Chapter 2

Nahcolite Resources in the Green River 

Formation, Piceance Basin, Colorado

By Michael E. Brownfield, Tracey J. Mercier, Ronald C. Johnson, and 

Jesse G. Self

Chapter 2 of 7

Oil Shale and Nahcolite Resources of the Piceance 

Basin, Colorado

By U.S. Geological Survey Oil Shale Assessment Team

U.S. Geological Survey Digital Data Series DDS–69–Y

U.S. Department of the Interior

U.S. Geological Survey

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Volume Title Page
U.S. Department of the Interior

KEN SALAZAR, Secretary

U.S. Geological Survey

Marcia K. McNutt, Director

U.S. Geological Survey, Reston, Virginia: 2010

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Suggested citation:

Brownfield, M.E., Mercier, T.J., Johnson, R.C., and Self, J.G., 2010, Nahcolite resources in the Green River Formation, 

Piceance Basin, Colorado: U.S. Geological Survey Digital Data Series DDS–69–Y, chp. 2, 51 p.

ISBN: 1–4113–2668–2
iii

Contents

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

Introduction.....................................................................................................................................................1

Location and Geologic Setting ....................................................................................................................4

Stratigraphy ....................................................................................................................................................7

Geology of the Nahcolite Deposits .............................................................................................................7

Nahcolite Resource Methodology............................................................................................................19

Calculating Nahcolite Content..........................................................................................................19

Calculating Nahcolite Resources ....................................................................................................20

Nahcolite Resources...................................................................................................................................22

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

Summary........................................................................................................................................................35

References Cited..........................................................................................................................................50

Plates

1. West to east cross section of halite and nahcolite beds and oil shale zones of 

the Parachute Creek Member of the Green River Formation in the north-central 

part of the Piceance Basin, northwestern Colorado......................................................... link

2. North to south cross section of halite and nahcolite beds and oil shale zones of 

the Parachute Creek Member of the Green River Formation in the 

north-central part of the Piceance Basin, northwestern Colorado ................................ link

Figures

1. Geologic map of northwest Colorado showing generalized outcrops of the 

Mesaverde Formation and Group, and the Wasatch, Green River, and 

Uinta Formations in the Piceance Basin, northwestern Colorado.......................................2

2. Stratigraphic column and correlation chart of stratigraphic nomenclature for 

oil shale zones for the Green River Formation, north-central 

Piceance Basin, Colorado...........................................................................................................2

3. Plot showing oil-yield (GPT) and nahcolite (weight percent) histograms and 

stratigraphic nomenclature for oil shale zones for the Wolf Ridge Minerals 

Corp., Dunn 20-1 core hole, north-central Piceance Basin, Colorado.................................3

4. Photograph showing Superior Oil Company’s nahcolite quarry located 

near the mouth of Piceance Creek, Piceance Basin, northwest Colorado ........................5

5. Photograph showing nahcolite nodules or aggregates in the R-5 oil shale 

zone in the Superior quarry.........................................................................................................5

6. Photographs showing site of the U.S. Bureau of Mine’s deep shaft project in the 

Piceance Basin, northwest Colorado........................................................................................6

7. Photograph showing excavated face in the Horse Draw Mine ...........................................7

8. Geologic map of northwest Colorado showing generalized outcrops of the 

Mesaverde Formation and Group, and the Wasatch, Green River, and 

Uinta Formations...........................................................................................................................8
iv

9. Map of northwest Colorado showing nahcolite-bearing core holes, cross 

section lines, and generalized area of the oil shale-bearing rocks in the 

Parachute Creek and Garden Gulch Members of the Green River 

Formation in the Piceance Basin, northwest Colorado........................................................11

10. Photograph showing drill core containing bands of light-brown nahcolite, 

small nodules of nahcolite, and nahcolite aggregates of bladed crystals in oil shale...13

11. Photograph showing drill core containing white, coarse crystals of nahcolite, 

small nodules of nahcolite, and dark-brown nahcolite aggregates of 

bladed crystals in oil shale........................................................................................................13

12. Photograph showing drill core containing alternating beds of light-brown 

nahcolite and oil shale...............................................................................................................14

13. Photograph showing drill core containing alternating beds of deeply dissolved 

halite and brown resistant wafer-like nahcolite....................................................................14

14. Photograph showing drill core containing collapsed breccia and brown 

nahcolite and oil shale...............................................................................................................15

15. Map of northwest Colorado showing nahcolite-bearing core holes and the 

inferred boundaries of the nahcolite-bearing zone and the saline zone of 

Pitman and others (1989)...........................................................................................................16

16. Chart showing oil yields, nahcolite contents, and rich and lean oil shale zones 

for C0034 core hole, north-central Piceance Basin, Colorado............................................17

17. Chart showing oil yields, nahcolite contents, and rich and lean oil shale 

zones for C0154 core hole, north-central Piceance Basin, Colorado................................18

18. Isopleth map showing in-place nahcolite (NaHCO3) resources in the R-2 oil 

shale zone in the Parachute Creek Member of the Green River Formation, 

Rio Blanco County, northwestern Colorado...........................................................................24

19. Map showing in-place nahcolite (NaHCO3) resources in the R-2 oil shale 

zone in the Parachute Creek Member of the Green River Formation by 

township, Rio Blanco County, northwestern Colorado.........................................................25

20. Isopleth map showing in-place nahcolite (NaHCO3) resources in the L-2 oil 

shale zone in the Parachute Creek Member of the Green River Formation, 

Piceance Basin, Rio Blanco County, northwestern Colorado.............................................27

21. Map showing in-place nahcolite (NaHCO3) resources in the L-2 oil shale 

zone in the Parachute Creek Member of the Green River Formation by 

township, Rio Blanco County, northwestern Colorado.........................................................28

22. Isopleth map showing in-place nahcolite (NaHCO3) resources of R-3 oil 

shale zone in the Parachute Creek Member of the Green River Formation, 

Piceance Basin, Rio Blanco County, northwestern Colorado.............................................30

23. Map showing in-place nahcolite (NaHCO3) resources in the R-3 oil shale zone 

in the Parachute Creek Member of the Green River Formation by township, 

Rio Blanco County, northwestern Colorado...........................................................................31

24. Isopleth map showing in-place nahcolite (NaHCO3) resources of L-3 oil 

shale zone in the Parachute Creek Member of the Green River Formation, 

Piceance Basin, Rio Blanco County, northwestern Colorado.............................................32

25. Map showing in-place nahcolite (NaHCO3) resources in the L-3 oil shale zone 

in the Parachute Creek Member of the Green River Formation 

by township, Rio Blanco County, northwestern Colorado ...................................................33

26. Isopleth map showing in-place nahcolite (NaHCO3) resources of R-4 oil 

shale zone in the Parachute Creek Member of the Green River Formation, 

Piceance Basin, Rio Blanco County, northwestern Colorado.............................................34
v

27. Map showing in-place nahcolite (NaHCO3) resources in the R-4 oil shale zone 

in the Parachute Creek Member of the Green River Formation, by township, 

Rio Blanco County, northwestern Colorado...........................................................................36

28. Isopleth map showing in-place nahcolite (NaHCO3) resources of L-4 zone 

in the Parachute Creek Member of the Green River Formation, Piceance 

Basin, Rio Blanco County, northwestern Colorado...............................................................37

29. Map showing in-place nahcolite (NaHCO3) resources in the L-4 oil shale zone 

in the Parachute Creek Member of the Green River Formation, by township, 

Rio Blanco County, northwestern Colorado...........................................................................38

30. Isopleth map showing in-place nahcolite (NaHCO3) resources of R-5 oil shale 

zone in the Parachute Creek Member of the Green River Formation, 

Piceance Basin, Rio Blanco County, northwestern Colorado.............................................40

31. Map showing in-place nahcolite (NaHCO3) resources in the R-5 oil shale zone 

in the Parachute Creek Member of the Green River Formation, by township, 

Rio Blanco County, northwestern Colorado...........................................................................41

32. Isopleth map showing in-place nahcolite (NaHCO3) resources of L-5 oil 

shale zone in the Parachute Creek Member of the Green River Formation, 

Piceance Basin, Rio Blanco County, northwestern Colorado.............................................43

33. Map showing in-place nahcolite (NaHCO3) resources in the L-5 oil shale zone 

in the Parachute Creek Member of the Green River Formation, by township, 

Rio Blanco County, northwestern Colorado...........................................................................44

34. Map showing thickness of nahcolite-bearing interval in the lower and upper 

parts of the Parachute Creek Member of the Green River Formation, 

Piceance Basin, Rio Blanco County, northwestern Colorado.............................................45

35. Isopleth map showing average nahcolite (NaHCO3) content of 

nahcolite-bearing interval in the lower and upper parts of the 

Parachute Creek Member of the Green River Formation, Piceance Basin, 

Rio Blanco County, northwestern Colorado...........................................................................46

36. Isopleth map showing total in-place nahcolite (NaHCO3) resources in the 

nahcolite-bearing interval in the lower and upper parts of the Parachute 

Creek and Garden Gulch Members of the Green River Formation, 

Piceance Basin, Rio Blanco County, northwestern Colorado.............................................47

37. Map showing total in-place nahcolite (NaHCO3) resources of the lower 

and middle parts of the Parachute Creek Member of the Green River 

Formation by township, Rio Blanco County, northwestern Colorado ................................49

Tables

1. Map number, USGS unique identification number, operator, drill hole name, and

location data for nahcolite-bearing core holes from the Piceance Basin, 

northwest Colorado......................................................................................................................9

2. Column names and definitions found in the nahcolite data spreadsheet.........................20

3. Total in-place nahcolite resources and average tons per acre, by township, in 

the R-2 oil shale zone in the nahcolite-bearing interval of the Parachute 

Creek Member of the Green River Formation, Piceance Basin, Rio 

Blanco County, northwestern Colorado..................................................................................26
vi

4. Total in-place nahcolite resources and average tons per acre, by township, 

in the L-2 oil shale zone in the nahcolite-bearing interval of the Parachute 

Creek Member of the Green River Formation, Piceance Basin, Rio 

Blanco County, northwestern Colorado..................................................................................26

5. Total in-place nahcolite resources and average tons per acre, by township, 

in the R-3 oil shale zone in the nahcolite-bearing interval of the Parachute 

Creek Member of the Green River Formation, Piceance Basin, Rio 

Blanco County, northwestern Colorado..................................................................................29

6. Total in-place nahcolite resources and average tons per acre, by township, 

in the L-3 oil shale zone in the nahcolite-bearing interval of the Parachute 

Creek Member of the Green River Formation, Piceance Basin, Rio 

Blanco County, northwestern Colorado..................................................................................29

7. Total in-place nahcolite resources and average tons per acre, by township, 

in the R-4 oil shale zone in the nahcolite-bearing interval of the Parachute 

Creek Member of the Green River Formation, Piceance Basin, Rio 

Blanco County, northwestern Colorado..................................................................................39

8. Total in-place nahcolite resources and average tons per acre, by township, 

in the L-4 oil shale zone in the nahcolite-bearing interval of the Parachute 

Creek Member of the Green River Formation, Piceance Basin, Rio 

Blanco County, northwestern Colorado..................................................................................39

9. Total in-place nahcolite resources and average tons per acre, by township, 

in the R-5 oil shale zone in the nahcolite-bearing interval of the Parachute 

Creek Member of the Green River Formation, Piceance Basin, Rio 

Blanco County, northwestern Colorado..................................................................................42

10. Total in-place nahcolite resources and average tons per acre, by township, 

in the L-5 oil shale zone in the nahcolite-bearing interval of the Parachute 

Creek Member of the Green River Formation, Piceance Basin, Rio 

Blanco County, northwestern Colorado..................................................................................42

11. Total in-place nahcolite resources and average tons per acre, by township, 

in the nahcolite-bearing interval of the Parachute Creek Member of the 

Green River Formation, Piceance Basin, Rio Blanco County, 

northwestern Colorado..............................................................................................................48
Abstract

Nahcolite (NaHCO3) is present in the oil shale deposits 

of the Parachute Creek Member of the Eocene Green River 

Formation in the Piceance Basin, northwest Colorado. Here 

nahcolite forms disseminated aggregates, nodules, bedded 

units of disseminated brown crystals, and white crystalline 

beds associated with dawsonite (NaAl(OH)2

CO3) and halite 

(NaCl). Nahcolite-bearing facies includes a lower part containing the nahcolite and halite, which is estimated to be as thick 

as 1,130 ft, and an upper leached part several hundreds of 

feet thick containing minor nahcolite aggregates and nodules. 

Locally thick beds of halite and brown, fine-grained nahcolite 

are found at the depocenter of the basin and thin away from 

the basin center grading laterally into beds of white, coarsegrained nahcolite. The top of the nahcolitic-bearing rocks in 

the central part of the study area range in depth from about 

1,300 to 2,000 ft below ground surface.

Dissolution of water-soluble minerals, mostly nahcolite 

and halite, in the upper part of the nahcolite-bearing facies 

has created a collapsed leached zone up to 580 ft thick, which 

consists of laterally continuous units of solution breccia and 

fractured oil shale containing solution cavities that once 

were filled with nahcolite. Several solution breccias can be 

traced across the dissolution surface that forms the base of the 

leached zone and into unleached beds of halite and nahcolite. 

The top of the leached zone is not yet defined in the basin, but 

it probably extends into the A-groove in the upper part of the 

Parachute Creek Member.

Resources of nahcolite in oil shale of the lower and 

middle parts of the Parachute Creek Member are evaluated as 

part of this oil shale assessment. In some areas nahcolite may 

be economically minable as a separate commodity. However, 

because most of the nahcolite occurs in variable-sized 

aggregates scattered through oil shale beds, in most areas it 

is subeconomic unless recovered as a co-product of oil shale 

extraction. Oil shale zones R-3, R-4, L-4, and R-5, from 150 

to about 370 ft thick, contain the largest amount of nahcolite 

by weight. Total amounts of nahcolite in the Parachute Creek 

Member are extrapolated from estimated mineral contents of 

58 core holes. Maps showing thickness, average content, and 

in-place resources are included in the assessment. Nahcolite 

resources are as much as 600 million tons per mi2

 in the 

nahcolite depocenter. The total in-place nahcolite resource is 

estimated to be about 43.3 billion short tons in the Parachute 

Creek Member of the Green River Formation in the northcentral part of the Piceance Basin. 

Introduction

Nahcolite (NaHCO3) is associated with high-grade oil 

shale (Ertl, 1947) of the Green River Formation, Piceance 

Basin, northwestern Colorado (figs. 1, 2, 3), and occurs in 

several forms in the oil shale deposits of the lower and middle 

parts of the Parachute Creek Member of the Green River 

Formation. Nonbedded, “semibedded,” and several distinctive 

bedded forms of the mineral, all occurring in close association 

with one another, attest to the complex geochemical conditions 

of the depositional environment in which the nahcolite was 

deposited.

The presence of nahcolite is a concern for the surface 

retorting and in-situ oil shale processes because nahcolite 

decomposes to natrite (Na2

CO3) or soda ash, carbon dioxide, 

and water at temperatures near 100°C during the two recovery processes. In addition, nahcolite is considered a leasable 

mineral and thus must not be destroyed during processes used 

to recover oil from oil shale.

Millions of tons of nahcolite (NaHC03

) occur in the 

Green River Formation in the Piceance Basin (fig. 1), northwest Colorado (Smith and Milton, 1966; Hite and Dyni, 1967; 

Trudell, and others, 1970; Young and Smith, 1970; Beard 

and others, 1974; Dyni, 1974a,b,c; Dyni, 1981). Although 

the oil shale potential has been reasonably well defined using 

published information (Stanfield, and others, 1954, 1957, 

1960, 1967; Smith, and others, 1968; Trudell and others, 1970; 

Pitman and others, 1989; Dyni, 1998), little reliable analytical 

data for nahcolite is available (Smith and Young, 1969; Young 

and Smith, 1970; Dyni and others, 1971a; Smith and others, 

1973). Smith and others (1972) developed a technique for 

estimating nahcolite from the oil-yield assay data, and Dyni 

and others (1971a) described a thermal method to determine 

the nahcolite content of oil shale samples. Beard and others 

(1974) and Dyni (1974b,c) combined their techniques with 

the geology of the mineral occurrence within the basin and 

Nahcolite Resources in the Green River Formation, 

Piceance Basin, Colorado

By Michael E. Brownfield, Tracey J. Mercier, Ronald C. Johnson, and Jesse G. Self
2 Nahcolite Resources in the Green River Formation, Piceance Basin, Colorado

City

County line

0 50 MILES

Colorado

Chaffee Delta

Eagle

Garfield

Grand

Gunnison

Hinsdale

Jackson

Lake

Larimer

Mesa

Moffat

Montrose

Ouray

Park

Pitkin

Rio Blanco

Routt

Saguache

San Miguel

40

40

40

285

70

70

50

Grand 

Junction

Gunnison Salida Montrose

Craig

Glenwood

Springs

39°00'

38°00'

41°00'

40°00'

109°00' 108°00' 107°00' 106°00'

Colorado River

Green River

Lake

Granby

Meeker

Rangely

Steamboat

Springs

64

13

13

139

Extrusive and intrusive

 volcanic rocks

Mesaverde Formation and Mesaverde

 Group coal-bearing rocks

Undivided Quaternary, Tertiary,

 Mesozoic, and Paleozoic

EXPLANATION

TERTIARY

CRETACEOUS

Uinta Formation and undivided

 Tertiary

Green River Formation

Wasatch Formation and undivided

 lower Tertiary

Piceance

Basin Rifle

Piceane Creek

Figure 1. Geologic map of northwest Colorado showing generalized outcrops of the Mesaverde Formation and Group, and the 

Wasatch, Green River, and Uinta Formations in the Piceance Basin, northwestern Colorado. Modified from Brownfield, Hettinger, 

and Johnson (2000).

Donnell and Blair Jr.

(1970); Cashion and

Donnell (1972)

A-groove A-groove

Mahogany zone

B-groove B-groove

Rich oil shale

zone R-6

Rich oil shale

zone R-5

Rich oil shale

zone R-4

Rich oil shale

zone R-3

Rich oil shale zone R-2

Mahogany

zone

Zone 7

Zone 1

Zone 6

Zone 5

Zone 4

Zone 3

Zone 2

Zone 8

Zone 13

Zone 12

Zone 11

Zone 10

Zone 9

Upper

Middle

Lower

Correlation chart of stratigraphic

nomenclature for oil-shale zones

Parachute Creek Member (in part) Garden Gulch Member

Green River Formation (in part)

Rich oil shale

zone R-1

Rich oil shale

zone R-0

Lean oil shale zone L-2

Lean oil shale zone L-1

Lean oil shale zone L-0

Lean oil shale zone L-4

Lean oil shale zone L-3

Lean oil shale zone L-5

Dyni (1974c)

Parachute Creek Member Garden Gulch Member

Green River Formation Uinta Formation

(in part)

Wasatch

Formation

(in part)

Age Unit Eocene

Figure 2. Stratigraphic 

column and correlation chart of 

stratigraphic nomenclature for oil 

shale zones for the Green River 

Formation, north-central Piceance 

Basin, Colorado. This assessment 

uses the nomenclature of Donnell 

and Blair (1970) and Cashion 

and Donnell (1972) highlighted in 

yellow.
100 80 60 40 0 2020 40 60 80 100

OIL IN GAL/TON NAHCOLITE (WT %)

Wolf Ridge Minerals Corp.,

Dunn 20–1, C0002

Sec 20 T. 1 S., R. 98 W.

1,5002,000

2,500

1,500

2,000

2,500

R–3

L–3

R–4

L–4

R–5

Unit Zone

Parachute Creek Member of the Green River Foramation (in part)

DEPTH IN FEET

A-groove

Mahogany zone

B-groove

Rich oil shale

zone R–6

Rich oil shale

zone R–5

Rich oil shale

zone R–4

Rich oil shale

zone R–1

Rich oil shale

zone R–0

Rich oil shale

zone R–3

Rich oil shale

zone R–2

Stratigraphic nomenclature for oil shale

zones (Donnell and Blair, 1970;

Cashion and Donnell, 1972)

Parachute Creek Member (in part) Garden Gulch

Member (in part)

Green River Formation

Lean oil shale zone L-2

Lean oil shale zone L–1Lean oil shale zone L–0

Lean oil shale

zone L–4

Lean oil shale zone L-3

Lean oil shale

zone L–5

EXPL

O S NN 

Figure 3. Plot showing oil-yield (GPT) and nahcolite (weight percent) histograms and stratigraphic nomenclature for oil shale zones (Donne1970; Cashion and Donnell, 1972) for the Wolf Ridge Minerals Corp., Dunn 20-1 core hole, north-central Piceance Basin, Colorado. WT %, we
4 Nahcolite Resources in the Green River Formation, Piceance Basin, Colorado

summarized the geologic occurrences and resources of nahcolite. Beard and others (1974) estimated about 29 billion tons 

of nahcolite using 14 boreholes with nahcolite-content data 

and eight holes for “0” points to determine the extent of the 

nahcolite-bearing zone. Dyni (1974c) estimated about 

32 billion tons of nahcolite using 10 boreholes with nahcolitecontent data. This nahcolite assessment will use the methodology described by Beard and others (1974).

In 2006, the United States consumed about 6,000 tons 

of soda ash, or about 55 percent of the total production (U.S. 

Department of the Interior, 2007). The estimated distribution 

of the 2006 consumption of soda ash by end users was glass 

(40 percent), chemicals (27 percent), soap and detergents (10 

percent), distributors (five percent), flue gas desulfurization 

(two percent), pulp and paper (two percent), water treatment 

(one percent), and unnamed uses (four percent). New domestic supplies of these materials are extremely important to the 

economy of the United States.

Nahcolite, a water-soluble mineral, is a potential raw 

material for the manufacture of a variety of basic industrial 

chemicals (Nielsen, 1969, 1972), but the mineral has perhaps 

received more attention for its potential use in removing sulfur 

dioxide from industrial stack gases. In the early 1970s, Superior Oil Company developed a small quarry near the mouth 

of Piceance Creek (figs. 1, 4) in the Parachute Creek Member 

for a bulk sample to test nahcolite’s effectiveness in scrubbing stack gases. Figure 5 shows boulders containing nodules 

or aggregates of nahcolite surrounded by oil shale. Several 

companies have pursued research in the use of nahcolite as a 

chemical agent for controlling the emission of sulfur dioxide in stack gases of coal-burning electric power plants and 

smelters. Because nahcolite seems to be a potentially valuable 

co-product of oil shale, it becomes important to know where 

and in what abundance nahcolite occurs in the oil shale.

To characterize nahcolite in the Piceance Basin, the U.S. 

Bureau of Mines (USBM) in the late 1970s drilled a 10-ftdiameter deep shaft (fig. 6) in the northern part of the basin 

near Piceance Creek. The shaft was drilled to the nahcolite 

(saline) zone where channel samples were collected (fig. 7) for 

analysis. 

The White River Nahcolite Minerals Company began 

solution mining the Boies nahcolite bed in 1990 (part of L-5A, 

Dyni, 1981, 1996) on a Federal lease tract located in the southeastern part of T. 1 S., R. 98 W., in the northern part of the 

Piceance Basin (fig. 1). The mined part of the Boies nahcolite 

bed is about 26 ft thick, at the depth of about 1,900 ft, and 

contains about 80 to 85 percent nahcolite (core holes C0154, 

C0177, and C0318, pl. 1, 2).

A Colorado company, AmerAlia Inc. (Natural Soda 

Inc.) purchased the operation and leases in 2003 and produced about 103,000 tons of sodium bicarbonate in 2007. 

This facility is the only operation currently producing sodium 

bicarbonate from nahcolite in the basin. The solution mining is 

currently conducted using in-situ leaching by drilling a vertical hole to the target bed and then drilling horizontally along 

the base of the nahcolite-bearing interval. Hot water is injected 

into the nahcolite-bearing zone which dissolves the nahcolite. 

This nahcolite-bearing brine is then pumped to the surface 

using a production hole located several hundreds of feet from 

the injection well (http://www.ameralia.com/). By reducing the 

temperature of the brine, sodium bicarbonate is recrystallized 

in the solution. Excess water is then removed by high-speed 

centrifuging (spin drying). The resultant damp crystal mass is 

further dried, screened, and packed for sale.

This paper presents data and histograms on the nahcolite 

content and oil yields (fig. 3) for 58 core holes (fig. 8) and 

databases that contain nahcolite-content and oil-yield data 

(nahdata.xls, Nahcolite_Data folder, this CD–ROM), and data 

on core hole locations, operator and well name, elevation, core 

location where known, intervals of lithologic log units and 

geophysical logs, and other data (nahdata.xls) in the Piceance 

Basin of northwestern Colorado. Table 1 contains data on 

location and total thickness of the nahcolite interval for the 

nahcolite-bearing core holes and is sorted by the USGS unique 

borehole number. Plates 1 and 2 contain detailed stratigraphic 

cross sections (fig. 9) through the nahcolite facies showing 

detailed histograms of hundreds of oil shale assays and 

nahcolite analyses. The oil shale deposits that include the 

nahcolite-bearing facies are divided into regionally 

correlatable stratigraphic zones of oil shale (Cashion and 

Donnell, 1972). Nahcolite-content (in weight percent) and 

oil-yield (in gallons per ton) histograms for the 58 boreholes 

used in this assessment are in the Oil_Nahcolite_Plot folder. 

Core holes used in the cross sections contain oil-yield data 

above and below the nahcolite-content data have the word 

“extended” added to the plot-file name and are included in the 

folder. This report also summarizes the potential resources 

of nahcolite by oil shale zone in the north-central part of the 

Piceance Basin following the methodology described by Beard 

and others (1974). Johnson and others (chapter 1, this CD–

ROM) gives a detailed discussion of these zones along with 

associated estimated in-place oil shale resources. 

Location and Geologic Setting

The nahcolite deposits of the Eocene Green River Formation are located in the north-central, and deeper, part of the 

Piceance Basin in northwest Colorado. Nahcolite-bearing oil 

shale, ranging from 100 ft to more than 1,100 ft thick, underlies an area in the basin of about 266 mi2

 (about 170,000 acres) 

in Rio Blanco County (figs. 8, 9). In the depocenter of the 

nahcolite and associated halite (Dyni, 1969, 1974b,c), north 

of the Rio Blanco County line, these rocks are about 1,130 ft 

thick, pinching out toward the basin margins. The top of the 

nahcolitic-bearing rocks in the central part of the study area 

range in depth from about 1,300 to 2,000 ft below ground surface. The 58 drill cores studied in this investigation are located 

mostly in the thicker part of the nahcolite-bearing sequence 

and their locations are shown on figures 8 and 9.
Location and Geologic Setting 5

Figure 4. Superior Oil Company’s nahcolite quarry located near the mouth of Piceance Creek, 

Piceance Basin, northwest Colorado. Quarry located in the R-5 oil shale zone (see figs. 2, 3; Cashion 

and Donnell, 1972) in the Parachute Creek Member of the Green River Formation. Nahcolite from the 

quarry was used to test its effectiveness in scrubbing coal-fired power plant stack gases. Inset shows 

location of figure 5.

Figure 5. Nahcolite nodules or aggregates in the R-5 oil shale zone (see figs. 2, 3; Cashion and Donnell, 

1972) in the Superior quarry in the Parachute Creek Member of the Green River Formation, near the 

mouth of Piceance Creek (see fig. 1), northern part of the Piceance Basin, Colorado. Bladed crystals of 

brown nahcolite can be seen in block on left.
6 Nahcolite Resources in the Green River Formation, Piceance Basin, Colorado

A

B

Figure 6. Site of the U.S. Bureau of Mine’s deep shaft project in the Piceance Basin, northwest 

Colorado. A, Drill site showing the oil rig that drilled the 10-ft-diameter shaft to the nahcolite (saline) 

zone in the Parachute Creek Member of the Green River Formation; B, the 10-ft-diameter composite 

drill used in the project.
Geology of the Nahcolite Deposits 7

Figure 7. An excavated face in the Horse Draw Mine, third 

level, U.S. Bureau of Mine’s deep-shaft project (1,834 ft to 

1,844 ft). Channel sample analyses of face from roof to floor: 

nahcolite, 63 weight percent; dawsonite, 3.5 weight percent; 

oil yield, 12.3 gallons per ton; water, 16.3 gallons per ton; spent 

shale percent, 85.2; and percent gas plus loss, 3.3. Shaft drilled, 

with a 10-ft-diameter composite drill bit (see fig. 6). Photograph 

was taken in 1979 by Robert Bolhmar (U.S. Bureau of Mines).

Stratigraphy

The Piceance Basin in northwestern Colorado (fig. 1) 

is a broad structural basin of early Tertiary age. During 

middle Eocene time the basin was occupied by a lake 

which sometimes covered the entire area, and at other times 

decreased significantly in size. More than 2,500 ft of organicrich marlstone (oil shale), sandstone, siltstone, and shale were 

deposited in this body of water and compose the present day 

Green River Formation. In the north-central part of the basin, 

significant amounts of nahcolite, dawsonite, and halite (NaCl) 

were deposited along with oil shale.

In the north-central part of the Piceance Basin, the Green 

River Formation is divided from oldest to youngest into a 

basal sandstone member (Hail, 1972), Garden Gulch, and 

Parachute Creek Members (fig. 2). The Green River Formation 

is deposited on the Wasatch Formation and is overlain by the 

Uinta Formation (Cashion and Donnell, 1974). The sequence 

of rocks within the study area extends upward from the base of 

the Garden Gulch Member to the top of the A-groove, a lean 

oil shale unit in the upper part of the Parachute Creek Member. 

Oil shale bearing rocks were divided from the base upward 

into numbered rich-oil and lean-oil zones, the B-groove, the 

Mahogany zone, and the A-groove (figs. 2, 3; Donnell and 

Blair, 1970; Cashion and Donnell, 1972). The “L” numbered 

zones and B- and A-grooves are thin units of relatively lowgrade oil shale, whereas the “R” numbered zones and the 

Mahogany zone are thick units of relatively higher-grade oil 

shale. The correlation of the numbered zones (Dyni, 1974c) 

of oil shale with the same, but differently numbered, oil shale 

zones of Donnell (Donnell and Blair, 1970; Cashion and 

Donnell, 1972) is shown by the correlation chart on figure 2. 

It is emphasized that the zonation of the oil shale deposits 

used in this study is based on economic stratigraphic units. 

The deposits of nahcolite (NaHCO3

) and associated dawsonite 

(NaAl(OH)2

CO3) and halite (NaCl) are restricted to the lower 

and middle parts of the Parachute Creek Member (fig. 3). The 

detailed nahcolite stratigraphy is shown on plates 1 and 2. 

Plate 1 is an east-west stratigraphic cross section (A–A’, fig. 9), 

and plate 2 is a roughly north-south cross section (B–B’, 

fig. 9). The stratigraphic datum for both cross sections is the 

top of the R-4 oil shale zone. The first occurrence of nahcolite is in the R-2 oil shale zone and extends through to the 

A-groove oil shale zone (fig. 2) in the north-central part of the 

Piceance Basin (figs. 8 and 9). 

Geology of the Nahcolite Deposits

Significant quantities of nahcolite are restricted to the 

lower and middle parts of the Parachute Creek Member and 

were extensively studied in the late 1960s and 1970s (Smith 

and Young, 1969; Young and Smith, 1970; Dyni and others, 

1971a,b; Smith and others, 1972; Beard and others, 1974; 

Dyni, 1974b,c) as part of a USBM and USGS effort. In this 

part of the section, nahcolite occurs both as individual nodules 

or aggregates and in beds. Nahcolite occurs mostly as brown 

fine-grained nodules and dark brown radiating nodular aggregates surrounded by oil shale and occasionally rimmed with 

pyrite (figs. 5, 10). Individual nodules range from less than 1 

in. to several ft in diameter (fig. 11), but most nodules range 

from 1 to 3 in. in diameter (Beard and others, 1974; Dyni, 

1974b,c). Although nodular nahcolite is not bedded, nodules 

do appear to be concentrated in discrete parallel-bedded zones 

(Dyni, 1974c, his figure 10).

Bedded nahcolite includes: (1) a white coarsely crystalline variety (fig. 11), (2) a brown micro-crystalline type, and 

(3) a crystal “mush.” The white coarsely crystalline form 
8 Nahcolite Resources in the Green River Formation, Piceance Basin, Colorado

City

Extrusive and intrusive

 volcanic rocks

Mesaverde Formation and

 Mesaverde Group coal-

 bearing rocks

Undivided Quaternary, Tertiary,

 Mesozoic, and Paleozoic

EXPLANATION

TERTIARY

CRETACEOUS

County line

Uinta Formation and

 undivided Tertiary

Green River Formation

Wasatch Formation and

 undivided lower Tertiary

0 50 MILES

Colorado

Index map

Corehole with nahcolite analyses

Delta

Eagle

Garfield

Gunnison

Mesa

Moffat

Pitkin

Rio Blanco

Routt

40

40

70

70

50

50

Grand 

Junction

Gunnison

Montrose

Craig

Glenwood

Springs

39°00'

41°00'

40°00'

109°00' 108°00' 107°00'

Colorado River

Yampa River

Green

River

Meeker

Rangely

Steamboat

Springs

64

13

13

139

Montrose

Rifle

Piceance

Creek Basin

Figure 8. Geologic map of northwest Colorado showing generalized outcrops of the Mesaverde Formation and 

Group, and the Wasatch, Green River, and Uinta Formations within the Piceance Basin and nahcolite-bearing core 

holes. Modified after Brownfield, Hettinger, and Johnson (2000).
Table 1. Map number, USGS unique identification number, operator, drill hole name, location data, and total thickness of the nahcolite interval (Nahnahcolite-bearing core holes from the Piceance Basin, northwest Colorado.

Map 

no.

USGS 

no. Operator Drill hole name Year Sec 1⁄4 Sec Tps Range Latitude 

1 C0001 Kaiser Alum. & Chem. Co. Nielsen 20-1 SE SE 20 01 S 097 W 39.945196 -

2 C0002 Wolf Ridge Minerals Corp. Dunn 20-1 1966 NE NE 20 01 S 098 W 39.953197 -

3 C0004 Sinclair Oil and Gas Co. Federal 8005 1965 C NE 29 01 N 097 W 40.029541 -

4 C0005 Juhan- Joe T. Juhan 4-1 1964 SW NE 4 02 S 098 W 39.907458 -

5 C0008 Sinclair Oil and Gas Co. Skyline 1 1963-64 NW NE 26 01 S 098 W 39.939896 -

6 C0034 U.S. Bureau of Mines/AEC Colorado 1 1965-66 NE SE 13 01 N 098 W 40.054067 -

7 C0035 U.S. Bureau of Mines/AEC Colorado 2 1966 NW NE 14 01 S 099 W 39.969743 -

8 C0116 Equity Oil Co. Boies Corehole 1 1964? SE SW 19 02 S 097 W 39.857189 -9 C0117 Equity Oil Co. BX-1 1964 NE SE 6 03 S 098 W 39.815737 -

10 C0121 Superior Oil Co. Core hole 19 1973? SW NE 7 01 N 097 W 40.071055 -

11 C0127 Superior Oil Co. Core hole 20 1972? SE NE 22 01 N 097 W 40.041339 -

12 C0128 Superior Oil Co. Core hole 21 1973? SE SE 16 01 N 097 W 40.049778 -

13 C0129 Superior Oil Co. Core hole 26 1973 SE SE 8 01 N 097 W 40.062654 -

14 C0151 Marathon Oil Square S No. 1 1963 NW NW 4 02 S 097 W 39.91304 -

15 C0153 Industrial Resources Inc. Colorado Minerals 28-1 1966 NE NW 28 01 S 098 W 39.940929 -

16 C0154 Wolf Ridge Minerals Corp. Savage 24-1 1966 NE NE 24 01 S 098 W 39.955157 -17 C0155 Wolf Ridge Minerals Corp. Colorado Minerals 14-1 1966 NW NE 14 01 S 098 W 39.969399 -

18 C0156 Kaiser Alum. & Chem. Co. Nielsen 17-1 1966 NW NE 17 01 S 097 W 39.968728 -

19 C0158 Shell Oil Co. Greeno 1-4 1962 NE NE 4 03 S 097 W 39.823832 -

20 C0171 U.S. Bureau of Mines/AEC Colorado 3 1967 SW SW 14 01 N 098 W 40.049687 -

21 C0176 Tosco Corp. TG-2-1 1968 NE SW 21 03 S 096 W 39.774583 -

22 C0177 Shell Oil Co. 22X-1 1968 SW NE 1 02 S 098 W 39.905936 -

23 C0179 Shell Oil Co. 23X-2 1968 NE SW 2 02 S 098 W 39.905464 -

24 C0185 Superior Oil Co. Core hole 01 1967? SE NW 15 01 N 097 W 40.056713 -

25 C0186 Superior Oil Co. Core hole 02 1967 NW SW 7 01 N 097 W 40.066628 -26 C0187 Superior Oil Co. Core hole 03 1968 SE SE 10 01 N 097 W 40.064201 -

27 C0188 Superior Oil Co. Core hole 04 1968 SW SE 16 01 N 097 W 40.049638 -

28 C0189 Superior Oil Co. Core hole 05 1968 NE NW 10 01 N 097 W 40.074038 -
Table 1. Map number, USGS unique identification number, operator, drill hole name, location data, and total thickness of the nahcolite interval (Nahnahcolite-bearing core holes from the Piceance Basin, northwest Colorado—Continued Map no. USGS no. Operator Drill hole name Year Sec 1⁄4 Sec Tps Range Latitude 

29 C0190 Superior Oil Co. Core hole 06 1968 SE SW 14 01 N 097 W 40.050616 -

30 C0191 Superior Oil Co. Core hole 07/07-A 1968 SE SW 8 01 N 097 W 40.063378 -

31 C0192 Superior Oil Co. Core hole 09 1971 SE NW 32 01 N 097 W 40.013724 -

32 C0196 Superior Oil Co. Core hole 10 1971 SW NW 6 01 N 097 W 40.086293 -33 C0198 Superior Oil Co. Core hole 11 1971 NE SW 21 01 N 097 W 40.037817 -

34 C0201 Tosco Corp. TG-71-1 1972 NE NW 13 03 S 097 W 39.793997 -

35 C0207 Cameron Engineers CE-705A 1971 SE NE 4 02 S 099 W 39.906745 -

36 C0209 Superior Oil Co. Core hole 12 1971 SE SW 27 01 N 097 W 40.021269 -

37 C0210 Superior Oil Co. Core hole 13 1971 SE SW 15 01 N 097 W 40.048516 -

38 C0211 Superior Oil Co. Core hole 14 1972 NW SE 27 01 N 097 W 40.025835 -

39 C0212 Superior Oil Co. Core hole 15 1972 SW SW 7 01 N 097 W 40.062682 

40 C0244 Superior Oil Co. Core hole 22 1973? NW SW 15 01 N 097 W 40.053192 -

41 C0249 Arco (C-b project) Sorghum Gulch 01 1974 SE 2 03 S 097 W 39.814632 -

42 C0250 Arco (C-b project) Sorghum Gulch 06 1974 NW SE 7 03 S 096 W 39.804134 -

43 C0251 Arco (C-b project) Sorghum Gulch 08 1974 NE SW 9 03 S 096 W 39.803361 -

44 C0252 Arco (C-b project) Sorghum Gulch 09 1974 SE SE 11 03 S 097 W 39.796995 -

45 C0253 Arco (C-b project) Sorghum Gulch 10 1974 NE NE 13 03 S 097 W 39.79633 -

46 C0254 Arco (C-b project) Sorghum Gulch 11 1974 SE SE 7 03 S 096 W 39.796703 -

47 C0255 Arco (C-b project) Sorghum Gulch 17 1974 SW SW 16 03 S 096 W 39.783535 -

48 C0260 Atlantic Richfield Co. AT-1A 1974 NE SW 7 03 S 096 W 39.800251 -

49 C0274 Superior Oil Co. Core hole 32 1974 NW NW 7 01 N 097 W 40.075636 -

50 C0275 Superior Oil Co. Core hole 30 1974 NW NW 28 01 N 097 W 40.032764 -

51 C0293 U.S. Geol. Survey CR-1 1975 NW SW 31 01 S 096 W 39.921119 -52 C0299 U.S. Bureau of Mines CH 02-A 1975-76 NW SW 29 01 S 097 W 39.933973 -

53 C0314 Multi Mineral Corp. MMC-IRI-01 1980 SE SW 26 01 S 098 W 39.927613 -

54 C0318 Multi Mineral Corp. MMC-IRI-03 1981 NW NE 27 01 S 098 W 39.938757 -

55 C0319 Multi Mineral Corp. MMC-IRI-05 1981 SW SE 23 01 S 098 W 39.943578 -

56 C0321 Multi Mineral Corp. MMC-IRI-10 1981 SE 14 01 S 098 W 39.96017 -

57 C0322 Multi Mineral Corp. MMC-IRI-11 1981 NW NE 25 01 S 098 W 39.931608 -

58 C0334 U.S. Bureau of Mines CH 01-A 1975 NW SW 29 01 S 097 W 39.933331 -
Geology of the Nahcolite Deposits 11

9

8

7

6

5

4

3

2 1 58

57

56 55

54

53

52 51

50

39

47

47

46

45

44 43

41

39

38

37

36

35

34

32

31

30

29

28

25

23 22

21

20

20

18

17

16

15

42

33

27

26 13 24

12

11

10

49

14

108° 30' 108°00'

40°00'

39° 30'

T. 2 N.

T. 1 N.

T. 1 S.

T. 2 S.

T. 3 S.

T. 4 S.

T. 5 S.

T. 8 S.

T. 7 S.

T. 6 S.

R. 101 W. R. 100 W. R. 99 W.

R 99 W

R. 98 W.

R 98 W

R. 97 W.

R 97 W

R. 96 W.

R 96 W R 95 W

R. 102 W. R. 95 W. R. 94 W.

Colorado

Index map

0 12 MILES

70

Pice ance

White River

Whit e River

64

64

13

13

139

139

Meeker

Rangely

Rifle

Rio Blanco

DeBeque

Parachute

City or town

Area underlain by

 oil shale rocks

EXPLANATION

County line

Core hole with nahcolite

 analyses—See table 1 for

 core hole location data

A A' Line of cross section

Colorado River

Creek

7

Creek

Parachute Creek

MESA

GARFIELD

RIO BLANCO

Roan

A

A'

B

B'

Figure 9. Map of northwest Colorado showing nahcolite-bearing core holes, cross section lines (A-A’, 

plate 1; B-B’, plate 2), and generalized area of the oil shale-bearing rocks in the Parachute Creek and Garden 

Gulch Members of the Green River Formation in the Piceance Basin, northwest Colorado.
12 Nahcolite Resources in the Green River Formation, Piceance Basin, Colorado

of bedded nahcolite commonly is closely associated with 

halite (Beard and others, 1974; Dyni, 1974b,c). Thin beds of 

dark-brown microcrystalline nahcolite (fig. 12) are scattered 

vertically throughout the lower Parachute Creek Member in 

the center of the basin. Beds of microcrystalline nahcolite 

commonly less than 1 ft thick, have a texture and appearance 

similar to brown sugar. The term crystal “mush” has been 

used to describe a distinct type of bedded nahcolite in which 

individual crystals of brown nahcolite, varying from 1/8 to 

1/2 in. in size, occur in an oil shale matrix (Beard and others, 

1974). In some cases the crystals are scattered, whereas in 

others they are quite closely spaced, comprising as much as 

85 percent of the rock. Generally, these crystal zones are less 

than 10 ft thick, but persist laterally for long distances. Bed 

thicknesses generally range from less than 1 ft to 10 ft but one 

nahcolite-bearing zone is more than 60 ft thick in the central 

part of the north-central Piceance Basin (core holes C0177 and 

C0318, pl. 1, 2). These thicker units of interbedded nahcolite 

and halite are present in the north-central portion of the basin 

(pl. 1, 2; Trudell and others, 1970; Dyni, 1974c). A portion of 

a thick halite bed recovered during coring (C0334) is shown in 

figure 13. The halite and nahcolite are preserved as alternating 

layers of dissolved halite and wafer-like nahcolite resulting 

from reaction to the drilling fluid.

The mineral composition of the nahcolite-bearing oil 

shales in the lower and middle parts of the Parachute Creek 

Member consist chiefly of Fe-bearing dolomite, dawsonite 

(NaA1(OH)2

(CO3)3), feldspar (K- and Na-feldspar), and quartz 

(Dyni, 1974c, p. 113). Generally, calcite, illite, and pyrite are 

present in small amounts. The mineral composition, including kerogen, for the entire nahcolite-bearing sequence of oil 

shale in core holes, was determined from hundreds of samples 

by using a variety of X-ray and chemical methods. Although 

nahcolite reduces the oil yields obtained by Fischer assay, 

nahcolite is not a component of the fine-grained matrix of 

oil shale and the oil shale laminae form around the nahcolite 

nodules and smaller crystals.

Overlying the nahcolite-bearing section is the so-called 

“leached zone” (pls. 1, 2). The leached interval is characterized by solution cavities, open fractures, local solution or collapsed breccia (fig. 14), and intervals of porous, earthy marlstone. Substantial amounts of nahcolite and halite originally 

deposited in this part of the section subsequently have been 

dissolved and removed by groundwater. Several collapsedbreccia zones can be traced across the dissolution surface that 

forms the base of the leached zone and into unleached beds 

of halite and nahcolite (Dyni, 1974c, 1981). The leached zone 

ranges in thickness from 350 to 580 ft thick and may extend 

upward into the lower part of the Mahogany zone (Dyni, 

1974c). The position of the approximate base of the leached 

zone does not correspond to any geologic markers and is 

stratigraphically highest in the vicinity of the basin’s depositional center and successively lower toward the basin margins. 

In some core holes, small amounts of nahcolite, mostly as nodules, may occur above the lowest evidence of leaching, but in 

this investigation, nahcolite in the leached zone was excluded 

from our resource estimations.

The nahcolite-bearing interval gradually thins and eventually disappears outward from the basin depositional center 

toward the margins of the basin. Most of the thinning is the 

result of post-depositional leaching, but a significant amount 

of thinning is depositional. Beneath the leached zone, stratigraphically correlatable units of nahcolite-bearing oil shale 

decrease both in thickness and in sodium carbonate mineral 

content toward the periphery of the basin (pl. 1, 2). Figure 15 

shows the inferred boundary of major nahcolite deposition 

(this report) and the boundary of sodium carbonate minerals 

(saline zone), including dawsonite, from the Pitman and others 

(1989) assessment. The inferred boundary was determined in 

this study by using the nahcolite-bearing holes in the database and selected non-nahcolite-bearing holes (zero points). 

The size of the area of nahcolite deposition is about 170,000 

acres. Much of the stratigraphic thinning is directly related to 

a reduction in the volume of nahcolite minerals deposited. In 

the areas peripheral to the main body of nahcolite, absence of 

nahcolite may be due either to leaching or to nondeposition.

Smith and Milton (1966) first noted that the lower Parachute Creek Member contained large quantities of dawsonite 

(NaA1(OH)2

(CO3)3) and had a greater lateral and vertical distribution than nahcolite (Young and Smith, 1970). This is most 

likely the reason that the saline zone (Pitman and others, 1989) 

extends further towards the basin margin than the nahcolite 

boundary defined in this study (fig. 15). Unlike nahcolite, 

dawsonite has not been dissolved by the groundwater system 

and the present distribution of this mineral reflects the original 

depositional patterns (Dyni, 1974c; 1981). Dawsonite occurs 

as minute crystals, 5 μm or less in size, disseminated throughout the oil shale matrix (Dyni, 1974c; 1981). Over short 

intervals, dawsonite may compose as much as 25 percent of 

the rock (Smith and Milton, 1966), but commonly it comprises 

less than 10 percent (Young and Smith, 1970). Over most of 

the basin, the base of the upper halite zone, or its stratigraphic 

equivalent, marks the top of abundant dawsonite. Above this 

horizon, only minor amounts of dawsonite are present. Little 

dawsonite is found below the base of the Parachute Creek 

Member (Trudell and others, 1970). The presence of dawsonite is also a concern for the surface retorting and in-situ 

oil shale processes, because dawsonite decomposes to natrite 

(Na2

CO3) or soda ash, carbon dioxide, and water at temperatures from 200° to 370°C during the two processes. The soda 

ash would be recovered as part of the retorting process. Dawsonite resources were not addressed in this study because there 

was not enough chemistry and X-ray diffraction data related to 

dawsonite in the Colorado oil shale database.

The first occurrence of nahcolite is in the upper part of 

the R-2 oil shale zone (pl. 1, 2) and forms disseminated crystals of nahcolite in oil shale (Dyni, 1974c, 1981). Dawsonite 

occurs for the first time also in the lower part of the R-2 oil 

shale zone (Dyni, 1981), and increases in abundance upwards 

marking the transition from illitic-rich oil shale to carbonaterich oil shale (Johnson, 1985, Johnson and others, chapter 1, 
Geology of the Nahcolite Deposits 13

Figure 10. Drill core containing bands of light-brown nahcolite, small nodules of 

nahcolite, and nahcolite aggregates of bladed crystals in oil shale. Some nahcolite 

aggregates are rimmed with pyrite. Recovered core from the U.S. Bureau of Mines 

01A (C0334) borehole (1,554.2 ft to 1,560.3 ft). Core is located in the U.S. Geological 

Survey’s Core Research Center, Denver, Colo.

Figure 11. Drill core containing white, coarse crystals of nahcolite, small nodules 

of nahcolite, and dark-brown nahcolite aggregates of bladed crystals in oil shale. 

Some nahcolite aggregates are rimmed with pyrite. Recovered core from the U.S. 

Bureau of Mines 01A (C0334) borehole (1,578.4 ft to 1,585.2 ft). Core is located at 

the U.S. Geological Survey’s Core Research Center, Denver, Colo.
14 Nahcolite Resources in the Green River Formation, Piceance Basin, Colorado

Figure 12. Drill core containing alternating beds of light-brown nahcolite and 

oil shale. White crystalline aggregate of nahcolite located in right part of upper 

piece of core. Recovered core from the U.S. Bureau of Mines 01A (C0334) 

borehole (1,566.5 ft to 1,574 ft). Core is located at the U.S. Geological Survey’s 

Core Research Center, Denver, Colo.

Figure 13. Drill core containing alternating beds of deeply dissolved halite 

and brown resistant wafer-like nahcolite. Recovered core from the U.S. Bureau 

of Mines 01A (C0334) borehole (1,512 ft to 1,519.4 ft). Core is located at the U.S. 

Geological Survey’s Core Research Center, Denver, Colo.
Geology of the Nahcolite Deposits 15

Figure 14. Drill core containing collapsed breccia and brown nahcolite and 

oil shale. Recovered core from the U.S. Bureau of Mines 01A (C0334) borehole 

(1,219.6 ft to 1,226.5 ft). Core is located at the U.S. Geological Survey’s Core 

Research Center, Denver, Colo.

this CD–ROM). Dyni (1981) reported that the alkaline lake 

waters most likely altered clays by hydrolysis and replaced 

them with authigenic minerals including dawsonite, feldspars, and quartz. As the lake waters became more alkaline, 

anaerobic bacteria reduced most of the sulfate, which in turn 

allowed for the production of bicarbonate and the precipitation 

of nahcolite. The nahcolite-bearing zone (saline zone) in the 

north-central part of the Piceance Basin became well established during the deposition of the R-3 oil shale zone with 

several thick beds of nahcolite-bearing oil shale (Dyni, 1981). 

The presence of these thick nahcolite-bearing oil shale beds 

is, in part, the reason for the increase in thickness of the R-3 

zone (Johnson and others, chapter 1, this CD-ROM). The L-3 

is a thin oil shale zone (maximum thickness, 68 ft, Johnson 

and others, chapter 1, this CD-ROM) and contains minor 

nahcolite-bearing oil shale. Nahcolite is essentially absent 

in the lower part of the R-4 oil shale zone (Dyni, 1974a,b,c, 

1981) in the nahcolite depocenter and only a few nahcolitebearing beds of oil shale occur from the central to upper parts 

of the R-4 zone (figs. 3, 16, 17). This would suggest that Lake 

Uinta was less saline at the beginning of the R-4 zone. Large 

amounts of nahcolite-bearing oil shale are found in the L-4 oil 

shale zone (Dyni, 1974a,b,c; 1981) in the depocenter (figs. 3, 

16, 17; pl. 1, 2). Several thick, persistent nahcolite beds can 

be traced throughout the depocenter, (pls. 1, 2). The basal bed 

of the R-5 oil shale zone contains significant nahcolite in the 

nahcolite depocenter (figs. 3, 16, 17). Thick beds of halite and 

nahcolite are found in the lower part of R-5 oil shale zone 

about 20 ft above the base (Dyni, 1974a,b,c, 1981) and plates 

1 and 2 show the regional extent of the thick halite and nahcolite beds within the nahcolite depocenter in the central and 

northern parts of the Piceance Basin. Thinner beds of halite 

with minor amounts of nahcolite occur in upper parts of the 

R-5 zone (Dyni, 1974a,b,c, 1981). Generally, nahcolite content 

is high in the R-5 zone.

The lower part of the L-5 oil shale zone contains two 

thick beds of halite with nahcolite (Dyni, 1974b) and core 

holes C0154 and C0155 (pl. 1, 2) show the thick halitebearing beds in the L-5 zone. These two beds are the highest 

stratigraphically preserved saline beds in the Parachute Creek 

Member of the Green River Formation. Above these beds is a 

regional collapse breccia indicating that the overlying salinerich beds have been leached out over much of their original 

extent (pl. 1, 2). The collapse breccia zone is named the 

leached zone and its base was called the dissolution surface 

as first defined by Dyni (1974c). We have adopted the name 

“base of the leached zone” for the dissolution surface (pl. 1, 

2). The R-6 oil shale zone contains only partially leached nodules of nahcolite and solution cavities or vugs that were once 

filled with nahcolite. These vugs were described by Pipiringos 

and Johnson (1976) in the upper part of the R-5 zone in an 

outcrop near the mouth of Piceance Creek (fig. 5). There are 

no collapse breccia zones in the R-6 zone (Dyni, 1974c) and it 

is unlikely that thick saline beds similar to those found in the 

underlying L-5 oil shale zone ever existed in the R-6 zone.
16 Nahcolite Resources in the Green River Formation, Piceance Basin, Colorado

9

8

7

6

5

4

3

2 1 58

57

56 55

54

53

52 51

50

39

47

47

46

45

44 43

41

39

38

37

36

35

34

32

31

30

29

28

25

23 22

21

20

20

18

17

16

15

42

33

27

26 13 24

12

11

10

49

14

108° 30' 108°00'

40°00'

39° 30'

T 99 W T 98 W T 97 W T 96 W T 95 W

Colorado

Index map

0 12 MILES

70

Pice ance

White River

Whit e River

64

64

13

13

139

139

Meeker

Rangely

Rifle

Rio Blanco

DeBeque

Parachute

City or town

Area underlain by

 oil shale rocks

EXPLANATION

County line

Core hole with nahcolite

 analyses—See table 1 for

 core hole location data

Colorado River

Creek

7

Creek

Parachute Creek

MESA

GARFIELD

RIO BLANCO

Roan

Boundary of nahcolite

 zone

Boundary of saline zone—

 Modified from Pitman and

 others (1989)

T. 2 N.

T. 1 N.

T. 1 S.

T. 2 S.

T. 3 S.

T. 4 S.

T. 5 S.

T. 8 S.

T. 7 S.

T. 6 S.

R. 102 W. R. 101 W. R. 100 W. R. 99 W. R. 98 W. R. 97 W. R. 96 W. R. 95 W. R. 94 W.

Figure 15. Map of northwest Colorado showing nahcolite-bearing core holes and the inferred boundaries of the 

nahcolite-bearing zone and the saline zone of Pitman and others (1989), and generalized outcrop of the oil shale 

bearing rocks in the Parachute Creek Member of the Green River Formation in the Piceance Basin, northwest Colorado.
Geology of the Nahcolite Deposits 17

20406080100 0 20 40 60 80 100

C0034

U.S. Bureau of Mines/AEC

Colorado 1

Sec. 13, T.1N., R.98W. 

1,000

1,500

2,000

2,500

3,000

20406080100 0 20 40 60 80 100

1,000

1,500

2,000

2,500

3,000

A-grove

zone

B-groove

R–6

L–5

L–4

R–4

L–3

R–3

L–2

R–2

R–1

L–0

R–0

R–5

Oil shale zone

Mahogany

EXPLANATION L–1

Oil-yield histogram—

 In gallons per ton

Nahcolite-rich bed

Nahcolite histogram—

 In weight percent

OIL IN GAL/TON NAHCOLITE (WT %)

OIL IN GAL/TON NAHCOLITE (WT %)

Figure 16. Chart showing oil yields, nahcolite contents, and rich and lean oil shale zones (Cashion 

and Donnell, 1972) for C0034 core hole, north-central Piceance Basin, Colorado. WT %, weight 

percent.
18 Nahcolite Resources in the Green River Formation, Piceance Basin, Colorado

1,800

1,900

2,000

2,100

2,200

2,300

2,400

2,500

2,600

2,700

2,800

DEPTH IN FEET

1,800

1,900

2,000

2,100

2,200

2,300

2,400

2,500

2,600

2,700

2,800

1,700

L-5

R-5

L-4

R-4

L-3

R-3

Oil shale

zone

1,700

EXPLANATION

Oil-yield histogram—

 In gallons per ton

Saline bed, halite,

 and nahcolite

Nahcolite-rich bed

C0154

Wolf Ridge Minerals Corp.

Savage 24–1

Sec. 24, T. 1 S., R. 98 W.

100 80 60 40 0 2020 40 60 80 100

100 80 60 40 0 2020 40 60 80 100

Nahcolite histogram—

 In weight percent

OIL IN GAL/TON NAHCOLITE (WT %)

OIL IN GAL/TON NAHCOLITE (WT %)

Figure 17. Chart showing oil yields, nahcolite contents, and rich and lean oil shale zones 

(Cashion and Donnell, 1972) for C0154 core hole, north-central Piceance Basin, Colorado. WT %, 

weight percent.
Nahcolite Resource Methodology 19

The stratigraphically highest evidence of nahcolite in 

the Parachute Creek Member is not fully understood but 

there is evidence of nahcolite and saline minerals, including 

minor solution breccias and disseminated crystals, found as 

high as the A-groove in 10 cores (Trudell and others, 1970). 

Dyni (1974b) reports that the B-groove, Mahogany zone, and 

A-groove contain disseminated crystals of nahcolite, possible 

halite, and solution cavities. We did not have access to the 

archived oil shale core (see the CO_Borehole_Info.xls, Nahcolite_Data folder, this CD–ROM) so we could not confirm 

many of these minor occurrences of nahcolite, halite, vuggy 

oil shale, and collapsed-solution breccia, and have relied on 

the observations of the earlier authors and core descriptions 

found in the USGS National Oil Shale Database located in 

Denver, Colo.

Nahcolite Resource Methodology

Calculating Nahcolite Content

Estimates of nahcolite content in oil shale samples from 

the lower part of the Parachute Creek Member of the Green 

River Formation have been compiled in a database containing 

58 core holes (nahdata.xls; naholes_info.xls) by oil shale zone 

(fig. 8; table 1). This database was compiled from U.S. Bureau 

of Mines (USBM) and USGS sample data that were analyzed 

at the USBM Laramie, Wyo., laboratory and contains data 

on sample interval, alumina (Al2

O3), Na, nahcolite values in 

weight percent, specific gravity of the sample, and oil yields 

in gallons per ton. Table 2 defines the column names in the 

nahcolite data spreadsheet.

Amounts of nahcolite are estimated using two methods 

described by Smith and Young (1969), Young and Smith 

(1970), and Smith and others (1972). The first method was 

developed by Smith and Young (1969) and involves the leaching of core samples with water to extract water-soluble nahcolite and then determining sodium (Na) content of the solution. 

Sodium was determined using either flame emission photometry or atomic absorption spectroscopy. Nahcolite content of 

each sample was determined using the following gravimetric 

formula (Smith and Young, 1969):

Weight % nahcolite = Weight % Na 3.654 

This method assumes that all the water-soluble Na is 

contained in nahcolite and the sample does not contain halite 

(NaCl). If a significant contribution of Na from halite is 

suspected, X-ray diffraction can be used to detect halite in 

amounts less than one weight percent. If halite is detected, 

chloride must be determined and a value for water-released Na 

released by halite can be determined.

The second method to calculate weight percent of nahcolite and dawsonite separately within a sample statistically was 

developed by Smith and others (1972). This method uses the 

water and gas contents released by nahcolite during Fischer 

assay procedures (American Society for Testing and Materials, 

1980). The Fischer assay standard method consists of heating 

a crushed and screened (-8 mesh (2.38-mm mesh) 100-gram 

sample in a small aluminum retort to 500°C at a rate of 12°C 

per minute and then held at that temperature for 40 minutes. 

The volatile vapors of shale oil, gas, and water pass through a 

condenser cooled with ice water (about 5°C) and collected in a 

graduated centrifuge tube. The oil and water are then separated by centrifuging and weighed. The quantities reported in 

the original sample are the weight percentages of shale oil, 

water, shale residue (contains carbon char), and “gas plus loss” 

(noncondensable gas yield) by difference. The specific gravity 

of the shale oil is measured and used to calculate the oil yield 

in gallons per ton.

The Fischer assay method does not determine the total 

amount of hydrocarbons in an oil shale sample. The method 

does not measure the amount or composition of the gases 

released during the heating of the sample. These gases—

chiefly light hydrocarbons, hydrogen, and carbon dioxide—are 

reported as the “gas plus loss.”

During the Fischer assay procedure, the nahcolite 

completely decomposes as follows at a temperature of about 

125°C:

 2NaHCO3=Na2CO3 +CO2 + H2O (1)

Dawsonite decomposes with the following formula at a 

temperature of about 370° C:

 2NaA1(OH)2CO3 = Na2CO3 + A12O3 + 2H2O +CO2 (2)

These reactions are rapid and easily reached during completion of a Fischer assay (Smith and others, 1972). During the 

Fischer assay procedure the water is produced by decomposition of nahcolite, dawsonite, and the inorganic and organic 

matrix of the oil shale is condensed and caught in an oil-water 

receiver (centrifuge tube), and the carbon dioxide (CO2

) 

produced escapes as a noncondensable gas. The FORTRAN 

program (Smith and others, 1972) for the estimation of nahcolite and dawsonite was developed from a data set consisting 

of 179 samples previously analyzed for nahcolite (Smith and 

Young, 1969; Young and Smith, 1970) using multiple linear 

regression techniques (Ezekial and Fox, 1959). Fischer assay 

data yields for oil, water, gas (plus loss) in weight percent, 

and oil specific gravity are the independent variables in the 

equations. Smith and others (1972) state that the estimates 

for nahcolite and the sum of the sodium carbonate minerals 

(nahcolite and dawsonite) obtained from Fischer assay data 

are sufficiently accurate for stratigraphic correlation, whereas 

individual dawsonite estimates were considered to be generalized. Resource estimates of both nahcolite and dawsonite were 

accurate within 10 percent. 

A third method described by Dyni and others (1971b) 

involves the heating of nahcolite-bearing oil shale. When 

nahcolite-bearing oil shale is heated at 105°C for 14 hours, 
20 Nahcolite Resources in the Green River Formation, Piceance Basin, Colorado

Table 2. Column names and definitions found in the nahcolite data spreadsheet 

(nahdata.xls).

Column name Column definition

OBSNO Sample number

SAMPLEID U.S. Bureau of Mines, Laramie, Wyo. laboratory number 

TOPFT Depth, in feet, measured from surface datum to top of sampled interval

BOTFT Depth, in feet, measured from surface datum to base of sampled interval

SAMPDEN Density of oil shale core sample

AL2O3_PCT Al2

O3 content, in weight percent

NA_PCT Na content, in weight percent

NAPLOT Na content, numeric data

NAHCO3_PCT Nahcolite content, in weight percent

NAHPLOT Nahcolite content, numeric data

OILWONAH Oil yield without nahcolite, in gallons per ton

OILWOPLOT Oil yield without nahcolite, numeric data in gallons per ton

OILWNAH Oil yield with nahcolite, in gallons per ton

OILWPLOT Oil yield with nahcolite, numeric data in gallons per ton

OILGPTWNAH Oil yield with nahcolite in gallons per ton, 0.00B = not analyzed 

OSZONE Oil shale zone (Cashion and Donnell, 1972)

LONGITUDE Longitude, in decimal degrees

LATITUDE Latitude, in decimal degrees

USGSID Unique drill-hole number assigned by the USGS

REMARKS Comment field

the nahcolite decomposes to sodium carbonate (Na2CO3) and 

releases carbon dioxide and water (see equation 1 above). The 

weight of the oil shale sample is determined prior to heating 

and then reweighed after heating and the weight loss is calculated. The nahcolite content of the sample is calculated using 

the following formula:

Nahcolite (weight percent) = weight loss (percent) 

2.690 + 0.375

Dyni and others (1971b) state that the statistical accuracy of 

the thermal method compared to the chemical method (Smith 

and Young, 1969) is ± 2 weight percent at the 95-percent confidence limit. Nahcolite contents were determined in 10 cores 

in the saline facies in the north-central Piceance Basin (Dyni 

and others, 1971a; Dyni and others, 1974a; Dyni, 1974b,c). 

The accuracy of the thermal method depends on the absence 

of other sodium carbonate minerals in the analyzed sample 

(Dyni, 1974c). The presence of halite in analyzed samples 

has no effect on Dyni’s thermal method because halite does 

not decompose during the heating of the sample (105°C). The 

thermal method cannot be used to determine dawsonite in 

samples of oil shale because the higher temperatures (about 

370°C) necessary to completely decompose dawsonite causes 

measurable thermal decomposition of kerogen at 220°C and 

would interfere with the weight-loss values for dawsonite.

Calculating Nahcolite Resources

The following data are required from the nahcolite 

database (nahdata.xls) to estimate nahcolite resources: (1) 

estimated weight-percent nahcolite for each sample or zone, 

(2) oil yield in gallon per ton (GPT) determined by Fischer 

assay, (3) sample or zone depth and thickness, and (4) depth to 

the top and bottom of the nahcolite intervals. This procedure 

compensates for the wide variation in oil shale specific gravity 

with changes in oil yield (Smith, 1956). The procedure, 

modified from Smith and others (1972), for determining the 

amount of nahcolite in each well by zone is as follows:

1. Calculate the weight fraction of nahcolite and oil shale in 

a sample or zone:

Weight-fraction nahcolite= Weight-percent nahcolite

100

Weight-fraction oil shale =1 Weight-fraction nahcolite −

2. Calculate oil yield of the oil shale weight fraction using 

Fischer assay oil yield and weight-fraction oil shale 

(step 1);

Oil yield,weight fraction, GPT = Oil yield,Fischer assay, GPT

Weight-fraction oilshale
Nahcolite Resource Methodology 21

3. Calculate specific gravity of the oil shale weight fraction using quadratic equation that relates oil yield to shale specific 

gravity (Smith, 1956) using the oil yield, weight fraction (step 2):

Specific gravity of oil shale fraction = 

205 988 326 624 2 . − (205.988) 4 31.563 + × × − ( . Oil yield, weight fraction GPT)

2 31.563 ×

4. Calculate volume of 1 gram (gm) of sample using nahcolite specific gravity as 2.18 and the specific gravity of the oil shale 

fraction (step 3):

Volume, 1gm nahcolite sample, cc= Weight-fraction nahcolite

2.18

+ Weight- fraction oil shale

Specific-gravity oil shale

5. Calculate specific gravity of whole sample using the volume of 1 gm of nahcolite (step 4):

Sample specific gravity= Volume of 1gm nahcolite sample

1

6. Calculate the weight of 1 cu ft of sample from the sample specific gravity (step 5) using 62.3 lb/cu ft as the weight of water 

at room temperature in air (Stanfield and others, 1960):

Nahcolitesample weight, lb/cu ft = Samplespecific gravity 62.3

7. Calculate the weight in pounds of 1 sq ft of sample as thick as the sample interval or zone thickness in the well using nahcolite sample weight (step 6) and interval or zone thickness from the nahcolite database:

Weight, interval or zone, lb/sq ft=Sample weight, lb/cu ft Sample or zone thickness, ft

8. Calculate the weight of nahcolite in the nahcolite-bearing interval or zone in the well using the weight fraction of nahcolite 

(step 1) and the weight of 1 sq ft of the interval or zone calculated in step 7:

Weight,nahcolite in well or zone, lb/sq ft=Nahcolite weight fraction weight, interval or zone

9. Calculate short tons of nahcolite per mile by multiplying the weight of nahcolite in a well or zone (step 8) by a given number of sq ft (1 mile = 27,878,400 sq ft) and divide by 2,000 lbs/short ton:

Weight of nahcolite, lb/sq ft 27,878,400 sq ft/mi Nahcolite, short tons/sq mi = 2,000 lbs/short ton

For this assessment Microsoft Excel spreadsheets were 

created that contained nahcolite weight-percent data derived 

from the original USBM analyses and USGS nahcolite analyses (nahdata.xls). These spreadsheets were combined into 

one spreadsheet using a public domain macro which can be 

obtained at the following site: http://www.vbaexpress.com/kb/

getarticle.php?kb_id=151. The combined spreadsheet was then 

imported to a master oil shale assessment Microsoft Access 

database and converted to a table. Once in Access, the table 

was able to be linked to other tables using a master form in 

order to perform calculations.

The methodology for calculating in-place nahcolite 

resources (Beard and others, 1974), shown above, was regenerated in the Access form module using several controls and 

Visual Basic scripting. The methodology and its associated 

control boxes were able to draw filtered data from the nahcolite table and from a Fischer Assay table for the Piceance 

Basin. To calculate in-place nahcolite resources an average 

nahcolite-weight percent was first calculated from the Fischer 

Assay table for each oil shale zone (Cashion and Donnell, 

1972). For each zone, an average gallons per ton (GPT) oil 

yield was also extracted from the Fischer Assay table using 

only that part of a particular oil shale zone which contained 

nahcolite. The resultant value from the formula yielded (tons 

of nahcolite per square mile) for each zone in each hole. The 

process was repeated for the average nahcolite value over the 

total thickness of the nahcolite-bearing interval in each drill 

hole, resulting in values in tons of nahcolite per square mile 

for the entire nahcolite-bearing interval. 

The resultant values were then linked to spatial data 

including the regional extent of oil shale bearing rocks and 

Public Land Survey System (PLSS) data in ArcGIS (Environmental Systems Research Institute, Inc. (ESRI), Redlands, 

Calif., 2006, ver. 9.2). As the assessment-analysis cell size was 
22 Nahcolite Resources in the Green River Formation, Piceance Basin, Colorado

one acre, all values for tons per square mile were converted to 

tons per acre. 

In this assessment we tried three spatial interpolation 

and extrapolation methods for generating resource maps and 

resource numbers: (1) Radial Basis Function (RBF) method 

in ArcGIS GeoStatistical Analyst (Environmental Systems 

Research Institute, Inc. (ESRI), Redlands, Calif., 2006, ver. 

9.2); (2) Inverse Distance Weighted (IDW) method in ArcGIS 

GeoStatistical Analyst (Environmental Systems Research 

Institute, Inc. (ESRI), Redlands, Calif., 2006, ver. 9.2); and (3) 

EarthVision’s minimum tension gridding method (Dynamic 

Graphics, Alameda, Calif., 2004, ver. 7.5). The three methods 

gave similar results, and we ultimately settled on the RBF 

method. EarthVision was limited with a maximum gridding 

size (2,001 × 2,001 cells) that was smaller than the Piceance 

Basin study area using our one-acre cell size. Pitman and 

others (1989) used geostatistical interpolation by kriging 

to generate their resource maps. However, kriging requires 

an understanding of advanced statistical concepts, and false 

results can be obtained if kriging is not done correctly. Pitman 

and others (1989) found that kriging gave good results in 

areas with large numbers of data points, but that it calculated 

unreasonable resource numbers with large error limits in areas 

with little control. We compared our results obtained by the 

RBF method with those derived by kriging (Pitman and others, 1989) and found that the two methods calculated similar 

resource numbers. A detailed discussion of this assessment 

and its comparison to the Pitman and others (1989) assessment 

is found in the oil shale assessment chapter included with this 

assessment (Johnson and others, chapter 1, this CD–ROM). 

The Radial Basis Function (RBF) method in GeoStatistical Analyst is an exact interpolator; it will honor all data 

points and not introduce any error at those locations. Where 

it is important for the modeling method to honor the measured values, RBF can also extrapolate values above or below 

the actual values outside the data-point locations. The final 

resource models for each nahcolite-bearing zone were created 

using a sampling method containing 10 moving window sectors with 15 neighbors or sample points in each sector except 

for the L-5 zone where the model was limited to 10 sample 

points. After numerous iterations, these parameters were found 

to yield the “best” nahcolite-resource models. It has been demonstrated that the RBF method can give comparable results to 

those from the kriging method (Rusu and Rusu, 2006).

Although the RBF method does not generate as complete an error estimate as kriging, it does give the difference 

between the predicted and measured value for each control 

point and an overall error for the entire map. To obtain the difference between the predicted value and the measured value, 

the RBF method predicts a value at a given control point from 

the nearest control points (in this assessment either 10 or 15) 

without knowing the actual value measured at that control 

point. That predicted value is then compared with the measured value, and the difference between the two is calculated.

Nahcolite-resource models using the nahcolite database 

(nahdata.xls) were created using ESRI’s ArcGIS GeoStatistical 

Analyst extension. The RBF in GeoStatistical Analyst was 

used to interpolate (and extrapolate) surfaces using a multiquadric gridding method. Once the models were created, 

we were then able to quantify total tonnages of nahcolite by 

using ESRI Spatial Analyst’s Zonal Statistics function. We 

determine tonnages per township by using the nahcolite model 

(208.71 ft = 63.615-m cell size) and a township grid which 

had been clipped with an outcrop file based on the base of 

the Mahogany zone of the Green River Formation for both 

nahcolite resources in the oil shale zones and the total in-place 

nahcolite within the inferred extent of the nahcolite-bearing 

interval. In short, as the cell size in the model is one acre, the 

function sum totals all of the cells contained by each polygon 

to be assessed in the zone data set.

A more detailed discussion of this methodology used in 

determining in-place nahcolite and oil shale resources is found 

in the methodology chapter included with this assessment 

(Mercier and others, chapter 3, this CD–ROM).

Nahcolite Resources

Nahcolite resources in oil shale of the lower and middle 

parts of the Parachute Creek Member of the Green River 

Formation (fig. 2) in the Piceance Basin, Colorado were evaluated and estimated using the methodology of Beard and others 

(1974). This report presents an in-place assessment of nahcolite resources using 58 core holes and geologic data defining 

the deposit in Rio Blanco County (fig. 8). The size of the area 

included in this assessment is about 170,000 acres. Table 1 

lists the nahcolite-bearing core holes used in this assessment 

and are sorted by the USGS unique borehole number (C0002, 

where C = Colorado). An Excel spreadsheet (nahdata.xls) containing data on weight-percent nahcolite, oil yield in gallons 

per ton, and oil shale zones, is included in this assessment. 

Table 2 describes the column names for the spreadsheet.

Nahcolite resources were determined by oil shale zone 

(fig. 2; Donnell and Blair, 1970; Cashion and Donnell, 1972) 

where sufficient data was available in the nahcolite-bearing 

interval (fig. 15). Plates 1 and 2 show nahcolite-content and 

oil-yield histograms and correlations of selected halite and 

nahcolite-rich beds within the oil shale zones in the northern 

and central parts of the Piceance Basin (fig. 5). The thickness of the nahcolite-bearing interval for each oil shale zone 

was determined for the 58 core holes and the average nahcolite content in weight percent was determined for each zone 

present in each core hole. Both average nahcolite content and 

nahcolite-bearing interval thickness are used to determine the 

total in-place nahcolite resources. Following the methodology 

of Beard and others (1974), described previously, nahcolite 

contents in tons per acre were determined for the core holes. 

Isopleth maps and resource tables were generated for each 

nahcolite-bearing zone. 

The first occurrence of nahcolite is in the upper part of 

the R-2 oil shale zone (pl. 1, 2) and consists mostly of disseminated crystals (Dyni, 1974c, 1981) marking the transition 
Nahcolite Resources 23

from illitic-rich oil shale to carbonate-rich oil shale (Johnson, 

1985, Johnson and others, chapter 1, this CD–ROM). Fifteen core holes contained nahcolite data within the R-2 zone 

(fig. 18, see fig. 9 and table 1). Nahcolite contents range from 

about 400 to more than 13,000 tons per acre. Regionally, the 

nahcolite content in the zone thins towards the margins of 

the inferred extent of the nahcolite-bearing zone (fig. 15). 

Nahcolite deposition is greatest in T. 1 S., R. 98 W. where 

one core hole contained a nahcolite content of about 13,250 

tons per acre (fig. 18, C0318, see fig. 9 and table 1) and the 

township contains about 205 million tons of nahcolite (fig. 19 

and table 3). The total in-place nahcolite resource in the R-2 

zone is about 386 million tons and covers an area of more than 

91,000 acres (table 3).

The central part of the nahcolite depocenter was less 

developed in L-2 oil shale zone than in the R-2 zone (fig. 20), 

but the L-2 zone covers more of the inferred nahcolite 

depositional area (fig. 15). Twenty core holes contained 

nahcolite data within the L-2 zone (see fig. 9 and table 1) 

and the nahcolite deposition is greatest in townships T. 1 S., 

R. 97 W. and T. 1 S., R. 98 W., where more than 1.4 billion 

tons of nahcolite is estimated to be in the L-2 zone (fig. 21) 

and nahcolite contents are greater than 50,000 tons per acre. 

The total in-place nahcolite resource in the L-2 zone is more 

than 2.75 billion tons (table 4) and covers an area more than 

158,000 acres in size.

The nahcolite depocenter in the north-central part of the 

Piceance Basin became well developed during the deposition 

of the R-3 oil shale zone (fig. 22, pl. 1, 2). Several thick beds 

of mostly nahcolite are found throughout the zone (Dyni, 

1974c, 1981) and can be correlated across the depocenter 

(pl. 1, 2). Thirty-five core holes contained nahcolite data 

within the R-3 zone (see fig. 9 and table 1). Several core holes 

contain nahcolite contents greater than 100,000 tons per acre 

(fig. 22). The nahcolite deposition is centered in T. 1 S., 

R. 98 W. where more than 2.489 billion tons of in-place 

nahcolite was estimated to be within the R-3 zone (fig. 23) 

where nahcolite contents are greater than 125,000 tons per 

acre (fig. 22). The nahcolite deposition thins towards the 

margins of the nahcolite-bearing zone (fig. 22). The total 

in-place nahcolite resource in the R-3 zone is more than 10 

billion tons (table 5) and covers an area of more than 166,000 

acres.

Nahcolite deposition in the L-3 oil shale zone (fig. 24) 

is considerably less than the R-3 zone (fig. 22, pl. 1, 2) but 

still covers most of the nahcolite-bearing interval (fig. 15). 

Twenty-eight core holes contain nahcolite data within the L-3 

zone (see fig. 9 and table 1). Two minor depositional centers 

developed: one near the southern margin of the depocenter and 

the other in the central part where maximum nahcolite contents are greater than 30,000 tons per acre (fig. 22). Nahcolite 

deposition thinned towards the margins of the nahcolitebearing interval (fig. 24). Over an area of more than 159,000 

acres, the total in-place nahcolite resource in the L-3 zone is 

more than 2.3 billion tons (fig. 25, table 6).

Nahcolite deposition is generally missing in the lower 

part of the R-4 oil shale zone and increases towards the top of 

the zone (pl. 1, 2). The central part of the depocenter redeveloped westward compared to the L-3 zone (fig. 24) 

where nahcolite contents are greater than 75,000 tons per acre 

(fig. 26). Thirty-one core holes contain nahcolite data within 

the R-4 zone (see fig. 9 and table 1). Nahcolite deposition is 

greatest in T. 1 S., R. 98 W. where more than 1.8 billion tons 

of nahcolite was estimated in the R-4 zone (fig. 27) and thins 

towards the margins of the inferred nahcolite-bearing zone 

(fig. 26). Over an area of more than 160,000 acres the total 

in-place nahcolite resource in the R-4 zone is more than 6.8 

billion tons (table 7).

The L-4 oil shale zone contains large amounts of 

nahcolite within the nahcolite-bearing zone (fig. 28, pl. 1, 2)

and several nahcolite beds have been correlated across the 

depocenter (Dyni, 1974c, 1981). Thirty-one core holes contain 

nahcolite data and were used in this assessment. The richest 

part of the nahcolite-bearing zone is located in T. 1 S., R. 97 

W. and T. 1 S., R. 98 W. where nahcolite contents in four core 

holes are greater than 150,000 ton per acre (fig. 28) and an 

in-place nahcolite resource of about 2.3 and 3.2 billion tons, 

respectively (fig. 29). The maximum content trends are in a 

northeasterly and southeasterly direction from the center of the 

depocenter (fig. 28). The total in-place nahcolite resource by 

township in the R-4 zone is more than 10 billion tons (table 8) 

over an area of more than 127,000 acres.

Thick beds of halite with minor nahcolite characterize the 

lower part of the R-5 oil shale zone with thinner beds of halite 

and nahcolite found in the upper part of the zone 

(pl. 1, 2). Although the nahcolite depocenter is smaller 

(fig. 30), the nahcolite contents in the R-5 zone are comparatively high. The richest area of nahcolite is mostly found in 

T. 1 S., R. 98 W. where nahcolite contents in a large area are 

greater than 300,000 tons per acre (fig. 30) and an in-place 

nahcolite resource of about 5 billion tons (fig. 31). Thick 

beds of nahcolite are correlatable across the nahcolite-bearing 

interval (pl. 1, 2). Twenty-seven core holes contain R-5 zone 

nahcolite data and were used in this assessment (fig. 30). The 

total in-place nahcolite resource in the R-5 zone is more than 

12.9 billion tons (fig. 31 and table 9) over an area of more than 

119,000 acres.

The lower part of the L-5 oil shale zone contains two 

thick beds of halite and minor nahcolite (pl. 1, 2). These two 

beds are the highest preserved halite beds in the nahcolitebearing part of the Parachute Creek Member of the Green 

River Formation in the Piceance Basin (Dyni, 1974c, 1981). 

Above these beds is the collapsed leach zone, which indicates 

that a saline bed was most likely present (pl. 1, 2). The nahcolite depocenter is considerably smaller in the L-5 zone due to 

both regional leaching and nondeposition (fig. 32) when compared to the R-5 zone (fig. 30). The nahcolite-bearing interval 

is characterized by two depocenters: one near the northern 

nahcolite-deposition boundary, and the second located near the 

center of the depocenter. Most of the L-5 nahcolite resource is 

located in T. 1 S., R. 98 W. where more than 498 million tons 
24 Nahcolite Resources in the Green River Formation, Piceance Basin, Colorado

T

2

N

T

1

N

T

1

S

T

2

S

T

3

S

0

0

0

0

0

0

0

703

2,614

11,970

13,248

9,428

0

0

0

0

0 0 0 0

0

0

705 0

0

0

0

0

12,146

0

0

0

0

0

0

3,311

2,974

399

0

0

0

0

0

0

1453

0

709

5,789

0

3,978

4,831

0

0

R. 99 W. R. 98 W. R. 97 W. R. 96 W.

108°30'

40°00'

0 1.5 3 6 MILES

0 31.5 6 KILOMETERS

EXPLANATION Index map

Top of Mahogany zone Nahcolite in-place resource, R–2 zone—In tons per acre

Base of Parachute Creek Member 7,501– <–2,500 Inferred extent of nahcolite 10,000

 depocenter 2,501– 10,001–

709 Core hole—Nahcolite content in 5,000 12,500

 tons per acre Colorado

5,001– 12,501–

 7,500 15,000

Figure 18. Isopleth map showing in-place nahcolite (NaHCO3) resources in the R-2 oil shale zone (Donnell and Blair, 

1970; Cashion and Donnell, 1972) in the Parachute Creek Member of the Green River Formation, Rio Blanco County, 

northwestern Colorado. Nahcolite resources reported in short tons per acre. Inferred extent of nahcolite depocenter 

outlined in red.
Nahcolite Resources 25

T

2

N

T

1

N

T

1

S

T

2

S

T

3

S

255,075 0 0

41,391,700 7,474,160 0

30,483,400 204,783,008 32,097,300 0

45,640,400 23,841,900

R. 99 W. R. 98 W. R. 97 W. R. 96 W.

108°30'

40°00'

0 1.5 3 6 MILES

0 31.5 6 KILOMETERS

EXPLANATION

Top of Mahogany zone

Base of Parachute Creek Member

Inferred extent of nahcolite depocenter

Colorado

Index map

Nahcolite in-place resource, R–2 zone—

 By township, in short tons 255,075

Figure 19. Map showing in-place nahcolite (NaHCO3) resources in the R-2 oil shale zone (Donnell and Blair, 1970; 

Cashion and Donnell, 1972) in the Parachute Creek Member of the Green River Formation by township, Rio Blanco County, 

northwestern Colorado. Nahcolite resources reported in short tons. Inferred extent of nahcolite depocenter outlined in red.
26 Nahcolite Resources in the Green River Formation, Piceance Basin, Colorado

Table 3. Total in-place nahcolite resources and average tons per acre, by township, in the R-2 oil shale zone in the 

nahcolite-bearing interval of the Parachute Creek Member of the Green River Formation, Piceance Basin, Rio Blanco 

County, northwestern Colorado.

[All values calculated by ESRIs ArcGIS GeoStatistical Analyst Extension with a Radial Basis Function (RBF) Multiquadratic Gridding 

Function; 1 acre = 4,047 m2]

Township Acres Area (m2) Average tons per acre Total in-place resource in tons

T1N R97W 7,560 30,594,300 1,430 23,842,000

T1N R98W 11,616 47,008,400 2,819 45,640,000

T1S R96W 0 0 0 0

T1S R97W 11,936 48,303,400 1,313 32,097,000

T1SR 98W 23,832 96,445,000 8,588 204,783,000

T1S R99W 4,881 19,752,800 6,245 30,483,000

T2S R96W 0 0 0 0

T2S R97W 9,992 40,436,300 318 7,474,000

T2S R98W 20,483 82,892,000 2,018 41,392,000

T3S R96W 0 0 0 0

T3S R97W 0 0 0 0

T3S R98W 744 3,010,870 30 255,000

Total 91,044 368,443,070 385,966,000

Table 4. Total in-place nahcolite resources and average tons per acre, by township, in the L-2 oil shale zone in the 

nahcolite-bearing interval of the Parachute Creek Member of the Green River Formation, Piceance Basin, Rio Blanco 

County, northwestern Colorado.

[All values calculated by ESRIs ArcGIS GeoStatistical Analyst extension with a Radial Basis Function (RBF) Multiquadratic Gridding 

Function; 1 acre = 4,047 m2]

Township Acres Area (m2

) Average tons per acre Total in-place resource in tons

T1N R97W 10,216 41,342,800 13,387 223,166,000

T1NR 98W 16,173 65,450,000 11,232 181,878,000

T1S R96W 4,844 19,603,000 20,560 99,594,000

T1S R97W 24,450 98,945,900 31,356 766,653,000

T1SR 98W 23,844 96,493,500 27,321 651,450,000

T1S R99W 4,881 19,752,800 14,665 71,581,000

T2S R96W 9,719 39,331,500 4,785 46,503,000

T2SR 97W 23,478 95,012,400 11,435 268,462,000

T2S R98W 20,507 82,989,100 18,694 383,348,000

T3S R96W 2,594 10,497,600 403 1,595,000

T3SR 97W 10,008 40,501,100 2,147 27,566,000

T3S R98W 8,033 32,508,500 3,757 32,356,000

Total 158,747 642,428,200 2,754,151,000
Nahcolite Resources 27

T

2

N

T

1

N

T

1

S

T

2

S

T

3

S

0

0

0

0

0

0

12,351

15,306

40,696

37099 34315

34971

11,584

0

0 0 0

0

0

157

10,993

0 110,048

0

0

14,572

0

0

0

0

0

0

35,615

30,669

10,643

4,023

0

0

0

0

0

17,964

11,891

11,467

27088

26,784

6,227

R. 99 W. R. 98 W. R. 97 W. R. 96 W.

108°30'

40°0'

0 3 6 12 MILES

0 5 10 2.5 KILOMETERS

EXPLANATION Index map

Top of Mahogany zone Nahcolite in-place resource, L–2 zone—In tons per acre

Base of Parachute Creek Member 75,001– <– 25,000 Inferred extent of nahcolitenah 100,000

 depocenter 25,001 100,001–

17,964 Core hole—Nahcolite content in 50,000 125,000

 tons per acre Colorado

50,001–

 75,000

Figure 20. Isopleth map showing in-place nahcolite (NaHCO3) resources in the L-2 oil shale zone (Donnell and Blair, 

1970; Cashion and Donnell, 1972) in the Parachute Creek Member of the Green River Formation, Piceance Basin, Rio 

Blanco County, northwestern Colorado. Nahcolite resource reported in short tons per acre. Inferred extent of nahcolite 

depocenter outlined in red.
28 Nahcolite Resources in the Green River Formation, Piceance Basin, Colorado

T

2

N

T

1

N

T

1

S

T

2

S

T

3

S

32,355,800 27,566,000 1,594,540

383,348,000 268,462,016 46,502,900

71,580,704 651,449,984 766,652,992 99,593,800

181,878,000 223,166,000

R. 99 W. R. 98 W. R. 97 W. R. 96 W.

108°30'

40°0'

0 1.5 3 6 MILES

0 31.5 6 KILOMETERS

Colorado

EXPLANATION Index map

Top of Mahogany zone

Base of Parachute Creek Member

Inferred extent of nahcolite

 depocenter

Nahcolite in-place resource, L–2 zone—

 By township, in short tons 383,348,000

Figure 21. Map showing in-place nahcolite (NaHCO3) resources in the L-2 oil shale zone (Donnell and Blair, 

1970; Cashion and Donnell, 1972) in the Parachute Creek Member of the Green River Formation by township, Rio 

Blanco County, northwestern Colorado. Nahcolite resources reported in short tons. Inferred extent of nahcolite 

depocenter outlined in red.
Nahcolite Resources 29

Table 5. Total in-place nahcolite resources and average tons per acre, by township, in the R-3 oil shale zone in the 

nahcolite-bearing interval of the Parachute Creek Member of the Green River Formation, Piceance Basin, Rio Blanco 

County, northwestern Colorado.

[All values calculated by ESRIs ArcGIS GeoStatistical Analyst extension with a Radial Basis Function (RBF) Multiquadratic Gridding 

Function; 1 acre = 4,047 m2]

Township Acres Area (m2) Average tons per acre Total in-place resource in tons

T1N R97W 14,145 57,243,000 37,302 621,858,000

T1NR 98W 16,191 65,522,800 70,709 1,144,990,000

T1S R96W 4,844 19,603,000 41,120 199,185,000

T1S R97W 24,450 98,945,900 57,445 1,404,520,000

T1SR 98W 23,844 96,493,500 104,429 2,490,000,000

T1S R99W 4,881 19,752,800 74,715 364,683,000

T2S R96W 9,719 39,331,500 31,562 306,752,000

T2SR 97W 23,478 95,012,400 62,465 1,466,560,000

T2S R98W 20,507 82,989,100 73,792 1,513,240,000

T3S R96W 2,820 11,412,200 6,716 26,569,000

T3SR 97W 12,540 50,747,700 26,055 334,498,000

T3S R98W 8,613 34,855,700 19,693 169,617,000

Total 166,032 671,909,600 10,042,472,000

Table 6. Total in-place nahcolite resources and average tons per acre, by township, in the L-3 oil shale zone in the 

nahcolite-bearing interval of the Parachute Creek Member of the Green River Formation, Piceance Basin, Rio Blanco 

County, northwestern Colorado.

[All values calculated by ESRIs ArcGIS GeoStatistical Analyst extension with a Radial Basis Function (RBF) Multiquadratic Gridding 

Function; 1 acre = 4,047 m2]

Township Acres Area (m2) Average tons per acre Total in-place resource in tons

T1N R97W 10,392 42,055,100 4,733 78,905,000

T1NR 98W 16,075 65,053,400 10,597 171,596,000

T1S R96W 4,844 19,603,000 5,480 26,547,000

T1S R97W 24,450 98,945,900 17,692 432,575,000

T1SR 98W 23,844 96,493,500 20,877 497,791,000

T1S R99W 4,881 19,752,800 16,784 81,920,000

T2S R96W 9,719 39,331,500 4,832 46,965,000

T2SR 97W 23,478 95,012,400 19,315 453,473,000

T2S R98W 20,507 82,989,100 14,644 300,297,000

T3S R96W 1,692 6,847,300 477 1,889,000

T3SR 97W 10,921 44,195,800 11,664 149,743,000

T3S R98W 8,613 34,855,700 9,918 85,422,000

Total 159,416 645,135,500 2,327,123,000
30 Nahcolite Resources in the Green River Formation, Piceance Basin, Colorado

T

2

N

T

1

N

T

1

S

T

2

S

T

3

S

0

0

0

0

0

0

68,441

104,726

120,836

104,552

134,871

129,531

59,412

71653

14,708

0 0 0

13,587

0 52,833

538 56,071

47,085

72,087

59,855

0

90,325

12,466

0

0

23,902

0

0

128,433

110,870

81,633

41,249

7,775

6,497

18,50716,044

14,930

6,557

72,504

69103

69,363

103,768

106,760

48016

R. 99 W. R. 98 W. R. 97 W. R. 96 W.

108°30'

40°00'

0 3 6 12 MILES

0 5 10 2.5 KILOMETERS

EXPLANATION

Top of Mahogany zone

Base of Parachute Creek Member

Core hole—Nahcolite content in

 tons per acre

17,964

 in-place resource, R–3 zone—In tons per acre

 25,000

25,001–

 50,000

50,001–

 75,000

75,001–

 100,000

100,001–

 125,000

Inferred extent of nahcolite

 depocenter

Colorado

Index map

125,001–

 150,000

<–

Nahcolite

Figure 22. Isopleth map showing in-place nahcolite (NaHCO3) resources of R-3 oil shale zone (Donnell and Blair, 

1970; Cashion and Donnell, 1972) in the Parachute Creek Member of the Green River Formation, Piceance Basin, 

Rio Blanco County, northwestern Colorado. Nahcolite resources reported in short tons per acre. Inferred extent of 

nahcolite depocenter outlined in red.
Nahcolite Resources 31

T

2

N

T

1

N

T

1

S

T

2

S

T

3

S

169,616,992

334,497,984

26,569,000

1,513,240,064 1,466,560,000

306,752,000

364,683,008

2,489,999,872 1,404,519,936 199,184,992

1,144,989,952 621,857,984

R. 99 W. R. 98 W. R. 97 W. R. 96 W.

108°30'

40°00'

0 1.5 3 6 MILES

0 31.5 6 KILOMETERS

Colorado

EXPLANATION Index map

Top of Mahogany zone

Base of Parachute Creek Member

Inferred extent of nahcolite

 depocenter

Nahcolite in-place resource, R–3 zone—

 By township, in short tons 383,348,000

Figure 23. Map showing in-place nahcolite (NaHCO3) resources in the R-3 oil shale zone (Donnell and 

Blair, 1970; Cashion and Donnell, 1972) in the Parachute Creek Member of the Green River Formation by 

township, Rio Blanco County, northwestern Colorado. Nahcolite resources reported in short tons. Inferred 

extent of nahcolite depocenter outlined in red.
32 Nahcolite Resources in the Green River Formation, Piceance Basin, Colorado

T

2

N

T

1

N

T

1

S

T

2

S

T

3

S

0

0

0

0

0

0

18,738

19,190

34,939

31,716

16,764

22,684

15,259 6894

13,078

523

0 0 0 0

0

0

0 5,632

0

4,744

8,709

0

14,346

0

0

0

2,884

0

0

18,670

22,869

8,466

35,220

17,642

31,033

613

0

0

527

5,199

22,942

19,242

10,844

19,617

12,229

9,644

34,499

R. 99 W. R. 98 W. R. 97 W. R. 96 W.

108°30'

0 1.5 3 6 MILES

0 31.5 6 KILOMETERS

EXPLANATION

Top of Mahogany zone

Base of Parachute Creek Member

Core hole—Nahcolite content in

 tons per acre

 in-place resource, L–3 zone—In tons per acre

 7,500

7,501–

 15,000

15,001–

 22,500

22,501–

 30,000

30,001–

 37,500

Inferred extent of nahcolite

 depocenter

Colorado

Index map

22,942

<–

Nahcolite

40°00'

Figure 24. Isopleth map showing in-place nahcolite (NaHCO3) resources of L-3 oil shale zone (Donnell and 

Blair, 1970; Cashion and Donnell, 1972) in the Parachute Creek Member of the Green River Formation, Piceance 

Basin, Rio Blanco County, northwestern Colorado. Nahcolite resources reported in short tons per acre. 

Inferred extent of nahcolite depocenter outlined in red.
Nahcolite Resources 33

T

2

N

R. 99 W. R. 98 W. R. 97 W. R. 96 W.

T

1

N

T

1

S

T

2

S

T

3

S

85,422,304 149,743,008 1,888,770

300,296,992 453,472,992 46,964,900

81,920,096 497,791,008 432,575,008 26,546,800

171,596,000 78,905,200

108°30'

40°00'

Colorado

EXPLANATION Index map

Top of Mahogany zone

Base of Parachute Creek Member

Inferred extent of nahcolite

 depocenter

Nahcolite in-place resource, L–3 zone—

 By township, in short tons 46,964,900

0 1.5 3 6 MILES

0 31.5 6 KILOMETERS

Figure 25. Map showing in-place nahcolite (NaHCO3) resources in the L-3 oil shale zone (Donnell and Blair, 

1970; Cashion and Donnell, 1972) in the Parachute Creek Member of the Green River Formation by township, 

Rio Blanco County, northwestern Colorado. Nahcolite resources reported in short tons. Inferred extent of 

nahcolite depocenter outlined in red.
34 Nahcolite Resources in the Green River Formation, Piceance Basin, Colorado

T

2

N

T

1

N

T

1

S

T

2

S

T

3

S

0

0

0

0

0

0

60,117

86,940

88,421

86,385

92,919

97,071 115,026

94,174 34584

28,076

2,382

0 0 0

0

0

0

18,321

15,642

38,827

10,003

1,133

68,005

0

0

0

0

0 0

65,180

86,786

63,709

24,948

61,724

79,143

677

0

0

977

12,133

49,048

19,161

33,592

65,527

44,941

,22,617

78,122

R. 99 W. R. 98 W. R. 97 W. R. 96 W.

108°30'

40°00'

0 1.5 3 6 MILES

0 31.5 6 KILOMETERS

EXPLANATION

Top of Mahogany zone

Base of Parachute Creek Member

Core hole—Nahcolite content in

 tons per acre

 in-place resource, R–4 zone—In tons per acre

 25,000

25,001–

 50,000

50,001–

 75,000

75,001–

 100,000

100,001–

 125,000

Inferred extent of nahcolite

 depocenter

Colorado

Index map

12,133

<–

Nahcolite

Figure 26. Isopleth map showing in-place nahcolite (NaHCO3) resources of R-4 oil shale zone (Donnell and Blair, 1970; 

Cashion and Donnell, 1972) in the Parachute Creek Member of the Green River Formation, Piceance Basin, Rio Blanco 

County, northwestern Colorado. Nahcolite resources reported in short tons per acre. Inferred extent of nahcolite 

depocenter outlined in red.
Summary 35

were estimated (fig. 33). Only nine core holes contain nahcolite data in the zone. The total in-place nahcolite resource in 

the L-5 zone is more than 850 million tons (fig. 33 and table 

10) over an area of more than 23,000 acres.

The total thickness of the nahcolite-bearing interval 

(saline zone) was determined for each core hole within the 

inferred extent of the nahcolite-bearing interval (fig. 15) and 

the average nahcolite content in weight percent was determined for each hole to estimate the total in-place nahcolite 

resource in the north-central part of the Piceance Basin. 

Figure 34 shows the thickness of the nahcolite-bearing interval 

in the Parachute Creek Member (fig. 2) in the north-central 

part of the Piceance Basin, and figure 35 shows the average 

nahcolite content in weight percent for the 58 core holes in the 

nahcolite-bearing depocenter. As with the in-place nahcolite 

resource calculations for the individual oil shale zones, the 

leached zone was not considered to be a part of the nahcolite 

interval and was excluded from the total in-place resource 

estimations. Average nahcolite content and the total nahcolitebearing interval thickness are still the two variables used in 

determining the total in-place nahcolite resources. Figure 36 

shows the isopach values of nahcolite content in tons per acre 

within the nahcolite depocenter and the individual core hole 

values in tons per acre.

The amount of in-place nahcolite is as much as 940 

thousand short tons per acre (853 million metric tons; see 

fig. 36, core hole C0321) or about 600 million tons per mi2

(210 million metric tons per km2) in the nahcolite depocenter 

(figs. 15, 36). The nahcolite resource decreases and eventually 

pinches out towards the Piceance Basin margin resulting from 

nondeposition or leaching by groundwater. The total in-place 

nahcolite resource is estimated to be about 43.3 billion short 

tons (39.1 billion metric tons) within the north-central part of 

the Piceance Basin (table 11). Figure 37 shows the in-place 

nahcolite resource by township in tons covering an area of 

about 170,000 acres.

Acknowledgments

The authors wish to thank Gayle Dumonceaux, Susan 

Hall, William Keefer, Douglas Nichols, and Christopher 

Schenk for their suggestions, comments, and editorial reviews, 

which greatly improved the manuscript.

Summary

Nahcolite (NaHCO3)-bearing rocks in rich deposits of oil 

shale are found in the lower and middle parts of the Parachute 

Creek Member of the Eocene Green River Formation in the 

north-central part of the Piceance Basin, northwestern Colorado. Associated minerals include dawsonite (NaAl(OH)2

CO3) 

and halite (NaCl). This nahcolite-bearing facies consists of 

a lower part containing the nahcolite and halite, which is 

estimated to be as thick as 1,130 ft, and an upper-leached 

part several hundreds of feet thick. Locally thick beds of 

halite with minor nahcolite are found in the nahcolite-bearing 

depocenter of the basin and thin from the basin center, grading laterally into beds of white, coarse-grained nahcolite. The 

top of the nahcolitic-bearing rocks in the central part of the 

study area ranges in depth from about 1,300 to 2,000 ft below 

ground surface in the central part of the assessment area and 

is overlain by a “leached zone” characterized by intervals of 

vuggy oil shale and collapsed solution breccia. The leached 

zone is several hundred feet thick and may extend upward to 

the lower part of the Mahogany zone.

The total in-place nahcolite resource is estimated to be 

about 43.3 billion short tons in the Parachute Creek Member of the Green River Formation, north-central part of the 

Piceance Basin. A few beds of nahcolite may have economic 

potential by themselves, but because most of the nahcolite 

occurs in variable-sized aggregates scattered through oil shale 

beds, it may be most feasibly recovered as a co-product of the 

oil shale industry.
36 Nahcolite Resources in the Green River Formation, Piceance Basin, Colorado

T

2

N

R. 99 W. R. 98 W. R. 97 W. R. 96 W.

T

1

N

T

1

S

T

2

S

T

3

S

139,547,008 128,165,000 5,074,140

827,630,976 944,654,976 135,399,008

161,184,000 1,838,700,032 1,407,559,936 132,329,000

820,129,984 316,460,000

108°30'

0 1.5 3 6 MILES

0 31.5 6 KILOMETERS

Colorado

EXPLANATION Index map

Top of Mahogany zone

Base of Parachute Creek Member

Inferred extent of nahcolite

 depocenter

Nahcolite in-place resource, R–4 zone—

 By township, in short tons 128,165,000

40°00'

Figure 27. Map showing in-place nahcolite (NaHCO3) resources in the R-4 oil shale zone (Donnell and 

Blair, 1970; Cashion and Donnell, 1972) in the Parachute Creek Member of the Green River Formation 

by township, Rio Blanco County, northwestern Colorado. Nahcolite resources reported in short tons. 

Inferred extent of nahcolite depocenter outlined in red.
Summary 37

T

2

N

T

1

N

T

1

S

T

2

S

T

3

S

0

0

0

0

0

0

45,195

132,713

146,826

152,609

156,227

142,077

117,030

161,221 146590

0

89,740

22,562

0 0 0 0

0

0

5,742

95,544

60,778

78,760

92,125

13,493

127,461

0

0

0

0

0

110,021

148,203

138,484

115,749

643

151,382

147,578

6,887 0

0

30,794

0

4,519

99,472

103,676

104,237

116,767

126,228

R. 99 W. R. 98 W. R. 97 W. R. 96 W.

108°30'

40°00'

0 1.5 3 6 MILES

0 31.5 6 KILOMETERS

EXPLANATION Index map

Top of Mahogany zone Nahcolite in-place resource, L–4 zone—In tons per acre

Base of Parachute Creek Member 90,001– <– 30,000 Inferred extent of nahcolite 120,000

 depocenter 30,001– 120,001–

17,964 Core hole—Nahcolite content in 60,000 150,000

 tons per acre Colorado

60,001– 150,001–

 90,000 180,000

Figure 28. Isopleth map showing in-place nahcolite (NaHCO3) resources of L-4 zone (Donnell and Blair, 1970; 

Cashion and Donnell, 1972) in the Parachute Creek Member of the Green River Formation, Piceance Basin, Rio 

Blanco County, northwestern Colorado. Nahcolite resources reported in short tons per acre. Inferred extent of 

nahcolite depocenter outlined in red.
38 Nahcolite Resources in the Green River Formation, Piceance Basin, Colorado

Figure 29. Map showing in-place nahcolite (NaHCO3) resources in the L-4 oil shale zone (Donnell and Blair, 1970; 

Cashion and Donnell, 1972) in the Parachute Creek Member of the Green River Formation by township, Rio Blanco 

County, northwestern Colorado. Nahcolite resources reported in short tons. Inferred extent of nahcolite depocenter 

outlined in red.

T

2

N

R. 99 W. R. 98 W. R. 97 W. R. 96 W.

T

1

N

T

1

S

T

2

S

T

3

S

108°30'

40°00'

0 1.5 3 6 MILES

0 31.5 6 KILOMETERS

Colorado

EXPLANATION Index map

Top of Mahogany zone

Base of Parachute Creek Member

Inferred extent of nahcolite

 depocenter

Nahcolite in-place resource, L–4 zone—

 By township, in short tons

14,198,900 8,532 0

1,185,420,032 367,251,008 0

407,873,984 3,200,219,904 2,263,729,920 100,116,000

1,668,749,952 892,611,968

14,198,900
Summary 39

Table 7. Total in-place nahcolite resources and average tons per acre, by township, in the R-4 oil shale zone in the 

nahcolite-bearing interval of the Parachute Creek Member of the Green River Formation, Piceance Basin, Rio Blanco 

County, northwestern Colorado.

[All values calculated by ESRIs ArcGIS GeoStatistical Analyst extension with a Radial Basis Function (RBF) Multiquadratic Gridding 

Function; 1 acre = 4,047 m2]

Township Acres Area (m2) Average tons per acre Total in-place resource in tons

T1N R97W 11,591 46,907,200 18,983 316,460,000

T1NR 98W 16,193 65,530,900 50,647 820,130,000

T1S R96W 4,844 19,603,000 27,318 132,329,000

T1S R97W 24,450 98,945,900 57,569 1,407,560,000

T1SR 98W 23,844 96,493,500 77,114 1,838,700,000

T1S R99W 4,881 19,752,800 33,023 161,184,000

T2S R96W 9,719 39,331,500 13,931 135,399,000

T2SR 97W 23,478 95,012,400 40,236 944,655,000

T2S R98W 20,507 82,989,100 40,359 827,631,000

T3S R96W 2,322 9,396,830 1,283 5,074,000

T3SR 97W 10,474 42,386,900 9,983 128,165,000

T3S R98W 8,613 34,855,700 16,202 139,547,000

Total 160,916 651,205,730 6,856,834,000

Table 8. Total in-place nahcolite resources and average tons per acre, by township, in the L-4 oil shale zone in the 

nahcolite-bearing interval of the Parachute Creek Member of the Green River Formation, Piceance Basin, Rio Blanco 

County, northwestern Colorado. 

[All values calculated by ESRIs ArcGIS GeoStatistical Analyst extension with a Radial Basis Function (RBF) Multiquadratic Gridding 

Function; 1 acre = 4,047 m2]

Township Acres Area (m2) Average tons per acre Total in-place resource in tons

T1N R97W 13,343 53,997,400 53,543 892,612,000

T1NR 98W 16,193 65,530,900 103,054 1,668,750,000

T1S R96W 4,465 18,069,300 20,668 100,116,000

T1S R97W 24,439 98,901,400 92,586 2,263,730,000

T1SR 98W 23,844 96,493,500 134,215 3,200,220,000

T1S R99W 4,881 19,752,800 83,564 407,874,000

T2S R96W 0 0 0 0

T2SR 97W 16,066 65,017,000 15,642 367,251,000

T2S R98W 20,507 82,989,100 57,806 1,185,420,000

T3S R96W 0 0 0 0

T3S R97W 13 52,609 1 9,000

T3S R98W 3,646 14,754,900 1,649 14,199,000

Total 127,397 515,558,909 10,100,180,000
40 Nahcolite Resources in the Green River Formation, Piceance Basin, Colorado

Figure 30. Isopleth map showing in-place nahcolite (NaHCO3) resources of R-5 oil shale zone (Donnell and Blair, 1970; 

Cashion and Donnell, 1972) in the Parachute Creek Member of the Green River Formation, Piceance Basin, Rio Blanco 

County, northwestern Colorado. Nahcolite resources reported in short tons per acre. Inferred extent of nahcolite 

depocenter outlined in red.

T

2

N

T

1

N

T

1

S

T

2

S

T

3

S

17,688

0

0

0

0

0

0

265,176

208,606

292,071

365,123

329,309

330,604

349,339

353,703

8,822

0

122,432

20,856

0 0 0 0

0

0

0 134,144

0 1,072

85,490

0

99,816

0

0

0

0

0

114,958

291,036

293,441

128,855

0

237,283

232,092

8,906 0

0

0

0

0

0

163,633

152,032

10,514

105,286

218,391

R. 99 W. R. 98 W. R. 97 W. R. 96 W.

108°30'

40°00'

0 1.5 3 6 MILES

0 31.5 6 KILOMETERS

EXPLANATION Index map

Top of Mahogany zone Nahcolite in-place resource, R–5 zone—In tons per acre

Base of Parachute Creek Member 225,001– <– 75,000 Inferred extent of nahcolite 300,000

 depocenter 75,001– 300,001–

10514 Core hole—Nahcolite content in 150,000 375,000

 tons per acre Colorado

150,001–

 225,000
Summary 41

T

2

N

R. 99 W. R. 98 W. R. 97 W. R. 96 W.

T

1

N

T

1

S

T

2

S

T

3

S

0 0 0

1,092,499,968 753,324,992 122,018

202,360,992 5,129,759,744 2,883,290,112 83,192,896

2,008,179,968 748,980,992

108°30'

40°00'

0 1.5 3 6 MILES

0 31.5 6 KILOMETERS

Colorado

EXPLANATION Index map

Top of Mahogany zone

Base of Parachute Creek Member

Inferred extent of nahcolite

 depocenter

Nahcolite in-place resource, R–5 zone—

 By township, in short tons 753,324,992

Figure 31. Map showing in-place nahcolite (NaHCO3) resources in the R-5 oil shale zone (Donnell and 

Blair, 1970; Cashion and Donnell, 1972) in the Parachute Creek Member of the Green River Formation 

by township, Rio Blanco County, northwestern Colorado. Nahcolite resources reported in short tons. 

Inferred extent of nahcolite depocenter outlined in red.
42 Nahcolite Resources in the Green River Formation, Piceance Basin, Colorado

Table 9. Total in-place nahcolite resources and average tons per acre, by township, in the R-5 oil shale zone in the 

nahcolite-bearing interval of the Parachute Creek Member of the Green River Formation, Piceance Basin, Rio Blanco 

County, northwestern Colorado.

[All values calculated by ESRIs ArcGIS GeoStatistical Analyst extension with a Radial Basis Function (RBF) Multiquadratic Gridding 

Function; 1 acre = 4,047 m2]

Township Acres Area (m2) Average tons per acre Total in-place resource in tons

T1N R97W 10,677 43,208,400 44,927 748,981,000

T1NR 98W 16,189 65,514,700 124,015 2,008,180,000

T1S R96W 4,438 17,960,000 17,174 83,193,000

T1S R97W 24,450 98,945,900 117,926 2,883,290,000

T1SR 98W 23,844 96,493,500 215,139 5,129,760,000

T1S R99W 4,592 18,583,200 41,459 202,361,000

T2S R96W 78 315,656 13 122,000

T2SR 97W 18,759 75,915,200 32,086 753,325,000

T2S R98W 16,759 67,821,500 53,274 1,092,500,000

T3S R96W 0 0 0 0

T3SR 97W 0 0 0 0

T3S R 98W 0 0 0 0

Total 119,786 484,758,056 12,901,712,000

Table 10. Total in-place nahcolite resources and average tons per acre, by township, in the L-5 oil shale zone in the 

nahcolite-bearing interval of the Parachute Creek Member of the Green River Formation, Piceance Basin, Rio Blanco 

County, northwestern Colorado.

[All values calculated by ESRIs ArcGIS GeoStatistical Analyst extension with a Radial Basis Function (RBF) Multiquadratic Gridding 

Function; 1 acre = 4,047 m2]

Township Acres Area (m2

) Average tons per acre Total in-place resource in tons

T1N R97W 2,020 8,174,670 2,871 47,862,000

T1NR 98W 3,355 13,577,200 4,811 77,910,000

T1S R96W 0 0 0 0

T1S R97W 2,930 11,857,300 3,588 87,728,000

T1SR 98W 9,854 39,877,800 20,886 498,013,000

T1S R99W 0 0 0 0

T2S R96W 0 0 0 0

T2SR 97W 3,035 12,282,200 3,038 71,324,000

T2S R98W 2,281 9,230,910 3,363 68,961,000

T3S R96W 0 0 0 0

T3SR 97W 0 0 0 0

T3S R 98W 0 0 0 0

Total 23,475 95,000,080 851,799,000
Summary 43

T

2

N

T

1

N

T

1

S

T

2

S

T

3

S

86,025

173,197

83,154

88,242

79,751 10,035

65,939

36,597

42,667

23,109

R. 99 W. R. 98 W. R. 97 W. R. 96 W.

108°30'

40°00'

0 1.5 3 6 MILES

0 31.5 6 KILOMETERS

EXPLANATION

Top of Mahogany zone

Base of Parachute Creek Member

Core hole—Nahcolite content in

 tons per acre

 in-place resource, L–5 zone—In tons per acre

 35,000

35,001–

 70,000

70,001–

 105,000

105,001–

 140,000

140,001–

 175,000

Inferred extent of nahcolite

 depocenter

Colorado

Index map

65,939

<–

Nahcolite

Figure 32. Isopleth map showing in-place nahcolite (NaHCO3) resources of L-5 oil shale zone (Donnell and Blair, 1970; 

Cashion and Donnell, 1972) in the Parachute Creek Member of the Green River Formation, Piceance Basin, Rio Blanco 

County, northwestern Colorado. Nahcolite resources reported in short tons per acre. Inferred extent of nahcolite 

depocenter outlined in red.
44 Nahcolite Resources in the Green River Formation, Piceance Basin, Colorado

T

2

N

R. 99 W. R. 98 W. R. 97 W. R. 96 W.

T

1

N

T

1

S

T

2

S

T

3

S

0 0 0

68,960,896 71,323,696 0

0 498,012,992 87,728,304 0

77,910,200 47,862,400

108°30'

40°00'

Colorado

EXPLANATION Index map

Top of Mahogany zone

Base of Parachute Creek Member

Inferred extent of nahcolite

 depocenter

Nahcolite in place resource, L–5 zone—

 By township, in short tons 87,728,304

0 1.5 3 6 MILES

0 31.5 6 KILOMETERS

Figure 33. Map showing in-place nahcolite (NaHCO3) resources in the L-5 oil shale zone (Donnell and Blair, 

1970; Cashion and Donnell, 1972) in the Parachute Creek Member of the Green River Formation by township, Rio 

Blanco County, northwestern Colorado. Nahcolite resources reported in short tons. Inferred extent of nahcolite 

depocenter outlined in red.
Summary 45

858

0

0

0

0

0

0

427.3

614.5

711.2

851.8

973

1109.3

1059.7

1006.9 987.2

1071 276

653

540

0

24 0 122

0 96

36 756

368

394

480

40

564.7

34

0

0

45

0 442

896

908.8

741

358.6

697.1

911.8

406

32

30

240

205.7

413.9

356.6

775.5

1027

560

683

679.1

108°30' 108°00'

40°00'

39°30'

0 1.5 3 6 MILES

0 31.5 6 KILOMETERS

EXPLANATION

Mahogany Bed outcrop

Base of Parachute Creek Member

Core hole—Thickness of nahcolite

 interval in feet

276

-bearing interval—Thickness in feet

 200

201–400

401–600

601–800

801–1,000

1,001–1,200

Inferred extent of nahcolite

 depocenter

Colorado

Index map

R 96 W R 95 W

R 101 W R 100 W R 99 W R 98 W R 97 W R 94 W

T

8

S

T

7

S

R 93 W

T

6

S

T

5

S

T

4

S

T

3

S

T

9

S

R 94 W

R 101 W R 100 W R 99 W R 98 W R 97 W

T

2

S

T

1

S

T

1

N

R 96 W R 95 W

T

2

N

<–

Nahcolite

Figure 34. Map showing thickness of nahcolite-bearing interval in the lower and upper parts of the Parachute 

Creek Member of the Green River Formation, Piceance Basin, Rio Blanco County, northwestern Colorado. Inferred 

extent of nahcolite depocenter outlined in red. Core holes show individual thicknesses of the nahcolite-bearing 

interval. See figure 7 and table 1 for core hole name and data.
46 Nahcolite Resources in the Green River Formation, Piceance Basin, Colorado

R 96 W R 95 W

R 101 W R 100 W R 99 W R 98 W R 97 W R 94 W

T

8

S

T

7

S

R 93 W

T

6

S

T

5

S

T

4

S

T

3

S

T

9

S

R 94 W

R 101 W R 100 W R 99 W R 98 W R 97 W

T

2

S

T

1

S

T

1

N

R 96 W R 95 W

T

2

N

14.7

17.4

28.8

27.1 29.7

30.9

27.9

27.8

33.2 31.5

35.3 11.8

14.7

2.6

2.2

3.4

17

15.5 3.6

10.5

27.7 17.1

7.2

18.8

8.9

17

14.2

26.1 29.3

16.3

11.6

24.4

27.3

1.3

17.2 14.3

4.9

6

12.6

11.5

17.2

21.7

18.1

18.6

26.6

108°30' 108°00'

40°00'

39°30'

0 1.5 3 6 MILES

0 31.5 6 KILOMETERS

EXPLANATION Index map

Top of Mahogany zone Nahcolite content—In average weight percent

Base of Parachute Creek Member

0–7 21.1–28 Inferred extent of nahcolite

 depocenter

7.1–14 28.1–35 24.4 Core hole—Nahcolite content in

 average weight percent Colorado

14.1–21

Figure 35. Isopleth map showing average nahcolite (NaHCO3) content of nahcolite-bearing interval in the 

lower and upper parts of the Parachute Creek Member of the Green River Formation, Piceance Basin, Rio 

Blanco County, northwestern Colorado. Inferred extent of nahcolite depocenter outlined in red. Nahcolite 

values reported in weight percent. Core holes show individual nahcolite contents.
Summary 47

R 96 W R 95 W

R 101 W R 100 W R 99 W R 98 W R 97 W R 94 W

T

8

S

T

7

S

R 93 W

T

6

S

T

5

S

T

4

S

T

3

S

T

9

S

R 94 W

R 101 W R 100 W R 99 W R 98 W R 97 W

T

2

S

T

1

S

T

1

N

R 96 W R 95 W

T

2

N

18 208

455

507

578

866

940

833

933 897

9

114

346

62

14 2

53

6 431

127

351

269

13

444

27

239

701768

423

107

491

612

24

19

16

51

24

190

132

461

503

325

311

549

108°30' 108°00'

40°00'

39°30'

0 1.5 3 6 MILES

0 31.5 6 KILOMETERS

EXPLANATION

Index map Top of Mahogany zone Nahcolite content—In tons per acre

Base of Parachute Creek Member 500,000.1– 0–100,000 Inferred extent of nahcolite 750,000

 depocenter 100,000.1– > 750,000 208 Core hole—Naholite content in 250,000

 thousands of tons per acre 250,000.1– Colorado

 500,000

Figure 36. Isopleth map showing total in-place nahcolite (NaHCO3) resources in the nahcolite-bearing interval in the 

lower and upper parts of the Parachute Creek and Garden Gulch Members of the Green River Formation, Piceance Basin, 

Rio Blanco County, northwestern Colorado. Inferred extent of nahcolite depocenter outlined in red. Nahcolite resources 

reported in short tons per acre while individual core holes show nahcolite resource in thousands of tons per acre.
48 Nahcolite Resources in the Green River Formation, Piceance Basin, Colorado

Table 11. Total in-place nahcolite resources and average tons per acre, by township, in the nahcolite-bearing interval of 

the Parachute Creek Member of the Green River Formation, Piceance Basin, Rio Blanco County, northwestern Colorado.

[All values calculated by ESRI’s ArcGIS GeoStatistical Analyst extension with a Radial Basis Function (RBF) Multiquadratic Gridding Function; 1 acre = 4,047 m2

]

Township Acres Area (m2) Average tons per acre Total in-place resource in tons

T1N R97W 16,671 67,465,300 186,593 3,110,690,000

T1N R98W 16,193 65,530,900 373,948 6,055,350,000

T1S R96W 4,844 19,603,000 128,893 624,360,000

T1S R97W 24,450 98,945,900 348,200 8,513,490,000

T1S R98W 23,844 96,493,500 542,541 12,936,300,000

T1S R99W 4,881 19,752,800 196,429 958,770,000

T2S R96W 9,719 39,331,500 41,166 400,090,000

T2S R97W 23,478 95,012,400 174,148 4,088,640,000

T2S R98W 20,507 82,989,100 268,289 5,501,810,000

T3S R96W 3,956 16,009,400 9,904 39,180,000

T3S R97W 12,838 51,953,700 48,726 625,540,000

T3S R98W 8,613 34,855,700 50,965 438,960,000

Total 169,994 687,943,200 43,293,190,000
Summary 49

R 96 W R 95 W

R 101 W R 100 W R 99 W R 98 W R 97 W R 94 W

T

8

S

T

7

S

R 93 W

T

6

S

T

5

S

T

4

S

T

3

S

T

9

S

R 94 W

R 101 W R 100 W R 99 W R 98 W R 97 W

T

2

S

T

1

S

T

1

N

R 96 W R 95 W

T

2

N

438,963,008 625,540,992

39,181,500

5,501,810,176 4,088,640,000

400,094,016

958,769,984

12,936,299,520 8,513,489,920

624,356,992

6,055,349,760 3,110,690,048

108°30' 108°00'

40°00'

39°30'

0 3 6 12 MILES

0 5 10 2.5 KILOMETERS

EXPLANATION

Top of Mahogany zone

Base of Parachute Creek Member

Inferred extent of nahcolite

 depocenter

Colorado

Index map

Nahcolite in-place resource by township—

 In short tons 4,088,640,000

Figure 37. Map showing total in-place nahcolite (NaHCO3) resources of the lower and middle parts of the 

Parachute Creek Member of the Green River Formation by township, Rio Blanco County, northwestern Colorado. 

Township resources reported in short tons. Individual core holes show nahcolite resources in short tons per acre. 

Inferred extent of nahcolite depocenter outlined in red.
50 Nahcolite Resources in the Green River Formation, Piceance Basin, Colorado

References Cited

American Society for Testing and Materials, 1980, Standard 

method of test for oil from oil shale: Annual Book of 

ASTM Standards, Part 25, Designation D 3904–80, 

p. 513–515.

Beard, T.N., Tait, D.B., and Smith, J.H., 1974, Nahcolite 

and dawsonite resources in the Green River Formation, 

Piceance Basin, in Murray, D.K., ed., Energy Resources of 

the Piceance Creek Basin, Colorado, 25th Field Conference: 

Rocky Mountain Association of Geologists, p. 101–109.

Brownfield, M.E., Hettinger, R.D., and Johnson, E.A., 2000, 

A summary of the stratigraphy, coal resources, and coal-bed 

methane potential of northwest Colorado, in Kirschbaum, 

M.A., Roberts, L.N.R., and Biewick, L.R.H., eds., Geologic assessment of coal in the Colorado Plateau—Arizona, 

Colorado, New Mexico, and Utah: U.S. Geological Survey 

Professional Paper 1625–B, chap. I, 25 p., CD-ROM.

Cashion, W.B., and Donnell, J.R., 1972, Chart showing correlation of selected key units in the organic-rich sequence 

of the Green River Formation, Piceance Basin, Colorado, 

and Uinta Basin, Utah: U.S. Geological Survey Oil and Gas 

Investigations Chart OC–65. 

Cashion W.B., and Donnell, J.R., 1974, Revision of nomenclature of the upper part of the Green River Formation, 

Piceance Creek Basin, Colorado, and eastern Uinta Basin, 

Utah: U.S. Geological Survey Bulletin, 1394–G, p. G1–G9.

Donnell, J.R., and Blair, R.W., Jr., 1970, Resource appraisal 

of three rich oil shale zones in the Green River Formation, 

Piceance Creek basin, Colorado: Colorado School of Mines 

Quarterly, v. 65, no. 4, p. 73–87.

Dyni, J.R., 1969, Structure of the Green River Formation, 

northern part of the Piceance Creek basin, Colorado: 

Mountain Geologist, v. 6, no. 2, p. 57–66.

Dyni, J.R., 1974a, Nahcolite analyses of seven drill cores from 

the Green River Formation, Rio Blanco County, Colorado: 

U.S. Geological Survey Open-File Report 74–1027 45 p. 

Dyni, J.R., 1974b, Stratigraphy and nahcolite resources of 

the saline facies of the Green River Formation, Rio Blanco 

County, Colorado: U.S. Geological Survey Open-File 

Report 74-56, 28 p.

Dyni, J.R., 1974c, Stratigraphy and nahcolite resources of 

the saline facies of the Green River Formation, Rio Blanco 

County, Colorado: in Murray, D.K., ed., Energy Resources 

of the Piceance Creek Basin, Colorado, 25th Field Conference: Rocky Mountain Association of Geologists, 

p. 111–122.

Dyni, J.R., 1981, Geology of the nahcolite deposits and associated oil shales of the Green River Formation in the Piceance 

Creek Basin, Colorado: Boulder, University of Colorado, 

Ph.D. dissertation, 144 p.

Dyni, J.R., 1996, Sodium carbonate resources of the Green 

River Formation: U.S. Geological Open-File Report 

96–729, 39 p.

Dyni, J.R., 1998, Fisher assays of oil shale drill cores and 

rotary cuttings from the Piceance Creek Basin, Colorado: 

U.S. Geological Survey Open-File Report 98–483, CD–

ROM.

Dyni, J.R., Beck, P.C., and Mountjoy, W., 1971a, Nahcolite 

analysis of three drill holes from the saline facies of the 

Green River Formation in northwest Colorado: U.S. 

Geological Survey Open-File Report 71–94, 13 p.

Dyni, J.R., Beck, P.C., and Mountjoy, W., 1971b, Thermal 

method for quantitative determination of nahcolite in 

Colorado oil shale: U.S. Geological Survey Professional 

Paper 750–B, p. B194–B198.

Ertl, Tell, 1947, Sodium bicarbonate (nahcolite) from Colorado oil shales: American Mineralogist, v. 32, no. 3-4, p. 

117–129.

Ezekial, M., and Fox, K.A., 1959, Methods of correlation and 

regression analysis, 3rd Ed.: John Wiley & Sons, Inc., New 

York, 548 p.

Hail, W.J., Jr., 1972, Preliminary geologic map of the Barcus Creek SE quadrangle, Rio Blanco County, Colorado: 

U.S. Geologic Survey Miscellaneous Field Studies Map 

MF–347, scale 1:24,000.

Hite, R.J., and Dyni, J.R., 1967, Potential resources of dawsonite and nahcolite in the Piceance Creek Basin, northwest 

Colorado: Colorado School Mines Quarterly, v. 62, no. 3,

p. 25–38.

Johnson, R.C.,1985, Early Cenozoic history of the Uinta and 

Piceance Creek basins, Utah and Colorado, with special reference to the development of Eocene Lake Uinta, in Flores, 

R.M., and Kaplan, S.S., eds., Cenozoic paleogeography of 

the west-central United States, Rocky Mountain Paleography Symposium 3: The Rocky Mountain Section, Society of 

Economic Paleontologists and Mineralogists, p. 247–276. 

Nielsen, I., 1969, The amazing Piceance mineral suite and its 

industrial potential for energy–oil–metals–chemicals: Engineering and Mining Journal, January, p. 57–60. 

Nielsen, I., 1972, Low-cost air and water pollution control 

chemicals from Colorado’s oil shale deposits: Address 

delivered to Air-Solid Wastes and Water Interface, ATCHE, 

February 20–23 meetings.
References Cited 51

Pipiringos, G.N., and Johnson, R.C., 1976, Preliminary geologic map and correlation diagram of the White River City 

quadrangle, Rio Blanco County, Colorado: U.S. Geological 

Survey Miscellaneous Field Studies Map MF–736, scale 

1:24,000.

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