Chapter Q

Geology and Coal Resources of the 

Upper Cretaceous Fruitland Formation,

San Juan Basin, New Mexico and Colorado

By James E. Fassett1

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

U.S. Department of the Interior

U.S. Geological Survey

National Coal

Resource

Assessment

Click here to return to Disc 1 

Volume Table of Contents

Chapter Q 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

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

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

Abstract........................................................................................................................................................Q1

Introduction ................................................................................................................................................... 2

Purpose and Scope ............................................................................................................................. 2

Location and Extent of Area............................................................................................................... 2

Earlier Investigations .......................................................................................................................... 2

Geography............................................................................................................................................. 4

Drainage....................................................................................................................................... 4

Landforms .................................................................................................................................... 5

Access.......................................................................................................................................... 5

General Geology ......................................................................................................................... 5

Regional Structure............................................................................................................................... 8

Energy Minerals................................................................................................................................... 8

Oil and Gas................................................................................................................................... 8

Upper Cretaceous Coal.............................................................................................................. 8

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

Geology of the Fruitland Formation and Related Rocks ......................................................................... 9

Depositional History ............................................................................................................................ 9

Lewis Shale.................................................................................................................................. 9

Huerfanito Bentonite Bed of the Lewis Shale........................................................................ 9

History and Definition........................................................................................................ 9

Subsequent Developments ............................................................................................ 10

Distribution and Character............................................................................................. 11

Pictured Cliffs Sandstone........................................................................................................ 12

General Discussion ......................................................................................................... 12

Shoreline Trends .............................................................................................................. 13

Rate of Regression .......................................................................................................... 15

Fruitland Formation................................................................................................................... 15

Kirtland Formation .................................................................................................................... 16

McDermott Member of the Animas Formation.................................................................... 16

Upper Cretaceous Chronostratigraphy of the San Juan Basin ................................................. 16

Earlier Publications .................................................................................................................. 16

Hunter Wash Study Area......................................................................................................... 16

Ash Beds ........................................................................................................................... 16

Ash-Bed Ages .................................................................................................................. 19

Magnetic Polarity ............................................................................................................ 19

Paleontology..................................................................................................................... 19

Chimney Rock Study Area....................................................................................................... 24

Ash Beds ........................................................................................................................... 24

Age of Ash Bed CR .......................................................................................................... 25
La Plata Mine Ash Bed ................................................................................................... 25

Ammonite Zonation of Lewis Shale at Chimney Rock Site ....................................... 25

Magnetic Polarity ............................................................................................................ 26

Summary of Chronostratigraphy ............................................................................................ 26

Ammonite Zones in Upper Lewis Shale ....................................................................... 26

Ash-Bed Ages .................................................................................................................. 27

Age of Magnetic Polarity Reversal from C33n to C32r .............................................. 27

Rates of Sediment Accumulation and Pictured Cliffs Shoreline Regression ........ 29

Rate of Subsidence of San Juan Basin Area During Pictured Cliffs Time ............. 32

Depositional Model for Lewis/Pictured Cliffs/Fruitland System ................................................ 34

This Report................................................................................................................................. 34

Ayers Model............................................................................................................................... 34

Basin Structure .................................................................................................................................. 37

Huerfanito Bentonite Bed Structure...................................................................................... 37

Pictured Cliffs Sandstone Structure...................................................................................... 40

Assessment of Fruitland Formation Coal Resources............................................................................ 40

Methodology....................................................................................................................................... 40

Base Map Preparation............................................................................................................. 40

Geophysical Logs...................................................................................................................... 42

Distribution of Data Points ...................................................................................................... 44

Core Data ................................................................................................................................... 46

Coal Outcrop Measurements.................................................................................................. 46

Database ............................................................................................................................................. 46

Data Point Locations ................................................................................................................ 46

Geophysical Log Data .............................................................................................................. 46

Contour Map Preparation........................................................................................................ 48

Data Screening for Errors ....................................................................................................... 48

Geographic Distribution of Fruitland Formation Coal .................................................................. 48

Net-Coal Isopach Map............................................................................................................. 48

Fruitland Coal Distribution....................................................................................................... 48

Map View .......................................................................................................................... 48

Coal-Bed Geometry ......................................................................................................... 49

Map–Cross Section Comparison .................................................................................. 50

Comparison with Earlier Studies................................................................................... 50

Basin-Wide Studies................................................................................................ 50

Other Studies........................................................................................................... 52

Fruitland Coal-Bed Correlations—Earlier Studies ....................................................................... 54

Surface Mapping ...................................................................................................................... 54

Subsurface Studies .................................................................................................................. 54

Local Studies .................................................................................................................... 54

Basin-Wide Studies......................................................................................................... 64

Fruitland Coal-Bed Correlations—This Report............................................................................. 64
Cross Section A-A’.................................................................................................................... 64

Computer Correlations............................................................................................................. 65

Altered Volcanic Ash Beds as Markers................................................................................ 65

Fruitland Coal Character................................................................................................................... 66

Coal Quality................................................................................................................................ 66

Maceral Content ....................................................................................................................... 67

Vitrinite Reflectance................................................................................................................. 69

Fruitland Coal Resources ................................................................................................................. 72

Coal Density............................................................................................................................... 72

Procedures, Categories, and Maps Used............................................................................. 73

Coal Tonnage ............................................................................................................................. 73

Strippable Coal Resources...................................................................................................... 75

Fruitland Coal Mining ........................................................................................................................ 77

References Cited ........................................................................................................................................ 77

Appendix 1—ArcView Files for Coal Assessment of the San Juan Basin, 

New Mexico and Colorado

[The digital fi les used for the coal resource assessment of the San Juan Basin

assessment unit are presented as views in the ArcView project. The ArcView project 

and the digital fi les are stored on both discs of this CD-ROM set—Appendix 1 

of chapter Q resides on both discs. Persons who do not have ArcView 3.1 may 

query the data by means of the ArcView Data Publisher on disc 1. Persons who 

do have ArcView 3.1 may utilize the full functionality of the software by accessing 

the data that reside on disc 2. An explanation of the ArcView project and data library

—and how to get started using the software—is given by Biewick and Mercier 

(chap. D, this CD-ROM). Metadata for all digital fi les are also accessible through 

the ArcView project]

Appendix 2—Database for Fruitland Formation Coal Assessment

[Location, lithologic, and stratigraphic data are available in ASCII format, 

DBF, and Excel spreadsheets on disc 2 of this CD-ROM set]

Appendix 3—Figures and Tables from Fassett and Hinds (1971)........................................................ 83

Appendix 4—Mean Vitrinite Reflectance Values for Fruitland Formation Coal Samples

in the San Juan Basin................................................................................................................. 100

Appendix 5—Gravity Anomaly Map with Thermal-Maturity Overlay .............................................. 116

Appendix 6—Fruitland Formation Coal Resources in Various Categories...................................... 117

Plate

 1. List of wells and stratigraphic cross section showing the interval from

the Huerfanito Bentonite Bed of the Lewis Shale to the top of the 

Ojo Alamo Sandstone, San Juan Basin, New Mexico and Colorado ............................Q132
Figures

 1. Index map—Colorado Plateau coal assessment areas ......................................................Q3

 2. Index map of San Juan Basin area ........................................................................................... 4

 3. Structural elements of San Juan Basin.................................................................................... 6

 4. Late Cretaceous stratigraphic section, San Juan Basin area.............................................. 7

 5. Paleogeographic map showing Western Interior Seaway in 

Late Cretaceous time................................................................................................................... 8

 6. Map of Regina Site area—outcrop of Huerfanito Bentonite Bed...................................... 10

 7. Stratigraphic column from drill hole near Huerfanito Regina site ..................................... 11

 8. Isopach map of interval between Huerfanito Bed and top of 

Pictured Cliffs Sandstone.......................................................................................................... 14

 9. Geologic map of Hunter Wash study area ............................................................................. 17

 10. Structural cross section in Hunter Wash area...................................................................... 18

 11. Magnetostratigraphic column in Hunter Wash area............................................................ 24

 12. Magnetostratigraphic column in Chimney Rock area.......................................................... 25

 13. Stratigraphic cross section from Hunter Wash area to Chimney Rock area ................... 26

 14. Bio-isochrone map showing Pictured Cliffs shorelines/

Western Interior ammonite zones ........................................................................................... 27

 15. Uncertainty-range chart for radiometric dates from Hunter Wash 

and Chimney Rock areas........................................................................................................... 28

 16. Chart showing interpolated ages for C33n–C32r paleomagnetic reversal 

in Hunter Wash area .................................................................................................................. 29

 17. Chronostratigraphic charts showing ash-bed ages, rock thicknesses, 

rates of deposition...................................................................................................................... 30

 18. Map showing Pictured Cliffs shorelines and ages at times 

dated ash beds were deposited............................................................................................... 31

 19. Paleogeographic map, Western Interior Seaway, showing 

San Juan Basin location ........................................................................................................... 33

 20. Time-sequence diagram showing mode of regression of 

Pictured Cliffs Sandstone shoreline........................................................................................ 35

 21. Stratigraphic cross section from Ayers and others (1994) .................................................. 36

 22. Contour map of Huerfanito Bentonite Bed............................................................................. 38

 23. Structural profiles for Huerfanito Bed and top of Pictured Cliffs 

Sandstone across San Juan Basin ......................................................................................... 39

 24. Contour map of top of Pictured Cliffs Sandstone.................................................................. 41

 25. Density log showing the response of coal beds ................................................................... 43

 26. Map showing ideal spacing for control points in San Juan Basin .................................... 44

 27. Coal reliability categories map for San Juan Basin ............................................................. 45

 28. Net-coal isopach map for Fruitland Formation coal beds ................................................... 47

 29. Comparison of three published net-coal isopach maps with 

net-coal map of this report ....................................................................................................... 51
 30. Density log of caved drill hole showing how caved areas look like 

coal on bulk-density log............................................................................................................. 53

 31. Map showing locations of local subsurface studies of Fruitland coals............................ 54

 32. Stratigraphic cross section from Ayers and Zellers (1994) 

and a revised interpretation ..................................................................................................... 57

 33. Coal-bed correlation diagram from Ayers and Zellers (1994) 

and revised interpretation......................................................................................................... 59

 34. Comparison of stratigraphic interpretations of Fruitland in 

Ayers and Zellers (1994) and this report ................................................................................. 60

 35. Fruitland coal-bed correlations near the Pine River gas seep area.................................. 62

 36. Fruitland coal-bed correlations near the Durango gas seep areas................................... 63

 37. Vitrinite-reflectance contour map of San Juan Basin.......................................................... 68

 38. Type bulk-density log showing densities for each coal bed in drill hole........................... 72

 39. Map of overburden thickness on top of Pictured Cliffs Sandstone 

(base of Fruitland Formation).................................................................................................... 74

Tables

 1. Analytical data for 40Ar/39Ar age determinations for sanidine crystals 

from outcrop samples of the Huerfanito Bentonite Bed....................................................Q12

 2. Localities and stratigraphic positions, relative to the Huerfanito Bentonite Bed, 

of known Didymoceras nebrascense and Baculites scotti fossil collections 

in the San Juan Basin, New Mexico....................................................................................... 13

 3. List of drill holes shown on figure 9; holes on cross section H-H’ (fig. 10) ....................... 18

 4. Analytical data for 40Ar/39Ar age determinations for six San Juan Basin 

altered volcanic ash beds from the Hunter Wash area in New Mexico and 

the Chimney Rock area in Colorado ........................................................................................ 20

 5. Summary table of estimated coal resources in beds 1.2 ft thick or greater, 

Fruitland Formation, San Juan Basin, Colorado and New Mexico .................................... 75

 6. Coal production from Fruitland Formation strip coal mines in the San Juan Basin........ 76
Abstract

The coal-bearing Fruitland Formation of Upper Cretaceous age is in the San Juan Basin of southwest Colorado and 

northwest New Mexico. The Fruitland crops out around the 

periphery of the basin and is a little more than 4,000 ft deep in 

several areas in the northeast part. The basin is an asymmetric 

structural feature that formed in early Tertiary time; the area 

of the basin within the Fruitland outcrop is about 6,500 mi2. 

The basin contains more than 14,000 ft of Cambrian through 

Holocene sedimentary rock, about 6,000 ft of which are Late 

Cretaceous in age. Upper Cretaceous rocks consist of a series 

of intertonguing marine and nonmarine strata deposited on 

the west side of the epicontinental Western Interior Seaway 

in Cenomanian through Campanian time. These strata were 

deposited as the shoreline of the seaway transgressed and 

regressed several times across the basin area. The fi nal regression of the shoreline occurred in late Campanian time (76–73 

Ma), resulting in deposition of the Pictured Cliffs Sandstone 

and associated rocks. Fruitland Formation coal beds were 

deposited in backshore swamps on top of Pictured Cliffs 

Sandstone shoreface deposits. The Kirtland Formation (revised 

name in this report) and the McDermott Member of the 

Animas Formation overlie the Fruitland and are the stratigraphically highest Upper Cretaceous rocks in the basin. The 

Tertiary Ojo Alamo Sandstone and upper part of the Animas 

Formation unconformably overlie Cretaceous strata across the 

basin; the hiatus at this contact is > 8 m.y. The youngest 

Tertiary rocks in the basin are Eocene in age. 

Fruitland Formation coal resources assessed in this study 

total 230 billion short tons. Coal beds are typically concentrated in the lowermost 200 ft of the Fruitland, and they are 

usually thickest at the base of the coal-bearing interval. Coal 

beds are generally not continuous for more than a few miles; 

however, in some areas coal zones are continuous for tens 

of miles. Coal beds range from paper thin to more than 50 

ft thick. Fruitland net-coal thicknesses range from 1.2 ft to 

more than 90 ft (1.2 ft is the minimum coal thickness for coalresource calculations in this report). The net-coal distribution 

pattern is marked by a thick coal band that trends northwest 

across the north-central part of the basin and is southwest of 

a large vertical buildup of the Pictured Cliffs Sandstone. Netcoal values in this band range from 40 to more than 90 ft 

thick. Thicker coal beds in this area refl ect peat swamps that 

occupied the same area for a sustained period of time as the 

position of the Pictured Cliffs Sandstone shoreline stabilized 

and backshore peat deposits built up vertically in tandem with 

the vertical buildup of the adjacent Pictured Cliffs shoreface 

sands. Northeast and southwest of this thick coal band are 

areas of relatively thin net coal. A large area of less than 20 

ft of net coal occupies the southwest part of the basin. A 

small, northwest-trending band of net coal more than 40 ft 

thick is present in the southwest part of the basin, just downdip 

from the Fruitland outcrop. Two areas containing no Fruitland 

coal are present on the eastern edge of the basin. A northeasttrending pattern of relatively narrow and linear thinner net-coal 

bands cut across the thick northwest-trending thick coal area. 

These thinner coal bands probably represent fl uvial channel 

systems that cut through the backshore peat swamps to the sea. 

In cross section, Fruitland coal beds occur in an overlapping, 

en echelon pattern rising stratigraphically to the northeast; coal 

beds in the southwest part of the basin are more than 2.5 m.y. 

older than in the northeast part of the basin.

Fruitland coal is low sulfur (average less than 1 percent) 

and high ash (averaging about 30 percent). Moisture content 

is variable, ranging from 5 to 10 percent at shallow depths 

near the outcrop to less than 3 percent in the deeper parts 

of the basin. Heating values range from 10,300 Btu (moist 

mineral-matter-free (mmmf)) along the southwest margin of 

the basin to nearly 16,000 Btu in the north-central part of the 

basin. Fixed-carbon percentages (mmmf) range from about 40 

percent in the southwest to more than 80 percent in the northcentral area. Coal rank ranges from subbituminous A in the 

south to low-volatile bituminous in the north-central part of the 

basin. Coal rank generally increases from the southwest edge 

of the basin to slightly north of the present basin axis and then 

diminishes northward to the edge of the basin. Fruitland coal is 

almost all non-agglomerating. 

The San Juan Basin is the second largest gas fi eld in 

North America. Most of the early gas production came from 

Geology and Coal Resources of the 

Upper Cretaceous Fruitland Formation, 

San Juan Basin, New Mexico and Colorado

By James E. Fassett

Q1
Upper Cretaceous, fractured shoreface-sandstone reservoirs. 

In the 1970’s, coal-bed methane was found to be present 

in Fruitland Formation coal beds in commercial quantities. 

Thousands of Fruitland coal-bed methane wells have been 

drilled throughout the basin, and yearly gas production from 

Fruitland coal beds now exceeds gas production from all of the 

sandstone reservoirs combined (about one trillion ft3 of gas in 

1999). Although this report is focused on the Fruitland coal 

resources, the basic data contained herein should contribute 

to a better understanding of coal-bed methane in the basin as 

well.

Bulk-density geophysical logs from oil and gas drill holes 

were the principal source of data for assessing Fruitland coal 

resources. Utilizing GIS software, locations of wells used for 

control points were precisely measured based on reported distances from section lines. (The public land survey system 

(PLSS) for the San Juan Basin containing township, range, and 

section boundaries was provided by the Bureau of Land Management in digital form.) Latitude and longitude coordinates 

for the spotted control points were determined by the GIS 

program. Maps showing net-coal thicknesses, structure, and 

overburden thicknesses were generated by a two-dimensional 

modeling program. Coal tonnages by State, county, township, 

overburden category, thickness range, and surface and coal 

ownership were calculated using the same program.

Introduction

Purpose and Scope

The geologic characterization of the Fruitland Formation 

and the assessment of Fruitland Formation coal resources in 

the San Juan Basin, New Mexico and Colorado, is part of 

the U.S. Geological Survey’s (USGS) National Coal Resource 

Assessment Project initiated in 1994. Five major coal-producing regions of the United States are included in the National 

Coal Assessment: (1) the Appalachian Basin, (2) the Illinois 

Basin, (3) the Gulf of Mexico Coastal Plain, (4) the Powder 

River Basin and the Northern Great Plains, and (5) the Colorado Plateau. The San Juan Basin is in the Colorado Plateau 

region (fi g. 1).

The purpose of this report is to illustrate and describe the 

occurrence of coal in the Fruitland Formation in the San Juan 

Basin and to assess the total coal resources of the Fruitland. 

Coal resources were measured and calculated in accordance 

with standard USGS methods and procedures as specifi ed in 

Wood and others (1983), except as noted. In addition, the geologic history of the deposition, burial, and subsequent structural deformation of the coal-bearing Fruitland Formation and 

associated strata is presented. Coal-thickness measurements 

are mostly based on geophysical log interpretations; a relatively few direct coal-thickness measurements are from drill 

core descriptions. No outcrop measurements of coal were used 

as data points for coal resource calculations. The geologic 

characterization of the Fruitland is based on direct examination on the outcrop and geophysical-log interpretations in the 

subsurface.

Published reports relating to the geology and coal 

resources of the Fruitland Formation are reviewed and discussed. Where there are differences in interpretation between 

previously published material and the data presented in this 

report, the differences are described to allow the reader to 

properly evaluate confl icting interpretations.

Location and Extent of Area

The San Juan Basin is located in what is called the Four 

Corners area near the common corners of the States of New 

Mexico, Colorado, Utah, and Arizona (fi g. 2). In this report, 

the basin is defi ned as the area lying within the outcrop of 

the base of the Fruitland Formation (top of the Pictured Cliffs 

Sandstone) as portrayed on fi gure 2. The basin outline has an 

elliptical shape and is about 100 mi long (north-south) and 

about 90 mi wide (east-west). The basin extends over an area 

of about 6,500 mi2.

The basin includes parts of San Juan, Rio Arriba, Sandoval, and McKinley Counties in New Mexico and La Plata 

and Archuleta Counties in Colorado. Parts of the Navajo, Ute 

Mountain Ute, Southern Ute, and Jicarilla Apache Indian Reservations are within the basin area (fi g. 2). Several developed 

archaeological sites are present in the San Juan Basin. The two 

primary sites are Chaco Canyon National Historical Park in 

New Mexico and Mesa Verde National Park in Colorado (fi g. 

2). A smaller archaeological site, Aztec National Monument, 

is located in the northwest part of the basin, in the town of 

Aztec, N. Mex. The Chimney Rock Archaeological Area is 

located just north of the Chimney Rock mine (fi g. 2) within 

the San Juan National Forest; the Salmon Ruins site is just 

west of Bloomfi eld, N. Mex. Large numbers of smaller, undeveloped archaeological sites dot the basin area, including large 

numbers of unexcavated sites on the river terraces along the 

La Plata River valley north of Farmington, N. Mex. The Bisti 

–De-na-zin Wilderness Area is located in the southwest part 

of the basin. 

Earlier Investigations

The fi rst detailed, basin-wide study of the coal resources 

of the Fruitland Formation was by Fassett and Hinds (1971). 

Prior to that report, a large number of publications, principally 

USGS reports and maps, described the occurrence of Fruitland 

coal in various parts of the basin; a complete list of those 

publications is in the Fassett and Hinds (1971) report. A report 

by the New Mexico Bureau of Mines and Mineral Resources 

by Shoemaker and others (1971) contained a series of papers 

on strippable Fruitland coal (maximum depth of 250 ft) in six 

areas on the western margin of the basin. Papers by Kelso 

Q2 Geologic Assessment of Coal in the Colorado Plateau: Arizona, Colorado, New Mexico, and Utah
Figure 1. Index map showing the occurrences of Upper Cretaceous coal-bearing rocks and coal study areas in the Colorado Plateau 

region of the Western United States.

Geology and Coal Resources of the Upper Cretaceous Fruitland Fm., San Juan Basin, New Mexico and Colorado Q3

Cretaceous Coalbearing strata

Colorado

Plateau area Coal study areas

EXPLANATION

CO

NM

UT

AR

San Juan

Basin

1. Kaiparowits Plateau

2. Henry Mountains

3. South Wasatch Plateau

4. North Wasatch Plateau

5. Lower White River

6. Danforth Hills

7. Yampa

8. South Piceance basin

 9. SAN JUAN BASIN

10. Black Mesa Basin

1

2

3

4

5

6

7

8

10

113°

113°

34° 34°

40° 40°

106°

106°

0 100 Miles

COAL STUDY AREAS

50

UT CO

AR NM

9

SAN JUAN BASIN
and others (1980), Kelso and Wicks (1988), Kelso and others 

(1987), Ayers and Ambrose (1990), and Ayers and others 

(1994) presented revised estimates of Fruitland coal resources 

in order to estimate Fruitland coal-bed methane resources in 

the basin. Papers by Biewick and others (1991) and Boger and 

Medlin (1991) calculated Fruitland coal resources for the New 

Mexico part of the basin using different computer-contouring 

models. Local studies of Fruitland coal were by Shoemaker 

and Holt (1973), Jentgen and Fassett (1977), Beach and Jentgen (1978), Wilson and Jentgen (1980), Kelso and Rushworth 

(1982), Sandberg (1986, 1988a, 1988b, 1990), Decker and 

others (1988), Roberts (1989, 1991), Roberts and Uptegrove 

(1991), Ambrose and Ayers (1994), Ayers and Zellers (1994), 

M’Gonigle and Roberts (1997), and Fassett and others 

(1997b). Studies of coal quality for strippable Fruitland coals 

in New Mexico were by Hoffman (1991) and Hoffman and 

others (1993). Nickelson (1988) published a historical account 

of coal mining in the New Mexico part of the San Juan Basin 

that includes all known Fruitland coal mines.

Geography

Drainage

The northeast-trending Continental Divide cuts across the 

southeast part of the San Juan Basin (fi g. 2). Streams west of 

Mesa

Verde N.

Park

 Ute Mountain

Indian Reservation

Pagosa

Springs

109° 108°

 37°

Durango

NEW MEXICO

 36°

McKINLEY CO

107°

SAN JUAN CO

RIO ARRIBA CO

SAN JUAN CO

COLORADO

Kf

Kf

Kf

Kf

0 10 20 30 MILES

Dulce

Cuba

Cortez

Newcomb

Shiprock

UTAH ARIZONA

Vallecito

reservoir

Navajo

Reservoir

San Juan

River

San

Juan

River

Animas

River

La

Plata

River Farmington Glade

Gallegos

Canyon

Chaco

River

Chaco

River

Hunter

Wash

De-na-zin Wash

River

Piedra

River

Los

Mancos River

Largo 

Canyon

Canyon

Canyon

Canyon

Canyon

Blanco

La

Jara

Bancos

Gobernador

Chimney

Rock

Mine

La Plata

Mine

San

Juan

Mine

Navajo

Mine

San Juan

Generating

Station

Four Corners

Generating

Station

Burnam

Mine

Gateway

Mine

De-na-zin

Mine

 Southern Ute

Indian Reservation

 Navajo

 Indian

Reservation

Chaco Culture

National

Historical Park

SANDOVAL CO

MONTEZUMA CO

LA PLATA CO

Navajo

River

Wash

Aztec

Bloomfield

Farmington

CONTINENTAL

DIVIDE

Jicarilla

 Apache

Indian

Reservation

Ignacio

 Amoco Hahn

Jessie 1 well

Turner and Webb

Huerfanito Unit 60

 well

Huerfanito

Bentonite

Bed outcrop

(Regina site)

B-DNZ

 W A

Hunter Wash

Study Area

ARCHULETA CO

LA PLATA CO

Piedra

Peak (8551') 

Pinos

Figure 2. Index map of the San Juan Basin area; the basin is defi ned in this report as the area inside the outcrop of the Fruitland Formation 

(Kf). Fruitland outcrop is modifi ed from Fassett and Hinds (1971). Indian Reservation boundaries are from USGS base maps for New Mexico 

and Colorado. Map does not show scattered tracts of Indian lands outside of reservation boundaries and non-Indian lands within some of 

the reservation boundaries. The mines shown are all Fruitland coal strip mines. Tonnages of coal produced from these mines are in table 

6. B-DNZ WA is Bisti–De-na-zin Wilderness Area.

Q4 Geologic Assessment of Coal in the Colorado Plateau: Arizona, Colorado, New Mexico, and Utah
the Divide are in the San Juan River drainage, streams east of 

the Divide are in the Rio Grande drainage. The San Juan River 

is the master stream in the basin area. Perennial streams fl ow 

into the San Juan River from the north and originate in the La 

Plata or San Juan Mountains in Colorado. These streams are 

the Animas, La Plata, Mancos, Los Pinos (Pine), Piedra, and 

Navajo Rivers. The San Juan River fl ows northwestward into 

the Colorado River in Utah. The principal intermittent streams 

draining the basin’s arid interior to the south are Chaco River 

and Largo Canyon. Navajo Reservoir occupies parts of the 

valleys of the San Juan, Los Pinos, and Piedra Rivers in the 

northeast quadrant of the basin. Water from Navajo Reservoir 

is used for irrigation of large tracts of Navajo land south of the 

towns of Farmington and Bloomfi eld (Navajo Indian Irrigation 

Project). Vallecito Reservoir is on the Los Pinos River on the 

north edge of the basin area.

Landforms

The San Juan Basin is in the Navajo physiographic 

section of the Colorado Plateau province (U.S. Geological 

Survey, 1946). The topographic relief in the basin is more than 

3,500 ft. Altitudes range from 8,551 ft on Piedra Peak west 

of the Piedra River in Colorado (fi g. 2) to about 5,050 ft on 

the west side where the San Juan River crosses the basin rim 

in New Mexico. The most prominent physiographic feature in 

the area is the relatively steeply dipping monocline (fi g. 3), 

which rims the basin on the northwest, north, and east sides 

and rises as much as 700 ft above the adjoining terrain on 

the west side of the basin. The central part of the basin is a 

dissected plateau, the surface of which slopes gently to the 

west. The principal streams have cut into the plateau to form 

deep, steep-walled canyons. On the upland plains between 

the canyons, stabilized sand dunes are numerous. Along the 

San Juan, Animas, and La Plata Rivers several stream-terrace 

levels can be distinguished.

The climate in much of the San Juan Basin is arid to 

semiarid. Rainfall ranges from as low as 3 or 4 inches a year 

at lower altitudes to nearly 20 inches a year at higher altitudes, 

and the annual average is less than 15 inches. Precipitation 

is generally rare in early and middle summer and is more 

frequent in late summer and spring. Temperatures range from 

below 0°F in the winter to above 100°F in the summer. The 

mean annual temperature at Farmington, N. Mex., is 52.6°F, 

and the annual range is about 115°F. The daily variation in 

temperature often exceeds 40°F.

At lower altitudes, short grass, sagebrush, and many varieties of cactus are common. The higher mesas of the basin 

generally support a growth of pinyon and juniper, scattered 

sagebrush, and sparse scrub oak. Ponderosa pine grows on the 

highest areas, mostly around the north and east rims of the 

basin. Cottonwood trees, tamarisk, and willows grow in the 

valleys of many of the streams.

Access

Two major U.S. Highways cross the San Juan Basin: U.S. 

550, from northwest to southeast, passes through Durango, 

Colo., and Aztec, Bloomfi eld, and Cuba, N. Mex.; U.S. 64, 

from west to east, passes through Shiprock, Farmington, 

Bloomfi eld, and Dulce, New Mexico. Several other paved 

New Mexico highways traverse the basin area and a myriad 

of unpaved oil-and-gas-well access roads and county roads 

furnish entry to almost every part of the basin.

General Geology

The San Juan Basin is an asymmetric structural depression that contains Cambrian, Devonian, Mississippian, Pennsylvanian, Permian, Triassic, Jurassic, Upper Cretaceous, Tertiary, and Quaternary rocks. The maximum known thickness of 

sedimentary rocks in the basin was penetrated by the Amoco 

Production Company Hahn Jessie 1 well in the SW1⁄4 sec. 15, 

T. 33 N., R. 8 W., La Plata County, Colorado (fi g. 2). This 

well was drilled to a total depth of 14,503 ft and penetrated 

Precambrian rocks at 14,288 ft. 

The coal-bearing Upper Cretaceous rocks of the basin are 

shown in a stratigraphic cross section on fi gure 4. The maximum thickness of Upper Cretaceous rocks in the basin is about 

6,000 ft. Upper Cretaceous strata consist of intertonguing 

marine and nonmarine units that represent four transgressiveregressive episodes: (1) the Dakota Sandstone–Gallup Sandstone cycle, (2) the Borrego Pass Sandstone Lentil–Dalton 

Sandstone Member subcycle, (3) the Hosta Tongue–upper 

Point Lookout Sandstone cycle, and (4) the Cliff House Sandstone–Pictured Cliffs Sandstone cycle. The fi nal regression 

of the sea resulted in deposition of the shoreface Pictured 

Cliffs Sandstone. All of the regressive shoreface sandstones are 

overlain by coal-bearing intervals (fi g. 4), but the thickest and 

most continuous coal beds in the basin are in the Fruitland Formation directly overlying the regressive Pictured Cliffs Sandstone.

The Upper Cretaceous rocks preserved in the San Juan 

Basin were deposited on the western edge of the Western 

Interior Seaway (fi g. 5) more or less continuously over a 

time span of about 22 m.y., from 95 Ma to 73 Ma. The one 

signifi cant break in Late Cretaceous deposition occurred at 

the end of the Turonian when an episode of localized tectonic 

uplift occurred in the north-central part of the present basin 

area (fi g. 4). This episode of erosion, and (or) nondeposition 

represents a hiatus of about 1 m.y. and was mostly a sub-sea 

event (Dyman and others, 1994, fi g. 9). Following this late 

Turonian event, subsidence of the basin area resumed uniformly through most of the rest of Late Cretaceous time. 

Tertiary rocks of the basin consist of the Paleocene Ojo 

Alamo Sandstone (as described by Fassett, 1987, Fassett and 

Steiner, 1997, and Fassett and others, 2000), part of the Animas 

Geology and Coal Resources of the Upper Cretaceous Fruitland Fm., San Juan Basin, New Mexico and Colorado Q5
Formation, and the Nacimiento Formation; the Eocene San 

Jose Formation; and intrusive rocks of possible Oligocene age. 

Quaternary deposits consist of Pleistocene and Holocene terrace 

gravels and alluvium. The hiatus at the unconformity between 

the Cretaceous Kirtland Formation and Tertiary Ojo Alamo 

Sandstone in the southern part of the basin represents about 8 

m.y. (Fassett and Steiner, 1997). The missing 8 m.y. is from the 

latest Cretaceous (Maastrichtian Stage) and earliest Paleocene. 

 37 

 36 

 35 

 37 

 36 

 35 

109 108 107 

109 108 107 

Cortez

UTAH

ARIZONA

COLORADO

NEW MEXICO

FOUR

CORNERS

La Plata

Sleeping Mtns

Ute

Mtn

Carrizo

Mtns

PLATFORM

ZUNI

UPLIFT

SLOPE

CENTRAL BASIN

DEFIANCE

UPLIFT

NACIMIENTO UPLIFT

SAN

JUAN

UPLIFT

San Juan CHACO

McKinley

Sandoval Valles

Caldera

HOGBACK

THE

0 30 miles 15

Dulce

Pagosa

Springs

Shiprock

Farmington

Aztec

Bloomfield

Gallup

Grants

Albuquerque

 Los

Alamos

Cuba

Durango

GALLUP

SAG

Bernalillo

Cibola

Rio Arriba

Archuleta

Hinsdale Mineral

La Plata

Montezuma

Dulce

San Juan Apache

Mesa Verde

National Park

Chaco Culture

National Historical

Park

Figure 3. Structural elements of the San Juan Basin. Structural features are generalized from a structure map of the basin area by 

Thaden and Zech (1984). Areas of steeper dip are shaded; arrows indicate the direction of dip. The dashed line separating the central 

basin from the Chaco slope is drawn approximately along the outcrop of the base of the Fruitland Formation (top of the Pictured Cliffs 

Sandstone). Modifi ed from Fassett (1991).

Q6 Geologic Assessment of Coal in the Colorado Plateau: Arizona, Colorado, New Mexico, and Utah
OF PT. LOOKOUT SS

MULATTO TONGUE

SATAN TONGUE

GALLUP

GALLUP

SANDSTONE

SANDSTONE

JUANA LOPEZ MEMBER

BRIDGE CREEK (GREENHORN) 

DAKOTA SANDSTONE

DILCO MEMBER

GIBSON COAL MEMBER Tocito Sandstone Lentil

GRANEROS SHALE MEMBER

MANCOS SHALE

MANCOS SHALE

DALTON SANDSTONE MEMBER

HOSTA TONGUE 

Kbpsl

LIMESTONE MEMBER JUANA LOPEZ MEMBER

 erosion surface Quaternary

POINT LOOKOUT SANDSTONE

CRETACEOUS

HUERFANITO BENTONITE BED

LA VENTANASANDSTONETONGUE

TSAYA CANYON SANDSTONE TONGUE

FRUITLAND FRUITLAND

KIRTLAND SHALE

FORMATION

PICTURED CLIFFS

SANDSTONE

CLIFF HOUSESANDSTONE

HogbackMountaintongue

MENEFEE FORMATION

(1800 ft)

(1200 ft)

MESAVERDE GROUP

MESAVERDE GROUP

CREVASSE CANYONFORMATION

SW

05001,0001,5002,000FEET

OJO ALAMO SANDSTONE TERTIARYAND YOUNGER ROCKS

DAT

Paleomagnetic reversal C33n

C32r

1

2

EXPLANATION

Marine Nonmarine (Cretaceous)

Nonmarine(Tertiary) Shoreface

Shelf

Coal-bearing

Borrego Pof Crevas

UnconforEnd-Turo

NOTES Kbpsl

Tsaya Canyon Sandstone Tongue (of Cliff House Sandstone)name from Fassett (1977)Hogback Mountain tongue (of Menefee Formation) name from Whyte and Shomaker (1977)

1

2

UT

NM

PagosaSprings

Gallup

Grants Albuquerque

Cuba

Durango

INDEX MAP

140 Miles

CO

AR

NM - LOS

F - LOS

Farmington

Paleomag

Figure 4. Stratigraphic section showing Upper Cretaceous rocks in the San Juan Basin, New Mexico and Colorado. Tocito Sandstone Lentil and coal-bea

diagrammatically. Stratigraphy of rock units from the Point Lookout Sandstone upward is modifi ed from Fassett (1977), stratigraphy for lower part of sectio

Nummedal and Molenaar (1995). F - LOS on index map is Fassett (1977) line of cross section; NM - LOS is Nummedal and Molenaar (1995) line of cross secpaleomagnetic reversal from chron C33n to C32r is from Fassett and Steiner (1997). Vertical exaggeration x 55.
Regional Structure

The structural elements of the San Juan Basin are portrayed on fi gure 3. The most prominent feature shown is 

the horseshoe-shaped, steeply dipping monocline that extends 

around the west, north, and east sides of the basin. The Zuni 

uplift to the southwest partially defi nes the southern limits of 

the structural basin, but there is no structural feature defi ning 

the limit of the basin in the southeast. The Carrizo Mountains, 

Sleeping Ute Mountain, and La Plata Mountains are laccoliths 

that punctuate the boundary of the Four Corners platform in 

the northwest. The central basin structural feature depicted 

on fi gure 3 is very nearly the same area shown enclosed 

by the Fruitland Formation outcrop shown on fi gure 2. The 

central basin of fi gure 3 began to form in early, but not 

earliest, Paleocene time and continued to downwarp through 

Eocene time (Fassett, 1985). Precursors of the formation of the 

basin proper were the intrusions of the Four Corners laccoliths 

(listed above) which began to form in latest Cretaceous time 

(Semken and McIntosh, 1997). These authors (p. 77, table 1) 

presented 40Ar/39Ar ages ranging from 73.8 Ma to 70.65 Ma 

for rock samples collected in the Carrizo Mountains.

Energy Minerals

Oil and Gas

The San Juan Basin is the second largest gas-producing 

basin in the conterminous United States, second in total estimated gas reserves to the Hugoton fi eld of Texas, Oklahoma, 

and Kansas. The basin has more than 19,000 producing oil and 

gas wells and through the end of 1997 had produced nearly 

20 trillion ft3 of gas (TCF) and more than 300 million barrels 

of oil (Oil and gas statistical information for Colorado was 

provided by Debbie Baldwin of the Colorado Oil and Gas 

Conservation Commission; for New Mexico by Ernie Busch 

of the New Mexico Energy Division). Historically, the basin 

has produced most of its natural gas from fractured sandstone 

reservoirs in the Dakota Sandstone, Mesaverde Group, and the 

Pictured Cliffs Sandstone (fi g. 4) in the central basin area (fi g. 

3). Starting in the late 1970’s, an increasing amount of gas 

production has come from Fruitland Formation coal beds, and 

annual Fruitland coal-gas production (about 1 TCF in 1999) 

now exceeds gas production from sandstone reservoirs. Most 

of the oil production in the basin has come from the Tocito 

Sandstone Lentil of the Mancos Shale and from fractured 

Mancos Shale reservoirs (fi g. 4). Relatively small amounts of 

oil and gas have been produced from Paleozoic reservoirs, 

mostly from structural traps on the Four Corners platform (fi g. 

3). 

Estimates of ultimate gas production from the San Juan 

Basin prior to the discovery of coal-bed methane in the basin 

were on the order of 25 TCF. A report by Kelso and Wicks 

(1988) estimates that Fruitland coal beds in the basin contain 

nearly 50 TCF of gas in place. If half of this gas is recoverable, 

the total cumulative production of gas from the San Juan Basin 

could exceed 50 TCF (25 TCF from sandstone reservoirs and 

25 TCF from Fruitland coals). The principal references for the 

oil and gas fi elds of the San Juan Basin are Fassett (1978, 

1983, 1991).

Upper Cretaceous Coal

All of the coal resources in the San Juan Basin are 

in Upper Cretaceous rocks, and these coal-bearing strata are 

shown on fi gure 4. In the early 1900’s, coal from these formations was mined from underground coal mines. Coal from the 

Crevasse Canyon Formation and the lower part of the Menefee 

Formation was extensively mined in the vicinity of Gallup, N. 

Mex.; Hogback Mountain Tongue coals were mined in the La 

Ventana area a few miles south of Cuba, N. Mex.; and lower 

Menefee and Fruitland coals were mined in the northwest 

part of the basin (fi g. 4). These old underground coal mines 

in New Mexico (now all abandoned) are discussed in detail 

by Nickelson (1988). All of the underground coal mines in 

the Colorado part of the basin produced from Fruitland or 

Menefee coals, and only one Menefee mine is still operating. 

30°

40°

50°

60°

70° Western

Interior

Seaway

0 300 miles

San Juan

Basin

Figure 5. Paleogeographic map of North America in Late Cretaceous (Turonian) time. From Roberts and Kirschbaum (1995, fi g. 1) 

after Williams and Stelk (1975, fi g. 5). Approximate location of San 

Juan Basin is shown.

Q8 Geologic Assessment of Coal in the Colorado Plateau: Arizona, Colorado, New Mexico, and Utah
Beginning in the late 1960’s and early 1970’s several 

large strip mines were opened to produce coal for electrical 

power generation from the Crevasse Canyon, Menefee, and 

Fruitland Formations. A discussion of the coal production 

from these large strip mines is in Fassett (1989); production 

from Fruitland strip mines is in table 6 of this report. The 

Fruitland Formation contains the bulk of the coal resources 

in the San Juan Basin, 230 billion short tons, as determined 

by this study. A detailed tabulation of Fruitland coal resources 

is in the “Fruitland Coal Resources” section of this report. 

Coal resources for all of the older Upper Cretaceous coalbearing units have not yet been compiled. A study of Menefee 

Formation coals in the southern San Juan Basin by Whyte and 

Shoemaker (1977) found that the lower Menefee coal zone 

contained about 1 billion short tons of coal between the depths 

of 250 and 4,000 ft and the Hogback Mountain Tongue of the 

Menefee (fi g 4) contained about 11.3 billion short tons of coal 

to depths in excess of 2,000 ft.

Acknowledgments

This report has benefi ted from the input of numerous 

colleagues within and outside the USGS. Robert Hettinger of 

the USGS, Denver, Colo., provided sound, practical advice 

regarding the intricacies of geophysical-log interpretations of 

coal-bearing and associated rocks throughout the 5-year life of 

this project, and I have benefi ted greatly from conversations 

with him regarding the basic geologic parameters that control 

the deposition of coal-bearing rocks throughout the Western 

Interior of North America. Vito Nuccio critically reviewed the 

section of this report related to Fruitland coal petrography 

and thermal maturity and provided decompaction ratios for 

the rocks discussed in this report using the BasinMod program. Bradford Boyce and Tom Ann Casey, geologic consultants, Durango, Colo., contributed greatly to my knowledge 

of Fruitland Formation coals as coal-bed methane reservoirs 

and source rocks. Joe Hewitt in the Farmington, N. Mex., 

U.S. Bureau of Land Management offi ce supplied me with 

copies of geophysical well logs and was a constant source 

of accurate information regarding problems of well locations, 

elevations, or designations. Gretchen Hoffman with the New 

Mexico Bureau of Mines and Mineral Resources, Socorro, 

N. Mex., provided invaluable information regarding Fruitland 

Formation coal resources and coal-mine production. Laura 

Biewick, USGS, and Tracy Mercier, contractor to the USGS, 

Denver, were my tutors in the use of the ArcView software 

program that was an integral part of the compilation of the 

database for this study. Laura Roberts, USGS, Denver, prepared all of the initial contour maps for this report using 

the EarthVision software program and taught me how to do 

geologic edits of those initial maps in that program. She also 

prepared all of the coal-tonnage tables for the Fruitland coal 

resources in the San Juan Basin using EarthVision. William 

Everham, USGS student aid, helped obtain copies of geophysical logs that were the backbone of the database for this study 

and did much of the early drill-hole-location spotting of these 

holes in the ArcView program. Marvin Millgate, USGS volunteer, provided invaluable assistance in helping to determine 

the depths of coal beds on bulk-density logs. This report was 

improved by the careful, detailed reviews of USGS colleagues 

Steve Condon, Laura Biewick, and Tom Judkins. Most of 

the chronostratigraphic data in this report were obtained as 

the result of a U.S. Geological Survey Gilbert Fellowship 

(awarded in 1988) to study the precise ages of the rocks 

adjacent to the Cretaceous-Tertiary boundary in the San Juan 

Basin. 

Geology of the Fruitland Formation 

and Related Rocks

Depositional History

The history of deposition of the Fruitland Formation is 

closely associated with the depositional history of subjacent 

stratigraphic units, principally the Pictured Cliffs Sandstone, 

the Lewis Shale, and the Huerfanito Bentonite Bed of the 

Lewis Shale (fi g. 4).

Lewis Shale

The Lewis Shale is the stratigraphically highest unit of 

marine shale in the San Juan Basin (fi g. 4). It is a lightto dark-gray and black shale that contains interbeds of lightbrown sandstone and siltstone, thin-bedded sandy to silty limestone layers, calcareous concretions, and bentonite beds. The 

Lewis ranges in thickness from 0 ft in the southwestern part of 

the basin to about 2,400 ft in the northeastern part (fi g. 4). 

Huerfanito Bentonite Bed of the Lewis Shale

History and Defi nition

The Huerfanito Bentonite Bed is an altered volcanic ash 

that was deposited in the Lewis sea at a time shortly after 

the Cliff House Sandstone shoreline had reached its maximum 

southwestward transgression and the Pictured Cliffs Sandstone 

regression had just begun (fi g. 4). This bed is in the upper 

part of the Upper Cretaceous (Campanian) Lewis Shale, and 

it exhibits unique characteristics on geophysical logs. The 

Huerfanito was named by Fassett and Hinds (1971, p. 6) for 

a type well, the Turner and Webb Huerfanito Unit 60-4 well 

that was completed in November 1960. This well is in the 

SW1⁄4SW1⁄4 sec. 4, T. 26 N., R. 9 W., San Juan County, New 

Mexico (fi g. 2). The geophysical log from this well is shown 

in Fassett and Hinds (1971, fi g. 2), and typical logs showing 

log responses to the Huerfanito are shown in fi gure 3 of 

Geology and Coal Resources of the Upper Cretaceous Fruitland Fm., San Juan Basin, New Mexico and Colorado Q9
that report. Plate 1 of this report is a northeast-trending stratigraphic cross section of the uppermost part of the Upper 

Cretaceous section in the San Juan Basin from the Huerfanito 

Bed upward. This cross section uses the Huerfanito as a datum 

and contains geophysical log traces for 20 wells, evenly spaced 

across the basin. The Huerfanito 60-4 well is well number 9 

on plate 1. 

At the time the Huerfanito Bed was defi ned, it was strictly 

a subsurface unit, not known to crop out anywhere in the basin, 

and it had never been cored in any of the thousands of oil 

and gas wells that had been drilled through it. Consequently, 

no sample of the bed had ever been obtained to confi rm its 

lithology or to possibly obtain a radiometric age for the bed. 

Because of its widespread occurrence throughout the subsurface of the San Juan Basin, it was assumed that the bed had 

originated as a large volcanic ash fall and thus was an isochronous rock unit. This marker bed has subsequently been widely 

used in numerous publications as a time-stratigraphic datum 

on geophysical-log cross sections that portray the stratigraphy 

of Upper Cretaceous rocks in the San Juan Basin.

Subsequent Developments

Fassett and others (1997a) reported the presence of the 

Huerfanito Bed at a road cut in the Lewis Shale on the southeast edge of the San Juan Basin, about 16 mi north of Cuba, 

N. Mex. (fi gs. 2, 6), at a locality named the Regina site. 

(The Huerfanito had been discovered at this outcrop by USGS 

geologists, C.M. Molenaar and W.A. Cobban in 1992.) Identifi cation of the Huerfanito Bed at this place was based on its 

position in the Lewis Shale as projected from the well log of 

the Badland Hills Federal 9-1 drill hole located 1.9 mi west 

NM Hwy 95

NM Hwy 112

NM Hwy 96

(Kmv)

T. 23 N., R. 1 W.

3

10 11

0 .5 1 mile

38

 (apparent dip

 along highway)

16

9

4

(Huerfanito 3,769 ft)

55

Huerfanito

 Bentonite

 Bed 

 THE

HOGBACK

(Toa/Kf)

THE

RIB

15

107 2

0 10 20 30 Mi.

Farmington

Cuba

37

36

COLORADO

NEW MEXICO

ARIZONA

Kkf

Kkf

109 108

 MAP

AREA

SAN

JUAN

BASIN

UTAH

Kkf

14

 USGS

D10842

 USGS

D13721

 USGS

D13719

USGS

D13718 NM Hwy 96

Kmv

Kmv

Durango

Pagosa

Springs

Badland Hills

Federal 9-1

 

Regina

3 miles 

Figure 6. Map showing locations of the Huerfanito Bentonite Bed outcrop, USGS fossil collection sites, and the 

Federal 9-1 drill hole. The Hogback monocline is held up by Mesaverde Group (Kmv) rocks, the Rib is composed 

of the Ojo Alamo Sandstone (Toa) and the Fruitland Formation (Kf). There is no Pictured Cliffs Sandstone at this 

locality; the Fruitland Formation directly overlies the Lewis Shale. A stratigraphic column of Upper Cretaceous and 

lowermost Tertiary rocks penetrated in the Federal 9-1 well is shown on fi gure 7. Table 1 contains analytical data 

for single-crystal, 40Ar/39Ar age determinations for sanidine crystals from samples of the Huerfanito Bed collected at 

this locality. Table 2 lists the stratigraphic levels (above and below the Huerfanito) of all collections of Didymoceras 

nebrascense and Baculites scotti at this and other fossil-collection sites in the San Juan Basin. This fi gure is 

modifi ed from fi gure 1 of Fassett and others (1997).

Q10 Geologic Assessment of Coal in the Colorado Plateau: Arizona, Colorado, New Mexico, and Utah
of the Regina-site road cut (fi gs. 6, 7). The Huerfanito was 

diffi cult to measure and describe at this outcrop because it is 

replaced, for the most part, by calcium carbonate in the form 

of large, lens-shaped limestone concretions that are locally 

much thicker than the original ash-bed thickness. As best as 

could be determined, however, the Huerfanito is about 9 inches 

thick here. This measured thickness is far less than the 12-ft 

thickness that was estimated by Fassett and Hinds (1971) on 

geophysical logs. In a discussion of the thickness of the Huerfanito Bed in Fassett and others (1997a, p. 232) the authors 

concluded that the Fassett and Hinds thickness of 12 ft is not 

correct and state, “The Huerfanito may well be thicker than 9 

in. in the subsurface of the San Juan Basin, but its maximum 

thickness there is probably no greater than ... 1.5 to 2 ft.”

Samples of the Huerfanito Bed were collected at the 

Regina site, and sanidine crystals separated from it were analyzed by J.D. Obradovich using single-crystal 40Ar/39Ar procedures. The analysis yielded a radiometric age of 75.76 ± 0.34 

Ma (table 1).

This age is virtually identical to the projected age of the 

Huerfanito Bentonite Bed (75.83 Ma) estimated by extrapolation from a dated ash bed 95 ft above the Huerfanito Bed in 

the vicinity of Hunter Wash (fi gs. 2, 9) in the southwest part of 

the basin (reported in Fassett and Steiner, 1997, and discussed 

in more detail in the “Summary of Chronostratigraphy” section 

of this report. This close match provides independent evidence 

that the ash bed identifi ed at the Regina site in the southeast 

part of the San Juan Basin is indeed the Huerfanito Bed.

Subsequent to the discovery of the Huerfanito Bed on 

the outcrop, ammonite fossils were found at the Regina site 

above and below the ash bed. This work placed the Huerfanito 

within a relatively thin biostratigraphic interval very near the 

boundary between the Baculites scotti and the Didymoceras 

nebrascense Western Interior Ammonite Zones (table 2). The 

best estimate is that the Huerfanito is within and near the top 

of the B. scotti zone (fi g. 7 and table 2).

Distribution and Character

Although the Huerfanito Bentonite Bed is present 

throughout the San Juan Basin, it seems to lose its distinctive 

character on geophysical logs in some areas. In addition, it 

has been known for some time that the Huerfanito changes 

character across the basin area from southwest to northeast 

(Fassett and Hinds, 1971, p. 7, 8 and fi g. 3). One explanation 

for these changes is that the Huerfanito was diluted by fi negrained clastic material carried across the Lewis sea shelf by 

sub-sea currents in parts of the basin. It is interesting to note 

that the Huerfanito is the most pristine and distinctive on 

conductivity and sonic logs in the southwest part of the basin 

on what would have been the shallowest part of the shelf (fi g. 

4 and plate 1), whereas farther offshore, in the northeast part 

of the basin where water depths were presumably the greatest, 

the log signature of the Huerfanito is the most blurred on 

geophysical logs due to dilution by clastic material. This could 

indicate relatively stronger sub-sea currents moving through 

Age

T

E

R

T

 I

A

R

Y

 Lithology Formation Log top

 (feet)

Thickness

 (feet)

Nacimiento Fm.

Ojo Alamo Ss.

3176

74

Fruitland Fm.

3250

100

Pictured Cliffs Ss.

3350

100

Lewis Shale

 (upper part)

Huerfanito

Bentonite Bed 

Lewis Shale

 (lower part)

319

3450

3769

3770 1

1420

Cliff House Ss. 

5190

15

Menefee Fm.

5205

452

Point Lookout Ss.

5657

177

Mancos Shale

5834

Log scale

 (in feet)

3000

3500

4000

4500

5000

5500

6000

L

A

T

E

C

R

E

T

A

C

E

O

U

S

(?)

Sandstone

Siltstone

Mudstone

Coal

USGS

D10842

USGS

D13718

D13721

Didymoceras

nebrascense

?

Baculites

 scotti

?

Ammonite zone

boundary Altered volcanic

ash bed

K

m

v

Figure 7. Stratigraphic column showing Upper Cretaceous 

(Campanian) rocks in the Badland Hills Federal 9-1 drill hole 

(location on fi gure 6). Kmv is Mesaverde Group. Projected levels 

of USGS fossil collections from vicinity of Huerfanito outcrop 

site (fi g. 6) are shown. Huerfanito Bed is in uppermost part of 

Baculites scotti ammonite zone. Figure is modifi ed from fi gure 2 

of Fassett and others (1997).

Geology and Coal Resources of the Upper Cretaceous Fruitland Fm., San Juan Basin, New Mexico and Colorado Q11
the deeper part of the shelf area. It is counterintuitive that this 

ash bed is preserved at all because the evidence for constant, 

continuous, even distribution of sediment across the entire 

shelf area during most of Late Cretaceous time is overwhelming, yet the Huerfanito is a distinct and clearly identifi able rock 

unit on geophysical logs throughout much of the basin—even 

near the base of the Pictured Cliffs Sandstone in the southwest 

part of the basin. On well 3 on plate 1 (the Tanner Unit 1), 

for example, the response of the conductivity curve to the 

Huerfanito is particularly distinctive where it is only 30 ft 

below the base of the Pictured Cliffs and thus was probably 

deposited relatively close to the beach environment. There is 

no easy explanation of how this ash fall was preserved in 

what would normally be thought of as a relatively high energy 

environment where even minor storm activity should have 

quickly dispersed and destroyed this deposit.

Roberts and McCabe (1992) briefl y discussed the Huerfanito and stated “We interpret this ‘bed’ (which is up to 4 

m thick), as a condensed interval, which may be a composite 

of several ash layers....” Observations of the Huerfanito at the 

Regina outcrop (fi g. 6) where it is less than a foot thick do 

not support this interpretation. The Huerfanito there appears to 

be single, 9-inch-thick bed of altered volcanic ash deposited 

by one volcanic eruption. Roberts and McCabe were clearly 

using the 12-ft thickness for the Huerfanito (“4 m thick”) 

given in Fassett and Hinds (1971) as part of the basis for 

their interpretation that the Huerfanito represents a “condensed 

interval.” Because the Huerfanito had not been observed on the 

outcrop at the time their report was published, their interpretation could only be based on geophysical-log interpretation, 

which, in terms of the thickness of the Huerfanito, has proven 

to be misleading. 

Pictured Cliffs Sandstone

General Discussion

The Pictured Cliffs Sandstone is a shoreface sandstone 

deposited during the fi nal regression of the Western Interior 

Seaway from the San Juan Basin area (fi g. 4 and plate 1). 

Plate 1 shows that the Pictured Cliffs is at the level of the 

Huerfanito Bed at well 1 in the southwest part of the basin 

whereas the top of the Pictured Cliffs is about 1,200 ft above 

the Huerfanito in well 20 on the northeast edge of the basin. 

The Pictured Cliffs is time transgressive and is considerably 

younger in the northeast than in the southwest part of the 

basin. The stratigraphic rise of the Pictured Cliffs occurs in a 

series of steps, a pattern typical of nearly all Upper Cretaceous 

regressive shoreface sandstone beds in the Western Interior of 

North America. This step-like rise in regressive sandstones was 

fi rst described and discussed in detail in a paper by Pike (1947) 

in his classic outcrop study of the Point Lookout Sandstone on 

the west side of the San Juan Basin. 

The geometry of the Point Lookout and the Pictured 

Cliffs Sandstones, as shown on fi gure 4, is very similar (except 

Table 1. Analytical data for 40Ar/39Ar age determinations for sanidine crystals from outcrop samples of the Huerfanito Bentonite Bed collected by C.M. Molenaar 

in 1992 and recollected by Fassett in 1997 at the Regina site (fig. 6). 

[From Fassett and others, 1997a. xtl, crystal; 40Ar*, radiogenic argon]  Ash bed name Irradiation Mineral Run Age Error  and J value number analysis number 40Ar/39Ar 37Ar/39Ar 36Ar/39Ar K/Ca %40Ar* 40Ar*/39ArK (Ma) (1 sigma)  Huerfanito Bed JD021-4 Sanidine 95Z0514 5.94189 0.006248 0.000045 78.42 99.63 5.92029 75.74 0.25  single xtl 95Z0515 5.95008 0.006189 0.000129 79.17 99.22 5.90369 75.54 0.28  J=0.007243 95Z0516 5.99998 0.006300 0.000216 77.78 98.79 5.92790 75.84 0.32  96Z0517 5.97914 0.005509 0.000055 88.94 99.58 5.95435 76.17 0.29  95Z0518 5.93312 0.006025 0.000081 81.33 99.45 5.90085 75.50 0.26  Unweighted mean and error of the mean at the 95 percent confidence level including the error in J 75.76 0.34 

Ca and K corrections and decay constants: (36Ar/37Ar)Ca = 2.69 ± 0.24×10–4

(39Ar/37Ar)Ca = 6.79 + 0.051×10–4

(40Ar/39Ar)

K = 9.1 ± 5.4×10–3

λε + λε′ = 0.581×10–10 yr–1

λβ = 4.962×10–10 yr–1 40K/K = 1.167×10–4 atom/atom

Q12 Geologic Assessment of Coal in the Colorado Plateau: Arizona, Colorado, New Mexico, and Utah
for the minor transgressive pulse in the Pictured Cliffs seen at 

well 11 of plate 1). The stratigraphic rise of the Point Lookout 

is about 800 ft over the same distance as the Pictured Cliffs 

regression shown on plate 1, compared to 1,300 ft for the 

Pictured Cliffs, indicating that the rate of sediment accumulation was greater during the Point Lookout regression. Rates of 

deposition are discussed in more detail in the “Summary of 

Chronostratigraphy” section of this report. The apparent differences in the geometry of the Pictured Cliffs as shown on fi gure 

4 and plate 1 are the result of more drill holes being used for 

plate 1 and because plate 1 has half the vertical exaggeration 

of fi gure 4. 

The contact of the base of the Pictured Cliffs with the 

underlying Lewis Shale is drawn as a series of steps with sharp 

bases on plate 1, but in reality the basal contact of the Pictured 

Cliffs, and indeed most Western Interior regressive sandstone 

units, is transitional. These sandstone bodies typically consist 

of massive sandstone beds at the top grading downward into 

thinner bedded and fi ner grained sandstones and siltstones and 

ultimately into marine shales. Picking the basal contact of a 

unit such as the Pictured Cliffs is extremely subjective and 

somewhat arbitrary because of the transitional nature of this 

contact. 

The top of the Pictured Cliffs at its interface with the 

Fruitland Formation, on the other hand, is almost always 

a sharp, distinct contact that is easily seen on geophysical 

logs. This contact is typically between the top of a massive 

sandstone and the base of an overlying coal bed (plate 1). 

These lithologies have distinct geophysical-log characteristics. 

The only diffi culty in locating the top of the Pictured Cliffs 

on geophysical logs is in distinguishing beach sandstones 

from fl uvial-distributary and estuarine deposits in those places 

where tongues of Pictured Cliffs sandstone extend into the 

Fruitland Formation. Because the interpretation of these 

tongues is quite subjective on logs, plate 1 was constructed 

in a conservative manner to show them extending a minimum 

distance into the Fruitland Formation. A tongue of Pictured 

Cliffs about 150 ft thick is shown extending into the Fruitland 

at well 16 on plate 1; a thinner Pictured Cliffs tongue is 

shown in the Fruitland in wells 18 and 19. The geometry 

of the Pictured Cliffs profi le on plate 1 is a product of the 

dynamics of the interplay between the rate of subsidence and 

sedimentation accumulation rate (discussed below).

Shoreline Trends

Streams carrying sediment to the Pictured Cliffs Sandstone shoreline were fl owing from southwest to northeast (Fassett and Hinds, 1971). The shoreline confi guration varied in 

its detail during the time of this regression but generally maintained a northwesterly trend. Fassett and Hinds (1971) suggested that isopach lines depicting the interval between the 

Huerfanito Bentonite Bed and the top of the Pictured Cliffs 

Sandstone should represent a close approximation of Pictured 

Cliffs shoreline trends (fi gure 7 of that report). They cautioned, 

however, that isopach lines would represent shoreline trends 

only if there had been no signifi cant local tectonism from the 

time the Huerfanito Bed was laid down until the time the 

Pictured Cliffs was deposited across the basin area. Figure 

8 of this report is an improved isopach map of the interval 

from the Huerfanito to the top of the Pictured Cliffs, and it 

is suggested that the isopach lines, except in one area in the 

northwest part of the basin, probably closely approximate successive shoreline confi gurations for the Pictured Cliffs during 

late Campanian time.

The 100-ft isopach line on fi gure 8 trends northwest 

Table 2. Localities and stratigraphic positions, relative to the Huerfanito Bentonite Bed, of 

known Didymoceras nebrascense and Baculites scotti fossil collections in the San Juan 

Basin, New Mexico 

[Numbers in bold from the Regina site. Adapted from table 2 of Fassett (1987); from Fassett and others, 

(1997a)] 

 Western Interior ammonite zone U.S. Geological Survey Distance above (+) or below (–)

 fossil locality number Huerfanito Bentonite Bed (ft) 

Didymoceras nebrascense D48341 +400 

D47972 +260 

 D108423 +121 

Baculites scotti D47962 –50 

 D137183 –105 

 D137213 –105 

1 Llaves locality ( Cobban and others, 1974; Fassett, 1987). 

2 Barker Dome locality (Cobban, 1973; Fassett, 1987). 

3 Regina locality (this report).

Geology and Coal Resources of the Upper Cretaceous Fruitland Fm., San Juan Basin, New Mexico and Colorado Q13
EXPLANATION

●

Control points are oil or gas wells or tests

Thickness of isopached interval (Huerfanito 

 Bentonite Bed to top of Pictured Cliffs Sand-

 stone) from geophysical logs. Contour interval 

 is 50 feet. Kf = Fruitland Formation. "T 34 N

 (NUL)" is north of Ute line, "T 34 N (SUL)"

 is south of Ute line. 

 

o

Study

area

COLORADO

NEW MEXICO

ARCHULETA

SAN JUAN

McKINLEY

MONTEZUMA

108 ̊ 107 ̊

 37 ̊ 37 ̊

 36 ̊ 36 ̊

108 ̊ 107 ̊

COLORADO

NEW MEXICO

Outcrop of Fruitland

 Formation

Farmington

Dulce

Cuba

Ignacio

Durango

0 5 10 15 20 miles

R 13 W

R 16 W

T 19 N

20

21

22

23

24

25

26

27

28

29

30

31

32

32

33

34

T 35 N

R 1 W R 1 E

R 1.5 W

2

R 1 W

2.5 R 16 W 15 14 13 12 11 10 9 8 7 6 5 4 3

6 5 4 3 2

7

8

9

10

11 12

T 34 N

 (NUL)

T 34 N

 (SUL)

R 1 W R 1 E

2 13 12 11 10 9 8 7 6 5 4 3

14

T 34.5 N

T 34 N (NUL)

T 34 N

 (SUL)

SANDOVAL

RIO ARRIBA

LA PLATA

Kf

Kf

15

250

500

750

750

750

1000

1250

1250

700

100

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10

11

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14

15

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17

18

19

1

2

3 4

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Figure 8. Isopach map of the interval between the Huerfanito Bentonite Bed of the Lewis Shale and the top of the Pictured Cliffs Sandstone. Kf, 

Fruitland Formation. Cross section A-A’ is shown on plate 1.

Q14 Geologic Assessment of Coal in the Colorado Plateau: Arizona, Colorado, New Mexico, and Utah
and is relatively straight and smooth. This indicates a wavedominated shoreline, where wave action dispersed sediment 

evenly along the shore. From the time the shoreline was at the 

100-ft position to the time it reached the 250-ft position, the 

shoreline regressed relatively evenly and maintained a northwest trend. Between the 250-ft and the 300-ft line in the 

southeast part of the basin, however, a relatively rapid regression of the shoreline is indicated over a broad lobe that probaably represents a delta complex that was being developed at 

the mouth of a major river system. The 300-ft line shows 

that this broad delta lobe, about 30 mi across, had moved the 

shoreline rapidly northward in the southeast part of the basin, 

while to the west the shoreline retained its northwesterly linear 

trend. Figure 8 shows that the increased rate of sediment infl ux 

recorded by this delta lobe gradually diminished but continued 

until the time the shoreline reached the 500-ft position.

From the 500-ft to the 650-ft positions, the shoreline 

retained a slightly sinuous, relatively linear confi guration as 

it regressed northward across the central part of the basin 

area. At the 700-ft position a small lobe bulged the shoreline 

seaward to the northeast in the central part of the basin. At the 

750-ft position, it is clear that this isopach line is no longer 

a good proxy for the shoreline position in the northwest part 

of the basin. In that area, the interval between the Huerfanito 

and the top of the Pictured Cliffs thins as shown by the 

700-ft depression contour. The only reasonable explanation 

for this curious confi guration is that at a time following deposition of the Huerfanito (75.76 Ma), a relatively small local 

tectonic event occurred in the area of the 700-ft line, slightly 

doming the strata on the Lewis seafl oor. The doming apparently occurred so slowly that this feature never became a 

positive high on the seafl oor because sedimentation dispersal 

across this part of the shelf area easily kept up with the slow 

rate of uplift and the seafl oor remained relatively smooth and 

fl at in this area. By the time the Pictured Cliffs shoreline had 

regressed across this area (around 74.5 Ma, see fi g. 17), this 

minor tectonic event had ended because the Pictured Cliffs and 

overlying Fruitland coals show no evidence of this event.

The origin of the domed area discussed above is problematic; however, research on the age of the intrusion of the 

Carrizo Mountains laccolith (fi g. 3) by Semken and McIntosh 

(1997, table 1) showed that the emplacement of the laccolith 

began at least 73.8±1.0 Ma. The Carrizos are about 40 mi 

southwest of the paleo-dome expressed between the Huerfanito and Pictured Cliffs in the northwest part of the basin 

(fi gs. 3, 8). It is postulated that the low-relief dome that 

formed on the Lewis seafl oor between 75.76 Ma and 74.5 Ma 

may be underlain by a small magmatic intrusion related to 

the emplacement of the Carrizo Mountains laccolith, however 

there is no direct evidence for this hypothesis.

At the position of the 800-ft line, the Pictured Cliffs 

shoreline has a strong northwest orientation that was retained 

throughout the rest of the time the Pictured Cliffs shoreline 

regressed northeastward to its last position in the basin area at 

the 1,250-ft line.

Rate of Regression

The rate of regression of the Pictured Cliffs shoreline can 

be inferred from fi gure 8. The farther apart the contour lines, 

the more rapid the regression of the shoreline; conversely, the 

closer together the lines, the slower the rate of regression. This 

relationship is best seen in cross section on plate 1 where the 

large stratigraphic rise in the position of the Pictured Cliffs is 

seen at wells 16, 17, and 18 and on fi gure 8 where the 750-ft 

through the 1,050-ft lines are close together. During the time 

interval from when the shoreline was at the 750-ft position 

to when it reached the 1,150-ft position, the deposition rate 

relative to subsidence slowed markedly and the Pictured Cliffs 

shoreline deposits built up vertically into a thick sandstone 

complex. The rate of deposition was so slow during this time 

interval that it fell below the rate of subsidence and the shoreline advanced shoreward 4 or 5 mi, transgressing over a thin 

tongue of Fruitland Formation backshore swamp deposits, as 

seen on well 16 of plate 1. The wide spacing between the 

1,050- and 1,100-ft lines along the line of section A-A′ indicates a rapid regression over that area, as seen between wells 

18 and 19 on plate 1. Another period of slower shoreline 

regression is represented by isopach lines 1,100 to 1,200 (fi g. 

8) that are closer together, suggesting a slowing in the deposition rate to the extent that another transgressive shift of the 

shoreline occurred from the position of well 20 back beyond 

well 18, a distance of about 12 mi. The tongue of Pictured 

Cliffs in the Fruitland Formation in wells 18 and 19 on plate 

1 records that event.

Fruitland Formation

The Fruitland Formation, defi ned by Bauer (1916, p. 274), 

is a mixture of mudstones, siltstones, sandstones, carbonaceous 

shales, and coals deposited in a nearshore swamp environment 

(Fassett and Hinds, 1971). The basal contact of the Fruitland 

with the underlying Pictured Cliffs Sandstone is a sharp and 

clear-cut contact, as discussed above. The upper contact of 

the Fruitland with the lower shale member of the Kirtland 

Formation was described by Bauer (1916, p, 274) as follows, 

“The Fruitland formation is more sandy than the overlying 

Kirtland Shale into which it merges by a gradational zone 

containing in many places sandstone lenses that are apparently 

of fl uviatile origin.” Subsequent workers, frustrated by the 

ambiguity of this description of the upper contact, and unaware 

of the time-transgressive nature of the Fruitland, selected 

different, discontinuous sandstone beds as the top of the 

Fruitland, but no general consensus was reached on how best to 

defi ne the Fruitland-Kirtland contact (Fassett and Hinds, 1971, 

p. 19). Fassett and Hinds suggested that the upper contact should 

be placed “... at the top of the highest coal bed or carbonaceous 

shale bed ....” Plate 1 shows the random nature of the occurrence 

of the highest Fruitland coal bed, from well to well. Because 

of the diffi culty in locating this contact on the outcrop, and 

Geology and Coal Resources of the Upper Cretaceous Fruitland Fm., San Juan Basin, New Mexico and Colorado Q15
especially in the subsurface on geophysical logs, the lower shale 

member of the Kirtland Formation and the Fruitland Formation 

are shown undivided in this report.

In a depositional sense, the Fruitland was the servant 

to the master Pictured Cliffs Sandstone. The essence of the 

Fruitland, in terms of its historical defi nition, is its contained 

coal beds, and the distribution of Fruitland coals across the 

basin is intimately related to the rate of regression of the 

Pictured Cliffs shoreline (plate 1) and to a lesser extent to the 

positions of northeast-trending distributary channel systems 

cutting through the Fruitland peat swamps. Fruitland coal distribution in the basin is discussed at greater length in the 

“Fruitland Coal Resources” section of this report. 

Kirtland Formation

The Kirtland Shale was defi ned by Bauer (1916, p. 274) 

as predominantly “clayey” but containing white and brown 

sandstones. He subdivided the Kirtland into a lower shale 

member, the Farmington Sandstone Member, and an upper 

shale member. Fassett and Hinds (1971, p. 23) recommended 

combining the upper shale member of the Kirtland with the 

Farmington Member, and stated, “In this report a two fold 

division of the Kirtland Formation is used: the lower shale 

member of Bauer and the undivided Farmington Sandstone 

Member and upper shale member of Bauer.” The Farmington 

Sandstone Member and upper shale member of the Kirtland 

Formation are likewise combined in this report and are referred 

to as the Farmington Sandstone Member of the Kirtland 

Formation. Because the Farmington Sandstone Member is such 

a signifi cant part of the Kirtland, the word “Shale” is not an 

accurate descriptor for the lithology of the Kirtland and the name 

is thus changed to Kirtland Formation.

McDermott Member of the Animas Formation

The McDermott Member of the Animas Formation is the 

youngest rock unit of Late Cretaceous age in the San Juan 

Basin. The McDermott (Fassett, 1985, p. 319) is a conglomeratic, predominantly volcaniclastic rock unit thought to have 

been produced by a short-lived, Late Cretaceous episode of 

volcanism in the vicinity of the present-day La Plata Mountains (fi g. 3). The McDermott is present only in the northwest 

part of the basin where it overlies the Kirtland Formation; thus, 

it does not appear on the cross sections in this report. 

Upper Cretaceous Chronostratigraphy 

of the San Juan Basin

Earlier Publications

Radiometric ages of the Lewis Shale, Huerfanito Bentonite Bed, Pictured Cliffs Sandstone, and Fruitland Formation 

were fi rst discussed in detail in a report by Fassett (1987). 

In that study, the ages of latest Cretaceous Western Interior 

ammonite zones in the San Juan Basin (based on collections 

from the upper part of the Lewis Shale) were estimated on 

the basis of radiometric ages obtained for altered volcanic 

ash beds associated with some of these ammonite zones in 

other localities in the Western Interior of North America. The 

principal reference for those ages was Obradovich and Cobban 

(1975). The ammonite-zone ages were projected into the Pictured Cliffs Sandstone and Fruitland Formation along time 

lines to determine the timing of the Pictured Cliffs Sandstone 

regression across the basin. Subsequent to the Fassett (1987) 

report, Fassett and Steiner (1997) reported the ages of a series 

of ash beds in the Fruitland Formation in the southwest part of 

the San Juan Basin and one ash bed from the upper part of the 

Lewis Shale in the northeast part of the basin near Chimney 

Rock in Colorado (near the Chimney Rock mine, fi g. 2).

Hunter Wash Study Area

Ash Beds

The localities for fi ve dated ash beds collected in the 

Hunter Wash study area (reported by Fassett and Steiner, 

1997) are shown on fi gure 9. Three of these beds are in the 

Fruitland Formation and two are in the Farmington Sandstone 

Member of the Kirtland Formation. Ash DEP, the stratigraphically lowest, is 7 inches thick and was collected from a thin, 

high-ash coal bed in the lowermost Fruitland Formation, very 

close to the top of the Pictured Cliffs Sandstone on the southwest edge of the San Juan Basin. (This coal bed may correlate 

with the basal coal bed in the USGS AMW 6-1 drill hole 

on plate 1.) Ash DEP is named for Dog Eye Pond, a stock 

tank near the collection site that is shown on the Tanner Lake, 

1:24,000-scale, USGS topographic quadrangle map. Ash 2 is 

8 inches thick and was collected from a coal bed in the 

lower Fruitland in Hunter Wash (fi g. 9). Ash 4 is 13 inches 

thick and was collected from the top of a thin, high-ash coal 

bed in Hunter Wash (fi g. 9). This is the stratigraphically highest Fruitland coal bed in Hunter Wash. This site marks the 

beginning of the paleomagnetic traverse of Fassett and Steiner 

(1997) in Hunter Wash (fi g. 9). 

Ash H is 11 inches thick and was collected from the 

Farmington Sandstone Member of the Kirtland Formation in 

a short, northwest-trending tributary of Hunter Wash (fi g. 9). 

This ash bed is underlain by green-gray mudstone and is overlain by a 4.5-ft-thick chocolate-brown, thin-bedded mudstone. 

Ash J is 8 inches thick and was collected from the uppermost 

part of the Farmington Member, only 16 ft below the base 

of the Paleocene Ojo Alamo Sandstone. It is underlain by 

a light-gray sandy siltstone bed and is overlain by 2.5 ft of 

chocolate-brown mudstone. The collection site is in a small 

rincon that provides a small window into a bedrock exposure 

of the uppermost Kirtland that is mostly covered by slopewash material in the rest of this area. The ash-bed-J site is on 

Q16 Geologic Assessment of Coal in the Colorado Plateau: Arizona, Colorado, New Mexico, and Utah
PMAG

NAVAJO INDIAN RESERVATION

EXPLANATION

Govt.

41-21

371

371

Barrel

Spring

Ash

 2

5500

 Ojo

Alamo

 site

TU-2

PF-1

R-1

C-1

TU-1

V-1

BF-1

 Mims

Garson 1

 Nariz

1-Fed.

AMW

 6-1

M-3

 CU34-24

Willow

De-na-zin Wash

 TL 27-1

Alamo

De-na-zin

River

SUF

1-12

Chaco

Wash

Wash

Wash

Wash

Alamo

Hunter

Hunter Wash

0 1 2 3 4 5 miles

H

H'

R. 13 W. R. 12 W. R. 11 W.

T. 23 N.

Bisti - De-na-zin Wilderness Area

Wash

FG-1

Bisti Trading

Post (ruins)

 Ash DEP

 site

T. 22 N.

T. 24 N.

Ash Ash J H

San Juan County

Road 7250

Old Bisti

Road

6000

Ash

 4

Tn

Tn

Tn

Toa

Toa

Toa

Kkf

Kkf

Kkf

Kfk

Kfk

Kfk

Kpc

Kpc

Kpc Kpc

Klo

Klo

Klo

Klo

Nacimiento Formation

Ojo Alamo Sandstone

Farmington Sandstone Member

of Kirtland Formation

Fruitland Formation and lower shale

member of Kirtland Formation

Pictured Cliffs Sandstone

Lewis Shale and older rocks

5000

Tn

T. 25 N.

Figure 9. Geologic map of the Hunter Wash study area (fi g. 2). Altered volcanic ash bed collection sites are labeled 

and shown with arrows. Geologic cross section H-H’ is shown on fi gure 10. Structure contour lines (green) are on the 

Huerfanito Bentonite Bed of the Lewis Shale; contour interval is 100 ft; datum is mean sea level. List of wells used for 

subsurface control is in table 3. PMAG is line of paleomagnetic traverse along the upper part of Hunter Wash from 

Fassett and Steiner (1997). Geology compiled and locally modifi ed by the author from USGS MF-Series maps: Brown 

(1982 a, 1982b), O’Sullivan, Scott, and Heller (1979), O’Sullivan and others (1986), Schneider and others (1979), Scott 

and others (1979), and Strobell and others (1985).

Geology and Coal Resources of the Upper Cretaceous Fruitland Fm., San Juan Basin, New Mexico and Colorado Q17
 USGS

AMW 6-1

Ash DEP site*

Lewis Shale and older rocks

HUERFANITO BENTONITE BED

Go41

Paleomagnetic traverse (projected)

 Nariz1-Fed.

Mims Garson No. 1

3.2 mi.

4.5 mi.

4.4 mi.

2.6 mi.

NORT

SOUTH

 Willow

 Wash

 Hunter

 Wash Hunter Ash 2 Ash 4 Wash

Ash J

Ash H

C32r

C33n

Pictured

Farmington Sandstone Member of Kirtland Formation

Ojo Alamo Ss

De-na-zin Wash

 Alamo

 Wash

*Subsurface interpretation at this locality is projected from the TL 27-1 drill hole located 2.1 miles to the northwest (fig. 9)

 Fruitland Formation and lower shale member of Kirtland Formation 

Cliffs Sandstone

H 

NacimientoFormation

Figure 10. Structural cross section in the Hunter Wash study area. Line of section is on fi gure 9. Drill holes used for control are shown in table 3. Radiometric 

Fassett and Steiner (1997) and Fassett and others, (1997). Analytical data for ash bed age determinations are in tables 1 and 4. Paleomagnetic data are from FaTopographic profi le is from USGS 1:24,000 topographic quadrangle maps. Vertical exaggeration is about 10 x.

Table 3. List of drill holes shown on figure 9—holes on cross section H-H' (fig. 10) in bold type.  Map Company Drill hole T. R. Sec. Quarter Longitude La designation name (N.) (W.) (N.)  PF-1 Magnolia Petroleum Postelle Federal 1 25 13 28 NE 108.21711 36 Govt. 41-21 Shell Oil Government 41-21 25 12 21 NE 108.10936 36 CU 34-24 Shell Oil Carson Unit 34-24 25 12 24 SW 108.06007 36 C-1 Monsanto Chemical Chaco 1 24 13 20 NW 108.25000 36 R-1 Davis Oil Riddle 1 24 13 10 NW 108.21880 36 SUF 1-12 R. E. Lauritsen Southern Union Federal 1-12 24 13 12 SE 108.16810 36 Nariz 1 Fed. Tesoro Petroleum Nariz 1-Federal 24 12 30 NW 108.16394 36 Mims Garson 1 Kenneth Murchison Mims Garson 1 24 12 4 NW 108.12660 36 TU-1 Humble Oil & Refining Tanner Unit 1 24 12 21 SW 108.12526 36 V-1 H. L. Fanning Vandersluice 1 24 12 13 SW 108.06836 36 M-3 Tenneco Oil Monument 3 24 11 5 NW 108.02822 36 BF-1 Magnolia Petroleum Beamon Fed 1 24 11 29 SE 108.01842 36 FG-1 Davis Oil Fannin Government 1 24 11 3 NW 107.99730 36 TL 27-1 U.S. Geological Survey Tanner Lake 27-1 23 13 27 SW 108.20853 36 AMW 6-1 U.S. Geological Survey Alamo Mesa West 6-1 23 12 6 SW 108.16370 36 TU-2 Humble Oil & Refining Tanner Unit 2 23 12 23 SW 108.09031 36
the topographic divide between the short tributary where ash H 

is exposed and Hunter Wash to the east (fi g. 9). 

Figure 10 is a structural cross section through the Hunter 

Wash study area (a list of the drill holes used for subsurface 

control for this cross section and throughout the Hunter Wash 

area is in table 3). On the south end of the cross section, 

the Huerfanito Bentonite Bed is shown projected into the 

basal Fruitland Formation at the outcrop. Because bedrock is 

masked by alluvium in this area, it is not possible to determine 

if the Huerfanito is preserved in the Fruitland here. Confi rmation of the projected level of the Huerfanito Bed in the basal 

Fruitland is found in the lithologic descriptions of rocks peneetrated in USGS drill hole TL 27-1 (fi g. 9) in Jentgen and 

Fassett (1977, p. 28). At a depth of 106 ft in this well there 

is the notation “Clay balls (changed bits).” The senior author 

of this report, Russell W. Jentgen, was on site when this hole 

was drilled and stated (oral commun., 1977, 1998) that at 106 

ft, a bentonitic shale was penetrated that swelled and clogged 

the drill bit and a new drill bit had to be installed in order to 

continue drilling. The top of the Pictured Cliffs Sandstone is at 

a depth of 113 ft in the TL 27-1 drill hole, thus the bentonitic 

shale was in the lower Fruitland, nearly at the top of the 

Pictured Cliffs, exactly where a projection of the Huerfanito 

Bentonite Bed is shown on fi gure 10. 

Ash-Bed Ages

Table 4 provides analytical data for 40Ar/39Ar age determinations for the Hunter Wash, Chimney Rock, and La Plata 

mine ash beds. All of the ages were determined by John 

Obradovich, U.S. Geological Survey, Denver, Colo. Sanidine 

crystals were separated from the ashes and dated using the 

40Ar/39Ar laser fusion method (methodology described in 

Obradovich, 1993). Most analyses were of single crystals, but 

one was of multiple crystals. The ages of the fi ve Hunter 

Wash ash beds plus the age of the Huerfanito Bentonite Bed 

(collected at the Regina site (fi gs. 2 and 6) and discussed in 

the “Huerfanito Bentonite Bed of the Lewis Shale” section of 

this report) are shown on the right side of cross section H-H′

(fi g. 10). The duration of the interval from the oldest to the 

youngest ash bed at Hunter Wash is 2.72 m.y. (75.76 to 73.04 

Ma)

Magnetic Polarity

Figure 11 shows the magnetic polarity column for Upper 

Cretaceous and lower Tertiary rocks in the Hunter Wash area. 

The Late Cretaceous polarity reversal from magnetic chron 

C33n to C32r is 1,076 ft above the Huerfanito Bentonite Bed. 

The age of the reversal was estimated to be 75.50±0.18 Ma 

by Fassett and Steiner (1997) on the basis of interpolation 

between the ages of two ash beds above and three ash beds 

below the reversal in this area. (The age of this reversal 

is reviewed in the “Summary of Chronostratigraphy” section 

of this report.) Fassett and Steiner (1997) reported a short 

normal-polarity interval in the Paleocene Ojo Alamo Sandstone and identifi ed it as chron C29n (fi g. 13). Butler and 

Lindsay (1984) discussed a short normal-polarity interval they 

had previously reported at several localities in the Ojo Alamo 

Sandstone in the southern San Juan Basin and had labeled 

chron C29n. One of their localities was near Alamo Wash, 

about 5 mi southeast of Hunter Wash (fi g. 9). On reexamination of their data, Butler and Lindsay (1984) decided that 

the normal zone in the Ojo Alamo represented a normal-fi eld 

overprint and they deleted this normal zone from the Ojo 

Alamo at all but one of their localities. The Fassett and Steiner 

report (1997, fi g. 2), however, shows that the normal zone in 

the Ojo Alamo on Hunter Wash represents certain “Cretaceous 

[or early Paleocene] magnetization of the polarities”—thus 

an interval of normal polarity (chron C29r of Fassett and 

Steiner, 1997) is indeed present in the Ojo Alamo in the Hunter 

Wash section. Because chron C29n is early Paleocene, the Ojo 

Alamo at Hunter Wash must be Paleocene in age. Chron C29n 

is underlain by a short reversed-polarity interval identifi ed as 

C29r in the lowermost part of the Ojo Alamo (fi g. 13). The 

lower part of chron C29r; chrons C30n and C30r, chrons C31n 

and C31r, chron C32n; and the upper part of chron C32r are 

missing at the unconformity at the base of the Ojo Alamo.

Paleontology

The Ojo Alamo Sandstone is conformably overlain by 

and intertongues with the Nacimiento Formation in the Hunter 

Wash area (Baltz and others, 1966), and Puercan (earliest 

Paleocene) mammals have been found at several localities in 

the lower part of the Nacimiento, 26–40 ft above the top of 

the Ojo Alamo (Williamson and Lucas, 1992, fi g. 5). This 

evidence indicates that the upper part of the Ojo Alamo is 

earliest Paleocene in age. Palynological data from the Ojo 

Alamo Sandstone from Hunter Wash and many other localities 

in the basin universally support an earliest Paleocene age for 

the entire Ojo Alamo (Fassett and others, 1987, Fassett and 

others, 2000) and a Late Cretaceous age for the underlying 

Kirtland Formation. 

The Kirtland Formation and the lower part of the Ojo 

Alamo Sandstone contain a rich and diverse vertebrate fauna 

in the Hunter Wash area, including dinosaurs, turtles, crocodiles, and mammals (Hunt and Lucas, 1992). The radiometric 

dating of upper Kirtland ash beds (discussed under “Ash Beds”

above) proves that this formation is Cretaceous in age (73.0 

Ma) to within a few feet of the basal Ojo Alamo unconformity. 

The dinosaurs of the Ojo Alamo Sandstone have long been 

an enigma because other evidence, discussed above, indicates 

that the Ojo Alamo is Paleocene in age. Vertebrate paleontologists have continued to insist that the lower part of the Ojo 

Alamo must be Cretaceous because of its contained dinosaurs 

(Hunt and Lucas, 1992). Two papers, however (Fassett, 1982, 

and Fassett and others, 1987), suggest that the weight of the 

evidence indicates that the Ojo Alamo is Paleocene in age 

and that the dinosaurs within the Ojo Alamo are Paleocene 

and not Cretaceous in age. The recent discovery of Paleocene 

pollen beneath a large hadrosaur femur, 50 ft above the base 

Geology and Coal Resources of the Upper Cretaceous Fruitland Fm., San Juan Basin, New Mexico and Colorado Q19
Table 4. Analytical data for 40Ar/39Ar age determinations for seven San Juan Basin altered volcanic ash beds from the Hunter Wash and La Plata min

and the Chimney Rock area in Colorado—modified from Fassett and Steiner (1997). 

[40Ar*, radiogenic argon] 

Ash bed name Irradiation Mineral Exp. 

and J value number analysis number 40Ar/39Ar 37Ar/39Ar 36Ar/39Ar K/Ca %40Ar* 40Ar*/39ArK 

Ash bed J JD022 Sanidine 96Z0082 5.84251 0.009032 0.000174 54.2 98.98 5.78315 

(Fassett K/T) single xtl 96Z0085 5.71103 0.007369 0.000006 66.5 99.82 5.70112 

J=0.006346 96Z0086 5.72075 0.009275 0.000009 52.8 99.81 5.71022 

 96Z0087 5.72830 0.008386 0.000086 58.4 99.41 5.69492  96Z0088 5.91112 0.013007 0.000050 37.7 99.61 5.88880 

 96Z0089 5.73928 0.009932 0.000181 49.3 98.93 5.67799  96Z0090 5.73461 0.009117 0.000024 53.7 99.73 5.71939 

Unweighted mean and standard deviation w/o errors in J Weighted mean and weighted standard deviation w/o errors in J Unweighted mean and error of the mean at the 95% confidence level including the error 

Ash bed H(1) JD06 Sanidine 91Z1277 5.98932 0.003994 0.000074 122.7 99.49 5.95875 

(Hunter Wash 6) single xtl 91Z1278 6.08627 0.003978 0.000412 123.2 97.85 5.95573 

J=0.006965 91Z1280 5.99126 0.005336 0.000101 91.8 99.36 5.95270 

 91Z1281 5.95985 0.003085 0.000006 158.9 99.82 5.94926  91Z1282 5.97041 0.004894 0.000016 100.1 99.77 5.95695 

Unweighted mean and standard deviation w/o errors in J Weighted mean and weighted standard deviation w/o errors in J Unweighted mean and error of the mean at the 95% confidence level including the error 

Ash bed H(2) JD06 Sanidine 91Z1283 5.97047 0.004577 0.000052 107.1 99.60 5.94633 

(Hunter Wash 10) single xtl 91Z1284 5.97268 0.003751 0.000093 130.6 99.39 5.93637 

J=0.006997 91Z1285 5.95048 0.004290 0.000056 114.2 99.57 5.92504 

 91Z1286 5.95753 0.004314 0.000014 113.6 99.78 5.94464  91Z1287 5.96512 0.010414 0.000054 47.1 99.72 5.96512 

Unweighted mean and standard deviation w/o errors in J 

Weighted mean and weighted standard deviation w/o errors in J Unweighted mean and error of the mean at the 95% confidence level including the error Mean age and uncertainty for two samples sets, H(1) and H(2) (standard error of mean) Mean age and uncertainty for two samples sets, H(1) and H(2) (95% confidence level) 
Table 4. Analytical data for 40Ar/39Ar age determinations for seven San Juan Basin altered volcanic ash beds from the Hunter Wash and La Plata min

and the Chimney Rock area in Colorado—modified from Fassett and Steiner (1997)—Continued. 

Ash bed name Irradiation Mineral Exp. 

and J value number analysis number 40Ar/39Ar 37Ar/39Ar 36Ar/39Ar K/Ca %40Ar* 40Ar*/39ArK 

Ash bed 4 JD029 Sanidine 99Z0566 5.87492 0.009246 0.000118 53.0 99.26 5.83201 

(Kirtland 86-0-07) 99Z0567 5.83590 0.008767 0.000075 55.9 99.48 5.80576 

J=0.007239 99Z0568 5.84367 0.008589 0.000002 57.1 99.84 5.83492 

 99Z0569 5.86337 0.008552 0.000040 57.3 99.65 5.84343  99Z0571 5.89673 0.009239 0.000214 53.0 98.79 5.82556 

Unweighted mean and standard deviation w/o errors in J Weighted mean and weighted standard deviation w/o errors in J Unweighted mean and error of the mean at the 95% confidence level including the error 

Ash bed 2(1) JD010 Sanidine 93Z0355 5.21431 0.016830 0.000068 29.1 99.47 5.18647 

(Kirtland 86-0-05) multiple xtl 93Z0356 5.20874 0.022911 0.000029 21.4 99.70 5.19303 

J=0.008114 93Z0357 5.20897 0.032658 0.000096 15.0 99.33 5.17419 

 93Z0358 5.22023 0.020443 0.000010 24.0 99.80 5.20991  93Z0359 5.21996 0.012477 0.000100 39.3 99.28 5.18231 

Unweighted mean and standard deviation w/o errors in J 

Weighted mean and weighted standard deviation w/o errors in J Unweighted mean and error of the mean at the 95% confidence level including the error 

Ash bed 2(2) JD021 Sanidine 95Z0555 5.89423 0.007657 0.000175 64.0 98.98 5.83445 

(Kirtland 86-0-05) single xtl 95Z0556 5.86859 0.007135 0.000071 68.7 99.50 5.83945 

J=0.007235 95Z0557 6.09035 0.007425 0.000863 66.0 95.68 5.82725 

 95Z0558 5.95920 0.007210 0.000349 68.0 98.13 5.84797  95Z0559 5.89310 0.006899 0.000121 71.0 99.25 5.84918  95Z0560 5.86243 0.005295 0.000020 92.5 99.75 5.84805 

Unweighted mean and standard deviation w/o errors in J 

Weighted mean and weighted standard deviation w/o errors in J Unweighted mean and error of the mean at the 95% confidence level including the error 
Table 4. Analytical data for 40Ar/39Ar age determinations for seven San Juan Basin altered volcanic ash beds from the Hunter Wash and La Plata min

and the Chimney Rock area in Colorado—modified from Fassett and Steiner (1997)—Continued. 

Ash bed name Irradiation Mineral Exp. 

and J value number analysis number 40Ar/39Ar 37Ar/39Ar 36Ar/39Ar K/Ca %40Ar* 40Ar*/39ArK 

Ash bed 2(3) JD022 Sanidine 96Z0091 5.88379 0.007845 0.000176 62.5 98.97 5.82352 

(Kirtland 86-0-05) single xtl 96Z0092 5.87229 0.007859 0.000158 62.3 99.06 5.81731 

J=0.007248 96Z0093 5.87863 0.006452 0.000143 75.9 99.13 5.82790 

 96Z0094 5.88236 0.007517 0.000135 65.2 99.18 5.83437  96Z0095 5.89134 0.007593 0.000218 64.5 98.76 5.81875  96Z0096 5.83790 0.007549 0.000093 64.9 99.38 5.80227 

Unweighted mean and standard deviation w/o errors in J Weighted mean and weighted standard deviation w/o errors in J Unweighted mean and error of the mean at the 95% confidence level including the error Mean age and uncertainty for three samples sets, 2(1), 2(2), and 2(3) (standard error of mean) Mean age and uncertainty for three samples sets, 2(1), 2(2), and 2(3) (95% confidence level) 

Ash DEP JD010 Sanidine 93Z0365 5.31701 0.009886 0.000057 49.6 99.53 5.29182 

(Lower Fruitland) multiple xtl 93Z0366 5.31513 0.006601 0.000002 74.2 99.83 5.30607 

J=0.008068 93Z0367 5.3147 0.022029 0.000002 22.2 99.85 5.30671 

 93Z0368 5.32145 0.001855 0.000014 264.2 99.75 5.30832  93Z0369 5.30936 0.009924 0.000016 49.4 99.75 5.29637 

Unweighted mean and standard deviation w/o errors in J 

Weighted mean and weighted standard deviation w/o errors in J Unweighted mean and error of the mean at the 95% confidence level including the error 

Ash CR(1) JD018 Sanidine 94Z0628 6.66639 0.012451 0.000058 39.4 99.62 6.64129 

(Chimney Rock single xtl 94Z0629 6.64388 0.012715 0.000002 38.5 99.87 6.63523 

9/6/89) 94Z0630 6.67716 0.011271 0.000132 43.5 99.29 6.63008 

J=0.006346 94Z0631 6.72427 0.012361 0.000228 39.6 98.88 6.64877 

 94Z0632 7.73688 0.011889 0.003877 41.2 85.09 6.58302  94Z0633 6.63383 0.011463 0.000002 42.8 99.87 6.62515  94Z0634 6.67627 0.010826 0.000088 45.3 99.49 6.64201 

Unweighted mean and standard deviation w/o errors in J 

Weighted mean and weighted standard deviation w/o errors in J Unweighted mean and error of the mean at the 95% confidence level including the error 
Table 4. Analytical data for 40Ar/39Ar age determinations for seven San Juan Basin altered volcanic ash beds from the Hunter Wash and La Plata min

and the Chimney Rock area in Colorado—modified from Fassett and Steiner (1997)—Continued. 

Ash bed name Irradiation Mineral Exp. 

and J value number analysis number 40Ar/39Ar 37Ar/39Ar 36Ar/39Ar K/Ca %40Ar* 40Ar*/39ArK 

Ash CR(2) JD018 Sanidine 94Z0581 6.65022 0.011035 0.000052 44.4 99.64 6.62666 

(Chimney Rock 260) single xtl 94Z0582 6.66070 0.011591 0.000148 42.3 99.22 6.60876 

J=0.006346 94Z0583 6.69819 0.011409 0.000249 43.0 98.78 6.61636 

 94Z0584 6.67044 0.011849 0.000155 41.4 99.19 6.61667  94Z0586 6.66142 0.010789 0.000075 45.4 99.54 6.63092  94Z0587 6.73294 0.012570 0.000374 39.0 98.24 6.61444  94Z0588 6.65070 0.011966 0.000124 41.0 99.33 6.60592  94Z0589 6.67283 0.011058 0.000100 44.3 99.44 6.63525 

Unweighted mean and standard deviation w/o errors in J 

Weighted mean and weighted standard deviation w/o errors in J Unweighted mean and error of the mean at the 95% confidence level including the error Mean age and uncertainty for two samples sets, CR(1) and CR(2) (standard error of mean) Mean age and uncertainty for two samples sets, CR(1) and CR(2) (95% confidence level) 

Ash LP JD010 Sanidine 93Z0360 5.22181 0.018976 0.000053 25.8 99.56 5.19871 

(La Plata Mine) single xtl 93Z0361 5.22126 0.028708 0.000045 17.1 99.61 5.20122 

J=008075 93Z0362 5.22103 0.025860 0.000047 19.0 99.60 5.20024 

 93Z0363 5.23686 0.025109 0.000045 19.5 99.61 5.21652  93Z0364 5.22582 0.010336 0.000001 17.4 99.83 5.21717 

Unweighted mean and standard deviation w/o errors in J 

Weighted mean and weighted standard deviation w/o errors in J Unweighted mean and error of the mean at the 95% confidence level including the error 

Ca and K corrections and decay constants: (36Ar/ 37Ar)Ca = 2.69 ± 0.24×10–4

(39Ar/ 37Ar)Ca = 6.79 ± 0.051×10–4

(40Ar/ 39Ar)K = 9.1 ± 5.4×10–3

λε + λε′ = 0.581×10–10 yr–1

λβ = 4.962×10–10 yr–1 40K/K = 1.167×10–4 atom/atom 

Notes: For ash beds H, 2, and CR, weighted-mean age determinations were made for multiple sample sets: for ash bed H, the two samples sets shown produced 

uncertainty of 73.37±0.08 (standard error of mean) and 73.37±0.18 Ma (95% confidence level); for ash bed 2, the three samples sets shown prouncertainty of 74.56±0.06 (standard error of mean) and 74.56±0.13 Ma (95% confidence level); for ash bed CR, the two samples sets shown prouncertainty of 74.25±0.06 (standard error of mean) and 74.25±0.13 Ma (95% confidence level). These mean ages and uncertainties are used for report. The underlined numbers for ash J in the “Age (Ma)” and “1 sigma” columns were excluded from the weighted-mean age determination f
of the Ojo Alamo Sandstone in the west-central part of the 

San Juan Basin (Fassett and others, 2000; Fassett and Lucas, 

2000), strongly supports the argument that the Ojo Alamo and 

its contained dinosaurs are Paleocene in age. A recent estimate 

for the age of the Cretaceous-Tertiary boundary is 65.5±0.1 

Ma (Obradovich, 1999); therefore, the Ojo Alamo in the San 

Juan Basin must have an age slightly less than 65.5 Ma. The 

unconformity at Hunter Wash between the Kirtland Shale and 

the Ojo Alamo Sandstone thus represents about 8 m.y. of 

missing time (73–65Ma).

Chimney Rock Study Area

Ash Beds

The Chimney Rock study area is on the northeast edge 

of the San Juan Basin near the Chimney Rock mine (fi g. 2). 

The geology of the upper part of the Lewis Shale, the Pictured 

Cliffs Sandstone, and the lower part of the Fruitland Formation 

was studied in detail in this area by Fassett and Steiner (1997) 

as part of a broader study of the paleomagnetism of uppermost 

Cretaceous rocks at several localities in the San Juan Basin. 

In the process of conducting paleomagnetic sampling through 

the upper part of the Lewis Shale at Chimney Rock, several 

very thin bentonite beds were discovered. Most of these 

altered volcanic ash beds are less than 1 inch thick, with 

the thickest being about 3 inches. Ash beds in this exposure 

are commonly replaced by calcium carbonate and sometimes 

grade into thicker zones of calcite concretions. Samples of 

several ash beds were collected at this site, but only one, the 

CR bed, contained sanidine crystals suitable for 40Ar/39Ar age 

determination. 

The CR ash bed (named for Chimney Rock) is located 

about 180 ft below the base of the Pictured Cliffs Sandstone 

at a stratigraphic level 909 ft above the level of the Huerfanito 

Bentonite Bed (fi gs. 12, 13). This ash ranges from 1 inch to 

less than 1/8 inch thick and is in places replaced by calcium 

270° 0° 90° 180° 270° -90° 0° +90°

Ojo Alamo

Sandstone

Ash J

73.04 0.25 Ma + 

- 

+ 

- 

Ash H

73.37 0.18 Ma + 

- 

Ash 4

74.55 0.29 Ma

 Farmington

 Sandstone

 Member of

 Kirtland

 Formation

 TERTIARY

(Danian-Puercan)

 CRETACEOUS

(Campanian-Edmontonian)

 lower shale

 member of

 Kirtland

 Formation & 

 Fruitland

 Formation

Declination Inclination

Stratigraphic position - feet above Huerfanito Bentonite Bed

600

700

800

900

1000

1100

1200

1300

Figure 11. Hunter Wash magnetostratigraphic data. Black is normal, white is reversed polarity, and hachures indicate an 

unsampled interval. The magnetic-polarity column width indicates the degree of certainty of the polarity interpretations; full 

column width indicates Cretaceous or early Paleocene (CP) magnetization of the polarities, two-thirds column width indicates 

probable CP magnetization, and one-third column width means some indication of CP polarity but with high uncertainty. 

Sample positions are shown by tick marks on the left side of the polarity column. The unconformity at the base of the Tertiary 

Ojo Alamo Sandstone is 1,276 ft above the Huerfanito Bentonite Bed. Paleomagnetic traverse in Hunter Wash is shown on 

fi gure 9. From Fassett and Steiner (1997).

Q24 Geologic Assessment of Coal in the Colorado Plateau: Arizona, Colorado, New Mexico, and Utah
carbonate. In spite of its thinness, it was possible to collect 

two samples of this bed: the fi rst from the lower, purer clay 

part and the second from the upper part that appeared to 

be contaminated by reworked Lewis Shale. These samples, 

CR(1) and CR(2) in table 4, have coarser and fi ner sanidinecrystal fractions and the lowermost sample, CR(1), contains 

the coarser fraction, as would be expected for an air-fall 

deposit.

Age of Ash Bed CR

Two single-crystal 40Ar/39Ar ages were obtained for samples CR(1) and CR(2) from the Chimney Rock site. Table 

4 shows the weighted mean age for the two samples with a 

resultant mean age for the CR ash bed of 74.23±0.13 Ma.

La Plata Mine Ash Bed

An altered volcanic ash bed about 14 inches thick was 

collected near the top of a thick coal bed in the lower part 

of the Fruitland Formation at the La Plata coal mine (fi g. 2). 

This ash bed, labeled LP (for La Plata mine), is estimated to 

be 980 ft above the Huerfanito Bentonite Bed. Table 4 shows 

the analytical data for this ash bed and its resultant mean age 

of 74.30±0.35 Ma.

Ammonite Zonation of Lewis Shale 

at Chimney Rock Site

Ammonite collections from the Chimney Rock area were 

reported by Cobban and others (1974) and Fassett (1987). 

270° 0° 90° 180° 270° -90° 0° +90°

Fruitland

Formation

Pictured

Cliffs

Sandstone

Ash CR

74.25 + 0.13 Ma -

Ammonite

Zones

A

A

A*

A*

Baculites

compressus

Didymoceras

cheyennense

Exiteloceras

jenneyi

top ? 

UPPER CRETACEOUS

 Campanian 

Lewis

Shale

700

800

900

1000

1100

1200

1300

1400

Feet

Stratigraphic position - feet above Huerfanito Bentonite Bed

Figure 12. Chimney rock magnetostratigraphic data. Black is normal, white is reversed polarity, and hachures indicate an 

unsampled interval. The magnetic-polarity column width indicates the degree of certainty of the polarity interpretations; full 

column width indicates Cretaceous magnetization of the polarities, two-thirds column width indicates probable Cretaceous 

magnetization, and one-third column width means some indication of Cretaceous polarity but with high uncertainty. Sample 

positions are shown by tick marks on the left side of the polarity column. Level of volcanic ash bed CR and its age are shown. 

A’s to the right of the lithologic column in the Lewis Shale designate levels of ammonite collections made for this study; A’s 

with asterisks indicate ammonite collections from Cobban and others (1974). Interval colored black in the lithologic column is a 

Fruitland coal bed. From Fassett and Steiner (1997).

Geology and Coal Resources of the Upper Cretaceous Fruitland Fm., San Juan Basin, New Mexico and Colorado Q25
More recent ammonite collections near Chimney Rock by Fassett and Cobban were reported in Fassett and Steiner (1997). 

Figures 12 and 13 show the stratigraphic levels of these ammonites collections and show the boundaries of the Exiteloceras 

jenneyi–Didymoceras cheyennense and D. cheyennense–Baculites compressus ammonite zones at this locality. 

Magnetic Polarity

The same magnetic-polarity reversal, from normal to 

reversed polarity (chron C33n to C32r), that was found at the 

Hunter Wash area in the continental Farmington Sandstone 

Member of the Kirtland Formation was found in the uppermost marine Lewis Shale in the Chimney Rock area. (A more 

detailed discussion of the paleomagnetic polarity at the Chimney Rock site is in Fassett and Steiner, 1997.) Figure 12 shows 

the paleomagnetic data obtained at the Chimney Rock site. 

The magnetic-polarity reversal from chron C33n to C32r is 

estimated to be 1,066 ft above the Huerfanito Bentonite Bed at 

the Chimney Rock site, virtually at the same stratigraphic level 

above the Huerfanito Bed as at the Hunter Wash site.

Summary of Chronostratigraphy

Ammonite Zones in Upper Lewis Shale

Figure 13 shows a northeast-trending stratigraphic cross 

section from Hunter Wash to the Chimney Rock area. All of 

the chronostratigraphic data discussed herein are summarized 

on this illustration. On the right side of this fi gure, the Western 

Interior ammonite zones are shown for the time represented by 

regression of the Pictured Cliffs Sandstone shorelines across 

the San Juan Basin. These ammonite-zone boundaries, fi rst 

Feet

(base ?)

Baculites

scotti

Didymoceras

nebrascense

Didymoceras

stevensoni

Didymoceras

cheyennense

Baculites

compressus

 Ammonite

 Zones

Chimney Rock

paleomagnetic

section

C32r

A

A

A

A

 74.25 Ma

 (ash CR)

C32r-1n

C32r

C33n

OUTCROP

OUTCROP

Hunter Wash

paleomagnetic

section

C28r

C29n

C29r

C32r

C33n

C32r

C33n

 (ash J)

73.04 Ma

74.56 Ma

 (ash 2)

 75.56 Ma

(ash DEP)

1 2 3 4 5 6 7 8 9 10 11

90 miles

Northeast

(top ?)

Exiteloceras

 jenneyi 

73.37 Ma

 (ash H)

1000

1100

1200

1300

1500

1600

1700

1800

1900

2000

1400

900

800

700

600

500

400

300

200

100

0

73.50 Ma

0 10 20 30miles

Durango

Farmington

Cuba

109° 108° 107°

37°

36°

COLORADO

NEW MEXICO

UTAH ARIZONA

Pagosa

Springs

Kf

Kf

Hunter Wash

study area

(interpolated)

8 m.y.

LP

HBB

(76.07 Ma)

Datum - Huerfanito Bentonite Bed

Lewis Shale

 Kirtland and

Fruitland Formations

Pictured Cliffs

Sandstone

CRETACEOUS

TERTIARY

Ojo

Alamo

Sandstone

Southwest

Kf

Chimney

Rock site

74.55 Ma

 (ash 4)

Animas Formation

 (upper part)

HW CR

74.30 Ma

 (ash LP)

 75.76 Ma

(ash HBB)

3

4

5

6

7

8

9

10

11

1

2

Figure 13. Stratigraphic cross section from Hunter Wash to Chimney Rock (modifi ed from Fassett and Steiner, 1997, fi g. 4). 

Ash-bed sample localities are shown on index map. Ash-bed ages are from tables 1 and 4. Ash-bed ages shown in red are 

projected into the Hunter Wash section. Letters A at the Chimney Rock section show levels of ammonite collection sites. Lower 

ammonite-zone boundaries are modifi ed from Fassett (1987). On magnetic chron sections, black is normal polarity, white is 

reversed polarity. Vertical exaggeration is 200 x. Age of magnetic-polarity reversal of 73.50 Ma is the mean of six interpolated 

reversal ages based on the fi ve dated ash beds from the Hunter Wash locality (fi g. 16).

Q26 Geologic Assessment of Coal in the Colorado Plateau: Arizona, Colorado, New Mexico, and Utah
shown in Fassett (1987), have been modifi ed in this report on 

the basis of additional ammonite collections from the Chimney 

Rock and Regina sites (fi gs. 2 and 6). The distances of the 

fi ve ammonite zone boundaries above the Huerfanito Bed (fi g. 

13) are plotted on the bio-isochrone map shown on fi gure 14. 

This map shows the positions of successive Pictured Cliffs 

Sandstone shorelines at times when the various Western Interior ammonites shown appeared or disappeared in the San Juan 

Basin. For example, at the time the shoreline was at the 60-ft 

contour line position, the Western Interior ammonite zone 

fossil Baculites scotti had become extinct and Didymoceras 

nebrascense fi rst appeared. This bio-isochrone map provides a 

useful tool for visualizing the regression of the Pictured Cliffs 

Sandstone shoreline across the San Juan Basin relative to the 

evolution of late Campanian ammonites. 

Ash-Bed Ages

Figure 15 is a chart showing the uncertainty ranges for the 

40Ar/39Ar ash-bed ages discussed above. Uncertainties range 

from ±0.13 m.y. for ash beds 2 and CR to ±0.41 m.y. for 

ash DEP. The greatest uncertainty is ±0.41 m.y. for ash DEP; 

the age of this ash was determined using the multiple-crystal 

method. 

Age of Magnetic Polarity Reversal from C33n to C32r

Fassett and Steiner (1997) estimated the age for the 

magnetic-polarity reversal (C33n to C32r) to be 73.50±0.18 

Ma on the basis of interpolation between fi ve dated ash beds 

collected in the Hunter Wash area that bracketed the reversal 

(fi g. 13). Subsequent to that study, ash bed 4, which had 

been fi rst dated using multicrystal methodology was redated 

using single-crystal procedures, and its age has changed from 

74.11±0.64 Ma to 74.55±0.29 Ma (table 4 and fi g. 15). In 

addition, the age of ash bed LP (La Plata mine ash bed) is used 

in this report to calculate the age of the C33n-C32r reversal. 

Figure 16 is a chart showing the eight known 40Ar/39Ar dated 

ash beds in the Fruitland and Kirtland Formations of the San 

Juan Basin projected into the magnetic polarity column at 

ARCHULETA

SAN JUAN

McKINLEY

MONTEZUMA

108 ̊ 107 ̊

 37 ̊ 37 ̊

 36 ̊ 36 ̊

108 ̊ 107 ̊

COLORADO

NEW MEXICO

Farmington

Dulce

Cuba

Durango

SANDOVAL

RIO ARRIBA

LA PLATA

Study

area

CO

NM

Kf

Kf

60

Baculites scotti

465

665

60 Paleoshoreline with feet

above Huerfanito Bentonite

Bed shown

755

975

Didymoceras cheyennense

Baculites compressus

Exiteloceras jenneyi

Didymoceras stevensoni

Didymoceras nebrascense

Outcrop of Fruitland

 Formation

EXPLANATION

Ammonite collection

site from Lewis Shale

0 5 10 15 20 MILES

Figure 14. Bio-isochrone map showing positions of Pictured-Cliffs-seaway shorelines 

at times of fi rst and last appearances of Western Interior ammonites in the upper 

Lewis Shale in late Campanian time. Paleo-shoreline positions are estimated based on 

positions of isopach lines of fi gure 8. Kf, Fruitland Formation This map is a modifi cation 

of fi gure 5 of Fassett (1987). 

Geology and Coal Resources of the Upper Cretaceous Fruitland Fm., San Juan Basin, New Mexico and Colorado Q27
Hunter Wash. Five of the ash beds, J, H, 4, 2, and DEP are 

located in an area of continuous exposure of the Fruitland and 

Kirtland about 12 mi long in the Hunter Wash study area (fi gs. 

9, 10). Figure 16 shows the interpolated age of the C33n-C32r 

reversal using two dated ash beds above the reversal (J and H) 

and six dated ash beds below the reversal (CR, LP, 4, 2, DEP, 

and HBB). As fi gure 16 shows, 12 age interpolations for the 

reversal are possible based on these dated ash beds. The results 

range from 73.39 Ma for bracketing ashes J and 2, to 73.71 Ma 

for ashes H and CR for a very tight spread of only 0.32 m.y. 

The mean age for all 12 interpolations is 73.54±0.17 Ma

If only the ages of the fi ve ash beds in the Hunter Wash 

area are considered, six interpolated ages for the magneticpolarity reversal result (fi g. 16). The range of these six ages is 

from 73.39 to 73.61 for a spread of 0.22 m.y. The mean age for 

the six interpolated Hunter Wash reversal ages is 73.50±0.19 

Ma, the same age reported by Fassett and Steiner (1997). 

At the Chimney Rock site, the C33n-C32r magnetic 

polarity reversal and dated ash CR are present in the same 

measured section (fi g. 13). The reversal cannot be dated by 

extrapolation at Chimney Rock because the rate of sediment 

accumulation for the interval between the reversal and ash 

bed CR is not known. The rock-accumulation rate for the 

interval between ashes CR and HBB at Chimney Rock is 602 

ft/m.y. (fi g. 17B), however, calculations based on data from 

the Hunter Wash site clearly indicate that the rock rate for 

this interval is extremely variable ranging from 475 to 1,285 

ft/m.y. (fi g. 17A). Thus, the rate of 602 ft/m.y. is only an 

75.15 Ma

75.97 Ma

74.84 Ma

74.38 Ma

74.26 Ma

73.29 Ma

72.79 Ma

J

DEP

Ash

Ash

75.56 Ma

73.04 Ma

(_+ 0.25 )

CR

Ash

74.25 Ma

( _+ 0.13 )

(_+ 0.41 )

76.10 Ma

75.42 Ma

73.19 Ma

73.55 Ma

H

2

HBB

Ash

Ash

Ash

75.76 Ma

73.37 Ma

74.69 Ma 74.56 Ma

74.43 Ma

73.95 Ma

74.65 Ma

(_+ 0.18 )

( 0.13 )

LP

Ash

+_

+_

(+_ 0.38 )

( 0.34 )

AGE

(Ma)

76.0

75.0

74.0

73.0

73.5

74.5

75.5

LEGEND

74.12 Ma

4

Ash

74.55 Ma

(_+ 0.29 )

74.30 Ma

Hunter Wash

area

Regina site Chimney Rock

site

Sample Localities

La Plata mine

Figure 15. Chart showing uncertainty ranges for dated ash beds in the San Juan Basin. Ash-bed ages are 

from tables 1 and 4; all ages (except for ash DEP) are based on single-crystal 40Ar/39Ar analyses of sanidine 

crystals from altered volcanic ash beds. Age for ash DEP is based on a multiple-crystal age determination. 

Sample localities are shown on fi gures 2, 9, and 13.

Q28 Geologic Assessment of Coal in the Colorado Plateau: Arizona, Colorado, New Mexico, and Utah
average and has no value for extrapolating the rock rate above 

ash CR. 

The age of the reversal at Chimney Rock can be estimated 

by projecting the two ashes stratigraphically higher than the 

CR ash bed in the Hunter Wash area to the Chimney Rock area 

(fi g. 13) and interpolating between these projected ages. Figure 

16 shows the results of these interpolations to be 73.68±0.14 

Ma for ashes J/CR and 73.71±0.12 Ma for ashes H/CR, within 

0.18–0.21 m.y. of the reversal age of 73.50 Ma calculated at 

Hunter Wash. Because the C33n-C32r paleomagnetic reversal 

was a geologically instantaneous event, it must be the same 

age at Chimney Rock as at Hunter Wash: 73.50±0.19 Ma. 

On the basis of this age, the rock-accumulation rate for the 

interval between ash bed CR and the reversal is 209 ft/m.y. and 

the sediment-accumulation rate is 375 ft/m.y. at the Chimney 

Rock locality (fi g. 17B).

The range for all calculated ages for the polarity reversal 

C33n-C32r at Hunter Wash and Chimney Rock (73.39 Ma 

to 73.71 Ma, fi g. 16) is only 0.32 m.y. This extremely tight 

grouping provides confi dence in the accuracy of the agedetermination process. It must be emphasized, however, that 

all of the calculations described above are based on an assumption of a linear rate of sediment accumulation between dated 

ash beds, and, as fi gure 17 illustrates, this is probably not the 

case. Fortunately, with eight dated ash beds distributed over 

a rock interval of 1,260 ft, potential errors due to changes 

in sediment-accumulation rates within intervals between the 

ash beds are minimized. Also, the geometry of the Pictured 

Cliffs Sandstone, as portrayed in map view (fi g. 8) and cross 

section (fi g. 13 and plate 1), provides an independent check 

on changes in sediment-accumulation rates. The age of the 

magnetic-polarity reversal from chron C33n to C32r in the San 

Juan Basin as determined in this report of 73.50±0.19 Ma. 

confi rms the age determination of Steiner and Fassett (1997) 

of 73.50±0.18 Ma. The biochronologic age of the C33n-C32r 

reversal in terms of Western Interior ammonite zones is B. 

compressus (fi g. 13). 

Rates of Sediment Accumulation and 

Pictured Cliffs Shoreline Regression

Figures 17A and 17B are chronostratigraphic charts for 

the Hunter Wash and Chimney Rock areas, respectively. Rates 

of sediment accumulation (decompacted rates) for the Hunter 

Wash area (fi g. 17A) vary from a low of 412 ft per million 

years for the interval between ashes H and J to a rate of 2,462 

ft per million years for the interval between ashes LP and 2. 

The sediment-accumulation rate for the Chimney Rock area 

(fi g. 17B) between beds HBB and CR is 1,086 ft/m.y., and 

between CR and the C33n-C32r reversal it is 373 ft/m.y. (fi g. 

17B). The overall average rate of sediment accumulation for 

the time of Pictured Cliffs Sandstone regression across the 

present basin area is 847 ft/m.y. at Hunter Wash and 850 

ft/m.y. at Chimney Rock (fi g. 17). 

Ash DEP 75.56 0.41 Ma

Ash HBB 75.76 0.34 Ma

Ash 2 74.56 0.13 Ma

Ash 4 74.55 0.29 Ma

Ash LP 74.30 0.38 Ma

Ash CR 74.25 0.13 Ma

Ash J 73.04 0.25 Ma

Ash H 73.37 0.18 Ma

C32r

C33n

+- +- +- +-

REVERSAL

J/CR

+ 

-

J/LP J/4 J/2 J/DEP J/HBB

+- + 

- +- +- +-

H/CR

+ 

-

H/LP H/4 H/2 H/DEP H/HBB

-

+

-

+

-

+

-

+

-

+

-

+

+-

+-

 73.68

 0.14 + 

-

 73.39

 0.20

 73.44

 0.22 73.44

 0.22 73.46

 0.20

 73.71

 0.12

 73.61

 0.16 73.54

 0.16 73.58

 0.17 73.58

 0.16

 73.53

 0.22 73.58

 0.17

Figure 16. Interpolated ages and uncertainties (in millions of years) for magnetic polarity reversal C33n-C32r in the Hunter Wash area. Black 

is normal polarity, white is reversed polarity. Mean interpolated age of the reversal using all ash beds is 73.54±0.17 Ma; mean age for the fi ve 

Hunter Wash ash beds is 73.50±0.19 Ma. Ash beds shown in blue are projected into the Hunter Wash section. Ash-bed ages are from tables 

1 and 4. Ash-bed localities are shown on fi gure 13. 

Geology and Coal Resources of the Upper Cretaceous Fruitland Fm., San Juan Basin, New Mexico and Colorado Q29
Time scale

 in m.y.

Time scale

 in m.y.

82

(136)

398

(712)

351

95

157

lower shale

member of

Kirtland Fm.

and Fruitland

Formation

Pictured Cliffs

Sandstone

Lewis Shale

Stratigraphic

column

Ash bed

name Rock thick.

 (feet)

Interval

duration

.33 m.y.

0.93 m.y.

1.00 m.y.

.20 m.y.

Rock rate

 (ft/m.y.)

248

428

351

475

Feet above

Huerfanito

Totals: 1,260 ft 2.72 m.y. 463

95

0

1,260

1,178

446

780

75.0

74.0

73.5

65.0

74.5

75.5 DEP

HBB

75.56

75.76

74.56 2

J

H

73.04

73.37

C33n

C32r 1,075

A - Hunter Wash area

B - Chimney Rock area

Ojo Alamo Ss

Farmington

Sandstone

Member of

Kirtland Fm.

Decompacted.

rate (ft/m.y.)

Decompacted.

rate (ft/m.y.)

73.50

412

766

(673) 673

(142) 710

(2,303 ft) 847

Totals: 1,066 ft 2.26m.y.

463

(1,920 ft) 850

(1,640)

40Ar/39Ar

ages Ma

74.30 LP

 334

(640) .26 m.y. 1,285 2,462

472

40Ar/39Ar

ages Ma

C33n

C32r

Magneticpolarity

reversal

Magnetic-

 polarity

 reversal

Fruitland

Formation

Pictured Cliffs

 Sandstone

Lewis Shale

Stratigraphic

column

Ash bed

name Rock thick.

 (feet)

Interval

duration

Feet above

Huerfanito

0

909

909 602

209

1.51 m.y. 1,086

.75 m.y.

75.0

74.0

73.0

73.5

74.5

75.5

75.76 HBB

1,066

74.25 CR

Rock rate

 (ft/m.y.)

(280) 373

73.50

(interpolated age)

Figure 17. Chronostratigraphic charts for A, Hunter Wash area, and B, Chimney Rock area. Ages of ash beds, 

thicknesses of intervals between dated ash beds, and distances above the Huerfanito Bentonite Bed for dated ash 

beds are shown. Ash bed 4 is not shown because it has the same age as ash 2 and the age for ash 2 is more 

precise. Rock rates (duration in m.y./thickness of rock interval) and rates of sediment accumulation (duration in 

m.y./decompacted rock thickness) are also shown. Decompacted rock thicknesses are shown in parentheses in 

“Rock thick.” column; these thicknesses were estimated from data generated by the BasinMod software program. 

Ash beds shown with dashed line are projected into the sections. Ash-bed collection localities are shown on 

fi gure 13.

Q30 Geologic Assessment of Coal in the Colorado Plateau: Arizona, Colorado, New Mexico, and Utah
The large volcanic eruptions that produced the Hunter 

Wash, Chimney Rock, and La Plata mine ash beds were 

random events. Not all ash falls that occurred in Campanian 

time are preserved in the rock record, and not all ash falls that 

are preserved contain sanidine crystals that can be radiometrically dated. Rates of sediment accumulation between dated ash 

falls, therefore, are averages for random intervals, and the ash 

beds themselves in no way mark boundaries where changes in 

rates of sediment accumulation took place as fi gure 17 might 

appear to indicate. 

Figure 18 shows the approximate positions of Pictured 

Cliffs shorelines at the times ash beds DEP, 2, 4, LP, CR, and 

H were deposited. (The shoreline position for ash bed J is 

at the 1,260-ft level above the Huerfanito Bed and is thus at 

or just beyond the outcrop of the Fruitland Formation in the 

northeast part of the basin.) Shoreline positions corresponding 

to dated volcanic ash beds (ash falls) are projected on the 

Huerfanito–Pictured Cliffs Sandstone isopach map (fi g. 18) 

based on their distances above the Huerfanito Bentonite Bed 

(fi g. 17). The distance between the Pictured Cliffs shoreline 

position at the time ash DEP was deposited and its position 

when ash 2 was deposited is about 25 mi, measured along 

the line of cross section HW-CR (fi g. 18). The time difference 

between these ash beds is 1 m.y.; thus the average rate of 

shoreline regression for this interval was 25 mi/m.y. (Ash beds 

2 and 4 have essentially the same ages, thus, the time interval 

between them cannot be used to determine rates of shoreline 

regression. Similarly, ash beds LP and CR have virtually the 

same age and so cannot be used to measure rates of shoreline 

regression.) The distance between shorelines 2 and CR is 37 

mi with a time difference of 0.31 m.y. for a regression rate 

of 119 mi/m.y. The distance between shorelines CR and H 

is 16 mi with a time difference of 0.88 m.y., yielding a regression rate of about 18 mi/m.y. The distance across the basin 

from shoreline DEP to shoreline H is 78 mi; the time difference between these two ash beds is 2.19 m.y. for an average 

shoreline regression rate of 36 mi/m.y. 

In human terms, the average rate of Pictured Cliffs shoreline retreat from Hunter Wash to Chimney Rock was 0.04 mi, 

or 211 ft per thousand years, 2.11 ft per 100 years, or .02 ft or 

LA PLATA

ARCHULETA

SAN JUAN

McKINLEY

MONTEZUMA

108° 107°

 37° 37°

 36° 36°

108° 107°

COLORADO

NEW MEXICO

Farmington

Dulce

Cuba

Durango

SANDOVAL

RIO ARRIBA

Study

area

CO

NM

250

500

750

750

750

1000

1250

700

Ash

Ash 2

Ash 4

74.56 Ma

74.55 Ma

75.56 Ma DEP

Outcrop of Fruitland

 Formation 74.25 Ma

73.50 Ash CR

900

Ash LP

74.30 Ma

 73.37 Ma Ash H

Ma

R

R

3

4

5

6

7

8

11

1

2

HW

CR

EXPLANATION

Paleoshorelines at

times dated ash falls

occurred 

Paleoshoreline at

time of C33n-C32r

reversal 

0 5 10 15 20 MILES

Kf

Kf

9

10

Figure 18. Map showing positions of Pictured Cliffs Sandstone shorelines at times 

when dated San Juan Basin ash beds were deposited and when paleomagnetic reversal C33n-C32r occurred. Ages of ash beds from table 4. Kf, Fruitland Formation; HW, 

Hunter Wash; CR, Chimney Rock. Cross section HW-CR is on fi gure 13. HuerfanitoPictured Cliffs isopach lines from fi gure 8.

Geology and Coal Resources of the Upper Cretaceous Fruitland Fm., San Juan Basin, New Mexico and Colorado Q31
0.2 inch per year. The average rate of sediment accumulation 

during this same time period was 925 ft per million years, 0.93 

ft or about 11 inches per thousand years, 0.9 inch per 100 

years, or 0.009 inch per year. (This thickness is equal to about 

the lower end of the diameter of a fi ne-grained particle (1⁄4 mm) 

on the Wentworth scale. Thus to move the shoreline back 0.2 

inch in a year required a sediment delivery rate to the shoreline 

equivalent to a thickness of 0.009 inch or a layer of very fi ne to 

fi ne-grained sandstone one grain thick.) 

Comparing the shoreline-position map of fi gure 18 with 

the cross section HW-CR on fi gure 13, the period of relatively 

slow deposition (673 ft/m.y., fi g. 17) and slow regression (25 

mi/m.y.) between ash beds DEP and 2 corresponds to the large 

vertical buildup and thickening of the Pictured Cliffs Sandstone between wells 1 and 4 on fi gure 13. Between shoreline 

positions 2 and CR (fi g. 18) the rate of sediment accumulation 

was high (2,700 ft/m.y.) and the rate of shoreline regression 

was fast (119 mi/m.y.). In cross section (fi g. 13), the Pictured 

Cliffs is relatively thin from about well 4 to between wells 8 

and 9, refl ecting this episode of rapid sediment accumulation 

and rapid shoreline regression. Between shoreline positions 

CR and H, the sediment-accumulation rate decreased (550 

ft/m.y.) and the rate of shoreline regression slowed to 18 

mi/m.y. Figure 13 again refl ects these changes with a large 

vertical rise in the stratigraphic level of the Pictured Cliffs 

Sandstone between wells 9 and 11. These changes in the 

rates of sediment accumulation and shoreline regression had a 

profound affect on the accumulation and distribution of coal in 

the Fruitland Formation, as will be discussed in detail in the 

“Fruitland Coal Resources” section of this report.

Rate of Subsidence of San Juan Basin Area 

During Pictured Cliffs Time

Figure 19 shows the location of the San Juan Basin area 

on the western edge of the Western Interior Seaway during the 

time the Pictured Cliffs Sandstone shoreline regressed across 

the basin area. Sediment accumulation and shoreline movements in the San Juan Basin area were controlled by two principal variables: the rate of creation of accommodation space 

and the rate of sediment delivery to the shoreline by rivers. 

The creation of accommodation space has two basic components—tectonic subsidence and eustatic sea-level change. 

Jervey (1988) observed, in his general discussion of the concept of accommodation space, that if the rate of subsidence 

greatly exceeded the rate of sea-level rise or fall, then no 

apparent change in the rate of creation of accommodation 

space would result from changes in sea level. In his words (p. 

47, 48), “At points in the basin where extremely rapid subsidence prevails, no decrease in accommodation is experienced, 

even though sea level is falling.” Because the rates of subsidence in the San Juan Basin (and, indeed, in much of the Western Interior Seaway) were extremely rapid throughout much 

of Late Cretaceous time, changes in eustatic sea level that 

may have occurred would have had no perceptible affect on 

the creation of accommodation space. Thus, accommodationspace creation in the San Juan Basin during the time that the 

Pictured Cliffs Sandstone was being deposited was essentially 

controlled by the rate of subsidence.

The average rate of sediment accumulation during Pictured Cliffs regression was 850 ft/m.y. (fi g. 17) and the rate of 

shoreline movement averaged 36 mi/m.y. Because the shoreline regressed 78 mi across the basin area (fi g. 18) between 

about 76 Ma and 73 Ma (fi g. 19), the rate of sediment 

infl ux during this time period must have exceeded the rate of 

basin subsidence. To try and separate the rate of basin subsidence from the sediment-supply rate, it is necessary to focus 

on segments of the rock record that record times when shoreline regression ceased and shoreline transgression occurred 

because, at those times, sediment-accumulation rates must 

have been lower than subsidence rates. 

Plate 1 shows that there are two places in the basin 

where the Pictured Cliffs Sandstone is signifi cantly thicker and 

intertongues with the overlying Fruitland Formation: between 

holes 15 and 17 and between holes 17 and 20. The tongues 

of Pictured Cliffs Sandstone in the Fruitland at hole 16 and 

at holes 18 and 19 (plate 1) represent times when the rate of 

sediment accumulation must have been less than the rate of 

basin subsidence, causing the Pictured Cliffs shoreline to halt 

its regression and briefl y transgress over the backshore swamp 

deposits of the Fruitland. Figure 13 shows the stratigraphic 

positions of the dated ash beds discussed in this report. Fortuitously, the intervals between ash bed CR and the C33n-C32r 

reversal (between holes 7 and 10) and ash beds H and J (in 

holes 10 and 11) on fi gure 13 include tongues of Pictured 

Cliffs Sandstone that represent transgressions of the shoreline.

The interval between ash bed CR and the C33n-C32r 

reversal (between holes 7 and 10, fi g. 13) contains, in its 

lower part, a large Pictured Cliffs Sandstone tongue in the 

Fruitland that represents a signifi cant southwestward transgression of the Pictured Cliffs shoreline nearly to hole 7. The top 

of this tongue represents an extremely rapid regression of the 

shoreline to a position northeast of hole 9 and then a stabilization of the location of the shoreline to well above the level of 

the C33n-C32r reversal. Stratigraphically, this interval can be 

divided into successive episodes of (1) shoreline transgression, 

(2) rapid regression, and (3) shoreline stabilization. Because 

373 ft/m.y. is an average sedimentation rate for this interval 

(fi g. 17B), the time of transgression of the Pictured Cliffs 

tongue in the lower part of this interval must represent a period 

of sediment accumulation less than the average of 373 ft/m.y., 

possibly 350 ft/m.y. Therefore, the basin-area subsidence rate 

must have been approximately 350–375 ft/m.y. during this 

time interval.

The interval between ash beds H and J (in holes 10 and 

11, fi g. 13) contains two transgressive tongues of Pictured 

Cliffs separated by vertical upbuilding of the Pictured Cliffs 

representing times of (1) a brief transgression of the shoreline, 

(2) rapid regression, and (3) a longer episode of shoreline 

transgression and stabilization. Because the average sedimentation rate for this interval is 412 ft/m.y., the times of transgression of the Pictured Cliffs tongues in this interval must 

Q32 Geologic Assessment of Coal in the Colorado Plateau: Arizona, Colorado, New Mexico, and Utah
Western

Interior

Seaway

79

Ma

72

Ma

Alluvial plain

and highlands

Shoreface Shallow

marine

Thrust fault

Coal-forming 30° Paleolatitude

Swamps 

Present-day

shoreline

USA-Mexico

border

EXPLANATION

Paleoshorelines,

San Juan Basin

76 Ma

73 Ma

SJB

45°

30°

30°

45°

Sevier Highlands

WESTERN

INTERIOR

SEAWAY

Figure 19. Paleogeographic map of western North America in latest Campanian time: 79 to 72 Ma (Late Cretaceous). 

Position of San Juan Basin (SJB) is shown in red. Paleoshoreline positions and ages for the Pictured Cliffs Sandstone in 

vicinity of San Juan Basin are shown. Map is modifi ed from fi gure 19 of Roberts and Kirschbaum (1995).

Geology and Coal Resources of the Upper Cretaceous Fruitland Fm., San Juan Basin, New Mexico and Colorado Q33
represent times of sediment accumulation less than the average 

of 412 ft/m.y., possibly 350 ft/m.y. Therefore, the basin-area 

subsidence rate must have been approximately 350–412 ft/m.y. 

during this time interval. The rate of subsidence of the San 

Juan Basin area during the regression of the Pictured Cliffs 

Sandstone shoreline is thus estimated to have been about 375 

ft/m.y. When the rate of sediment supply exceeded 375 ft/m.y., 

regression occurred; when it fell below this threshold, transgression of the Pictured Cliffs shoreline took place.

Depositional Model for Lewis/

Pictured Cliffs/Fruitland System

This Report

As discussed above, two principal interactive processes 

control rates of shoreline regression: the rate of creation of 

accommodation space and the rate of sediment infl ux. Figure 

20 is a diagrammatic portrayal, in cross section, of the dynamics of the deposition of the Pictured Cliffs Sandstone and associated rocks during the time that the Pictured Cliffs shoreline 

regressed across the basin area. This fi gure is greatly simplifi ed 

in order to focus on the basic elements of this depositional 

model. In the three panels, the downward-pointing arrows are 

meant to indicate a constant and even subsidence rate for the 

basin area throughout the time represented. At time A, the 

shoreline is at the extreme left side of the diagram and the 

volcanic ash fall that will ultimately become the Huerfanito 

Bentonite Bed has just been deposited on the seafl oor. From 

time A to time B, sediment infl ux has exceeded the rate of 

subsidence and the shoreline has migrated to the right to about 

the middle of the diagram. Between times A and B, sediment 

has been more or less uniformly distributed across the entire 

area. At time B, continental sediments are accumulating on 

the left, marine shoreface sediments in the center, and offshore 

marine rocks are accumulating to the right. Note that the 

subaerial surface of deposition is essentially continuous with 

the shoreface and submarine surfaces of deposition and the 

combined surfaces have the same slope. (The beach environment is shown as being slightly elevated above the backshore 

area; the magnitude of this elevation is greatly exaggerated on 

this diagram.)

As the shoreline regressed, sediment was being deposited 

simultaneously in the continental, shoreface, and marine environments. Sediment size graded from the beach environment 

where relatively well sorted, fi ne- to medium-grained sandstones were being deposited out into the marine realm where 

clay-sized material was being distributed evenly across the 

shelf. The continuous continental-shoreface-marine surface of 

deposition was, of course, always a time line in cross section 

and a time plane in three dimensions. Note that in the panel 

representing time B, this surface of deposition is parallel to 

the Huerfanito Bentonite Bed. Another hypothetical time line 

is shown in the time B panel to emphasize the parallelism of 

depositional surfaces in this model.

At time C (fi g. 20) the shoreline had regressed all the 

way to the right side of the diagram. During this period 

of regression, sediment infl ux continued to exceed the rate 

of subsidence and sediment was evenly dispersed across the 

continental-shoreface-marine surface of deposition. From time 

B to time C, the surface of deposition maintained a consistent 

slope, resulting in time lines and planes continuing to be parallel surfaces so that the surface of deposition at time C was 

still parallel to the Huerfanito Bentonite Bed. A comparison 

of the stratigraphic cross section on fi gure 13 drawn with 

the Huerfanito as a datum shows the same basic relations of 

the continental, shoreface, and marine rocks as shown on the 

time-C panel of fi gure 20. The validity of this model of deposition for the Lewis/Pictured Cliffs/Fruitland is confi rmed by the 

two isochrons shown on fi gure 13: the Huerfanito Bentonite 

Bed and the magnetic polarity reversal from chron C33n to 

C32r are essentially parallel as the depositional model depicted 

on fi gure 20 predicts. 

Ayers Model

A new and substantially different model for deposition of 

the Fruitland Formation, its coal beds, and associated rocks 

was presented by Ayers and Ambrose (1990) and Ayers and 

others (1994). This model (herein called the Ayers model) 

suggested that differential tectonism within the San Juan Basin 

had controlled the regression of the Pictured Cliffs Sandstone 

shoreline and accumulation of Fruitland coal beds. The Ayers 

model was offered as an alternative to the model for deposition 

of the Fruitland Formation and associated rocks presented in 

Fassett and Hinds (1971). (The Fassett and Hinds model is 

essentially the same as the model of this report.) 

Whitehead (1993, fi gs. SJ 1.7, SJ 1.10) presented the Ayers 

model as a valid alternative to the model of Fassett and Hinds 

(1971). In a discussion of the origin of Fruitland Formation coal 

beds in the San Juan Basin, Whitehead stated (p. 119),

These coal deposits are interpreted (Ayers et al., 1991) [sic—the 

date for this citation is actually 1990] as coastal swamps 

that accumulated landward of the wave-dominated Pictured 

Cliffs shoreline. Increased subsidence northeast of an inferred 

hingeline created accommodation space allowing thick, strikeelongate Pictured Cliffs sandstones and Fruitland peats to form 

(Ayers and Zellers, 1988; fi g. SJ-1.10a). In this model, coal 

beds are extensive and may override Pictured Cliffs barrier 

sandstones. Alternatively, uniform aggradation of the area has 

been proposed (fi g. SJ-1.10b) using the Huerfanito Bentonite as 

a datum (Fassett and Hinds, 1971; Fassett, 1987). In this model, 

coal seams terminate against the Pictured Cliffs sandstone 

tongues, and thus the coal beds are much less extensive.

Because two confl icting models have been offered for 

deposition of the Pictured Cliffs Sandstone, the Fruitland Formation and its contained coal beds, and associated rocks, it is 

necessary to evaluate and compare these models to determine 

which one best fi ts the available data. 

Q34 Geologic Assessment of Coal in the Colorado Plateau: Arizona, Colorado, New Mexico, and Utah
Shoreline

Shoreline

Seafloor

Sea level

Volcanic ash fall

(Huerfanito Bentonite Bed)

Seafloor

Seafloor

Sea level

Huerfanito Bentonite Bed

Huerfanito Bentonite Bed

Time A

Time B

Time C

Land surface

Land surface Coal swamps

Coal swamps

EXPLANATION

Continental

Coal-bearing

Shoreface

Marine

TIME LINE

TIME LINE

TIME LINE

TIME LINE

TIME LINE

TIME LINE

Normal polarity

Reversed polarity

(paleomagnetic field reversal)

Figure 20. Diagrammatic time-sequence diagrams showing in cross section the deposition of a regressive shoreface 

sand and associated marine and continental sediments at three points in time. The arrows at the bottom of each 

sequence are meant to indicate continuous, even subsidence of the basin area as these rocks were being deposited. 

After Fassett (1987).

Geology and Coal Resources of the Upper Cretaceous Fruitland Fm., San Juan Basin, New Mexico and Colorado Q35
Figure 21 shows a northeast-trending stratigraphic cross 

section across the San Juan Basin taken from Ayers and 

Ambrose (1990) and Ayers and others (1994). This cross section (fi gure 2.2 of Ambrose and Ayers, 1994) is described 

and discussed in detail in Ayers and Zellers (1994). The cross 

section is constructed using the contact between the Fruitland 

Formation and the lower shale member of the Kirtland Shale 

as a datum. The stratigraphic cross sections on plate 1 and 

fi gure 13 that illustrate the depositional model of this report 

have the same northeast orientation and are close to the line 

of section of fi gure 21 of the Ayers reports; traces of the three 

sections are shown on the index map on fi gure 21.

Ayers and Zellers (1994) discuss the depositional setting 

for the Pictured Cliffs Sandstone and the Fruitland Formation 

and state (p. 73), “Principal aspects of these relations are summarized ... in the depositional model (Ayers and others, this 

volume, fi g. 2.20).” They discuss the geologic history of the 

Pictured Cliffs Sandstone regression as follows (p. 83):

The Pictured Cliffs shoreline prograded rapidly basinward 

across the southern half of the basin. After the shoreline 

crossed the structural hingeline, sporadic structural activity 

began and the northern part of the basin subsided more rapidly 

to accommodate greater thickness of sediment. The changing 

balance between sediment input and pulsatory subsidence 

FARMINGTON SANDSTONE MEMBERS

FRUITLAND FORMATION

PICTURED CLIFFS SANDSTONE

LEWIS SHALE

Huerfanito Bentonite Bed

C32r

C33n

LOWER SHALE MEMBER

UPPER SHALE AND 

KIRTLAND

SHALE

UP 3 UP 2 UP 1

New Mexico Colorado

Northeast

Southwest

Stratigraphic marker (of Ayers and others, 1994)

3143 1527 1503 1426 1403 1354 1343 1247 1256 1143 1135 3157 237 106 3158 3159 1576 1738 1762

DATUM

HingeLine

0

0

400

20 miles

Feet

73.50 Ma

75.76 Ma

EXPLANATION

Paleomagnetic reversal (of Fassett and Steiner, 1997)

OJO ALAMO SANDSTONE

0 10 20 30miles

Durango

Farmington

Cuba

109 108 107 

37 

36 

COLORADO

NEW MEXICO

UTAH ARIZONA

Pagosa

Springs

Fruitland

Formation

outcrop

Chimney

Rock site

Hunter

Wash area

 Fig. 2.2 

A&O (1994) 

HW-CR

(fig. 13)

 A-A'

(plate 1) ●

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●

Figure 21. Stratigraphic cross section redrawn from Ayers and others (1994, fi g. 2.2); vertical exaggeration is 132 x. 

Line of this section is labeled “Fig. 2.2 A&O (1994)” on index map. Vertical breaks in coal beds indicate fractures in 

continuous coal beds, according to Ayers and others. Paleomagnetic reversal from normal polarity (C33n) to reversed 

polarity (C32r) has been drawn on this cross section to show the true attitude of a time line in this rock sequence. 

Magnetic polarity data and radiometric ages are from Fassett and Steiner (1997). “HW-CR (fi g. 13)” on index map is 

line of section for stratigraphic cross section on fi gure 13 of this report. “A-A’ (plate 1)” on index map is line of section 

for cross section A-A’ on plate 1 of this report.

Q36 Geologic Assessment of Coal in the Colorado Plateau: Arizona, Colorado, New Mexico, and Utah
north of the hingeline resulted in oscillation and aggradation of 

the shoreline, accounting for the most signifi cant stratigraphic 

rise of the Picture Cliffs in the basin .... Further testing is needed 

to verify the existence of the structural hingeline; seismic 

studies would be especially useful.

The Ayers depositional model (fi g. 21) is the fi rst model 

to suggest that tectonic events caused the accumulation of 

thick, vertical buildups of the Pictured Cliffs Sandstone and 

thick Fruitland coals in the north-central San Juan Basin. 

Figure 21 shows the top of the Pictured Cliffs Sandstone as a 

relatively fl at surface across the southwest half of the basin. 

In the north-central part of the basin, the top of the Pictured 

Cliffs is shown as gently curving downward. In the northeast 

part of the basin, three tongues of sandstone labeled upper 

Pictured Cliffs 1, 2, and 3 are shown stacked on top of the 

Pictured Cliffs proper. The Huerfanito Bentonite Bed is shown 

dipping into the Lewis Shale parallel to several other Lewis 

Shale “stratigraphic marker” beds. These beds are time lines, 

according to Ayers and others (1994), that represent deposits 

on successive, Lewis Shale clinoform surfaces. The datum for 

this cross section is the base of the lower shale member of the 

Kirtland Shale, a horizontal time line in continental deposits. 

Another “stratigraphic marker” and time line is shown in the 

Farmington Sandstone Member of the Kirtland Shale parallel 

to the lower shale member contact. Fruitland Formation coal 

beds are shown to be continuous across most of the length of 

this cross section and exhibit a stratigraphic rise over the sandstone unit labeled Pictured Cliffs 1, 2, and 3 in the northeast 

(correlations of Fruitland coal beds are discussed in detail in 

the “Fruitland Coal-Bed Correlations” sections of this report). 

Ayers and others attribute the geometry of the rock units 

shown on fi gure 21 to a tectonic bending of the basin area over 

a “hingeline” at the time these rocks were being deposited. 

(The location of the “hingeline” is shown at the bottom of their 

cross section (fi g. 21); this “hingeline” is further discussed in 

the “Basin Structure” section of this report).

The depositional model illustrated by fi gure 21 can be 

criticized for many of its details but the basic nature of the 

model does not survive the simple test of superimposing the 

magnetic polarity reversal between magnetic chrons C33n and 

C32r on this illustration. As discussed in the “Upper Cretaceous Chronostratigraphy of the San Juan Basin” section of 

this report, the C33n-C32r magnetic-polarity reversal represents a virtually instantaneous geologic event and is thus a 

time plane in three dimensions. When this time line is drawn 

on fi gure 21 at its proper orientation at a level 1,076 ft above 

the Huerfanito Bed, it is clear that the portrayal of time lines 

on fi gure 21 by Ayers and others, especially in the continental 

Fruitland and Kirtland, is incorrect. If the Ayers and others 

model were correct, the C33n-C32r reversal would be within 

the Farmington Sandstone Member across the basin and would 

be parallel to the base of the lower shale member of the 

Kirtland Formation and the “stratigraphic marker” shown in 

the upper part of the Farmington Sandstone Member, which 

it clearly is not. The entire weight of the evidence compiled 

to date for the chronostratigraphy of the Lewis/Pictured Cliffs/

Fruitland depositional system supports the depositional model 

portrayed on fi gure 13. 

Roberts and McCabe (1992, p. 119) also challenged the 

interpretation of Ayers and others and wrote:

Ayers and Zellers (1991) use the base of the Ojo Alamo 

Sandstone as a datum to show that Fruitland Formation 

coal beds migrated over Pictured Cliffs shoreline sandstones. 

However, the base of the Ojo Alamo Sandstone is an erosional 

surface that truncates underlying formations from northwest to 

southeast across the basin (Fassett and Hinds, 1971). In addition, 

the base of the Ojo Alamo is Tertiary in age whereas the 

Huerfanito Bentonite is much closer in age (Campanian) to the 

Fruitland and may be genetically related, as discussed above. 

We do not agree with Ayers and Zellers’ (1991) premise that 

individual coal beds can be parallel to the Huerfanito Bentonite 

Bed only if the stratigraphic rise of the Fruitland Formation is due 

entirely to eustasy or to uniform basin subsidence: Fassett (1987) 

has clearly shown that the base of the Fruitland is diachronous.

Basin Structure

Huerfanito Bentonite Bed Structure

Figure 22 is a structure map of the San Juan Basin contoured on the Huerfanito Bentonite Bed of the Lewis Shale. 

Geophysical logs from 350 drill holes were used as control 

points for this map. The Huerfanito Bed is most easily distinguished in the southern two-thirds of the basin on conductivity 

logs. The Huerfanito 60-4 well (hole 9, plate 1), the type log 

for the Huerfanito Bentonite Bed (Fassett and Hinds, 1971, fi g. 

2, p. 6), shows the distinctive log signature of the Huerfanito 

Bed on the conductivity log. In the northern part of the basin, 

the gamma-ray log is a better tool to distinguish the Huerfanito 

on geophysical logs. (A more detailed discussion of the character of the Huerfanito Bentonite Bed on geophysical logs is 

in Fassett and Hinds, 1971, p. 6, 8, and fi g. 3.) As discussed 

above, in some parts of the basin, primarily in the north-central 

part, there is no recognizable response to the Huerfanito on 

any geophysical logs, and it is thought that in those areas the 

ash fall was dispersed and destroyed by currents moving along 

the seafl oor. Although Huerfanito control points are somewhat 

sparse in the northern part of the basin (fi g. 22), there are 

still suffi cient points to delineate the basin structure there. 

Because 100-ft contours do not add signifi cant detail outside 

the 3,000-ft contour line, only 500-ft contour lines are shown 

on fi gure 22 in those areas.

The structural axis of the San Juan Basin is in the northcentral part (fi g. 22) where the basin fl oor is irregular. The 

deepest part of the basin is outlined by the 2,100-ft contour 

line in a relatively small northwest-trending area. The 2,200- 

and 2,300-ft contour lines show a northwest trend but bend 

around a southeast-trending structural nose (fi gs. 22, 23). 

Some smaller structural wrinkles are indicated by the 2,700- 

and 2,800-ft lines in the northwest part of the basin.

Geology and Coal Resources of the Upper Cretaceous Fruitland Fm., San Juan Basin, New Mexico and Colorado Q37
Figure 22. Contour map of the Huerfanito Bentonite Bed of the Lewis Shale. Structural profi le is on fi gure 23.

ARCHULETA

LA PLATA

SAN JUAN

McKINLEY

RIO ARRIBA

SANDOVAL

MONTEZUMA

108 ̊ 107 ̊

 37 ̊

 36 ̊ 36 ̊

108 107 

COLORADO

NEW MEXICO 37 ̊

Outcrop of Fruitland

 Formation

Kf

Kf

Farmington

Dulce

Ignacio

Durango

Cuba

0 5 10 15 20 MILES

R 13 W

R 16 W 15

T 19 N

20

21

22

23

24

25

26

27

28

29

30

31

32

32

33

34

T 35 N

R 1 W R 1 E

R 1.5 W

2

R 1 W

2.5 R 16 W 15 14 13 12 11 10 9 8 7 6 5 4 3

6 5 4 3 2

7

8

9

10

11 12

T 34 N

 (NUL)

T 34 N

 (SUL)

R 1 W R 1 E

2 13 12 11 10 9 8 7 6 5 4 3

14

T 34.5 N

T 34 N (NUL)

T 34 N

 (SUL)

2500

3000

3500

4000

4500

5000

5500

6000

3000

3500

4000

4500

5000 5500

2500

6000

6500

5500

3000

2500

5000

4500

3500

4000

EXPLANATION

●

Control points are oil or gas wells or tests

Depths to Huerfanito Bentonite Bed from geo-

 physical logs. Datum is mean sea level. Contour

 interval is 500 and 100 feet. "T 34 N (NUL)" is 

 north of Ute line, "T 34 N (SUL)" is south of Ute

 line. Kf = Fruitland Formation. 

Study

area

COLORADO

NEW MEXICO

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Q38 Geologic Assessment of Coal in the Colorado Plateau: Arizona, Colorado, New Mexico, and Utah
Figure 23 shows a northeast-trending structural profi le of 

the Huerfanito Bed across the basin. This line of profi le is 

curved to maintain a right-angle orientation to the Huerfanito 

structure lines and to pass through the structurally deepest part 

of the basin (fi g. 22). The Huerfanito profi le is at the 6,000-ft 

level in the southwest, dips gently to a structural deep slightly 

below the 2,100-ft level nearly 75 mi to the northeast, and rises 

steeply over the last 12 mi to the 6,500-ft level on the northeast 

edge of the basin. A prominent structural hinge point is present 

in the northeast in the deepest part of the basin (fi g. 23). 

The regional dip of the Huerfanito Bed averages 0.80°

from the southwest part of the basin to a structural fl exure 

shown with an arrow labeled FP1 (fi g. 23). This fl exure is at an 

elevation of about 2,750 ft. Between the southwest edge of the 

basin and FP1, three minor fl ex points occur and dips between 

these points range from 0.56° to 0.97°.) Between FP1 and FP2, 

at the next fl exure point (elevation of about 2,500 ft), the dip of 

the Huerfanito decreases to 0.52°. And between FP2 and FP3, 

(elevation of about 2,200 ft), the dip fl attens to 0.23°. Between 

FP3 and LP, the lowest point on the Huerfanito structural 

profi le on fi gure 23, the dip of the Huerfanito reverses over a 

structural nose. And, fi nally, between the structural hinge point 

and the northeast end of the line of profi le, the Huerfanito rises 

evenly toward the surface with an average dip of 4.6°.

Ayers and others (1994) attached great signifi cance to 

the area of structural fl exure between points FP1 and FP2 on 

fi gure 23. On their Huerfanito structure map (their fi gure 2.5) 

they show a linear feature that, for the most part, follows the 

2,600-ft Huerfanito structure-contour line. They labeled this 

line “structural hingeline” and in their discussion of the feature 

stated (p. 18):

An inferred structural hingeline coincides with the 2,600-ft 

contour at the southwestern margin of the basin fl oor and 

projects to crop out at the La Plata mine (fi g. 2.5).... This 

structural hingeline is interpreted to be a zone of complex, 

northwest-trending, en echelon normal faults, with net 

downdrop to the north; width of the zone is 6 to 10 mi. Its 

presence is inferred from the coincidence of geologic anomalies 

that are apparent in regional maps and cross sections.

Ayers and others (1994, p. 18) list nine “geologic anomalies” that occur at the “hingeline” including “marked thickening of the interval from the Huerfanito Bentonite to the top of 

the uppermost Pictured Cliffs sandstone”, changes in marker 

beds in the Lewis Shale, changes in thermal maturity patterns, 

and changes in coal-bed methane composition. Elsewhere in 

their report they stated (p. 37, 38):

... we conclude that syndepositional tectonic activity controlled 

the depositional system [Pictured Cliffs Sandstone and Fruitland 

Formation] and, indirectly, the occurrence of thick Fruitland coal. 

Pulsatory differential subsidence across the hingeline at the 

southwestern margin of the basin fl oor caused a relative sealevel rise, which resulted in stillstands of the Pictured Cliffs 

shoreline. 

B

New Mexico Colorado

Northeast

Southwest

A

STRUCTURAL

HINGE POINT

2000

3000

4000

5000

6000

2000

3000

4000

5000

6000

7000

FP3 FP2 FP1

LP

Average dip = 0.23 0

Average dip = 0.80 0 Av. dip = 0.520

Average dip = 4.6 0

Structural

 nose

TOP - PICTURED

CLIFFS SANDSTONE

HUERFANITO

BENTONITE BED

 TERTIARY

 AND

UPPER CRETACEOUS

 ROCKS

Figure 23. Structural profi les for Huerfanito Bentonite Bed and top of Pictured Cliffs Sandstone (base of Fruitland 

Formation) across San Juan Basin. Lines of profi le are slightly different in the structurally deepest part of the basin. Profi le 

lines are shown on fi gures 22 and 24. Vertical exaggeration for view A is x 24; view B has no vertical exaggeration. FP1, 

FP2, and FP3 are fl ex points where the structural dip changes in the Huerfanito Bed. LP is lowest structural point on the 

Huerfanito Bed in the basin.

Geology and Coal Resources of the Upper Cretaceous Fruitland Fm., San Juan Basin, New Mexico and Colorado Q39
It is clear from this statement that these authors thought 

that the “inferred structural hingeline” had been a signifi cant 

tectonic element in the San Juan Basin at the time that the 

Pictured Cliffs Sandstone and the Fruitland Formation were 

being deposited.

On fi gure 23, the “hingeline” of Ayers and others would 

lie between fl ex points FP1 and FP2 at an elevation between 

2,500 and 2,750 ft (in good agreement with their placement of 

the “hingeline” at an elevation of 2,600 ft). Figure 23 shows 

that the regional dip between the south edge of the basin and 

FP1 is 0.80°, the dip between FP1 and FP2 is 0.52°, and 

north of FP2 the dip fl attens to 0.23°. The change in dip at 

FP1 is 0.28° (from 0.8° to 0.52°), and the change in dip at 

FP2 is 0.29° (from 0.52° to 0.23°). It is puzzling that Ayers 

and others selected this area of very gentle fl exure as the site 

of a Late Cretaceous “hingeline” having a profound infl uence 

on deposition of the Pictured Cliffs Sandstone and overlying 

Fruitland Formation coal beds. A more signifi cant tectonic 

fl exure is present near the north edge of the basin where the 

Huerfanito bends sharply upward (labeled “structural hinge 

point” on fi g. 23) yet Ayers and others attribute no signifi cance 

to this feature.

The present basin structure began to form in Paleocene 

time following deposition of the Ojo Alamo Sandstone and 

continued into late Eocene time when the basin reached its 

fi nal form around 35 Ma (Fassett, 1985). The “hingeline”

referred to by Ayers and others is therefore a mid-Paleocene 

to late-Eocene feature. The inference by Ayers and others that 

the “hingeline” was an active tectonic feature in Campanian 

time (around 74 Ma) is an interesting conjecture that does not 

appear to be supported by any data. 

Pictured Cliffs Sandstone Structure

Geophysical logs from 710 drill holes were used to construct a structure contour map on top of the Pictured Cliffs 

Sandstone (fi g. 24). This map was prepared primarily to determine the maximum thickness of overburden on Fruitland coal 

beds (fi g. 39). The Pictured Cliffs structure map does not 

portray the true basin structure because of the 1,200 ft of 

stratigraphic rise of the top of the Pictured Cliffs northeastward across the basin (plate 1, fi g. 13). A comparison of 

the Huerfanito and Pictured Cliffs structure maps shows a 

similar structural pattern, but only the Huerfanito shows the 

true structure of the basin. For example, the structural nose 

seen in the deepest part of the basin on the Huerfanito structure 

map (fi g. 22) and on the structure profi le of the Huerfanito (fi g. 

23) is not seen on the Pictured Cliffs structure map (fi g. 24) 

or profi le (fi g. 23) because this part of the basin is an area of 

abrupt stratigraphic rise in the top of the Pictured Cliffs that 

masks this structural feature. The structure profi le for the top 

of the Pictured Cliffs (fi g. 23) is horizontal from just northeast 

of point FP2 to beyond the area of the structural nose shown on 

the Huerfanito structure profi le because the structural deepening of the basin in this area of about 500 ft (fi g. 22) is exactly 

offset by the 500 ft of stratigraphic rise in the top of the 

Pictured Cliffs across this same area (plate 1, fi g. 13).

The Pictured Cliffs structure map (fi g. 24) is included 

in this report because it is a useful tool in visualizing the 

depth distribution of Fruitland coals throughout the basin. In 

addition, if the surface elevation of a point on this map is 

known, the depth to the base of the Fruitland at that point can 

be quickly estimated.

Assessment of Fruitland Formation 

Coal Resources

Methodology

Base Map Preparation

The base map used for all of the San Juan Basin maps 

in this report was assembled using ARC/INFO and ArcView 

GIS (Geographic Information System) software. The land grid, 

consisting of township and section polygons, was provided by 

the Bureau of Land Management in digital form for the States 

of New Mexico and Colorado. County lines are from USGS 

digital fi les, and other cultural features are from numerous 

sources including digital fi les of USGS base maps for New 

Mexico and Colorado. The Fruitland Formation outcrop was 

added to the base map as follows: (1) the geologic map of 

the San Juan Basin from Fassett and Hinds (1971, plate 1) 

was scanned, (2) the outcrop lines for the top and bottom of 

the Fruitland Formation were digitized on the computer screen 

using the scanned image of the geology of the basin as a 

template in ArcView, (3) the resultant fi le was fi tted to the 

land-grid fi le in ARC/INFO, and (4) in some areas the outcrop 

pattern was modifi ed by the author to correct the outcrop 

placement based on newer, larger scale mapping, matching 

of outcrop position to topographic expression using USGS 

1:24,000 topographic quadrangle maps, and fi eld-checking. 

The various contour maps for this report were prepared using 

EarthVision; those fi les were fi tted to the base-map fi le using 

ArcView. Final drafting of the maps was done in Adobe Illustrator after importing the ArcView shape fi les via the MapPublisher extension. The ArcView fi les for this report are in 

Appendix 1.

The Fruitland Formation outcrop shown on the maps in 

this report is the most accurate presentation for the entire basin 

prepared to date. For the New Mexico part of the basin, a 

report by Beaumont (1998) shows the base of the Fruitland 

outcrop on two maps at a scale of 1:250,000. Beaumont’s 

maps were prepared using all published large-scale geologic 

maps available and included his unpublished geologic mapping; thus, they show the base of the Fruitland outcrop in 

more detail in places than the Fruitland outcrop map in this 

report. However, the maps in the Beaumont report were not 

Q40 Geologic Assessment of Coal in the Colorado Plateau: Arizona, Colorado, New Mexico, and Utah
ARCHULETA

LA PLATA

SAN JUAN

McKINLEY

RIO ARRIBA

SANDOVAL

MONTEZUMA

108 ̊ 107 ̊

 37 ̊ 37 ̊

 36 ̊ 36 ̊

108 ̊ 107 ̊

COLORADO

NEW MEXICO

Outcrop of Fruitland

 Formation

Kf

Kf

Farmington

Dulce

Ignacio

Durango

Cuba

0 5 10 15 20 MILES

R 13 W

R 16 W 15

T 19 N

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R 1 W R 1 E

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7

8

9

10

11 12

T 34 N

 (NUL)

T 34 N

 (SUL)

R 1 W R 1 E

2 13 12 11 10 9 8 7 6 5 4 3

14

T 34.5 N

T 34 N (NUL)

T 34 N

 (SUL)

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EXPLANATION

●

Control points are oil or gas wells or tests

Depths to top of Pictured Cliffs Sandstone from geo-

 physical logs. Datum is mean sea level. Contour

 interval is 500 feet and 100 feet. "T 34 N (NUL)"

 is north of Ute line, "T 34 N (SUL)" is south of Ute

 line.

 

Study

area

COLORADO

NEW MEXICO

3100

3200

3300

3400

3400

3300

3200

3100

3400

3200

3100

3300

3000

Line of 

structural

profile

Figure 24. Contour map on the top of the Pictured Cliffs Sandstone–base of the Fruitland Formation. Structural profi le is on fi gure 23. 

Note: Because of the stratigraphic rise of the top of the Pictured Cliffs Sandstone northeastward across the basin, this map is not a true 

representation of the structure of the basin. The true structure is shown on the Huerfanito structure map (fi g. 22).

Geology and Coal Resources of the Upper Cretaceous Fruitland Fm., San Juan Basin, New Mexico and Colorado Q41
fi tted to the land grid using modern GIS procedures. The largescale geologic map of the Hunter Wash area (fi g. 9) compiled 

from published 1:24,000 geologic maps and extensively fi eldchecked by the author is the most accurate geologic map available for that area. 

The outcrop is labeled “Fruitland Formation outcrop”

around the entire periphery of the basin on the maps in this 

report, but on the east side of the basin, the Kirtland and 

Fruitland have been mapped together, undivided. The Fruitland 

is missing in two areas on the east side of the basin (for 

example, fi g. 8). In those areas, the unconformable contact 

between the Ojo Alamo Sandstone and the Lewis Shale is 

shown as a dashed line. The Fruitland is present in a 10-milong outcrop in T. 27, 28 N., R. 1 W. on the east side of 

the basin. (See fi gure A2-3 for more detail on the outcrop 

distribution of the Kirtland and Fruitland Formations and the 

Ojo Alamo Sandstone.) 

Geophysical Logs

More than 20,000 publicly available geophysical logs 

from oil or gas wells or tests exist in the San Juan Basin. 

This vast database allowed for careful selectivity in choosing 

only the highest quality geophysical logs for geologic interpretations and coal-thickness determinations for this study. In 

addition, because of the large numbers of logs available, the 

spacing of data points could be optimized to maximize the 

accuracy of the assessment in a reasonable time frame. 

The quality and types of geophysical logs available in 

the San Juan Basin is extremely variable. The earliest coal 

assessment study for the basin (Fassett and Hinds, 1971) used 

mostly resistivity logs in conjunction with gamma ray–neutron 

and sonic logs to measure coal thicknesses because those 

were the best logs available at that time. In the 1970’s, with 

the discovery of large quantities of coal-bed methane in Fruitland Formation coal beds, an intense coal-bed-methane drilling 

boom began that resulted in thousands of new wells being 

drilled through the Fruitland Formation. It quickly became 

standard procedure to run bulk-density logs in these wells 

to identify the coal-bed reservoirs, precisely determine their 

depths and thicknesses, and evaluate the coal beds in terms 

of their ash content. Those high-defi nition logs were used 

exclusively in this study for measuring Fruitland coal beds and 

determining the density of coal beds.

The quality of bulk-density logs varies, but the tops and 

bottoms of coal beds and thicknesses of layers of non-coal 

material within coal beds (partings) can usually be selected 

on these logs to within 1 ft. Figure 25 is an example of a 

good-quality bulk-density log; such logs are almost always 

confi gured with a caliper and gamma-ray log trace, as shown 

here. The log on fi gure 25 is representative of the majority of 

the logs used to determine coal-bed thicknesses in this report. 

Typically, bulk-density logs through Fruitland coals in coalbed methane wells have a depth scale in 2-ft increments as 

shown on fi gure 25. 

The bulk-density curve on fi gure 25 has two density 

scales at the top of the log. The upper scale goes from a 

density of 2.0 on the left to 3.0 on the right; units of measurement are in grams per cubic centimeter (g/cm3). The primary 

log curve is on the left side of the log track (here shown in 

brown) and measures the densities of most sedimentary rocks. 

The lower bulk-density scale goes from 1.0 to 2.0 g/cm3 and 

measures the rock densities tracked by the backup bulk-density 

curve on the right side of the log track (shown in blue). In 

the Fruitland Formation, the only rocks that have a density 

less than 2.0 g/cm3 are carbonaceous shales and coal beds. To 

distinguish coal beds from carbonaceous shale beds on bulkdensity logs, a density value of 1.75 g/cm3 is used as the 

maximum density for coal because it is at about this density 

value that coals contain 50 percent ash; rock with a higher 

density is not considered to be coal. (The American Society 

for Testing and Materials (1995) has defi ned coal as “A readily 

combustible rock containing more than 50 % by weight and 

more than 70 % by volume of carbonaceous material including 

inherent moisture ....”) 

In this study, the tops and bottoms of coal beds were 

selected on bulk-density logs at the point where the backup 

bulk-density curve crosses the vertical line with a value of 

1.75 g/cm3 on the log scale. On fi gure 25, the portion of the 

bulk-density log to the left of the 1.75-g/cm3 line is shaded 

to emphasize the presence of coal beds. The lowest density 

reading in a coal bed on this log (1.3 g/cm3) is at 1,056 ft. Coal 

of this density is pure coal and contains no ash.

The only signifi cant pitfall in the use of bulk-density logs 

for coal-bed-thickness determinations occurs in badly caved 

drill holes. The walls of the drill hole logged on fi gure 25 

are relatively smooth, as shown by the caliper-log trace; only 

two, thin, caved intervals at depths of 1,105 ft and 1,132 ft are 

recorded. Both of these caved intervals are in coal beds and the 

cavings are only about 1 inch deep. Such small cavings have 

little affect on the bulk-density log reading. In some wells, 

however, cavings can be quite deep—sometimes exceeding the 

original width of the drill hole. In those holes, the bulk-density 

log will read an average density of the rock deep within the 

caving and the fl uid that is fi lling the caving (usually water 

or drilling mud). Thus, the bulk density measured in a deeply 

caved drill bore will be substantially less than the true density 

of the rock penetrated by the drill hole. Every effort was made 

not to use density logs from badly caved drill holes for this 

study, but in rare instances where such holes had to be used 

(in areas of limited availability of density logs) the tops and 

bottoms of coal beds in caved intervals were selected on the 

gamma-ray curve because this curve is much less affected by 

caving. It is good practice in drill holes that contain deeply 

caved intervals to compare the resistivity log to the bulkdensity log to determine whether coal beds are present within 

the caved interval. A bulk-density log in a badly caved drill 

hole through the Fruitland is shown on fi gure 30 and is discussed in the “Comparison with Earlier Studies” part of the 

“Geographic Distribution of Fruitland Formation Coal” section 

of this report. 

Q42 Geologic Assessment of Coal in the Colorado Plateau: Arizona, Colorado, New Mexico, and Utah
 Base Fruitland Formation -

top Pictured Cliffs Sandstone

2.0 2.25 2.5 2.75 3.0

1.0 1.25 1.5 1.75 2.0

Bulk density scales (gm/cc)

0 100 200

Gamma ray curve (API units)

6 11 16

Caliper curve (inches)

1200

1250

1100

1150

1050

1110

1103

5

7

1053

1058

1131

1137

6

1207

1210

1212

1218

1242

1252

3

6

10

 Density of

1.75 gms/cubic cm

 Density of

1.30 gms/cubic cm

Gamma ray

Caliper

Bulk density

Bulk density

Figure 25. Good-quality density log showing the bulk-density, gamma ray, and caliper log traces for Fruitland Formation 

coal beds. Log is from the Amoco Production Company State of Colorado Ax No. 1 well located in NE1⁄4NE1⁄4 sec. 16, T. 35 

N., R. 7 W., La Plata County, Colorado. Coal is defi ned in this report as having a density of less than 1.75 grams per cubic 

centimeter (shown in green). Depths to top and base of coal beds and coal-bed thicknesses are shown in feet on right side 

of column. Total coal thickness in this well is 37 ft.

Geology and Coal Resources of the Upper Cretaceous Fruitland Fm., San Juan Basin, New Mexico and Colorado Q43
Distribution of Data Points

U.S. Geological Survey standards for coal classifi cation 

(Wood and others, 1983, fi g. 4) describe four reliability cateegories for making coal assessments based on distances from 

control points at which coal thicknesses are measured. These 

categories are measured, 0 to 0.25 mi; indicated, 0.25 to 0.75 

mi; inferred, 0.75 to 3.0 mi; and hypothetical, beyond 3.0 

mi. Identifi ed coal is the sum of the measured, indicated, and 

inferred coal and includes all the coal that is within 3.0 mi of a 

control point. In this report, coal quantities are reported for the 

identifi ed and hypothetical categories. 

One of the primary goals for this assessment was to have 

most of the assessed coal be in the identifi ed category (control 

points less than 3 mi apart). The ideal placement of control 

points to meet this spacing requirement is in sections 8, 11, 29, 

and 26 in each township in the basin (fi g. 26). An additional 

criterion for coal-thickness control points was that they be 

exclusively bulk-density logs, as discussed above.

Figure 27 shows the distribution of the 734 control points 

in which more than 1.2 ft of coal was measured for this 

coal assessment. (The total database for this coal assessment 

contains 752 drill holes; 18 of these holes, along the east 

side of the basin, contained coal beds less than 1.2 ft thick 

or no coal and are not shown on fi gure 27.) Figure 27 was 

constructed in EarthVision by striking 3-mi-radius arcs around 

each control point; the areas shown in blue are within 3 mi of 

a control point and thus are areas of identifi ed coal resources in 

the basin. Areas shown in brown are areas of hypothetical coal 

(more than 3 mi from a control point). This map shows that 

most of the Fruitland coal assessed in this report (88 percent) 

is in the identifi ed category.

The two largest areas of hypothetical coal are along the 

east and west sides of the basin (fi g. 27). The four areas of 

hypothetical coal on the west side, south of Farmington, N. 

Mex., are on the Navajo Indian Reservation (fi g. 2). Although 

this area has been densely drilled in various coal exploration 

projects, the Navajo Tribe prefers to keep this data proprietary. 

Coal thicknesses in these areas, however, do not appear to be 

greatly variable, and coal thicknesses can be projected into 

these areas with a good degree of confi dence. (Coal thicknesses are discussed in more detail in the “Geographic Distribution of Fruitland Formation Coal” section of this report.) 

The areas of hypothetical coal in the southeast—near Cuba, N. 

6 5 4 3 2 1

7 9 10 12

18 17 16 15 14 13

19 20 21 22 23 24

30 28 27 25

31 32 33 34 35 36

6 5 4 3 2 1

7 9 10 12

18 17 16 15 14 13

19 20 21 22 23 24

30 28 27 25

31 32 33 34 35 36

6 5 4 3 2 1

7 9 10 12

18 17 16 15 14 13

19 20 21 22 23 24

30 28 27 25

31 32 33 34 35 36

6 5 4 3 2 1

7 9 10 12

18 17 16 15 14 13

19 20 21 22 23 24

28 27 25

8 11

29 26

8 11

29 26

8 11

29 26

8 11

30 29 26

31 32 33 34 35 36

3 mi. 3 mi. 3 mi.

3 mi. 3 mi. 3 mi.

Figure 26. Diagram showing the ideal spacing for drill holes for coal assessment in the San 

Juan Basin.

Q44 Geologic Assessment of Coal in the Colorado Plateau: Arizona, Colorado, New Mexico, and Utah
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COLORADO

NEW MEXICO

Study

area

EXPLANATION

"T 34 N (NUL)" is north of Ute line, "T 34 N (SUL)"

 is south of Ute line. Kf = Fruitland formation. 

Identified Coal: < 3 miles from control point

Hypothetical Coal: > 3 miles from control point

COAL RELIABILITY CATEGORIES

●

Control points are oil or gas wells, dry holes, or

coal-test holes

ARCHULETA

SAN JUAN

McKINLEY

MONTEZUMA

108° 107°

 37° 37°

 36° 36°

108° 107°

COLORADO

NEW MEXICO

Outcrop of Fruitland

 Formation

Farmington

Dulce

Cuba

Ignacio

Durango

0 5 10 15 20 MILES

R 13 W

R 16 W 15

T 19 N

20

21

22

23

24

25

26

27

28

29

30

31

32

32

33

34

T 35 N

R 1 W R 1 E

R 1.5 W

2

R 1 W

2.5 R 16 W 15 14 13 12 11 10 9 8 7 6 5 4 3

6 5 4 3 2

7

8

9

10

11 12

T 34 N

 (NUL)

T 34 N

 (SUL)

R 1 W R 1 E

2 13 12 11 10 9 8 7 6 5 4 3

14

T 34.5 N

T 34 N (NUL)

T 34 N

 (SUL)

SANDOVAL

RIO ARRIBA

LA PLATA

Kf

Kf

Figure 27. Map of San Juan Basin showing coal-reliability categories as defi ned by Wood and others (1983). The 752 drill holes used for control 

for the San Juan Basin Fruitland Formation coal assessment are shown. Kf, Fruitland Formation.

Geology and Coal Resources of the Upper Cretaceous Fruitland Fm., San Juan Basin, New Mexico and Colorado Q45
Mex. (fi g. 27), and along the east-central and northeast edges 

of the basin—contain few drill holes but there is little Fruitland 

coal in those areas; in fact, the only areas of zero Fruitland coal 

in the basin are on the east side within these hypothetical coal 

areas (fi g. 28). The large block of hypothetical coal in Ts. 32, 

33 N., Rs. 4, 5 W. is on the east side of the Southern Ute Indian 

Reservation (fi g. 2) and has never been drilled. Fruitland coals 

appear to be thin in that area based on nearby outcrop data 

and projections of coal-thickness isopach lines (fi g. 28). The 

other scattered small areas of hypothetical coal in the basin 

are artifacts of being just beyond the 3-mi limit from several 

control points and do not represent signifi cant data gaps in 

those areas.

Three clusters of data points are present on fi gure 27 in 

the northwest part of the basin near the Fruitland outcrop. The 

cluster of data points in T. 35 N., R. 7 W. and the one south of 

Durango, Colo., are from detailed, large-scale studies of coalbed methane gas seeps (Fassett and others, 1997b). The cluster 

of data points on the west edge of the basin just north of the 

Colorado State line is from a cooperative USGS–Southern Ute 

Indian Tribe core-drilling project (Roberts, 1989). Data from 

these reports are discussed in detail in the “Fruitland Coal-Bed 

Correlations—Earlier Studies” section of this report.

Core Data

Core data were used for control for the coal assessment 

in four areas (fi g. 28). The cluster of core data points north 

of the State line near the Fruitland outcrop was discussed 

above. The four core data points near the Fruitland outcrop 

on the northwest edge of the basin, just south of the State 

line, the four core data points on the Fruitland outcrop west of 

Farmington, and the row of core holes parallel to the Fruitland 

outcrop along the southern edge of the basin (fi g. 28) are from 

a core-drilling project conducted by the New Mexico Bureau 

of Mines and Mineral Resources (Hoffman, 1991; Hoffman 

and others, 1993). Three USGS core-drilling projects were 

conducted to evaluate Fruitland coal in New Mexico; the data 

from those projects are reported in Jentgen and Fassett (1977), 

Wilson and Jentgen (1978), and Beach and Jentgen (1980). 

These projects generally had a drilling density of four coal 

test holes per section and thus represent very dense data sets 

compared to the basin-wide density of four holes per township 

used for this assessment. These core-hole data were not used 

for the assessment because the drill holes were too close 

together to be shown and contoured at the scale of the maps 

used in this report, and average coal thicknesses for these 

dense data sets were similar to thicknesses of the more widely 

spaced data points used for this coal assessment in the areas 

of the core drilling. Many other private coal-coring projects 

were conducted on coal leases and Preference-Right Lease 

Application areas along the Fruitland outcrop in the southwest 

and south parts of the basin. That information is in the fi les of 

the U.S. Bureau of Land Management offi ces in Farmington 

and Albuquerque, N. Mex. No attempt was made to integrate 

those data into this study because coal thicknesses were relatively well known in those core-drilling areas and the data sets 

were too dense to be easily shown at the scale of this project. 

Hundreds of Fruitland coal core holes have been drilled on 

the Navajo Reservation (fi g. 2) on the west side of the basin, 

but, as mentioned above, data from those holes have not been 

released by the Navajo Indian Tribe.

Coal Outcrop Measurements

No measurements of outcropping Fruitland coal beds are 

used as control points for this assessment. Outcrop coal measurements were rejected because they seldom represent the 

total Fruitland coal thickness at any outcrop locality because 

of partial cover by alluvium and (or) burning or weathering 

of the coal. Large numbers of Fruitland coal outcrop measurements have been published over the years in USGS map and 

book publications, and many of those measurements are shown 

on the net-coal isopach map (fi g. 28). Outcrop measurements 

of coal are useful to provide a minimum total-coal-thickness 

value at various points around the Fruitland outcrop, especially 

in areas where well-log or core data are sparse. 

Database

Data Point Locations

Locations for the data points used for construction of 

the contour maps in this report were determined in decimal 

degrees of latitude and longitude in the ArcView GIS software 

program using a custom tool designed to measure locations 

of the data points in feet from section lines. The map was 

scaled in meters, distance units were in feet, projection was 

Lambert Conformal Conic, and the central meridian was at 

long 107.75°W. Locations for oil and gas wells or tests (given 

in feet from the nearest section lines) were from geophysical 

log headers. Some core-hole and other data-point locations 

were determined by measuring footages of data points from 

section lines on USGS 1:24,000 topographic quadrangle maps 

and then placing these points on the ArcView map using the 

custom measuring tool. After the data points had been entered 

into the ArcView fi le, the projection of the fi le was changed 

to geographic decimal degrees, converting the data-point locations to decimal degrees of latitude and longitude. Latitude 

and longitude coordinates for all of the data points shown on 

the various maps in this report were determined using this 

procedure.

Geophysical Log Data

Coal-bed depths measured from bulk-density logs (see 

example, fi g. 25) were entered into the StratiFact database 

Q46 Geologic Assessment of Coal in the Colorado Plateau: Arizona, Colorado, New Mexico, and Utah
EXPLANATION

Drill holes -- oil or gas well or dry hole

Study

area

COLORADO

NEW MEXICO

 "T 34 N (NUL)" = north of Ute line, "T 34 N (SUL)" = south of Ute line.

Greater than 80 feet

40 to 80 feet

20 to 40 feet

Zero coal

R 13 W

R 16 W 15

T 19 N

20

21

22

23

24

25

26

27

28

29

30

31

32

32

33

34

T 35 N

R 1 W R 1 E

R 1.5 W

2

R 1 W

2.5 R 16 W 15 14 13 12 11 10 9 8 7 6 5 4 3

6 5 4 3 2

7

8

9

10

11 12

T 34 N

 (NUL)

T 34 N

 (SUL)

R 1 W R 1 E

12 11 10 9 8 7 6 5 4 3 2 13

14

0 5 10 15 20 MILES

108 ̊ 107 ̊

 37 ̊ 37 ̊

 36 ̊ 36 ̊

107 ̊ 108 ̊

ARCHULETA

LA PLATA

SAN JUAN

McKINLEY

RIO ARRIBA

SANDOVAL

MONTEZUMA

T 34.5 N

T 34 N (NUL)

T 34 N

 (SUL)

Farmington

Dulce

Ignacio

Durango

Outcrop of Fruitland

 Formation

COLORADO

NEW MEXICO

30 70

50 60

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60

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90

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70 80

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90

60

Surface measured section - total-coal thickness shown

NET COAL THICKNESS CATEGORIES

Less than 20 feet

20

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40

0

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4

Cuba

Figure 28. Net-coal isopach map for Fruitland Formation coal beds. Outcrop coal measurements from Fassett and Hinds (1971). Coal 

thicknesses at control points are net coal in beds 1.2 ft thick or greater. Coal measurements are from density logs or drill core. A maximum 

density of 1.75 g/ cm3

 was used as a cutoff for coal measurements on density logs (fi g. 25). Contour interval is 10 ft. Cross section A-A’ is 

on plate 1. Kf, Fruitland Formation.

Geology and Coal Resources of the Upper Cretaceous Fruitland Fm., San Juan Basin, New Mexico and Colorado Q47
management system along with a unique point ID, the latitude 

and longitude coordinates, drill-hole elevation and total depth, 

selected geologic formation tops, and other relevant information for each data point. (An edited version of the StratiFact 

database is in table A2-1.) After data clean-up (discussed 

below under “Data Screening for Errors”) x, y, z (data point) 

fi les were created from the StratiFact data fi les and exported as 

Excel spread sheets containing x, y locations in longitude and 

latitude and the total coal thickness or other geologic parameeters as the z value. USGS classifi cation standards (Wood and 

others, 1983) do not allow the inclusion of bituminous coal 

beds less than 14 inches thick in the resource base; thus, the 

coal thickness data set was run through another program that 

deleted all coal beds less than 14 inches thick, deleting the 

1-ft-thick coal beds from the database. (The impact of deleting 

these thin coal beds was minimal because there were few 1-ftthick coal beds in the original database.)

Contour Map Preparation

Data fi les for the geologic and coal-thickness parameters 

were imported into the EarthVision software program for gridding and contouring. After the fi rst contour map was generated 

for each data set, the maps were modifi ed in EarthVision by 

the author to incorporate his geologic knowledge of the area. 

The fi nal contour maps were imported into Adobe Illustrator 

using the MapPublisher extension for fi nal drafting. All of 

the other illustrations in this report were also prepared in 

Adobe Illustrator. Various contour intervals were tested for 

each map in this report; the fi nal selection was based on the 

contour interval that best presented the data legibly on a pagesize illustration without loss of geologically signifi cant data. 

Contour intervals range from 10 ft for the net-coal isopach 

map (fi g. 28) to 500 ft for the Huerfanito and Pictured Cliffs 

structure maps (fi gs. 22, 24). Control points used to construct 

each contour map are shown along with the township-andrange land grid to enable users to easily locate contour lines 

and data points geographically.

Data Screening for Errors

The data used to create the contour maps in this report 

were checked for accuracy in two ways: (1) generating a 

preliminary contour map in StratiFact and reexamining data 

sources for anomalous values at single points (sometimes 

called “bull’s-eyes”), and (2) having a second person review 

the basic data source (usually geophysical logs) to confi rm the 

original data selection points. All of the contour maps were 

checked with the preliminary-map method. This method is 

highly effi cient because the most common errors of incorrect 

well site elevations, incorrect well locations, mistakes in the 

selection of geologic formation tops, and typographical errors 

in data entry are obvious as bull’s-eyes. The preliminary-map 

method works well in identifying errors that are about the 

same magnitude or larger than the contour interval selected for 

the contour map. For example, a 100-ft error in the elevation 

of a drill hole would be obvious on a structure map contoured 

at 100 ft, whereas an error in elevation of 50 ft might not be 

so apparent. The preliminary-map procedure was used for all 

of the contour maps in this report to eliminate apparent errors 

in data values.

The isopach map of total coal thickness (fi g. 28) was 

more diffi cult to check using the preliminary-map method 

because coal-thickness values are more random and what may 

at fi rst appear to be an anomaly may in actuality be an abrupt 

change in coal thickness and not a data error. About 20 percent 

of the bulk-density logs were reexamined in the process of 

checking apparent anomalies on the StratiFact preliminary 

maps. Approximately 50 percent of the bulk-density logs were 

examined by a second person to confi rm coal depth and thickness data. The author was the fi nal reviewer for all of the data 

in this report. 

A few data points that appeared to be anomalous after 

careful checking of the basic data were found to have deviated 

(inclined) well bores. Lists of deviated wells in the basin 

were obtained from the New Mexico and Colorado Oil and 

Gas authorities and all deviated holes were purged from the 

database.

Geographic Distribution of 

Fruitland Formation Coal

Net-Coal Isopach Map

Figure 28 is the net-coal isopach map for Fruitland coal 

in the San Juan Basin. (“Coal” or “coal thickness” refer to netcoal thickness in this discussion.) The distribution of control 

points averages about four per township throughout most of 

the basin, or one control point every 3 mi. The principal areas 

of sparser data are in the northeast, east-central, and westcentral parts of the basin (see “Distribution of Data Points”

section for more detail on these areas). Outcrop coal-thickness 

measurements (including zero-coal data points) were not used 

to construct the net-coal isopach map (fi g. 28), but they represent minimum coal-thickness values that are useful for estimating coal thicknesses in areas where subsurface data are 

sparse. Zero-coal areas on the east side of the basin are discussed in more detail below.

Fruitland Coal Distribution

Map View

Areas underlain by more than 40 ft of net coal are colored 

brown on fi gure 28. In the northern part of the basin, fi ve 

such areas collectively form a northwest-trending wedge that 

is widest in the northwest and tapers to the southeast. In the 

Q48 Geologic Assessment of Coal in the Colorado Plateau: Arizona, Colorado, New Mexico, and Utah
southwest part of the basin, two small areas are underlain by 

more than 40 ft of coal. Five small areas are underlain by 

coal more than 80 ft thick in the northwest part of the basin 

(colored orange, fi g. 28); four of these areas are close together 

near the northwest edge of the basin. The fi fth area is defi ned 

by one control point near well 15 on line of cross section 

A-A′. Several areas underlain by coal less than 20 ft thick 

(shown in yellow) are present in the southern part of the basin; 

these areas collectively form a broad, northwest-trending band 

of thinner coal. Another band of coal less than 20 ft thick is 

parallel to the east edge of the basin; this band is narrow to the 

south and broadens to the north.

A large area of coal less than 10 ft thick is present in the 

southeast part of the basin. This area corresponds remarkably 

well to the area between the 250-ft and 300-ft contour lines 

of fi gure 8. In the “Shoreline Trends” section of this report, 

it was suggested that the shoreline had regressed rapidly to 

the north in this area because a large delta was building out 

into the Pictured Cliffs sea at that time. The area of coal less 

than 10 ft thick (fi g. 28) thus records a time when a major 

distributary channel complex was rapidly depositing a broad 

wedge of mostly sand-size material in the southeast part of 

the basin area, preventing the formation of signifi cant peat 

swamps there. 

In addition to the northwest-trending areas of thin and 

thick coal that parallel Pictured Cliffs Sandstone paleoshoreline orientations (fi gs. 8, 14, 18), a northeast-trending pattern 

of thick and thin coal is also visible on the net-coal isopach 

map (fi g. 28). For example, three ribbons of thin coal (less 

than 40 ft thick) trending northeast cut through the wedge of 

thicker net coal discussed above. These features are normal 

to paleoshoreline trends and probably represent the positions 

of paleo-river channels that apparently maintained their geographic positions during the Pictured Cliffs shoreline retreat 

across those areas. The most prominent of these thin coal 

bands trends slightly north of east in the north-central part of 

the basin, crossing the New Mexico–Colorado State line in T. 

32 N., R. 6 W. (fi g. 28). Within this relatively narrow, linear 

band, the total coal thickness is less than 40 ft thick to less than 

30 ft thick. Two other bands of thin coal trending northeast are 

in the east central part of the basin southeast and parallel to 

the line of cross section A-A′. These bands of thinner coal abut 

two linear bands of thicker coal also with a northeast trend. 

Other, less well defi ned linear bands of northeast-trending 

thick and thin coal are present in other parts of the map area.

Two areas of zero coal are present on the east side of the 

basin. A northeast-trending lobe of zero coal is present in the 

northeast part of the basin, mostly south of the New Mexico 

State line (fi g. 28). Another band of zero coal parallels the 

southeast edge of the basin; this band is narrow to the south 

and thickens to nearly 10 mi wide to the north. As noted above, 

the Fruitland is missing in two areas on the east side of the 

basin (fi g. 28). In Tps. 29, 30 N., R. 1 W. the area of missing 

Fruitland is shown by a dashed line. Because there is no 

Fruitland coal in this area, there should be a narrow band 

of zero Fruitland coal paralleling and west of the dashed 

contact line; however, the computer contouring program had 

insuffi cient drill-hole data to generate a zero coal line in this 

area.

Fruitland coal beds thin abruptly eastward near the east 

side of the basin. For example, in the east-central part, (Tps. 

25–28 N., Rs. 2, 3 W.) net-coal thicknesses of more than 40 

ft decrease to 0 ft of coal over a very short distance. Fassett 

and Hinds (1971, p. 53, 54) suggested that this thinning of 

Fruitland coals along the east edge of the basin was the result 

of slight uplift along a linear, northerly trend in that area 

that occurred as the Pictured Cliffs shoreline was regressing 

across the basin. That uplift could not have been very great 

or it would have created a clastic wedge of sediment in the 

Fruitland with an eastern source and no such clastic wedge 

is present. An alternative explanation is that thicker Fruitland 

coals were deposited across this area but tectonic uplift along 

the east side of the basin, prior to deposition of the Tertiary 

Ojo Alamo Sandstone, resulted in their removal by erosion. 

(See appendix fi gures A3-1 through A3-5 for more detail on 

the geometry of the Fruitland Formation and associated rocks 

in the San Juan Basin.) The true answer regarding why Fruitland coals thin abruptly on the east side of the San Juan 

Basin is probably a complex combination of these two possible 

causes. 

Coal-Bed Geometry

The line of section A-A’ is shown on the net-coal isopach 

map to facilitate comparison of Fruitland coal distribution in 

map view with its distribution as seen in cross section. Plate 

1 is a northeast-oriented stratigraphic cross section across the 

San Juan Basin constructed with the Huerfanito Bentonite Bed 

as a datum. The rock units shown are the Upper Cretaceous 

Lewis Shale, Pictured Cliffs Sandstone, Fruitland Formation 

and lower shale member of the Kirtland Formation (undivided) 

and the Farmington Sandstone Member of the Kirtland Formation. The Tertiary Ojo Alamo Sandstone unconformably overlies the Cretaceous rocks. The general distribution of Fruitland 

coal beds (plate 1) shows an area of thicker coal in the southwest (drill holes 1–6), a zone of relatively thin coals (holes 

7–10), a zone of increasing coal thickness (holes 11–17), and 

a zone of relatively thin coal in the northeast part of the basin 

(holes 18–20). The magnetic-polarity reversal from chron C33n 

to C32r (73.50-Ma isochron) is shown as a red dashed line 

in the upper part of the Farmington Sandstone Member in the 

southwest and in the Pictured Cliffs Sandstone in the northeast. 

As discussed previously, the Pictured Cliffs Sandstone 

rises stratigraphically across the basin more than 1,200 ft 

and is nearly 2.5 m.y. younger in the northeast than in the 

southwest; thus, the coal beds in drill hole 1 on plate 1 are 

nearly 2.5 million years older than the coals in drill hole 20. 

It is helpful to keep this relationship in mind when comparing 

the coal distribution shown on the map on fi gure 28 and in 

cross section on plate 1. The three-dimensional distribution of 

Fruitland coals in time and space in the San Juan Basin is 

termed the geometry of the coal.

Geology and Coal Resources of the Upper Cretaceous Fruitland Fm., San Juan Basin, New Mexico and Colorado Q49
Map–Cross Section Comparison

The geophysical drill-hole logs shown on cross section 

A-A′ (plate 1) are nearly all resistivity logs; these logs were 

used because they are the most defi nitive for selecting formation boundaries. Resistivity logs are not, however, the best logs 

on which to measure coal beds. Consequently, the coal beds 

illustrated on this cross section are not as precisely measured 

as the coal beds measured on bulk-density logs that were used 

to construct the net-coal isopach map of fi gure 28. (Net-coal 

thicknesses for the drill holes shown on cross section A-A′

were not used as control points for the net-coal isopach map 

(fi g. 28); these two illustrations were prepared independently.) 

In the northern part of the basin, the identifi cation of coal beds 

on resistivity logs is diffi cult (see discussion in Fassett and 

Hinds, 1971, p. 50–52). A good example is drill hole 14 where 

a high-resistivity bed is present just below 3,300 ft. This bed 

appears to be a coal bed on the resistivity log, but the bulkdensity logs from nearby drill holes show that in reality it is a 

sandstone bed. In this part of the basin, bulk-density logs were 

examined from drill holes as near as possible to the drill holes 

on this cross section to confi rm all of the coal picks shown. 

Cross section A-A′ (plate 1) shows that coal beds have 

very little lateral continuity and are at an increasingly higher 

stratigraphic level from southwest to northeast. The net-coal 

thicknesses for the drill holes shown on this cross section 

include a different set of coal beds at every control point. 

For example, drill hole 2 on the cross section contains 7 thin 

Fruitland coal beds with a net-coal thickness of nearly 30 ft. 

Drill hole 3 contains one thick and two thin coal beds with a 

net thickness of a little over 30 ft. The net coal thickness in 

holes 2 and 3 is nearly identical, but a close examination of 

the coal beds in these two holes shows that the thick coal bed 

in hole 3 splits into two thinner coal beds in hole 2. The next 

lower thin coal bed in hole 3 correlates perfectly with a thin 

coal in hole 2, and the lowest thin coal bed in hole 3 pinches 

out to the southwest and is not present in hole 2. The lowermost 4 coal beds in hole 2 pinch out to the northeast, and none 

are present in hole 3. Generally, coal beds correlate across only 

two holes and many coal beds are present in only one of the 

drill holes shown on section A-A′. This lack of continuity of 

coal beds between drill holes is true as well for most of the 

drill-hole control points shown on the net-coal isopach map 

(fi g. 28). (Correlation of Fruitland coal beds is discussed in 

more detail in another section of this report.)

Cross section A-A′ (plate 1) crosses the northwest-trending thick net-coal band (fi g. 28) between holes 11 and 17. Netcoal thicknesses across this band range from 40 ft to more than 

80 ft near hole 15. On the net-coal isopach map (fi g. 28), this 

band of thick coal appears to be somewhat variable in thickness but relatively continuous. Cross section A-A′, however, 

portrays the geometry of the individual coal beds. The 60 ft 

of net coal at hole 12 includes 10 coal beds, whereas the 60 

ft of net coal at hole 16 includes 6 totally different coal beds. 

Moreover, the coal beds in hole 16 are tens to hundreds of 

thousands of years younger than the coal beds in hole 12. 

The cross section, between holes 18 and 20, clearly shows the 

details of the thinning coal seen on the net-coal isopach map in 

the northeast part of the basin. 

Comparison with Earlier Studies

Basin-Wide Studies.—Three earlier reports portrayed the distribution of Fruitland Formation coal beds throughout the San 

Juan Basin: Fassett and Hinds (1971), Kelso and Wicks (1988), 

and Ayers and others (1994). A comparison of the net-coal 

isopach maps from those reports with the net-coal map of this 

report is on fi gure 29. The procedures and methods used to 

determine Fruitland coal thicknesses for each of these maps 

were somewhat different.

Fassett and Hinds (1971).—This report was the fi rst 

attempt to quantify coal resources in the subsurface of a Western Interior coal basin using geophysical logs of oil and gas 

wells to measure coal thicknesses. (The use of geophysical 

logs for coal resource assessment was pioneered by the Illinois 

State Geological Survey in the 1950’s; one of the fi rst publications to provide a detailed discussion of the methodology of 

using resistivity logs to measure coal thicknesses in the subsurface was Hopkins (1968).) As discussed in the “Geophysical 

Logs “ section of this report, Fassett and Hinds (1971) relied 

primarily on resistivity logs (supported by radioactivity logs, 

sonic logs, and drilling-rate records) on which to measure 

coal-bed thicknesses. In the late 1960’s when the database 

for that report was compiled, the geophysical log fi le for the 

San Juan Basin primarily consisted of resistivity logs. The 

authors used geophysical logs from 270 drill holes and 54 

coal measurements made on the outcrop as control points 

to construct the total-coal isopach map shown on panel B 

of fi gure 29. Coal beds less than 16 inches thick were generally ignored and non-coal partings more than 1 ft thick were 

excluded from the total coal thicknesses determined from geophysical logs (Fassett and Hinds, 1971, p. 52).

Kelso and others (1987) and Kelso and Wicks 

(1988).—These reports contained identical net-coal isopach 

maps (panel C of fi g. 29) for Fruitland coal beds in the 

San Juan Basin. These authors recalculated Fruitland coal 

resources to establish a more detailed database for coal-bedmethane resource estimates for the basin. The 1987 report 

contains more detail regarding the methodology used to measure coal thicknesses and states (p. 121), “A net coal isopach 

map was constructed using data from gamma-density, densityporosity, and a limited number of gamma ray–neutron geophysical logs .... Net coal values do not include coals thinner 

than 2 ft with efforts made to exclude partings and shaley units 

within individual coals.” (Parting thicknesses excluded were 

not given.) Kelso and Wicks (1988, p. 71) state that 549 well 

logs were used to characterize Fruitland coals but only 471 

wells are present on their net-coal isopach map (their fi g. 5).

Ayers and Ambrose (1990) and Ayers and others 

(1994).—This study was conducted to estimate the amount of 

coal-bed methane in Fruitland coal beds in the San Juan Basin. 

Even though the 1990 and 1994 reports are similar, the netQ50 Geologic Assessment of Coal in the Colorado Plateau: Arizona, Colorado, New Mexico, and Utah
20

B

A. This Report B. Fassett and Hinds (1971)

C. Kelso and Wicks (1988) D. Ayers and others (1994)

EXPLANATION

80 to 100 feet

(70 to 100 feet on D)

Greater than 100 feet 60 to 80 feet

40 to 60 feet

(50 to 70 feet on D)

Zero coal

("Fruitland Fm. truncated" on D)

Net Coal Thickness Categories

20 to 40 feet

(30 to 50 feet on D)

Less than 20 feet

(less than 30 feet on D)

A

A

ARCHULETA

SAN JUAN

McKINLEY

MONTEZUMA

108° 107°

 37° 37°

 36° 36°

108° 107°

COLORADO

NEW MEXICO

Outcrop of Fruitland

 Formation

Farmington

Dulce

Cuba

Ignacio

Durango

SANDOVAL

RIO ARRIBA

LA PLATA

ARCHULETA

SAN JUAN

McKINLEY

MONTEZUMA

108° 107°

 37° 37°

 36° 36°

108° 107°

COLORADO

NEW MEXICO

Outcrop of Fruitland

 Formation

Farmington

Dulce

Cuba

Ignacio

Durango

0 5 10 15 20 MILES 0 5 10 15 20 MILES

0 5 10 15 20 MILES

SANDOVAL

RIO ARRIBA

LA PLATA ARCHULETA

SAN JUAN

McKINLEY

MONTEZUMA

108° 107°

 37° 37°

 36° 36°

108° 107°

COLORADO

NEW MEXICO

Outcrop of Fruitland

 Formation

Farmington

Dulce

Cuba

Ignacio

Durango

SANDOVAL

RIO ARRIBA

LA PLATA

Kf

Kf

Kf

B

ARCHULETA

SAN JUAN

McKINLEY

MONTEZUMA

108° 107°

 37° 37°

 36° 36°

108° 107°

COLORADO

NEW MEXICO

Outcrop of Fruitland

 Formation

Farmington

Dulce

Cuba

Ignacio

Durango

SANDOVAL

RIO ARRIBA

LA PLATA

0 5 10 15 20 MILES

Kf

Kf

Figure 29. Comparison of three, published, Fruitland Formation net-coal isopach maps with the net-coal isopach map of this report. Kf, 

Fruitland Formation. Arrows on panels A, C, and D indicate small areas or bull’s-eyes of thick coal discussed in text. Area of coal 60–80 ft 

thick on panel C outlined by dashed line is also discussed in the text.

Geology and Coal Resources of the Upper Cretaceous Fruitland Fm., San Juan Basin, New Mexico and Colorado Q51
coal isopach map from the 1994 report is a modifi ed version 

of the map in the 1990 report and is the isopach map shown 

on panel D of fi gure 29. Ayers and others stated (p. 38, 39) 

that logs from 1,731 wells were used “to evaluate and map 

Fruitland coal beds.” Wells used as control points for the 

net-coal isopach map in the 1994 report are not shown, but 

the 1990 net-coal isopach map shows 1,350 wells used as 

control points. It is not clear what kinds of geophysical logs 

were used to measure Fruitland coal-bed thicknesses, but the 

implication is that a variety of log types was used including 

density logs, gamma ray–neutron, sonic logs, and resistivity 

logs. The methodology used to measure coal beds on logs is 

summarized in Ayers and others (1994, p. 26), “On geophysical logs, the thickness of a bed is commonly measured halfway 

between the shale baseline and the peak corresponding to 

that bed. On the bulk-density log ... coal-seam thickness was 

measured at a density of approximately 1.80 g/cm3, which is a 

slightly conservative measurement. We recorded the thickness 

of coal seams thicker than 2 ft (>0.6 m); partings thinner 

than 2 ft (,0.6 m) in thick coal seams were included as coal 

because of the limits of resolution of the geophysical logs.”

The Ayers and others net-coal isopach excluded Fruitland coal 

beds shallower than 400 ft. 

The original versions of the net-coal isopach maps shown 

on panels A and B (fi g. 29) had a contour interval of 10 ft; 

those maps were redrawn to show only the 20-ft contour lines 

to more directly compare the thick and thin coal patterns of 

those maps with the net-coal isopach maps on panels C and 

D. The map on panel C was published with a 20-ft contour 

interval and is shown here as it was published. The map on 

panel D is also shown as published with contours of 30 ft, 50 

ft, 70 ft, and 100 ft.

The northwest-trending distribution pattern for areas of 

thicker and thinner net coal in the San Juan Basin is seen on 

all of the net-coal isopach maps on fi gure 29. The northeasttrending pattern is not seen on panel B, but is evident on the 

other three isopach maps. (Figure 28 of this report has a 10-ft 

contour interval and thus shows the northeast trend in greater 

detail.)

The net-coal isopach maps of panels C and D generally 

show thicker coal than the panel A map of this report. The 

C and D maps also contain several bull’s-eyes of thick coal 

(60–80 ft thick on panel C and greater than 70 ft thick on panel 

D) southwest of the main thick coal trend. These bull’s-eyes 

are shown by arrows on fi gure 29 on panels C and D. The 

bull’s-eye areas are in different places on maps C and D except 

for the one shown with a blue arrow (labeled A) on both maps. 

This small, thick-coal area of map D is shown superimposed 

on the larger area of thick coal on map C. 

Examination of the bulk-density logs in the areas shown 

by arrows on maps C and D indicates that, in those areas, 

cavings in the bore holes were measured as coal beds on bulkdensity logs thus infl ating the net-coal thicknesses in those 

holes. None of the thick coal areas shown with arrows on maps 

C and D actually exist including the relatively large area of 

coal 60–80 ft thick outlined by a dashed line on map C. 

Figure 30 shows the density log for the drill hole that 

defi nes the bull’s-eye of thick coal (more than 70 ft thick) 

shown with a green arrow and labeled B on panel D of fi gure 

29. On panel A, this same well (shown with a green arrow 

labeled B) is in the 20 to 40 ft interval of net-coal thickness, 

near the 20-ft line. Figure 30 shows how these greatly differing net-coal thicknesses were obtained from the log of the 

same well. This fi gure shows the bulk-density, gamma ray, and 

caliper logs for this drill hole. Intervals with a density less 

than 1.75 g/cm3 to the left of the 1.75 g/cm3 line, are shaded, 

for emphasis, on the bulk-density curve. Intervals with a hole 

diameter greater than 11 inches are shaded on the caliper log 

trace; normal drill hole diameter is 7 7/8 inches and cavings 

in the hole to a diameter greater than 11 inches have a defi nite 

impact on the bulk-density log trace, causing it to mimic coal 

beds. Tops and bottoms of “coal beds” using the criteria of 

Ayers and others (1994) are listed under column A on fi gure 

30. True tops and bottoms of coal beds as measured for this 

study are listed under column B on fi gure 30. Intervals where 

the caved drill hole caused the bulk-density log to give a false 

coal signature are shown with a rectangle with an X in it in 

the shaded portion of the bulk-density log trace. The 1.8 g/cm3

density is shown with a dashed line on fi gure 30 to indicate 

at what point Ayers and others picked the tops and bottoms of 

coal beds for their study. 

Figure 30 shows that Ayers and others (1994) obtained a 

net coal thickness of 72 ft for this hole—nearly three times 

greater than its true thickness of 26 ft—for two reasons: (1) 

they used a coal-density cut-off of 1.8 g/cm3 rather than 1.75 

g/cm3 to measure coal thicknesses on the bulk-density log, 

and (2) they were apparently unaware that caved zones in 

bore holes can mimic the low-density coal response on a bulkdensity log. In general, net-coal isopach maps C and D show 

thicker coal throughout the basin than net-coal isopach map 

A (fi g. 29). 

Other Studies

Biewick and others (1991).—This study of Fruitland coal 

resources was limited to the New Mexico part of the San 

Juan Basin and used data in the U.S. Geological Survey’s 

National Coal Resources Data System (NCRDS) to construct 

a net-coal isopach map and for resource calculations. The 

net-coal isopach map (their fi g. B2) used 630 data-point locations. Because most of the data points in the NCRDS database 

came directly from the Fassett and Hinds (1971) report, the 

Biewick and others isopach map was very similar to the netcoal isopach of that report (panel B, fi g. 29). Their isopach 

map is also similar to the net-coal isopach map of this report 

(fi g. 28), except that it does not show the northeasterly pattern 

of thick and thin coals that are present in the northwesttrending thick coal area. 

Boger and Medlin (1991).—This study also calculated 

Fruitland coal resources using the database generated by Biewick and others (1991) from the NCRDS database but used an 

experimental kriging methodology to contour the data points. 

The resulting net-coal isopach (fi g. C3) for the New Mexico 

Q52 Geologic Assessment of Coal in the Colorado Plateau: Arizona, Colorado, New Mexico, and Utah
part of the San Juan Basin is quite similar in its portrayal of 

Fruitland coal distribution throughout the New Mexico part of 

the basin to the Biewick and others net-coal isopach and the 

Fassett and Hinds (1971) net-coal isopach.

Several other local studies of Fruitland coal resources 

were conducted by Shoemaker and Holt (1973), Kelso and 

others (1980), Sandberg (1988a, 1988b, 1990), Roberts (1991), 

Ayers and Zellers (1994), Ambrose and Ayers (1994), and 

0 100 200

Gamma ray curve (API units)

6 11 16

Caliper curve (inches)

Gamma ray

Caliper

Base Fruitland Formation -

top Pictured Cliffs Sandstone

 1.75 gms/cubic cm

(density cut-off, this report)

 1.8 gms/cubic cm

(density cut-off, Ayers and others, 1994)

2.0 2.25 2.5 2.75 3.0

1.0 1.25 1.5 1.75 2.0

Bulk density scales (gm/cc)

4 1686

1690

1737

1742

1754

1756

3 1686

1689

1789

1791 2

5

2

1763

1765 2

1740

1742

1754

1756

2

2

1764

1765 1

2

6

13

1796

1807

11

1804

1806 2

1796

1801 5

1827

1852

1853

1855

2

2

4

1850

1852

1858

1864

3

1858

1860

1867 1867

1870

1873

1877

1880

25

Bulk density

Bulk density

1700

1750

1800

1850

1900

 Net coal 

= 72 feet

 Net coal 

= 26 feet

A B

LEGEND

Pictured Cliffs Sandstone

Drill hole caved; diameter

greater than 11 inches

Density less than

1.75 gms/cubic cm

Bulk-density log mimics

coal beds in caved zone

Figure 30. Density log from the Southland Royalty Company Federal 12-14 well in SE1⁄4SW1⁄4 sec. 12, T. 

26 N., R. 11 W., San Juan County, New Mexico. Well location is shown with green arrow labeled B on 

panels A and D of fi gure 29. Column A contains all intervals of density less than 1.8 g/cm3

; column B lists 

true coal thicknesses in this well with a density less than 1.75 g/ cm3

 and excluding low-density intervals 

resulting from cavings in drill hole. This fi gure illustrates how incorrect (thicker than true values) net-coal 

determinations were made for the bull’s-eye areas shown by arrows on panels C and D of fi gure 29.

Geology and Coal Resources of the Upper Cretaceous Fruitland Fm., San Juan Basin, New Mexico and Colorado Q53
M’Gonigle and Roberts (1997). All of these reports contained 

net-coal isopach maps showing Fruitland coal distribution in 

their study areas. A more detailed discussion of each of these 

reports is presented in the following section of this report. 

Fruitland Coal-Bed Correlations—

Earlier Studies

Surface Mapping

Mapping of Fruitland Formation coal beds by the U.S. 

Geological Survey began in the early 1900’s, and, by the late 

1950’s, maps of the entire coal-bearing outcrop of the Fruitland 

had been published at a variety of scales. Those map publications are listed and discussed in Fassett and Hinds (1971, p. 

54–57). All of the early mappers reporting on Fruitland coal 

beds on the outcrop stated that the beds were lensing and discontinuous and could rarely be correlated for more than a few 

miles. More recent mapping of outcropping Fruitland coal beds 

has been conducted by Roberts (1991), Roberts and Uptegrove 

(1991), and Fassett and others (1997b) in the northwest part of 

the basin. These reports also note the lensing nature of Fruitland 

coal beds and state that, even though zones of coal appear to 

be relatively continuous, individual coal beds usually cannot be 

correlated for more than a few miles at the most.

Subsurface Studies

Local Studies

The locations of local subsurface study areas for Fruitland 

coal in the San Juan Basin are shown on fi gure 31, and an 

abbreviated citation for each study is also provided. Full citations for these reports are in the “References Cited” section of 

this report. Some of the study areas overlap, especially in the 

Colorado part of the basin. Each of the studies is briefl y summarized below in chronological order. The letter designating 

the area on fi gure 31 and the author(s) and year of the report 

are listed at the beginning of each summary. 

C/D—Shoemaker and Holt (1973).—This was the fi rst 

local study that characterized subsurface Fruitland coal in 

detail using the geophysical-log methodology developed by 

Fassett and Hinds (1971). This study focused on the coal 

resources underlying the Ute Mountain Ute and Southern Ute 

Indian Reservations (fi g. 2). On the Ute Mountain Ute Reservation, geophysical logs from 11 oil and gas tests and 13 

coal test holes were used to estimate the coal resources underlying the reservation area. Coal thicknesses for each hole were 

given, but no attempt was made to correlate the coal beds. 

For the Southern Ute Reservation, 228 oil and gas tests and 

90 coal test holes were used to evaluate Fruitland coal beds 

in the subsurface. To the extent possible, the authors of this 

20

ARCHULETA

SAN JUAN

McKINLEY

MONTEZUMA

108° 107°

 37° 37°

 36° 36°

108° 107°

COLORADO

NEW MEXICO

Outcrop of Fruitland

 Formation

Farmington

Dulce

Cuba

Ignacio

Durango

SANDOVAL

RIO ARRIBA

LA PLATA

0 5 10 15 20 MILES

Kf

Kf

B

1

2

3

A

A'

A P

D K

I

F

H

G

E

L

C

J

J

J

References For Areas Shown on Map

A/P- - Fassett and others, 1997b

B - - - Roberts, 1989 and Roberts and Uptegrove, 1991

C- - - Roberts, 1991

D - - - Sandberg, 1988a, 1988b, 1990

C/D - Shomaker and Holt, 1973

E - - - Sandberg, 1986

F - - - Ambrose and Ayers, 1994

G - - - Ayers and Zellers, 1994

H - - - Decker and others, 1988

I - - - Kelso and others, 1980 and Kelso and Rushworth, 1982

J - - - Hoffman, 1991 and Hoffman and others, 1993

K- - - M'Gonigle and Roberts, 1997

L - - - Hoffman and Jones, 1998 

●

●

●

● ●

●

●

●

●

●

●

●

●

●

●

●

●

●

●

●

A

A'

Study

area

COLORADO

NEW MEXICO

4

5

6

7

8

9

10

11

12

13

14

15

16

17

18

19

20

0 coal

 area

0 coal

 area

0 coal

 area

Figure 31. Map showing areas of published detailed subsurface studies of Fruitland coal beds. Base map is Fruitland net-coal isopach 

map from panel A, fi gure 29; darker colors indicate thicker coal. Basin-wide cross section A-A’ is on plate 1. Short cross section A-A’

in area G is on fi gure 32. Kf, Fruitland Formation.

Q54 Geologic Assessment of Coal in the Colorado Plateau: Arizona, Colorado, New Mexico, and Utah
report selected one oil and gas drill hole per section to measure 

Fruitland coal beds. No cross sections were constructed, and 

only the most general observations were made regarding the 

continuity of Fruitland coal beds in this area. This report 

has been largely superseded by the Sandberg (1990, area D), 

Roberts (1991, area C), and in part by the Ambrose and Ayers 

(1994, area F) reports.

I—Kelso and others (1980).—This study included the 

western two-thirds of the Southern Ute Indian Reservation. 

The primary focus of the study was to determine Fruitland 

Formation coal tonnage in order to estimate the amount of 

coal-bed methane that might be present in the coal beds. Geophysical logs from 231 oil and gas test holes were used to 

measure coal-bed thicknesses throughout the area. Most of 

these holes are located in T. 32 N., Rs. 6–11 W., T. 33 N., Rs. 

7–11 W., and T. 34 N., Rs. 9, 10 W. Some of these townships 

contain as many as 26 holes used for coal-thickness measurements. The average number of holes for the townships listed 

is 18. The report states that gamma ray–neutron logs were 

used exclusively to measure Fruitland coal beds. The warning 

is given, however, that (p. 14) “The response of gas bearing 

sandstones and coals can be confused on gamma ray–neutron 

logs. Since this type of log was used for picking coals in this 

study, it should be noted that the total coal thickness may be 

exaggerated by the inclusion of gas-bearing sandstones.”

Three stratigraphic cross sections across the study area 

were included in the report. These sections utilized a mixture 

of gamma ray–neutron logs and resistivity logs, but coal beds 

were not shown on the logs and no attempts were made to 

correlate Fruitland coal beds or zones on these cross sections. 

All of the cross sections used the top of the Pictured Cliffs 

Sandstone as a datum. The Kelso and Rushworth (1982) report 

describes Fruitland coals in two holes about a half-mile apart 

just northwest of Ignacio, Colo. (within area I—the Kelso and 

others, 1980, study area). Correlation of coal beds between 

these holes is not discussed.

E—Sandberg (1986).—This report focused on correlating 

Fruitland coal beds in the subsurface in a rectangular area in 

the southwest part of the San Juan Basin. Five stratigraphic 

resistivity-log cross sections on which all Fruitland coal beds 

are correlated are included in the report. All of these cross 

sections use the Huerfanito Bentonite Bed as a datum. The 

average spacing of drill holes on the cross sections is about 

2 mi. Sandberg identifi ed and named six coal beds in this 

report and showed the distribution of these beds on a map of 

the area. In the four northeast-trending cross sections, the top 

of the Pictured Cliffs Sandstone is shown to be rising stratigraphically and Sandberg states, “Where the Pictured Cliffs 

Sandstone–Fruitland Formation contact rises stratigraphically, 

progressively younger coal beds appear at the base of the 

Fruitland .... [Lower coal beds] end abruptly northeastward, 

and stratigraphically higher ones take their place.” Most of the 

beds shown consist of two or more benches separated by noncoal partings, and these benches are usually quite variable in 

their thickness and continuity. 

Sandberg’s Navajo bed is the most continuous coal bed 

in the area. It is about 10 ft thick and is correlated for 11 

mi on northwest-trending cross section E-E′ and for 12 mi 

on northeast-trending cross section B-B′. Sandberg states that 

“The Navajo bed underlies much of the southern two-thirds of 

the area but disappears against the Pictured Cliffs Sandstone 

northeast of the Bisti oil fi eld.” Drill holes 41 and 42 on 

Sandberg’s cross section D-D′ are the same holes as holes 3 

and 4, respectively on stratigraphic cross section A-A′ (plate 

1) of this report. Plate 1 shows the Huerfanito at a depth of 

665 ft in the Tanner Unit 1 hole, whereas Sandberg shows 

the Huerfanito at a depth of 680 ft in this same drill hole. A 

relatively minor difference, but moving the Tanner Unit 1 log 

up 15 ft makes the thick coal bed in that hole correlate better 

with the thick coal bed in drill hole 4 on plate 1, which in the 

author’s opinion is not the case. This “coal bed” is named the 

Bisti bed in Sandberg’s report.

D—Sandberg (1988a, 1988b, 1990).—These three reports 

describe the results of a study of the Fruitland coal resources 

of the Southern Ute Indian Reservation. The 1990 report is 

the preferred reference because the illustrations are at a larger 

scale and it is more readily available. The 1988a report, however, contains a northeast-trending stratigraphic cross section 

of the Pictured Cliffs–Fruitland interval that is not present in 

the 1990 report. This section is on a line between Farmington, 

N. Mex., and Ignacio, Colo., and shows the Fruitland coal 

beds at each control point, identifi es coal zones, but does not 

correlate individual coal beds. Geophysical logs from about 

500 oil and gas drill holes and 24 coal test holes were used 

as a database for this study. Three east-trending and two northtrending stratigraphic cross sections are included in the report, 

and all use the Huerfanito Bentonite Bed as a datum. Fruitland 

coal beds are shown at each control point, but coal beds are 

not correlated. Three coal zones are correlated across the study 

area. Geophysical logs of fi ve of the drill holes included in the 

cross sections are shown to demonstrate the log characteristics 

of Fruitland coal beds. The cross sections show that Fruitland 

coal beds are lensing and are generally not continuous for 

more than a few miles. 

H—Decker and others (1988).—This report is a study 

of the Cedar Hill gas fi eld, the fi rst coal-bed methane fi eld 

discovery in the San Juan Basin. The report focuses on gas 

production and reservoir characteristics but includes an arcuate cross section across the fi eld showing the occurrence and 

continuity of Fruitland coal beds. The basal Fruitland coal 

is shown to be continuous over about a 1-mi2 area on this 

cross section but the authors state that this bed (p. 222) “... is 

commonly split into several individual coal benches by shale 

partings ...” and varies in thickness from 4 to 26 ft. An upper 

zone of Fruitland coals is also shown on the cross section and 

consists of from one to four thin beds.

B—Roberts (1989).—This study consisted of a detailed 

exploratory core drilling project in the Fruitland Formation 

near the west side of the San Juan Basin in Colorado on 

the Southern Ute Indian Reservation. The report describes 

the results of the 23-hole core drilling project in which the 

Fruitland was cored along a 9-mi corridor east of and parallel 

Geology and Coal Resources of the Upper Cretaceous Fruitland Fm., San Juan Basin, New Mexico and Colorado Q55
to the Fruitland outcrop. The average spacing for these holes 

was less than half a mile. Roberts (p. 5) observed “Individual 

coal beds present in the drill holes are lenticular and cannot 

be correlated between drill holes; however the zones in which 

coal beds occur can be correlated.” The distribution and correlation of Fruitland coal zones was shown on a northeasttrending cross section using 22 of the core holes as control 

points; the top of the Pictured Cliffs Sandstone is the datum. 

This section shows that the lowermost A coal zone is continuous across the entire area and the D coal zone is continuous 

across about half the area, splitting into an Upper D and Lower 

D coal to the north. Stratigraphically higher “local” coal beds 

were discontinuous in this area. The Roberts and Uptegrove 

(1991) study mapped Fruitland coal beds on the outcrop adjacent to the area where the core hole drilling project was 

conducted. A correlation diagram was constructed showing the 

variability of Fruitland coal beds in the area. No attempt was 

made to correlate the outcropping coal beds with the coal beds 

in the core holes.

C—Roberts (1991).—In a study of subsurface Fruitland 

coal on the Ute Mountain Ute Indian Reservation Roberts 

examined geophysical logs from 50 drill holes. Density, 

gamma ray–neutron, and resistivity logs were used for coal 

identifi cation and correlation. Subsurface coals were correlated 

with nearby outcropping Fruitland coal beds. Roberts used 

34 of the 50 drill holes plus three measured surface sections 

as control points to construct three cross sections showing 

correlation and distribution of Fruitland coal beds in this area. 

Average spacing of control points was about 1 mi. Roberts 

reported that two informally named coal beds, the Main coal 

bed and the Ute Canyon coal bed, were present throughout the 

study area for a distance of about 10 mi on section B. The 

Upper Main coal bed, lower Ute Canyon coal bed, and other 

“local” coal beds were discontinuous in the area.

J—Hoffman and others (1993).—This study involved the 

drilling of Fruitland coal test holes in three areas in New 

Mexico—two in the northwest and one paralleling the Fruitland outcrop along the southern edge of the basin. The principal focus of the study was to obtain samples of Fruitland coal 

for physical and chemical analyses. Four stratigraphic cross 

sections show the distribution of Fruitland coal beds in the 

cored areas; all use the Pictured Cliffs Sandstone as a datum. 

Fruitland coal beds are correlated between drill holes. The 

cross section in the northwest contains nine drill holes and 

trends northeast, extending across the two areas labeled J on 

fi gure 31. Four holes are present in the southern of these 

two areas, and fi ve holes are in the northern area with a gap 

of about 10 mi separating the two areas. The three cross sections in the south contain 38 drill holes and trend southeast, 

parallel to the Fruitland outcrop over a distance of about 75 

mi. Fruitland coals are most continuous in the southwest part 

of the study area (Bisti area) with some beds being continuous 

for as much as 15 mi even though they thicken, thin, and split 

over this distance.

F—Ambrose and Ayers (1994).—This study was essentially focused on coal-bed-methane-producing wells in the 

Cedar Hill gas fi eld area but also included studies of Fruitland 

coal beds in adjacent areas including the core-hole data 

from the Roberts (1991) report discussed above. The report 

includes a northwest-trending, two-hole, stratigraphic cross 

section showing the distribution of Fruitland coal beds over 

this 4.5-mi area. The traces of the resistivity logs of the two 

holes are shown on the section; the datum is the top of the Pictured Cliffs Sandstone. The distribution of coal beds is quite 

different in these two wells, and no apparent correlations of 

coal beds are visible. The authors, however, put the coals into 

lower, middle, and upper coal groups. A 12-hole, northeasttrending structural cross section correlates Fruitland coal beds 

along a 14-mi-long area. This section shows great discontinuity of coal beds with beds thickening, thinning, pinching out, 

and splitting over relatively short distances. Lower Fruitland 

coal beds are shown pinching out against the stratigraphically 

higher tongues of the Pictured Cliffs Sandstone; stratigraphically higher coal beds appear to the northeast.

Figure 3.12 of Ambrose and Ayers is a stratigraphic cross 

section using the core holes for the northern part of the Roberts 

(1991) core-hole study area and using the top of the lowest 

coal bed as a datum. These authors offer a slightly different 

correlation of the Fruitland coal beds in this area than the one 

presented in the Roberts report.

G—Ayers and Zellers (1994).—This report focused on the 

coal-bed-methane resources of a 220-mi2 area in the northcentral part of the basin. The study involved the use of 

400 drill-hole logs, mostly from producing Fruitland coal-bed 

methane wells. The Ayers and Zellers study is signifi cant 

because it suggested an interpretation of the geometry and 

depositional history of the Pictured Cliffs Sandstone and the 

correlation of Fruitland coal beds that was greatly different 

from previous studies of the Pictured Cliffs and Fruitland 

in the San Juan Basin. Ayers and Zellers suggested that Pictured Cliffs–Fruitland deposition was controlled in the northcentral part of the basin by tectonic subsidence along what 

they termed a “hingeline” that trended northwest across the 

basin. They wrote, “We suggest that structural activity caused 

a higher rate of subsidence in the northern part of the basin 

northeast of the structural hingeline .... This greater subsidence 

created more accommodation space, causing a stillstand of 

the Pictured Cliffs shoreline and allowing the accumulation 

of thick Fruitland peats.” Ayers and Zellers offered no data 

to support this interpretation but provided illustrations in their 

report to show the results of their proposed geologic history. 

Three of their illustrations are herein reproduced and discussed 

in order to evaluate their interpretations.

Figure 32 contains two panels showing A, a reproduction 

of fi gure 4.1 of the Ayers and Zellers report, and B, a more 

conventional interpretation of this cross section. The line of 

this cross section is A-A′ in area G of fi gure 31. Panel B 

uses the same coal-bed and formation-boundary intercepts as 

on panel A (except for the top of the Pictured Cliffs in well 

112); no attempt was made to reinterpret the original well logs 

to redraw this fi gure. The relationship of the Pictured Cliffs 

Sandstone to tongue UP1 of the Pictured Cliffs as depicted 

Q56 Geologic Assessment of Coal in the Colorado Plateau: Arizona, Colorado, New Mexico, and Utah
FARMINGTON

SANDSTONE

AND UPPER

SHALE MEMBER

LOWER SHALE MEMBER

FRUITLAND

FORMATION

PICTURED CLIFFS SANDSTONE PICTURED CLIFFS

SHOREFACE AND

 SHELF

LEWIS

SHALE

DATUM

 upper shale member and

Farmington Sandstone Member

lower shale member

Fruitland

Formation

Pictured Cliffs Sandstone

Lewis Shale

DATUM

B. Reinterpretation of figure 4.1 of Ayers and Zellers (1994) KIRTLAND SHALE

259 205

156

112 167 50 79 203

EXPLANATION

UP2

UP1 Upper Pictured Cliffs sandstone units Kirtland Formation

259 205

156

112 167 50 79 203

EXPLANATION

0

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1500

2000

FEET

0 5 miles

OJO ALAMO SANDSTONE

UP1

UP2

Coal

Huerfanito Bentonite

0

500

1000

1500

2000

FEET

0 5 miles

Ojo Alamo Sandstone

Coal

Huerfanito Bentonite

A. Figure 4.1 from Ayers andZellers (1994)

PC Ss

PC Ss

Southwest

Northeast A A'

Southwest

A Northeast

A'

Figure 32. Two interpretations of Pictured Cliffs Sandstone–Fruitland Formation stratigraphy in the north-central San Juan 

Basin. Panel A is cross section A-A’ from Ayers and Zellers (1994, fi g. 4.1). Panel B is a more conventional portrayal of these 

rocks. Line of cross section is shown in area G of fi gure 31.

Geology and Coal Resources of the Upper Cretaceous Fruitland Fm., San Juan Basin, New Mexico and Colorado Q57
on panel A is geologically not possible. Ayers and Zellers 

state in their report that the main body of the Pictured Cliffs 

represents a regression of the Pictured Cliffs shoreline to the 

northeast and that the Pictured Cliffs rises stratigraphically 

to the northeast, as shown on panel A, northeast of well 79. 

They state that tongue UP1 represents a transgression of the 

Pictured Cliffs shoreline to the southwest. Yet on panel A, 

UP1 is shown descending stratigraphically to the southwest. 

This interpretation could not be correct because by the time 

the Pictured Cliffs shoreline had reached well 205 on panel 

A, Fruitland sediments would have accumulated to at least the 

level of the top of the main body of the Pictured Cliffs at well 

205 and probably slightly higher to allow for some regional 

slope of the land surface from the position of well 50 to the 

position of well 205. A transgressive pulse of the Pictured 

Cliffs shoreline from the position of well 205 would thus have 

resulted in, at the most, a relatively fl at base to tongue UP1 

or even a slight stratigraphic rise in a landward direction to 

the southwest. 

A more realistic portrayal of the data presented in panel 

A is shown on panel B, where the Pictured Cliffs tongue 

at well 50 connects to the main body of the Pictured Cliffs 

between wells 79 and 112. The geologic history resulting 

in this geometry was (1) regression of the Pictured Cliffs 

shoreline to about the position of well 112, (2) transgression 

of the shoreline to a position southwest of well 50, and fi nally, 

(3) regression of the Pictured Cliffs shoreline to the northeast 

edge of the area at well 205. This scenario calls for no lowering in the stratigraphic level of the Pictured Cliffs tongues 

to the southwest. The two Pictured Cliffs Sandstone tongues 

present in wells 259 and 205 represent two additional pulses of 

Pictured Cliffs shoreline transgression and regression following the regression of the Pictured Cliffs shoreline northeast of 

well 205.

Figure 4.16 of Ayers and Zellers shows coal-bed correlations on their structural cross section C-C′ over a distance 

of 5 mi along the same line of section as their cross section 

4.1 (A-A′ of area G, fi g. 31), discussed above. Wells 50 and 

167 are common to both cross sections (note that the numbers 

of coal beds, their thicknesses, and their positions are quite 

different for wells 50 and 167 on fi gures 4.1 and 4.16). Ayers 

and Zellers’ structural cross section C-C′ is shown on panel 

A of fi gure 33. Because coal-bed correlation is more diffi cult 

on a structural cross section, the panel A cross section was 

changed to a stratigraphic cross section on panel B of fi gure 

33 using the top of the Pictured Cliffs as a datum but maintaining the original coal-bed correlations shown on panel A. The 

resultant correlations of panel B, however, appear unrealistic in 

terms of the upper two coal beds being time-transgressive and 

climbing over the tongue of Pictured Cliffs between wells 12 

and 403. Panel C is a modifi cation of the panel B correlation 

diagram showing a more probable correlation of these coal 

beds. This diagram shows that, even over a distance as short as 

5 mi, Fruitland coal beds are lensing and discontinuous.

Panel A of fi gure 34 shows cross section B-B′ from the 

Ayers and Zellers report (their fi gure 4.18). The line of section 

for B-B′ is almost identical to the northern two-thirds of their 

cross section A-A′ (fi gure 4.1) shown in area G on fi gure 

31. Well 205 is common to both cross sections (note again 

that coal-bed numbers, thicknesses, and positions are different 

in well 205 of fi gures 4.18 and 4.1). On fi gure 4.18, Ayers 

and Zellers presented two interpretations of the geometry of 

the Fruitland and associated rocks; the fi rst interpretation (a) 

uses the Huerfanito Bentonite Bed as a datum; the second, 

interpretation (b) uses the base of the Ojo Alamo Sandstone as 

a datum. There are problems with both of these depictions. On 

the section using the Huerfanito as a datum (interpretation a), 

the geometry of the stratigraphically rising main body of the 

Pictured Cliffs appears to be appropriate, but again, as in their 

cross section A-A′ (fi g. 32 of this report), the authors show 

the transgressing tongue of Pictured Cliffs, UP1, becoming 

stratigraphically lower to the southwest. It is suggested that the 

lowermost part of UP1 connects with the main body of the 

Pictured Cliffs near well 213 as drawn on panel B of fi gure 32 

and discussed above. In addition, Ayers and Zellers show the 

Ojo Alamo Sandstone rising stratigraphically between wells 

70 and 213 and intertonguing with the Farmington Sandstone 

Member. This depiction is incorrect because there is a substantial unconformity (7–8 m.y.) separating the Tertiary Ojo Alamo 

from the Upper Cretaceous Farmington Sandstone Member. 

This contact should be drawn as a straight line between wells 

70 and 213 and depicted as an unconformable contact.

Ayers and Zellers justifi ed the use of the base of the Ojo 

Alamo as a datum on cross section 4.18b (fi g. 34) as follows 

(p. 80–81):

Using a datum above the Fruitland Formation (fi g. 4.18b) gives 

a different perspective of basin-fi lling processes and suggests 

structural control of the Pictured Cliffs shoreline and, indirectly, 

the distribution of thick Fruitland coal seams .... Therefore, the 

base of the Ojo Alamo Sandstone was used as a local datum. 

From fi g. 4.18b we surmise that differential subsidence north of 

a structural hingeline ... controlled movement of the Pictured 

Cliffs shoreline by creating more accommodation space in the 

northern part of the basin. In fi g. 4.18b, it is apparent that (1) if 

the increased thickness of Lewis Shale between wells 70 and 

213 is due to differential subsidence, then thick coals in well 

70 may override UP1 and UP2 in well 213 rather than terminate 

against them as suggested in fi g. 4.18a, and (2) if less rapid 

aggradation is required at well 70 to keep pace with aggradation 

in well 213, then more time is available for uninterrupted peat 

accumulation at well 70, and hence the greater thickness of peat 

southwest of UP1. Because Upper Cretaceous strata thicken 

basinward, in part because of increased basin subsidence, coal 

seams are not parallel to the Huerfanito Bentonite.

It is clear from this quotation that Ayers and Zellers considered their depiction of the Fruitland Formation and associated rocks on fi gure 4.18b to be a linchpin for their arguments 

that “differential subsidence” north of a “structural hingeline”

was the explanation for thick coals overriding tongues of Pictured Cliffs Sandstone. The fl aw in this argument is that the 

base of the Ojo Alamo Sandstone is an unconformity representing about 7–8 m.y. of missing time (fi g. 13, plate 1). 

Q58 Geologic Assessment of Coal in the Colorado Plateau: Arizona, Colorado, New Mexico, and Utah
0

100

200

300

FEET

0

100

200

300

FEET

0

100

200

300

FEET

188 167 18 71 12 50 403 35 31

PICTURED CLIFFS SANDSTONE

UP 1

188 167 18 71 12 50 403 35 31

188 167 18 71 12 50 403 35 31

PICTURED CLIFFS SANDSTONE

PICTURED CLIFFS SANDSTONE

A. Structural correlation diagram

B. Stratigraphic correlation diagram

C. Modified stratigraphic correlation diagram

5 miles

5 miles

5 miles

PICTURED CLIFFS

 SANDSTONE

 TONGUE

UP 1

Figure 33. Alternative interpretations of coal-bed correlation diagram C-C’ from Ayers and Zellers (1994, fi g. 

4.16). Panel A shows original fi gure which is a structural cross section; panel B is modifi cation of A showing 

coal-bed correlations unchanged but with a stratigraphic datum—the top of the Pictured Cliffs Sandstone; 

panel C is a modifi ed stratigraphic cross section portraying a more likely correlation of these coal beds. Line 

of cross section is nearly the same as the south end of section A-A’ of Ayers and Zellers (1994, fi g. 4.1). Line 

of section A-A’ is in area G of fi gure 31, section A-A’ is on fi gure 32; control points 50 and 167 are common 

to A-A’ and this cross section.

Geology and Coal Resources of the Upper Cretaceous Fruitland Fm., San Juan Basin, New Mexico and Colorado Q59
70 213 205

OJO ALAMO

SANDSTONE FARMINGTON SANDSTONE

 MEMBER

LOWER SHALE MEMBER

PICTURED CLIFFS SS

KIRTLAND

 SHALE

LEWIS SHALE

DATUM

HUERFANITO BENTONITE BED

UP1

11.5 mi 3 mi

a

70 213 205

FARMINGTON SANDSTONE

 MEMBER

FRUITLAND FORMATION

FRUITLAND FORMATION

LEWIS SHALE

HUERFANITO BENTONITE BED

UP2

UP1

UP2

KIRTLAND

 SHALE

PICTURED CLIFFS SS

OJO ALAMO

SANDSTONE

11.5 mi 3 mi

DATUM

b

LOWER SHALE MEMBER

A. Figure 4.18 from Ayers and Zellers (1994)

39

40

41

42

43

24

25

26

27

28

29

31

32

33

34

35

36

37

38

39

40

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36

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31

33

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34

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32

33

36

38

28

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30

31

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33

34

38

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35

36

39

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41

42

43

44

GR Induction

GR Induction

GR Induction duction

GR

GR

Conductivity

Conductivity Conductivity

3.6 4.1 5.3 6.1

San Juan 29-7 65

Daum 4A Barron Kid 7

Rosa Unit 24

14

15 16

17

25

26

27

28

29

30

31

32

33

34

35

36

37

38

39

40

41

San Juan 32-5 2

18

B. Segment of cross section A-A' (plate 1 of this report)

Ojo Alamo

Sandstone

C33n

C32r

Paleomagnetic

field reversal

SP Resistivity

Northeast

Southwest

Farmington

Sandstone

Member of

Kirtland

Formation

lower shale member of

 Kirtland and Fruit-

 land Formation

Pictured Cliffs

Sandstone

Lewis Shale

Huerfanito Bentonite

 Bed

73.50 Ma

DATUM 75.76 Ma

30 32

LEGEND

SP - Spontaneous potential curve GR - Gamma ray curve

Tertiary (65 Ma)

Cretaceous (73 Ma)

B

B' B B'

DATUM

Figure 34. Comparison of stratigraphic interpretations of Fruitland Formation and associated rocks as 

presented by Ayers and Zellers (1994) and this report. Panel A shows two interpretations of stratigraphy 

for section B-B’ by Ayers and Zellers with different datums. Line of section B-B’ is nearly the same as 

section A-A’ shown in area G of fi gure 31; control point 205 is common to both sections. Panel B shows 

part of cross section A-A’ (plate 1) of this report; this section is parallel to and about 6 miles southeast of 

the Ayers and Zellers cross sections (fi g. 31).

Q60 Geologic Assessment of Coal in the Colorado Plateau: Arizona, Colorado, New Mexico, and Utah
During that 7- to 8-m.y. time span, subsidence of the basin 

area ceased; Upper Cretaceous rocks were uplifted, especially 

in the southeast part of the basin; and erosion subsequently 

removed as much as 1,200 ft of strata on the east side of 

the basin (fi gs. A3-2 through A3-5). Next, uplift, north or 

northwest of the present basin area, created a highland that 

became the source of high-energy, braided-stream deposits that 

are now the conglomeratic Ojo Alamo Sandstone. (See Fassett, 

1985, p. 318–322, for a detailed description of these geologic 

events.) These events effectively decoupled the erosion surface 

on which the Ojo Alamo Sandstone was deposited from any 

events that may have controlled the deposition of the Pictured 

Cliffs Sandstone and overlying Fruitland coal beds more than 

10 m.y. earlier. The use of an overlying unconformity as a 

datum to interpret the depositional history of underlying rocks 

is geologically invalid, and the use of that interpretation to 

justify a radically new structural interpretation for deposition 

of the Pictured Cliffs and Fruitland cannot be defended.

Cross section A-A′ (plate 1) of this report is parallel to 

and about 6 mi southeast of the Ayers and Zellers cross sections discussed above and shown in area G of fi gure 31. Panel 

B of fi gure 34 shows the segment of the A-A′ cross section 

that corresponds to the cross sections of Ayers and Zellers. 

The radiometric ages of the Huerfanito Bentonite Bed and the 

reversal in the Earth’s magnetic fi eld from magnetic chron 

C33n to C32r are shown on this cross section to emphasize 

the temporal evolution of the Lewis Shale, Pictured Cliffs 

Sandstone, and Fruitland Formation and to emphasize the parallelism of time lines within these rock units. Correlation of 

Fruitland coal beds and other rock units on panel B are more 

realistic and accurate than either of the two depictions shown 

on panel A.

A/P—Fassett and others (1997b).—This report was a 

study of two separate areas near the outcrop of the Fruitland 

Formation in the northern part of the San Juan Basin. The 

study was conducted to try to determine the source of methane 

seeping from Fruitland Formation coal beds at several gas 

seeps on the northern rim of the basin. An integral part of 

this study was to conduct the most precise correlation of 

Fruitland coal beds possible, especially from the outcrop into 

the subsurface, to determine if these coals could be conduits 

for gas moving updip from producing gas wells. The study 

included large-scale surface mapping of Fruitland coal beds 

adjacent to the seep areas. 

In the Pine River gas-seep study area (area P on fi gure 

31), four closely spaced test holes were drilled downdip from 

gas seeps to try to determine the source of the gas seeps. 

These holes are less than 0.2 mi apart, and three of them 

were cored through the Fruitland coals to provide a closely 

spaced subsurface data set with which to correlate Fruitland 

coal beds. (Coal thickness measurements from drill core from 

these three holes confi rmed the accuracy of determinations of 

coal thicknesses and coal quality based on the density logs of 

these holes.) 

Stratigraphic cross section A-A′ on fi gure 35 is a copy of 

fi gure 1-3a from the Fassett and others study (1997b) showing 

detailed correlations of Fruitland coal beds in the Pine River 

area over a distance of 4.4 mi using fi ve wells and drill holes 

for control. This east-trending cross section is parallel to the 

Fruitland Formation outcrop. The basal coal lying directly on 

top of the Pictured Cliffs is continuous across the area but 

splits and thins to the east. The thick middle coal bed also 

extends across the area but splits both to the east and west. 

Other coal beds on this cross section are discontinuous along 

the line of section. 

Cross section B-B′ on fi gure 35 is fi gure 1-4a from the 

Fassett and others study (1997b), showing detailed correlations 

of Fruitland coal beds over a distance of 3 mi using seven 

wells and drill holes for control. The three northernmost drill 

holes are cored. This north-trending cross section is at right 

angles to the Fruitland outcrop, and the base of the Fruitland 

ranges from a depth of 221 ft in the Killian Deep hole in the 

north to 1,968 ft in the Streeter GU 1 gas well to the south. All 

of the coal beds shown are clearly discontinuous and lensing, 

and the lowermost thicker coal beds on the southwest end 

of the cross section either pinch out or split, thin, and grade 

into carbonaceous shales on the north end of the cross section 

near the Fruitland outcrop. The stratigraphically higher and 

thinner coal beds on the north end of the section are all 

discontinuous and none are present in the deeper, coal-bedmethane-producing wells to the south. Two additional larger 

scale and more detailed cross sections in the vicinity of the 

Pine River gas seeps are in the Fassett and others report (fi g. 

1-6).

Figure 36 is a stratigraphic coal-correlation diagram from 

the Fassett and others study (fi g. 1-8) in the Durango, Colo., area 

(area A, fi g. 31). This cross section is 6.8 mi long and uses 8 

coal-bed methane gas wells for control. More than 50 separate 

coal beds are present on this section, all of which, to a greater 

or lesser degree, are discontinuous, lensing, or splitting. None of 

the coal beds extend across the entire line of section. The most 

continuous coal bed is the one directly overlying the Pictured 

Cliffs Sandstone in the northeast part of the section, but this 

bed pinches out to the southwest between the University 9-2 

and the Wheeler 8-1 wells. The very thick tongue of Pictured 

Cliffs Sandstone in the Federal 4-1 well (but not present in the 

University 9-2 well less than a mile to the southwest) is the 

most striking feature on this cross section. All of the thick lower 

Fruitland coal beds southwest of this Pictured Cliffs tongue 

pinch out against it to the northeast or wedge out into it as 

seen in the Federal 4-1 well. This thick Pictured Cliffs tongue 

was mapped on the outcrop less than a mile northwest of this 

well. From the Federal 4-1 well to the northeast, a different, 

stratigraphically higher sequence of thick lower Fruitland coals 

appear, but these coal beds are discontinuous and none are 

present in the Day-V-Ranch 35-1 well. Three additional coalcorrelation diagrams oriented at right angles to the section on 

fi gure 36 are in the Fassett and others report. Those sections 

appear to show somewhat more continuity of the coal beds along 

the line of depositional strike of the Fruitland (southeasterly), 

but they are relatively short cross sections (about 1.5 mi long) 

and only use two or three wells each for correlation purposes.

Geology and Coal Resources of the Upper Cretaceous Fruitland Fm., San Juan Basin, New Mexico and Colorado Q61
Estuarine

deposits

250

200

150

100

50

0

300

FEET

Pictured Cliffs Sandstone

Streeter

GU 1 Conrad Ranch

 GU B

Huntington

 GU A-1

 GURR

Fed GU 1

Pole

Barn

Killian

Deep

Salmon

 No. 1

SOUTHWEST

NORTHEAST

? Qal

100'

200'

400'

500

600'

700'

800'

900'

1000'

1100'

1200'

1400'

1500'

1600'

1600'

1700'

1800'

1700'

1800'

1900'

900'

Fruitland

Formation

B .75 .85 .68 .14 .42 .21 B'

Ground

surface

Fluvial channel sandstone

Fluvial channel

 sandstone

Fluvial channel

 sandstone

Fluvial channel

 sandstone

Vertical exaggeration = X 62

Vertical exaggeration = X 34

WEST

Colorado

 AX

Huntington

 GU A-1

Conrad

GU A-1

Wommer

 GU A-1

Magoon

 Fed 1

0

50

100

150

200

FEET

1100'

1200'

1600'

1500'

1500'

1400'

1600'

1700'

1500'

Fruitland

Formation

A A' 1.2 .65 1.4 1.15

PICTURED CLIFFS

 SANDSTONE

 TONGUE

Fluvial channel sandstone

Fluvial channel

Fluvial channel

sandstone

sandstone

1600'

PICTURED CLIFFS SANDSTONE

EAST

Figure 35. Fruitland Formation coal-bed correlation diagrams from the Pine River gas-seep study (Fassett and others, 1997). 

These cross sections are in area P on fi gure 31. Cross section A-A’ is parallel to and about 1.5 mi south of the Fruitland 

Formation outcrop; section B-B’ is at right angles to section A-A’. The Huntington GU A-1 well is common to both sections. 

The datum for both cross sections is the top of the Pictured Cliffs Sandstone. Cross sections are from fi gures 1-3a (A-A’) and 

1-4a (B-B’) of Fassett and others (1997). Drill holes shown in red were cored.

Q62 Geologic Assessment of Coal in the Colorado Plateau: Arizona, Colorado, New Mexico, and Utah
K—M’Gonigle and Roberts (1997).—This study focused 

on determining the Fruitland coal resources in the part of the 

San Juan National Forest that overlies the northwest part of 

the San Juan Basin. Geophysical logs from 82 drill holes 

were used to measure the thicknesses of Fruitland coal beds 

in the study area. The report does not indicate what kind of 

geophysical logs were used but L.N.R. Roberts (oral commun., 

1999) states that a mixture of density, gamma ray–neutron, and 

resistivity logs were used to measure the coal for that study. 

The report states, “The lenticular nature of Fruitland Formation coal beds precludes consistent correlation of individual 

beds between wells; therefore, it was not practical to calculate 

resources for individual beds.” This report did not include a 

Fruitland coal-bed correlation diagram.

K—Hoffman and Jones (1998).—This study was sponsored by the USGS to determine the availability of Fruitland 

coal in a block of four 71⁄2-minute quadrangles: Bisti Trading 

Post, Alamo Mesa West, Tanner Lake, and The Pillar 3 NE, 

in the southwest part of the San Juan Basin (fi gs. 31, A6-1). 

(This report is also part of Rohrbacher and others. chap. F, this 

CD-ROM.) Fruitland coals were shown to be present in four 

zones in the study area named, from bottom up, the red, green, 

blue, and yellow coal zones. 

Three structural cross sections in this report show correlations of the four coal zones. Cross section A-A′ is about 12 mi 

long and parallels the outcrop of the Fruitland Formation; 25 

drill holes were used for control for this section. Coal depths 

on this section range from about 30 ft to 200 ft. The red coal 

zone is continuous across the entire line of section, although 

individual coal beds within the zone are quite variable in 

number and thickness and do not correlate well. The green 

zone is present only in the northwest part of the study area, and 

the blue and yellow zones are present across most of the study 

area with some gaps in their continuity. Individual coal beds 

within these zones are not readily correlateable.

Two cross sections at right angles to the outcrop, B-B′

and C-C′, also show coal-zone correlations in the study area. 

Each of these sections uses 12 drill holes for control. Depths 

of coal beds range from 30 ft to 460 ft on these two sections. 

As in cross section A-A′, the basal red coal zone is the most 

A 1.04 mi.

0.5 mi.

0.88 mi. 1.52 mi.

0.48 mi.

1.07 mi. 1.3 mi. A'

 SE Durango

Fed. 34.5 34-1

Indian Creek

 SU 12U-2

W. Animas

 Wheeler

 8-1

W. Animas

University

 9-2 SE Durango

 Fed. 4-1

 SE Durango

 34-1

Day-V-Ranch

 35-1 

Truman-Baird

 1-25

SOUTHWEST NORTHEAST

250

200

150

100

50

0

300

450

400

350

500

FEET

T.D. 7309'

T.D. 2189'

T.D. 2400'

T.D. 2347'

T.D. 2399'

T.D. 2311'

1800'

1700'

1600'

1900'

2000'

2100'

2000'

1900'

1800'

2200'

2300'

2100'

2000'

1900'

1800'

1900'

2000'

2100'

2200'

T.D. 2263'

T.D. 2305'

1800'

1900'

1700'

2000'

2200'

2000'

1900'

1800'

2100'

2200' 2300'

2200'

2100'

2000'

1900'

2100'

2000'

1900'

1800'

1700'

2100'

2300' 2100'

Fruitland

Formation

Pictured Cliffs Sandstone

Pictured Cliffs Sandstone

DATUM

DATUM

Figure 36. Fruitland Formation coal-bed correlation diagram from the Durango gas-seeps study area. This cross section is in the 

area labeled A on fi gure 31. Cross section is parallel to and about 1 mi south of the Fruitland Formation outcrop. Cross section is 

fi gure 1-8 of Fassett and others (1997). Vertical exaggeration is x 48.

Geology and Coal Resources of the Upper Cretaceous Fruitland Fm., San Juan Basin, New Mexico and Colorado Q63
continuous, and the overlying green, blue, and yellow zones 

are less continuous. The numbers and thicknesses of coal 

beds within each coal zone appear to be quite variable, and 

individual coal beds do not appear to correlate well. 

Basin-Wide Studies

Fassett and Hinds (1971).—In this study of the Fruitland 

and its contained coal beds throughout the subsurface of the 

San Juan Basin, the authors (p. 54–57) discussed the diffi culty 

in correlating Fruitland coal beds in the subsurface and stated 

that Fruitland coals are extremely lenticular and can only 

rarely be correlated for even a few miles. They wrote (p. 57), 

“Dependable correlation of the coal beds requires control spacing of not more than 1 or 2 mi and even less spacing in areas 

of very abrupt facies change. Because of the spacing of control 

points used in this study, individual coal beds have not been 

correlated.” These authors did, however, graphically portray 

the distribution of coal beds at each of the 324 control points 

used for their Fruitland coal study on plate 3 of their report 

and identifi ed, by name and location, all of the drill holes used 

for control.

Kelso and others (1987), Kelso and Wicks (1988).—Kelso 

and others (p. 121) stated that “The spacing between control 

points averages 5 mi and correlation of individual beds was not 

possible at this scale. No grouping or zone determinations was 

established due to the lack of traceable markers.” Kelso and 

Wicks referred to two cross sections that were constructed to 

help determine the distribution of Fruitland coal beds across 

the San Juan Basin, but these cross sections were not included 

in these two reports and, as far as is known, have never been 

published. 

Ayers and others (1994).—This report did not directly 

address the correlation of individual Fruitland coal beds in 

their basin-wide study of Fruitland coal. The authors did state, 

however, in a section of their report headed “Number of Coal 

Seams” (p. 30) that “Fruitland coal occurs in as many as 16 

seams in the San Juan Basin (fi g. 2.18); these coal seams 

are most abundant in a 40-mi-wide, northwest-trending belt 

of six or more coal seams that bisects the basin; seams are 

most numerous in the northwestern half of this trend.” On 

a northeast-trending stratigraphic cross section (fi g. 2.2, reproduced herein on fi gure 21), these authors present a basin-wide 

correlation of Fruitland coal beds. On this cross section these 

authors have correlated two Fruitland coal beds in the upper 

part of the Fruitland in the northern part of the basin for nearly 

60 mi to the southwest. In the southwest part of the basin 

they correlate the basal Fruitland coal bed for more than 50 

mi to the northeast. These correlations show these coal beds 

parallel to the Fruitland Formation–Kirtland Formation contact 

(the datum for the cross section) except in the northern part 

where several coal beds are shown overriding Pictured Cliffs 

Sandstone tongues. 

The correlations of Fruitland coal beds shown on the 

fi gure 2.2 of the Ayers and others report are not correct. 

These long-distance correlations of Fruitland coals are based 

on showing these continuous coal beds as being parallel to 

the Fruitland-Kirtland contact and on the assumption that this 

contact is a time line. It has been demonstrated in earlier 

discussions that the Fruitland and overlying Kirtland are timetransgressive across the basin by as much as 2 m.y. (fi gs. 4, 

13, and plate 1); thus, the basic assumption that coal beds can 

be correlated parallel to the Fruitland-Kirtland contact is seriously in error and cannot be defended. The statement by Ayers 

and others (p. 30) that there are no more than 16 Fruitland 

coal beds in the basin is also in error. There are hundreds of 

Fruitland coal beds in the basin; specifi c numbers of coal beds 

are discussed in detail below.

Fruitland Coal-Bed Correlations—This Report

Cross Section A-A′

Stratigraphic cross section A-A′ (plate 1) portrays the 

correlations of Fruitland Formation coal beds in 20 drill holes 

across the basin from southwest to northeast. Where there was 

a question regarding the presence or thickness of coal beds 

on the resistivity logs on this cross section, bulk-density logs 

from nearby wells were examined to confi rm the existence and 

thicknesses of the coals. As the net-coal isopach map shows 

(fi g. 28), there is a bulk-density log within a mile of almost all 

of the drill holes shown on cross section A-A′. 

There are hundreds of individual Fruitland coal beds in 

the San Juan Basin. Cross section A-A′ has more than 60 coal 

beds on it. The short cross section (less than 7 mi long) shown 

on fi gure 36 contains more than 50 coal beds. The distribution 

of Fruitland coals is intimately related to the regression and 

stratigraphic rise of the Pictured Cliffs Sandstone from southwest to northeast. Coal beds are commonly in the lowermost 

200 ft of the Fruitland—within 200 ft stratigraphically of the 

top of the Pictured Cliffs Sandstone. Thus, as the Pictured 

Cliffs rises across the basin, so do the overlying Fruitland coal 

beds. Many of the coal beds shown on cross section A-A′, 

especially in the upper part of the Fruitland, are only present in 

one drill hole. The number of coal beds in a drill hole ranges 

from two in holes 4, 8, 19, and 20 to 10 in holes 12, 14, and 

17. Two of the drill holes on the cross section on fi gure 36, the 

West Animas Wheeler 8-1 and the West Animas University 9-2 

wells, each have 21 coal beds.

Correlation of coal beds on cross section A-A′ (plate 

1) was based on using the Huerfanito Bentonite Bed as the 

datum. The basic assumption was that coal beds are generally 

not time-transgressive and thus they will generally correlate 

along time planes parallel to the Huerfanito Bed. A further 

assumption was that no differential tectonism had occurred 

between the time the Huerfanito was deposited and the time 

when Fruitland peats were being deposited. These assumptions are validated by the presence of a second time line, the 

magnetic-chron reversal from C33n to C32r, well above the 

level of most of the Fruitland coals that is essentially parallel 

Q64 Geologic Assessment of Coal in the Colorado Plateau: Arizona, Colorado, New Mexico, and Utah
to the Huerfanito Bentonite Bed. If a coal bed occurs at the 

same stratigraphic level in adjacent drill holes, it is assumed to 

be the same bed. In reality this may not be true because coal 

beds at the same level in adjacent holes may pinch out between 

those holes, and undoubtedly that probably occurs for some 

of the beds that are shown to correlate on this cross section. 

Thus the correlations shown on cross section A-A′ should be 

considered to be probable, but by no means certain. 

It is the exception for a Fruitland coal bed to correlate 

across more than two of the drill holes shown on section A-A′. 

There are only four instances where this occurs: The thin basal 

coal in drill hole 4 correlates to holes 3 and 2 to the southwest 

but pinches out against the stratigraphically rising Pictured 

Cliffs to the northeast. A thin coal bed splits from the top of a 

thicker coal bed in hole 12 and can be correlated in holes 11, 

10, 9, and 8 to the southwest, a distance of about 19 mi. (This 

is by far the longest distance a Fruitland coal bed is correlated 

on this cross section.) From drill hole 14, the lowest Fruitland 

coal bed correlates to hole 13 and splits into two coal beds in 

hole 12. And the coal bed that pinches out between massive 

tongues of the Pictured Cliffs northeast of hole 16 can be 

correlated to the southwest to holes 15 and 14 where it splits 

and pinches out to the southwest.

Computer Correlations

Earlier studies of Fruitland coal beds in the basin, principally Fassett and Hinds (1971), indicated that, even though 

Fruitland coals were discontinuous in a northeasterly direction, 

at right angles to Pictured Cliffs shoreline trends, Fruitland 

coal beds would probably correlate better in a southeasterly 

direction along depositional strike of the Pictured Cliffs. This 

paradigm was tested using the StratiFact PC software program. 

The graphics part of the StratiFact program allows for quick 

and easy construction of cross sections by selecting a series of 

drill holes in map view and viewing a cross section of those 

drill holes. The display shows all of the coal beds in each drill 

hole and a variety of correlation lines can be quickly drawn 

between coal beds to try and fi nd the best correlations possible. 

A dozen cross sections can easily be constructed in an hour in 

this way using any combination of drill holes in the database.

After the database for the 752 drill holes selected for this 

study had been entered into the StratiFact program, hundreds 

of different cross sections were generated to test whether Fruitland coal beds could be correlated in any preferred orientation 

of cross section lines. The results of those correlation experiments were essentially negative. It was found that Fruitland 

coals were just as lensing and discontinuous parallel to Pictured Cliffs shoreline trends as they were at right angles to 

those trends. Other experimental cross sections were drawn in 

areas of thick coal shown on the net-coal isopach map (fi g. 28) 

to test whether better correlations would be found parallel to 

those trends. The results of these attempted correlations were 

again essentially negative—even though thicker Fruitland net 

coal occurs in a specifi c area along a trend, the individual 

coal beds in the drill holes within that trend were found to 

be quite discontinuous and lensing. Because no areas of the 

basin appear to contain extensively correlateable coal beds, 

no additional coal-correlation diagrams were prepared for this 

report. (The StratiFact digital database for this study has been 

added to the USGS NCRDS (National Coal Resources Data 

System) and is in Appendix 2 of this report and is thus available for interested users to conduct their own coal-correlation 

studies.)

Altered Volcanic Ash Beds as Markers

Fruitland coal beds contain altered volcanic ash beds in 

many parts of the San Juan Basin. Rarely, these ash beds occur 

in non-coal strata of the Fruitland. In the process of measuring 

coal beds on bulk-density logs, every effort was made to 

identify possible ash beds, and these beds were included in 

the database as possible aids for coal-bed correlation. Altered 

ash beds do not produce a unique response on geophysical 

logs. On some logs, they produce an off-scale kick on the 

gamma ray log trace, and they can also produce a high-level 

resistivity response on conductivity logs. These log characteristics, however, appear to be somewhat variable. Ash beds are 

seen mostly in coal beds because they are best preserved in 

a sequestered peat-swamp environment as opposed to higher 

energy environments outside the swamps where they normally 

would be quickly dispersed and diluted by mixing with other 

clastic material following rainfall and runoff. The StratiFact 

cross-section program was used to try to correlate all of the ash 

beds in the database, but with little success. In only one or two 

very limited areas could an altered ash be correlated between 

adjacent drill holes. 

In the area of the Roberts (1989) report (area B on fi g. 

31), altered ash beds were reported in coal beds in drill core, 

on geophysical logs, and in coal beds on the nearby outcrop. 

Roberts and McCabe (1992) found that Fruitland coal beds 

in this area contained distinctive ash beds that could be used 

as coal-bed correlation tools both on the outcrop and in the 

subsurface. They stated (p. 125), “One tonstein within the D 

coal zone can be traced in the subsurface for over 5 km.”

In the southwest part of the basin, the DEP ash bed 

(discussed in the “Hunter Wash Study Area” section of this 

report and shown on fi gs. 9 and 10) and the thin dirty coal 

bed in which it occurs were found to be present on the outcrop 

about 3 mi west of the DEP ash-bed collection site. This 

coal bed is poorly exposed and cannot be continuously traced 

between the two localities. The presence of the ash bed in 

the same position within this coal bed, however, makes the correlation of this coal bed certain. In summary, altered ash beds 

have not been found to be a useful aid for coal-bed correlation 

except in limited areas in the San Juan Basin.

Geology and Coal Resources of the Upper Cretaceous Fruitland Fm., San Juan Basin, New Mexico and Colorado Q65
Fruitland Coal Character

Coal Quality

Early USGS reports and maps contained proximate analyses of coal samples collected from small active or abandoned 

Fruitland coal mines around the northern rim of the San Juan 

Basin. The locations of 30 of these mines are shown in Fassett 

and Hinds (1971, fi g. 19), and the relevant data for these mines 

is in table 8 of that report. Figure A3-6 is modifi ed from fi gure 

19 of Fassett and Hinds (1971); table A3-1 is a modifi cation 

of table 8 from that report. Many of the measured sections 

in the northwest and north parts of the basin shown on fi gure 

28 were measured at or near these old Fruitland coal mines. 

No composite report summarizing these coal analyses has been 

published. Fassett and Hinds (1971, table 4) presented results 

from proximate analyses of Fruitland coal samples from 65 

locations throughout the basin. (At two locations, two coal 

beds were sampled; thus, table 4 contains analyses of 67 coal 

samples.) Four coal samples were from outcropping coal beds, 

three were from core holes, and the remaining 58 were cuttings 

samples collected from drilling oil or gas wells in the interior 

part of the basin. On the basis of these data, Fassett and Hinds 

(1971) constructed a series of maps showing the distribution 

of coal-quality values throughout the basin. The Fassett and 

Hinds report has been out of print for many years and thus 

is no longer readily available and because no newer Fruitland 

coal quality data have been published for the deep basin, the 

coal-quality table and coal-quality fi gures from Fassett and 

Hinds (1971) are discussed briefl y herein and are reproduced 

in Appendix 3 of this report for easy reference.

The 58 coal cuttings samples discussed above were processed in an unorthodox manner. The cuttings samples were 

collected from drilling oil or gas wells and consisted of a 

mixture of fragments of coal and other rock types coated with 

drilling mud. It was thus necessary to process these samples 

to remove extraneous, non-coal material prior to submitting 

the coal samples for analyses. This processing involved thoroughly washing the coal cuttings with water to remove drilling 

mud, air-drying the samples at ambient temperatures, and then 

immersing the cuttings in carbon tetrachloride (specifi c gravity 

1.59) to remove non-coal fragments with a density greater 

than 1.59. The resulting samples submitted for analyses thus 

consisted of a mixture of coal fragments ranging from nearly 

pure coal to coal containing no more than 40 percent ash.

Table A3-2 (table 4 of Fassett and Hinds) presents these 

high-graded coal analyses. The as-received values certainly 

do not fully represent coal beds in the ground. The drilled 

coal beds would have contained thin interbeds of non-coal 

rock and high-ash coal (typical of most Fruitland coal beds 

on the outcrop) and fragments of these non-coal layers would 

have been eliminated from the samples in the fl otation process 

described above. The as-received heating values are higher and 

ash values are lower in table A3-2 than these values would be 

for an in-the-ground complete-coal-bed sample. The calculated 

analyses values, however, such as the moisture- and ash-free 

heating values and fi xed carbon and sulfur percentage values 

(table A3-2) are more representative of the coal in place from 

which the cuttings samples came. (Subsequent analyses of 

Fruitland coal core samples from the few drill holes for which 

such data have been published have confi rmed the accuracy of 

these calculated values.) 

Figure A3-7 (fi g. 23 of Fassett and Hinds, 1971) shows 

the sample locations and as-received heating values in Btu’s 

(British thermal units) for coal samples from those locations. 

Figure A3-8 (fi g. 25 of Fassett and Hinds) is a contour map 

of moisture- and ash-free Btu values in the basin showing that 

these values range from 13,460 Btu in the southwest to 15,720 

in the north-central part of the basin. Figure A3-9 (fi g. 26 of 

Fassett and Hinds) is a contour map of fi xed carbon percentages (moisture and ash free). This map shows that fi xed carbon 

ranges from 54.8 percent in the southwest to 72.4 percent 

in the north-central part of the basin. The moisture- and ashfree Btu map and the fi xed-carbon percentage map both show 

increasing thermal maturity of Fruitland coals toward the present basin axis and refl ect greater depth of burial in that area. 

(The thermal maturity of Fruitland coals is discussed in more 

detail below in the “Vitrinite Refl ectance” section of this 

report.) 

Sulfur percentages (as-received) range from 0.5 to 2.2 

percent; only six of the 67 samples analyzed had a sulfur 

percentage in excess of 1.0 percent (table A3-2, fi g. A3-10). 

The average sulfur content for all samples was 0.75 percent. 

Figure A3-10 (not from Fassett and Hinds, 1971) shows the 

distribution of as-received sulfur values listed in table A3-2 

and plotted on a map of the San Juan Basin. This map shows 

remarkable uniformity of sulfur content throughout the basin, 

and there are no discernible trends in these values. The fi ve 

sulfur values in excess of 1.0 percent on fi gure A3-10 (localities 10, 12, 13, 54, 58) appear to be anomalous, and, if these 

values are excluded, the average sulfur value for the other 60 

localities is 0.67 percent. 

Moisture content for Fruitland coals is generally higher in 

samples from the outcrop or from shallower drill holes (< 112 

ft deep) near the outcrop and ranges from 2.5 to 12.0 percent 

in those areas. Coal samples from drill holes in the deeper 

parts of the basin have moisture contents ranging from 0.8 to 

9.5 percent; only three deep samples had moisture contents 

exceeding 5 percent. Average moisture content for deep coals 

is 2.5 percent. (Ash-content percentages are discussed below 

in the “Coal Density” section of this report.)

Hoffman and others (1993) published a detailed study 

of Fruitland coal quality based on coal core samples from 

relatively shallow holes in the northwest and southern parts 

of the basin. Core-hole depths were less than 400 ft except 

for one hole that was nearly 800 ft deep. Coal test holes 

were drilled at 49 sites; nine in the northwest and 40 in the 

southern part of the basin. At each site a pilot hole was drilled 

to determine depths to coal beds and a twin hole was drilled 

nearby in which all coal beds 2.5 ft thick or greater were 

cored. Partings in the coal less than 0.8 ft thick were included 

Q66 Geologic Assessment of Coal in the Colorado Plateau: Arizona, Colorado, New Mexico, and Utah
in the coal samples that were analyzed; thicker partings were 

excluded. A total of 252 coal samples from 45 core holes were 

analyzed; 90 samples from nine core holes in the northwest 

areas and 162 samples from 36 core holes in the southern part 

of the basin. The Hoffman and others study areas are shown 

on fi gure 31 of this report; the core hole locations are shown 

on fi gure 28.

Analyses results for the northwest area (named the Fruitland area by Hoffman and others, 1993) are summarized in 

table 6 of their report. The weighted average, moist mineralmatter-free (mmmf) heating value was 10,732 Btu. Other 

values were presented as the mean for coal samples analyzed 

on a dry basis as follows: ash 21.17 percent, sulfur 0.88 

percent, and fi xed carbon 42.29 percent. Moisture was 7.61 

percent equilibrium moisture and 6.70 on the as-received basis. 

Coal rank for this area was reported to be high-volatile B to 

C bituminous. Hoffman and others subdivided the southern 

area into the Bisti and Star Lake coal fi elds. The Bisti area 

(northwest) contained 16 core holes and the Star Lake area 

(southeast) contained 20 core holes. Analyses results for the 

Bisti area were: weighted average, mmmf heating value 10,308 

Btu; mean dry-basis ash value, 21.32 percent; sulfur 0.59 

percent; and fi xed carbon 41.71 percent. Moisture, as-received, 

was 13.81 percent; equilibrium moisture was 14.88 percent. 

Star Lake analyses were: weighted average, mmmf heating 

value 11,253 Btu; mean dry-basis ash value, 25.62 percent; 

sulfur 0.63 percent; and fi xed carbon 38.45 percent. Moisture, 

as-received, was 11.34 percent, and equilibrium moisture was 

14.11 percent. Coal rank for the Star Lake area was reported to 

be subbituminous A extending into high-volatile C bituminous. 

For the Bisti area, coal rank was reported to be subbituminous 

A.

Two test holes were drilled by the Southern Ute Indian 

Tribe and the U.S. Department of Energy about 3 mi north of 

Ignacio, Colo. (fi g. 37), in sec. 25, T. 34 N., R. 8 W., La Plata 

County, Colorado, to determine the coal-bed methane potential 

of Fruitland coal beds in that area (Kelso and Rushworth, 

1982). Samples of coal and non-coal material, each less than 1 

ft thick from core samples from these test holes were analyzed. 

The results of the analyses of just the coal samples from each 

drill hole were averaged, as follows: Oxford No. 1 (NE1⁄4SE1⁄4

sec. 25)—four samples—moist mineral-matter-free (mmmf) 

heating value 15,474 Btu, fi xed carbon 78.9 percent. As 

received basis: moisture 1.6 percent, ash 35.5 percent, sulfur, 

1.17 percent. Oxford No. 2 (SE1⁄4SW1⁄4 sec. 25)—four samples—moist mineral-matter-free (mmmf) heating value 15,959 

Btu, fi xed carbon 81.3 percent. As-received basis: moisture 

1.0 percent, ash 32.8 percent, sulfur 0.51 percent. The rank of 

the coal from these drill holes, low-volatile bituminous, is the 

highest reported in the basin.

Roberts (1989) presented coal analyses for 155 samples 

of coal from core in the northwest part of the basin in Colorado (see fi g. 31 for location of the Roberts study area). Noncoal partings exceeding 3/8 inch thick were excluded from 

the sampled coal. An additional 71 samples of the thicker partings, roof, and fl oor rock were also analyzed, but composite 

weighted-average analyses for coal and partings was not done. 

On the basis of the analyses of the 155 coal samples, coal 

rank appears to range from high-volatile C bituminous to 

high-volatile A bituminous in the Roberts study area. Ash, 

moisture, and sulfur percentages appear to be similar to those 

of Fruitland coals from other parts of the basin. Roberts and 

McCabe (1992) discuss the ash content of Fruitland coals in 

the Roberts’ (1989) study area in great detail but do not discuss 

the other components of these coals there. 

In summary, Fruitland coal is low sulfur (average less 

than 1 percent) and high ash (probably averaging about 30 

percent). Moisture content is variable, ranging from 5 to 10 

percent at shallow depths near the outcrop to less than 3 

percent in the deeper parts of the basin. Heating values range 

from 10,300 Btu (mmmf) along the southwest margin of the 

basin to nearly 16,000 Btu in the north-central part. Fixedcarbon percentages (mmmf) range from around 40 percent in 

the southwest to more than 80 percent in the north-central 

area. Coal rank ranges from subbituminous A in the south to 

low-volatile bituminous in the north-central part of the basin. 

Coal rank generally increases from the southwest edge of the 

basin to north of the present basin axis and then diminishes 

somewhat to the north to the northern edge of the basin. (See 

“Vitrinite Refl ectance” section, below, for a more detailed discussion of the thermal maturity of Fruitland coals.) Fruitland 

coal is almost all non-agglomerating with the exception of one 

small area at the Chimney Rock mine (fi g. 2) on the northeast 

edge of the basin.

Maceral Content

There are no published, basin-wide studies of the petrography of Fruitland coals in the San Juan Basin; however, Hoffman and others (1993) and Hoffman (1991) presented maceral 

content for Fruitland coals from 33 core samples from drill 

holes in two areas near the Fruitland outcrop—from four drill 

holes in the northwest and 13 drill holes in the southern part of 

the basin (areas J and L on fi g. 31). The results of that study 

showed that the average Fruitland coal maceral content for 

both areas is about 70 percent vitrinite, 16 percent inertinite, 

and 14 percent liptinite,. Mavor and Nelson (1997, table 4-2) 

presented Fruitland coal maceral data for three wells in the 

northern part of the basin and showed that the average maceral 

content for these wells was 84.5 percent vitrinite, 12.8 percent 

inertinite, and 2.7 percent exinite (a liptinite maceral). The 

higher percentage of vitrinite and lower percentage of exinite 

in the northern San Juan Basin data set could indicate a change 

in the kinds of organic material accumulating in Fruitland 

coal swamps at that time or could be an artifact of liptinite 

macerals becoming more refl ective with greater depth of burial 

and heating. Levine (1993, p. 56) states that “The refl ectivity 

of the liptinite macerals is initially lower than vitrinite ... but 

changes very rapidly at around 1 % refl ectance to match that 

of vitrinite. Above around 1.2 % Ro, the liptinite macerals are 

essentially indistinguishable from vitrinite.” Thus the decrease 

Geology and Coal Resources of the Upper Cretaceous Fruitland Fm., San Juan Basin, New Mexico and Colorado Q67
3100

ARCHULETA

SAN JUAN

McKINLEY

MONTEZUMA

108 107 

 37 37 

 36 36 

108 107 

COLORADO

NEW MEXICO

Outcrop of Fruitland

 Formation

Farmington

Dulce

Cuba

Ignacio

0 5 10 15 20 MILES

R 13 W

R 16 W 15

T 19 N

20

21

22

23

24

25

26

27

28

29

30

31

32

32

33

34

T 35 N

R 1 W R 1 E

R 1.5 W

2

R 1 W

2.5 R 16 W 15 14 13 12 11 10 9 8 7 6 5 4 3

6 5 4 3 2

7

8

9

10

11

12

T 34 N

 (NUL)

T 34 N

 (SUL)

R 1 W R 1 E

2 13 12 11 10 9 8 7 6 4 3

14

T 34.5 N

T 34 N (NUL)

T 34 N

 (SUL)

SANDOVAL

RIO ARRIBA

LA PLATA

Study

area

COLORADO

NEW MEXICO

Kf

Kf

0.5

0.6

0.7

0.9

1.0

1.1

1.2

1.3

1.2

1.1

1.0

0.8

1.4

1.4

1.6

1.2

0.8

0.7

1.3

1.1

0.7

0.8

1.3

0.6

0.7 0.6

0.8

0.9

1.3

1.5

0.9

1.6

1.5

0.45

Areas where Rm >1.6%

Basin floor - contoured on base of

Fruitland Formation (from fig. 24) 

Contour interval is 0.10% Rm (except for 0.45 line).

"T 34 N (NUL)" is north of Ute line, "T 34 N (SUL)"

is south of Ute line.

3100

Tertiary intrusive (dike)

Tertiary intrusive (sill)

from Fassett and

Hinds (1971, pl. 1)

0.58

EXPLANATION

Cuttings sample Core sample

Outcrop sample with Rm value

Drill hole with sill intruded into Fruitland Formation

0.76

0.74

.42 .39

0.47

0.45 0.42

.47

.46

.51

.45

0.44

0.43

.44

0.46

0.45

0.42

.49

.49

.51

0.51

.49 0.44

0.47

0.46

0.46

0.44

0.490.47

0.47

.42

.42

.46

.46

0.45 0.48

0.59

0.55

0.63 0.61 0.65

0.60 0.64 0.61 0.68

0.68

0.60

0.61

0.62

0.61

0.55

0.61

0.60

0.57 0.60 0.53

0.59

0.53

0.75 0.75 0.77

0.76

0.67 0.76

0.69

0.68

0.65

0.62 0.62 0.61

0.61

0.73

0.73

0.74

0.70

0.73

0.71 0.66

0.79 0.73 0.72

0.72 0.71 0.66

0.73 0.69

0.68

0.72

0.68

0.66

0.70

0.65

0.67

0.68

0.66 0.65

0.64 0.64

0.62

0.58

0.59

0.57

0.62

0.59

0.82

0.94 0.93 0.96

0.95 1.0.3 0.94 1.01

0.97

1.02

0.96

0.97 0.93 0.92

0.96

0.96

0.98

0.94

0.94

0.93 0.95

0.96

0.90 0.95

0.89

0.92

0.99

0.89

0.88 0.90

0.88 0.89 0.830.85

0.84

0.81

0.87

0.76 0.78

0.79

0.83

0.76

0.81 0.91

0.84 0.82

0.81

0.78 0.81

0.71

0.73 0.79

0.81

0.81

0.80

0.720.76

0.71 0.76 0.80

0.71 0.72 0.73 0.75 0.74

0.65 0.69 0.72

0.72 0.76 0.76

0.74

0.74 0.79 0.740.69

0.76

0.74 0.68

0.68 0.77

0.75 0.71

0.72

0.67 0.73

0.76

0.650.65 0.66

0.65

0.63

0.61 0.62

0.67

0.63

0.65 0.66

0.63

0.63

0.66

0.60

0.52

0.52

.59

1.19

1.10

1.05

1.07

1.04

1.08 0.92

1.04

0.96

0.92 0.91

0.86

0.98

0.97

0.84

0.89

0.94

0.97 0.88

0.92

0.96

0.95 0.92 0.87

0.77 0.84

0.94

0.88 0.94

0.820.87 0.93

0.75

0.83

0.76

0.80 0.90

0.83

0.90

0.83

0.73

0.79

0.780.79

0.81 0.84 0.76 0.780.720.80 0.72

0.80

0.74

0.74

0.71 0.75

0.64

0.62

0.67 0.71 0.68

0.70 0.65 0.66

0.64

0.67 0.65

0.69

0.66 0.66

0.66

0.60

0.62

0.67

0.63 0.67

0.65

0.57

0.56

0.58

0.80

1.31 1.38

1.30 1.27

1.27

1.28

1.27

1.26

1.22

1.21

1.24 1.23

1.24 1.23

1.28

1.24 1.26

1.41

1.17 1.18 1.18 1.22 1.24 1.21

1.18 1.14

1.15

1.17

1.19 1.30

1.25 1.17 1.19

1.20 1.17 1.19 1.23

1.15 1.12 1.18 1.18

1.19

1.15 1.16 1.17

1.16

1.15

1.08

1.15

1.09

1.07

1.15

1.12

1.06 1.14

1.03

1.07 1.19

1.15

1.15

1.07

0.93

0.94

1.09

0.98 0.91

0.83 0.97 0.97

0.88

0.82 0.97

0.91

0.79 0.86 0.80

0.71 0.77 0.77 0.87

0.84

0.79 0.76

0.75

0.74

0.77

0.76 0.79

0.78 0.73 0.76

0.66 0.72 0.73

.52

0.75

0.65

0.67

0.65

.52 .54

.54

0.79

1.44

1.22

1.29

1.17 1.26

1.11

1.23

1.13

1.00 1.05

1.05

1.09 1.15 1.09

0.90 0.88 0.94 1.02

0.89 0.90

0.88

0.950.93

0.98 0.97

0.77

0.87 0.84

1.42

1.42

1.60 1.41

1.49 1.551.55

1.51

1.25

1.31

1.31

1.28

1.41

1.26

1.29 1.43

1.40

1.32 1.28

1.36

1.36

1.34

1.32 1.21

1.28

1.13

1.22

1.21

1.21

1.15

1.10 1.10

1.15

1.17

1.18

1.06 1.06

1.08 1.03

1.16

1.02

1.01

1.01

1.08

0.79

0.79

1.03

1.01

1.04

0.92 0.76

0.73

0.68

0.70

0.71

0.75

0.74

0.93

0.97 1.01

1.24

1.02

1.27

1.42

1.57

1.46

1.66 1.49

1.59

1.63

1.40

1.34 1.28 1.28

1.30

1.36

1.60

1.56

1.37 1.44

1.40

1.54

1.50 1.33

1.49

1.55

1.64

1.05

1.15

1.17 1.22

1.02

1.14

0.90

1.05

0.81

1.10

1.15 1.16

1.14

1.34

1.07

0.96

0.92 1.13

0.90 1.15 1.06

1.04

1.49

1.13 1.35 1.24 1.29

0.99

0.58

0.70

0.66

0.80

0.80

0.80 0.57 0.56 0.81

0.86

0.79

0.64

0.64

0.64

●

●

● ●

● ●

●

● ●

● ●

Area containing drill holes in which Fruitland Formation

is intruded by sills

Figure 37. Thermal-maturity map of Fruitland Formation coal samples from 568 locations. Mean vitrinite refl ectance values in percent (Rm) 

are contoured.

Q68 Geologic Assessment of Coal in the Colorado Plateau: Arizona, Colorado, New Mexico, and Utah
in the liptinite-maceral (exinite) percentage in the northern 

part of the basin may only be apparent. Available data are 

too limited to demonstrate any signifi cant basin-wide trends in 

maceral percentages for Fruitland Formation coals.

Vitrinite Refl ectance

The fi rst published vitrinite refl ectance maps of the San 

Juan Basin were in Rice (1983, fi gs. 12, 13). The map in 

that report showing Rm values for Fruitland coal samples (fi g. 

12) contained only 19 data points and only two contour lines 

with values of 0.6 and 1.0. Rice (1983, p. 1207) noted that 

the highest Rm-value data point had a value of 1.45 and was 

located at the north end of the basin, north of the present-day 

structural axis. He further noted that the “maximum depth 

of burial combined with typical or present-day geothermal 

gradients cannot account for temperatures necessary for highrank coal formation.” Rice suggested that batholiths, emplaced 

in Oligocene time in the nearby San Juan Mountains “provided 

an added heat source required for the advanced levels of thermal maturation.”

Bond (1984) discussed the thermal maturity of Upper 

Cretaceous rocks in the northern part of the San Juan Basin 

and stated that maximum heat fl ow and greatest depth of burial 

coincided with intrusive and extrusive activity in the San Juan 

volcanic fi eld in late Oligocene time. He stated that at that 

time (30–25 Ma) an apron of volcaniclastic material from the 

San Juan volcanic center to the northeast was deposited in the 

northern part of the basin area. His estimate for maximum 

burial of basal Fruitland coal beds at that time was 8,750 ft. 

Bond (1984) did not call upon exotic heat sources to account 

for the thermal maturity of Upper Cretaceous rocks in the San 

Juan Basin. Subsequently, other workers discussed heat fl ow in 

the basin (see Clarkson and Reiter, 1988) and suggested that an 

external heat source must have contributed to the high thermal 

maturity of Fruitland coals in the northern San Juan Basin and 

proposed that the heat-transfer mechanism was heat advection 

by ground-water fl ow from the nearby San Juan volcanic fi eld 

to the north. 

Law (1992, fi g. 4) constructed a thermal maturity map of 

the basin based on 98 data points with a contour interval of 

0.1 Rm and contour lines having values ranging from 0.5 to 1.5 

Rm. This map shows a northerly increase in thermal maturity 

values toward the northeast part of the basin from 0.5 to 1.3 

Rm over a distance of more than 70 mi. A relatively narrow, 

linear, northwest-trending area of thermal maturity 1.3 Rm or 

higher is shown in the northeast part of the basin; this area 

is nearly 35 mi long. Northward from this axis of highest 

thermal maturity, contour lines are closely spaced and decrease 

in value from 1.3 Rm to about 0.7 Rm at the Fruitland outcrop 

(a distance of less than 15 mi). Law (1992, p. 206) suggested 

that because present-day heat fl ow is insuffi cient to account for 

the elevated levels of thermal maturity for Fruitland coals in 

the northern part of the basin “a convective heat-transfer event 

40–20 m.y. ago” resulting from “the circulation of relatively 

hot fl uids into the basin from a heat source located north of the 

San Juan Basin, in the vicinity of the San Juan Mountains” was 

the most likely cause of the elevated levels of thermal maturity 

in Fruitland coals in the northern San Juan Basin.

Scott and others (1994, fi g. 9.3) constructed a thermal 

maturity map of the basin based on “more than 140 measured 

and 72 calculated vitrinite refl ectance values.” Calculated 

values were based on the mathematical conversion to vitriniterefl ectance values of published volatile percentages for Fruitland coals (mostly from Fassett and Hinds, 1971). The pattern 

of vitrinite-refl ectance contour lines on this map is similar 

to the map produced by Law (1992, fi g. 4) discussed above, 

except for the position of the 0.5-Rm line. This line is shown 

to be much farther south on the Law map than on the Scott 

and others map. Scott and others point out that there is “a 

general correlation between the structural confi guration of the 

San Juan Basin ... and Fruitland coal rank” but point out that 

“in the northern third of the basin, low-volatile bituminous 

coals are structurally higher than lower rank coals located to 

the south along the structural axis of the basin.” Scott and 

others (1994, p. 167) briefl y discuss the various heat-fl ow studies in the northern part of the basin (discussed above) and offer 

the opinion that “The correlation between vitrinite refl ectance 

and structure in the San Juan Basin suggests that burial depth 

and structural evolution of the basin were probably the major 

factors controlling the thermal maturity of Fruitland coals”

obviously rejecting the “introduction of additional heat” theories espoused by earlier researchers. 

Mean vitrinite refl ectance values in percent (Rm) for 

Fruitland Formation coal-bed samples presented in this report 

are from the following published sources: Fassett and Nuccio 

(1990), Pawlewicz and others (1991), Law (1990, 1992), Hoffman (1991), Hoffman and others (1993), and Kelso and Rushworth (1982). Unpublished data were provided by Amoco 

Production Company, EnerVest San Juan Operating LLC, and 

Emerald San Juan Co. Coal samples were mostly from drill 

holes, but 14 coal samples were from Fruitland coal mines or 

from outcropping Fruitland coal beds. Most drill-hole samples 

were cuttings; however, 36 coal samples were from drill core. 

At some data points, vitrinite-refl ectance values were 

determined from coal samples at different stratigraphic levels 

within the Fruitland. In this report, only one Rm value per data 

point is shown on the thermal maturity map for the basin (fi g. 

37). In the southern part of the basin where Rm values are low 

(less than 0.5 percent), values from multiple coal samples in 

the same drill hole were averaged. In the northern part of the 

basin where Rm values are much higher, the highest Rm value, 

usually from the deepest sample in the drill hole, is used.

Rm values for Fruitland coals from 350 drill holes (Fassett 

and Nuccio, 1990, and Pawlewicz and others, 1991)—were 

determined by the USGS in a cooperative program with the 

Aztec, N. Mex., District Offi ce of the New Mexico Oil Conservation Division. Beginning in 1988, the New Mexico Oil 

Conservation Division required all oil and gas operators to 

send drill cuttings from coal beds in the Fruitland and Menefee Formations to the USGS in Denver. The samples were 

Geology and Coal Resources of the Upper Cretaceous Fruitland Fm., San Juan Basin, New Mexico and Colorado Q69
cleaned, crushed, and mounted in epoxy on a microscope 

slide and then planed and polished. Mean random vitrinite 

refl ectance was measured from randomly oriented vitrinite 

grains in immersion oil using a non-rotating stage on a Zeiss 

Universal research microscope. Plane-polarized incident white 

light and a 546-nm monochromatic fi lter were used (for a 

complete explanation of this procedure see Stach and others, 

1982). The number of readings per sample varied depending 

on the amount of clean vitrinite in the sample. In most of the 

samples, vitrinite was abundant, the number of readings per 

sample was between 30 and 50, and the resulting histograms 

were unimodal. If the number of readings was greater than 30 

and the standard deviation was small, then the mean vitrinite 

refl ectance value was statistically valid. Depths of coal cuttings 

were provided by the companies drilling the wells and no 

attempt was made to correct or adjust these depths precisely 

to specifi c coal beds on geophysical logs. Rm values published 

in the Law (1990) report were also determined in the USGS 

Denver laboratory using the procedures described above.

Vitrinite-refl ectance values for Fruitland coal samples 

from the Amoco and EnerVest drill holes were determined 

using procedures similar to those of the USGS. Slightly different analytical procedures used in the other published reports 

listed above are described in those publications. Because each 

data set used to construct the vitrinite-refl ectance contour map 

(fi g. 37) overlapped with at least one other data set, it was 

possible to compare values from adjacent drill holes, (or the 

same drill hole in a few instances) from the different data sets. 

These comparisons showed that vitrinite-refl ectance values 

from overlapping data sets were virtually identical.

The vitrinite-refl ectance database for Fruitland coals presented in this report (table A4-1) consists of mean Rm values 

from 620 selected locations. This selected database was compiled by deleting data points from the source databases (listed 

above) that were judged to be anomalous, that is those with 

Rm values more than 0.3 percent lower than nearby data points. 

The assumption was that these anomalously low values could 

have come from cavings from higher coal beds. Anomalously 

high values were not deleted from the database in this initial 

screening process. 

Figure 37 is a thermal maturity map for the San Juan 

Basin contoured on vitrinite-refl ectance values. To create this 

map, fi rst, a preliminary contour map was created by the 

Golden Software program, Surfer, using the 620 data points in 

table A4-1. This preliminary contour map was examined and 

53 data points having anomalous Rm values were deleted. The 

fi nal Surfur-drawn map was then created using the remaining 

567 data points and that map was imported into Adobe Illustrator where the contour lines were edited to produce the fi nal 

thermal maturity map (fi g. 37). 

This map shows that Rm values for Fruitland coals range 

from less than 0.45 to more than 1.6 and are highest in the 

northern part of the basin. Along the southern edge of the 

basin, the 0.45 contour line is near, and parallel to, the Fruitland Formation outcrop. (Control for the 0.45 contour line 

is from the Hoffman, 1991, and Hoffman and others, 1993, 

database.) The thermal-maturity contours in the southern part 

of the basin, in the area between the 0.45 and the 0.9 contour 

lines, show a pattern of decreasing distances between successively higher value contours: The distance between the 0.45 

and the 0.5 lines is about 15 mi; between the 0.5 and 0.6 

lines, it is about 15 mi; between the 0.6 and 0.7 lines, it is 

about 8 mi; between the 0.7 and 0.8 lines, it is about 4 mi; 

and between the 0.8 and 0.9 lines, the distance is about 2 mi. 

These distances are somewhat variable, but the general pattern 

is apparent.

This pattern of decreasing spacing between Rm contour 

lines is a good example of the observation by Levine (1993, 

p. 58) that “Vitrifi cation increases exponentially with rank, 

increasing only very slowly at low rank and more rapidly at 

high rank.” At higher Rm values than 0.9, however, the pattern 

of decreasing spacing of the thermal maturity contour lines 

ends and from the 0.9 contour line to the 1.6 line, the contour 

lines are more or less evenly spaced. The reason for this 

apparent contradiction beyond the 0.9 contour line is that the 

structural deepening of the basin decreases in this area. Figures 

22–24 show this decrease for the present-day structure of the 

basin in the vicinity of the 0.9 contour line. Thus, the decreasing rate of increase in depth of burial in the area between the 

0.9 and the 1.5 Rm contour lines has offset the exponential 

increase in thermal maturity with depth of burial in this area.

Scott and others (1994, p. 167) stated that “The rather 

abrupt increase in vitrinite refl ectance values greater than 0.70 

% in the northern basin coincides with a structural “hingeline.”

Because of their more limited vitrinite-refl ectance database, 

the thermal maturity map of these authors (fi g. 9.3) did not 

clearly portray the regularly decreasing distances between contours that are shown on fi gure 37 of this report. As a result, 

these authors saw an apparent “abrupt” change in spacing 

of thermal maturity contours at the 0.7 Rm line, whereas, 

in reality, the increase of vitrinite-refl ectance values north of 

the 0.7 Rm line is an artifact of the pattern of decreasing 

distances between contours northward in accord with Levine’s 

(1993) observation that “vitrifi cation increases exponentially 

with rank.”

In the northern part of the basin, thermal maturity of 

Fruitland coals decreases over a distance of about 10 mi, from 

1.6 Rm at the basin’s thermal-maturity axis, to 0.56 Rm at 

the Fruitland outcrop (fi g. 37). The spacing pattern of the 

thermal-maturity contours refl ecting the exponential relationship discussed above is masked by the steeper dip of the rocks 

in the northern part of the basin (see fi gs. 23, 24). 

Several localized perturbations occur in the vitriniterefl ectance contour lines in the central part of the basin, especially for the 0.6- to 0.9-Rm lines. The data points causing 

these perturbations generally have vitrinite-refl ectance values 

of 0.05 Rm higher or lower than the prevailing values in these 

areas. In these areas, where clusters of two or more apparently 

anomalous data points occur, the data points are retained 

and honored by the vitrinite-refl ectance contour lines. These 

anomalies all occur in an elliptical area that trends northeast, 

suggesting that there may have been some related local causes 

Q70 Geologic Assessment of Coal in the Colorado Plateau: Arizona, Colorado, New Mexico, and Utah
for these features. Even though vitrinite-refl ectance values are 

primarily a recorder of maximum heat, they are to some extent 

affected by coal maceral composition (Levine, 1993, p. 58). 

Thus, the origin of these relatively small, local variations in 

vitrinite values may be the result of local variations in heat 

fl ow at the time of maximum burial of the coal beds or refl ect 

physical and (or) chemical changes in the peat-bog environments at the time the material was deposited.

In the northeast part of the basin, a large number of dikes 

and sills are present. These intrusives, discussed in Fassett and 

Hinds (1971, p. 34), are shown on fi gure 37. It is notable 

that this intrusive complex has had no apparent affect on the 

regional pattern of thermal maturity in this area of the basin as 

indicated by the surface outcrop samples along the northeast 

edge of the basin; however, subsurface data points in this area 

are sparse. In T. 32 N., R. 3 W., New Mexico, a single vitriniterefl ectance data point has an elevated Rm value of 1.3. This 

anomalous value is almost certainly the result of the sampled 

coal bed having been heated by a nearby dike or sill. 

Ten of the drill holes used for determining Fruitland coal 

thicknesses in this study were found to contain what appear 

to be igneous sills on geophysical logs. (Undoubtedly, the 

Fruitland has been intruded by sills in other wells in this 

area, but examining the logs of all of the wells in this area 

for Fruitland sills was beyond the scope of this project.) The 

locations of these 10 holes are shown on fi gure 37 and the 

depths to the sills in each hole are in table A2-1. The numbers 

of sills in these holes range from 1 to 5 and the sills are mostly 

concentrated in the lower, coal-bearing part of the Fruitland. 

The Fruitland sills occur at depths ranging from 3,461 ft to 

3,776 ft in this area. No samples of coal from these drill 

holes were available for vitrinite-refl ectance determinations. 

The sills range in thickness from 1 ft to 10 ft and average about 

4 ft thick. It appears on the geophysical logs that the sills have 

selectively intruded into coal beds and have, at least in part, 

digested the coal beds in the process.

In 1989, the Ojo Alamo Sandstone was found to contain 

gas in this area in four wells (Hoppe, 1992). Hoppe stated (p. 

371), “Except for the presence of H2S, gas composition of the 

Ojo Alamo, Fruitland coal and Pictured Cliffs is similar.” In 

his paper, Hoppe discussed the presence of igneous sills in the 

Fruitland in this area and suggested that “igneous solutions 

intruded the area, heated and forced gas from the coal seams, 

which then migrated to the structural highs and porous zones 

of an overlying reservoir—the Ojo Alamo.” He further stated 

that alternatively, the gas could have migrated from deeper 

source rocks. 

In 1997, the East Blanco gas fi eld, was developed in the 

Ojo Alamo Sandstone in T. 30 N., R. 3 W. (Oil and Gas 

Journal, 1998) within the area shown on fi gure 37 where the 

Fruitland is intruded by sills. In 1999, about 50 gas wells 

were producing methane from the Ojo Alamo Sandstone in 

that area. As Hoppe (1992) pointed out, the Ojo Alamo does 

not normally produce natural gas in the San Juan Basin, and 

he suggested that the most probable source of the Ojo Alamo 

gas was the underlying Fruitland Formation coal beds. The 

discovery of numerous igneous sills intruding the coal-bearing 

part of the Fruitland in 10 of the wells used for Fruitland coal 

measurements in this area (fi g. 37) supports the suggestion that 

the presence of these sills contributed to the liberation of 

gas from Fruitland coal beds. Rather than “hot solutions”

associated with the sills heating the coal beds and driving 

off the gas, however, it seems apparent that the hot magma 

itself intruded into the Fruitland coals, partly or completely 

digesting them, resulting in the release and generation of large 

volumes of coal-bed methane in this area. This process would 

have resulted in extreme over pressuring of the Fruitland Formation causing the gas to migrate upward into the next-highest 

available reservoir, the overlying Ojo Alamo Sandstone, where 

it was trapped. The intrusion and digestion of the Fruitland 

coals by magma is probably also responsible for the high 

levels of H2S in the Ojo Alamo gas because H2S is never 

present in methane generated from coal beds under normal 

conditions.

The Ojo Alamo, throughout the basin, consists of a series 

of overlapping, disconnected, channel-sandstone lenses interbedded with mudstones (Fassett and Hinds, 1971, p. 28), thus 

each sandstone lens is an isolated sandstone reservoir and trap. 

The intrusion of large numbers of dikes and sills in an area of 

structural tension may have created fracture pathways facilitating the migration of Fruitland gas upward into the Ojo Alamo 

sandstone lenses.

As discussed above, the high thermal maturity of Fruitland coal beds in the northern part of the San Juan Basin has 

been attributed to conductive heating from a nearby buried 

batholith, heat transfer by hot fl uids, and simply depth of 

burial. Figure A5-1 is an isostatic residual gravity anomaly 

map of the San Juan Basin reprinted from Heywood (1992) 

on which the thermal maturity contour lines of fi gure 37 are 

superimposed. This fi gure clearly illustrates that the areas of 

highest thermal maturity of Fruitland coals in the northern part 

of the basin are not underlain by high-density, shallow, intrusive bodies; thus, conductive heating of Fruitland coals by an 

anomalous underlying heat source can be ruled out. Of interest 

on this fi gure is the presence of the high-gravity anomaly 

located just east of the dikes and sills discussed above. The 

area of this anomaly is overlain by Upper Cretaceous rocks 

and there is no surface expression of this feature in this area. 

This higher density rock body is a logical source for the 

intrusives in the northeast part of the San Juan Basin. 

The transfer of heat into the northern San Juan Basin 

by hot fl uids that originated in the San Juan volcanic area to 

the north does not seem to be supported by available data. 

Certainly these hot fl uids did not move through the Fruitland 

Formation or older Cretaceous rocks from the north because, 

if they had, thermal-maturity values for these rocks would 

increase northward. Figure 37 clearly shows vitrinite-refl ectance values for Fruitland coals decreasing from the basin’s 

thermal axis to its northern edge. Turner and Fishman (1991) 

discuss the thermal history of the basin as it affected the 

Brushy Basin Member of the Morrison Formation and state (p. 

553) that a coal sample from the Dakota Sandstone between 

Geology and Coal Resources of the Upper Cretaceous Fruitland Fm., San Juan Basin, New Mexico and Colorado Q71
the San Juan Basin and the San Juan volcanic fi eld “has the 

lowest refl ectance value thus far obtained from the study area 

(Rmean = 0.53±0.07 %).” They conclude, “Thus, heat associated with the San Juan volcanic fi eld was apparently conducted 

vertically rather than laterally away from the volcanic center or 

associated batholith.”

Law (1992, p. 206) suggested that hot fl uids “heated by 

the deeply buried batholith [in the San Juan volcanic area]”

moved laterally southward “along faults and fractures into the 

north end of the San Juan Basin. As the heated fl uids ascended 

through Cretaceous and Tertiary rocks, the high-temperature 

fl uids would have raised subsurface temperatures and altered 

the organic matter to higher levels of thermal maturity.” The 

even spacing of the vitrinite-refl ectance contours from the 0.9 

to the 1.6 lines would seem to argue against an elevation 

of the thermal gradient by hot fl uids moving up from depth 

along a northwest-trending fracture zone in the areas of highest 

thermal maturity shown on fi gure 37. Such a process would 

presumably have created a relatively narrow zone or series of 

zones of high thermal maturity values and thermal-maturity 

values abruptly diminishing on both sides of that zone, rather 

than the even pattern shown on fi gure 37 in the northern part 

of the basin. 

Because the spacing pattern of thermal-maturity contours 

(fi g. 37) mimics the structural form of the basin, it seems 

most likely that the pattern of thermal maturity of Fruitland 

coal beds is refl ecting depth of burial of these rocks, as suggested by Bond (1984) and Scott and others (1994) rather 

than an exotic heat source that pumped heat into the basin 

center from the San Juan volcanic center to the north. The 

present structural basin fl oor for Fruitland coals—depicted on 

the Pictured Cliffs structure map (fi g. 24) and superimposed on 

the thermal maturity map (fi g. 37)—is about 20 mi southeast 

of the thermal-maturity axis in the basin. It is suggested that 

the structural axis of the basin was once located northwest 

of its present position (in the position of the thermal-maturity 

axis shown on fi gure 37) but as the structural evolution of the 

basin proceeded, the structural axis shifted through time to its 

present location. 

Fruitland Coal Resources

Coal Density

Coal tonnage determinations are the product of three 

parameters: coal thickness, the area underlain by coal, and 

coal density. Coal thickness and area are determined by direct 

measurements, and the product of these values is conventionally reported in acre-ft. Coal density determinations are more 

diffi cult because coal beds are complex mixtures of organic 

matter, inorganic matter, and water (moisture). The primary 

factor affecting Fruitland coal density in the San Juan Basin 

is ash content. Ash in coals is present in two forms: as dispersed inorganic mineral grains in a coal matrix and as discrete 

layers of inorganic material (partings) within coal beds. Partings range from carbonaceous shales (more than 50 percent 

ash) to relatively pure layers of inorganic rock material.

The ash content of Fruitland coal samples determined by 

proximate analyses of fl oated Fruitland coal samples collected 

as drill cuttings (table A3-2) ranges from 10.5 to 35.7 percent 

and averages about 19 percent. Because processing of these 

cuttings samples essentially removed all fragments of coal 

partings that contained more than 40 percent ash, the ashcontent values for this sample set must represent mostly dispersed inorganic mineral grains in the coal matrix. Figure 

A3-11 is a contour map of these ash-content values (from 

Fassett and Hinds, 1971, fi g. 24) showing a pattern of higher 

ash coal (> 20 percent) in the eastern part of the basin and 

an area of lower ash coal (< 15 percent) in the west-central 

part of the basin.

Bulk-density logs can be used to accurately determine 

the density of coal beds in the ground. Figure 38 shows the 

 Pictured Cliffs Sandstone

2.0 2.25 2.5 2.75 3.0

1.0 1.25 1.5 1.75 2.0

Bulk density scales (gm/cm )

1200

1250

1100

1150

1050

1110

1103

5

7

1053

1058

1131

1137 6

1207

1210

1212

1218

1242

1252

3

6

10

Bulk density

Bulk density

1.3 1.35 1.4 1.45 1.55 1.6 1.65 1.7

1.431

1.483

1.598

1.592

1.547

1.485

 1.30 gms/cm3 1.75 gms/cm3

3

3

(gms/cm ) 

 Density

3

3

 Average density by bed = 1.523 gm/cm

 Over-all average density = 1.514 gm/cm

 Depth &

thickness

Coal

bed

A

B

C

D

E

F

Depth

Figure 38. Type bulk-density log (fi g. 25) showing the density of each 

of the Fruitland Formation coal beds in this drill hole. Log is from the 

Amoco Production Company State of Colorado Ax No. 1 well located 

in NE1⁄4NE1⁄4 sec. 16, T. 35 N., R. 7 W., La Plata County, Colorado. 

Density was determined by averaging densities in 1-ft increments for 

each coal bed.

Q72 Geologic Assessment of Coal in the Colorado Plateau: Arizona, Colorado, New Mexico, and Utah
bulk-density curves from the type bulk-density log of fi gure 

25. This log was used to measure the average density of each 

coal bed using the procedure described in Mavor and Nelson 

(1997, example 5-2). The average density for each coal bed 

was measured on the bulk-density log in 1-ft increments, and 

these densities were averaged to determine the density of each 

coal bed. The average density for all coal is an average of 

the densities for all of the 1-ft increments. The average coal 

density for the drill hole on fi gure 38 is 1.514 g/cm3. The 

ash content for coal of this density is about 30 percent for a 

typical Fruitland coal (Mavor and Nelson, fi g. 7-7). To convert 

coal density to short tons of coal per acre-ft, the density is 

multiplied by 1,360, the weight of an acre-ft of water. For the 

drill hole on fi gure 38, this computation yields a value of 2,059 

short tons of coal per acre-ft. 

Coal densities for the Amoco Ax 1 well (fi g. 38) range 

from 1.431 g/cm3 for bed A (about 8 percent ash) to 1.598 

g/cm3 for bed C (about 40 percent ash). Converting these 

densities to short tons per acre-ft, as above, yields a range 

of 1,946 to 2,173 short tons per acre-ft for beds A and C, 

respectively. Because the precise distribution of ash percentages or coal-bed densities are not known for the entire basin, 

an average density of 1.47 (about 28 percent ash) is assumed 

for Fruitland coals. The resultant density value of 2,000 short 

tons of coal per acre-ft was used for coal-tonnage determinations in this report. This number may be slightly low, but it 

provides a conservative estimate of Fruitland coal tonnage in 

the basin. 

Traditionally, coal densities used for resource calculations 

in USGS reports are those of Wood and others (1983, p. 21, 22, 

and table 2). These authors state: 

The specifi c gravity of coal varies considerably with rank and 

with differences in ash content. The values shown in table 2 are 

close to the average specifi c gravities of unbroken or unmined 

coal in the ground (in situ) for the four major rank categories and 

are to be used in preparing U.S. Geological Survey estimates of 

coal resources and reserves. 

Table 2 of Wood and others (1983) gives the specifi c 

gravity and short tons per acre-ft for the four coal ranks as 

follows: lignite, 1.29 g/cm3, 1,750 short tons/acre-ft; subbituminous, 1.30 g/cm3, 1,770 short tons/acre-ft; bituminous, 1.32 

g/cm3, 1,800 short tons/acre-ft; and anthracite, 1.47 g/cm3, 

2,000 short tons/acre-ft. Comparing Wood and other’s density 

of 1.32 g/cm3 for “average” bituminous coal with the density 

value of 1.3 derived for pure (0 percent ash) Fruitland bituminous coals of the San Juan Basin (Mavor and Nelson, 

1997) indicates that “average specifi c gravities of unbroken or 

unmined coal in the ground” (Wood and others, 1983), refers 

to extremely low ash coal (less than 5 percent). Because the 

densities for the high-ash Fruitland coals can be conservatively 

estimated to be on the order of 1.47 g/cm3 (about 28 percent 

ash), it is clear that to use 1,800 short tons per acre-ft as 

prescribed in Wood and others (1983) would seriously underestimate Fruitland coal resources.

Procedures, Categories, and Maps Used

Fruitland coal tonnages for the San Juan Basin were 

calculated using the EarthVision software program. The netcoal isopach map (fi g. 28) was the source for coal thicknesses 

and 2,000 short tons of coal per acre-ft was used for all tonnage calculations. The bounding polygon for the basin for coal 

resource calculations was the top of the Pictured Cliffs Sandstone (base of the Fruitland Formation). Coal tonnages were 

determined in fi ve overburden categories: 0–500 ft, 500–1,000 

ft, 1,000–2,000 ft, 2,000–3,000 ft, and more than 3,000 ft. 

Coal tonnages were calculated for (1) the States of Colorado 

and New Mexico, (2) counties, (3) 71⁄2-minute quadrangles, (4) 

townships, (5) areas of Federal and non-Federal surface ownership, and (6) areas of Federal and non-Federal coal ownership. In addition, for the two States and six counties, coal tonnages were calculated by reliability categories of identifi ed and 

hypothetical coal and by standard USGS thickness categories 

of 1.2–2.3 ft, 2.3–3.5 ft, 3.5–7.0 ft, 7.0 –14.0 ft, and greater 

than 14 ft. All coal tonnages are in tables A6-1–A6-5.

State, county, and township boundary lines are shown on 

most of the basin maps in this report (fi g. 28, for example). 

Maps showing other areas for which coal tonnages were determined are in Appendix 6, as follows: Figure A6-1, shows 

71⁄2-minute quadrangles within the basin, fi gure A6-2 shows 

Federal and non-Federal surface ownership, and fi gure A6-3 

shows Federal and non-Federal coal ownership. Figure A6-4 

shows the distribution of net Fruitland coal in the standard 

USGS coal-thickness categories listed above.

Figure 39 shows overburden thicknesses for the Fruitland 

throughout the basin. This overburden map primarily refl ects 

the basin structure on the base of the Fruitland Formation 

as portrayed on fi gure 24, but topography also plays a role, 

especially in the Colorado part of the basin where the land 

surface is considerably higher than it is in most of the New 

Mexico part of the basin. The San Juan River canyon is clearly 

evident in the north-central part of the basin. This overburden 

map was the source of data for the overburden categories in 

tables in Appendix 6.

Coal Tonnage

Table 5 is a summary table showing short tons of coal 

resources by State and county and by fi ve overburden categories. The table shows that the total Fruitland coal resource for 

the San Juan Basin is 230 billion short tons; 180 billion short 

tons in New Mexico and 50 billion short tons in Colorado. 

(Detailed tables of Fruitland coal tonnage are in Appendix 6.) 

By overburden categories, 39 percent of the coal is deeper 

than 3,000 ft, 29 percent is between 2,000 and 3,000 ft deep, 

17 percent is between 1,000 and 2,000 ft deep, 7 percent is 

between 500 and 1,000 ft deep, and 8 percent is less than 

500 ft deep. The 4,000-ft depth-of-overburden line is shown 

on the overburden map (fi g. 39), but coal resources were not 

calculated for this category. 

The fi rst basin-wide coal-tonnage estimate for Fruitland 

Geology and Coal Resources of the Upper Cretaceous Fruitland Fm., San Juan Basin, New Mexico and Colorado Q73
COLORADO

NEW MEXICO

Study

area

EXPLANATION

Control points are oil or gas wells, dry holes,

or coal-test holes

0-500

500-1000

1000-2000

2000-3000

3000-4000

> 4000

Overburden thicknesses in feet

3000

2000

1000

500

500

1000

3000

0

0

ARCHULETA

LA PLATA

SAN JUAN

McKINLEY

RIO ARRIBA

SANDOVAL

MONTEZUMA

108 107 

 37 37 

 36 36 

108 107 

COLORADO

NEW MEXICO

Farmington

Dulce

Ignacio

Durango

Cuba

0 5 10 15 20 MILES

R 13 W

R 16 W 15

T 19 N

20

21

22

23

24

25

26

27

28

29

30

31

32

32

33

34

T 35 N

R 1 W R 1 E

R 1.5 W

2

R 1 W

2.5 R 16 W 15 14 13 12 11 10 9 8 7 6 5 4 3

6 5 4 3 2

7

8

9

10

11 12

T 34 N

 (NUL)

T 34 N

 (SUL)

R 1 W R 1 E

2 13 12 11 10 9 8 7 6 5 4 3

14

T 34.5 N

T 34 N (NUL)

T 34 N

 (SUL)

2000

4000

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Figure 39. Overburden on top of the Pictured Cliffs Sandstone (base of the Fruitland Formation) in the San Juan Basin.

Q74 Geologic Assessment of Coal in the Colorado Plateau: Arizona, Colorado, New Mexico, and Utah
coals in the San Juan Basin by Fassett and Hinds (1971, table 

7) was 201 billion short tons. That study used a fi gure of 

1,770 short tons of coal per acre-ft to calculate the basin’s coal 

resources. If 2,000 short tons of coal per acre-ft is substituted 

for the calculation, the total coal tonnage becomes 227 billion 

short tons; virtually the same tonnage number in this report 

when rounded to two signifi cant fi gures. Kelso and Wicks 

(1988, p. 75) estimated the coal resources for the San Juan 

Basin to be 219 billion short tons. They used a coal-tonnage 

value between 1,800 and 1,900 short tons per acre-ft on a 

township-by-township basis according to the rank of the coal 

in each township, thus it is diffi cult to recreate a tonnage 

for their report had they used 2,000 short tons per acre-ft. 

However, if an average of 1,850 short tons per acre-ft is 

assumed for their original calculation and their tonnage is 

adjusted using a value of 2,000 short tons per acre-ft, their 

tonnage would have been 237 billion short tons of coal; 240 

billion short tons rounded to two signifi cant fi gures. In the 

“Comparison with Earlier Studies” section under the “Geographic Distribution of Fruitland Formation Coal” section of 

this report, it was concluded that Kelso and Wicks had infl ated 

coal thicknesses due to inclusion of caved portions of some 

drill holes as coal; thus, their tonnage fi gure of 240 billion 

short tons is probably too large.

Ayers and others (1994, p. 38) estimated the total Fruitland coal resource in the basin to be 245 billion short tons. 

These authors provided no indication of the number of short 

tons of coal per acre-ft that they used to calculate this number; 

thus, it is impossible to compare their total coal tonnage 

number with that from other reports in a meaningful way. 

There is no question, however, that Ayers and others overestimated coal thicknesses in several parts of the basin as the 

result of including cavings in drill holes as measured coal (see 

fi g. 30 and related discussion above). It is suggested, therefore, 

that the 245-billion-short-ton resource number for Fruitland 

coals in the basin is too high. 

Two other reports calculated Fruitland coal tonnage for 

the New Mexico part of the San Juan Basin. Biewick and 

others (1991, p. 25) estimated total Fruitland coal tonnage for 

the New Mexico part of the basin as 168 billion short tons 

using a coal tonnage of 1,770 short tons per acre-ft. Substituting 2,000 short tons per acre-ft yields 190 billion short tons of 

coal compared to 180 billion short tons for this report (table 

5). Boger and Medlin (1991, p. 42) calculated total Fruitland 

coal tonnage for New Mexico as 160 billion short tons, again 

using 1,770 short tons of coal per acre-ft for the coal density. 

Substituting 2,000 short tons per acre-ft yields an adjusted 

tonnage of 181 billion short tons of coal; virtually the same 

number calculated in this report.

Strippable Coal Resources

Shoemaker and others (1971, table 13) considered coal 

to a depth of 250 ft to be strippable and estimated that these 

reserves in New Mexico total about 5.041 billion short tons; 

of this total, 2.441 billion short tons are less than 150 ft 

deep. These authors did not include coal beds less than 3 ft 

thick at depths less than 150 ft and beds 5 ft thick between 

depths of 150–250 ft. Layers of non-coal material more than 

0.7 ft thick were excluded from their coal measurements. Hoffman (1996) calculated the demonstrated reserve base for strippable Fruitland coal in New Mexico for depths of overburden 

between 20 and 200 ft, assuming that coal with less than 20 

ft of overburden would be too badly weathered to be mined. 

That study only included coal within 1 mi of a point of 

measurement, and coal beds thinner than about 2.5 ft were not 

included. Mined Fruitland coal was subtracted from the total. 

Hoffman’s strip-coal tonnage was 3.674 billion short tons. 

Beaumont (1998) discussed near-surface coal deposits in the 

San Juan Basin (less than 200 ft of overburden). He showed 

a 200-ft depth line for Fruitland coals, but did not offer an 

estimate of the tonnage of remaining strippable Fruitland coal. 

Table 5 of this report shows 19 billion short tons of coal 

in the 0–500 ft of overburden category for the Fruitland, basin 

wide, and 16 billion short tons at 0–500 ft in the New Mexico 

Table 5. Estimated coal resources (in millions of short tons) in beds 1.2 ft thick or greater, Fruitland Formation, 

San Juan Basin, Colorado and New Mexico. 

[Values rounded to two significant figures. Totals may not add due to independent rounding] 

State County Overburden categories (ft) Grand Total 

 0-500 500-1,000 1,000-2,000 2,000-3,000 >3,000 

Colorado Archuleta 970 690 1,400 3,100 3,600 9,800 

 La Plata 1,600 1,000 3,900 19,000 14,000 40,000 

Colorado Totals 2,600 1,700 5,400 22,000 18,000 50,000 

New Mexico McKinley 1,700 300 0 0 0 2,000 

 Rio Arriba 140 85 380 13,000 53,000 66,000 

 San Juan 14,000 12,000 32,000 29,000 17,000 100,000 

 Sandoval 490 1,400 2,300 1,700 250 6,200 

New Mexico Totals 16,000 14,000 34,000 44,000 70,000 180,000 

Grand Total 19,000 16,000 40,000 66,000 88,000 230,000 

Geology and Coal Resources of the Upper Cretaceous Fruitland Fm., San Juan Basin, New Mexico and Colorado Q75
Table 6. Coal production in short tons by year from Fruitland Formation strip-coal mines in the San Juan Basin. 

[Data for New Mexico through 1997 from Beaumont (1998); data for 1998 from the New Mexico Energy, Minerals, and Natural Resources Department. Colorado 

coal production data from Colorado Geological Survey] 

 New Mexico Colorado Basin yearly 

Year Navajo San Juan La Plata Gateway De-Na-Zin Burnham Chimney Rock Martinez Strip totals 

1963 1,190,763 1,190,763 

1964 2,116,069 2,116,069 

1965 2,397,982 2,397,982 

1966 2,032,447 2,032,447 

1967 2,435,318 2,435,318 

1968 2,332,652 2,332,652 

1969 3,337,419 342 3,337,761 

1970 6,020,950 6,020,950 

1971 6,652,049 6,652,049 

1972 6,898,262 6,898,262 

1973 7,389,321 350,724 7,740,045 

1974 6,955,000 956,688 7,911,688 

1975 6,073,000 1,245,449 7,318,449 

1976 7,010,000 1,223,670 8,233,670 

1977 7,420,066 1,843,076 4,366 9,267,508 

1978 6,100,000 2,613,038 38,676 8,751,714 

1979 5,203,000 4,000,534 3,370 9,206,904 

1980 7,733,000 4,538,000 13,177 38,340 8,425 12,330,942 

1981 6,845,000 4,119,000 211,145 50,581 255,013 11,480,739 

1982 7,144,802 4,906,034 229,585 89,459 259,477 12,629,357 

1983 8,958,056 4,975,770 202,229 23,000 363,338 252,500 14,774,893 

1984 8,403,000 5,151,579 213,846 9,697 31,221 267,809 14,077,152 

1985 6,978,000 5,110,790 202,733 34,077 193,885 12,519,485 

1986 6,841,000 5,215,966 594,643 188,168 31,378 12,871,155 

1987 7,343,000 3,128,220 1,628,034 172,324 51,185 12,322,763 

1988 9,087,000 2,847,000 1,538,133 116,485 106,113 13,694,731 

1989 8,874,000 4,737,379 1,467,309 15,078,688 

1990 8,670,000 4,572,231 1,908,093 15,150,324 

1991 7,385,000 2,920,611 1,054,097 11,359,708 

1992 9,087,000 3,062,200 1,327,408 13,476,608 

1993 9,082,000 3,871,052 1,651,149 14,604,201 

1994 7,781,000 4,430,304 1,686,899 13,898,203 

1995 8,412,000 4,164,909 1,851,295 14,428,204 

1996 7,031,000 4,381,946 2,418,800 13,831,746 

1997 7,505,000 3,055,151 3,413,694 13,973,845 

1998 8,420,000 2,880,000 3,880,000 15,180,000 

Totals 233,144,156 90,301,321 24,419,554 1,095,785 709,357 576,309 1,229,026 51,467 351,526,975 

Q76 Geologic Assessment of Coal in the Colorado Plateau: Arizona, Colorado, New Mexico, and Utah
part of the basin. The Fruitland outcrop dips steeply in the 

Colorado part of the basin, probably precluding large-scale 

strip mining of Fruitland coals in that area for the foreseeable 

future. An approximation of the original strippable coal tonnage for the Fruitland in New Mexico can be made by taking a 

fraction of the 16 billion short tons determined to be present in 

the 0- to 500-ft overburden category. At a maximum stripping 

depth of 200 ft, the tonnage is 6.4 billion short tons. This 

total includes all coal beds greater than 1.2 ft thick. If this 

6.4 billion short tons of coal is reduced by 10 percent for 

weathered coal with less than 20 ft of overburden (640 million 

short tons) and by the total Fruitland coal mined through the 

end of 1998 (350 million short tons, table 6), the remaining 

tonnage is about 5.3 billion short tons of coal. 

Hoffman’s (1996) number of 3.7 billion short tons of 

Fruitland coal between 20 and 200 ft of overburden in the 

New Mexico demonstrated reserve base is a minimum number 

because she did not include areas that were more than a mile 

from a point of measurement. The actual remaining reserve 

base for Fruitland coal in the New Mexico part of the San Juan 

Basin (through 1998) is thus greater than 3.7 but probably not 

more than 5.3 billion short tons of coal. These numbers do 

not represent recoverable coal because environmental, societal, 

technologic, and economic conditions that are involved in any 

coal-mining operation will determine how much of the reserve 

base can be recovered.

Fruitland Coal Mining

Fassett and Hinds (1971, p. 70) stated that “Approximately 30 known mines and prospect drifts have been excavated in Fruitland coal beds; the majority of these were small 

truck mines, which were operated briefl y for local markets.”

That study showed the locations of these small operations (fi g. 

A3-6) and presented production data for them (table A3-1) 

where it was known. Nickelson (1988) discussed all of the 

known Fruitland coal mines in the New Mexico part of the 

San Juan Basin. 

A new generation of large Fruitland strip-coal mines 

began with the opening of the Navajo coal mine in 1963, the 

San Juan mine in 1973, and the La Plata mine in 1986 (fi g. 

2). Four smaller strip mines were opened in the 1970’s and 

1980’s, but the last of these was shut down in 1988. Nearly 

all of the coal produced from these mines has been used to 

produce electricity at the Four Corners Generating Station and 

the San Juan Generating Station (fi g. 2). An overview of these 

power plants and coal mines is in Fassett (1989). Table 6 

shows reported coal production from Fruitland strip mines 

by year; total Fruitland coal production from these mines 

through 1998 was 352 million short tons. A detailed discussion 

of Fruitland coal mining is beyond the scope of this report 

but the reports by Shoemaker and others (1971), Nickelson 

(1988), Hoffman (1996), and Beaumont (1998) provide excellent overviews of the strippable Fruitland coal resources and 

mining in the New Mexico part of the San Juan Basin.

References Cited

Ambrose, W.A., and Ayers, W.B., 1994, Geologic controls on coalbed 

methane occurrence and production in the Fruitland Formation, 

Cedar Hill fi eld and the COAL site, in Ayers, W.B., Jr., and Kaiser, 

W.R., eds., Coalbed Methane in the Upper Cretaceous Fruitland Formation, San Juan Basin, New Mexico and Colorado: New Mexico 

Bureau of Mines and Mineral Resources Bulletin 146, p. 41–61.

American Society for Testing and Materials [ASTM], 1995, Standard 

classifi cation of coals by rank [ASTM designation F388-395]: 1995 

Annual book of ASTM Standards, v. 05.05, p. 169–171.

Ayers, W.B., Jr., and Ambrose, W.A., 1990, Geologic controls on the 

occurrence of coalbed methane, Fruitland Formation, San Juan 

Basin, in Ayers, W.B., Jr., Kaiser, W.R., Ambrose, W.A., Swartz, T.E., 

Laubach, S.E., Tremain, C.M., and Whitehead, N.H., III, eds., Annual 

Report Prepared for the Gas Research Institute: The University of 

Texas at Austin, Bureau of Economic Geology, GRI-90-0014.1, p. 

9–72.

Ayers, W.B., Jr., Ambrose, W.A., and Yeh, J.S., 1994, Coalbed methane 

in the Fruitland Formation, San Juan Basin—Depositional and 

structural controls on occurrence and resources, in Ayers, W.B., 

Jr., and Kaiser, W.R., eds., Coalbed Methane in the Upper Cretaceous Fruitland Formation, San Juan Basin, New Mexico and 

Colorado: New Mexico Bureau of Mines and Mineral Resources 

Bulletin 146, p. 13–40.

Ayers, W.B., and Zellers, S.D., 1991, Geologic controls on Fruitland 

coal occurrence, thickness, and continuity, Navajo Lake area, 

San Juan Basin, in Geologic Controls on Occurrence and Producibility of Coalbed Methane, Fruitland Formation: Chicago, Ill., Gas 

Research Institute, Report GRI 91/0072, p. 9–46.

Ayers, W.B., and Zellers, S.D., 1994, Coalbed methane in the Fruitland 

Formation, Navajo Lake area: Geologic controls on occurrence and 

producibility, in Ayers, W.B., Jr., and Kaiser, W.R., eds., Coalbed 

Methane in the Upper Cretaceous Fruitland Formation, San Juan 

Basin, New Mexico and Colorado: New Mexico Bureau of Mines 

and Mineral Resources Bulletin 146, p. 63–85.

Baltz, E.H., Ash, S.R., and Anderson, R.Y., 1966, History of nomenclature and stratigraphy of rocks adjacent to the Cretaceous-Tertiary 

boundary, western San Juan Basin, New Mexico: U.S. Geological 

Survey Professional Paper 524-D, 23 p.

Bauer, C.M., 1916, Stratigraphy of a part of the Chaco River valley: U.S. 

Geological Survey Professional Paper 98-P, p. 271–278 [1917].

Beach, L.J., and Jentgen, R.W., 1978, Coal test drilling for the San Juan 

mine extension, San Juan County, New Mexico: U.S. Geological 

Survey Open-File Report 80-1289, (unpaginated).

Beaumont, E.C., 1998, Distribution of near-surface coal deposits in 

San Juan Basin, New Mexico: New Mexico Bureau of Mines and 

Mineral Resources Resource Map 19, 2 sheets, scale 1:250,000.

Biewick, L.R.H., Medlin, A.L., Hunter, J.F., and Kohn, K.K., 1991, Coal 

resources of the San Juan Basin, in Molnia, C.L., Jobin, D.A., 

O’Connor, J.T., and Kottlowski, F.E., eds., Coalfi elds of New Mexico: 

Geology and Resources: U.S. Geological Survey Bulletin 1972, p. 

15–33.

Boger, L.W., and Medlin, A.L., 1991, Coal resource estimation in the 

Geology and Coal Resources of the Upper Cretaceous Fruitland Fm., San Juan Basin, New Mexico and Colorado Q77
San Juan Basin using geostatistical methods, in Molnia, C.L., Jobin, 

D.A., O’Connor, J.T., and Kottlowski, F.E., eds., Coalfi elds of New 

Mexico: Geology and Resources: U.S. Geological Survey Bulletin 

1972, p. 35–43.

Bond, W.A., 1984, Application of Lopatin’s method to determine burial 

history, evolution of the geothermal gradient, and timing of hydrocarbon generation in Cretaceous source rocks in the San Juan 

Basin, northwestern New Mexico and southwestern Colorado, in

Woodward, J., Meissner, F.F., and Clayton, J.L., eds., Hydrocarbon 

Source Rocks of the Greater Rocky Mountain Region: Rocky Mountain Association of Geologists Guidebook, p. 433–447.

Butler, R.F., 1985, Mineralogy of magnetic minerals and revised magnetic polarity stratigraphy of continental sediments, San Juan 

Basin, New Mexico: Journal of Geology, p. 535–554.

Brown, J.L., 1982a, Geologic map of the Alamo Mesa East quadrangle: 

U.S. Geological Survey Miscellaneous Field Studies Map MF-1497, 

scale 1:24,000.

Brown, J.L., 1982b, Geologic map of the Huerfano Trading Post SW 

quadrangle: U.S. Geological Survey Miscellaneous Field Studies 

Map MF-1498, scale 1:24,000.

Clarkson, G., and Reiter, M., 1988, An overview of geothermal studies 

in the San Juan Basin, New Mexico and Colorado, in Fassett, J.E., 

ed., Geology and Coal-Bed Methane Resources of the Northern 

San Juan Basin, Colorado and New Mexico: Rocky Mountain Association of Geologists Guidebook, p. 285–291.

Cobban, W.A., 1973, Signifi cant ammonite fi nds in uppermost Mancos 

Shale and overlying formations between Barker dome, New 

Mexico, and Grand Junction, Colorado, in Fassett, J.E., ed., Cretaceous and Tertiary Rocks of the Southern Colorado Plateau: Four 

Corners Geological Society Memoir, p. 148–153.

Cobban, W.A., Landis, E.R., and Dane, C.H., 1974, Age relations of 

upper part of Lewis Shale on east side of San Juan Basin, New 

Mexico, in Siemers, C.T., ed., Ghost Ranch Central-Northern New 

Mexico: New Mexico Geological Society Guidebook 25, p. 279–282.

Decker, D, Jeu, S.J., Cooper, J.D., and Wicks, D.E., 1988, Geology, 

geochemistry, reservoir engineering, and completion methods at 

the Cedar Hill fi eld, San Juan County, New Mexico: A fi eld study of 

classic coal degasifi cation behavior, in Fassett, J.E., ed., Geology 

and Coal-Bed Methane Resources of the Northern San Juan Basin, 

Colorado and New Mexico: Rocky Mountain Association of Geologists Guidebook, p. 221–235.

Dyman, T.S, Merewether, E.A., Molenaar, C.M., Cobban, W.A., Obradovich, J.D., Weimer, R.J., and Bryant, W.A., 1994, Stratigraphic 

transects for Cretaceous rocks, Rocky Mountains and Great Plains 

regions, in Caputo, M.V., Peterson, J.A., and Franczyk, K.J., eds., 

Mesozoic Systems of the Rocky Mountain Region, USA: Denver, 

Colo., Rocky Mountain Section of the Society for Sedimentary Geology, p. 365–391.

Fassett, J.E., 1977, Geology of the Point Lookout, Cliff House, and 

Pictured Cliffs Sandstones of the San Juan Basin, New Mexico 

and Colorado, in Fassett, J.E., ed., San Juan Basin III: New Mexico 

Geological Society Guidebook 28, p. 193–197.

Fassett, J.E., ed., 1978, Oil and gas fi elds of the Four Corners area: Four 

Corners Geological Society, v. I and II, 728 p.

Fassett, J.E., ed., 1983, Oil and gas fi elds of the Four Corners area: Four 

Corners Geological Society, v. III, p. 729–1143.

Fassett, J.E., 1985, Early Tertiary paleogeography and paleotectonics 

of the San Juan Basin area, New Mexico and Colorado, in Flores, 

R.M., and Kaplan, S.S., eds., Cenozoic Paleogeography of the WestCentral United States (Rocky Mountain paleogeography symposium 

3): Denver, Colo., Rocky Mountain Section, Society of Economic 

Paleontologists and Mineralogists, p. 317–334.

Fassett, J.E., 1987, The ages of the continental Upper Cretaceous 

Fruitland Formation and Kirtland Shale based on a projection of 

ammonite zones from the Lewis Shale, San Juan Basin, New 

Mexico and Colorado, in The Cretaceous-Tertiary Boundary in the 

San Juan and Raton Basins, New Mexico and Colorado: Geological 

Society of America Special Paper 209, p. 5–16.

Fassett, J.E., 1989, Coal resources of the San Juan Basin, in Anderson, 

O.J., Lucas, S.G., Love, D.W., and Cather, S.M., eds., Southeastern 

Colorado Plateau: New Mexico Geological Society 40th Annual 

Field-Trip Guidebook, p. 303–307.

Fassett, J.E., 1991, Oil and gas resources of the San Juan Basin, New 

Mexico and Colorado, in Gluskoter, H.J., Rice, D.D., and Taylor, 

R.B., eds., Economic Geology, Geological Society of America, The 

Geology of North America Series, v. P-2., p. 357–372.

Fassett, J.E., Cobban, W.A., and Obradovich, J.D., 1997a, Biostratigraphic and isotopic age of the Huerfanito Bentonite Bed of the 

Upper Cretaceous Lewis Shale at an outcrop near Regina, New 

Mexico, in Anderson, O.J., Kues, B.S., and Lucas, S.G., eds., Mesozoic Geology and Paleontology of the Four Corners Region: New 

Mexico Geological Society 48th Annual Field-Conference Guidebook, p. 229–232.

Fassett, J.E., Condon, S.M., Huffman, A.C., and Taylor, D.J., 1997b, 

Geology and structure of the Pine River, Florida River, Carbon Junction, and Basin Creek gas seeps, La Plata County, Colorado: U.S. 

Geological Survey Open-File Report, OF-97-59, 125 p.

Fassett, J.E., and Hinds, J.S., 1971, Geology and fuel resources of the 

Fruitland Formation and Kirtland Shale of the San Juan Basin, New 

Mexico and Colorado: U.S. Geological Survey Professional Paper 

676, 76 p.

Fassett, J.E., and Lucas, S.G., 2000, Evidence for Paleocene dinosaurs 

in the Ojo Alamo Sandstone, San Juan Basin, New Mexico, in 

Lucas, S.G., and Heckert, A.B., eds., Dinosaurs of New Mexico: 

New Mexico Museum of natural History and Science Bulletin 

No. 17.

Fassett, J.E., Lucas, S.G., Zielinski, R.A., and Budahn, J.R., 2000, Compelling new evidence for Paleocene dinosaurs in the Ojo Alamo 

Sandstone, San Juan Basin, New Mexico and Colorado, USA, in

Catastrophic Events and Mass Extinctions: Impacts and Beyond: 

Houston, Tex., LPI Contribution no. 1053, Lunar and Planetary Institute, p. 45–46.

Fassett, J.E., and Nuccio, V.F., 1990, Vitrinite refl ectance values of coal 

from drill-hole cuttings from the Fruitland and Menefee Formations, 

San Juan Basin, New Mexico: U.S. Geological Survey Open-File 

Report 90-290, 21 p.

Fassett, J.E., and Steiner, M.B., 1997, Precise age of C33n-C32r magnetic polarity reversal, San Juan Basin, New Mexico and Colorado, 

in Anderson, O.J. and others, eds., Mesozoic Geology and PaleonQ78 Geologic Assessment of Coal in the Colorado Plateau: Arizona, Colorado, New Mexico, and Utah
tology of the Four Corners Region: New Mexico Geological Society 

Guidebook 48, p. 239–247.

Heywood, C.E., 1992, Isostatic residual gravity anomalies of New 

Mexico: U.S. Geological Survey Water-Resources Investigations 

Report 91-4065, 27 p.

Hoffman, G.K., 1991, Quality assessment of strippable coals in northwest New Mexico: drilling data, chemical, and petrographic analyses for the Fruitland, Menefee, Crevasse Canyon, and Moreno 

Hill Formation[s]: New Mexico Bureau of Mines and Mineral 

Resources Open-File Report 377, (unpaginated).

Hoffman, G.K., 1996, Demonstrated reserve base for coal in New 

Mexico, modifi ed from fi nal report for cooperative agreement 

DOE-FC0193EI23974: New Mexico Bureau of Mines and Mineral 

Resources Open-File Report 428, 89 p., 2 appendixes.

Hoffman, G.K., Campbell, F.W., and Beaumont, E.C., 1993, Quality 

assessment of strippable coals in northwest New Mexico: Fruitland, Menefee, and Crevasse Canyon Formation coals in San Juan 

Basin, and Moreno Hill Formation coals in Salt Lake fi eld: New 

Mexico Bureau of Mines and Mineral Resources Bulletin 111, 84 p.

Hoffman, G.K., and Jones, G.E., 1998, Availability of coal resources in 

the Fruitland Formation, San Juan Basin, northwest New Mexico: 

New Mexico Bureau of Mines and Mineral Resources Open-File 

Report 438, 15 p.

Hoppe, W.F., 1992, Hydrocarbon potential and stratigraphy of the Pictured Cliffs, Fruitland, and Ojo Alamo Formations in the northeastern San Juan Basin, New Mexico, in Lucas, S.G., Kues, B.S., Williamson, T.E., and Hunt, A.P., eds., San Juan Basin IV: New Mexico 

Geological Society Guidebook 43, p. 359–371.

Hopkins, M.E., 1968, Harrisburg (No. 5) coal reserves of southeastern 

Illinois: Illinois State Geological Survey Circular 431, 25 p.

Hunt, A.P., and Lucas, S.G., 1992, Stratigraphy, paleontology and age 

of the Fruitland and Kirtland Formations (Upper Cretaceous), San 

Juan Basin, New Mexico, in Lucas, S.G., Kues, B.S., Williamson, 

T.E., and Hunt, A.P., eds., San Juan Basin IV: New Mexico Geological Society Guidebook 43, p. 217–239.

Jentgen, R.W., and Fassett, J.E., 1977, Sundance-Bisti-Star Lake 1976 

drilling in McKinley and San Juan Counties, northwestern New 

Mexico: U.S. Geological Survey Open-File Report 77-369, 80 p.

Jervey, M.T., 1988, Quantitative geological modeling of siliciclastic 

rock sequences and their seismic expression, in Wilgus and others, 

eds., Sea Level Changes: An Integrated Approach: Society of Economic Paleontologists and Mineralogists Special Publication No. 

42, p. 47–69.

Kelso, B.S., Decker, A.D., Wicks, D.E., and Horner, D.M., 1987, GRI 

geologic and economic appraisal of coalbed methane in the San 

Juan Basin, in Proceedings, 1987 Coalbed Methane Symposium: 

Tuscaloosa, University of Alabama, School of Mines and Energy 

Development, p. 119–125.

Kelso, B.S., Goolsby, S.M., and Tremain, C.M., 1980, Deep coal bed 

methane potential of the San Juan River coal region, southwestern 

Colorado: Colorado Geological Survey Open-File Report 80-2, 56 p.

Kelso, B.S., and Rushworth, P., 1982, Southern Ute/Department of 

Energy coalbed methane test wells: Colorado Geological Survey 

Open-File Report 82-4, 22 p.

Kelso, B.S., and Wicks, D.E., 1988, A geologic analysis of the Fruitland 

Formation coal and coal-bed methane resources of the San Juan 

Basin, southwestern Colorado and northwestern New Mexico, in

Fassett, J.E., ed., Geology and Coal-Bed Methane Resources of 

the Northern San Juan Basin, Colorado and New Mexico: Rocky 

Mountain Association of Geologists Guidebook, p. 69–79.

Law, B.E., 1990, Vitrinite refl ectance data from Cretaceous and Tertiary 

rocks, San Juan Basin, New Mexico and Colorado: U.S. Geological 

Survey Open-File Report 90-659, 18 p.

Law, B.E.,1992, Thermal maturity patterns of Cretaceous and Tertiary 

rocks, San Juan Basin, Colorado and New Mexico: Geological 

Society of America Bulletin, v. 104, p. 192–207.

Levine, J.R., 1993, Coalifi cation: The evolution of coal as source rock 

and reservoir rock for oil and gas, in Law, B.E., and Rice, D.D., 

Hydrocarbons from Coal: American Association of Petroleum Geoloogists Studies in Geology 38, p. 39–77.

Mavor, Matt, and Nelson, C.R., 1997, Coalbed reservoir gas-in-place 

analysis: Chicago, Ill., Gas Research Institute, GRI Report no. GRI97/0263, 134 p.

M’Gonigle, J.W., and Roberts, L.N.R., 1997, Coal geology and 

resources, in Van Loenen, R.E., and Gibbons, A.B., eds., Mineral 

Resource Potential and Geology of the San Juan National Forest, 

Colorado: U.S. Geological Survey Bulletin 2127, p. 101–115.

Nickelson, H.B., 1988, One hundred years of coal mining in the San 

Juan Basin, New Mexico: New Mexico Bureau of Mines and Mineral Resources Bulletin 111, 227 p.

North American Stratigraphic Code, 1983: The North American Commission on Stratigraphic Nomenclature: American Association of 

Petroleum Geologists Bulletin, v. 67, no. 5, p. 841–875.

Nummedal, Dag, and Molenaar, C.M., 1995, Sequence stratigraphy of 

ramp-setting strand plain successions: The Gallup Sandstone, New 

Mexico, in Van Wagoner, J.C., and Bertram, G.T., eds., Sequence 

Stratigraphy of Foreland Basin Deposits: American Association of 

Petroleum Geologists Memoir 64, p. 277–310.

Obradovich, J.D., 1993, A Cretaceous time scale, in Caldwell, W.G.E., 

and Kauffman, E.G., eds., Evolution of the Western Interior Basin: 

Geological Association of Canada, Special Paper 39, p. 379–396.

Obradovich, J.D., and Hicks, J.F., 1999, A review of the isotopic calibration points for the geomagnetic polarity time scale in the interval 

83 to 33 Ma (C34n to C13n): Denver, Colo., Geological Society of 

America 1999 Annual Meeting, Abstracts with Programs Volume, v. 

31, no. 7, p. A-71.

Obradovich, J.D., and Cobban, W.A., 1975, A time scale for the Late 

Cretaceous of the Western Interior of North America, in Caldwell, 

W.G.E., ed., The Cretaceous System in the Western Interior of North 

America: Geological Association of Canada, Special Paper 13, p. 

31–54.

Oil and Gas Journal, 1998, Multiwell Ojo Alamo development advancing in San Juan Basin: Oil and Gas Journal, April 27, 1998, p. 77.

O’Sullivan, R.B., Mytton, J.W., Strobell, J.D., Jr., Scott, G.R., and Erpenbeck, M.F., 1986, Geologic map of the Tanner Lake quadrangle: 

U.S. Geological Survey Miscellaneous Field Studies Map MF-1864, 

scale 1:24,000.

Geology and Coal Resources of the Upper Cretaceous Fruitland Fm., San Juan Basin, New Mexico and Colorado Q79
O’Sullivan, R.B., Scott, G.R., and Heller, J.S., 1979, Geologic map of 

the Bisti Trading Post quadrangle: U.S. Geological Survey Miscellaneous Field Studies Map MF-1075, scale 1:24,000.

Pawlewicz, M.J., Nuccio, V.F., and Fassett, J.E., 1991, Vitrinite refl ectance values of coal from drill-hole cuttings, San Juan Basin, New 

Mexico: U.S. Geological Survey Open-File Report 91-302, 10 p.

Pike, W.S., Jr., 1947, Intertonguing marine and nonmarine Upper Cretaceous deposits of New Mexico, Arizona, and southwestern Colorado: Geological Society of America Memoir 24, 103 p.

Rice, D.D., 1983, Relation of natural gas composition to thermal 

maturity and source rock type in San Juan Basin, northwestern 

New Mexico and southwestern Colorado: American Association of 

Petroleum Geologists Bulletin, v. 67, p. 1199–1218.

Roberts, L.N.R., 1989, Results of 1988 coal exploratory drilling in the 

Fruitland Formation, western part of the Southern Ute Indian Reservation, La Plata County, Colorado: U.S. Geological Survey Open-File 

Report 89-487, 221 p.

Roberts, L.N.R., 1991, Coal resources of the Fruitland Formation in part 

of the Ute Mountain Ute Indian Reservation, San Juan County, New 

Mexico: U.S. Geological Survey Bulletin 1938, 15 p.

Roberts, L.N.R., and Kirschbaum, M.A., 1995, Paleogeography of the 

Late Cretaceous of the Western Interior of Middle North America—Coal distribution and sediment accumulation: U.S. Geological 

Survey Professional Paper 1561, 115 p.

Roberts, L.N.R., and McCabe, P.J., 1992, Peat accumulation in coastalplain mires: A model from coals of the Fruitland Formation (Upper 

Cretaceous) of southern Colorado, USA: International Journal of 

Coal Geology, v. 21, p. 115–138.

Roberts, L.N.R., and Uptegrove, Jane, 1991, Coal geology and coal 

zone correlations in the Fruitland Formation, western part of the 

Southern Ute Indian Reservation, La Plata County, Colorado: U.S. 

Geological Survey Coal Investigations Map C-138, scale 1:24,000.

Sandberg, D.T., 1986, Correlation of coal beds in the Fruitland Formation as interpreted from geophysical logs, east-central San Juan 

County, New Mexico: U.S. Geological Survey Miscellaneous Field 

Studies Map MF-1848.

Sandberg, D.T.,1988a, Coal resources and coal-bed geometry, Fruitland Formation, Southern Ute Indian Reservation, Archuleta and 

La Plata Counties, Colorado, in Fassett, J.E., ed., Geology and 

Coal-Bed Methane Resources of the Northern San Juan Basin, 

Colorado and New Mexico: Rocky Mountain Association of Geologists Guidebook, p. 39–50.

Sandberg, D.T.,1988b, Distribution of coal beds in the Fruitland Formation, Southern Ute Indian Reservation, Archuleta and La Plata 

Counties, southwestern Colorado: U.S. Geological Survey Open-File 

Report 88-230, 5 maps, scale 1:100,000.

Sandberg, D.T., 1990, Coal resources of Upper Cretaceous Fruitland 

Formation in the Southern Ute Indian Reservation, southwestern 

Colorado: U.S. Geological Survey Professional Paper 1505-D, 24 p.

Schneider, G.B., Weide, D.L., Mytton, J.W., and Scott, G.R., 1979, Geologic map of the Pueblo Bonito NW quadrangle: U.S. Geological 

Survey Miscellaneous Field Studies Map MF-1118, scale 1:24,000.

Scott, A.R., Kaiser, W.R., and Ayers, W.B., Jr., 1994, Thermal maturity 

of Fruitland coals and composition of Fruitland Formation and Pictured Cliffs Sandstone gases, in Ayers, W.B., Jr., and Kaiser, W.R., 

eds., Coalbed Methane in the Upper Cretaceous Fruitland Formation, San Juan Basin, New Mexico and Colorado: New Mexico 

Bureau of Mines and Mineral Resources Bulletin, p. 165–186.

Scott, G.R., O’Sullivan, R.B., and Mytton, J.W., 1979, Geologic map of 

the Alamo Mesa West quadrangle: U.S. Geological Survey Miscellaneous Field Studies Map MF-1074, scale 1:24,000.

Semken, S.C., and McIntosh, W.C., 1997, 40Ar/39Ar age determinations 

for the Carrizo Mountains laccolith, Navajo Nation, Arizona, in 

Anderson, O.J. and others, eds., Mesozoic Geology and Paleontology of the Four Corners Region: New Mexico Geological Society 

Guidebook 48, p. 75–80.

Shoemaker, J.W., Beaumont, E.C., and Kottlowski, F.E., 1971, Strippable low-sulfur coal resources of the San Juan Basin in New 

Mexico and Colorado: New Mexico Bureau of Mines and Mineral 

Resources Memoir 25, 189 p.

Shoemaker, J.W., and Holt, R.D., 1973, Coal resources of Southern 

Ute and Ute Mountain Ute Indian Reservations, Colorado and 

New Mexico: New Mexico State Bureau of Mines and Mineral 

Resources Circular 134, 22 p.

Stach, E., Mackowsky, M.T., Taylor, G.H., Chandra, D., Teichmuller, M., 

and Teichmuller, R., 1982, Stach’s text book of coal petrology (3rd 

ed.): Stuttgart, Germany, Borntraeger, 535 p.

Strobell, J.D., O’Sullivan, R.B., Mytton, J.W., and Erpenbeck, M.F., 

1985, Geologic map of the Pretty Rock quadrangle: U.S. Geological 

Survey Miscellaneous Field Studies Map MF-1788, scale 1:24,000.

Thaden, R.E., and Zech, R.S., 1984, Preliminary structure contour map 

of the San Juan Basin: U.S. Geological Survey Miscellaneous Field 

studies Map MF-1673, scale 1:500,000.

Turner, C.E., and Fishman, N.S., 1991, Jurassic Lake T’oo’dichi’: A 

large alkaline, saline lake, Morrison Formation, eastern Colorado 

Plateau: Geological Society of America Bulletin, v. 104, p. 538–558.

U.S. Geological Survey, 1946, Physical Divisions of the United States 

[prepared by Fenneman]: U.S. Geological Survey map.

Whitehead, Neil H, III, 1993, SJ-1. Fruitland Formation, in Hjellming, 

Carol A., ed., Atlas of Major Rocky Mountain Gas Reservoirs: New 

Mexico Bureau of Mines and Mineral Resources, p. 119–122.

Whyte, M.R., and Shoemaker, J.W., 1977, A geological appraisal of the 

deep coals of the Menefee Formation of the San Juan Basin, New 

Mexico, in Fassett, J.E., ed., Supplemental Articles to San Juan 

Basin III: New Mexico Geological Society 40th Annual Field Trip 

Guidebook, p. 41–48.

Williams, G.D., and Stelk, C.R., 1975, Speculation on the Cretaceous 

paleogeography of North America, in Caldwell, W.G.E., ed., The 

Cretaceous System in the Western Interior of North America: Geological Association of Canada Special Paper 13, p. 1–20.

Williamson, T.E., and Lucas, S.G., 1992, Stratigraphy and mammalian 

biostratigraphy of the Paleocene Nacimiento Formation, southern 

San Juan Basin, New Mexico, in Lucas, S.G., Kues, B.S., Williamson, T.E., and Hunt, A.P., eds., San Juan Basin IV: New Mexico 

Geological Society 43rd Annual Field Conference Guidebook, p. 

265–296.

Q80 Geologic Assessment of Coal in the Colorado Plateau: Arizona, Colorado, New Mexico, and Utah
Wilson, R.W., and Jentgen, R.W., 1980, Coal test drilling for the Dena-zin Bisti area, San Juan County, New Mexico: U.S. Geological 

Survey Open-File Report 78-960, 87 p.

Wood, G.H., Jr., Kehn, T.M., Carter, M.D., and Culbertson, W.C., 1983, 

Coal resource classifi cation system of the U.S. Geological Survey: 

U.S. Geological Survey Circular 891, 65 p.

Geology and Coal Resources of the Upper Cretaceous Fruitland Fm., San Juan Basin, New Mexico and Colorado Q81
Appendix 1—ArcView Files for Coal Assessment of the San Juan Basin, 

New Mexico and Colorado

The ArcView fi les used for the coal resource assessment of the San Juan Basin include geographic, geologic, coal-resource, 

and coal- and surface-ownership information—these fi les are presented as views in the ArcView project. The ArcView project 

and the digital fi les are stored on both discs of this CD-ROM set—Appendix 1 of chapter Q resides on both discs. Persons who 

do not have ArcView 3.1 may query the data by means of the ArcView Data Publisher on disc 1. Persons who do have ArcView 

3.1 may utilize the full functionality of the software by accessing the data that reside on disc 2. An explanation of the ArcView 

project and data library—and how to get started using the software—is given by Biewick and Mercier (chap. D, this CD-ROM). 

Metadata for all digital fi les are also accessible through the ArcView project.

Appendix 2—Database for the Fruitland Formation Coal Assessment of the 

San Juan Basin, New Mexico and Colorado

This database was the basis for the net-coal isopach map (fi g. 28); this map was used to determine Fruitland coal resources 

for the basin. The database contains location, lithologic, and stratigraphic data (including top and bottom depths of coal beds) 

from the StratiFact database. This fi le consists of ASCII format, DBF, and Excel spreadsheets on disc 2 of this CD-ROM.

Q82 Geologic Assessment of Coal in the Colorado Plateau: Arizona, Colorado, New Mexico, and Utah
Appendix 3—Figures and Tables from Fassett and Hinds (1971)

These illustrations, labeled fi gures A3-1 through A3-11 and tables A3-1 and A3-2 are adapted, with one exception, from 

stratigraphic and coal-quality data in Fassett and Hinds (1971). Data points, contour lines, and geologic information were 

copied from scanned images of the original maps and fi tted to the San Juan Basin base map of this report. Line drawings were 

traced from the original scanned images. Figure A3-10 (not previously published) shows the distribution of sulfur percentages 

throughout the basin (sulfur data from table A3-2). Detailed discussions of these fi gures are in Fassett and Hinds (1971).

ARCHULETA

SAN JUAN

McKINLEY

MONTEZUMA

108° 107°

 37° 37°

 36° 36°

108° 107°

COLORADO

NEW MEXICO

Outcrop of Fruitland

 Formation

Farmington

Dulce

Cuba

Ignacio

Durango

0 5 10 15 20 MILES

R 13 W

R 16 W 15

T 19 N

20

21

22

23

24

25

26

27

28

29

30

31

32

32

33

34

T 35 N

R 1 W R 1 E

R 1.5 W

2

R 1 W

2.5 R 16 W 15 14 13 12 11 10 9 8 7 6 5 4 3

6 5 4 3 2

7

8

9

10

11 12

T 34 N

 (NUL)

T 34 N

 (SUL)

R 1 W R 1 E

2 13 12 11 10 9 8 7 6 5 4 3

14

T 34.5 N

T 34 N (NUL)

T 34 N

 (SUL)

SANDOVAL

RIO ARRIBA

LA PLATA

Study

area

COLORADO

NEW MEXICO

K & F

absent

"T 34 N (NUL)" is north of Ute line, "T 34 N (SUL)"

 is south of Ute line. Kf = Fruitland Formation. 

EXPLANATION

Drill hole

Kf

Kf

K & F

absent

Farmington Sandstone

 and uppper shale

 members of Kirtland

 Formation absent

Ojo Alamo

 absent

Figure A3-1. Map showing areas in the subsurface of the San Juan Basin where rock units of the Fruitland Formation, Kirtland 

Formation, and Ojo Alamo Sandstone are absent. All drill holes used for stratigraphic subsurface control are shown. K&F, Kirtland 

and Fruitland Formations. Map is modifi ed from fi gure 9 of Fassett and Hinds (1971)

Geology and Coal Resources of the Upper Cretaceous Fruitland Fm., San Juan Basin, New Mexico and Colorado Q83
ARCHULETA

SAN JUAN

McKINLEY

MONTEZUMA

108° 107°

 37° 37°

 36° 36°

108° 107°

COLORADO

NEW MEXICO

Outcrop of Fruitland

 Formation

Farmington

Dulce

Cuba

Ignacio

Durango

0 5 10 15 20 MILES

R 13 W

R 16 W 15

T 19 N

20

21

22

23

24

25

26

27

28

29

30

31

32

32

33

34

T 35 N

R 1 W R 1 E

R 1.5 W

2

R 1 W

2.5 R 16 W 15 14 13 12 11 10 9 8 7 6 5 4 3

6 5 4 3 2

7

8

9

10

11 12

T 34 N

 (NUL)

T 34 N

 (SUL)

R 1 W R 1 E

2 13 12 11 10 9 8 7 6 5 4 3

14

T 34.5 N

T 34 N (NUL)

T 34 N

 (SUL)

SANDOVAL

RIO ARRIBA

LA PLATA

Study

area

COLORADO

NEW MEXICO

2,000

1,900

1,800

1,700

1,600

1,500

1,400

1,300

1,200

1,100

1,000

900

800

700

600

500

400

300

200

100

0

0

Isopached interval from top of Kirtland

 Formation to base of Fruitland Formation;

 contour interval is 100 ft. "T 34 N (NUL)"

 is north of Ute line, "T 34 N (SUL)" is

 south of Ute line. Kf = Fruitland Formation. 

EXPLANATION

Locations of Kirtland-Fruitland

thickness determinations

Drill hole Outcrop measured

section

Kf

Kf

Figure A3-2. Isopach map of the Fruitland Formation and Kirtland Shale. Modifi ed from fi gure 11 of Fassett and Hinds (1971).

Q84 Geologic Assessment of Coal in the Colorado Plateau: Arizona, Colorado, New Mexico, and Utah
E

E '

2600

2500

2500

2400

2300

2200

2100

2000

1900

1800

1700

1600

1500

1400

1300

1200

1100

1000

900

800

700

600

500

Isopached interval is from the Huerfanito

 Bentonite Bed to the base of the Ojo Alamo

 Sandstone; contour interval is 100 ft. Kf =

 Fruitland Formation; Kkf = Kirtland and

 Fruitland Formations, undivided; Toa = Ojo

 Alamo Sandstone. "T 34 N (NUL)" is north

 of Ute line, "T 34 N (SUL)" is south of Ute

 line. 

EXPLANATION

Drill hole

Farmington Sandstone

and upper shale members

of Kirtland Formation

Fruitland Formation and lower shale

member of Kirtland Formation

Lewis Shale

Huerfanito Bentonite Bed

Pictured Cliffs Sandstone

E E'

Northwest

Southeast

 LATE

CRETACEOUS

TERTIARY

Kkf

Kkf

Toa

Fruitland

Formation

 Ojo

Alamo

 Ss

ARCHULETA

SAN JUAN

McKINLEY

MONTEZUMA

108 107 

 37 37 

 36 36 

108 107 

COLORADO

NEW MEXICO

Dulce

Cuba

Ignacio

Durango

0 5 10 15 20 MILES

R 13 W

R 16 W 15

T 19 N

20

21

22

23

24

25

26

27

28

29

30

31

32

32

33

34

T 35 N

R 1 W R 1 E

R 1.5 W

2

R 1 W

2.5 R 16 W 15 14 13 12 11 10 9 8 7 6 5 4 3

6 5 4 3 2

7

8

9

10

11 12

T 34 N

 (NUL)

T 34 N

 (SUL)

R 1 W R 1 E

2 13 12 11 10 9 8 7 6 5 4 3

14

T 34.5 N

T 34 N (NUL)

T 34 N

 (SUL)

SANDOVAL

RIO ARRIBA

LA PLATA

Study

area

COLORADO

NEW MEXICO

Kf

Base of Paleocene

 (K-T boundary)

Kirtland

Formation

Toa

Kf

Farmington

Ojo Alamo Sandstone and younger rocks

Figure A3-3. Isopach map of the interval between the Huerfanito Bentonite Bed of the Lewis Shale and the base of the 

Ojo Alamo Sandstone (modifi ed from fi gure 13 of Fassett and Hinds, 1971). Kirtland Formation and Ojo Alamo Sandstone 

outcrops are from plate 1 of Fassett and Hinds. Stratigraphic cross section below map shows thinning of Kirtland and 

Fruitland Formations southeastward across San Juan Basin (modifi ed from cross section E-E’ on plate 2 of Fassett and Hinds 

(1971). Line of section is on map. 

Geology and Coal Resources of the Upper Cretaceous Fruitland Fm., San Juan Basin, New Mexico and Colorado Q85
Fruitland and Kirtland Formations 

Fruitland and Kirtland Formations 

Huerfanito Bentonite Bed Lewis

Shale

Pictured Cliffs Sandstone

Pictured Cliffs Sandstone

Lewis Shale

and older rocks

Present

topography

5000 ft above sea level Ojo Alamo Sandstone and younger rocks

South

North

South

South

North

North

Paleosurface

Paleosurface

Fruitland and Kirtla nd For mations

Huerfanito Ben tonite Be d

Pictured Cliffs

 Sandstone

Animas Formation

and younger rocks

0

500

1000

1500

2000

FEET

5 10 15 MILES

VERTICAL EXAGGERATION ABOUT X34

L ewis S hale

a nd older rock s

Huerfanito Ben tonite Bed

A - about 71 Ma, end of Campanian

B - about 65 Ma, beginning of Paleocene

C - present

Figure A3-4. North-trending diagrammatic cross sections showing the structural evolution of the San Juan Basin from Late Cretaceous time 

to the present. A, shows the paleosurface at the time the Kirtland Formation was being deposited; datum is Huerfanito Bentonite Bed. B, shows 

an erosional paleosurface after the basin area was uplifted in the southeast and the Fruitland and Kirtland were beveled by erosion prior to 

depositon of the Ojo Alamo Sandstone; datum is paleosurface line. C, shows the present topography and structure of the basin; datum is mean 

sea level. Modifi ed from fi gure 17 of Fassett and Hinds (1971).

Q86 Geologic Assessment of Coal in the Colorado Plateau: Arizona, Colorado, New Mexico, and Utah
West

West

West

East

East

East

Fruitland and Kirtland Formations 

Fruitland and Kirtland Formations 

Huerfanito Bentonite Bed

Huerfanito Bentonite Bed

Lewis

Shale

Lewis

Shale

Pictured Cliffs Sandstone

Pictured Cliffs

 Sandstone

Paleosurface

Paleosurface

A - about 71 Ma, end of Campanian

Present topography

5000 ft above sea level

0

500

1000

1500

2000

FEET

5 10 15 MILES

VERTICAL EXAGGERATION ABOUT X34

B - about 65 Ma, beginning of Paleocene

C - present

O jo Al amo Sandston e a nd you nger r ock s

Fruitland and Kirtland Formations

Lewis

Shale

Pictured Cliffs Sa ndston e

Huerfanit o Be nton it e Bed

Figure A3-5. East-trending diagrammatic cross sections showing the structural evolution of the San Juan Basin from Late Cretaceous time 

to the present. A, shows the paleosurface at the time the Kirtland Formation was being deposited; datum is Huerfanito Bentonite Bed. B, 

shows an erosional paleosurface after the basin area was uplifted in the southeast and the Fruitland and Kirtland were beveled by erosion 

prior to depositon of the Ojo Alamo Sandstone; datum is paleosurface line. C, shows the present topography and structure of the basin; 

datum is mean sea level. Modifi ed from fi gure 18 of Fassett and Hinds (1971).

Geology and Coal Resources of the Upper Cretaceous Fruitland Fm., San Juan Basin, New Mexico and Colorado Q87
Figure A3-6. Map of San Juan Basin showing locations of small, underground, Fruitland Formation coal mines; all of these mines are now 

abandoned. Coal-mine numbers are keyed to table A3-1(below). Map is modifi ed from fi gure 19 of Fassett and Hinds (1971).

ARCHULETA

SAN JUAN

McKINLEY

MONTEZUMA

108° 107°

 37° 37°

 36° 36°

108° 107°

COLORADO

NEW MEXICO

Outcrop of Fruitland

 Formation

Farmington

Dulce

Cuba

Ignacio

Durango

0 5 10 15 20 MILES

R 13 W

R 16 W 15

T 19 N

20

21

22

23

24

25

26

27

28

29

30

31

32

32

33

34

T 35 N

R 1 W R 1 E

R 1.5 W

2

R 1 W

2.5 R 16 W 15 14 13 12 11 10 9 8 7 6 5 4 3

6 5 4 3 2

7

8

9

10

11 12

T 34 N

 (NUL)

T 34 N

 (SUL)

R 1 W R 1 E

2 12 11 10 9 8 7 6 5 4 3 13

14

T 34.5 N

T 34 N (NUL)

T 34 N

 (SUL)

SANDOVAL

RIO ARRIBA

LA PLATA

Study

area

COLORADO

NEW MEXICO

24 23

25

1

2

34

5 9 8 7 6

10

11

12

14 13

15

16

17

18

19

20

21 22

26

27

28 29

30 "T 34 N (NUL)" is north of Ute line, "T 34 N (SUL)"

 is south of Ute line. Kf = Fruitland Formation. 

EXPLANATION

Abandoned underground

coal mine

Kf

Kf

Q88 Geologic Assessment of Coal in the Colorado Plateau: Arizona, Colorado, New Mexico, and Utah
Figure A3-7. Map showing distribution of heating values (Btu) from analyses of Fruitland Formation coal beds in the San Juan Basin. Complete 

analyses are in table A3-2. Modifi ed from fi gure 23 of Fassett and Hinds (1971).

ARCHULETA

SAN JUAN

McKINLEY

MONTEZUMA

108° 107°

 37° 37°

 36° 36°

108° 107°

COLORADO

NEW MEXICO

Outcrop of Fruitland

 Formation

Farmington

Dulce

Cuba

Ignacio

Durango

0 5 10 15 20 MILES

R 13 W

R 16 W 15

T 19 N

20

21

22

23

24

25

26

27

28

29

30

31

32

32

33

34

T 35 N

R 1 W R 1 E

R 1.5 W

2

R 1 W

2.5 R 16 W 15 14 13 12 11 10 9 8 7 6 5 4 3

6 5 4 3 2

7

8

9

10

11 12

T 34 N

 (NUL)

T 34 N

 (SUL)

R 1 W R 1 E

2 13 12 11 10 9 8 7 6 5 4 3

14

T 34.5 N

T 34 N (NUL)

T 34 N

 (SUL)

SANDOVAL

RIO ARRIBA

LA PLATA

Study

area

COLORADO

NEW MEXICO

Kf

Kf

11,840

7,370 8,350 8,610 9,450

10,270

10,990

11,840

11,410

11,970

11,810

11,540

12,370

9,280

11,760

9,960

11,790

10,440

12,520 11,440

11,650

9,170 9,900

12,690

12,130

11,080 10,780

11,580

10,640 10,270

11,670

13,310

11,760 12,190 12,010

11,740

11,910 11,600

11,580

12,390

12,370

12,340

12,340

12,010

13,080

13,300

12,360 12,830

12,960

11,250 11,310

10,780

11,850

9,670

11,320

1

3 2

4

5

6

7

8 9 10

11

12

14 13

15

16

17

18

19

20 21

22

23 26 25 24

27

29 28

30

31 32

34 33

35 37 36

38

40 39

41 43 42

44

45 46

47

48

49

50

51

52 53

54

55

56 57

57

58

59

60

63 62 Top figure is location number keyed to coal- 64

 analysis-table A3-2; other number is as-

 received Btu from table A3-2. "T 34 N (NUL)" is

 north of Ute line, "T 34 N (SUL)" is south of

 Ute line. Kf = Fruitland Formation. 

EXPLANATION

Sample location and as-received Btu value

61

65

11,460

11,550

11,020

12,830

10,690

13,350 13,090

12,040

12,070 12,140

11,230

Geology and Coal Resources of the Upper Cretaceous Fruitland Fm., San Juan Basin, New Mexico and Colorado Q89
ARCHULETA

SAN JUAN

McKINLEY

MONTEZUMA

108° 107°

 37° 37°

 36° 36°

108° 107°

COLORADO

NEW MEXICO

Outcrop of Fruitland

 Formation

Farmington

Dulce

Cuba

Ignacio

Durango

0 5 10 15 20 MILES

R 13 W

R 16 W 15

T 19 N

20

21

22

23

24

25

26

27

28

29

30

31

32

32

33

34

T 35 N

R 1 W R 1 E

R 1.5 W

2

R 1 W

2.5 R 16 W 15 14 13 12 11 10 9 8 7 6 5 4 3

6 5 4 3 2

7

8

9

10

11 12

T 34 N

 (NUL)

T 34 N

 (SUL)

R 1 W R 1 E

2 13 12 11 10 9 8 7 6 5 4 3

14

T 34.5 N

T 34 N (NUL)

T 34 N

 (SUL)

SANDOVAL

RIO ARRIBA

LA PLATA

Study

area

COLORADO

NEW MEXICO

14,460

14,770

14,700

1

3 2

4

5

6

7

8 9 10

11

12

14 13

15

16

17

18

20 21

22

23 26 25 24

27

29 28

30

31 32

34 33 35 37 36

38

40 39

41

43 42

44

45 46

47

48

49

50

51

52 53

54

55

56 57

57

58

59

60

Top figure is location number keyed to coal- 63 62

 analysis-table A3-2; other number is Btu

 value (m&a-free) from table A3-2 (for

 drill holes). "T 34 N (NUL)" is north of Ute

 line, "T 34 N (SUL)" is south of Ute line.

 Kf = Fruitland Formation 

EXPLANATION

Sample location and Btu value

Drill hole

or outcrop

13,500

14,000

14,000

13,000

12,000

14,500

15,000

15,500

15,000

14,510

64

?

?

?

?

?

65

61

19

Kf

Kf

Mine - published

analysis

14,830

14,310

14,410

14,370 14,480

14,240

14,580

14,160 11,730 11,590 11,620

14,260

14,570

14,430

14,140

14,140

14,510

14,840 14,660

15,480

15,440 15,600

15,440

15,470

15,280 15,100 14,760

15,160 15,170

15,190

15,470

15,720

15,380

15,330 15,470

15,480

15,070

15,010

15,020 15,120

14,720 15,150 14,700

14,700

14,920

15,160

14,920

14,800

14,820

14,870

15,070

14,750 14,820

14,670

14,600

14,440

14,430

13,820

13,820

13,460

13,680

14,190

14,290

14,420 14,560

14.400 14,370

Figure A3-8. Map showing distribution of moisture-and-ash-free heating values (Btu) from analyses of Fruitland Formation coal beds in the San 

Juan Basin. Complete analyses are in table A3-2. Map is modifi ed from fi gure 25 of Fassett and Hinds (1971). Contour interval is 500 Btu.

Q90 Geologic Assessment of Coal in the Colorado Plateau: Arizona, Colorado, New Mexico, and Utah
ARCHULETA

SAN JUAN

McKINLEY

MONTEZUMA

108° 107°

 37° 37°

 36° 36°

108° 107°

COLORADO

NEW MEXICO

Outcrop of Fruitland

 Formation

Farmington

Dulce

Cuba

Ignacio

Durango

0 5 10 15 20 MILES

R 13 W

R 16 W 15

T 19 N

20

21

22

23

24

25

26

27

28

29

30

31

32

32

33

34

T 35 N

R 1 W R 1 E

R 1.5 W

2

R 1 W

2.5 R 16 W 15 14 13 12 11 10 9 8 7 6 5 4 3

6 5 4 3 2

7

8

9

10

11 12

T 34 N

 (NUL)

T 34 N

 (SUL)

R 1 W R 1 E

2 13 12 11 10 9 8 7 6 5 4 3

14

T 34.5 N

T 34 N (NUL)

T 34 N

 (SUL)

SANDOVAL

RIO ARRIBA

LA PLATA

Study

area

COLORADO

NEW MEXICO

Kf

Kf

46.3

60

70

65

60

55

50

50

55

?

?

?

?

?

?

?

50

1

3 2

4

5

6

7

8 9 10

11 12

14 13

15

16

17

18

20 21

22

23 26 25 24

27

29 28

30

31 32

34 33

35 37 36

38

40 39

41 43 42

44

45 46

47

48

49

50

51

52 53

54

55

56 57

58

60

63 62

49.5

64

50.7 47.0

48.6

19

59

61

65

Mine - published

analysis

57

Top figure is location number keyed to coal-

 analysis-table A3-2; other number is fixed

 carbon percentage (m&a-free) from table

 A3-2 (for drill holes). "T 34 N (NUL)" is

 north of Ute line, "T 34 N (SUL)" is south

 of Ute line. Kf = Fruitland Formation. 

EXPLANATION

Sample location and fixed carbon value

Drill hole

or outcrop

59.4 59.2

71.3

72.4 69.8

71.1

68.1

53.0 64.7

53.5 54.5 53.9

59.4

51.9

51.9

52.5

52.6

53.9 54.3

51.6 53.3

56.0 67.2

60.5

60.6

53.2

54.0

52.8 52.4 55.3

53.8

51.1

51.5 52.1 53.2

52.2

51.5

50.3

52.1

53.0

58.4

58.4

54.8

56.6

49.6

49.2

51.9

52.1 52.9

51.4

52.8 51.1

53.1

53.4

52.8 51.6

51.9

51.4

48.8

50.9

50.1 49.8 48.7

52.2

Figure A3-9. Map showing distribution of fi xed-carbon values in percent for moisture-and-ash-free coal from analyses of Fruitland Formation 

coal beds in the San Juan Basin. Complete analyses are in table A3-2. Map is modifi ed from fi gure 26 of Fassett and Hinds (1971). Contour 

interval is variable.

Geology and Coal Resources of the Upper Cretaceous Fruitland Fm., San Juan Basin, New Mexico and Colorado Q91
ARCHULETA

SAN JUAN

McKINLEY

MONTEZUMA

108° 107°

 37° 37°

 36° 36°

108° 107°

COLORADO

NEW MEXICO

Outcrop of Fruitland

 Formation

Farmington

Dulce

Cuba

Ignacio

Durango

0 5 10 15 20 MILES

R 13 W

R 16 W 15

T 19 N

20

21

22

23

24

25

26

27

28

29

30

31

32

32

33

34

T 35 N

R 1 W R 1 E

R 1.5 W

2

R 1 W

2.5 R 16 W 15 14 13 12 11 10 9 8 7 6 5 4 3

6 5 4 3 2

7

8

9

10

11 12

T 34 N

 (NUL)

T 34 N

 (SUL)

R 1 W R 1 E

2 13 12 11 10 9 8 7 6 5 4 3

14

T 34.5 N

T 34 N (NUL)

T 34 N

 (SUL)

SANDOVAL

RIO ARRIBA

LA PLATA

Study

area

COLORADO

NEW MEXICO

Kf

Kf

.8

.8

.8

.8

.8 .8

.8

.8

.6

.6

.6 .6

.6

.6

.6

.6

.6

.6 .6

.6

.6

.6

.9

.9

1.8

1.1

.5

.7

.7

.7

.7

.7

.7

.7

.7

.7

.7

.7

.7

.7

.7

.7

.7

.7

.7

.6

.6

.6

.6

.6

.6 .6

.6

.6 .5

.7 .6

.6

.6

.5

.5 .5

1.3

1.8

2.2

5

6

7

8 9 10

11

12

14 13

15

16

17

18

19

20 21

22

23 26 25 24

27

29 28

30

31 32

34 33

35

37 36

38

40 39

41 43 42

44

45 46

47

48

49

50

51

52 53

54

55

56 57

57

58

59

60 61

62 63 64 65

1

3 2

4

.6

Top figure is location number keyed to coal-

 analysis-table A3-2; other number is sulfur

 percentage from table A3-2. "T 34 N (NUL)" is

 north of Ute line, "T 34 N (SUL)" is south of

 Ute line. Kf = Fruitland Formation. 

EXPLANATION

Sample location and as-received sulfur values

Figure A3-10. Map showing distribution of sulfur values from analyses of Fruitland Formation coal beds in the San Juan Basin. Complete 

analyses are in table A3-2. 

Q92 Geologic Assessment of Coal in the Colorado Plateau: Arizona, Colorado, New Mexico, and Utah
ARCHULETA

SAN JUAN

McKINLEY

MONTEZUMA

108° 107°

 37° 37°

 36° 36°

108° 107°

COLORADO

NEW MEXICO

Outcrop of Fruitland

 Formation

Farmington

Dulce

Cuba

Ignacio

Durango

0 5 10 15 20 MILES

R 13 W

R 16 W 15

T 19 N

20

21

22

23

24

25

26

27

28

29

30

31

32

32

33

34

T 35 N

R 1 W R 1 E

R 1.5 W

2

R 1 W

2.5 R 16 W 15 14 13 12 11 10 9 8 7 6 5 4 3

6 5 4 3 2

7

8

9

10

11 12

T 34 N

 (NUL)

T 34 N

 (SUL)

R 1 W R 1 E

2 13 12 11 10 9 8 7 6 5 4 3

14

T 34.5 N

T 34 N (NUL)

T 34 N

 (SUL)

SANDOVAL

RIO ARRIBA

LA PLATA

Study

area

COLORADO

NEW MEXICO

1

3 2

4

5

6

7

8 9 10

11

12

14 13

15 17

18

20 21

22

23 26 25 24

27

29 28

30

31 32

35 37 36

38

39

41 42 43

44

45 46

47

48

49

50

51

52

54

55

56 57

57

58

59

60 61

Top figure is location number keyed to coal- 64 63 62

 analysis-table A3-2; other number is ash

 percentage (as received) from table A3-2 

 (for drill holes). "T 34 N (NUL)" is north

 of Ute line, "T 34 N (SUL)" is south of

 Ute line. 

EXPLANATION

Sample location and ash value

Drill hole

or outcrop

19

11.4

16

10.7

34 33

40

53

65

11.4

14.7

23.4 16.8

13.5

12.6

16.9

13.1

11.0

12.7

8.3

10.2

10.2

26.6

21.3

19.5

29.2 27.7

24.9

16.2

10.9 11.0

15.8

25.0

23.7 28.5

24.3

13.1

11.2

9.8

13.1 14.4 11.3

17.3

13.7

12.1

12.5

14.1

13.7

13.7

13.7

15.3

11.4

15.7

12.0

16.5

13.4

14.7 19.3

20.4

29.3

19.9

18.6

35.7 30.5

14.8

18.2

18.4

26.8

23.6

23.0

26.0

16.3

16.2

16.2

10.5

27.0

24.5

13.5

14.7

14.2

22.5

30.7

27.4 21.5

20

20

15

15

15

20

20

30

15

Mine - published

analysis

31.0

20.5

Kf

Kf

Figure A3-11. Map showing distribution of ash from analyses of Fruitland Formation coal beds in the San Juan Basin. Complete analyses are in 

table A3-2. Map is modifi ed from fi gure 24 of Fassett and Hinds (1971). Contour interval is variable.

Geology and Coal Resources of the Upper Cretaceous Fruitland Fm., San Juan Basin, New Mexico and Colorado Q93
Table A3-1. Production and dates of operation of abandoned, underground

Fruitland coal mines shown on figure A3-6. 

Map Period of Production Map Period of Production

no. Name of mine operation (short tons) no. Name of mine operation (short tons)

1 Archuleta N.D.A N.D.A. 16 La Plata 1893-1902 5,447

2 Talian 1913-1915 7,637 17 Unknown N.D.A N.D.A.

3 Columbine 1938-1956 10,596 18 Mormon N.D.A N.D.A.

4 Cooper N.D.A N.D.A. 19 Fort Lewis 1943-1949 1,395

5 Triple S 1941-1951 5,348 Henderson N.D.A N.D.A.

Shamrock No. 1 1928-1936 3,916 20 Soda Spring 1928-1947 5,218

Shamrock No. 2 1937-1941 2,398 21 Cinder Butte (Pruitt?) N.D.A N.D.A.

6 Morning Glory 1930-1936 4,207 22 New Mexico (Kempton) 1928-1945 10,361

7 Palmer N.D.A N.D.A. 23 Bill Thomas (Morgan) 1931-1947 7,521

8 Blue Jay 1935-1944 3,135 24 Jones ?-1918(?) N.D.A.

9 Love N.D.A N.D.A. 25 Prospect drift N.D.A N.D.A.

10 Excelsior (3 shafts) 1927-1938 3,914 26 Marcelius (Caudell?) 1924-1938 10,318

11 Schutz (2 shafts) N.D.A N.D.A. 27 Blanchard N.D.A N.D.A.

12 Prospect pit N.D.A N.D.A. 28 Black Diamond 1918-1933(?) N.D.A.

13 Unknown N.D.A N.D.A. (Christenson), (3 mines?) N.D.A. N.D.A.

14 do N.D.A N.D.A. 29 L. W. Hendrickson 1929-1930(?) N.D.A.

15 do N.D.A N.D.A. 30 Prospect drift N.D.A N.D.A.

[N.D.A., no data available. Modified from Fassett and Hinds (1971)]

Q94 Geologic Assessment of Coal in the Colorado Plateau: Arizona, Colorado, New Mexico, and Utah
Table A3-2. Analyses of coal samples from the Fruitland Formation, San Juan Basin. (After table 4 of Fassett and Hinds, 1971.) 

[Form of analyses: A, as-received; B, moisture free; C, moisture and ash free] 

Locality USBM Location Approx. Form Proximate Heat

number lab. no. Well or source Quarter T. N. R. W. sample of Moisture Volatile Fixed Ash Sulfur valu

 section depth (ft) analysis matter carbon (Btu

Colorado 

1 H-38041 El Paso Nat. Gas 36 34 10 2,406-2,438 A 0.9 20.8 51.7 26.6 0.8 11,2

 Bondad 34-lO No. 3X B 21.0 52.2 26.8 0.8 11,3 C 28.7 71.3 1.1 15,4

2 H-55350 Mobil Oil NE 5 32 7 2,656-2,669 A 0.8 21.5 56.4 21.3 0.7 12,1

 Schofield Auto 31X-5 B 21.6 66.9 21.5 0.7 12,2 C 27.6 72.4 0.8 15,6

3 H-46452 Atlantic Rein NE 4 15.32 10 2,825-2,890 A 2.3 23.6 54.6 19.6 0.7 12,0

 Southern Ute 32-10 B 24.2 55.9 19.9 0.7 12,3 No. 15-1 C 30.2 69.8 0.9 15,4

New Mexico 

4 H-33642 La Plata Gathering SE 27 32 6 2,811-2,830 A 1.1 20.6 50.6 27.7 0.6 11,0

 San Juan Unit 32-50 B 20.8 51.2 28.0 0.6 11,1 No. 2-27 C 28.9 71.1 0.9 15,4

5 H-55381 Delhi Taylor NE 24 32 10 3,370-3,400 A 1.6 24.4 44.9 29.2 0.7 10,6

 Wickens No.1 B 24.8 45.5 29.7 0.7 10,8 C 35.3 64.7 1.0 15,4

6 H-16696 El Paso Nat. Gas SW 5 31 5 3,124-3,136 A 1.6 23.5 50.0 24.9 0.7 11,5

 Rosa Unit No. 41 B 23.8 50.9 25.3 0.7 11,7 C 31.9 68.1 1.0 15,7

7 H-50012 Delhi Taylor SW 20 31 9 3,230-3,255 A 1.3 33.7 49.2 15.8 0.7 12,8

 Barrett No. 1 B 34.1 49.9 16.0 0.7 13,0 C 40.6 59.4 0.9 15,4

8 H-16777 E1 Paso Nat. Gas SW 8 31 11 2,710-2,740 A 1.7 40.3 47.0 11.0 0.7 13,3

 Case No.9 B 41.0 47.9 11.1 0.7 13,5 C 46.1 53.9 . 0.8 15,2

9 H-19884 Consolidated Oil & Gas SW 5 31 12 2,215-3,000 A 2.4 39.4 47.3 10.9 0.5 13,0

 Mitchell No.1-5 B 40.4 48.5 11.1 0.5 13,4 C 45.5 54.5 0.6 15,1

10 H-15141 Consolidated Oil & Gas NE 11 31 13 1,776-1, 782 A 2.3 37.9 43.6 16.2 1.3 12,0

 Freeman No. 1-11 B 38.8 44.7 16.5 1.3 12,3 C 46.5 53.5 1.6 14,7

11 H-15142 El Paso Nat. Gas NE 10 30 6 3,100-3,105 A 1.5 24.1 49.4 25.0 0.7 11,3

 S.J.U. 30-6 No. 37 B 24.5 50.1 25.4 0.7 11,4 C 32.8 67.2 0.0 15,3

12 H-50079 Delhi Taylor NE 5 30 8 2,800-3,028 A 1.7 32.6 41.4 24.3 1.8 11,2

 Moore No.6 B 33.2 42.1 24.7 1.8 11,4 C 44.0 56.0 2.4 15,1
Table A3-2. Analyses of coal samples from the Fruitland Formation, San Juan Basin. (After table 4 of Fassett and Hinds, 1971)—Continued. 

Locality USBM Location Approx. Form Proximate Heat

number lab. no. Well or source Quarter T. N. R. W. sample of Moisture Volatile Fixed Ash Sulfur valu

 section depth (ft) analysis matter carbon (Btu

New Mexico—Continued

13 H-35925 El Paso Nat. Gas SE 28 30 9 2,385-2,390 A 1.5 39.9 45.5 13.1 2.2 12,9

 Turner No.3 B 40.5 46.2 13.3 2.2 13,1 C 46.7 53.3 2.5 15,1

14(a) H-19882. El Paso Nat. Gas SW 29 30 10 2,340-2,360 A 2.3 33.1 39.9 24.7 0.7 10,8

 Ludwick No. 20 B 33.9 40.9 25.2 0.7 11,0 C 45.3 54.7 0.9 14,7

14(b) H-19883 El Paso Nat. Gas SW 29 30 10 2,505-2,515 A 2.6 41.7 44.5 11.2 0.6 13,0

 Ludwick No. 20 B 42.9 45.6 11.5 0.6 13,4 C 48.4 51.6 0.7 15,1

75 H-13062 Aztec Oil & Gas NE 7 30 11 2,020-2,030 A 1.4 37.2 44.1 17.3 0.6 12,0

 Ruby Jones No. 1 B 37.7 44.8 17.5 0.6 12,1 C 45.7 54.3 0.7 14,7

16 H-15140 Southwest Production NE 22 30 12 1,713-1,742 A 2.2 38.8 45.3 13.7 0.6 12,3

 Sullivan No. 1 B 39.7 48.3 14.0 0.6 12,6 C 46.1 53.9 0.7 14,7

17 H-16308 R & G Drilling NW 18 30 13 1,425-1,440 A 2.8 40.4 44.7 12.1 0.6 12,3

 Lunt No. 62 B 41.6 45.9 12.5 0.6 12,7 C 47.5 52.5 0.7 14,5

18 H-19399 Compass Exploration NE 31 30 13 1,070-1,080 A 5.7 38.8 43.0 12.5 0.6 11,8

 Federal B 41.2 45.5 13.3 0.6 12,5 No. 131-A C 47.4 52.6 0.7 14,4

19 H-78945 N.M.P.S.C.C 21 30 15 69-70 A 5.6 39.7 43.3 11.4 0.7 11,8

 Core Hole No. 7 B 42.0 46.0 12.0 0.7 12,5 C 47.8 52.2 0.8 14,2

20 H-18102 El Paso Nat. Gas NE 5 29 5 3,175-3,200 A 2.2 29.3 44.8 23.7 0.8 11,4

 S.J. U. 295 No. 17 B 30.0 45.8 24.2 0.8 11,7 C 39.5 60.5 1.1 15,4

21 H-7560 El Paso Nat. Gas SW 9 29 6 3,575-3,580 A 1.2 27.7 42.6 28.5 0.6 10,7

 S.J. U. 29-6 No. 66 B 28.0 43.1 28.9 0.6 10,9 C 39.4 60.6 0.8 15,3

22 H-16310 Aztec Oil & Gas SW 30 29 9 1,985-2,005 A 1.6 41.1 46.6 10.7 0.7 13,3

 Cain No. 16-D B 41.7 47.5 10.8 0.7 13,5 C 46.8 53.3 0.7 15,1

23(a) H-27541 Aztec Oil & Gas SW 5 29 10 2,065-2,080 A 2.3 39.1 42.1 16.5 1.9 12,0

 Grenier "B" No. 3 B 40.0 43.1 16.9 2.0 12,3 C 48.1 51.9 2.4 14,8

23(b) H-27540 Aztec Oil & Gas SW 5 29 10 2,150-2,160 A 2.0 40.6 47.6 9.8 0.5 13,3

 Grenier "B" No. 3 B 41.4 48.6 10.0 0.5 13,5 C 46.0 54.0 0.6 15,0
Table A3-2. Analyses of coal samples from the Fruitland Formation, San Juan Basin. (After table 4 of Fassett and Hinds, 1971)—Continued. 

Locality USBM Location Approx. Form Proximate Heat

number lab. no. Well or source Quarter T. N. R. W. sample of Moisture Volatile Fixed Ash Sulfur valu

 section depth (ft) analysis matter carbon (Btu

New Mexico—Continued

24 H-13060 Tidewater SE 12 29 11 2,065-2,070 A 2.1 38.7 47.9 11.3 0.6 12,8

 N.M. Fed. No. 12-E B 39.5 48.9 11.6 0.6 13,1 C 44.7 55.3 0.7 14,8

25 H-3028 International Oil NW 9 29 11 1,905-1,910 A 1.8 39.9 43.9 14.4 0.7 12,3

 Fogelson No. 1-9 B 40.6 44.8 14.6 0.7 12,5 C 47.6 52.4 0.8 14,7

26 H-3030 Tennessee Oil & Gas NW 10 29 12 1,740-1,750 A 2.1 40.0 44.8 13.1 0.5 12,3

 Cornell Gas Unit A B 40.9 45.7 13.4 0.5 12,6 No. 1 C 47.2 52.8 0.6 14,5

27 H-8360 Aztec Oil & Gas SW 20 29 13 1,125-1,140 A 5.6 39.0 41.3 14.1 0.6 11,5

 Hagood No. 21-G B 41.3 43.8 14.9 0.6 12,2 C 48.5 51.5 0.7 14,4

28 H-4052 Aztec Oil & Gas SE 34 29 13 1,635-1,640 A 3.5 39.6 43.2 13.7 0.5 11,9

 Hagood No. 13-G B 41.0 44.8 14.2 0.6 12,3 C 47.8 51.2 0.6 14,3

29 H-4051 Humble Oil & Gas SE 36 29 14 1,490-1,495 A 4.1 40.0 40.6 15.3 0.7 11,6

 Humble No. L-9 B 41.7 42.3 16.0 0.7 12,1 C 49.7 50.3 0.9 14,4

30 H-3855 El Paso Nat. Gas NE 19 28 4 4,115-1,120 A 1.6 31.1 43.7 23.6 0.7 11,5

 S.J.U. 28-4 No. 28 B 31.6 44.4 24.0 0.7 11,7 C 41.6 58.4 0.9 15,4

31 H-7224 El Paso Nat. Gas SW 28 28 5 3,323-3,345 A 2.6 31.6 39.0 26.8 0.6 10,6

 S.J.U. 28-5 No.50 B 32.5 40.0 27.5 0.6 10,9 C 44.8 55.2 0.9 15,0

32 H-13779 E1 Paso Nat. Gas NE 30 28 8 2,185-2,195 A 1.9 33.7 35.1 29.3 0.6 10,2

 Florence No. l0-C B 34.3 35.8 29.9 0.7 10,4 C 48.9 51.1 0.9 14,9

33 H-13061 Aztec Oil & Gas SW 17 28 9 1,985-1,990 A 1.4 36.1 42.1 20.4 0.8 11,6

 Reid No. 23-D B 36.6 42.7 20.7 0.8 11,8 C 46.2 53.8 1.0 14,9

34 H-5472 Aztec Oil & Gas NW l6 28 10 1,842-1,853 A 1.6 38.4 40.7 19.3 0.6 11,7

 Caine No.13 B 39.0 41.4 19.6 0.6 11,9 C 48.5 51.5 0.8 14,8

35 H-12704 Redfern & Herd SW 10 28 11 1,490-1,500 A 2.1 39.8 43.4 14.7 0.6 12,1

 Redfern & Herd No. 5 B 40.7 44.3 15.0 0.6 12,4 C 47.9 52.1 0.7 14,6

36 H-24567 Sunray Mid-Continent NW 18 28 12 1,305-1,315 A 3.0 38.9 44.4 13.7 0.6 12,0

 Gallegos No.122 B 40.1 45.8 14.1 0.6 12,3 C 46.8 53.2 0.7 14,4
Table A3-2. Analyses of coal samples from the Fruitland Formation, San Juan Basin. (After table 4 of Fassett and Hinds, 1971)—Continued. 

Locality USBM Location Approx. Form Proximate Heat

number lab. no. Well or source Quarter T. N. R. W. sample of Moisture Volatile Fixed Ash Sulfur valu

 section depth (ft) analysis matter carbon (Btu

New Mexico—Continued

37 H-7225 Pan American NW 16 28 13 1,705-1,715 A 4.1 39.4 42.8 13.7 0.6 11,7

 Holder No. 7 B 41.1 44.6 14.3 0.6 12,2 C 47.9 52.1 0.7 14,2

38 H-18101 E1 Paso Nat. Gas SW 32 27 4 3,935-3,945 A 2.2 33.9 37.9 26.0 0.7 10,7

 S.J.U. 274 No. 30 B 34.6 38.8 26.6 0.7 11,0 C 47.2 52.8 0.9 15,0

39 H-33317 E Paso Nat. Gas SE 23 27 5 3,250-3,260 A 3.1 34.4 39.5 23.0 0.8 11,0

 S.J.U. 275 No. 74 B 35.6 40.7 23.7 0.9 11,4 C 46.6 53.4 1.1 15,0

40 H-33643 E1 Paso Nat. Gas SW 21 27 6 3,165-3,180 A 1.4 39.3 44.5 14.8 0.9 12,6

 Rincon Unit No. 171 B 39.8 45.2 15.0 0.9 12,8 C 46.9 53.1 1.1 15,1

41 H-35788 E1 Paso Nat. Gas SE 13 27 7 3,130-3,140 A 2.3 32.9 34.3 30.5 0.8 9,90

 Rincon Unit No. 177 B 33.7 35.1 31.2 0.8 10,1 C 48.9 51.1 1.2 14,7

42 H-21490 E1 Paso Nat. Gas NE 8 27 8 2,800-2,820 A 1.9 29.5 32.9 35.7 0.6 9,17

 Schwerdtfeger No. 20-A B 30.0 33.6 36.4 0.6 9,35 C 47.2 52.8 1.0 14,7

43 H-12705 Aztec Oil & Gas SW 8 27 9 2,215-2,230 A 2.2 36.7 41.2 19.9 0.8 11,4

 Whitley No. 6-D B 37.5 42.1 20.4 0.8 11,7 C 47.1 52.9 1.1 14,7

44 H-13063 Aztec Oil & Gas NW 29 27 9 2,135-2,145 A 2.7 38.3 40.4 18.6 0.8 11,6

 Hudson No. 5-D B 39.3 41.6 19.1 0.8 11,9 C 48.6 51.4 . 1.0 14,8

45 H-15776 Aztec Oil & Gas SW 12 27 10 1,900-1,905. A 2.2 40.4 44.0 13.4 0.6 12,5

 Hanks No. 14-D B 41.3 45.1 13.6 0.6 12,7 C 47.9 5'2, l 0.7 14,8

46 H-5021 British American Oil NE 14 27 11 1,920-1,930 A 3.3 40.8 43.9 12.0 0.6 12,3

 Fullerton No. 8 B 42.2 45.4 12.4 0.6 12,7 C 48.1 51.'9 . 0.7 14,6

47 H-3031 Southwest Production NE 26 27 12 1,900-1,910 A 2.6 41.2 40.5 15.7 0.6 11,8

 Cambell No .2 B 42.3 41.6 16.1 0.6 12,1 C 50.4 49.6 0.7 14,4

48 H-36175 Royal Development SW 6 27 13 1,214-1,245 A 4.3 39.7 44.6 11.4 0.7 11,9

 Ojo Amarillo No. 2 B 41.4 46.7 11.9 0.7 12,5 C 47.0 53.0 0.8 14,1

49 H-32698 Caulkins Oil NE 12 26 6 3,184-3,200 A 1.3 38.9 41.4 18.4 0.7 12,1

 State "A" MD No. 62 B 39.4 41.9 18.7 0.7 12,2 C 48.4 51.6 0.9 15,1
Table A3-2. Analyses of coal samples from the Fruitland Formation, San Juan Basin. (After table 4 of Fassett and Hinds, 1971)—Continued. 

Locality USBM Location Approx. Form Proximate Heat

number lab. no. Well or source Quarter T. N. R. W. sample of Moisture Volatile Fixed Ash Sulfur valu

 section depth (ft) analysis matter carbon (Btu

New Mexico—Continued

50 H-5020 Kay Kimbell SW 19 26 7 2,105-2,150 A 2.5 38.1 41.2 18.2 0.6 11,7

 Leiberman No. 5 B 39.1 42.2 18.7 0.6 12,0 C 48.1 51.9 0.8 14,8

51 H-12706 Southwest Production NE 5 26 11 1,700-1,705 A 3.6 40.6 39.3 16.5 0.7 11,5

 Ted Henderson No. l B 42.1 40.8 17.1 0.7 11,9 C 50.8 49.2 0.8 14,4

52 H-37832 Merrion & Associates SW 35 25 6 2,455-2,465 A 3.6 36.3 35.6 24.5 0.8 10,4

 Federal No. 3-35 B 37.7 36.9 25.4 0.8 10,8 C 50.5 49.5 1.1 14,5

53 H-16695 Century Exploration SW 21 25 9 1,620-1,625 A 4.2 31.5 33.3 31.0 0.9 9,28

 Mobil Rudman No. 2 B 32.8 34.8 32.4 0.9 9,68 C 48.6 51.4 1.4 14,3

54 H-40806 Standard of Texas SW 16 25 13 1,156-1208 A 9.5 30.9 43.3 16.3 1.8 10,2

 State No. 1 B 34.1 47.9 18.0 2.0 11,3 C 41.6 58.4 2.5 13,8

55 H-32405 El Paso Nat. Gas NE 22 24 3 3,194-3,205 A 2.1 38.7 36.7 22.5 0.7 10,9

 Lindrith No. 42 B 39.5 37.5 23.0 0.7 11,2 C 51.3 48.7 1.0 14,5

56 H-22075 Val Reese & Assoc. NE 31 24 6 2,070-2090 A 3.6 41.1 40.6 14.7 0.7 11,8

 Bobby "B" No. 2-31 B 42.6 42.2 15.2 0.7 12,2 C 50.2 49.8 0.9 14,4

57 H-31101 Val Reese & Assoc. NE 27 24 7 2,140-2150 A 4.4 40.9 41.2 13.5 0.6 11,7

 Lybrook No.7-27 B 42.8 43.1 14.1 0.6 12,3 C 49.9 50.1 0.7 14,3

58 H-5022 Dorfman Production SE 12 24 8 2,525-2,535 A 3.9 35.4 33.7 27.0 1.1 9,96

 Nancy Fed. No. 1 B 36.8 35.1 28.1 1.1 10,3 C 51.2 48.8 1.5 14,4

59 H-19885 N.M.P.S.C.C NW 32 24 13 100-112 A 12.0 32.5 39.3 16.2 0.5 9,67

 DH-32-1 B 36.9 44.7 18.4 0.6 10,9 C 45.2 54.8 0.7 13,4

60 H-16309 Val Reese & Assoc. NW 15 23 7 2,180-2,195 A 5.7 39.3 40.8 14.2 0.6 11,4

 Betty "B" No. 1-15 B 41.7 43.3 15.0 0.7 12,1 C 49.1 50.9 0.8 14,2

61 H-22722 N.M.P.S.C.C SW 3 23 13 42-44 A 6.7 35.9 46.9 10.5 0.6 11,3

 DH-3-2. B 38.6 50.3 11.2 0.6 1214 C 43.4 56.6 0.7 13,6

62 I-2723 Fruitland outcrop SW 3 19 2 Surface A 5.9 33.6 29.8 30.7 0.6 7,37

 B 35.7 31.7 32.6 0.7 7,83

 C 53.0 47.0 1.0 11,6
Appendix 4—Table of Mean VitriniteRefl ectance Values in Percent (Rm) for 

Fruitland Formation Coal Samples in 

the San Juan Basin

The data in this table were used to construct the thermal 

maturity map on fi gure 37. The database contains location 

and vitrinite-refl ectance data, depths to samples, source of 

data, drill-hole names and elevations, and kinds of samples 

analyzed. 

Table begins on next page.

Table A3-2. Analyses of coal samples from the Fruitland Formation, San Juan Basin. (After table 4 of Fassett and Hinds, 1971)

—Continued. 

Locality USBM Location Approx. Form Proximate Heating 

number lab. no. Well or source Quarter T. N. R. W. sample of Moisture Volatile Fixed Ash Sulfur value Remarks 

 section depth (ft) analysis matter carbon (Btu) 

New Mexico

—Continued

63 I-2722 Fruitland outcrop SE 7 19 2 Surface A 6.5 37.0 35.0 21.5 0.7 8,350 Weathered coal 

 B 39.6 37.4 23.0 0.7 8,930 from surface  C 51.4 48.6 0.9 11,590 exposure 

64 H-99246. Fruitland outcrop NE 11 19 4 Surface A 6.2 36.2 37.1 20.6 0.5 8,610 Weathered coal 

 B 38.6 39.6 21.8 0.5 9,170 from surface 

 C 49.3 50.7 0.6 11,730 exposure 

65 I-53220 Pit sample SE 9 19 5 Surface A 5.8 35.8 31.0 27.4 0.6 9,450 Sample from 

 B 38.1 32.8 29.1 0.6 10,040 small prospect 

 C 53.7 46.3 0.9 14,160 pit 

Q100 Geologic Assessment of Coal in the Colorado Plateau: Arizona, Colorado, New Mexico, and Utah
Table A4-1. Mean vitrinite reflectance values (Rm) for coal samples from the Fruitland Formation. 

[Sample localities shown on figure 37. NMBMMR, New Mexico Bureau of Mines and Mineral Resources; NA, not available] 

Point ID Well Name Elev. Depth Sample Rm

(%) 

Footage Longitude Latitude 

New Mexico 

19-04-01-NE NMBMMR coal test hole 6811 347 Core 0.39 NA -107.20277 35.91229 H19-04-03-NE NMBMMR coal test hole 6721 185 Core 0.42 NA -107.24409 35.91044 H20-05-28-SW NMBMMR coal test hole 6793 406 Core 0.47 NA -107.37640 35.92853 H20-05-31-SW NMBMMR coal test hole 6665 197 Core 0.45 NA -107.41439 35.91421 H20-05-34-SW NMBMMR coal test hole 6645 140 Core 0.42 NA -107.35738 35.91601 H20-06-18-SW NMBMMR coal test hole 6699 172 Core 0.47 NA -107.51998 35.96116 H20-06-26-SW NMBMMR coal test hole 6657 161 Core 0.46 NA -107.44990 35.92983 H20-06-28-NW NMBMMR coal test hole 6619 94 Core 0.51 NA -107.48592 35.93641 H20-07-08-NW NMBMMR coal test hole 6637 200 Core 0.45 NA -107.60454 35.98371 H20-07-10-SE NMBMMR coal test hole 6631 190 Core 0.44 NA -107.55807 35.97343 H21-07-33-SW NMBMMR coal test hole 6624 366 Core 0.43 NA -107.58856 36.00572 H21-08-07-SW NMBMMR coal test hole 6610 268 Core 0.44 NA -107.72677 36.06377 H21-08-17-SW NMBMMR coal test hole 6588 186 Core 0.46 NA -107.70578 36.04771 H21-08-22-SE NMBMMR coal test hole 6540 375 Core 0.45 NA -107.66831 36.03134 H21-08-36-NW NMBMMR coal test hole 6587 140 Core 0.42 NA -107.64151 36.01228 H22-09-36-SW NMBMMR coal test hole 6474 289 Core 0.49 NA -107.74057 36.09576 H22-10-17-SE NMBMMR coal test hole 6315 219 Core 0.49 NA -107.91934 36.13936 H23-04-14-NE Chase Oil Jicarilla Apache 47-34 7309 2845 Cuttings 0.51 310 FNL, 800 FEL -107.21736 36.23052 P23-07-05-NW Dugan-SAPP C 4 7087 2000 Cuttings 0.51 900 FNL, 1660 FWL -107.59950 36.26120 P23-07-15-NW BCO-Betty B 2 7294 1920 Cuttings 0.44 1850 FNL, 790 FWL -107.56693 36.22940 F23-07-16-SW BCO-State J 4 7237 1820 Cuttings 0.49 1940 FNL, 2070 FWL -107.58082 36.22924 P23-07-21-NE BCO Fed B 7 NA 2110 Cuttings 0.47 790 FNL, 890 FEL -107.57376 36.21767 F23-07-29-NW Yates Henry AGC Fed 1 6903 1534 Cuttings 0.46 860 FNL, 590 FWL -107.60380 36.20261 F23-09-24-NW Yates Hurricane Federal 1 6758 1100 Cuttings 0.46 400 FNL, 900 FWL -107.74529 36.21859 F23-10-05-SE Dugan Champ 5 6542 960 Cuttings 0.44 2150 FSL, 800 FEL -107.91242 36.25423 F23-11-01-NE Dugan Flo-Jo 1 6555 990 Cuttings 0.47 660 FNL, 330 FEL -107.94624 36.26057 P23-11-01-NW Dugan Flo-Jo 2 6575 930 Cuttings 0.49 660 FNL, 1980 FWL -107.95628 36.26086 P23-11-19-NE NMBMMR coal test hole 6115 303 Core 0.47 NA -108.03829 36.21821 H23-11-27-NE NMBMMR coal test hole 6726 366 Core 0.42 NA -107.98675 36.19881 H23-12-04-NW NMBMMR coal test hole 6065 300 Core 0.42 NA -108.12512 36.26250 H23-12-12-SW NMBMMR coal test hole 6049 292 Core 0.46 NA -108.06446 36.23563 H23-13-02-NW NMBMMR coal test hole 6601 254 Core 0.46 NA -108.19869 36.25712 H24-06-31-NW BCO Federal Bobby B 3 6730 1826 Cuttings 0.48 1850 FNL, 930 FWL -107.51465 36.27044 P24-09-32-SE Yates Ristra AGW 1 6846 1145 Cuttings 0.45 2180 FSL, 2145 FEL -107.80990 36.26932 P26-07-12-NE UNOCAL Rincon Unit 270 6472 2740 Cuttings 0.59 1658 FNL, 2311 FEL -107.52461 36.50216 P26-08-18-SW Meridian Kah-Des-Pah 2 6193 1860 Cuttings 0.55 1430 FSL, 2210 FWL -107.72382 36.48483 P27-06-16-NE UNOCAL-Rincon Unit 257 6521 3180 Cuttings 0.61 2223 FNL, 1835 FEL -107.46922 36.57527 P27-06-18-NE UNOCAL-Rincon Unit 252 6545 3190 Cuttings 0.63 1640 FNL, 1605 FEL -107.50418 36.57634 P27-06-18-SW UNOCAL-Rincon Unit 239 6660 3101 Cuttings 0.65 1810 FSL, 1645 FWL -107.51003 36.57211 F
Table A4-1. Mean vitrinite reflectance values (Rm) for coal samples from the Fruitland Formation—Continued. 

Point ID Well Name Elev. Depth Sample Rm

(%) 

Footage Longitude Latitude 

New Mexico—Continued

27-06-20-SW UNOCAL-Rincon Unit 255 6490 3020 Cuttings 0.60 1185 FSL, 1840 FWL -107.49297 36.55515 P27-06-21-SW UNOCAL-Rincon Unit 240 6623 3190 Cuttings 0.64 1500 FSL, 1750 FWL -107.47519 36.55666 F27-06-22-SW UNOCAL-Rincon Unit 241 6532 3135 Cuttings 0.61 1500 FSL, 990 FWL -107.45975 36.55680 F27-06-23-SW UNOCAL-Rincon Unit 242 6622 3230 Cuttings 0.68 790 FSL, 1810 FWL -107.43904 36.55509 F27-07-13-NE UNOCAL-Rincon Unit 276 6636 3200 Cuttings 0.68 1080 FNL, 1240 FEL -107.51974 36.57851 P27-07-14-SW Rincon Unit 279 6734 3231 Cuttings 0.60 1735 FSL, 1456 FWL -107.54687 36.57227 P27-07-23-NE UNOCAL-Rincon Unit 281 6628 3100 Cuttings 0.61 880 FNL, 830 FEL -107.53824 36.56542 P27-07-27-SW UNOCAL-Rincon Unit 287 6653 2900 Cuttings 0.62 1056 FSL, 1088 FWL -107.56688 36.53988 P27-09-04-NE Meridian Turner Hughes 272 6864 2940 Cuttings 0.61 790 FNL, 1330 FEL -107.78506 36.60831 P27-09-19-SW UNOCAL Lodewick 13 6505 2280 Cuttings 0.58 975 FSL, 1665 FWL -107.83143 36.55602 P27-09-21-NE Meridian Cleveland 220 6218 2060 Cuttings 0.61 850 FNL, 1470 FEL -107.78872 36.56531 P27-10-11-SW McKenzie Angel Peak 11K 2 6258 2135 Cuttings 0.60 1350 FSL, 1360 FWL -107.86850 36.58603 P27-10-13-SW McKenzie Angel Peak 13M 1 6140 1886 Cuttings 0.60 900 FSL, 1190 FWL -107.85083 36.57020 P27-10-15-SW McKenzie Angel Peak 15M 7 6121 1865 Cuttings 0.57 940 FSL, 800 FWL -107.88814 36.57041 P27-10-17-SW Meridian Rowley 155 6152 1916 Cuttings 0.53 1420 FSL, 1850 FWL -107.92053 36.57196 P27-10-22-NE Meridian Gordon 500 6189 2020 Cuttings 0.59 2500 FNL, 1400 FEL -107.87777 36.56077 P27-11-16-SW Marathon Schwerdtfeger 15C 6266 1938 Cuttings 0.53 1600 FSL, 1355 FWL -108.01290 36.57233 F28-04-18-SW Meridian SJ 28-4 Unit 202 7533 4475 Cuttings 0.64 1450 FSL, 1030 FWL -107.29613 36.65783 P28-05-15-NE Meridian-SJ 28-5 Unit201 6717 3546 Cuttings 0.77 1040 FNL, 1100 FEL -107.34083 36.66545 F28-05-16-NE Meridian-SJ 28-5 U 202 6605 3500 Cuttings 0.71 1850 FNL, 790 FEL -107.35772 36.66329 P28-05-17-NE Meridian-SJ 28-5 Unit203 6589 3440 Cuttings 0.75 1280 FNL, 1725 FEL -107.37887 36.66487 F28-05-18-NE Meridian-SJ 28-5 U 204 6719 3587 Cuttings 0.75 790 FNL, 1185 FEL -107.39493 36.66610 P28-06-10-SW Meridian-SJ 28-5 U 401 6495 3345 Cuttings 0.67 1095 FSL, 2225 FWL -107.45538 36.67166 P28-06-12-SW Meridian-SJ 28-5 U 403 6498 3777 Cuttings 0.76 1540 FSL, 1980 FWL -107.42010 36.67279 F28-06-19-SW Meridian-SJ 28-5 U 406 6625 3339 Cuttings 0.69 680 FSL, 1140 FWL -107.51079 36.64137 F28-08-12-SW Meridian-Hardie D 800 6437 3010 Cuttings 0.68 790 FSL, 1850 FWL -107.63452 36.67060 P28-08-26-NE Meridian-Howell 800 5887 2300 Cuttings 0.65 1340 FNL, 1685 FEL -107.64659 36.63538 P28-09-26-SW Meridian Lackey "H" 709 5981 2170 Cuttings 0.62 790 FSL, 1450 FWL -107.76138 36.62797 P28-09-30-SW Meridian Hancock 713 6265 2362 Cuttings 0.62 980 FSL, 1920 FWL -107.83070 36.62838 P28-10-25-SW Meridian Omler 500 5838 1880 Cuttings 0.61 2335 FSL, 790 FWL -107.85061 36.62969 P28-10-36-SW Meridian Omler 501 5903 1922 Cuttings 0.61 1670 FSL, 1920 FWL -107.85097 36.61565 P29-07-05-NE Meridian-SJ 29-7 U 505 6151 2910 Cuttings 0.73 1050 FNL, 1690 FEL -107.59084 36.75885 P29-07-16-NE Meridian-SJ 29-7 U 509 6266 3030 Cuttings 0.73 795 FNL, 1090 FEL -107.57069 36.73088 P29-07-18-SW Meridian-SJ 29-7 U 511 6929 3624 Cuttings 0.64 910 FSL, 1055 FWL -107.61478 36.72128 P29-07-19-NE Meridian-SJ 29-7 U 512 6686 3370 Cuttings 0.74 1460 FNL, 2365 FEL -107.61080 36.71458 P29-07-30-NW Meridian-SJ 29-7 Unit513 6347 2930 Cuttings 0.70 790 FNL, 1450 FWL -107.61362 36.70216 F29-07-33-SE Meridian-SJ 29-7 U 514 6240 2948 Cuttings 0.73 1190 FSL, 1655 FEL -107.57216 36.67810 P29-07-36-NE Meridian-SJ 29-7 U 515 6543 3198 Cuttings 0.71 1755 FNL, 1055 FEL -107.51640 36.68456 P29-07-36-SW Meridian-SJ 29-7 U 516 6833 3622 Cuttings 0.66 1720 FSL, 1540 FWL -107.52566 36.67965 P29-08-01-NE Meridian Howell "C" 200 6080 2790 Cuttings 0.79 800 FNL, 1350 FEL -107.62285 36.75907 P29-08-02-NE Meridian State Com 100 6296 3009 Cuttings 0.72 1300 FNL, 890 FEL -107.63833 36.75673 P
Table A4-1. Mean vitrinite reflectance values (Rm) for coal samples from the Fruitland Formation—Continued. 

Point ID Well Name Elev. Depth Sample Rm

(%) 

Footage Longitude Latitude 

New Mexico—Continued

29-08-05-NE Meridian Sunray 210 6269 2850 Cuttings 0.73 1120 FNL, 1450 FEL -107.69344 36.75792 P29-08-07-NE Amoco Day B 12 6208 2836 Cuttings 0.72 1380 FNL, 1190 FEL -107.72377 36.75651 P29-08-09-NW Meridian Day Com 200 6468 3230 Cuttings 0.71 880 FNL, 790 FWL -107.68555 36.74411 P29-08-10-SW Meridian Roelofs "A" 200 6328 3000 Cuttings 0.66 790 FSL, 1655 FWL -107.66526 36.73463 P29-08-12-SW Meridian Vanderwart 200 6346 3020 Cuttings 0.73 790 FNL, 1155 FWL -107.63160 36.73438 P29-08-14-NW Meridian Roelofs "A" Com 201 6328 3016 Cuttings 0.69 790 FNL, 1090 FWL -107.64957 36.72984 P29-08-17-SW Meridian Day 201 6413 3020 Cuttings 0.68 1425 FSL, 1425 FWL -107.70166 36.72181 P29-08-24-NW Meridian Hardie "A" Com 210 6613 3228 Cuttings 0.72 1810 FNL, 1660 FWL -107.73422 36.71298 P29-08-26-NW Meridian Hardie "A" 211 6361 2960 Cuttings 0.68 790 FNL, 1840 FWL -107.75296 36.70147 P29-09-01-NE Meridian Riddle "A" 717 6394 2960 Cuttings 0.66 1560 FNL, 1545 FEL -107.72494 36.75568 P29-09-13-NE Meridian Feuille 718 6420 2860 Cuttings 0.66 920 FNL, 1145 FEL -107.72551 36.72938 P29-09-14-SE Amoco Shane Gas Com-A 6405 2959 Cuttings 0.70 1790 FSL, 1030 FEL -107.74317 36.72282 A29-09-21-SW D.J. Simmons A. B. Geren No. 1 5624 2042 Cuttings 0.65 475 FSL, 1060 FWL -107.78783 36.70486 F29-09-22-SW Meridian Grambling 720 5665 2106 Cuttings 0.67 1330 FSL, 1270 FWL -107.77008 36.70736 F29-09-23-SW D.J. Simmons A. B. Geren No. 2 5903 2393 Cuttings 0.68 1505 FSL, 1755 FWL -107.75027 36.70777 F29-09-28-NE Meridian Grambling 722 5627 1957 Cuttings 0.65 790 FNL, 1830 FEL -107.78074 36.70149 P29-09-29-NE D.J. Simmons A. B. Geren No. 6 5824 2195 Cuttings 0.66 965 FNL, 1690 FEL -107.80575 36.69181 F29-10-08-NE Meridian Nye 290 5791 2161 Cuttings 0.64 790 FNL, 805 FEL -107.90162 36.74498 P29-10-12-NE Meridian Lackey "A" 292 5710 2060 Cuttings 0.64 1795 FNL, 1490 FEL -107.83169 36.74160 P29-10-20-NE Meridian Hubbell Com 296 5589 1740 Cuttings 0.62 1310 FNL, 2270 FEL -107.90642 36.71467 P29-10-23-SW Union Texas Albright 19 5595 1770 Cuttings 0.58 1010 FSL, 800 FWL -107.85974 36.70744 P29-10-27-NE Union Texas Albright 20 5502 1680 Cuttings 0.59 2205 FNL, 825 FEL -107.86530 36.69840 P29-11-01-SW Meridian Lloyd "B" 600 5865 2050 Cuttings 0.57 1450 FSL, 1085 FWL -107.94744 36.75160 P29-11-05-NE Fifield Com 800 5776 1800 Cuttings 0.62 1600 FNL, 790 FEL -108.00810 36.75700 P29-11-27-NW Manana Marian S 1 5421 1585 Cuttings 0.59 1547 FNL, 1583 FWL -107.98192 36.69975 F30-04-20-NE Meridian-SJ 30-4 U 101 7556 4230 Cuttings 0.82 790 FNL, 1495 FEL -107.27355 36.80200 P30-06-07-NE Meridian-SJ 30-6 U 451 6282 1110 Cuttings 0.88 1515 FNL, 960 FEL -107.49797 36.83018 P30-06-07-SW Meridian-SJ 30-6 U 450 6365 3260 Cuttings 0.94 1530 FSL, 1830 FWL -107.50644 36.82428 P30-06-08-NE Meridian-SJ 30-6 U 430 6273 3080 Cuttings 0.93 2235 FNL, 1605 FEL -107.48205 36.82805 P30-06-08-SW San Juan 30-6 Unit 459 NA 3160 Cuttings 0.96 1490 FSL, 1188 FWL -107.49056 36.82399 P30-06-10-NE Meridian-SJ 30-6 U 432 6299 3085 Cuttings 0.95 800 FNL, 1840 FEL -107.44658 36.83191 P30-06-11-NE Meridian-SJ 30-6 U 437 6304 3090 Cuttings 10.30 1670 FSL, 845 FEL -107.42525 36.82962 P30-06-11-SW Meridian-SJ 30-7 U 433 6136 2850 Cuttings 0.94 1820 FSL, 1175 FWL -107.43639 36.82474 P30-06-12-NE Meridian-SJ 30-6 U 438 6220 3029 Cuttings 1.01 2045 FNL, 1015 FEL -107.41027 36.82869 P30-06-12-SW Meridian-SJ 30-6 U 434 6200 2980 Cuttings 0.88 900 FSL, 790 FWL -107.41964 36.82233 P30-06-13-SW Meridian-SJ 30-6 U 445 6164 2964 Cuttings 0.97 1450 FSL, 1025 FWL -107.41890 36.80925 P30-06-14-NE Meridian-SJ 30-6 U 442 6349 3152 Cuttings 1.02 790 FNL, 850 FEL -107.42530 36.81758 P30-06-14-SW Meridian-SJ 30-6 U 439 6377 3180 Cuttings 0.96 900 FSL, 975 FWL -107.43709 36.80779 P30-06-15-NE Meridian-SJ 30-6 U 436 6210 3020 Cuttings 0.93 1840 FNL, 1560 FEL -107.44575 36.81459 P30-06-16-NE Meridian-SJ 30-6 U 407 6302 3092 Cuttings 0.97 1540 FNL, 1175 FEL -107.46268 36.81560 F30-06-16-SW Meridian-SJ 30-6 U 408 6560 3360 Cuttings 0.92 1660 FSL, 1275 FWL -107.47213 36.81002 P
Table A4-1. Mean vitrinite reflectance values (Rm) for coal samples from the Fruitland Formation—Continued. 

Point ID Well Name Elev. Depth Sample Rm

(%) 

Footage Longitude Latitude 

New Mexico—Continued

30-06-17-NE Meridian-SJ 30-6 U 454 6293 3129 Cuttings 0.96 1190 FNL, 1090 FEL -107.48030 36.81654 P30-06-17-SW Meridian-SJ 30-6 U 453 6668 3590 Cuttings 0.96 1450 FSL, 1635 FWL -107.48895 36.80957 P30-06-18-NE Meridian-SJ 30-6 U 456 6394 3330 Cuttings 0.98 565 FNL, 735 FEL -107.49723 36.81832 P30-06-18-SW Meridian-SJ 30-6 U 455 6641 3470 Cuttings 0.94 1080 FSL, 1510 FWL -107.50770 36.80849 P30-06-19-NE Meridian-SJ 30-6 U 458 6370 3190 Cuttings 0.87 1470 FNL, 1180 FEL -107.49869 36.80137 P30-06-19-SW Meridian-SJ 30-6 U 457 6210 3010 Cuttings 0.94 915 FSL, 1170 FWL -107.50877 36.79335 P30-06-21-NE Meridian-SJ 30-6 U 470 6440 3350 Cuttings 0.93 1580 FNL, 1330 FEL -107.46318 36.80096 P30-06-21-SW San Juan 30-6 Unit 471 6330 2550 Cuttings 0.95 1820 FSL, 1430 FWL -107.47160 36.79592 P30-06-22-NE Meridian-SJ 30-6 U 472 6453 3240 Cuttings 0.96 790 FNL, 1305 FEL -107.44499 36.80300 P30-06-22-SW Meridian-SJ 30-6 U 473 6415 3210 Cuttings 0.91 1140 FSL, 960 FWL -107.45534 36.79399 P30-06-26-NE Meridian-SJ 30-6 U 410 6683 3490 Cuttings 0.95 1220 FNL, 910 FEL -107.42573 36.78713 P30-06-27-NE Meridian-SJ 30-6 U 474 6484 3325 Cuttings 0.90 1230 FNL, 1660 FEL -107.44613 36.78722 P30-06-28-SW Meridian-SJ 30-6 U 477 6286 3110 Cuttings 0.89 1230 FSL, 790 FWL -107.47393 36.77974 P30-06-30-NE Meridian-SJ 30-6 U 480 6270 3127 Cuttings 0.92 790 FNL, 1305 FEL -107.49923 36.78851 P30-06-34-NE Meridian-SJ 30-6 U 483 6512 3449 Cuttings 0.99 1330 FNL, 790 FEL -107.44323 36.77243 P30-06-36-SW Meridian-SJ 30-6 U 444 6543 3470 Cuttings 0.89 1450 FSL, 790 FWL -107.42001 36.76565 P30-07-02-NE Blackwood/Nichols NE Blanco 415 6407 3205 Cuttings 0.90 1540 FNL, 1480 FEL -107.53581 36.84452 P30-07-03-NE Blackwood/Nichols NE Blanco 485 6263 3080 Cuttings 0.88 1240 FNL, 1175 FEL -107.55294 36.84551 F30-07-04-Sw Blackwood/Nichols NE Blanco 421R 6224 3110 Cuttings 0.88 1070 FSL, 465 FWL -107.58341 36.83746 P30-07-06-NE Blackwood/Nichols NE Blanco 451 6206 3085 Cuttings 0.89 210 FNL, 1900 FEL -107.61050 36.84202 P30-07-06-SW Blackwood/Nichols NE Blanco Unit 453 6190 3090 Cuttings 0.83 930 FSL, 610 FWL -107.61563 36.83715 P30-07-07-NE Blackwood/Nichols NE Blanco Unit 432 6301 3125 Cuttings 0.85 195 FNL, 790 FEL -107.60590 36.83394 P30-07-10-NE Meridian NE-Blanco 411 6265 3151 Cuttings 0.91 1465 FNL, 1350 FEL -107.55361 36.83033 P30-07-11-SW Meridian-SJ 30-6 U 461 6300 3090 Cuttings 0.84 1185 FSL, 1095 FWL -107.54512 36.82338 P30-07-13-SW Meridian-SJ 30-6 U 401 6133 3350 Cuttings 0.81 790 FSL, 1800 FWL -107.52469 36.80773 P30-07-14-NE Meridian-SJ 30-6 U 464 6284 3080 Cuttings 0.87 1710 FNL, 1555 FEL -107.53624 36.81518 P30-07-15-SE Meridian-SJ 30-6 U 465 6249 2980 Cuttings 0.76 1530 FSL, 1845 FEL -107.55518 36.80953 P30-07-16-NE Meridian-Francis Creek S 100 6262 3040 Cuttings 0.78 2485 FNL, 790 FEL -107.56948 36.81310 P30-07-20-NW Blackwood/Nichols NE Blanco Unit 479 6328 3235 Cuttings 0.79 1166 FNL, 2315 FWL -107.59501 36.80239 P30-07-21-SW Blackwood/Nichols NE Blanco Unit 405 6736 3650 Cuttings 0.83 875 FSL, 1145 FWL -107.58087 36.79330 P30-07-29-NE Blackwood/Nichols NE Blanco Unit 477 6336 3165 Cuttings 0.76 1650 FNL, 1160 FEL -107.58884 36.78632 F30-07-34-NE Meridian San Juan 30-6 Unit 426 6230 3070 Cuttings 0.81 1460 FSL, 1450 FWL -107.56200 36.76592 P30-07-36-SW Meridian San Juan 30-6 Unit 468 6317 3744 Cuttings 0.91 1895 FSL, 1465 FWL -107.52577 36.76705 F30-08-01-NE Blackwood/Nichols NE Blanco Unit 465 6432 3250 Cuttings 0.84 1020 FNL, 780 FEL -107.62031 36.84460 P30-08-04-NE Amoco Moore A-8 6271 3106 Cuttings 0.82 1395 FNL, 1490 FEL -107.67648 36.84324 F30-08-04-SW Meridian, Howell "A" 301 6239 3050 Cuttings 0.81 460 FSL, 1180 FWL -107.68567 36.83415 P30-08-05-NE Amoco Moore B-3 6283 3008 Cuttings 0.81 1290 FNL, 1220 FEL -107.69359 36.84362 F30-08-06-NE Meridian Florance H-3 6095 2897 Cuttings 0.78 1480 FNL, 1025 FEL -107.71074 36.84309 P30-08-07-NE Amoco Howell com "C" 300 NA 2870 Cuttings 0.71 1660 FNL, 1320 FWL -107.71838 36.82841 P30-08-08-SW Amoco Moore C-3 6436 3156 Cuttings 0.73 1120 FSL, 1325 FWL -107.70269 36.82096 F30-08-09-SW Amoco Moore Gas Com 1 5875 2663 Cuttings 0.79 1550 FSL, 1690 FWL -107.68321 36.82274 P
Table A4-1. Mean vitrinite reflectance values (Rm) for coal samples from the Fruitland Formation—Continued. 

Point ID Well Name Elev. Depth Sample Rm

(%) 

Footage Longitude Latitude 

New Mexico—Continued

30-08-10-NE Amoco Howell Gas Com 1 6252 3109 Cuttings 0.81 890 FNL, 910 FEL -107.65586 36.82948 P30-08-12-SW Meridian NE Blanco Unit 437 6085 2995 Cuttings 0.81 1240 FSL, 1650 FWL -107.62821 36.82038 F30-08-14-SW Amoco Florance I-3 6476 3334 Cuttings 0.80 1420 FSL, 1630 FWL -107.64727 36.80781 P30-08-18-NE Amoco Florance X-1 6415 3159 Cuttings 0.76 1015 FNL, 790 FEL -107.70986 36.81497 P30-08-18-NW Meridian Howell "C" Com 301 6290 3048 Cuttings 0.72 1660 FNL, 1320 FWL -107.71804 36.81381 P30-08-21-NW Meridian Howell "K" 303 5858 2610 Cuttings 0.71 1840 FNL, 995 FWL -107.68631 36.79887 P30-08-22-NW Meridian Howell "K" 302 5822 2645 Cuttings 0.76 2056 FNL, 1675 FWL -107.66572 36.79831 P30-08-23-NE Amoco Florance J-3 6396 3188 Cuttings 0.80 2200 FNL, 1630 FEL -107.64118 36.79784 P30-08-25-SW Amoco Florance K-3 6208 2920 Cuttings 0.75 1788 FSL, 790 FWL -107.63272 36.78041 F30-08-26-SW Amoco Gartner Gas Com B-1 5927 2697 Cuttings 0.73 1443 FSL, 1154 FWL -107.64936 36.77922 P30-08-27-SW Amoco Gartner A-12 6155 2886 Cuttings 0.72 1920 FSL, 1060 FWL -107.66784 36.78099 P30-08-28-SW Amoco Gartner A-14 6287 2977 Cuttings 0.71 1830 FSL, 1810 FWL -107.68317 36.78025 F30-08-29-SW Meridian Howell E-301 5933 2620 Cuttings 0.74 1140 FSL, 1850 FWL -107.70025 36.77828 P30-08-31-SW Meridian Howell M-300 6278 2929 Cuttings 0.65 1590 FSL, 875 FWL -107.71668 36.76448 P30-08-32-SW Meridian Beaver Lodge Com 320 5813 2400 Cuttings 0.69 1850 FSL, 790 FWL -107.70394 36.76566 F30-08-33-NE Amoco Gartner A-15 6319 2958 Cuttings 0.72 1790 FNL, 840 FEL -107.67416 36.77058 P30-08-34-SW Amoco Florance A-1 6334 2941 Cuttings 0.72 1370 FSL, 1210 FWL -107.66710 36.76540 P30-08-35-NE Amoco Florance P-3 6070 2820 Cuttings 0.76 1970 FNL, 1670 FEL -107.64116 36.76996 P30-08-36-SW Meridian EPNG Com "D" 300 6004 2780 Cuttings 0.76 800 FNL, 950 FEL -107.62121 36.77351 P30-09-01-NE Amoco Pritchard A-10 6337 3125 Cuttings 0.74 1730 FNL, 1810 FEL -107.72916 36.84221 F30-09-02-SE Meridian Turner "B" Com "A" 200 5946 2737 Cuttings 0.74 1000 FSL, 1545 FEL -107.74615 36.83549 P30-09-03-NE Amoco Florance L 6039 2879 Cuttings 0.79 2465 FNL, 1220 FEL -107.76260 36.84042 A30-09-03-NW Meridian Riddle 250 6115 3042 Cuttings 0.70 795 FNL, 1040 FWL -107.77270 36.84504 P30-09-05-NE Amoco Florance M-3 6240 2969 Cuttings 0.69 1730 FNL, 1290 FEL -107.79862 36.84222 F30-09-05-NW Meridian Woodriver 250 6300 2870 Cuttings 0.74 1710 FNL, 1495 FWL -107.80688 36.84266 P30-09-06-SW Meridian Quigley Com 250 6540 3280 Cuttings 0.76 1030 FSL, 850 FWL -107.82349 36.83651 P30-09-07-NE Meridian Pierce 250 6374 3086 Cuttings 0.74 1030 FNL, 1180 FEL -107.81585 36.83005 P30-09-08-NE Meridian Pierce Com 251 6239 2984 Cuttings 0.68 950 FNL, 1175 FEL -107.79788 36.82994 P30-09-09-SW Meridian Duff Com 260 6210 2840 Cuttings 0.68 790 FSL, 1785 FWL -107.78760 36.82049 P30-09-10-SW Amoco Florance Gas Com D-1 6192 2938 Cuttings 0.77 2160 FSL, 1260 FWL -107.77170 36.82417 P30-09-11-NE Meridian Lindsey Com 250 5853 2656 Cuttings 0.75 1190 FNL, 855 FEL -107.74376 36.82947 P30-09-11-SW Amoco Florance 114 FT 2 6035 2793 Cuttings 0.71 2390 FSL, 980 FWL -107.75479 36.82474 P30-09-15-NW Meridian Riddle "A" Com 201 6392 3120 Cuttings 0.72 935 FNL, 1480 FWL -107.77089 36.81562 P30-09-21-SW Meridian Florence Com 260 6052 2740 Cuttings 0.67 1200 FSL, 2100 FWL -107.78666 36.79325 P30-09-22-SE Amoco Florance AC 4 5878 2580 Cuttings 0.73 1550 FSL, 1120 FEL -107.76212 36.79356 A30-09-24-NE Meridian Florance O-3 5810 2472 Cuttings 0.76 1845 FNL, 1560 FEL -107.72712 36.79864 P30-09-28-NE Meridian Turner 251 5845 2500 Cuttings 0.65 1450 FNL, 1150 FEL -107.78010 36.78551 P30-09-28-NW Meridian Mansfield Com 260 5896 2540 Cuttings 0.65 1490 FNL, 1100 FWL -107.79023 36.78578 P30-09-29-SW Meridian Mansfield Com 251 6066 2610 Cuttings 0.66 1130 FNL, 940 FWL -107.80838 36.78676 P30-10-01-SW Meridian Sunray "B" 201 6445 3150 Cuttings 0.65 1390 FSL, 1340 FWL -107.83720 36.83736 P30-10-06-NW Meridian Atlantic "C" 202 6033 2600 Cuttings 0.63 790 FNL, 805 FWL -107.92909 36.84565 P
Table A4-1. Mean vitrinite reflectance values (Rm) for coal samples from the Fruitland Formation—Continued. 

Point ID Well Name Elev. Depth Sample Rm

(%) 

Footage Longitude Latitude 

New Mexico—Continued

30-10-07-SW Meridian Sunray "J" 210 6118 2930 Cuttings 0.61 790 FSL, 880 FWL -107.92933 36.82099 P30-10-10-SE Meridian San Juan 200 6487 2920 Cuttings 0.62 1120 FSL, 1145 FWL -107.87509 36.82273 P30-10-12-NE MeridianGrambling "C" 200 6341 3048 Cuttings 0.67 1180 FNL, 605 FEL -107.82859 36.83031 P30-10-13-NE Meridian Turner Federal 210 6366 3360 Cuttings 0.63 950 FNL, 1790 FEL -107.83247 36.81636 P30-10-13-SW Meridian Pierce "A" 210 6400 2993 Cuttings 0.65 1190 FSL, 1800 FWL -107.83776 36.80783 P30-10-15-SW Meridian Sunray "B" 215 6338 2820 Cuttings 0.66 800 FSL, 800 FWL -107.87625 36.80630 P30-10-21-NE Meridian Sunray "D" 225 6317 2790 Cuttings 0.63 1490 FNL, 1100 FEL -107.88293 36.79982 P30-10-23-NE Meridian Riddle "B" 223 6260 2840 Cuttings 0.54 1850 FNL, 830 FEL -107.84696 36.79933 P30-10-25-NW Meridian Florence "A" 210 6074 2510 Cuttings 0.63 845 FNL, 1590 FWL -107.83884 36.78792 P30-10-28-SW Amoco Stewart B-1 6223 2663 Cuttings 0.66 870 FSL, 1210 FWL -107.89452 36.77801 P30-11-16-NE Mesa Oper. Ltd FC State Com 16 5777 2140 Cuttings 0.60 1870 FNL, 1705 FEL -107.99211 36.81377 P30-14-11-SE Dugan Blazer 2 6045 1680 Cuttings 0.52 1190 FSL, 1500 FEL -108.27370 36.82455 F30-14-17-SW Dugan Turks Toast 5625 1140 Cuttings 0.52 1850 FSL, 790 FWL -108.33791 36.81203 P30-15-03-SW NMBMMR coal test hole 5365 153 Core 0.59 NA -108.41232 36.83658 H31-05-19-SE Northwest Pipelineline Rosa Unit 204 6342 3195 Cuttings 1.19 1590 FSL, 1465 FEL -107.39889 36.88230 A31-05-29-NE Meridian Rosa Unit 200 6388 3260 Cuttings 1.10 1265 FNL, 1475 FEL -107.38105 36.87439 P31-06-11-SW Meridian Rosa Unit 216 6273 3071 Cuttings 1.05 1500 FSL, 1705 FWL -107.43468 36.91097 P31-06-21-SW Meridian Rosa Unit 260 6350 3170 Cuttings 1.07 1040 FSL, 1310 FWL -107.47232 36.88080 P31-06-22-NE Meridian Rosa Unit 201 6250 3083 Cuttings 1.04 1640 FNL, 420 FEL -107.44210 36.88803 P31-06-23-NE Meridian Rosa Unit 213 6285 3127 Cuttings 0.97 1020 FNL, 1535 FEL -107.42773 36.88963 P31-06-26-NE Meridian Rosa Unit 211 6405 3232 Cuttings 1.08 2275 FNL, 1410 FEL -107.42731 36.87163 P31-06-30-SW Blackwood/Nichols NE Blanco Unit 495 6348 3260 Cuttings 0.92 1658 FSL, 957 FWL -107.50958 36.86808 P31-07-01-SW Blackwood/Nichols NE Blanco Unit 462 6571 3280 Cuttings 1.04 805 FSL, 1370 FWL -107.52575 36.92364 P31-07-11-NE Blackwood/Nichols NE Blanco Unit 440 6534 3160 Cuttings 0.96 1156 FNL, 903 FEL -107.53364 36.91814 P31-07-13-NE Blackwood/Nichols NE Blanco Unit 458 6519 3165 Cuttings 0.92 1135 FNL, 1125 FEL -107.51624 36.90380 P31-07-15-NE Blackwood/Nichols NE Blanco Unit 452 6553 3175 Cuttings 0.91 1785 FNL, 1770 FEL -107.55432 36.90185 P31-07-15-SW Blackwood/NicholsNE Blanco Unit 482 6548 3395 Cuttings 0.86 890 FSL, 790 FWL -107.56372 36.89485 P31-07-16-NE Blackwood/Nichols NE Blanco Unit 484 6540 3420 Cuttings 0.98 990 FNL, 790 FEL -107.56914 36.90408 P31-07-20-NE Blackwood/Nichols NE Blanco Unit 408 6460 3160 Cuttings 0.97 1035 FNL, 1305 FEL -107.58910 36.88943 P31-07-22-SW Blackwood/Nichols NE Blanco Unit 476 6464 3190 Cuttings 0.84 1200 FSL, 840 FWL -107.56382 36.88128 P31-07-24-NE Blackwood/Nichols NE Blanco Unit 428 6457 3155 Cuttings 0.89 1075 FNL, 790 FEL -107.51534 36.88912 P31-07-25-NE Blackwood/Nichols NE Blanco Unit 493 6297 3200 Cuttings 0.94 1477 FSL, 793 FEL -107.51558 36.86748 P31-07-27-NE Blackwood/Nichols NE Blanco Unit 470 6419 3210 Cuttings 0.88 1400 FNL, 960 FEL -107.55224 36.87389 P31-07-29-NE Blackwood/Nichols NE Blanco Unit 472 6451 3333 Cuttings 0.97 1330 FNL, 1330 FEL -107.58946 36.87405 P31-07-29-SW Blackwood/Nichols NE Blanco Unit 412 6303 3175 Cuttings 0.92 840 FSL, 1725 FWL -107.59708 36.86584 P31-07-30-NE Blackwood/Nichols NE Blanco Unit 414 6390 3275 Cuttings 0.96 2330 FNL, 150 FEL -107.60351 36.87134 P31-07-32-NE Blackwood/Nichols NE Blanco Unit 448 6388 3165 Cuttings 0.78 1515 FNL, 1340 FEL -107.58948 36.85916 P31-07-32-SW Blackwood/Nichols NE Blanco Unit 450 6363 3240 Cuttings 0.95 795 FSL, 2010 FWL -107.59612 36.85124 P31-07-33-SW Blackwood/Nichols NE Blanco Unit 446 6316 3190 Cuttings 0.92 2045 FSL, 1395 FWL -107.58015 36.85478 P31-07-34-NW Blackwood/Nichols NE Blanco Unit 404 6297 3153 Cuttings 1.03 1730 FNL, 260 FWL -107.56596 36.85860 A31-07-36-NE Meridian NE-Blanco,483 6220 3142 Cuttings 0.99 1750 FNL, 2045 FEL -107.51988 36.85855 P
Table A4-1. Mean vitrinite reflectance values (Rm) for coal samples from the Fruitland Formation—Continued. 

Point ID Well Name Elev. Depth Sample Rm

(%) 

Footage Longitude Latitude 

New Mexico—Continued

31-07-36-SW Meridian NE-Blanco,481 6483 3390 Cuttings 0.87 1005 FSL, 1835 FWL -107.52446 36.85176 P31-08-19-NW Union Texas Quinn 2A 6404 3150 Cuttings 0.77 1690 FNL, 1520 FWL -107.71677 36.88572 F31-08-22-NW Northwest Pipelineline SK 32-8 Unit 7A 6528 3110 Cuttings 0.84 880 FNL, 870 FWL -107.66816 36.88738 A31-08-25-NE Blackwood/Nichols NE Blanco Unit 471 6415 3280 Cuttings 0.94 1315 FNL, 1710 FEL -107.62372 36.87212 P31-08-25-SW Blackwood/Nichols NE Blanco Unit 445 6404 3275 Cuttings 0.94 990 FSL, 815 FWL -107.63255 36.86422 P31-08-27-SW Meridian Hale 350 6326 3170 Cuttings 0.88 815 FSL, 1180 FWL -107.66712 36.86383 P31-08-28-NE Amoco Kernaghan B-5 6332 3184 Cuttings 0.93 1210 FNL, 1115 FEL -107.67422 36.87186 F31-08-28-NW Meridian Howell "D" 350 6509 3393 Cuttings 0.87 1450 FNL, 790 FWL -107.68574 36.87153 P31-08-29-NE Amoco Kernaghan B-6 6581 3426 Cuttings 0.82 1280 FNL, 1800 FEL -107.69465 36.87190 P31-08-29-SW Meridian Howell "D" 351 6508 3330 Cuttings 0.75 1180 FSL, 1840 FWL -107.70087 36.86520 P31-08-30-NE Amoco Kernaghan B-7 6554 3367 Cuttings 0.83 1440 FNL, 1040 FEL -107.71002 36.87183 F31-08-31-NE Meridian Howell "D" 352 6350 3192 Cuttings 0.76 1165 FNL, 1000 FEL -107.71088 36.85856 P31-08-31-SW Amoco Dawson Gas Com 1 6328 3117 Cuttings 0.80 1210 FSL, 660 FWL -107.72078 36.85055 A31-08-33-SW Amoco Kernaghan B-8 6407 3224 Cuttings 0.90 1140 FSL, 1700 FWL -107.68350 36.85037 F31-08-34-NE Meridian Hale 353 6242 3128 Cuttings 0.83 620 FNL, 2360 FEL -107.66168 36.85965 P31-09-02-NE Meridian San Juan 32-9 Unit 201 6469 3210 Cuttings 0.90 2275 FNL, 885 FEL -107.74277 36.92760 P31-09-08-NE Amoco San Juan 32-9 105 6767 3488 Cuttings 0.83 1400 FNL, 790 FEL -107.79712 36.91566 P31-09-19-SW Amoco Barrett Gas Com A 6676 3439 Cuttings 0.73 1810 FSL, 925 FWL -107.82301 36.88153 A31-09-21-NW Meridian Sunray "G" 251 6475 3330 Cuttings 0.79 830 FNL, 1165 FWL -107.78967 36.88824 P31-09-21-SE Meridian Sunray "G" 250 6167 3020 Cuttings 0.78 800 FSL, 1175 FEL -107.78059 36.87834 P31-09-22-SW Amoco Riddle B-1 2 6283 3052 Cuttings 0.79 1980 FSL, 1095 FWL -107.77239 36.88174 P31-09-25-SW Amoco Trigg Fed Gas Com C 5998 2801 Cuttings 0.81 2240 FSL, 865 FWL -107.73761 36.86770 A31-09-27-NE Amoco Schwerdtfeger Gas Com 6237 3049 Cuttings 0.84 1760 FNL, 1910 FEL -107.76471 36.87132 A31-09-27-SW Amoco Pritchard B-5 6211 3013 Cuttings 0.76 1840 FSL, 1175 FWL -107.77213 36.86674 F31-09-27-SW Amoco Schwerdtfeger A-3 6085 2897 Cuttings 0.80 1120 FSL, 810 FWL -107.77329 36.86475 F31-09-28-SW San Juan Production Sheets 6150 2957 Cuttings 0.78 990 FSL, 1650 FWL -107.78732 36.86413 A31-09-28-SW Meridian Sheets 250 6172 2993 Cuttings 0.72 1135 FSL, 1840 FEL -107.78242 36.86461 P31-09-30-NE Amoco Riddle Gas Com 1B1 6392 3037 Cuttings 0.72 2380 FNL, 1370 FEL -107.81640 36.86964 A31-09-34-SW Amoco Pritchard B 5 6211 3000 Cuttings 0.80 1840 FSL, 1175 FWL -107.77221 36.85232 A31-10-02-NE Meridian San Juan 32-9 Unit 209 6321 2900 Cuttings 0.74 1545 FNL, 1640 FEL -107.84924 36.92971 P31-10-02-SW Meridian San Juan 32-9 Unit 210 6148 2973 Cuttings 0.82 900 FSL, 1500 FWL -107.85554 36.92230 P31-10-04-NE Amoco Wood Gas Com-A 5833 2372 Cuttings 0.74 1155 FNL, 1745 FEL -107.88373 36.93109 A31-10-21-NE Meridian Lambe Com 200 6153 2909 Cuttings 0.71 915 FNL, 1330 FEL -107.88257 36.88804 F31-10-23-NE Meridian Atlantic (D Com) 205 6370 3140 Cuttings 0.75 1190 FNL, 1450 FEL -107.84710 36.88750 F31-10-29-NE Meridian Atlantic "A" 211 5992 2510 Cuttings 0.64 1450 FNL, 1850 FEL -107.90218 36.87227 P31-10-29-SW Meridian Atlantic "A" 210 6041 2710 Cuttings 0.62 1450 FSL, 1530 FWL -107.90861 36.86618 P31-10-31-NE Meridian Atlantic "C" 215 6056 2689 Cuttings 0.67 1580 FNL, 1460 FEL -107.91877 36.85762 P31-10-34-NW Tenneco Atlantic 1E 6215 2810 Cuttings 0.71 1030 FNL, 840 FWL -107.87512 36.85902 A31-10-35-NE Meridian Atlantic "C" 200 6420 3155 Cuttings 0.68 1450 FNL, 1545 FEL -107.84759 36.85829 P31-11-01-NE Amoco Mudge A 55 6058 2780 Cuttings 0.70 1410 FNL, 1610 FEL -107.93754 36.93049 A31-11-04-NE Amoco Neal A 24 6163 2442 Cuttings 0.65 2050 FNL, 820 FEL -107.98887 36.92815 A
Table A4-1. Mean vitrinite reflectance values (Rm) for coal samples from the Fruitland Formation—Continued. 

Point ID Well Name Elev. Depth Sample Rm

(%) 

Footage Longitude Latitude 

New Mexico—Continued

31-11-05-NE Amoco Case B 19 6417 3055 Cuttings 0.71 880 FNL, 1560 FEL -108.00803 36.93164 A31-11-05-SW Amoco Case A 18 6197 2635 Cuttings 0.66 1270 FSL, 1625 FWL -108.01555 36.92349 A31-11-06-NE Meridian Grenier 100 6522 2980 Cuttings 0.64 1640 FNL, 1790 FEL -108.02609 36.92966 P31-11-07-SW Southland Royaltyty Grenier 101 6218 2590 Cuttings 0.67 1925 FSL, 1830 FWL -108.03602 36.90904 P31-11-17-SW Amoco Case B-1 6168 2730 Cuttings 0.70 1250 FSL, 1370 FWL -108.01705 36.89498 P31-11-18-SW Southland Royaltyty Grenier 102 6090 2630 Cuttings 0.69 1865 FSL, 1330 FWL -108.03505 36.89706 P31-11-20 Meridian Grenier 103 6035 2550 Cuttings 0.66 2135 FSL, 1290 FWL -108.01726 36.88313 F31-11-24-SE H. F. Petroleumtigrew Ruple Pool Unit 1-X 5771 2620 Cuttings 0.66 654 FSL, 1980 FEL -107.93885 36.87819 A31-11-27-SE Meridian Calloway 1-A 5686 2248 Cuttings 0.66 1175 FSL, 1470 FEL -107.97370 36.86552 P31-11-30-NW Tenneco Heaton 1-E A 5913 2310 Cuttings 0.60 790 FNL, 1520 FWL -108.03482 36.87526 A31-11-36-SE Grt. West. D.Pubco State Com A-1 6061 2373 Cuttings 0.62 1690 FSL, 935 FEL -107.93507 36.85240 F31-12-09-NW Tenneco Newberry 2-E A 6140 2380 Cuttings 0.67 560 FNL, 1720 FWL -108.10320 36.91931 A31-12-09-SE El Paso Newberry 8-A 6193 2459 Cuttings 0.63 1030 FSL, 1625 FEL -108.09686 36.90886 A31-12-11-NE Southland Royaltyty Davis 504 6322 2720 Cuttings 0.70 1065 FNL, 1475 FEL -108.06031 36.91726 A31-12-11-NE Southland Royaltyty Davis 504 6322 2720 Cuttings 0.70 1065 FNL, 1475 FEL -108.06018 36.91710 P31-12-11-SE Southern Union Davis NA 2780 Cuttings 0.65 990 FSL, 990 FEL -108.05949 36.90861 A31-12-12-SW Meridian Davis 502 6264 2808 Cuttings 0.67 2085 FSL, 1330 FWL -108.05118 36.91183 P31-12-14-NE Southland Royalty Harper Com 100 6228 2550 Cuttings 0.65 1915 FNL, 1625 FEL -108.06248 36.90064 P31-12-19-SW Colorado Western Govt-South Union 5903 2270 Cuttings 0.57 1090 FSL, 1090 FWL -108.14232 36.88080 A31-13-02-NE Quinoco Chavez H 2-2 5748 1999 Cuttings 0.70 2440 FNL, 828 FEL -108.16596 36.92960 P31-13-02-SW Quinoco Jaquez K 2-2 5720 2033 Cuttings 0.56 2270 FSL, 1765 FWL -108.17492 36.92798 P31-14-27-SE Wintershall Corp Ute MinUte 27 NA 635 Cuttings 0.58 995 FSL, 1055 FEL -108.29274 36.86552 A32-02-25-SW Outcrop NA Outcrop 0.64 2084 FSL, 2328 FWL -106.99570 36.95662 A32-03-22-SE Stanolind O&G Jicarilla Apache 6988 1092 Cuttings 0.80 3830 FSL, 840 FEL -107.13128 36.97630 A32-03-23-NW Pan American Petroleumroleum Pagosa NA 3612 Cuttings 1.38 1030 FNL, 1190 FWL -107.12430 36.97717 A32-04-14-NW McHugh Carracas Mesa 14 6273 2888 Cuttings 1.31 1100 FNL, 1100 FWL -107.22860 36.99088 A

32-04-15-NE Nassau Carracas Unit 15 B- 7 6548 3364 Cuttings 1.24 1650 FNL, 1850 FEL -107.23876 36.98929 F32-04-17-SE Nassau Carracas Unit 17 B- 15 6883 4200 Cuttings 1.30 650 FSL, 2070 FEL -107.27519 36.98104 F32-04-18-SE Nassau Carracas Unit 18 B-15 7329 4128 Cuttings 1.27 580 FSL, 1710 FEL -107.29190 36.98081 F32-04-18-SW Nassau Carracas U 18 B-13 7432 4160 Cuttings 1.14 790 FSL, 900 FWL -107.30052 36.98150 F32-04-19-NE Nassau Carracas U 19 B-1 7353 4115 Cuttings 1.27 750 FNL, 400 FEL -107.28732 36.97725 F32-04-20-NW Nassau Carracas U 20B 3 7400 4137 Cuttings 1.28 1170 FSL, 1480 FWL -107.28086 36.96971 F32-04-21-NW Nassau Carracas U 21B 5 7346 4300 Cuttings 1.27 1655 FNL, 1185 FWL -107.26397 36.97479 F32-04-26-SE Nassau Carracas U 26B 16 7048 4003 Cuttings 1.26 790 FSL, 790 FEL -107.21691 36.95271 F32-04-26-SW Nassau Resource Carracas Unit PC 26B 13 NA 4001 Cuttings 1.33 1100 FSL, 790 FSL -107.22856 36.95341 A32-04-27-NW Nassau Carracas U 27B 5 7253 4285 Cuttings 1.22 1740 FNL, 800 FWL -107.24720 36.95999 F32-04-28-NW Nassau Carracas U 28B 5 7333 4045 Cuttings 1.30 1850 FNL, 790 FWL -107.26533 36.95979 F32-04-30-NE Nassau Carracas U 30B 8 7212 3947 Cuttings 1.21 2240 FNL, 620 FEL -107.28815 36.95860 F32-04-32-NW Nassau Carracas U 32B 5 7203 4125 Cuttings 1.24 1630 FNL, 790 FWL -107.28337 36.94584 F32-04-34-NE Nassau Carracas U 34B 2 7284 4178 Cuttings 1.23 790 FNL, 1850 FEL -107.23844 36.94832 F32-04-35-SE Nassau Carracas U 35B 9 6993 3934 Cuttings 1.24 1850 FSL, 790 FEL -107.21695 36.94119 F
Table A4-1. Mean vitrinite reflectance values (Rm) for coal samples from the Fruitland Formation—Continued. 

Point ID Well Name Elev. Depth Sample Rm

(%) 

Footage Longitude Latitude 

New Mexico—Continued

32-04-36-SE Nassau Carracas U 36B 15 7033 4006 Cuttings 1.23 1190 FSL, 1850 FEL -107.20258 36.93942 F32-05-11-SE Nassau Carracas U 11A 9 7519 4255 Cuttings 1.28 1675 FSL, 1190 FEL -107.32567 36.99193 F32-05-13-SW Nassau Carracas U 13A 14 7418 4128 Cuttings 1.24 800 FSL, 1760 FWL -107.31546 36.97522 F32-05-14-NE Nassau Carracas U 14A 1 7393 3966 Cuttings 1.20 1000 FNL, 680 FEL -107.32383 36.98462 F32-05-14-SW Nassau Carracas Unit 14 A 13 7269 3824 Cuttings 1.26 230 FSL, 380 FWL -107.33841 36.97354 F32-05-17-NE Amoco Seibel Gas Unit B 6114 2624 Cuttings 1.41 1850 FNL, 770 FEL -107.37912 36.98218 A32-05-21-SE Nassau Carracas U 21A 15 7043 3714 Cuttings 1.17 790 FSL, 1850 FEL -107.36418 36.96048 F32-05-22-SE Nassau Carracas Unit 22 A 16 7065 3781 Cuttings 1.18 790 FSL, 790 FEL -107.34244 36.96065 F32-05-22-SW Nassau Carracas U 22A 13 7034 3730 Cuttings 1.18 620 FSL, 540 FWL -107.35597 36.96014 F32-05-23-NE Nassau Carracas U 23A 2 7424 3960 Cuttings 1.08 1190 FNL, 1850 FEL -107.32789 36.96954 F32-05-23-SW Nassau Carracas Unit 23 A 12 7185 3940 Cuttings 1.22 1650 FSL, 1190 FWL -107.33565 36.96314 F32-05-24-NW Nassau Resource Carracas Unit PC 24A 7327 3954 Cuttings 1.24 790 FNL, 1140 FWL -107.31765 36.97069 A32-05-26-NE Nassau Carracas U 26A 2 7215 3970 Cuttings 1.21 790 FNL, 1450 FEL -107.32657 36.95627 F32-05-27-NE Nassau Carracas U 27A 8 7188 3882 Cuttings 1.18 1480 FNL, 990 FEL -107.34317 36.95440 F32-05-27-SW Nassau Resource Carracas Unit 27A 6843 3582 Cuttings 1.27 970 FSL, 1580 FWL -107.35235 36.94663 A32-05-28-SW Meridian Quint Mesa C 100 7160 3905 Cuttings 1.14 2360 FSL, 1740 FWL -107.37034 36.95059 P32-05-33-SE Schalk John E USA-62 6303 2200 Cuttings 1.15 1190 FSL, 890 FEL -107.36088 36.93268 A32-05-35-NE Nassau Carracas U 35A 8 6922 3673 Cuttings 1.17 1500 FNL, 1020 FEL -107.32503 36.93977 F32-06-07-NE Meridian Allison Unit 133 6236 2760 Cuttings 1.19 790 FNL, 2490 FEL -107.49912 36.99756 P32-06-10-NE Pacific NW Pipelineline San Juan 32-5 Unit 6194 2660 Cuttings 1.30 990 FNL, 990 FEL -107.43905 36.99727 A32-06-16-SW Meridian Allison Unit 100 6137 2781 Cuttings 1.25 1780 FSL, 1540 FWL -107.46702 36.97829 P32-06-17-SW Meridian Allison Unit 101 6596 3210 Cuttings 1.03 1840 FSL, 1190 FWL -107.48678 36.97838 P32-06-18-NE Meridian Allison Unit 111 6507 3060 Cuttings 1.17 2480 FNL, 1450 FEL -107.49580 36.98102 P32-06-18-SW Meridian Allison Unit 112 6517 3128 Cuttings 1.19 1850 FSL, 1190 FEL -107.50432 36.97824 P32-06-19-NE Meridian Allison Unit 114 6513 3150 Cuttings 1.20 1240 FNL, 1120 FEL -107.49480 36.96979 P32-06-19-NW Meridian Allison Unit 136 6681 3260 Cuttings 1.17 2360 FNL, 925 FWL -107.50514 36.96659 P32-06-20-NW Meridian Allison Unit 116 6385 2960 Cuttings 1.26 1850 FNL, 880 FWL -107.48784 36.96820 P32-06-20-SW Meridian Allison Unit 115 6522 3169 Cuttings 1.19 2400 FSL, 1975 FWL -107.48413 36.96523 P32-06-21-NE Meridian EPNG A 100 6385 3076 Cuttings 1.23 2030 FNL, 1905 FEL -107.45856 36.96982 P32-06-21-SW Meridian Allison Unit 117 6482 3161 Cuttings 1.15 930 FSL, 1540 FWL -107.46700 36.96127 P32-06-23-NE Meridian-SJ 32-5 U,101 6416 3112 Cuttings 1.18 2325 FNL, 1010 FEL -107.42125 36.96683 P32-06-23-SW Meridian-SJ 32-5 U,100 6331 4369 Cuttings 1.12 1765 FSL, 1485 FWL -107.43073 36.96364 P32-06-24-SW Meridian-SJ 32-5 U,102 6369 3000 Cuttings 1.18 1820 FSL, 1635 FWL -107.41202 36.96375 P32-06-25-SW Meridian-SJ 32-5 U,104 6411 3121 Cuttings 1.19 540 FSL, 985 FWL -107.41434 36.94576 P32-06-26-NE Meridian-SJ 32-5 U,107 6353 3080 Cuttings 1.15 2045 FNL, 645 NEL -107.41997 36.95293 P32-06-27-NE Meridian-SJ 32-5 U 108 6428 3158 Cuttings 1.24 2100 FNL, 100 FEL -107.43630 36.95319 F32-06-28-NE Meridian EPNG "B" 100 6463 3100 Cuttings 1.17 1015 FNL, 2485 FEL -107.46258 36.95563 P32-06-29-NE Meridian Allison Unit 102 6507 3200 Cuttings 1.16 860 FNL, 1950 FEL -107.47909 36.95619 P32-06-29-SW Meridian Allison Unit 119 6381 3077 Cuttings 1.16 1595 FSL, 1765 FWL -107.48488 36.94820 P32-06-30-NE Meridian Allison Unit 120 6404 3087 Cuttings 1.15 1070 FNL, 1100 FEL -107.49475 36.95556 P32-06-30-SW Meridian Allison Unit 121 6576 3087 Cuttings 1.08 1780 FSL, 930 FWL -107.50540 36.94886 P
Table A4-1. Mean vitrinite reflectance values (Rm) for coal samples from the Fruitland Formation—Continued. 

Point ID Well Name Elev. Depth Sample Rm

(%) 

Footage Longitude Latitude 

New Mexico—Continued

32-07-09-SE Meridian Allison Unit 123 6586 3240 Cuttings 1.22 1015 FSL, 1850 FEL -107.56946 36.9903 P32-07-12-SW Meridian Allison Unit 125 6542 3158 Cuttings 1.15 790 FSL, 1595 FWL -107.52109 36.98972 P32-07-14-NE Meridian Allison Unit 126 6636 3275 Cuttings 1.25 1900 FNL, 1765 FEL -107.53276 36.98217 P32-07-14-SW Meridian Allison Unit 127 6829 3458 Cuttings 1.09 1080 FSL, 790 FWL -107.54293 36.97604 P32-07-15-NW Meridian Allison Unit 107 6600 3080 Cuttings 1.07 941 FNL, 1510 FWL -107.55811 36.98496 P32-07-22-NE Pacific NW Pipelineline San Juan 32-7 Unit NA 3230 Cuttings 1.10 1650 FNL, 1650 FEL -107.55133 36.96844 A32-07-23-SE Meridian Allison Unit 108 6549 3266 Cuttings 1.15 841 FSL, 790 FWL -107.54273 36.96089 P32-07-25-NE Meridian Allison Unit 132 6472 3168 Cuttings 1.12 1460 FNL, 790 FEL -107.51119 36.95447 P32-07-25-SW Meridian Burnt Mesa 101 6603 3339 Cuttings 1.14 1175 FSL, 1500 FWL -107.52156 36.94736 P32-07-26-SW Meridian Burnt Mesa 100 6734 3433 Cuttings 1.06 1164 FSL, 790 FWL -107.54230 36.94735 P32-07-36-NE NW Pipelineline San Juan 32-7 204 6472 3188 Cuttings 1.03 815 FNL, 2005 FEL -107.51551 36.94156 P32-08-08-SE Southland Royalty Trail Canyon 101 6730 3350 Cuttings 1.07 1850 FSL, 850 FEL -107.69020 36.99660 P32-08-12-NE Meridian Reese Mesa 104 7103 3760 Cuttings 1.19 840 FNL, 1465 FEL -107.62162 36.99760 P32-08-13-NW Southland Royalty Reese Mesa 100 7100 3950 Cuttings 1.15 1450 FNL, 805 FWL -107.63153 36.97972 A32-08-13-NW Meridian Reese Mesa 100 7100 3961 Cuttings 1.15 1450 FNL, 805 FWL -107.63145 36.98635 P32-08-20-SW Pacific NW Pipelineline San Juan32-8 Unit NA 3700 Cuttings 1.07 1600 FSL, 1150 FWL -107.70225 36.96718 A32-08-32-SE Meridian Rattlesnake Canyon 102 6550 3440 Cuttings 0.93 1185 FSL, 1185 FEL -107.69252 36.93645 P32-09-36-NE Meridian San Juan 32-9 Unit 228 6592 3380 Cuttings 0.94 1160 FNL, 1350 FEL -107.72642 36.94354 P32-10-11-NE Meridian Carter Ute 100 6659 3270 Cuttings 1.09 1180 FNL, 1450 FEL -107.84650 36.99815 P32-10-16-NE Meridian Burroughs Com "A" 100 6367 3099 Cuttings 0.98 2025 FNL, 1625 FEL -107.88338 36.98664 P32-10-16-SW Meridian EPNG Com "C" 100 6767 3425 Cuttings 0.86 1850 FSL, 1487 FWL -107.89029 36.98295 P32-10-17-SW Amoco Decker Gas Com A 6115 2853 Cuttings 0.91 1550 FSL, 960 FWL -107.91060 36.98202 A32-10-20-SE Meridian Oil Payne 6 6334 3109 Cuttings 0.83 1667 FSL, 805 FEL -107.89817 36.96789 A32-10-23-SE Meridian Carter Ute 104 6650 3263 Cuttings 0.97 945 FSL, 720 FEL -107.64790 36.96706 P32-10-24-NE Amoco San Juan 32-9 Unit 104 6813 3263 Cuttings 0.97 1430 FNL, 1450 FEL -107.83082 36.97299 A32-10-27-SW Amoco Keys Gas Com G 1 5952 2728 Cuttings 0.88 1480 FSL, 1620 FWL -107.87207 36.95307 A32-10-28-NE Amoco Holmberg Gas Com C 1 6043 2824 Cuttings 0.97 1255 FNL, 1450 FEL -107.88258 36.96002 A32-10-29-NE El Paso Scott 21 6058 2952 Cuttings 0.82 1760 FNL, 1860 FEL -107.90197 36.95854 A32-10-32-NE Amoco State Gas Com-BW 5919 2690 Cuttings 0.91 790 FNL, 1480 FEL -107.90800 36.96017 A32-10-32-SW Amoco State Gas Com-BX 6087 2848 Cuttings 0.79 1490 FSL, 1790 FWL -107.90784 36.93852 A32-10-33-NE Amoco Ealum Gas Com C 1 5998 2562 Cuttings 0.86 1645 FNL, 1615 FEL -107.88319 36.94444 A32-10-33-NW Amoco Cahn Gas Com 1 6012 2807 Cuttings 0.80 1030 FNL, 1600 FWL -107.89037 36.94600 A32-11-07-SW Grt. West. Dr. J. E. Decker 10 6481 2937 Cuttings 0.71 1690 FSL, 1775 FWL -108.03095 36.99683 P32-11-08-SW Grt. West. Dr. Decker-11 6619 3135 Cuttings 0.77 910 FSL, 955 FWL -108.01630 36.99491 P32-11-09-NW Union Texas Petroleumroleum Ute 39 NA 2590 Cuttings 0.77 1195 FNL, 1750 FWL -107.99610 36.99655 F32-11-12-NW Union Texas Petroleumroleum Ute 34 NA 2900 Cuttings 0.87 2470 FNL, 2260 FWL -107.94200 36.99322 F32-11-12-SE Union Texas Petroleumroleum Ute 33 NA 3080 Cuttings 0.84 2210 FSL, 1220 FEL -107.93606 36.99832 F32-11-13-SW Amoco Barnes B 21 6223 2926 Cuttings 0.76 1250 FSL, 800 FWL -107.94687 36.98128 A32-11-14-SW Meridian Primo Mudge 100 NA 3090 Cuttings 0.79 1120 FSL, 1450 FWL -107.96198 36.98068 A32-11-16-NW Northwest Pipelineline Cox Canyon Unit NA 3572 Cuttings 0.75 890 FNL, 1525 FWL -107.99684 36.98967 A32-11-22-SW Amoco Barnes Gas Com B 1 6475 3172 Cuttings 0.74 1180 FSL, 1390 FWL -107.97930 36.96599 A
Table A4-1. Mean vitrinite reflectance values (Rm) for coal samples from the Fruitland Formation—Continued. 

Point ID Well Name Elev. Depth Sample Rm

(%) 

Footage Longitude Latitude 

New Mexico—Continued

32-11-23-NE Amoco Barnes GC A-1 6251 2903 Cuttings 0.77 1090 FNL, 1530 FEL -107.95487 36.97475 P32-11-23-SW Amoco Barnes Gas Com C 1 6334 3059 Cuttings 0.76 1660 FSL, 1330 FWL -107.96227 36.96758 A32-11-24-SW Meridian Primo Mudge 100 6348 3090 Cuttings 0.79 1120 FSL, 1450 FWL -107.94480 36.96646 F32-11-25-SW Amoco Fields A 21 6325 3067 Cuttings 0.78 1330 FSL, 1150 FWL -107.94626 36.95260 A32-11-26-NE Amoco Barnes Gas ComE E 6366 3086 Cuttings 0.83 1010 FNL, 1470 FEL -107.95503 36.96049 A32-11-26-NW Tenneco Barnes NA 3150 Cuttings 0.76 1520 FNL, 1490 FWL -107.96188 36.95882 A32-11-27-NE Amoco Barnes A 20 6463 3122 Cuttings 0.76 1230 FNL, 800 FEL -107.96972 36.95946 A32-11-28-NE Amoco Fields A 19 6287 2970 Cuttings 0.73 1940 FNL, 1180 FEL -107.98841 36.95737 A32-11-30-SE Nassau Bettin' on Bisti 30 9 NA 1210 Cuttings 0.43 1980 FSL, 660 FEL -108.02135 36.95414 P32-11-33-NE Amoco Neal A 21 6132 2791 Cuttings 0.66 2305 FNL, 1120 FEL -107.98882 36.94195 A32-11-33-SW Amoco Neal A-1 6181 2857 Cuttings 0.70 2140 FSL, 910 FWL -107.99903 36.93992 P32-11-34-NE Amoco Fields A 23 6149 2840 Cuttings 0.72 1580 FNL, 2270 FEL -107.97548 36.94401 A32-11-35-NE Amoco Storey Gas Com B 1 6340 3056 Cuttings 0.73 1040 FNL, 1400 FEL -107.95516 36.94596 A32-12-08-SW NMBMMR coal test hole 5958 205 Core 0.52 NA -108.12056 36.99523 H32-12-12-SW Great Western Dr. J. E. Decker 9 6252 2649 Cuttings 0.75 1506 FSL, 938 FWL -108.05150 36.99788 F32-12-14-SE Outcrop Prewitt mine NA Surface Outcrop 0.58 624 FSL, 1618 FEL -108.10833 37.00969 L32-12-21-NW Aztec Culpepper-Martin 102 NA 2127 Cuttings 0.65 990 FNL, 1650 FWL -108.10293 36.97612 A32-12-25-NE Amoco Moore GC B-1 6423 2740 Cuttings 0.61 1570 FNL, 1030 FEL -108.04042 36.9594 P32-12-27-NE Amoco Moore D 6189 2557 Cuttings 0.67 1180 FNL, 1570 FEL -108.07821 36.96106 A32-12-28-SW Meridian Culpepper Martin 103 5790 2350 Cuttings 0.65 1335 FSL, 1845 FWL -108.10228 36.95349 P32-13-13-SW NMBMMR coal test hole 6050 293 Core 0.54 NA -108.14842 36.98517 H32-13-14-SE NMBMMR coal test hole 6072 152 Core 0.52 NA -108.17045 36.98026 H32-13-28-SW NMBMMR coal test hole 6032 387 Core 0.54 NA -108.21223 36.95578 H

Colorado 

32c-03-22-NE Stanolind, S. Ute 1 7188 1950 Cuttings 0.79 NE NW NE -107.15954 37.01003 L32c-05-08-SE Amoco Seibel Gas Unit A 1 6153 2702 Cuttings 1.44 690 FSL, 860 FEL -107.40877 37.02717 A32c-06-02-SE Tiffany Gas Glover 1 6490 3084 Cuttings 1.22 1650 FSL, 990 FEL -107.46337 37.04379 A32c-06-15-NW Pac. NW Pipeline. Arboles 32-6 6197 2640 Cuttings 1.29 1525 FNL, 1525 FWL -107.49076 37.0204 L32c-06-19-NW Meridian Oil Allison Unit 136 6681 3250 Cuttings 1.17 2360 FNL, 925 FWL -107.54677 37.00325 A32c-06-20-NW Meridian Oil Allison Unit 116 6385 2940 Cuttings 1.26 1850 FNL, 880 FWL -107.52919 37.00459 A32c-07-04-SE Mobil Oil Colorado 32-7 10-2 NA 2554 Cuttings 1.11 1476 FSL, 895 FEL -107.60759 37.04278 A32c-07-14-SW Bakke W E Oil Ute NA 3180 Cuttings 1.02 1000 FSL, 1000 FWL -107.58283 37.01268 A32c-07-16-NW Sohio S. Ute 15-16 6373 3450 Cuttings 1.23 1167 FNL, 1024 FWL -107.61899 37.02101 L32c-07-16-SW Bakke W E Oil Southern Ute NA 2040 Cuttings 1.03 1265 FSL, 990 FWL -107.61921 37.01328 A32c-10-02-NE NCRA S. Ute 2-3 NA 2888 Cuttings 1.13 1035 FNL, 1280 FEL -107.89780 37.05027 L32c-10-03-SE Ladd Cox Canyon 2-3 6602 3105 Core 1.05 1600 FSL, 1600 FEL -107.91660 37.0433 L32c-10-05-SW Amoco SO Ute Tribal XX PLA 9 7281 3780 Cuttings 1.00 1650 FSL, 2360 FWL -107.95739 37.04366 A32c-10-07-SE Amoco Southern Ute Tribal J 6649 3195 Cuttings 1.05 1470 FSL, 1990 FEL -107.97229 37.02877 A32c-10-10-NE Pac. NW Pipeline. NW Cedar Hill 8-10 6411 3010 Cuttings 1.12 SE NW SE -107.91664 37.03611 L32c-10-11-NE Meridian Oil Carter Ute 100 6659 3270 Cuttings 1.09 1180 FNL, 1450 FEL -107.89827 37.03540 A
Table A4-1. Mean vitrinite reflectance values (Rm) for coal samples from the Fruitland Formation—Continued. 

Point ID Well Name Elev. Depth Sample Rm

(%) 

Footage Longitude Latitude 

Colorado—Continued

32c-10-12-NE Amoco MH Montgomery GU APLA-9 1 6219 2779 Cuttings 1.09 1610 FNL, 1040 FEL -107.87902 37.03404 A32c-10-12-NE Pacific NW Pipelineline NW Cedar Hill 7-12 6025 2600 Cuttings 1.15 NE NE NE -107.87662 37.03755 L32c-10-15-SW Amoco Southern Ute 32-10 15-3 6466 3118 Cuttings 0.94 1610 FSL, 1390 FWL -107.92425 37.01448 A32c-10-16-SW Amoco Southern Ute 32-10 16.2 6364 3027 Cuttings 0.88 1765 FSL, 1990 FWL -107.94054 37.01499 A32c-10-17-SW Amoco GRI Observation NA 3151 Cuttings 0.90 1880 FSL, 1530 FWL -107.96015 37.01547 A32c-10-18-NW Amoco Southern Ute Tribal H 1 6583 3118 Cuttings 1.02 830 FNL, 1040 FWL -107.97989 37.02247 A32c-10-19-NW Amoco Clark/Cummins GU A PLA-9 1 6553 3241 Cuttings 0.89 2250 FNL, 1420 FWL -107.97852 37.00415 A32c-10-20-NE Amoco Hendrickson GU B PLA-9 1 6638 3258 Cuttings 0.90 2240 FNL, 1580 FEL -107.95296 37.00404 A32c-10-20-NW Amoco Hendrickson GU A PLA-9 1 6481 3113 Cuttings 0.88 2590 FNL, 1490 FWL -107.96031 37.00313 A32c-10-22-NW Amoco JB Gardner GU APLA-9 1 6255 2929 Cuttings 0.95 2150 FNL, 1120 FWL -107.92546 37.00412 A32c-10-22-SW Pacific NW Pipeline NW Cedar Hill 32-10 NA 2980 Cuttings 0.93 1190 FSL, 1190 FWL -107.92525 37.00328 A32c-10-23-NW Amoco Robin Frazier GU APLA-9 1 6320 2985 Cuttings 0.98 1000 FNL, 990 FWL -107.90739 37.00731 A32c-10-23-SE Meridian Oil Inc Carter Ute 104 6650 3240 Cuttings 0.97 945 FSL, 720 FEL -107.89586 37.00269 A32c-11-07-NE Amax O&G Southern Ute 5-7 6204 1448 Cuttings 0.80 1020 FNL, 1050 FEL -108.07748 37.03668 A32c-11-07SE Ladd S. Ute 1-7 6150 1690 Cuttings 0.74 1320 FSL, 1260 FEL -108.07823 37.02866 L32c-11-09-NW Union Texas Petroleum Ute NA 2590 Cuttings 0.77 1195 FNL, 1750 FWL -108.04978 37.03609 A32c-11-12-NW Union Texas Petroleum Ute NA 2900 Cuttings 0.87 2470 FNL, 2260 FWL -107.99391 37.03242 A32c-11-12-SE Union Texas Petroleum Ute NA 3080 Cuttings 0.84 2210 FSL, 1220 FEL -107.98768 37.03088 A32c-12-12-NW Outcrop NA 0 Outcrop 0.70 961 FSL, 1000 FWL -108.10621 37.03679 A33-02-32-NE Outcrop-coal mine NA Surface Outcrop 0.64 1266 FNL, 2282 FEL -108.15638 36.97805 L33-03-16-SW Outcrop Cat Creek Gap NA Surface Outcrop 0.64 372 FSL, 1527 FWL -107.08975 37.06405 L33-05-10-NW Amoco Canderlaria NA 2750 Cuttings 1.42 600 FNL, 2285 FWL -107.38034 37.12490 A33-06-03-NW Amoco Southern Ute Tribal-B 7441 Cuttings 1.42 1020 FNL, 990 FWL -107.49263 37.13753 A33-06-17-NW Perlman William Southern Ute 17-2 6750 Cuttings 1.60 1240 FNL, 1560 FWL -107.52682 37.10770 A33-06-18-NE Perlman Baird 18-2 6698 3170 Core 1.41 1490 FNL, 1000 FEL -107.53565 37.10709 L33-06-20-SW Perlman Hott 20-2 6610 3130 Core 1.49 1500 FSL, 1360 FWL -107.52737 37.08633 L33-06-21-SE Amoco Southern Ute Tribal C 4 6926 Cuttings 1.55 1000 FSL, 1120 FEL -107.49999 37.08540 A33-06-21-SW Amoco Southern Ute Tribal C 1 6722 Cuttings 1.55 1190 FSL, 990 FWL -107.51053 37.08578 A33-06-29-NW Amoco HOTT Unit 2 6566 3104 Cuttings 1.51 1150 FNL, 1755 FWL -107.52604 37.07904 A33-06-33-NW Amoco Southern Ute Gas Unit AA 1 6806 2732 Cuttings 1.25 830 FNL, 810 FWL -107.51118 37.06563 A33-07-17-NW Stanolind Ute 6-B 6515 2740 Cuttings 1.23 2310 FWL, 2310 FNL -107.63257 37.10495 L33-07-20-SW Amoco S Ute Gas Unit AA 1 6607 2723 Cuttings 1.31 1650 FSL, 1630 FWL -107.63510 37.08695 A33-07-21-NW Amoco Southern Ute Gas 3 6383 2402 Cuttings 1.31 1070 FNL, 1650 FWL -107.61686 37.09374 A33-07-28-NW Amoco Salvador Gas Unit A 1 6364 2452 Cuttings 1.28 1060 FNL, 1150 FWL -107.61858 37.07929 A33-07-30-NW Amoco Simms Gas Unit E 1 6491 2738 Cuttings 1.41 820 FNL, 1630 FWL -107.65298 37.08000 A33-07-34-SE Pac. NW Pipeline. Ignacio 3-34 6623 2890 Cuttings 1.26 1450 FSL, 1190 FEL -107.59053 37.05717 L33-08-01-SW Pac. NW Pipeline. Ignacio 2-1 6644 2740 Cuttings 1.28 1850 FSL, 1320 FWL -107.67229 37.13098 L33-08-07-NW Amerada Fassett 1 6658 2850 Cuttings 1.29 990 FNL, 1650 FWL -107.76237 37.12278 L33-08-10-NE Amoco Ford Gas Unit A 1 6664 Cuttings 1.43 1150 FNL, 1100 FEL -107.69882 37.12257 A33-08-16-NW Amerada Herrera 1 6692 2890 Cuttings 1.16 1320 FNL, 1320 FWL -107.72673 37.10762 L33-08-23-NE Amoco Pan American Fee NA 2950 Cuttings 1.40 1090 FNL, 1020 FEL -107.68033 37.09374 A
Table A4-1. Mean vitrinite reflectance values (Rm) for coal samples from the Fruitland Formation—Continued. 

Point ID Well Name Elev. Depth Sample Rm

(%) 

Footage Longitude Latitude 

Colorado—Continued

33-09-04-SE Amoco John Barnes Gas Unit A PLA-6 1 6280 2664 Cuttings 1.32 1210 FSL, 1460 FEL -107.82665 37.12899 A33-09-06-SE Amoco Clovis Gas Unit A 1 6473 2722 Cuttings 1.28 435 FSL, 1880 FEL -107.86379 37.12683 A33-09-07-NE Amoco Lyle Short Gas Unit A 1 6467 2805 Cuttings 1.42 1630 FNL, 1590 FEL -107.86280 37.12114 A33-09-07-SE Pac. NW Pipeline. Bondad 17-7 6453 2490 Cuttings 1.09 1420 FSL, 1100 FEL -107.86120 37.11502 L33-09-08-NW Amoco Clovis Gas Unit B 6460 2721 Cuttings 1.36 2506 FNL, 115 FWL -107.85695 37.11870 A33-09-13-NW Pac. NW Pipeline. Bondad 7-13 6678 2930 Cuttings 1.36 1070 FNL, 1340 FWL -107.78135 37.10808 L33-09-16-SE NCRA Southern Ute 504 7-16 6670 3070 Cuttings 1.32 2200 FSL, 900 FEL -107.82490 37.10272 A33-09-16-SE NCRA S. Ute Unit 504 2-16 6692 3158 Cuttings 1.34 880 FSL, 1280 FEL -107.82618 37.09912 L33-09-18-SE Amoco Roy Eshelman Gas Unit PLA-6 6411 2842 Cuttings 1.21 1640 FSL, 1400 FEL -107.86230 37.10103 A33-09-19-SE Amoco Raymond Koon Gas Unit A PLA-6 1 6357 2899 Cuttings 1.28 2270 FSL, 1450 FEL -107.86253 37.08827 A33-10-01-SE Meridian Bondad 33-10 Com 104 6263 2980 Cuttings 1.13 1400 FSL, 1135 FEL -107.87938 37.12950 P33-10-03-SE Amoco Frank Davis Gas Unit A PLA-6 1 6392 2615 Cuttings 1.09 1610 FSL, 2010 FEL -107.91859 37.13012 A33-10-08-NW Enervest Black Ridge SU 8-2 NA 3151 Cuttings 1.13 1545 FNL, 1360 FWL -107.96126 37.12155 E33-10-11-SE Amoco Presentacion Medina Gas Unit 1 6213 2561 Cuttings 1.22 1010 FSL, 1620 FEL -107.89926 37.11378 A33-10-13-SE Amoco S Ute Tribal Gas Unit QQ PLA-6 1 6175 2603 Cuttings 1.21 1560 FSL, 1530 FEL -107.88078 37.10078 A33-10-14-NW Amoco Thomas Jacques Gas Unit A PLA-6 1 6323 2694 Cuttings 1.21 1650 FNL, 1070 FWL -107.90798 37.10654 A33-10-15-SE Amoco Thomas Jacques Gas Unit B PLA-6 1 6319 2638 Cuttings 1.15 1640 FSL, 1290 FEL -107.91608 37.10129 A33-10-17-NE Emerald Gas Operating Black Ridge 17-2 7588 2842 Cuttings 1.10 845 FNL, 1705 FEL -107.95361 37.10908 P33-10-17-SE Enervest Black Ridge SU 17-1 (Dev) NA 3191 Cuttings 1.15 1126 FSL, 1338 FEL -107.95226 37.10005 E33-10-23-NW Amoco Thomas Jacques Gas Unit F 1 6254 2721 Cuttings 1.17 990 FNL, 1110 FWL -107.90776 37.09399 A33-10-25-SE Amoco MF Sharp Gas Unit A PLA-6 1 6088 2536 Cuttings 1.18 1210 FSL, 990 FEL -107.87891 37.07076 A33-10-25-SW Amoco Sharp Gas Unit NA Cuttings 1.07 1510 FSL, 1440 FWL -107.88860 37.07138 A33-10-28-NW Amoco Southern Ute 28-3, 33-10 PLA-6 NA 3145 Cuttings 1.06 1070 FNL, 2180 FWL -107.94019 37.07942 A33-10-30-NW Palo Petroleum Eldridge 30-1 6680 3185 Cuttings 1.06 1774 FNL, 1017 FWL -107.98024 37.07805 A33-10-31-NW Palo Petroleum Eldridge 31-1 6564 3096 Cuttings 1.08 990 FNL, 1002 FWL -107.98022 37.06577 A33-10-33-SE Amoco Cyrus Johnson Gas Unit A PLA 6 6569 3192 Cuttings 1.16 1410 FSL, 1280 FEL -107.93379 37.05719 A33-10-34-NW Pac. NW Pipeline. Bondad 2-34 6575 2685 Cuttings 1.03 1650 FNL, 990 FWL -107.92600 37.06321 L33-10-35-SE NCRA S. Ute Unit 503 4-35 6288 2852 Cuttings 1.16 1315 FSL, 1880 FEL -107.89995 37.05673 L33-11-12-200 Meridian Ute 200 7060 3470 Cuttings 1.02 725 FSL, 1165 FEL -107.98793 37.11363 P33-11-12-NW Meridian Ute 201 7004 3275 Cuttings 0.91 2030 FNL, 1790 FWL -107.99558 37.12066 P33-11-13-SE Palo Petroleum Southern Ute 13 1 6777 3435 Cuttings 1.01 1274 FSL, 1538 FEL -107.98910 37.10097 A33-11-14-NW Palo Petroleum Southern Ute 14 1 7104 3442 Cuttings 1.01 1805 FNL, 1791 FWL -108.01402 37.10674 A33-11-14-SE Palo Petroleum Southern Ute 14 2 6820 3264 Cuttings 1.08 1300 FSL, 1350 FEL -108.00693 37.10104 A33-11-20-NE Enervest Valencia Canyon SU 20-4 6678 1408 Cuttings 0.79 1597 FNL, 330 FEL -108.05723 37.09251 E33-11-20-SE Enervest Valencia Canyon SU 20-1 6596 1450 Cuttings 0.79 1083 FSL, 1098 FEL -108.05979 37.08557 E33-11-23-NW Palo Petroleum Southern Ute 23 1 6782 3218 Cuttings 1.03 1596 FNL, 1507 FWL -108.01505 37.09287 A33-11-23-SE Palo Petroleum Southern Ute 23 2 6669 3140 Cuttings 1.01 1377 FSL, 2613 FEL -108.01111 37.08675 A33-11-24-NW Palo Petroleum Southern Ute 24 1 6665 3124 Cuttings 1.04 890 FNL, 1390 FWL -107.99742 37.09506 A33-11-27-SE MonSanto Ute 1 6736 3120 Cuttings 0.92 1650 FEL, 1650 FSL -108.02570 37.07286 L33-11-29-NW Enervest Valencia Canyon SU 29-2 6523 1291 Cuttings 0.76 1818 FNL, 2500 FWL -108.06528 37.07766 E33-11-29-SE Enervest Valencia Canyon SU 29-1 6443 1963 Cuttings 0.73 740 FSL, 845 FEL -108.05887 37.07010 E
Table A4-1. Mean vitrinite reflectance values (Rm) for coal samples from the Fruitland Formation—Continued. 

Point ID Well Name Elev. Depth Sample Rm

(%) 

Footage Longitude Latitude 

Colorado—Continued

33-11-30-NE Enervest Valencia Canyon SU 30-4 6471 422 Cuttings 0.68 1841 FNL, 775 FEL -108.07658 37.07761 E33-11-31-NE Enervest Valencia Canyon SU 31-4 6280 621 Cuttings 0.70 1167 FNL, 1204 FEL -108.07810 37.06506 E33-11-31-SE Enervest Valencia Canyon SU 31-1 6366 956 Cuttings 0.71 2019 FSL, 1324 FEL -108.07842 37.05950 E33-11-32-NW Enervest Valencia Canyon SU 32-2 6352 1415 Cuttings 0.75 2005 FNL, 1320 FWL -108.06936 37.06262 E33-11-32-SE Enervest Valencia Canyon SU 32-1 6320 1950 Cuttings 0.74 1157 FSL, 2474 FEL -108.06432 37.05690 E33-11-33-NW Meridian Southern Ute 300 6435 2480 Cuttings 0.73 1850 FNL, 1255 FWL -108.05155 37.06299 E33-11-34-NW Palo Petroleum Southern Ute 34 1R NA 3091 Cuttings 0.93 1304 FNL, 1542 FWL -108.03261 37.06458 A33-11-35-SE Palo Petroleum Southern Ute 35 1 6432 2870 Cuttings 0.97 1465 FSL, 1782 FEL -108.00815 37.05763 A33-11-36-SE Palo Petroleum Eldridge 36 2 6459 3000 Cuttings 1.01 1168 FSL, 1029 FEL -107.98709 37.05690 A34n-05-09-NE Outcrop Yellow Jacket NA Surface Outcrop 0.79 1395 FNL, 1170 FEL -107.42036 37.23394 L34n-06-18-NW Amoco Beaver Creek Gas Unit B 1 6819 2190 Cuttings 1.24 1470 FNL, 1650 FWL -107.57199 37.21742 A34n-07-01-SE Amoco Taliaferro Trust Gas Unit A 1 7055 1666 Cuttings 1.02 1740 FSL, 1640 FEL -107.58359 37.24090 A34n-07-06-SW Natomas North Gearhart 1-6 7123 Cuttings 1.20 1485 FSL, 1935 FWL -107.68009 37.24076 A34n-07-15-NW M. Anderson Sitton&Gray 1 6825 2340 Cuttings 1.27 C NE NW -107.62443 37.2209 L34n-08-02-SE Pan American Keyes NA 2202 Cuttings 1.42 1980 FSL, 720 FEL -107.70712 37.24213 A34n-08-10-SW Perlman William Mayfield 1-10U 6862 Cuttings 1.57 1125 FSL, 1325GEL -107.73670 37.22547 A34n-08-18-SE Fuelco Sun-Tyner Lunt 1 6778 2720 Cuttings 1.46 1783 FSL, 1946 FEL -107.78415 37.21981 L34n-09-04-NW Outcrop NA 0 Outcrop 0.80 2153 FNL, 2097 FEL -107.86366 37.23891 A34s-04-30-NE Outcrop Chimney Rock Mine NA Surface Outcrop 0.86 2150 FNL, 2120 FEL -107.32296 37.16369 L34s-05-32-SE Amoco Pargin Mountain Unit 3 6653 3109 Cuttings 1.66 740 FSL, 2360 FEL -107.41442 37.14313 A34s-05-35-SW Amoco Bull Creek Federal A 1 6376 2032 Cuttings 1.49 640 FSL, 1360 FWL -107.36549 37.14270 A34s-06-14-NE Amoco Pargin Mounatin Unit 2 8730 5166 Cuttings 1.59 550 FNL, 1600 FEL -107.46553 37.19684 A34s-06-14-NE Lecada Natural Federal NA Cuttings 1.63 1450 FNL, 1120 FEL -107.46384 37.19438 A34s-06-19-SE Amoco Boone Gas Unit 1 6909 2874 Cuttings 1.40 1090 FSL, 1850 FEL -107.53840 37.17207 A34s-06-20-NW Natomas Smith 1-20 7058 2900 Cuttings 1.28 1470 FNL, 990 FWL -107.52849 37.17946 L34s-07-20-NW Amoco HN Pearson A 1 6804 2783 Cuttings 1.34 1650 FNL, 1080 FWL -107.63678 37.17926 A34s-07-21-NE Perlman S. Ute 21-1 6825 2220 Core 1.28 990 FNL, 990 FEL -107.60762 37.18116 L34s-07-23-SE Perlman S. Ute 23-1 6731 2311 Core 1.30 1550 FSL, 18440 FEL -107.57418 37.17346 L34s-07-25-NW Amoco Gary Beebe Gas Unit A 1 6739 2783 Cuttings 1.36 1010 FNL, 1210 FWL -107.56368 37.16633 A34s-08-11-SW Perlman William Mayfield 1-11U 6883 Cuttings 1.60 1440 FSL, 1210 FWL -107.69084 37.20248 A34s-08-20-SW Perlman William McCaw 20-1 6709 Cuttings 1.56 860 FSL, 550 FWL -107.74784 37.17149 A34s-08-25-SE S Ute Dpt Energy Oxford 1 NA 2819 Core 1.37 2142 FSL, 542 FEL -107.66048 37.16064 K34s-08-25-SW S Ute Dpt Energy Oxford 2 6706 2840 Cuttings 1.44 1120 FSL, 2450 FWL -107.66840 37.15790 K34s-08-36-SE Amoco Southern Ute Tribal NA 2794 Cuttings 1.40 1120 FSL, 1650 FEL -107.66435 37.14343 A34s-09-12-Se Tenneco Larson 1-12 6927 2311 Core 1.34 1550 FSL, 1400 FEL -107.77259 37.20269 L34s-09-13-NE Tenneco Fassett 2-13 6848 2504 Core 1.54 1650 FNL, 1850 FEL -107.77423 37.19384 L34s-09-15-NW Amoco Linder Gas Unit A 1 NA 2664 Cuttings 1.30 1407 FNL, 1976 FWL -107.81420 37.19445 A34s-09-16-SE Amoco McMahan Gas Unit A 1 6841 2701 Cuttings 1.50 1030 FSL, 2020 FEL -107.82797 37.18652 A34s-09-19-NE Amoco Weasel Skin Gas Unit 1 6638 2484 Cuttings 1.33 380 FNL, 160 FEL -107.85790 37.18282 A34s-09-21-NE Amoco Simon Land and Cattle 21U-1R Unit 1 6801 2756 Cuttings 1.37 1250 FNL, 1180 FEL -107.82510 37.18027 A34s-09-22-SE Amoco Roger D. Kelly Gas Unit 1 6778 2771 Cuttings 1.49 1600 FSL, 1325 FEL -107.80894 37.17369 A
Table A4-1. Mean vitrinite reflectance values (Rm) for coal samples from the Fruitland Formation—Continued. 

Point ID Well Name Elev. Depth Sample Rm

(%) 

Footage Longitude Latitude 

Colorado—Continued

34s-09-26-NW Amoco Cugnini Gas Unit A 1 6764 2956 Cuttings 1.55 1490 FNL, 910 FWL -107.80112 37.16515 A34s-09-27-NW Greenbrier & Mendota Simon 1 6787 2805 Cuttings 1.24 W1/2 NW NW -107.81993 37.16743 L34s-09-36-NW Amoco Federal Land Bank Unit C 1 6697 3033 Cuttings 1.64 1030 FNL, 1530 FWL -107.78099 37.15179 A34s-10-11U-SE Enervest Indian Creek SU 11U-1 6891 2207 Cuttings 0.99 946 FSL, 1559 FEL -107.89884 37.20025 E34s-10-12U-NW Enervest Indian Creek SU 12U-2 6696 2163 Cuttings 1.05 1562 FNL, 1906 FWL -107.88682 37.20777 E

34s-10-12U-SE Enervest Indian Creek Wheeler 12U-1 6574 2412 Cuttings 1.15 1150 FSL, 2298 FEL -107.88330 37.20089 E

34s-10-13-NW Enervest Indian Creek Wheeler 13-2 6539 2552 Cuttings 1.17 1792 FNL, 2464 FWL -107.88494 37.19277 E34s-10-13-SE Enervest Indian Creek SU 13-1 6285 2386 Cuttings 1.22 943 FSL, 1646 FEL -107.88100 37.18615 E34s-10-14-NW Enervest Indian Creek SU 14-2 6923 2510 Cuttings 1.02 1456 FNL, 1797 FWL -107.90526 37.19384 E34s-10-14-SE Enervest Indian Creek SU 14-1 6646 2626 Cuttings 1.14 1681 FSL, 1626 FEL -107.89908 37.18824 E34s-10-15-NE Enervest 44 Canyon SU 15-4 6835 1513 Cuttings 0.90 1340 FNL, 1053 FEL -107.91511 37.19422 E34s-10-15-SE Enervest 44 Canyon Wheeler 15-1 6632 2397 Cuttings 1.05 1003 FSL, 1774 FEL -107.91760 37.18636 E34s-10-16-SE Enervest 44 Canyon Wheeler 16-1 NA 1367 Cuttings 0.81 646 FSL, 857 FEL -107.93256 37.18523 E34s-10-21-SE Enervest 44 Canyon McCulloch 21-2 6803 2847 Cuttings 0.98 1097 FSL, 1321 FEL -107.93415 37.17208 E34s-10-22-NW Enervest Indian Creek Wheeler 22-2 6790 2831 Cuttings 1.10 1758 FNL, 1187 FWL -107.92548 37.17866 E34s-10-22-SE Enervest Indian Creek Wheeler 22-3 NA 2774 Cuttings 1.15 1000 FSL, 1573 FEL -107.91683 37.17200 E34s-10-23-NW Enervest Indian Creek Wheeler 23-2 6607 2770 Cuttings 1.10 1070 FNL, 1758 FWL -107.90538 37.18072 E34s-10-24-NW Enervest Indian Creek SU 24-2 6380 2490 Cuttings 1.16 2180 FNL, 1548 FWL -107.88823 37.17762 E34s-10-28-NW Enervest 44 Canyon McCulloch 28-2 6927 3196 Cuttings 1.14 1557 FWL, 1856 FNL -107.94240 37.16384 E34s-10-36-NE McKenzie Methane Southern Ute-Mobil 36-1 6247 2441 Cuttings 1.34 1445 FNL, 1130 FEL -107.87928 37.15074 A34s-11-36-SE Enervest Bridge Timber SU 36-1 7662 4048 Cuttings 1.07 1413 FSL, 1206 FEL -107.98826 37.14418 P

35-06-14-N1/2 Outcrop NA Surface Outcrop 0.57 1856 FNL, 2332 FEL -107.49555 37.30275 L35-06-16-NE Outcrop NA 0 Outcrop 0.80 1234 FNL, 1612 FEL -107.52930 37.30449 A35-06-30-SE Amoco Parry Gas Company Gas Unit B 1 7089 1455 Cuttings 0.96 2350 FSL, 430 FEL -107.56160 37.27168 A35-06-32-NW Natomas Jones 1-32 7107 1730 Cuttings 0.92 1735 FL, 1320 FNL -107.55409 37.26151 L35-06-34-NW Amoco Sauls Creek 1 7259 2331 Cuttings 1.13 900 FNL, 1410 FWL -107.51894 37.26250 A35-07-08-N1/2 Outcrop NA Surface Outcrop 0.56 1964 FNL, 2362 FEL -107.65777 37.3178 L35-07-14-NW Outcrop NA 0 Outcrop 0.81 2016 FNL, 1416 FWL -107.60881 37.30286 A35-07-15-SE Amoco Gurr Federal Gas Unit 1 7271 1032 Cuttings 0.90 1130 FSL, 1060 FEL -107.61744 37.29717 A35-07-19-NW Amoco Wilbourn Federal Gas Unit 1 7692 1898 Cuttings 1.15 1080 FNL, 2070 FWL -107.67935 37.29176 A35-07-22-NE Amoco Huntington Gas Unit A 1 7379 1595 Cuttings 1.06 2380 FNL, 1905 FEL -107.62027 37.28749 A35-07-23-SW Amoco Cibrad Gas Unit A 1 7178 1454 Cuttings 1.04 770 FSL, 880 FWL -107.61057 37.28182 A35-07-31-SE Amoco Gearhart Gas Unit A 1 7257 2219 Cuttings 1.49 950 FSL, 730 FEL -107.67046 37.25387 A35-07-35-NW Amoco Robert Dulin Gas Unit 1 7024 1602 Cuttings 1.13 1630 FNL, 205 FWL -107.61295 37.26063 A35-08-36-SE Amoco State of Colorado AV 1 7197 2004 Cuttings 1.35 1780 FSL, 2010 FEL -107.69357 37.25627 A35-08-36-SW M. Anderson State 1 7288 2123 Cuttings 1.23 676 FSL, 662 FWL -107.70248 37.25324 L35-09-24-NE Outcrop NA 0 Outcrop 0.66 1425 FNL, 1436 FEL -107.80010 37.29042 A35-09-27-SW Outcrop NA 0 Outcrop 0.80 1150 FSL, 2006 FWL -107.84067 37.26718 A35-09-35-SE Enervest 44 Canyon Day-V-Ranch 35-2 6988 2110 Cuttings 1.24 535 FSL, 2476 FEL -107.82184 37.25264 E35-09-36-SE Fuel ResourceS State 36-2 7110 2400 Cuttings 1.29 683 FSL, 1643 FEL -107.80078 37.25338 A35-09-36-SE Natomas State 1-36 7115 2400 Cuttings 1.29 905 FSL, 1825 FEL -107.80142 37.25398 L
Appendix 5—Isostatic-Residual-Gravity Anomaly Map of the 

San Juan Basin Area (from Heywood, 1992)

The Heywood (1992) map is a scanned image of the original illustration. The overlay of vitrinite-refl ectance contour lines, 

dikes, and sills are from fi gure 37.

0.45

0.6

0.7

0.9

1.0

1.1

1.2

1.3

1.2

1.1

1.0

0.8

1.4

1.4

1.6

1.2

0.8

0.7

1.3

1.1

0.7

0.8

1.3

0.6

0.7

0.6

0.8 0.9

1.3

1.5

0.9

1.6

1.5

0.5

Figure A5-1. Isostatic residual gravity anomalies of the San Juan Basin area (modifi ed from fi gure 12 of Heywood, 1992). Overlay of vitrinite-refl ectance contour 

lines and dikes and sills from fi gure 37.

Q116 Geologic Assessment of Coal in the Colorado Plateau: Arizona, Colorado, New Mexico, and Utah
Appendix 6—Tables and Figures for Fruitland Formation Coal Resources in 

Various Categories for the San Juan Basin

Five tables labeled A6-1 through A6-5 contain coal resources in millions of short tons by quadrangle, township, surface 

ownership, coal ownership, and overburden categories, respectively. Four fi gures labeled A6-1 through A6-4 show 71⁄2-minute 

quadrangles, surface ownership, coal ownership, and distribution of Fruitland coal in standard USGS categories, respectively.

Table A6-1. Estimated Fruitland Formation coal resources (in millions of short tons) in five overburden categories by 

7.5’ quadrangle and State in beds 1.2 ft thick or greater, San Juan Basin, Colorado and New Mexico. 

[Quadrangle areas are shown on figure A5-1. Coal tonnages are rounded to two significant figures. Totals may not add due to 

independent rounding] 

Quadrangle Overburden (ft) Grand total 

 0-500 500-1000 1000-2000 2000-3000 >3000 

Colorado 

Abode Downs Ranch 0.91 0.0 0.93 0.0 0.0 1.8 

Allison 0.0 0.0 0.0 1200 1600 2700 

Baldy Mountain 180 140 180 150 15 670 

Basin Mountain 550 240 600 1700 560 3700 

Bayfield 0.0 0.0 280 2300 660 3300 

Bondad Hill 0.0 0.0 0.0 1100 3200 4300 

Carracas 0.0 0.0 240 1100 860 2200 

Chimney Rock 220 280 500 75 0.0 1100 

Durango East 120 84 380 260 0.0 840 

Gem Village 0.0 0.0 0.0 3000 4.8 3000 

Ignacio 0.0 0.0 0.0 770 2700 3400 

Kline 86 60 100 43 0.0 290 

La Plata 0.56 0.0 0.0 0.0 0.0 0.56 

Loma Linda 40 43 140 4100 69 4300 

Lonetree Canyon 53 19 1.3 0.0 0.0 73 

Long Mountain 0.0 0.0 0.0 1400 3800 5200 

Ludwig Mountain 150 140 860 370 5.5 1500 

Pagosa Junction 250 200 320 220 0.0 980 

Pargin Mountain 110 91 260 700 2000 3100 

Pinkerton Mesa 390 240 700 1700 780 3800 

Redmesa 3.9 0.0 0.0 0.0 0.0 3.9 

Rules Hill 250 160 820 690 0.0 1900 

Tiffany 0.0 0.0 0.0 1400 1800 3200 

Trujillo 190 1.7 0.0 0.0 0.0 190 

Colorado totals 2600 1700 5400 22000 18000 50000 

New Mexico 

Abode Downs Ranch 12 39 300 1800 870 3000 

Alamo Mesa East 350 1200 360 0.0 0.0 2000 

Alamo Mesa West 900 1100 350 0.0 0.0 2300 

Anastacio Spring 0.0 0.0 0.0 67 3800 3900 

Archuleta 0.0 0.0 0.0 2500 1300 3800 

Arroyo Chijuillita 0.0 0.3 89 150 0.0 240 

Aztec 0.0 0.0 27 2100 210 2400 

Bancos Mesa 0.0 0.0 0.0 28 1700 1700 

Bancos Mesa Nw 0.0 0.0 0.0 680 1600 2300 

Billy Rice Canyon 0.0 0.0 0.0 520 1600 2100 

Bisti Trading Post 530 880 0.59 0.0 0.0 1400 

Bixler Ranch 0.0 0.0 0.0 0.0 1000 1000 

Blanco 0.0 0.0 1000 2600 49 3600

Geology and Coal Resources of the Upper Cretaceous Fruitland Fm., San Juan Basin, New Mexico and Colorado Q117
Table A6-1. Estimated Fruitland Formation coal resources (in millions of short tons) in five overburden categories by 

7.5’ quadrangle and State in beds 1.2 ft thick or greater, San Juan Basin, Colorado and New Mexico—Continued. 

Quadrangle Overburden (ft) Grand total 

 0-500 500-1000 1000-2000 2000-3000 >3000 

New Mexico—Continued

Blanco Trading Post 0.0 0.0 1500 0.0 0.0 1500 

Bloomfield 0.0 0.0 1600 410 0.0 2000 

Burnham Trading Post 970 40 0.0 0.0 0.0 1000 

Burnt Mesa 0.0 0.0 0.0 160 2800 3000 

Canada Ojitos 0.0 0.0 0.0 0.79 240 240 

Carracas Canyon 0.0 1.9 52 190 750 990 

Carson Trading Post 0.0 0.0 1700 0.0 0.0 1700 

Cedar Canyon 6 7.5 25 69 200 310 

Cedar Hill 0.0 0.0 0.0 1900 1300 3100 

Cement Lake 0.0 0.0 0.0 0.0 2000 2000 

Cordova Canyon 87 51 100 61 28 330 

Counselor 0.0 0.0 370 240 0.0 610 

Crow Mesa East 0.0 0.0 52 940 0.0 990 

Crow Mesa West 0.0 0.0 610 360 0.0 970 

Cuba 0.0 0.0 27 1 0.0 28 

Cutter Canyon 0.0 0.0 2.7 2300 840 3100 

Deer Mesa 0.0 26 370 0.13 0.0 400 

Delgadito Mesa 0.0 0.0 0.0 550 3800 4300 

Dulce 9.2 6.6 2.5 0.0 0.0 18 

East Fork Kutz Canyon 0.0 0.0 1700 530 0.0 2300 

Espinosa Ranch 0.0 0.0 0.0 0.0 2100 2100 

Farmington North 0.0 5.4 1800 530 0.0 2300 

Farmington South 0.0 51 1500 0.0 0.0 1600 

Fire Rock Well 910 840 0.0 0.0 0.0 1800 

Five Lakes Canyon NE 0.0 0.0 0.0 580 500 1100 

Five Lakes Canyon NW 0.0 0.0 5.3 470 290 760 

Flora Vista 0.0 0.0 1000 1200 0.0 2200 

Fourmile Canyon 0.0 0.0 0.0 0.0 3000 3000 

Fresno Canyon 0.0 0.0 320 2400 89 2900 

Fruitland 1100 86 0.0 0.0 0.0 1100 

Gallegos Trading Post 0.0 0.0 1900 0.0 0.0 1900 

Gobernador 0.0 0.0 0.0 0.0 2700 2700 

Gomez Ranch 0.0 0.0 0.0 270 3100 3300 

Gonzales Mesa 0.0 0.0 0.0 1800 480 2300 

Gould Pass 0.0 0.0 0.0 1600 1300 2900 

Horn Canyon 0.0 0.0 1600 3.9 0.0 1600 

Huerfanito Peak 0.0 0.0 230 2500 0.0 2700 

Huerfano Trading Post 0.0 0.0 630 970 0.0 1600 

Huerfano Trading Post NW 0.0 0.0 1400 180 0.0 1600 

Huerfano Trading Post SW 0.0 760 1300 0.0 0.0 2100 

Hugh Lake 0.0 0.0 1500 0.0 0.0 1500 

John Mills Lake 0.0 0.0 2.6 57 600 660 

Johnson Trading Post 95 96 51 0.0 0.0 240 

Kimbeto 260 1500 230 0.0 0.0 2000 

Kirtland 130 690 240 0.0 0.0 1100 

Kirtland SE 0.0 270 1300 0.0 0.0 1600 

Kirtland SW 1000 870 0.94 0.0 0.0 1900 

La Plata 190 190 550 1700 0.0 2700 

Laguna Gurule 0.0 0.06 0.73 35 950 990 

Lapis Point 0.0 0.0 0.0 550 2300 2800

Q118 Geologic Assessment of Coal in the Colorado Plateau: Arizona, Colorado, New Mexico, and Utah
Table A6-1. Estimated Fruitland Formation coal resources (in millions of short tons) in five overburden categories by 

7.5’ quadrangle and State in beds 1.2 ft thick or greater, San Juan Basin, Colorado and New Mexico—Continued. 

Quadrangle Overburden (ft) Grand total 

 0-500 500-1000 1000-2000 2000-3000 >3000 

New Mexico—Continued

Leandro Canyon 0.0 0.0 0.0 0.0 1900 1900 

Leavry Canyon 0.0 0.0 0.0 0.0 810 810 

Lindrith 0.0 0.0 0.0 180 2000 2200 

Los Indios Canyon 0.0 0.0 0.0 0.0 1.8 1.8 

Lybrook 0.0 2.6 480 180 0.0 660 

Lybrook NW 0.0 470 680 2.1 0.0 1100 

Lybrook SE 140 950 100 0.0 0.0 1200 

Mesa Portales 65 25 14 0.0 0.0 100 

Moncisco Wash 0.0 0.65 2900 0.0 0.0 2900 

Mule Dam 0.0 290 340 0.0 0.0 630 

Navajo Dam 0.0 0.0 0.0 710 3600 4300 

Newcomb NE 620 0.0 0.0 0.0 0.0 620 

Newcomb SE 190 0.0 0.0 0.0 0.0 190 

Ojito 0.0 0.0 0.0 0.0 2100 2100 

Ojo Encino Mesa 350 64 4.1 0.0 0.0 420 

Otero Store 0.0 0.0 0.0 1400 200 1600 

Pine Lake 0.0 0.0 0.0 0.0 2800 2800 

Pretty Rock 1400 7.4 0.0 0.0 0.0 1400 

Pueblo Alto Trading Post 570 13 0.0 0.0 0.0 580 

Pueblo Bonito 130 0.0 0.0 0.0 0.0 130 

Pueblo Bonito NW 1500 1000 0.82 0.0 0.0 2500 

Pueblo Pintado 61 0.0 0.0 0.0 0.0 61 

Purgatory Canyon 25 3.3 0.0 0.0 0.0 29 

Regina 0.0 0.12 15 73 110 190 

Rincon Marquez 1.2 0.0 0.0 0.0 0.0 1.2 

Santos Peak 0.0 0.0 0.0 250 3900 4100 

Sargent Ranch 440 63 0.0 0.0 0.0 500 

Schmitz Ranch 0.0 0.0 0.0 0.0 2900 2900 

Smouse Mesa 0.0 0.0 0.0 2300 0.0 2300 

Star Lake 760 250 0.0 0.0 0.0 1000 

Tafoya Canyon 0.0 0.0 9.6 1000 0.0 1000 

Tancosa Windmill 0.0 0.0 460 630 0.0 1100 

Tank Mountain 0.0 0.0 0.0 400 3000 3400 

Tanner Lake 580 0.0 0.0 0.0 0.0 580 

Taylor Ranch 0.0 0.0 100 180 0.0 280 

The Hogack North 0.36 0.0 0.0 0.0 0.0 0.36 

The Hogback South 640 0.0 0.0 0.0 0.0 640 

The Pillar 0.0 690 1800 0.0 0.0 2500 

The Pillar 3 NE 60 0.0 0.0 0.0 0.0 60 

The Pillar NW 1000 820 50 0.0 0.0 1900 

Thompson Mesa 0.0 0.0 550 1600 0.0 2200 

Tinian 47 0.0 0.0 0.0 0.0 47 

Turley 0.0 0.0 0.0 2000 1400 3400 

Vigas Canyon 0.0 0.0 0.0 0.0 3700 3700 

Waterflow 500 100 0.0 0.0 0.0 600 

Wirt Canyon 35 17 20 14 42 130 

Wolf Stand 62 0.0 0.0 0.0 0.0 62 

Youngs Lake 200 680 1100 0.0 0.0 2000 

New Mexico totals 16000 14000 34000 44000 70000 180000 

Grand totals 19000 16000 40000 66000 88000 230000 

Geology and Coal Resources of the Upper Cretaceous Fruitland Fm., San Juan Basin, New Mexico and Colorado Q119
Table A6-2. Estimated Fruitland Formation coal resources (in millions of short tons) in five overburden categories by 

township and State in beds 1.2 ft thick or greater, San Juan Basin, Colorado and New Mexico. 

[Township boundaries are shown on most of the San Juan Basin maps in this report. Coal tonnages are rounded to two significant 

figures. Totals may not add due to independent rounding. Note: T34N R3W(s): (s) is south of Ute line (fig. 28)] 

Township Overburden (ft) Grand total 

 0-500 500-1000 1000-2000 2000-3000 >3000 

Colorado 

T32N 1W 0.01 0.0 0.0 0.0 0.0 0.01 

T32N 1.5W 0.85 0.0 0.0 0.0 0.0 0.85 

T32N 2W 110 0.0 0.0 0.0 0.0 110 

T32N 3W 57 55 160 67 0.0 340 

T32N 4W 0.0 0.0 1.1 570 180 750 

T32N 5W 0.0 0.0 0.0 680 230 910 

T32N 6W 0.0 0.0 0.0 740 260 1000 

T32N 7W 0.0 0.0 0.0 4.8 1200 1200 

T32N 8W 0.0 0.0 0.0 0.0 1600 1600 

T32N 9W 0.0 0.0 0.0 240 1500 1800 

T32N 10W 0.0 0.0 0.0 180 1700 1900 

T32N 11W 6 51 330 1200 300 1900 

T32N 12W 200 62 32 0.0 0.0 290 

T33N 2W 53 0.0 0.0 0.0 0.0 53 

T33N 3W 230 81 68 0.0 0.0 380 

T33N 4W 22 120 470 410 170 1200 

T33N 5W 0.0 0.0 76 480 1100 1600 

T33N 6W 0.0 0.0 0.0 20 1900 1900 

T33N 7W 0.0 0.0 0.0 1800 240 2100 

T33N 8W 0.0 0.0 0.0 640 1100 1700 

T33N 9W 0.0 0.0 0.0 1400 1200 2500 

T33N 10W 0.0 0.0 0.0 1400 1900 3300 

T33N 11W 200 150 390 700 990 2400 

T33N 12W 12 0.0 0.0 0.0 0.0 12 

T34N 3W(s) 6.4 0.0 0.0 0.0 0.0 6.4 

T34N 4W(s) 130 110 38 0.0 0.0 280 

T34N 5W1

 210 230 500 540 520 2000 

T34N 6W1

 0.0 0.0 140 920 1600 2700 

T34N 7W1

 0.0 0.0 150 2200 3.3 2300 

T34N 8W1

 0.0 0.0 0.0 2700 0.0 2700 

T34N 9W1

 84 70 160 2600 68 3000 

T34N 10W(s) 400 150 490 1200 320 2600 

T34N 11W(s) 150 80 120 99 1.9 440 

T34.5N 9W 16 13 25 69 0.0 120 

T35N 5W 120 75 52 17 0.0 260 

T35N 6W 170 150 520 490 19 1300 

T35N 7W 130 130 840 390 0.0 1500 

T35N 8W 220 120 700 390 0.0 1400 

T35N 9W 57 46 93 110 0.0 310 

Colorado totals 2600 1700 5400 22000 18000 50000 

New Mexico 

T19N R2W 17 0.0 0.0 0.0 0.0 17 

T19N R3W 57 0.0 0.0 0.0 0.0 57 

T19N R4W 180 0.0 0.0 0.0 0.0 180 

T19N R5W 340 0.0 0.0 0.0 0.0 340 

T19N R6W 190 0.0 0.0 0.0 0.0 190

Q120 Geologic Assessment of Coal in the Colorado Plateau: Arizona, Colorado, New Mexico, and Utah
Table A6-2. Estimated Fruitland Formation coal resources (in millions of short tons) in five overburden categories by 

township and State in beds 1.2 ft thick or greater, San Juan Basin, Colorado and New Mexico—Continued. 

Township Overburden (ft) Grand total 

 0-500 500-1000 1000-2000 2000-3000 >3000 

New Mexico—Continued

T20N R2W 26 12 4.6 0.0 0.0 43 

T20N R3W 33 77 43 0.0 0.0 150 

T20N R4W 41 57 16 0.0 0.0 110 

T20N R5W 180 88 0.0 0.0 0.0 270 

T20N R6W 440 210 0.0 0.0 0.0 650 

T20N R7W 450 1.9 0.0 0.0 0.0 450 

T20N R8W 60 0.0 0.0 0.0 0.0 60 

T21N R1W 0.0 0.0 2.5 0.0 0.0 2.5 

T21N R2W 0.0 0.42 68 35 0.0 100 

T21N R3W 0.0 0.0 68 63 0.0 130 

T21N R4W 0.0 4.4 120 11 0.0 140 

T21N R5W 0.0 38 210 0.0 0.0 250 

T21N R6W 0.0 410 110 0.0 0.0 510 

T21N R7W 140 710 12 0.0 0.0 860 

T21N R8W 810 320 0.0 0.0 0.0 1100 

T21N R9W 220 0.0 0.0 0.0 0.0 220 

T21N R10W 8.5 0.0 0.0 0.0 0.0 8.5 

T22N R1W 0.0 0.0 29 27 0.0 56 

T22N R2W 0.0 0.0 11 250 1.8 260 

T22N R3W 0.0 0.0 0.0 270 0.0 270 

T22N R4W 0.0 0.0 160 66 0.0 230 

T22N R5W 0.0 0.0 510 0.0 0.0 510 

T22N R6W 0.0 0.0 290 6.4 0.0 300 

T22N R7W 0.0 110 250 0.0 0.0 360 

T22N R8W 6 790 150 0.0 0.0 940 

T22N R9W 250 620 0.0 0.0 0.0 870 

T22N R10W 1000 57 0.0 0.0 0.0 1100 

T22N R11W 510 0.0 0.0 0.0 0.0 510 

T22N R12W 72 0.0 0.0 0.0 0.0 72 

T22N R13W 6.8 0.0 0.0 0.0 0.0 6.8 

T23N R1W 0.0 0.18 1.8 20 100 120 

T23N R2W 0.0 0.0 0.0 420 550 980 

T23N R3W 0.0 0.0 0.0 170 420 590 

T23N R4W 0.0 0.0 7.3 630 94 730 

T23N R5W 0.0 0.0 180 330 0.0 510 

T23N R6W 0.0 0.0 100 280 0.0 380 

T23N R7W 0.0 0.0 250 180 0.0 430 

T23N R8W 0.0 33 550 2.4 0.0 590 

T23N R9W 0.0 680 360 0.0 0.0 1000 

T23N R10W 100 1200 120 0.0 0.0 1500 

T23N R11W 1200 450 0.0 0.0 0.0 1700 

T23N R12W 1000 0.0 0.0 0.0 0.0 1000 

T23N R13W 370 0.0 0.0 0.0 0.0 370 

T24N R1W 0.0 0.0 0.09 27 570 600 

T24N R2W 0.0 0.0 0.0 140 1100 1200 

T24N R3W 0.0 0.0 0.0 180 1100 1300 

T24N R4W 0.0 0.0 0.0 880 230 1100 

T24N R5W 0.0 0.0 0.0 760 0.0 760 

T24N R6W 0.0 0.0 11 490 0.0 500 

T24N R7W 0.0 0.0 27 500 0.0 530

Geology and Coal Resources of the Upper Cretaceous Fruitland Fm., San Juan Basin, New Mexico and Colorado Q121
Table A6-2. Estimated Fruitland Formation coal resources (in millions of short tons) in five overburden categories by 

township and State in beds 1.2 ft thick or greater, San Juan Basin, Colorado and New Mexico—Continued. 

Township Overburden (ft) Grand total 

 0-500 500-1000 1000-2000 2000-3000 >3000 

New Mexico—Continued

T24N R8W 0.0 0.0 320 190 0.0 510 

T24N R9W 0.0 0.0 770 0.0 0.0 770 

T24N R10W 0.0 96 890 0.0 0.0 990 

T24N R11W 5.7 920 330 0.0 0.0 1300 

T24N R12W 440 960 1.4 0.0 0.0 1400 

T24N R13W 480 660 0.0 0.0 0.0 1100 

T25N R1W 0.0 0.0 0.0 6.8 380 390 

T25N R2W 0.0 0.0 0.0 0.0 1400 1400 

T25N R3W 0.0 0.0 0.0 0.0 1500 1500 

T25N R4W 0.0 0.0 0.0 54 1300 1400 

T25N R5W 0.0 0.0 0.0 1000 360 1400 

T25N R6W 0.0 0.0 0.0 870 0.0 870 

T25N R7W 0.0 0.0 0.0 1000 0.0 1000 

T25N R8W 0.0 0.0 240 800 0.0 1000 

T25N R9W 0.0 0.0 730 130 0.0 860 

T25N R10W 0.0 0.0 1100 93 0.0 1200 

T25N R11W 0.0 0.47 840 0.0 0.0 840 

T25N R12W 0.0 87 1200 0.0 0.0 1200 

T25N R13W 0.0 270 1600 0.0 0.0 1900 

T25N R14W 4.8 950 410 0.0 0.0 1400 

T26N R1W 0.0 0.0 0.0 0.0 7.5 7.5 

T26N R2W 0.0 0.0 0.0 0.0 350 350 

T26N R3W 0.0 0.0 0.0 0.0 1800 1800 

T26N R4W 0.0 0.0 0.0 0.0 2100 2100 

T26N R5W 0.0 0.0 0.0 500 1700 2200 

T26N R6W 0.0 0.0 0.0 1100 520 1600 

T26N R7W 0.0 0.0 0.0 1700 0.0 1700 

T26N R8W 0.0 0.0 180 1300 0.0 1500 

T26N R9W 0.0 0.0 410 850 0.0 1300 

T26N R10W 0.0 0.0 240 660 0.0 890 

T26N R11W 0.0 0.0 1200 3.7 0.0 1200 

T26N R12W 0.0 0.0 1300 0.0 0.0 1300 

T26N R13W 0.0 0.0 1600 0.0 0.0 1600 

T26N R14W 0.0 100 670 0.0 0.0 770 

T27N R2W 0.0 0.0 0.0 0.0 62 62 

T27N R3W 0.0 0.0 0.0 0.0 1100 1100 

T27N R4W 0.0 0.0 0.0 0.0 1800 1800 

T27N R5W 0.0 0.0 0.0 0.0 2300 2300 

T27N R6W 0.0 0.0 0.0 170 2400 2600 

T27N R7W 0.0 0.0 0.0 740 910 1700 

T27N R8W 0.0 0.0 49 1700 69 1800 

T27N R9W 0.0 0.0 130 1400 0.0 1600 

T27N R10W 0.0 0.0 750 840 0.0 1600 

T27N R11W 0.0 0.0 1400 66 0.0 1400 

T27N R12W 0.0 0.0 910 0.0 0.0 910 

T27N R13W 0.0 0.0 790 0.0 0.0 790 

T27N R14W 0.0 18 900 0.0 0.0 920 

T27N R15W 130 480 83 0.0 0.0 680 

T27N R16W 320 0.0 0.0 0.0 0.0 320 

T28N R1W 0.0 0.0 0.0 5.4 33 39

Q122 Geologic Assessment of Coal in the Colorado Plateau: Arizona, Colorado, New Mexico, and Utah
Table A6-2. Estimated Fruitland Formation coal resources (in millions of short tons) in five overburden categories by 

township and State in beds 1.2 ft thick or greater, San Juan Basin, Colorado and New Mexico—Continued. 

Township Overburden (ft) Grand total 

 0-500 500-1000 1000-2000 2000-3000 >3000 

New Mexico—Continued

T28N R2W 0.0 0.0 0.0 0.0 810 810 

T28N R3W 0.0 0.0 0.0 0.0 1600 1600 

T28N R4W 0.0 0.0 0.0 0.0 1100 1100 

T28N R5W 0.0 0.0 0.0 0.0 1900 1900 

T28N R6W 0.0 0.0 0.0 16 1400 1500 

T28N R7W 0.0 0.0 0.0 730 1000 1800 

T28N R8W 0.0 0.0 0.0 1200 44 1200 

T28N R9W 0.0 0.0 43 1400 49 1500 

T28N R10W 0.0 0.0 920 440 0.0 1400 

T28N R11W 0.0 0.0 800 0.0 0.0 800 

T28N R12W 0.0 0.0 490 0.0 0.0 490 

T28N R13W 0.0 0.0 450 0.0 0.0 450 

T28N R14W 0.0 240 200 0.0 0.0 430 

T28N R15W 680 320 0.0 0.0 0.0 1000 

T28N R16W 240 0.0 0.0 0.0 0.0 240 

T29N R1W 7.1 13 32 73 59 180 

T29N R2W 0.0 0.0 0.0 0.0 820 820 

T29N R3W 0.0 0.0 0.0 0.0 910 910 

T29N R4W 0.0 0.0 0.0 0.0 1000 1000 

T29N R5W 0.0 0.0 0.0 0.0 1300 1300 

T29N R6W 0.0 0.0 0.0 0.0 2000 2000 

T29N R7W 0.0 0.0 0.0 13 2600 2600 

T29N R8W 0.0 0.0 0.0 980 960 1900 

T29N R9W 0.0 0.0 150 1800 38 2000 

T29N R10W 0.0 0.0 1100 630 0.0 1700 

T29N R11W 0.0 0.0 610 96 0.0 700 

T29N R12W 0.0 0.0 1300 0.0 0.0 1300 

T29N R13W 0.0 54 990 0.0 0.0 1000 

T29N R14W 63 550 180 0.0 0.0 800 

T29N R15W 690 75 0.0 0.0 0.0 770 

T29N R16W 0.24 0.0 0.0 0.0 0.0 0.24 

T30N R1W 72 31 55 22 1.1 180 

T30N R2W 0.0 0.0 19 68 420 510 

T30N R3W 0.0 0.0 0.0 0.0 280 280 

T30N R4W 0.0 0.0 0.0 0.0 1100 1100 

T30N R5W 0.0 0.0 0.0 43 1300 1300 

T30N R6W 0.0 0.0 0.0 240 2200 2400 

T30N R7W 0.0 0.0 0.0 420 2200 2600 

T30N R8W 0.0 0.0 0.0 1500 630 2100 

T30N R9W 0.0 0.0 0.0 1600 180 1800 

T30N R10W 0.0 0.0 0.0 950 750 1700 

T30N R11W 0.0 0.0 170 1500 0.0 1600 

T30N R12W 0.0 0.0 810 440 0.0 1200 

T30N R13W 0.0 0.0 1200 130 0.0 1300 

T30N R14W 11 310 1000 0.0 0.0 1300 

T30N R15W 390 260 0.18 0.0 0.0 650 

T31N R1W 18 15 2.1 0.0 0.0 35 

T31N R2W 15 10 32 31 110 200 

T31N R3W 0.0 0.0 0.0 0.0 110 110 

T31N R4W 0.0 0.0 0.0 0.0 950 950

Geology and Coal Resources of the Upper Cretaceous Fruitland Fm., San Juan Basin, New Mexico and Colorado Q123
Table A6-2. Estimated Fruitland Formation coal resources (in millions of short tons) in five overburden categories by 

township and State in beds 1.2 ft thick or greater, San Juan Basin, Colorado and New Mexico—Continued. 

Township Overburden (ft) Grand total 

 0-500 500-1000 1000-2000 2000-3000 >3000 

New Mexico—Continued

T31N R5W 0.0 0.0 0.0 25 1000 1100 

T31N R6W 0.0 0.0 0.0 140 950 1100 

T31N R7W 0.0 0.0 0.0 310 1500 1800 

T31N R8W 0.0 0.0 0.0 140 2500 2700 

T31N R9W 0.0 0.0 0.0 360 2000 2300 

T31N R10W 0.0 0.0 0.0 1000 750 1800 

T31N R11W 0.0 0.0 0.0 1200 88 1300 

T31N R12W 0.0 0.0 0.0 1300 14 1400 

T31N R13W 37 62 470 1000 0.0 1600 

T32N R2W 11 1 0.0 0.0 0.0 12 

T32N R3W 15 14 61 110 57 250 

T32N R4W 0.0 0.0 0.0 98 620 720 

T32N R5W 0.0 0.0 0.0 5 940 940 

T32N R6W 0.0 0.0 0.0 550 700 1200 

T32N R7W 0.0 0.0 0.0 41 1400 1500 

T32N R8W 0.0 0.0 0.0 0.0 1500 1500 

T32N R9W 0.0 0.0 0.0 0.0 1200 1200 

T32N R10W 0.0 0.0 0.0 770 990 1800 

T32N R11W 0.0 0.0 0.0 250 1500 1700 

T32N R12W 55 79 420 870 210 1600 

T32N R13W 110 93 190 540 0.0 940 

Unsurveyed2

 4400 1600 400 0.0 0.0 6400 

N. Mex. totals 16000 14000 34000 44000 70000 180000 

Grand totals 19000 16000 40000 66000 88000 230000 

1 T34N is present as two tiers of townships; one north and one south of the Ute line (fig. 28). Coal tonnages shown for each of 

these five townships are totals for the two townships. 

2 Unsurveyed areas are not bounded by official township boundaries and are all Tribal lands.

Q124 Geologic Assessment of Coal in the Colorado Plateau: Arizona, Colorado, New Mexico, and Utah
Table A6-3. Estimated Fruitland Formation coal resources (in millions of short tons) in five overburden categories by surface 

ownership and by State in beds 1.2 ft thick or greater, San Juan Basin, Colorado and New Mexico. 

[Surface ownership is shown on figure A5-2. Non-Federal surface includes State, private, and Tribal land. Coal tonnages are rounded to two 

significant figures. Totals may not add due to independent rounding] 

State Surface owner Overburden (ft) Grand totals 

 0-500 500-1000 1000-2000 2000-3000 >3000 

Colorado Federal 520 360 700 1800 2200 5500 

 Non-Federal 2100 1300 4700 21000 16000 44000 

Colorado totals 2600 1700 5400 22000 18000 50000 

New Mexico Federal 4600 6000 12000 28000 39000 89000 

 Non-Federal 11000 8200 23000 16000 31000 89000 

New Mexico totals 16000 14000 34000 44000 70000 180000 

Grand Total 19000 16000 40000 66000 88000 230000 

Table A6-4. Estimated Fruitland Formation coal resources (in millions of short tons) in five overburden categories by coal ownership 

and State in beds 1.2 ft thick or greater, San Juan Basin, Colorado and New Mexico. 

[Coal ownership is shown on figure A5-3. Non-Federal surface includes State, private, and Tribal land. Coal tonnages rounded to two significant 

figures. Totals may not add due to independent rounding] 

 Overburden (ft) 

State Coal Ownership 0-500 500-1000 1000-2000 2000-3000 >3000 Grand totals 

Colorado Federal 1100 680 1800 11000 6200 21000 

 Non-Federal 1500 1000 3500 12000 12000 29000 

Colorado totals 2600 1700 5400 22000 18000 50000 

New Mexico Federal 6400 7700 18000 31000 48000 110000 

 Non-Federal 9500 6400 16000 14000 21000 67000 

New Mexico totals 16000 14000 34000 44000 70000 180000 

Grand Total 19000 16000 40000 66000 88000 230000 

Geology and Coal Resources of the Upper Cretaceous Fruitland Fm., San Juan Basin, New Mexico and Colorado Q125
Table A6-5. Estimated Fruitland Formation coal resources (in millions of short tons) in beds 1.2 ft thick or greater, San Juan Basin, Colorado and New Mexic

[Resources are given in five overburden categories; five thickness categories; and by county, State, and reliability category. Distribution of coal resources by net-thickness catCoal tonnages rounded to two significant figures. Totals may not add due to independent rounding]

 0-500 ft overburden 0-500 500-1000 ft overburden 500-1000 1000-2000 ft ove

County Reliability Net-coal thickness categoriy total Net-coal thickness categoriy total Net-coal thicknes

 1.2-2.3 2.3-3.5 3.5-7.0 7.0-14.0 >14.0 1.2-2.3 2.3-3.5 3.5-7.0 7.0-14.0 >14.0 1.2-2.3 2.3-3.5 3.5-7.0 

Colorado 

Archuleta Identified 0 0 5.8 100 250 360 0 0 0 98 300 400 0 0 0  Hypothetical 7.5 11 88 130 380 610 0 0 0 1.2 290 290 0 0 0 Archuleta total 7.5 11 93 230 630 970 0 0 0 99 590 690 0 0 0 La Plata Identified 0 0 0 0 1600 1600 0 0 0 0 1000 1000 0 0 0  Hypothetical 0 0 0 0 16 16 0 0 0 0 1.3 1.3 0 0 0 La Plata total 0 0 0 0 1600 1600 0 0 0 0 1000 1000 0 0 0 Colorado total 7.5 11 93 230 2200 2600 0 0 0 99 1600 1700 0 0 0 

New Mexico 

McKinley Identified 1.3 8 33 440 1200 1700 16 25 23 69 170 300 0 0 0  Hypothetical 0 0 0 0.21 5 5.2 0 0 0 0 0 0 0 0 0 McKinley total 1.3 8 33 440 1200 1700 16 25 23 69 170 300 0 0 0 Rio Arriba Identified 1.7 3.9 17 18 0 41 1 0.7 4.9 21 0.0 28 3.6 4.2 28  Hypothetical 2.5 4.2 35 54 0 96 1.2 1.7 13 42 0.0 57 0.59 1.2 20 Rio Arriba total 4.3 8.1 52 72 0 140 2.2 2.4 18 63 0.0 85 4.2 5.4 48 San Juan Identified 0 0 12 530 7800 8400 0 0 0 320 9000 9300 0 0 35  Hypothetical 0 0 33 610 4600 5300 0 0 0 17 3000 3100 0 0 0.49 San Juan total 0 0 44 1100 12000 14000 0 0 0 340 12000 12000 0 0 35 Sandoval Identified 65 52 92 48 140 400 33 64 100 350 870 1400 48 160 680  Hypothetical 2.9 6.3 0 83 0 93 0 0 0 0.04 0 0.04 12 34 17 Sandoval total 68 58 92 130 140 490 33 64 100 350 870 1400 60 190 700 New Mexico total 74 74 220 1800 14000 16000 51 91 140 820 13000 14000 64 200 780 Grand total 81 85 310 2000 16000 19000 51 91 140 920 15000 16000 64 200 780 
Table A6-5. Estimated Fruitland Formation coal resources (in millions of short tons) in beds 1.2 ft thick or greater, San Juan Basin, Colorado and 

Continued. 

 2000-3000 ft overburden 2000-3000 >3000 ft overburden 

County Reliability Net-coal thickness categoriy total Net-coal thickness categoriy 

 1.2-2.3 2.3-3.5 3.5-7.0 7.0-14.0 >14.0 1.2-2.3 2.3-3.5 3.5-7.0 7.0-14.0 >14.0 

Colorado 

Archuleta Identified 0 0 0 0 2500 2500 0 0 0 0 2500  Hypothetical 0 0 0 0 660 660 0 0 0 0 1100 Archuleta total 0 0 0 0 3100 3100 0 0 0 0 3600 La Plata Identified 0 0 0 0 19000 19000 0 0 0 0 14000 1 Hypothetical 0 0 0 0 0 0 0 0 0 0 0 La Plata total 0 0 0 0 19000 19000 0 0 0 0 14000 1Colorado total 0 0 0 0 22000 22000 0 0 0 0 18000 1

New Mexico 

Mc Kinley Identified 0 0 0 0 0 0 0 0 0 0 0  Hypothetical 0 0 0 0 0 0 0 0 0 0 0 Mc Kinley total 0 0 0 0 0 0 0 0 0 0 0 Rio Arriba Identified 7.7 13 140 1300 12000 13000 16 32 200 1400 50000 5 Hypothetical 1.2 2.5 19 150 1.1 180 4.6 7.8 40 260 790 Rio Arriba total 9 15 160 1500 12000 13000 21 40 240 1700 51000 5San Juan Identified 0 0 0 340 29000 29000 0 0 0 8.1 17000  Hypothetical 0 0 0 0 7.2 7.2 0 0 0 0 42 San Juan total 0 0 0 340 29000 29000 0 0 0 8.1 17000 1Sandoval Identified 16 89 400 740 460 1700 0.23 0.75 6 67 170  Hypothetical 0 7.3 5.9 0 0 13 0 0 0 0 0 Sandoval total 16 96 400 740 460 1700 0.23 0.75 6 67 170 New Mexico total 25 110 570 2600 41000 44000 21 40 250 1700 68000 7Grand total 25 110 570 2600 63000 66000 21 40 250 1700 86000 8
ARCHULETA

LA PLATA

SAN JUAN

McKINLEY

RIO ARRIBA

SANDOVAL

MONTEZUMA

108° 107°

 37° 37°

 36° 36°

108° 107°

COLORADO

NEW MEXICO

Outcrop of Fruitland

 Formation

Kf

Kf

Farmington

Dulce

Ignacio

Durango

Cuba

0 5 10 15 20 MILES

R 13 W

R 16 W 15

T 19 N

20

21

22

23

24

25

26

27

28

29

30

31

32

32

33

34

T 35 N

R 1 W R 1 E

R 1.5 W

2

R 1 W

2.5 R 16 W 15 14 13 12 11 10 9 8 7 6 5 4 3

6 5 4 3 2

7

8

9

10

11 12

T 34 N

 (NUL)

T 34 N

 (SUL)

R 1 W R 1 E

2 13 12 11 10 9 8 7 6 5 4 3

14

T 34.5 N

T 34 N (NUL)

T 34 N

 (SUL)

San Pablo 

Pueblo

 Pintado 

Fire Rock Cuba 

Well 

Lybrook Gallina 

Tanner Lake

The Pillar

3 NE 

French

Mesa Laguna

 Gurule Lindrith Tafoya

 Canyon 

Burnham

Trading Post 

Newcomb

SE 

Canada Llaves

Ojitos 

Smouse Ojito 

Mesa

Thompson

Mesa 

The Pillar The Pillar 

NW 

Newcomb

NE 

Los Indios

Canyon 

Fresno

 Canyon 

The

Hogback

South 

Cedar

 Canyon 

Cement

Lake

Delgadito

Mesa 

Cutter

Canyon 

Kirtland 

Cordova

 Canyon 

Gomez Navajo Ranch Dam 

Youngs

Lake Waterflow 

Dulce Burnt

Mesa 

Abode

Downs

 Ranch 

La

Plata 

Purgatory

Canyon

Edith 

Pagosa Trujillo Junction Long Ignacio Pinkerton Mountain 

Mesa 

Oakbrush

Hill 

Lonetree

Canyon 

Chimney

Rock 

Gem

Village

Loma

Basin Linda 

Mountain 

Kline 

Baldy

 Mountain 

Durango

West 

Tiffany 

Bayfield 

Bondad Redmesa Hill

Fruitland 

Huerfanito

Peak 

East Fork

Kutz Canyon

Gallegos

Trading Post Hugh Lake 

Fourmile

Canyon 

Horn Bloomfield Blanco

Canyon

Farmington

South

Farmington Flora Vista Aztec Turley Archuleta North

Bancos

Mesa NW 

Anastacio

Spring

Tank

Mountain 

Cedar

Hill 

Leavry

Canyon 

Vigas

Canyon Kirtland SE Gould Pass Santos Peak Kirtland SW

Leandro

Canyon 

The Hogack Gobernador North

John Mills

Lake 

Bixler

 Ranch 

Espinosa

Ranch 

Wirt

Canyon

Carracas

Canyon Bancos

Mesa

Five Lakes Regina

Canyon NE 

Five Lakes

Canyon NW 

Tancosa Counselor Windmill

Billy Rice

Canyon 

Otero

Store

Crow Mesa

East 

Schmitz

Ranch 

Lapis

Point

Gonzales

Mesa 

Pounds

Mesa

Kimbeto Lybrook NW Pueblo

Bonito NW

Pretty

Rock

Crow Mesa

West 

Blanco

Trading Post 

Huerfano 

Trading

Post SW

Alamo Mesa

East 

Alamo Mesa

West 

Bisti

Trading Post 

Huerfano

Trading Post

Huerfano

Trading

Post NW

Carson

Trading Post 

Moncisco

Wash 

Wolf Stand Tinian Rincon

Marquez 

Johnson

Trading Post 

Ojo Encino

Mesa 

Star Lake 

Sargent Mule Dam Deer Mesa Taylor Ranch 

Ranch 

Pueblo

 Bonito 

Pueblo Alto

 Trading Post 

Durango

East Rules

Hill Ludwig

Mountain 

Allison Carracas 

Pargin

Mountain 

Mesa

Portales 

Lybrook SE 

Pine Lake 

Arroyo

Chijuillita 

COLORADO

NEW MEXICO

Study

area

 "T 34 N (NUL)" is north of Ute line, "T 34 N (SUL)"

 is south of Ute line. 

Figure A6-1. Map showing 71⁄2-minute topographic quadrangles in the San Juan Basin.

Q128 Geologic Assessment of Coal in the Colorado Plateau: Arizona, Colorado, New Mexico, and Utah
ARCHULETA

LA PLATA

SAN JUAN

McKINLEY

RIO ARRIBA

SANDOVAL

MONTEZUMA

108 107 

 37 37 

 36 36 

108 107 

COLORADO

NEW MEXICO

Outcrop of Fruitland

 Formation

Farmington

Dulce

Ignacio

Durango

Cuba

0 5 10 15 20 MILES

R 13 W

R 16 W 15

T 19 N

20

21

22

23

24

25

26

27

28

29

30

31

32

32

33

34

T 35 N

R 1 W R 1 E

R 1.5 W

2

R 1 W

2.5 R 16 W 15 14 13 12 11 10 9 8 7 6 5 4 3

6 5 4 3 2

7

8

9

10

11 12

T 34 N

 (NUL)

T 34 N

 (SUL)

R 1 W R 1 E

2 13 12 11 10 9 8 7 6 5 4 3

14

T 34.5 N

T 34 N (NUL)

T 34 N

 (SUL)

Study

area

COLORADO

NEW MEXICO

Federal surface

Non-Federal surface 1

1

 Includes State, Indian, and private lands

EXPLANATION

Figure A6-2. Map showing Federal and non-Federal surface ownership for the San Juan Basin.

Geology and Coal Resources of the Upper Cretaceous Fruitland Fm., San Juan Basin, New Mexico and Colorado Q129
ARCHULETA

LA PLATA

SAN JUAN

McKINLEY

RIO ARRIBA

SANDOVAL

MONTEZUMA

108 107 

 37 37 

 36 36 

108 107 

COLORADO

Outcrop of Fruitland

 Formation

Farmington

Dulce

Ignacio

Durango

Cuba

0 5 10 15 20 MILES

R 13 W

R 16 W 15

T 19 N

20

21

22

23

24

25

26

27

28

29

30

31

32

32

33

34

T 35 N

R 1 W R 1 E

R 1.5 W

2

R 1 W

2.5 R 16 W 15 14 13 12 11 10 9 8 7 6 5 4 3

6 5 4 3 2

7

8

9

10

11 12

T 34 N

 (NUL)

T 34 N

 (SUL)

R 1 W R 1 E

2 13 12 11 10 9 8 7 6 5 4 3

14

T 34.5 N

T 34 N (NUL)

T 34 N

 (SUL)

Study

area

COLORADO

NEW MEXICO

Federal coal

Non-Federal coal1

1

 Includes State, Indian, and private

 coal lands

EXPLANATION

Figure A6-3. Map showing coal ownership in the San Juan Basin.

Q130 Geologic Assessment of Coal in the Colorado Plateau: Arizona, Colorado, New Mexico, and Utah
14

14

14 14

14

14

14

14

14

14

14

14

14

14

14

14

14

14

14

14

14

14

7

7

7 7

7

7

3.5

3.5

3.5

3.5

3.5 3.5

3.5

3.5

2.3

2.3

2.3

2.3

2.3

2.3

1.2

1.2

2.3

7

1.2

7

7

2.3

R 13 W

R 14 W

R 15 W

R 16 W 15

T 19 N

20

21

22

23

24

25

26

27

28

29

30

31

32

32

33

34

T 35 N

R 1 W R 1 E

R 1.5 W

2

R 1 W

2.5 R 16 W 15 14 13 12 11 10 9 8 7 6 5 4 3

6 5 4 3 2

7

8

9

10

11

12

T 34 N

 (NUL)

T 34 N

 (SUL)

R 1 W R 1 E

2 13 12 11 10 9 8 7 6 5 4 3

14

0 5 10 15 20 MILES

108° 107°

 37° 37°

 36° 36°

108° 107°

ARCHULETA

LA PLATA

SAN JUAN

McKINLEY

RIO ARRIBA

SANDOVAL

MONTEZUMA

T 34.5 N

T 34 N (NUL)

T 34 N

 (SUL)

Farmington

Cuba

Dulce

Ignacio

Durango

Outcrop of Fruitland

 Formation

COLORADO

NEW MEXICO

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EXPLANATION

Control points are oil or gas wells, dry holes,

or coal-test holes

COAL THICKNESS CATEGORIES (in feet)

1.2- 2.3 2.3-3.5

3.5-7.0 7.0-14.0 > 14.0

< 1.2

COLORADO

NEW MEXICO

Study

area

Coal thicknesses at control points are total net coal

 in beds 1.2 ft thick or greater. Coal measurements

 are from density logs or drill-core. A maximum

 density of 1.75 gm/cubic cm was used as a cutoff

 for coal measurements on density logs. "T 34 N

 (NUL)" is north of Ute line, "T 34 N (SUL)" is

 south of Ute line. Kf = Fruitland Formation. 

Kf

Kf

Figure A6-4. Map showing distribution of net Fruitland coal in standard USGS thicknesses categories in the San Juan Basin.

Geology and Coal Resources of the Upper Cretaceous Fruitland Fm., San Juan Basin, New Mexico and Colorado Q131
Click on image below to bring up high-resolution image of plate 1.

Plate 1. Stratigraphic cross section trending northeast across San Juan Basin showing stratigraphy and Fruitland coal-bed correlations.

National Coal

Resource

Assessment

Click here to return to Disc 1 

Volume Table of Contents

Q132 Geologic Assessment of Coal in the Colorado Plateau: Arizona, Colorado, New Mexico, and Utah