Chapter 6

Calculation of Overburden above the 

Mahogany Bed in the Uinta Basin, Utah

and Colorado

By Tracey J. Mercier

Chapter 6 of 7

Oil Shale Resources of the Uinta Basin, Utah and Colorado 

By U.S. Geological Survey Oil Shale Assessment Team

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

U.S. Department of the Interior

U.S. Geological Survey

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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:

Mercier, T.J., 2010, Calculation of overburden above the Mahogany bed in the Uinta basin, Utah and Colorado: 

U.S. Geological Survey Digital Data Series DDS–69–BB, chp. 6, 7 p.
iii

Contents

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

Procedure........................................................................................................................................................1

Conclusion.......................................................................................................................................................1

References Cited............................................................................................................................................7

Figures

1–5. Maps showing:

1. Structure contours on top of the Mahogany bed drawn on the 

Digital Elevation Model (DEM) clipped to the Uinta Basin ...........................................2

2. Triangular Irregular Network (TIN) model of the top of the Mahogany 

bed subsurface structure...........................................................................................................3

3. Overburden above the Mahogany bed in the Uinta Basin ...........................................4

4. Overburden above the Mahogany bed in the Uinta Basin, hillshade 

effect applied..............................................................................................................................5

5. Cubic miles of overburden per township above the Mahogany bed 

in the Uinta Basin.................................................................................................................6
Introduction

As part of the U.S. Geological Survey (USGS) National 

Oil Shale Assessment, the volume of overburden material 

was calculated above the Mahogany bed of the Eocene 

Green River Formation in the Uinta Basin, Utah. A common 

Geographic Information System (GIS) method was used to 

calculate the amount of overburden by subtracting a model of 

the Mahogany surface from a Digital Elevation Model (DEM). 

To maintain consistency with other models in the assessment, 

all overburden calculations and resultant files were analyzed 

using a one-acre (63.615 m (208.7106 ft) per side) raster 

model cell size with an effective area of 4,047 m2

/43,560 ft2.

Procedure 

The first step was to digitize (1) the locations of 

the Mahogany bed outcrops (fig. 1) from four published 

1:250,000-scale geologic maps (Bryant, 1992; Cashion, 

1973; Rowley and others, 1985; Witkind, 1995); and (2) the 

detailed structure contours (elevation in ft) on the top of the 

Mahogany bed (Cashion, 1967). Next, the Mahogany outcrop 

lines and an approximate 6,000-ft-depth contour to the top 

of the Mahogany bed were combined to delineate a limitingresource polygon for calculation purposes; the boundary of 

the polygon file was confined in the west and northeast due to 

lack of control (fig. 1). The structure contour map was created 

by combining the structure contours from the southern part 

of the basin (Cashion, 1967) and a digital version of structure 

contours on the top of the Mahogany bed of the northern Uinta 

Basin by Johnson and Roberts (2003). The resultant structure 

Calculation of Overburden Above the Mahogany Bed in the 

Uinta Basin, Utah and Colorado

By Tracey J. Mercier

contour file was converted to a point file containing elevation values for the top of the Mahogany bed. This point file 

was then processed using the GeoStatistical Analyst’s Radial 

Basis Function (RBF) contouring method to generate a surface 

model in ArcGIS (ESRI, 2006). The RBF surface model was 

then converted to an ESRI GRID as well as a Triangulated 

Irregular Network (TIN) model (fig. 2) to use in ArcGIS’s 3D 

Analyst extension. 

An ArcGIS GRID (fig. 3) containing values of total 

overburden, in ft, above the Mahogany bed for each oneacre cell was created by subtracting the Mahogany surface 

GRID from the DEM GRID using the ArcGIS Spatial Analyst 

Raster Calculator. The overburden GRID was converted to a 

TIN. Figure 4 shows the effect of applying hillshade to the 

overburden TIN to aid in visual analysis. In order to calculate 

the volume of overburden material contained in specific 

polygonal areas, the ArcToolbox’s TIN Polygon Volume 

function was used to calculate the total volume of overburden, 

in mi3

, within the basin, and the amount of overburden within 

each Public Land Survey System (PLSS) township (fig. 5).

Conclusion

This analysis determined the total volume of overburden above the defined resource area for the Mahogany bed 

in the Uinta Basin to be approximately 1,410 mi3

 of rock 

and other material. For comparison, that amount is approximately equal to 162 times the volume of water in Lake Mead; 

2,350,000,000 Olympic-size swimming pools; 2,104 times the 

amount of rock removed during the Mt. St. Helens eruption; 

1.4 times the volume needed to fill the Grand Canyon; or over 

52 billion hopper cars at 4,000-ft3

 capacity.
R 3 W R 2 W R 12 W R 11 W R 10 W R 9 W R 8 W R 7 W R 6 W R 5 W R 4 W R 1 W R 1 E R 24 E 

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111°00' 110°30' 110°00' 109°30' 

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EXPLANATION

Top of Mahogany bed outcropDepth to Mahogany bed, 6,000-ft contourBase of Parachute Creek MemberDefined boundary for assessment

Structure contours on top of Mahogany bed, elevation in ft

> 8,000 (100 ft contour interval)6,001–8,000 (100 ft contour interval)4,001–6,000 (100 ft contour interval)2,001–4,000 (500 ft contour interval)500–2,000 (500 ft contour interval)-1,000–499 (500 ft contour interval)

0

2,000

4,000

6,000

8,000

8,800

-1,000

Figure 1. Structure contours on top of the Mahogany bed drawn on the Digital Elevation Model (DEM) clipped to the Uinta Basin.
R 3 W R 2 W R 12 W R 11 W R 10 W R 9 W R 8 W R 7 W R 6 W R 5 W R 4 W R 1 W R 1 E R 24 E R 

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111°00' 110°30' 110°00' 109°30' 

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0 6 12 MILES

Top of Mahogany bed outcropDepth to Mahogany bed, 6,000-ft contourBase of Parachute Creek Member outcropDefined boundary for assessment

Mahogany bed structure, elevation in ft

> 8,0006,001–8,0004,001–6,0002,001–4,0000–2,000< 0

0 5 10 KILOMETERS 

EXPLANATION

Figure 2. Triangular Irregular Network (TIN) model of the top of the Mahogany bed subsurface structure.
Figure 3. Overburden above the Mahogany bed in the Uinta Basin.

R 3 W R 2 W R 12 W R 11 W R 10 W R 9 W R 8 W R 7 W R 6 W R 5 W R 4 W R 1 W R 1 E R 24 E 

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111°00' 110°30' 110°00' 109°30' 

40°00'39°30'39°00'

0 6 12 MILES0 5 10 KILOMETERS 

EXPLANATION

Top of Mahogany bed outcropDepth to Mahogany bed, 6,000-ft contourBase of Parachute Creek Member outcropDefined boundary for assessment

Mahogany Overburden, depth in ft

5,001–6,0003,751–5,0002,501–3,7501,250–2,500< 1,250
Figure 4. Overburden above the Mahogany bed in the Uinta Basin, hillshade effect applied. 

R 3 W R 2 W R 12 W R 11 W R 10 W R 9 W R 8 W R 7 W R 6 W R 5 W R 4 W R 1 W R 1 E R 24 E 

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111°00' 110°30' 110°00' 109°30' 

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0 6 12 MILES0 5 10 KILOMETERS 

Top of Mahogany bed outcropDepth to Mahogany bed, 6,000-ft contourBase of Parachute Creek Member outcropDefined boundary for assessment

 Mahogany overburden, depth in ft

> 5,2504,501–5,2503,751–4,5003,001–3,7502,251–3,0001,501–2,250751–1,500

< 750 _

EXPLANATION
Figure 5. Cubic miles of overburden per township above the Mahogany bed in the Uinta Basin. 

R 3 W R 2 W R 12 W R 11 W R 10 W R 9 W R 8 W R 7 W R 6 W R 5 W R 4 W R 1 W R 1 E R 24 E R 

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15.5 12.7 17.5 17.6 15.6 14.1 8.3 18.4 17.5 17.6

23.1 21.4 16.8 

23.3 15.9

0.3

6.9 10.3 11 1.7

0.1 0.3 0.6 1.5 3.5 2.7

17.8 

20.9 24.1 32.7 30.5

3.2

0.2 3.9 8.6 12.8 15.1 13.6 4.6

2.8

11.1

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0.10.1

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2.1

0.9 0.6

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14.4 12.9 11.3 11.7 13.1 12.7 11.5 9.7 6.5 10.4

0.2 1.3

32.7

111°00' 110°30' 110°00' 109°30' 

40°00'39°30'39°00'

0 6 12 MILES0 5 10 KILOMETERS 

EXPLANATION

Top of Mahogany bed outcropDepth to Mahogany bed, 6,000-ft contourBase of Parachute Creek Member outcropDefined boundary for assessmentCubic miles of overburden within township

Mahogany overburden, in mi3 per township

> 3022.6–3015.1–22.57.6–15 7.5

<_
References Cited 7

References Cited

Bryant, B.H., 1992, Geologic and structure maps of the Salt 

Lake City 1 degree by 2 degrees quadrangle, Utah and Wyoming: U.S. Geological Survey Miscellaneous Investigation Map I-1997, scale 1:250,000, http://pubs.er.usgs.gov/

usgspubs/i/i1997.

Cashion, W.B., 1967, Geology and fuel resources of the Green 

River Formation, southeastern Uinta Basin, Utah and Colo-

rado: U.S. Geological Survey Professional Paper 548, plate 

1, 48 p., http://pubs.er.usgs.gov/usgspubs/pp/pp548.

Cashion, W.B., 1973, Geologic and structure map of the Grand 

Junction quadrangle, Colorado and Utah: U.S. Geological 

Survey Miscellaneous Investigation Map I-736, scale 

1:250,000, http://pubs.er.usgs.gov/usgspubs/i/i736.

Environmental Systems Research Institute, Incorporated 

(ESRI), 2006, ArcGIS, ver. 9.2: ESRI, Redlands, Calif., 

http://www.esri.com/software/arcgis/index.html.

Johnson, R.C., and Roberts, L.N., 2003, Depths to selected 

stratigraphic horizons in oil and gas wells for upper Cretaceous and lower Tertiary strata of the Uinta Basin, Utah: 

U.S. Geological Survey Digital Data Series 69-B, Chapter 

13, 33 p., http://pubs.usgs.gov/dds/dds-069/dds-069-b/.

Rowley, P.D., Hansen, W.R., Tweto, Ogden, Carrara, P.E.,

1985, Geologic map of the Vernal 1 degree by 2 degrees 

quadrangle, Colorado, Utah, and Wyoming: U.S. Geological Survey Miscellaneous Investigation Map I-1526, scale 

1:250,000, http://pubs.er.usgs.gov/usgspubs/i/i1526.

Witkind, I.J., 1995, Geologic map of the Price 1 degree 

by 2 degrees quadrangle, Utah: U.S. Geological Survey 

Miscellaneous Investigation Map I-2462, scale 1:250,000, 

http://pubs.er.usgs.gov/usgspubs/i/i2462.

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