 

17). Lithologies associated with the Fruitland Formation coal 

seams are typically mudstone, siltstone, and fi ne-grained, friable sandstone.

Coal Geology

In the study area (fi g. 18), the Fruitland Formation 

includes four defi ned coal seams. El Paso Natural Gas Navajo 

Lease group (Conpaso-Burnham), the Public Service Company of New Mexico, and the Sun Belt Mining and Arch Coal 

group defi ned these four seams. Using their terminology, the 

seams from bottom to top are: Red, Green, Blue, and Yellow. 

Coal Availability, Recovery, Economic Evaluations of Coal Resources, Colorado Plateau: Colo., N. Mex., and Utah F29
of thickness in the two most laterally consistent coal seams 

within the study area. The Red coal seam typically includes 

two major and several minor coal beds, whereas the remaining 

coal seams generally contain one major and several minor coal 

beds. Major coal-bed thickness averages from 6 to 8 ft, with 

the thickest coal bed being in the Green coal seam (fi g. 22). 

In parts of the study area where the Yellow coal seam is not 

present, the average thickness of the coal-bearing Fruitland 

Formation coal zone is 102 ft. In areas where the Yellow 

coal seam does occur, the average thickness of the Fruitland 

Formation coal zone is 172 ft. Coal is present above the Yellow 

zone, but because these coal beds are very thin and lenticular, 

they were not included in this study. The lenticularity of these 

seams is illustrated in cross sections shown in fi gures 23–25. 

Cross-section locations are shown in fi gure 18. Correlation of 

beds on these cross sections and for resource calculation is by 

seam rather than by bed, meaning that one coal bed does not 

necessarily represent the same bed in the adjacent section but 

rather the same seam.

Coal Quality

The western part of the Bisti coal fi eld was considered for 

coal availability studies in part because the sulfur analysis (fi g. 

26) indicated a potential compliance coal resource containing 

0.41–0.60 lb of sulfur per million Btu (Energy Information 

Administration, 1993). Coal in the entire Bisti coal fi eld averages 0.61 lb sulfur per million Btu, which is slightly above 

the 0.60-lb-sulfur-per-million-Btu compliance levels. The large 

coal resource, low-sulfur coal distribution, and the availability 

of State-owned property for an industrial site were the primary 

reasons for New Mexico Public Service to consider building a 

coal-fi red power plant in this area.

(Cretaceous 

outcrops)

ALBUQUERQUE GRANTS

STAR 

LAKE

CUBA

STANDING

ROCK

GALLUP

BISTI

FARMINGTON

1 54 MILES

Colorado

Arizona

Puerco 

fault belt

Mt. Taylor

volcanics

Central 

basin

Four 

Corners 

platform

Chaco slope

Nacimiento uplift

Rio Grande trough

Chama

embayment

Archuleta

Zuni

uplift

Gallup sag

Acoma sag

Hogback monocline

Chuska Mtns.

Defiance

uplift

arch

Figure 15. Tectonic map of the San Juan Basin, New Mexico (from 

Beaumont, 1982, fi gure 3, reprinted with permission of the American 

Association of Petroleum Geologists, courtesy of E.C. Beaumont).

Figure 16. Photograph taken near Bisti Trading Post, looking to the 

northeast. Foreground, badlands topography of weathered carbonaceous shale. A knoll of red clinker (burned coal) is visible in the 

mid-ground adjacent to Hunter Wash. (Photograph by Tim Rohrbacher, 

1998).

Figure 17. Photograph taken south of Bisti Trading Post, looking to the 

north. The red clinker of burned coal seams in the Fruitland Formation 

are prominent in the middle part of the photo north of De-Na-Zin 

Wash. (Photograph by Tim Rohrbacher, 1998).

A generalized stratigraphic column (fi g. 19) shows the general 

relationship of the seams.

The average seam thickness ranges from 11 to 14.5 ft, 

including parting. The average net coal within a seam varies 

from 7 to 9 ft thick. Total net coal and parting isopach maps for 

the Red and Green seams (fi gs. 20, 21) illustrate the variability 

F30 Geologic Assessment of Coal in the Colorado Plateau: Arizona, Colorado, New Mexico, and Utah
108 30' 108 

36 30'

36 

Study Area

B'

B

A

A'

C

C'

A A'

Drill hole

Line of cross section

Nacimiento Fm (Tn)

Ojo Alamo Ss Fm (Toa)

Kirtland/Fruitland Fms (undifferentiated)

 (Kkf)

Pictured Cliffs Fm (Kpc)

Cliff House Fm (Kch)

Menefee Fm (Kmf)

Lewis Shale Fm (Kl)

1 4 MILES

Figure 18. Geologic map of Bisti study area showing the location of drill-hole data, cross-section locations, and the Upper 

Cretaceous and lower Tertiary surfi cial geology (after Hoffman and Jones, 1999).

Coal Availability, Recovery, Economic Evaluations of Coal Resources, Colorado Plateau: Colo., N. Mex., and Utah F31
Red

Green

Blue

Yellow

Coal

Seams

Lithology

SeriesDepth (ft.)

Upper Cretaceous

Formation Fruitland Formation Pictured Cliffs Ss Kirtland Shale

200

100

Legend

Interbedded mudstone, 

siltstone and sandstone

Shale or claystone

Coal

Sandstone

Figure 19. Generalized stratigraphic column of Fruitland Formation 

showing coal seams in the Bisti study area, San Juan Basin, New 

Mexico (after Hoffman and Jones, 1999).

Total Coal Thickness Fruitland

Formation

Outcrop > 40 ft

35-40 ft

30-35 ft

25-30 ft

20-25 ft

15-20 ft

10-15 ft

5-10 ft

<5 ft

36 07'30"

108 07'30"

36 22'30"

108 22'30"

5

5

5

5 5

5

5

5

5

10

10

10

10

10

10

10

10

10

15

15

20

20

25

25

30

1 4 MILES

Figure 20. Isopach map of total coal in the Red coal seam in the Bisti 

study area, northwest New Mexico (after Hoffman and Jones, 1999).

10 5

5

5

Total Coal Thickness Fruitland

Formation > 40 ft Outcrop 35-40 ft

30-35 ft

25-30 ft

20-25 ft

15-20 ft

10-15 ft

5-10 ft

<5 ft

36 07'30"

108 07'30"

36 22'30"

108 22'30"

5

5

10

10

10

15

15

20

25

5

1 4 MILES

Figure 21. Isopach map of total coal in the Green coal seam in the 

Bisti study area, northwest New Mexico (after Hoffman and Jones, 

1999).

F32 Geologic Assessment of Coal in the Colorado Plateau: Arizona, Colorado, New Mexico, and Utah
0

5

10

15

20

25

30

35

40

45

50

Thickness in feet

Seams

Seam avg 5.88 5.89 7.92 5.97

Seam max 19.5 28 30 21

Total coal avg 7.66 8.19 9.04 8.52

Total coal max 29 30 40 45.5

Interburden avg 14.12 10.24 5.52 7.34

Coal Seam Yellow (167) Blue (263) Green (280) Red (438)

Thickness (ft.)

Figure 22. Histograms comparing thickness and parting characteristics for each coal seam, northwest New Mexico (after 

Hoffman and Jones, 1999). Numbers in parentheses represent number of data points. “Total coal avg” and “Total coal 

max” refer to coals within a zone.

NL336

0

-100

-200

-200

-100 -100

0 0 NL312 1419

-200

0

-100

219 0

-100 -100 -100

-100

0 0

0 0

0 0

0

0

-100

-100

B-102 402

0

0

701

501 138

AMW-5

-200

AMW-3

-100

0

B-19

0

A-11

A-12

0

A-13

0

B-54 -100 0

0

0 0

0 P22

304A DH-4

B-23-B

P17 0

-100

NL258 NL223 808

805

A'

A

100'

50'

0

0.5 1 mi

Yellow Coal Seam

Blue Coal Seam

Green Coal Seam

Red Coal Seam

Explanation

Figure 23. Cross section along structural strike in Bisti study area. See fi gure 18 for location (after Hoffman and Jones, 1999).

Coal Availability, Recovery, Economic Evaluations of Coal Resources, Colorado Plateau: Colo., N. Mex., and Utah F33
B

B'

100'

50

0 0.5 1 mi

NL362

386

B-102

B-106 

242 A-5

244

B-4

B-5

164

-300

-400

-400

-300 163

162

-300

0

-100

-200

-200

-100

0

0

0 0

0

0

0

0

-100 -100 -100

? ? ?

Yellow Coal Seam

Blue Coal Seam

Green Coal Seam

Red Coal Seam

Explanation

Figure 24. Cross section down structural dip in western part of the Bisti study area. See fi gure 18 for location (after Hoffman and Jones, 1999).

Weighted averages of sulfur in coal beds in the study area 

indicate that sulfur values are higher than weighted average 

sulfur values for the entire fi eld (fi g. 26). However, fewer 

sample analyses were available for coal in the study area 

relative to the entire coal fi eld, and therefore, the values are 

statistically less valid, particularly in regard to the Green coal 

seam. The weighted average values of sulfur in the study area 

suggest that these coal seams would not meet the New Source 

Performance Standards of the Clean Air Act. That standard 

considers coal to be in compliance if the sulfur content is 0.60 

lb, of sulfur per million Btu’s or 1.2 lb of SO2 per million 

Btu’s (Energy Information Administration, 1993). About 0.1 

percent of the total sulfur in these samples is pyritic. Washing 

the coal to remove the pyritic sulfur might lower the sulfur 

content. Also, with blending, these coals might meet compliance standards. 

Coal in the Bisti area is non-agglomerating subbituminous in rank. The weighted average heat of combustion values 

range from 10,817 to 11,051 Btu’s on a moist, mineral-matterfree Btu/lb basis (MMFBtu/lb). Ash yields are generally high 

(> 15 percent), with high ash yield a common characteristic 

of Fruitland Formation coal seams (fi g. 26). An average of the 

few oxide analyses available reveal the major constituent of the 

ash is SiO2 (58 percent), followed by AlO2 (25 percent), Fe2O3

(4 percent), CaO (3.5 percent), and Na2O (1.9 percent). 

Available Data

The database for the Bisti study area is a subset of the 

data collected and entered by the New Mexico Bureau of 

Mines and Mineral Resources (NMBMMR) into the USGS’s 

National Coal Resources Data System (NCRDS) as part of a 

long-term (19-year) cooperative grant with the U.S. Geological 

Survey (USGS). Several exploration projects in the study area 

have resulted in a data set of drill holes (fi g. 18) that are 

concentrated in areas suitable for surface mining. Less data are 

available for the deep subsurface coal seams except in areas 

where oil and gas logs are available. Other sources of drill-hole 

data include mine plans, Coal Resource Occurrence and Coal 

Development Potential maps (CROCDP), NMBMMR drilling, 

and USGS investigations. After the study began, additional 

data were entered into the database to help fi ll in gaps. These 

data were from recently relinquished leases and Preference 

Right Lease Applications on Federal lands obtained from the 

Bureau of Land Management (BLM) offi ces in Farmington, 

N. Mex. 

A total of 238 data points were evaluated for the fourquadrangle study area (Alamo Mesa West, Bisti Trading Post, 

Tanner Lake, and The Pillar 3 NE). Additionally, 316 data 

points from the quadrangles surrounding this area were used in 

coal resource calculations. 

F34 Geologic Assessment of Coal in the Colorado Plateau: Arizona, Colorado, New Mexico, and Utah
Coal Availability Studies in New Mexico

Detailed Methodology

Fruitland coals in the Bisti study area are subbituminous. 

Therefore, resource calculations are based on a minimum 

thickness of 2.5 ft and 1,770 short tons/acre-ft (Wood and 

others, 1983). The density of coal increases with the amount of 

compaction and alteration that the coal has experienced and its 

in-place water content. Wood and others (table 2, 1983) note 

that subbituminous coal has an average density of 1.30, that is, 

1.30 times the weight of water or 81.076 lb/ft3. Coal resources 

in short tons may be quickly calculated by fi nding the surface 

area of a coal bed and multiplying it times the thickness of 

the coal bed. Normally, acres are used for the surface area 

and calculations using acre-feet (ac-ft); therefore you need 

only multiply the total acres times the appropriate density 

(short tons/ac-ft) times the thickness of the coal seam to obtain 

the total short tons in the resource area. Short tons/ac-ft is 

calculated by multiplying the density of the coal times the 

area of an acre, divided by the pounds in a short ton. For 

subbituminous coal (using a density of 1.30), short tons/ac-ft 

= 81.076 lb coal/ft3 times 43,560 ft2/acre divided by 2,000 

= 1,765.8 short tons/ac-ft. To make the calculation easier, 

the short tons/ac-ft were rounded to 1,770 short tons/ac-ft 

(Wood and others, 1983). Detailed estimates for minable coal 

resources require coal, parting, interburden, and overburden 

densities to be measured to three decimal places.

Because of the lenticularity of the coals, total coal (≥

2.5 ft thick) within a seam (instead of individual beds) is the 

basis of resource calculations. Coal seams thinner than 2.5 ft 

and above or below coals meeting the thickness criteria, but 

separated by a parting less than the thickness of the thinner 

C'

C

B-12-W

0

0

0 0 P118

DH-3 P174

0 0

0

0

P227 AMW6-2

141

142 -100

0

151

152

0

156

0

157 -300

-400

-400

-300

-200

-100

-100

-200

-300

-300 -200

-200 -100

-100

-100

-200

-200

-100

0

50

100'

0.5 1 mi

Yellow Coal Seam

Blue Coal Seam

Green Coal Seam

Red Coal Seam

Explanation

Figure 25. Cross section down structural dip in eastern part of the Bisti study area. See fi gure 18 for location (after Hoffman and Jones, 1999).

Coal Availability, Recovery, Economic Evaluations of Coal Resources, Colorado Plateau: Colo., N. Mex., and Utah F35
coal, are included in the seam calculation. A stripping ratio of 

15:1 was used to delineate the difference between surface-minable resources and underground-minable resources. Reliability 

categories are limited to measured, indicated, and inferred. No 

hypothetical reliability category was used in this study because 

of the lenticularity of these coal beds.

The contact between the Pictured Cliffs Sandstone and 

the Fruitland Formation was digitized from USGS maps 

(O’Sullivan and others, 1979, 1986; and Scott and others, 

1979. Additional Fruitland Formation outcrop data (Beaumont, 

1998) were digitized. Drill-hole data fi les were used to create 

gridded, three-dimensional coal seam models in ARC/INFO. 

The top coal seam surface was constructed from grids of elevation and overlain with a Digital Elevation Model (DEM) grid 

from the 1:100,000-scale Toadlena topographic map. Overburden isopach maps for each coal seam were generated, 

beginning at the coal seam outcrop, by subtracting the top 

surface of the coal-seam model from the DEM model. Coalseam resources were then calculated by depth-to-coal-seam 

category, thickness of each coal-seam category, and by reliability category. The following are the criteria for the resource 

calculations used in this study: 

 Depth-to-top-of-coal-seam categories: 0–250 ft, 

250–500 ft, 500–1,000 ft, >1,000 ft.

 Total-coal-seam-thickness categories: 2.5–5 ft, 5–10 ft, 

10–20 ft, >20 ft.

 Reliability categories: measured (1/4 mi), indicated 

(1/4–3/4 mi), inferred (3/4–3 mi).

Overburden maps for the Red and Green zones are shown in 

fi gures 27 and 28. The upper depth limits for the categories are 

highlighted on these maps.

A major utility of a GIS is the assimilation of similar 

graphical information, such as longitude and latitude, into a 

database and the ability to present the information on a map 

as a “layer.” Other layers, such as topography, roads and trails, 

geology, etc., can be placed on the same map until it exhibits 

the desired information. It is also possible to add and subtract 

information layers derived from modeling a two- or threedimensional database of similar information. For example, 

from the original drill-hole database created for the Bisti study, 

subset fi les were produced for each coal seam that included 

latitude, longitude, coal and parting thickness, and point identifi cation. Three-dimensional models were developed from this 

data to represent the variation in thickness of a coal seam and 

the lateral distribution of that coal seam. The top and bottom 

coal seam surfaces are developed during the modeling and 

those surfaces can then be subtracted from other surfaces to 

produce other models.

The fi les developed for the Bisti study included data from 

quadrangles outside the four-quadrangle study area. Modeling 

errors involving truncation and expansion of seams were 

reduced when the model was extended outside the study area. 

The drill hole data fi les were used to produce coal thickness 

grids for resource calculations. The reliability category polygons were generated and each grid cell was assigned a thickness from the coal-seam model. By overlaying the overburden 

layer onto the reliability layers, the total area for each thickness, depth, and reliability category were determined for the 

four-quadrangle study area. Volumes of coal resources were 

calculated in acre-feet using the thickness attribute of the 

cells, and multiplying by 1,770 short tons/acre-ft to calculate 

original resource tonnage (tables 11, 12) for each seam.

Land-use restrictions were digitized from the Toadlena 

topographic quadrangle (scale = 1:100,000). The De-Na-Zin 

and Gateway mine plan outlines were drawn on the Toadlena 

quadrangle and then digitized. Resources calculated in the 

mined-out areas were subtracted from the original calculated 

coal resources to estimate remaining coal resources. Technological restriction fi lters were applied to the remaining coal 

resources for each seam. Appropriate buffers, as discussed 

in the following section, were assigned to the digitized landuse restrictions. These restriction layers were consecutively 

overlain on the combined overburden, reliability, and thickness 

layers with the mined-out areas and technical restrictions to 

calculate the resource tonnage removed by each restriction 

(tables 11, 12, fi g. 29).

Review of Restrictions

The following is a list of restrictions that were considered 

for this area. The buffers applied to these restrictions adhere to 

the New Mexico Coal Surface Mining Regulations, 19 NMAC 

8.2, which follow the Federal regulations:

0

2

4

6

8

10

12

14

16

18

20

22

24

Percent

Seams

Ash 21.52 17 15.3 18.91 19.29

Moisture 14.88 15.19 15.99 15.91 13.93

Sulfur 0.55 0.52 0.49 0.67 0.52

Lbs sulfur/MMBtu 0.79 0.91 0.83 0.92 0.61

Coal Seam Yellow (22) Blue (24) Green (9) Red (26) Bisti field (44)

Figure 26. Histograms comparing weighted average analyses of ash, 

sulfur, and lb sulfur per million Btu’s for the Fruitland Formation coal by 

seam in the study area and in the entire Bisti coal fi eld.

 Restrictions Buffer 

 County roads 200 ft 

 NM State Highway 371 200 ft 

 Pipelines, powerlines 100 ft 

 Buildings, public or private 300 ft 

 Wilderness Areas (entire area) 

 Streams and washes 100 ft 

F36 Geologic Assessment of Coal in the Colorado Plateau: Arizona, Colorado, New Mexico, and Utah
0

0

0 50

50

50

50

50

100

100

100

150

150

150

200

200

200

250

300

300

350

350

350

400

400

450

450

450

500

550

550

550

600

600

650 600

650

650

700

700

700

750

750

750

800

800

850

850

900

900

950

950

1000

1050 1100

1150

500

500

250

0

0

50

50

50

0

Fruitland

Formation

 Outcrop

36 07' 30"

108 07'30"

36 22' 30"

108 22'30"

1 2.5 MILES

Figure 27. Map showing the thickness of overburden above the Red coal seam, Bisti study area, New Mexico. Contour interval 50 ft.

Technological Restrictions

Technological restrictions that infl uence the resources calculated in this study are coal too close to the surface and coal 

too thin at depth. Coal with less than 20 ft of overburden is 

subtracted from the remaining resource coal estimate because 

coal within this interval is generally weathered or burned and 

cannot be used for energy production. Most operating surface 

mines in the Western United States use the greater-than-20-ft 

depth guideline for calculating mine reserves. Coal too thin at 

depth (coal beds 2.5 ft to 5 ft thick) was not considered minable at depths greater than 250 ft. The original coal resources 

are calculated for this depth category, but these results are 

removed under the technological restrictions.

Coal Availability, Recovery, Economic Evaluations of Coal Resources, Colorado Plateau: Colo., N. Mex., and Utah F37
Land-Use Restrictions

Restrictions to mining in the project area are few, but some 

are signifi cant. The restrictions considered are those listed in 

the New Mexico Coal Surface Mining Regulations 19 NMAC 

8. The Bisti Wilderness Area (3,946 acres) is entirely within the 

study area and removes a signifi cant area of surface-minable 

coal. A small part of the De-Na-Zin Wilderness Area is within 

the study area. In 1996, the area linking the Bisti and De-NaZin Wilderness Areas offi cially became a Wilderness Area. This 

addition to the combined Bisti–De-Na-Zin Wilderness Area 

withdrew 16,000 acres from the resource evaluation (fi g. 29). 

The De-Na-Zin and Hunter Washes cut across the Bisti 

study area. These are intermittent streams, but are major 

0

0

0

50

50

50

50

50

100

100

150

150

200

200

250

300

300

300

350

350

350

450

450

350

400

450

500

500

550

550

600

650

700

750 750

800

850

900

950

1000

1050

1100 1100

0

0 0

0

250

500

600

700

800

900 850

750

650

550

400

400

Fruitland

Formation

Outcrop

108 22'30" 108 07'30"

36 22'30"

36 07'

1 2.5 MILES

Figure 28. Map showing the thickness of overburden above the Green coal seam, Bisti study area, New Mexico. Contour interval 50 ft.

F38 Geologic Assessment of Coal in the Colorado Plateau: Arizona, Colorado, New Mexico, and Utah
Table 11. Summary of surface- and underground-minable and available coal resources reported by seam for the Bisti study area, New Mexico. 

[Coal resources are reported in millions of short tons. Note: “15:1 stripping ratio” depth category is a subset of “Surface” depth category] 

 Likely restrictions to mining Restrictions 

to be m

Depth 

categories 

Coal seam 

name 

Original coal 

resources 

Minedout areas Technological restrictions 

Land-use 

restrictions: 

Wilderness 

Area 

Land-use 

restrictions: 

powerlines, 

pipelines, roads 

Total 

restrictions 

Available 

coal 

resources 

Percent 

available 

total coal 

resource 

Buildings 

15:1 Yellow 232 10 38 38 4 89 143 62% 1 

stripping Blue 436 11 77 84 6 179 257 59% 1 

ratio Green 400 3 69 210 8 290 110 28% 1 

 Red 355 11 49 60 7 127 227 64% 1  Total 1,422 35 233 392 25 685 737 52% 4 

Surface Yellow 398 10 35 111 7 163 236 59% 1 

(0-250 ft) Blue 501 12 76 107 6 201 300 60% 1 

 Green 394 6 70 93 10 179 215 55% 2  Red 496 15 50 82 9 155 340 69% 2  Total 1,788 43 231 393 31 698 1,091 61% 6 

Underground Yellow 425 0 42 73 8 123 302 71% 2 

(>250 ft) Blue 698 0 191 108 6 305 393 56% 1 

 Green 1,096 0 53 419 12 484 612 56% 3  Red 1,132 0 177 260 20 456 676 60% 3  Total 3,350 0 462 860 45 1,368 1,983 59% 9 

Table 12. Summary of original and available coal resources and restrictions to mining reported by seam for the Bisti study area, New Mexico. [Coal resources reported in millions of short tons] 

 Likely restrictions to mining Restrictions with poten

mitigation 

Coal seam 

name 

Original coal 

resources 

Mined-out 

areas 

Technological 

restrictions 

Land-use 

restrictions: 

Wilderness 

Area 

Land-use 

restrictions: 

powerlines, 

pipelines, roads 

Total 

restrictions 

Total coal 

resources 

available 

Total coal 

resources—

percent 

available 

Buildings Lan

restr

streams 

Yellow 823 10 77 184 15 285 537 65% 3 Blue 1,199 12 267 215 11 506 693 58% 3 Green 1,490 6 123 513 22 663 827 55% 4 Red 1,628 15 226 341 29 611 1,016 62% 5 Total 5,139 43 693 1,253 77 2,066 3,073 60% 15 
washes in the area. These streams are not considered alluvial 

valley fl oors, which are defi ned as supporting agriculture by 

the Coal Surface Mining Regulations. However, during certain 

times of the year, signifi cant water fl ows in these washes. A 

major highway from Farmington (New Mexico State Highway 

371), a few county roads, pipelines, and power lines transect 

the study area (fi g. 29). The Bisti Trading Post and a few 

hogans (Native American Indian dwellings) are the only buildings in the area. The building locations were digitized from 

the 7.5-minute quadrangles and checked in the fi eld. Although 

archeological sites are present in the study area, they would 

likely be mitigated and were not considered as restrictions.

Previous Mining

The De-Na-Zin and Gateway mines, operated by Sunbelt 

Mining, are within the study area (fi gs. 7, 29). These small 

mines produced 1.8 million short tons of coal from 1980 

through 1988. Mined areas were removed from the original 

coal resource calculations for the 0- to 250-ft depth category 

and from the 15:1-stripping-ratio category to estimate the 

remaining coal resources. It is diffi cult to know what coal 

beds/seams were mined at these two operations, but it is 

assumed that all coal seams were mined within 250 ft of the 

surface.

36 07’ 30”

36 22’ 30”

108 22’ 30” Study Area 108 07’ 30”

De-Na-Zin mine

Fruitland Fm

outcrop

Powerline

Road

Pipeline

Major Drainage

Mine

County road

Gateway mine

Wilderness Area

Drainage Restriction

Building

Hunter

Wash

Chaco River

De-Na-Zin Wash

NM

371

NM

371

1 4 MILES

Figure 29. Mined-out areas and land-use restrictions in Bisti study area (modifi ed after Hoffman and Jones, 1999).

F40 Geologic Assessment of Coal in the Colorado Plateau: Arizona, Colorado, New Mexico, and Utah
Bisti Study Area Resources

The original coal resources calculated for the Bisti study 

area are 5.1 billion short tons (table 12, fi g. 30). Production 

at the Gateway and De-Na-Zin surface mines totaled 1.8 million short tons of coal. Excluding resources in the mine plan 

areas from the 0- to 250-ft-depth category decreased the original coal resources by 43 million short tons. Applying the 

15:1-stripping-ratio category in the mine plan areas reduced 

the original coal resources by 35 million short tons.

The technological restrictions (near surface coal and thin 

coal at depths greater than 250 ft) removed 693 million short 

tons from the total original resource. However, the largest 

restriction to mining the original resources is the Bisti–De-NaZin Wilderness Area. This restriction withdraws 1.25 billion 

short tons (28.5 percent) from the original resource, and 392 

million short tons of this total falls within the 15:1-strippingratio category. Of the total original coal resource, the 1996 

addition to the Wilderness Area removes 1.1 billion short tons 

of coal (0.15 billion short tons of coal resource were removed 

in the initial Wilderness Area withdrawal). The combined Wilderness Areas exclude the greatest tonnage from the Green 

zone, which has on average the thickest coal seams (8 ft thick). 

To illustrate the impact of the Wilderness Area on the coal 

resources of the area, compare the area covered by the Wilderness Area (fi g. 29) with the total coal isopachs for the Red and 

Green zone (fi gs. 20, 21). One can see that thick coal areas in 

the Green coal seam and one of the thick coal areas in the Red 

coal seam fall within the Wilderness Area. 

Restrictions related to pipelines, power lines, and major 

roads in the study area remove 77 million short tons from the 

remaining available resource. It is unlikely that New Mexico 

State Highway 371 would be rerouted although some of the 

county roads might be. Figure 31 illustrates the proportion of 

coal removed by these restrictions and the remaining available 

coal resource for each of the seams. Figure 30 demonstrates 

how the restrictions infl uence the availability of the coal in 

each seam by tonnage. This diagram clearly points out how 

greatly the original coal resources are impacted by the presence of the combined Bisti–De-Na-Zin Wilderness Area.

Restrictions with Potential for Mitigation

The restrictions applied to the remaining coal resources 

that have a potential for mitigation include buildings, streams 

and washes. Buildings impact some 15 million short tons of 

coal resource. If mining were to take place, these buildings, 

which are mostly Navajo hogans, could be moved and the 

owners compensated. The De-Na-Zin and Hunter Washes 

impact another 51 million short tons of coal resources. However, these washes are not considered alluvial valley fl oors 

and they lack signifi cant fl ow except during rainy seasons. 

Consequently, mining might not be restricted in the wash areas. 

0

1,000

2,000

3,000

4,000

5,000

6,000

Millions of short tons

Y e llo w B lu e G re e n R e d Total

Coal seams

Original coal resources

Original excluding mined-out

and technological restrictions

Remaining coal resources

excluding the Wilderness 

Areas

Available coal resources

Figure 30. Histograms summarizing the calculated coal resources by seam in the Bisti study area, New Mexico (after Hoffman and Jones, 

1999).

Coal Availability, Recovery, Economic Evaluations of Coal Resources, Colorado Plateau: Colo., N. Mex., and Utah F41
Other Coal-Resource Studies

The U.S. Department of Energy (DOE), Energy Information Administration’s (EIA) Demonstrated Reserve Base (DRB) 

coal resource update study (Hoffman, 1996a) reported an estimated 2 billion short tons of coal resource for the entire Bisti 

coal fi eld. These estimated coal resource tonnages cannot be 

compared to the available coal resource estimates for the fourquadrangle study area because the DRB coal resource update 

study did not include calculations for inferred reliability and did 

not include coal resources found at overburden depths greater 

than 1,000 ft. Also, a signifi cant amount of new point-source 

data was available from BLM fi les and added to our coal availability study database fi les. These new data increased the accuracy of the coal availability resource estimate by fi lling in areas 

of no data. The impact of the Wilderness Area to the entire Bisti 

fi eld was signifi cantly greater for this study, in part because 

the addition between the Bisti and De-Na-Zin Wilderness Areas 

did not exist at the time of the DRB study. Consequently, landuse restrictions have a greater infl uence on the available coal 

resources calculated in this study.

Summary

Four Fruitland Formation coal seams, designated as the 

Yellow, Blue, Green, and Red, are recognized in the study 

area. Coal beds within the coal seams are highly variable in 

thickness. The average coal seam is 6–8 ft thick. The coal 

contains high ash, low sulfur, and is subbituminous A in rank. 

The average quality of all the coal resources does not meet 

compliance coal standards of less than 0.6 lb sulfur/MMBtu, 

but with blending or washing, these coals could potentially 

meet this guideline. Original coal resources in this study area 

are 5.1 billion short tons (st). Technological restrictions and 

previous mining decrease the original coal resources by about 

0.7 billion short tons. The Bisti–De-Na-Zin Wilderness Area 

is the largest land-use restriction, removing 28.5 percent (1.3 

billion short tons) of remaining coal resource. The available 

coal resource is 3 billion short tons in the Bisti study area (fi g. 

30). Of this available resource, 0.7 billion short tons is within 

the 15:1-stripping-ratio category (table 11).

Mined-out areas

1%(10)

Technological

restrictions

9%(77)

Land use:Wilderness

area

22%(184)

Land use: pipelines,

powelines, roads

2%(15)

Available

66%(537)

Landuse:Wilderness

area

18%(215)

Landuse: pipelines,

powelines, roads

1%(11)

Technological

restrictions

22%(267)

Mined-out areas

1%(12)

Available

58%(693)

Technological

restrictions

8%(123)

Mined-out areas

0.4%(6)

Land use:Wilderness

area

35%(513)

Land use: pipelines,

powelines, roads

1%(22)

Available

56%(827)

Mined-out areas

1%(15) Technological

restrictions

14%(226)

Land use: pipelines,

powelines, roads

2%(29)

Land use: Wilderness

area

21%(341)

Available

62%(1,016)

Red seam, coal resources (million short tons) Green seam, coal resources (million short tons)

Blue seam, coal resources (million short tons) Yellow seam, coal resources (million short tons)

Figure 31. Pie diagrams illustrating coal resources excluded by likely restrictions to mining (after Hoffman and Jones, 1999). 

F42 Geologic Assessment of Coal in the Colorado Plateau: Arizona, Colorado, New Mexico, and Utah
Coal Availability in the Northern 

Wasatch Plateau Coal Field, Utah

Abstract

Calculations show that the Northern Wasatch Plateau coal 

fi eld originally contained more than 9.2 billion short tons of 

coal. Underground-minable coal accounts for 5.4 billion short 

tons of this total. Comparison of underground mine maps with 

associated coal-bed thickness maps shows that past mining 

has removed, or made unrecoverable, approximately1 billion 

short tons of this coal. If restrictions to mining (such as the 

prohibition to mining under streams, lakes, and roads) are also 

considered, derived maps show that 3.8 billion short tons of 

coal are available for future mining. 

Introduction

This section summarizes the amount and distribution of 

available coal resources in the northern half of the Wasatch 

Plateau coal fi eld in central Utah (fi g. 32); additional information is provided in Utah Geological Survey Circular 100 (Tabet 

and others, in press). Available coal resources are calculated 

using a Geographic Information System (GIS) software program. Using the GIS software, coal tonnage is estimated from 

maps that show the distribution and thickness of individual 

coal beds. Comparison of maps that show the original inground coal, the extent of past mining, and those areas where 

mining is unlikely due to technical and land-use restrictions 

allows tabulation of the remaining available coal.

Location and Mining History

All of the coal currently produced in Utah comes from 

the Upper Cretaceous Blackhawk Formation in the Wasatch 

Plateau and Book Cliffs coal fi elds. These coal fi elds follow 

a broad arc in central Utah (fi g. 8) where the massive, cliffforming sandstones associated with the coals form a prominent 

escarpment. The study area corresponds to the northern half of 

the Wasatch Plateau coal fi eld outlined by the nine 7.5-minute 

quadrangles shown on fi gures 8 and 32. Because the coal 

beds in this area are deeply buried, coal is produced from 

underground mines. In 1997, more than 70 percent of Utah’s 

coal production came from seven underground mines in the 

northern Wasatch Plateau. The location of entrances (portals) 

to these active mines, as well as abandoned mines, is shown 

in fi gure 32. 

Figure 33 shows the mining areas and structural features 

(grabens) in the study area. Commercial coal production began 

in the Pleasant Valley mining area in the late 1870’s and later 

expanded to include numerous mines in the Book Cliffs coal 

fi eld and throughout the northern Wasatch Plateau. Since 1900, 

Utah coal production has been variable. In the early 1970’s a 

period of sustained growth began (Jahanbani, 1997). Between 

1985 and 1997, coal production from the study area more than 

doubled (fi g. 34). 

Geology

The Wasatch Plateau lies along the gently dipping western fl ank of the San Rafael Swell. Dips of the strata are 

generally low angle, usually no more than six degrees to 

the west or northwest. The strata are broken by a series of 

en-echelon, north-trending grabens with displacements on the 

graben-bounding faults of as much as 1,500 ft. The Joes Valley 

and Pleasant Valley grabens cut the Northern Wasatch Plateau 

study area (fi g. 33).

Major coal beds in the study area occur within a few 

hundred feet of the bottom of the 700- to 1,100-ft-thick 

Upper Cretaceous Blackhawk Formation (Doelling, 1972). 

The Blackhawk Formation conformably overlies the Star Point 

Sandstone and is unconformably overlain by the Castlegate 

Sandstone Member of the Price River Formation. These Cretaceous strata, as well as some younger Tertiary units, cap the 

highly dissected Wasatch Plateau. 

The quality of coal produced at active mines in the study 

area is reported by Sanda and others (1998). Coal rank varies 

from high-volatile C bituminous to high-volatile B bituminous. 

Sulfur content of the mined coal is consistently low (near 0.5 

percent), whereas moisture content and ash yield are more 

variable (typically 8 percent moisture and 10 percent ash).

Figure 35 shows an idealized stratigraphic section for 

13 coal beds in the study area—coal-bed names are largely 

based on maps and cross sections presented by Blanchard 

(1981), Sanchez and Brown (1986, 1987), and Brown and 

others (1987). Prior to these studies the Acord Lakes, Axel 

Anderson, and Cottonwood beds were considered a single 

coal bed called the Hiawatha bed. A better understanding of 

intertonguing of the basal Star Point Sandstone within the 

Blackhawk Formation allowed us to distinguish multiple coal 

beds.

Figure 36 shows that four coal beds (Axel Anderson, 

Cottonwood, Blind Canyon, and Wattis) account for almost 90 

percent of the original minable coal in the Northern Wasatch 

Plateau coal fi eld. Other coal beds with signifi cant minable 

coal tonnage include the Castlegate A and D, the Acord Lakes, 

and the Gordon. Not all of this coal is available for future 

mining; some has been removed by past mining and some 

occurs in areas that are unlikely to be mined due to technological and (or) land-use restrictions.

Methodology

Figure 37 shows the location of 612 drill holes and measured sections that were processed through GIS software to 

make maps showing the extent, thickness, and elevation of 

Coal Availability, Recovery, Economic Evaluations of Coal Resources, Colorado Plateau: Colo., N. Mex., and Utah F43
Explanation

' 111 ̊00'

Figure 32. Quadrangle index map of the Northern Wasatch Plateau study area with locations of active 

and abandoned mine portals (locations from Doelling, 1972; Utah Division of Oil Gas and Mining; and Utah 

Geological Survey records; after Tabet and others, 1999).

F44 Geologic Assessment of Coal in the Colorado Plateau: Arizona, Colorado, New Mexico, and Utah
Explanation

Figure 33. Coal mining areas and major grabens in the northern Wasatch Plateau, Utah (adapted from 

Doelling, 1972; after Tabet and others, 1999).

Coal Availability, Recovery, Economic Evaluations of Coal Resources, Colorado Plateau: Colo., N. Mex., and Utah F45
individual coal beds. For comparison with earlier studies, we 

defi ne the minimum minable coal bed thickness to be 4 ft. 

We also exclude coal in rider beds and sub-beds from the 

available coal resource. Although such coal might be produced 

using surface-mining techniques, it is not accessible by underground-mining techniques used in the area. Maps showing the 

original minable coal resource do not distinguish areas where 

the coal has been removed by past mining or, because of 

technological or regulatory reasons, is unlikely to be mined. 

Restrictions to mining are examined by construction of associated maps, each corresponding to a particular restriction. Various map-to-map subtractions allow tabulation of the (remaining) available coal. Table 13 lists specifi c restrictions considered in this study.

Past Mining

Maps of abandoned and active underground mine workings are used to delineate areas where coal beds have been 

mined or undermined and are not available for future mining. 

Comparison of these maps with maps of the original minable 

coal shows that 674 million short tons of coal was originally 

present within the perimeters of active and abandoned mines. 

An additional 296 million short tons of coal is observed in 

coal beds directly above the mine workings. We assume that 

undermining destroys the continuity of the overlying coal bed 

and creates diffi cult roof and fl oor conditions that cause the 

higher beds to be unminable. Figure 38 shows that the impact 

of past mining varies for different coal beds. The basal Acord 

Lakes bed is not affected by past mining activity, whereas 

stratigraphically higher coal beds are more extensively mined 

and undermined. Combining the mined-out and undermined 

coal shows that roughly one billion short tons of coal have 

been either removed or made unrecoverable by past mining.

Technical Restrictions

Technical restrictions (table 13) are used to identify areas 

where otherwise minable coal is unlikely to be mined due 

to problems related to the safe and economic recovery of 

coal. For example, to avoid unstable roof conditions and possible water infusions, most mines leave a 50-ft barrier near 

known faults. Burned or oxidized near-surface coal is typical 

in the study area and commonly causes operators to avoid 

mining coal close to the outcrop; a 100-ft minimum overburden restriction is used to avoid this weathered coal. In areas 

where vertically adjacent beds can be sequentially mined, 40-ft 

minimum interburden is required for stable roof and fl oor 

conditions; where interburden is less than 40 ft thick, one of 

the adjacent coal beds is excluded from the available coal 

resources. Although most Wasatch Plateau mines plan for a 

maximum 2,500 ft overburden, some are considering mining 

coal at depths as deep as 3,000 ft. In anticipation of such deep 

mines we use a 3,000-ft burial depth restriction. 

5

10

15

20

Year

1980 1985 1990 1995

Annual production (millions of short tons)

Figure 34. Annual coal production from 1980 to 1997 for mines in the 

northern half of the Wasatch Plateau coal fi eld, Utah (data adapted 

from Jahanbani, 1997, and records from the U.S. Mine Safety and 

Health Administration; after Tabet and others, 1999).

900 FEET

800

700

600

500

400

300

200

100

0 FEET

Rock Canyon

Gilson

Castlegate D

Castlegate C

Castlegate B

Castlegate A

Gordon

Wattis

Bear Canyon

Blind Canyon

Cottonwood

Axel Anderson

Acord Lakes

Aberdeen Ss Mbr

of BLACKHAWK Fm

B L A C K H A WK F O R MA T I ON

Spring Canyon

 Mbr

of

BLACKHAWK

Fm

STAR POINT Ss

Storrs Tongue

STAR POINT Ss

Panther Tongue

STAR POINT Ss - lower tongues

SW NE

Figure 35. Idealized stratigraphic section showing named coal beds 

in the Blackhawk Formation, northern Wasatch Plateau, Utah. Modifi ed from Blanchard (1991), Sanchez and Brown (1986, 1987), and 

Brown and others (1987) (after Tabet and others, 1999).

F46 Geologic Assessment of Coal in the Colorado Plateau: Arizona, Colorado, New Mexico, and Utah
We calculate that 490 million short tons of coal in the 

study area is unlikely to be mined because of technical restrictions. The most signifi cant technical restriction (excess thickness) is due to weathered coal near the outcrop (fi g. 39). 

The second most signifi cant technical restriction occurs where 

coal beds are too thick for full-bed-thickness extraction using 

current mining equipment. This restriction affects parts of 

the Axel Anderson, Cottonwood, Blind Canyon, Wattis, and 

Gordon coal beds because they are sometimes more than 14 ft 

thick. The least signifi cant technical restriction is overburden 

depth—none of the coal is at depths that prevent underground 

mining. Cumulatively, technical restrictions eliminate 490 million short tons of coal from the resource available for future 

mining.

Land-Use Restrictions

Land-use restrictions considered in this study (table 13) 

prohibit mining under certain surface features to avoid damage 

due to ground subsidence. Minable coal under the buffered 

perimeters of these features is not part of the available coal 

resource. Cumulatively, land-use restrictions eliminate 146 

million short tons of coal from the resource available for future 

mining. Nearly half of this total is attributed to the prohibition 

of mining under streams and lakes (fi g. 40).

28% Blind Canyon

24% Axel Anderson

21% Wattis

16% Cottonwood

4% Castlegate D

3% Acord Lakes

1% Gordon

1% Castlegate A

2% Other coal beds

5,376 MILLION SHORT TONS OF ORIGINAL MINABLE COAL

(1,484 million short tons)

(1,272 million short tons)

(1,140 million short tons)

(879 million short tons)

(209 million short tons)

(158 million s.t.)

(69 million short tons)

(69 million short tons)

Figure 36. Pie chart showing the amount of original minable coal by coal bed, Northern Wasatch Plateau study area, Utah (after Tabet 

and others, 1999).

Table 13. Restrictions, and their associated buffers and factors, that 

prevent mining in the Northern Wasatch Plateau coal field. 

[After Tabet and others, 1999] 

Past mining Factor 

Barrier for abandoned mines 50 ft around margin 

Barrier for active mines none 

Technical restrictions Factor 

Minimum bed thickness 4 ft 

Maximum bed thickness 14 ft 

Minimum overburden 100 ft 

Maximum overburden 3,000 ft 

Minimum interburden 40 ft 

Faults 1 50 ft on either side 

Land-use restrictions Buffer 

Power lines 100 ft on either side 

Pipelines 100 ft on either side 

Highways 100 ft on either side 

Railroads 100 ft on either side 

Perennial streams 100 ft on either side 

Lakes or reservoirs 100 ft inland from shore 

Radio towers 100-ft radius 

Oil and gas wells 100-ft radius 

Towns or residences 300-ft perimeter 

1 Includes igneous dikes.

Coal Availability, Recovery, Economic Evaluations of Coal Resources, Colorado Plateau: Colo., N. Mex., and Utah F47
Explanation

Figure 37. Location of drill holes and measured sections used to calculate coal resources in the Blackhawk 

Formation, northern Wasatch Plateau, Utah (after Tabet and others, 1999).

F48 Geologic Assessment of Coal in the Colorado Plateau: Arizona, Colorado, New Mexico, and Utah
Resource Categories

Reliability

Calculation of the amount of minable coal in the study 

area is based on maps constructed from records of coalbed-thickness measurements at specifi c locations (fi g. 37). 

Confi dence in these maps is high in areas close to measurement points and decreases farther away from the measurement 

points. Consequently, the reliability of the derived tonnage 

estimate depends on the spatial distribution of the measurement points in relation to the mapped coal-bed thickness.

Wood and others (1983) defi ne the three reliability cateegories used in this report; they include demonstrated (measured + indicated) coal resources, inferred coal resources, and 

hypothetical coal resources. Demonstrated coal resources are 

within 0.75 mi of a thickness-measurement point. Inferred 

coal resources are between 0.75 and 3 mi of a thicknessmeasurement point. Hypothetical coal resources are more than 

3 mi from a thickness-measurement point. Figure 41 shows 

that most of the original minable coal tonnage in the study area 

is within 0.75 mi of a measurement location.

Acord Lakes

Axel Anderson

Cottonwood

Blind Canyon

Bear Canyon

Wattis

Gordon

Castlegate A

Castlegate D

0 50 100 150 200 250 300

Mined-out

Undermined

Million short tons coal

COAL BED

Figure 38. Bar graph showing the amount of coal no longer available 

due to past mining (through December 1997), northern Wasatch Plateau, Utah (after Tabet and others, 1999).

Weathered (40%)

Excess thickness (26%) Interburden conflict (19%)

Too close to fault (15%)

Figure 39. Pie chart showing technical restrictions that exclude 490 

million short tons of coal from the available coal resources of the 

Northern Wasatch Plateau study area, Utah (after Tabet and others, 

1999).

Streams and lakes (47%)

Towns (30%)

Roads (10%)

Pipelines (6%)

Railroads (3%)

Power lines (2%)

Buildings etc. (2%)

Figure 40. Pie chart showing land-use restrictions that exclude 146 

million short tons of coal from the available coal resources of the 

Northern Wasatch Plateau study area, Utah (after Tabet and others, 

1999).

Acord Lakes

Axel Anderson

Cottonwood

Blind Canyon

Bear Canyon

Wattis

Gordon

Castlegate A

Castlegate D

0 20 40 60 80 100

Demonstrated

Inferred

Hypothetical

Percent of coal-bed tonnage

Reliability Class

Coal bed

Figure 41. Data reliability of original minable coal bed tonnage 

estimates for nine coal beds, Northern Wasatch Plateau study area, 

Utah (after Tabet and others, 1999).

Thickness

Standard coal-bed-thickness categories for bituminous 

coal resources (Wood and others, 1983) are not appropriate 

for this study given the characteristically thick beds and current mining practice in the northern Wasatch Plateau. ConseCoal Availability, Recovery, Economic Evaluations of Coal Resources, Colorado Plateau: Colo., N. Mex., and Utah F49
quently, we used thickness categories suited to local conditions. Minable coal resources are assigned to one of four 

coal-bed-thickness categories: 4 to 6 ft, 6 to 10 ft, 10 to 14 

ft, and greater than 14 ft. Figure 42 shows the range of thickness variation for coal beds in the study area. In general, the 

stratigraphically lower coal beds are thicker than those higher 

in the section. 

Results

Available Coal Resources

Including all coal beds greater than 1 ft thick, we estimate 

that the study area originally contained more than 9 billion 

short tons of coal. However, only 5.4 billion short tons of 

this coal is in beds more than 4 ft thick, therefore suitable 

for underground mining. Subtracting coal that is no longer 

available due to past mining, as well as coal that is unlikely 

to be mined because of technical and land-use restrictions, 

leaves 3.8 billion short tons of coal available for future mining. 

Figure 45 shows these relationships for nine coal beds in the 

study area.

Coal beds that contain more than 100 million short tons 

of available coal include the Acord Lakes (156 million short 

tons), Axel Anderson (1,019 million short tons), Cottonwood 

(495 million short tons), Blind Canyon (1,056 million short 

tons), Wattis (752 million short tons), and Castlegate D (132 

million short tons). Besides containing different amounts of 

available coal, the aerial extent of these coal beds also varies 

as shown in fi gures 46 and 47. The basal Acord Lakes coal 

bed is only present in the southernmost quadrangle (fi g. 46) 

whereas the stratigraphically higher coal beds tend to occur in 

the central to northern half of the study area (fi g. 47). These 

fi gures also show the extensive mine workings in the study 

area. 

Acord Lakes

Axel Anderson

Cottonwood

Blind Canyon

Bear Canyon

Wattis

Gordon

Castlegate A

Castlegate D

0 20 40 60 80 100

4 to 6 feet

6 to 10 feet

10 to 14 feet

More than 

14 feet

Coal-bed Thickness

Percent of coal-bed tonnage

COAL BED

Figure 42. Bar graph comparing coal bed thickness of the nine 

minable coal beds in the Northern Wasatch Plateau study area, Utah 

(after Tabet and others, 1999).

Overburden

We report four overburden categories: 0 to 100 ft, 100 to 

1,000 ft, 1,000 to 2,000 ft, and 2,000 to 3,000 ft. Wood and 

others (1983) recommend a 0- to 500-ft overburden category 

to identify potentially strippable coal resources. However, the 

responsible land management agencies in Utah do not favor 

strip mining on the steep terrain characteristic of the study 

area. Consequently, we ignore the recommended 500-ft overburden category, but include a 0- to 100-ft category to identify 

coal that is not minable because it is commonly weathered 

or burned near the outcrop. Figure 43 shows that most of the 

coal is at depths between 100 and 2,000 ft, which is ideal for 

underground mining. All of the coal in the study area is at 

depths less than 3,000 ft and is potentially minable.

Figure 44 shows overburden maps for four major coal 

beds in the study area. The deep coal is in the western and 

southern parts of the study area, whereas the shallow coal 

(less than 100 ft of burial) is widely distributed along narrow, 

(barely visible) strips marking the coal outcrops. 

Acord Lakes

Axel Anderson

Cottonwood

Blind Canyon

Bear Canyon

Wattis

Gordon

Castlegate A

Castlegate D

0 20 40 60 80 100

Less than 100 feet

100 to 1,000 feet

1,000 to 2,000 feet

2,000 to 3,000 feet COAL BED

Percent of coal-bed tonnage

Burial Depth

Figure 43. Bar graph comparing the burial depth of the nine minable 

coal beds in the Northern Wasatch Plateau study area, Utah (after 

Tabet and others, 1999).

F50 Geologic Assessment of Coal in the Colorado Plateau: Arizona, Colorado, New Mexico, and Utah
Coal Bed Coal Bed Coal Bed Coal Bed 

Figure 44. Overburden thickness maps showing depth to the top of major coal beds, Blackhawk Formation, Northern Wasatch Plateau study area, Utah (after 
450

140

113

1,019

427

220 164

495

799

280

148

1,056

403

240

149

752

159

51

353

18 48

162

21

11 37

584

64

14 132

Acord Lakes Axel Anderson Cottonwood

Blind Canyon Wattis Bear Canyon

Gordon Castlegate A Castlegate D

KEY

Numbers indicate

millions of short tons 

where >10 million

Coal too thin

to mine 

Mined-out or

undermined

Restricted from

mining

Available for

mining

110

156

Figure 45. Pie charts summarizing the availability of coal resources for nine coal beds, northern Wasatch Plateau, Utah (after Tabet and 

others, 1999).

Recovery Factors

From the time mining began in the 1870’s through the end 

of 1996, 351 million short tons of coal have been produced 

from mines in the northern Wasatch Plateau (Jahanbani, 1997). 

This equals 52 percent of the estimated 674 million short tons 

of original coal that occurs within the perimeters of active and 

abandoned mines. This suggests a resource recovery factor of 

more than 50 percent. However, if the 296 million short tons of 

undermined coal is also considered, then a 36 percent resource 

recovery factor is more likely.

The 36 percent resource recovery factor we observe for 

the northern Wasatch Plateau is higher than Doelling’s (1972) 

prediction of a 30 percent resource recovery factor for the 

total Wasatch Plateau coal fi eld. This difference might be 

explained, in part, by the recent introduction of effi cient longwall mining techniques. However, ultimate recovery of the 

resource is likely to be lower than the 36 percent observed 

to date. As noted by Doelling (1972, p. 129), “much of the 

easy-to-get coal has been mined.” Indeed, fi gure 48 shows that 

past mining has disproportionately targeted thicker coal beds; 

remaining coal resources are less attractive in this respect. Past 

mining has also resulted in isolated blocks of coal that may be 

diffi cult to economically recover. For example, an examination 

of the Blind Canyon available coal indicates that 16 percent is 

in blocks smaller than 1,000 acres. Thus, the ultimate recovery 

of coal from this area will probably be closer to the 30 percent 

as predicted by Doelling (1972) rather than the 36 percent 

recovery factor we observed.

Future Production

Maps like those shown in fi gures 46 and 47 are being 

used in prefeasibility engineering studies undertaken by the 

USGS to estimate how much coal will ultimately be recovered 

from the northern half of the Wasatch Plateau coal fi eld. 

Although such studies should allow well-constrained estimates 

of future coal production, data presented here are suffi cient for 

useful predictions. At continued coal production of 19 million 

short tons per year (fi g. 34), and assuming 30 percent coal 

recovery, the 3.8 billion short tons available coal resource will 

be mined out by 2054. However, only 2.7 billion short tons 

of the available coal resource is in beds that are more than 6 

ft thick. If companies continue to select this thicker coal for 

mining (fi g. 48), then the most attractive coal resources will 

F52 Geologic Assessment of Coal in the Colorado Plateau: Arizona, Colorado, New Mexico, and Utah
Coal Bed Coal Bed Coal Bed Coal Bed

Figure 46. Map showing the distribution of available coal for the Acord Lakes, Axel Anderson, Cottonwood, and Blind Canyon coal beds, northern Wasatch P
Wattis

Coal Bed

Gordon

Coal Bed

Castlegate A

Coal Bed

Castlegate D

Coal Bed

N

Figure 47. Map showing the distribution of available coal for the Wattis, Gordon, Castlegate A, and Castlegate D coal beds, northern Wasatch Plateau, Utah (
be depleted by 2040. Although coal production will probably 

decline when the remaining large tracts of thick coal are gone, 

production by relatively small mining operations from thinner, 

less extensive coal beds is likely. Thus, some production can 

be anticipated beyond 2054. Nonetheless, State and local planners should consider the impacts of resource depletion as coal 

production shifts to other areas. 

Summary

GIS analyses indicate that 3.8 billion short tons of coal 

are available for future mining in the northern half of the 

Wasatch Plateau coal fi eld; this is about 70 percent of the 

original minable coal. Factors responsible for reduction of the 

original minable coal resource include past mining activity 

(–970 million short tons), technical restrictions to mining 

(–490 million short tons), and coal made unavailable due to 

land-use restrictions (–146 million short tons). Table 14 shows 

coal resource values for individual coal beds.

Our estimate of original minable coal is about 27 percent 

higher than previously estimated for this area (Doelling, 1972). 

Greater availability of drill-hole information, more extensive 

extrapolation of coal resources, and inclusion of less signifi -

cant coal beds contributed to our higher resource estimate. 

Assuming current mining practice and 30 percent resource 

recovery, coal production from this area can be expected to 

decline by 2040.

Resource Recovery, 

Economic Evaluation of 

Minable Coal Resources, 

and Project Summary

Introduction

Coal availability studies have been conducted in three 

locations on the Colorado Plateau since 1997: the Somerset 

quadrangle (Somerset coal fi eld) in west-central Colorado, a 

four quadrangle area in the Bisti coal fi eld in northwestern 

New Mexico, and a nine-quadrangle area in the Northern 

Wasatch Plateau coal fi eld in central Utah (fi g. 4). Coal mining 

began in the northern Wasatch area in the 1870’s and in the 

Somerset area in the late 1880’s (fi g. 5). All of the production 

was from underground mines. A limited amount of coal was 

produced from the Bisti coal fi eld in the 1980’s, all from surface mines using draglines and truck/shovel mining methods 

for stripping. The Bisti operations have ceased and the mines 

have been reclaimed.

Past Mining Methods

Early underground mines in both the Somerset and northern Wasatch Plateau areas were room and pillar operations 

using the mining technology of drilling and blasting coal, and 

loading small rail cars by hand-shoveling. As mining equipment became more automated, electric-powered undercutting 

machines, gathering-arm loaders, continuous miners, roof bolters, coal-haul trucks, and conveyor systems became common. 

During the 1960’s and 1970’s, longwall mining became more 

common in mines where large production rates were needed 

(>2.5 million short tons/year). 

Present Mining Methods—Somerset and 

Northern Wasatch Plateau Coal Fields

Most of the surface and mineral ownership in the Somerset quadrangle and the Northern Wasatch Plateau study areas 

is Federal and administered by the U.S. Forest Service or the 

U.S. Bureau of Land Management. The U.S. Forest Service 

does not allow surface mining on their properties and they 

allow only restricted access to underground mines. The BLM 

does allow surface mining on its property. However, in the case 

of both of these study areas, the coal is present in areas where 

the natural ground slope is too steep to conduct surface mining 

operations. As previously noted, the coal quality in both of 

Coal-bed thickness (feet)

Percent

0

10

20

30

40

4 8 10 12 14 16 18 20 22 24 26 28 6

Original minable coal Coal that has been

mined up to 1998

Figure 48. Bar graph showing the distribution of original minable coal 

by bed thickness compared to the percent of coal in each thickness 

interval that has been mined, northern Wasatch Plateau, Utah (after 

Tabet and others, 1999).

Coal Availability, Recovery, Economic Evaluations of Coal Resources, Colorado Plateau: Colo., N. Mex., and Utah F55
these areas is excellent: high Btu, low sulfur, low ash (tables 

15, 16), and many of the coal beds exceed 6 ft of thickness 

over large areas. This is a perfect scenario for longwall mining. 

Currently there are six longwall mines in the northern Wasatch 

Plateau, one longwall mine in the Somerset area, and one 

new longwall mine permit application being reviewed in the 

Somerset area. These mines are some of the most productive 

underground mines in the United States. Also helping the 

marketability of the coal is the transportation infrastructure. 

The mine loadouts (tipples) are directly served by rail spurs 

from the mainline railroad. Highway truck-haul distances to 

rail loadouts are relatively short.

Present Mining Methods—Bisti Study Area

The Bisti coal fi eld study area contains coal in multiple 

seams of lesser thickness than in the Colorado and Utah study 

areas but with acceptable thickness (12–60 inches) to support 

surface mining—either in large area mines using trucks and 

Table 14. Total, minable, and available coal resources, northern Wasatch Plateau, Utah. 

[Resources in millions of short tons. After Tabet and others, 1999] 

Deductions 

Coal bed Original total 

coal 1

Original minable 

coal 2 Past mining 3

Technologic 

restrictions 4

Land-use 

restrictions 5

Remaining 

available coal 6

 

 Rock Canyon 174.1 30.2 0.4 5.7 3.9 20.1 

 Gilson 102.8 0.0 0.0 

 Castlegate D 793.5 209.4 64.0 12.3 1.6 131.6 

 Castlegate C 33.7 4.2 0.0 1.5 0.1 2.6 

 Castlegate B 64.5 2.0 0.0 0.1 0.0 1.9 

 Castlegate A 230.3 68.7 21.1 10.1 0.9 36.6 

 Gordon 421.8 69.0 2.8 17.8 0.3 48.0 

 Wattis 1,543.3 1,140.4 240.3 106.6 41.9 751.5 

 Bear Canyon 217.4 58.0 2.4 3.7 0.8 51.2 

 Blind Canyon 2,282.7 1,483.9 279.8 113.8 34.3 1,056.3 

 Cottonwood 1,306.6 879.2 219.7 129.9 34.3 495.2 

 Axel Anderson 1,722.0 1,272.2 139.7 87.4 25.9 1,019.1 

 Acord Lakes 268.7 158.4 0.0 1.0 1.6 155.8 

TOTAL 6 9,161.4 5,375.6 970.0 489.9 145.6 3,769.9 

1 Coal in beds at least one ft thick that was present in the study area prior to mining. 

2 Coal in beds at least 4 ft thick that was present in the study area prior to mining and can be mined underground. 

3 Includes coal within the perimeter of underground mines as well as subjacent coal above these mines (deducted from original minable coal). 

4 Coal that is unlikely to be mined because of problems related to its safe and economic recovery (deducted from the original minable coal 

remaining after subtraction of coal not available due to past mining). 

5 Coal that is unlikely to be mined because it occurs under certain surface features that might be damaged by ground subsidence (deducted from the 

original minable coal remaining after subtractions due to past mining and technical restrictions). 

6 Values may differ from those obtained by addition and subtraction of row and column data due to independent rounding to the nearest 0.1 million 

tons. 

Table 15. Wasatch Plateau study area, Utah: as-received, coal quality 

by bed.1 

 Seam Sulfur Ash Btu/lb SO2 Est. sales price2

 name (%) (%) (lb/MMBtu) ($/short ton) 

Castlegate D 0.33 7.2 12,855 0.51 $26.61 

Castlegate A 0.69 8.4 12,174 1.14 $26.61 

Wattis 0.61 6.5 12,333 0.99 $26.61 

Blind Canyon 0.54 7.6 12,456 0.87 $26.61 

Cottonwood 0.61 8.4 12,205 1.00 $26.61 

Axel Anderson 0.61 8.9 12,439 0.98 $26.61 

Acord Lakes 0.61 8.9 12,439 0.98 $26.61 

1 Information for this table is from Scott and others (written commun, 1999) 

and Tabet and others (1999). 

2 Information for this column was summarized from Resource Data 

International, Inc., COALdat database (1998).

Table 16. Somerset study area, Colorado: as received, coal quality by 

bed.1

 Seam Sulfur Ash Btu/lb SO2 Est. sales price2

 name (%) (%) (lb/MMBtu) ($/short ton) 

E (Hawksnest) 0.5 10 12,000 0.83 $26.61 

D (Oliver) 0.6 9 12,250 0.98 $26.61 

Lower D (L. Oliver) 0.6 9 12,250 0.98 $26.61 

C (Bear) 0.5 8 12,850 0.78 $26.61 

B (Somerset) 0.5 10 12,250 0.82 $26.61 

A 1.2 12 11,600 2.07 $26.61 

1 Information for this table is from Eakins and others (1998). 

2 Information for this column was summarized from Resource Data 

International, Inc., COALdat database (1998). 

F56 Geologic Assessment of Coal in the Colorado Plateau: Arizona, Colorado, New Mexico, and Utah
shovels, or in dragline stripping operations, or combinations 

of both. The dip of the coal beds is low (2–3 degrees) and 

ground slopes are gentle enough to allow long narrow cuts or 

pits conducive to surface mining and to reclamation. Most coal 

seams are low in sulfur, have moderate Btu’s, but are high in 

ash (table 17).

Most of the surface and underground coal ownership is 

Federal (BLM), and until the early 1990’s the land was open 

to leasing for coal mining. During the 1970’s many coal companies noticed the great potential for the Bisti coal fi eld, and 

during a moratorium on standard coal leasing, those companies fi led Preference Right Lease Applications for large blocks 

of coal resources there. Coal mined in the Bisti area during 

the 1980’s was hauled by truck to the San Juan Power Plant 

west of Farmington, N. Mex. The biggest problems facing the 

Bisti mines were: (1) the lack of railroad infrastructure and the 

fact that the roads were not designed for heavy truck loads, 

(2) truck-trains (tractors pulling multiple light-weight trailers) 

had not yet been perfected for public highways and (3) a lack 

of water to wash the ash (15 to 20 percent ash yield) from 

the coal. Several attempts were made to permit and build minemouth power plants that would burn the low sulfur coal and 

haul the coal ash back into the open pits for disposal. Mines 

were planned that would produce as much as 16 million short 

tons of coal per year for a multi-unit power plant. As with 

so many other new mine projects, the development and expansion of the low-production-cost Powder River Basin mines in 

Wyoming and Montana made development of the Bisti coal 

fi eld uneconomic in the 1980’s and 1990’s. The Bisti area 

mines that did open closed after a few years of operation.

After reclamation of the Bisti area mines (those subject 

to the 1977 reclamation laws), much of the area was withdrawn from the Federal leasing program because of the designation of the large Bisti and De-Na-Zin Wilderness Areas. 

The purpose of these Wilderness Areas was to protect the 

cultural remains of ancient people who had lived in the area. 

The Wilderness Areas also coincided with much of the shallow coal resource.

Resource Evaluations

The Somerset Quadrangle Study Area (59 mi2)

Coal availability evaluations in the Somerset quadrangle 

were conducted on the six major coal beds using methodology 

described in USGS Circular 891 (Woods and others, 1983) 

and USGS Circular 1055 (Eggleston and others, 1990). No 

coal recoverability or economic analyses were complete at the 

time of this writing for this study area. However, from current 

practice and issues concerning the surface ownership and steep 

natural slope, we can assume that all mining will be done by 

underground (room and pillar and longwall) methods. Of the 

original 3,087.8 million short tons of coal resources in the 

Somerset quadrangle, 9 percent have been mined out, only a 

small amount (< 1 percent) are restricted by environmental 

considerations, and 16 percent of the resources are restricted 

by technical restrictions (table 18). Due to the low number 

of restrictions and the modest production to date, the amount 

of coal available to mine in the study area is estimated to be 

75 percent of the original resource. The Somerset quadrangle 

availability results indicate that the Somerset area has the highest percentage of coal available for mining on the Colorado 

Plateau compared to the Bisti study area and the Northern 

Wasatch Plateau study area.

Table 17. Bisti study area, New Mexico: as received coal quality by 

bed.1

 Seam Sulfur Ash Btu/lb SO2 Est. sales price2

 name (%) (%) (lb/MMBtu) ($/short ton) 

Yellow zone 0.55 21.5 10,817 1.02 $21.87 

Blue zone 0.52 17.0 10,956 0.95 $21.87 

Green zone 0.49 15.3 11,051 0.89 $21.87 

Red zone 0.67 18.9 10,995 1.22 $21.87 

1 Information for this table is from Hoffman and Jones (1999). 

2 Information for this column was summarized from Resource Data 

International, Inc., COALdat database (1998).

Table 18. Results of Colorado Plateau coal availability studies in Colorado, New Mexico, and Utah. 

[Tonnages in millions of short tons] 

 Somerset quad Bisti area N. Wasatch Plateau 

 Tonnage % orig. Tonnage % orig. Tonnage % orig. 

Original coal resources 3,088 1 5,139 1 6,980 1

Mined-out coal resources 275 9% 43 <1% 674 9% 

Environmental restrictions 2 <1% 1,253 24% 146 2% 

Societal restrictions -- 77 1% -- 

Technical restrictions 486 16% 693 14% 2,390 34% 

Available coal resources 2,326 75% 3,073 60% 3,770 54% 

1 USGS Circulars 891 and 1055 were used for resource calculation methodology.

Coal Availability, Recovery, Economic Evaluations of Coal Resources, Colorado Plateau: Colo., N. Mex., and Utah F57
The Bisti Coal Field Study Area (238 mi2

)

The methodologies of coal availability (Eggleston and 

others, 1990) (table 18) and recoverability and mining economics evaluations (Rohrbacher and others, 1993) (table 19) 

were used to evaluate the Bisti study area. Although the Bisti 

coal beds were evaluated as seams, including coal and parting 

material, the stratigraphers (Hoffman and Jones, 1999) were 

able to trace the seams over the entire study area. Again, it 

must be pointed out that two different methodologies have 

been used to determine the coal available for mine development. In the Eggleston and others (1990) methodology, 

only coal beds were included in the resource database (no 

parting material was included) used to calculate the available 

coal resource. The methodology used to calculate minable 

and recoverable coal resources (Rohrbacher and others, 1993) 

includes that portion of the parting material that must be 

extracted with the coal at the time of mining. Thus, the estimates for original and available resources differ between the 

two methods. Additionally, the technologic restrictions were 

considered differently in the two methods. These differences 

in calculated coal tonnages are clearly shown when the original tons and available tons (table 18) are compared to those 

in table 19. The original and the available tonnages were 

increased by 14 percent and 26 percent respectively over the 

same tonnage categories.

During prefeasibility mine planning, engineers found that 

much of the low-stripping-ratio coal (cubic yards of in-place 

overburden divided by in-place short tons of minable coal) was 

restricted from mining because it was within the Bisti Wilderness Area boundaries. This would effectively limit the use of 

large draglines. However, the use of truck/shovel operations 

was considered feasible for surface mining. Augering operations were planned for all “fi nal” highwalls in the truck/

shovel pits. The remaining underground-minable resources 

were planned for room and pillar mining using continuous 

miners and for longwall mining methods. Table 20 shows the 

recoverable coal resources categorized by mining method.

Only one marketing/transportation scenario was examined for the Bisti coal resource evaluation: all produced coal 

was assumed to be transported via highway “truck-trains”

(multiple trailers pulled by one tractor) over the State Highway system to the electrical generation power plant (San 

Juan Power Plant) west of Farmington, N. Mex. Two other 

marketing/coal transportation plans might be employed in the 

future: (1) Develop a rail line from the Bisti coal fi eld to 

the San Juan Power Plant west of Farmington, N. Mex.; and 

(2) Mine-mouth electrical generation in the Bisti coal fi eld. 

Table 19. Results of Colorado Plateau coal recoverability and economic evaluation studies in 

Colorado, New Mexico, and Utah. 

[All coal tonnages in millions of short tons] 

 Somerset quad Bisti area N. Wasatch Plateau 

 Tonnage % orig. Tonnage % orig. Tonnage % orig. 

Original coal resources 3,088 1 5,860 2 6,971 2 

Mined-out resources 275 9% 48 1% 565 8% 

Environmental restrictions 2 <1% 1,633 28% 76 1% 

Societal restrictions -- -- -- 

Technical restrictions 486 16% 294 8% 2,134 31% 

Available coal resources 2,326 75% 3,886 66% 4,196 60% 

Mining losses 469 8% 1,127 16% 

Washing losses 666 11% 77 1% 

Recoverable coal resources 2,750 47% 2,993 43% 

Percent compliance 2,750 47% 2,993 43% 

Coal reserve/cost curves 3

@ market value (sales price) 0 0 2,534 36% 

@ $12-<15/ton market -- -- 289 4% 

@ $15-<20/ton market -- -- 1,016 15% 

@ $20-<25/ton market 5 <1% 1,229 18% 

@ $25-<30/ton market 188 3% 217 3% 

@ $30-<40/ton market 2,260 38% 242 3% 

@ $40-<50/ton market 297 5% -- -- 

@ >$50/ton market 40 1% -- -- 

1 USGS Circulars 891 and 1055 were used for resource calculation methodology—no recoverability 

evaluations. 

2 USBM Circular 9368 (coal resource recoverability methodology) was used for all resource calculations. 

Coal, parting, and out-of-seam dilution were included in the resource calculation. 

3 Mine costs do not include income taxes and corporate return on investments. 

F58 Geologic Assessment of Coal in the Colorado Plateau: Arizona, Colorado, New Mexico, and Utah
Future mining in the Bisti coal fi eld will be infl uenced by 

(1) the increasing demand for electricity in the Southwestern 

United States, (2) the ability to negotiate land-use easements 

and water usage with the land owners, (3) the available usage 

life remaining in the San Juan Power Plant, and (4) the amount 

of coal reserves left that would supply the San Juan Power 

Plant.

Table 19 shows the available coal resources, recoverable 

coal resources, reserves, and minable coal resource cost curves 

in today’s coal market, assuming the coal quality and coal sale 

prices as reported in table 17. It is interesting to note that 

the amount of coal tonnage that would be profi table to mine 

increases signifi cantly when the sales price is in the $30- to 

$40-per-short-ton range. This mining cost range might be a 

baseline marker to compare against when evaluating the cost 

of alternatives in electrical energy generation for the region. 

The Northern Wasatch Plateau Study Area (535 mi2)

Two areas in the northern Wasatch Plateau have been 

evaluated for coal availability, resource recovery, and mining 

economics. The fi rst of these evaluations was conducted by 

Osmonson, (written commun., 1994) to determine if the geology and mine planning of large areas could be modeled. 

Osmonson reported that approximately 52 percent of the original coal resource was available for mining, 31 percent was 

recoverable, and 13 percent of the recoverable coal resources 

could be mined at a profi t in the coal market of that time. 

The second study, done by the Utah Geological Survey (Tabet 

and others, 1999), encompassed the area of the fi rst study and 

included coal data that was not accessible to Osmonson. Tabet 

and others (1999) recorrelated the coal beds and completed a 

detailed coal availability study. In 1999, the USGS completed 

the coal recoverability and mining economics study of the 

same area (DST and Associates, written commun., 1999).

The geology, geography, and land ownership in the 

Northern Wasatch Plateau coal fi eld is very similar to that of 

the Somerset coal fi eld. The differences are that the mountains 

in the northern Wasatch Plateau area have a steeper front face 

and the average minable coal-bed thickness is slightly greater, 

and perhaps the coal beds are more continuous over the study 

area. Mineral ownership in the Northern Wasatch study area, 

like the Bisti study area, is primarily by the Federal Government; however, the surface is managed by the U.S. Forest 

Service. This precludes surface mining of any type; therefore, 

all mine planning was done for underground mining methods.

The largest obstacles to mine planning in the Northern 

Wasatch Plateau study area are the large fault zones and interburden between minable seams containing less than the minimum thickness for stable mining conditions. All coal resources 

were considered for underground mining methods (table 21) 

using room and pillar with continuous miners and longwall 

methods. The room and pillar mine plan employs retreat pillar 

extraction to increase recovery rates and lower the cost/ton of 

mining. Table 19 indicates that most of the recoverable coal is 

profi table in today’s market.

Conclusion

Coal resource evaluations continue in the Colorado Plateau with cooperative studies between the U.S. Geological 

Survey and the Colorado and Utah State geological surveys 

and the New Mexico Bureau of Mines and Mineral Resources. 

Coal availability studies for an area of fi ve 7.5-minute quadrangles in the Somerset coal fi eld was completed in late 1999 

(DST and Associates, written commun., 1999), and the recoverability and mining economics studies will be completed in 

late 2000. Other areas that will receive detailed evaluations 

in Colorado (fi g. 4) include the Yampa coal fi eld (near Craig, 

Colo.), the Danforth Hills coal fi eld (near Meeker, Colo.) and 

the Lower White River coal fi eld (near Rangely, Colo.). 

Additional new evaluation areas by the NMBMMR and 

the USGS in the San Juan Basin (fi g. 4) of New Mexico 

comprise the Menefee coal fi eld (near Lake Valley, N. Mex.) 

and the La Ventana coal fi eld (near Cuba, N. Mex.). Other 

areas that will be evaluated for potential minability and economics of coal extraction are the coal resources in the southern 

Wasatch Plateau, by the USGS (near Emery, Utah; fi g. 4), the 

North and South Book Cliffs coal fi elds (near Price, Utah) and 

the Henry Mountains coal fi eld (near Hanksville, Utah) by the 

UGS and the USGS. 

The information provided in these evaluations supports 

the energy-planning efforts of Federal and State governments. 

Detailed coal-bed data and maps developed from these studies 

will also help identify viable targets for coal-bed-methane 

exploration. 

It may be argued that the Somerset quadrangle and the 

northern Wasatch Plateau studies have not addressed all of the 

potential restrictions to mining. For instance, available coal 

in these studies included moderately thin coal (less than 6 ft 

thick), coal resources in isolated peninsulas, and blocks of coal 

between major faults. Additional cost would be incurred in 

mining these resources. These diffi cult-to-develop resources 

Table 20. Recoverable coal resources as planned by mining method 

for the Bisti study area, New Mexico. 

 Mining method Saleable tonnage 

 (short tons) 

Surface-minable resources 

 Truck/shovel—area mining 2,136,000,000 

 Auger mining 12,000,000 

Underground mining 

 Room and pillar—continuous miner 92,000,000 

 Longwall mining 506,000,000 

Total minable coal resources 2,750,000,000 

Coal Availability, Recovery, Economic Evaluations of Coal Resources, Colorado Plateau: Colo., N. Mex., and Utah F59
were not always subtracted from the original coal resource 

when determining available coal. These additional deletions 

from the minable resource could reduce the calculated life of 

the coal fi eld by several years.

Results of these Colorado Plateau coal studies substantiate the coal industry’s claim that the amount of undeveloped 

economically minable and marketable coal resources in the 

United States is far less than the public has been led to believe 

from past coal resource assessments and reserve estimates.

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 Mining method Saleable tonnage 

 (short tons) 

Surface-minable resources 

 0 

Underground mining 

 Room and pillar—continuous miner 702,000,000 

 Longwall mining 2,290,000,000 

Total minable coal resources 2,993,000,000 

F60 Geologic Assessment of Coal in the Colorado Plateau: Arizona, Colorado, New Mexico, and Utah
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National Coal

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F64 Geologic Assessment of Coal in the Colorado Plateau: Arizona, Colorado, New Mexico, and Utah