The Wilcox Group of central Texas contains shallow (<500 ft) coal deposits that are mined for use in mine-mouth electric power generating plants. These coal deposits range in apparent rank from lignite to sub-bituminous (Tewalt, 1986), and are similar in rank and composition to shallow coal deposits in the northeast and south Texas areas (fig. 1). The coal zones and associated strata in the central Texas study area generally dip to the southeast toward the Gulf of Mexico coastline and basin center. The central Texas resource assessment area includes parts of eight counties (fig. 2). The assessment area was selected to encompass current mining areas and because of the availability of subsurface stratigraphic data in the area. The assessment area is roughly 160 miles long and 5 to 25 miles wide and generally follows the outcrop of the Paleocene - Eocene Wilcox Group in central Texas (figs. 1 and 2). Approximately 1,800 subsurface stratigraphic records from rotary and core drill holes were used to assess the resources of the central Texas assessment area. Of the 1,800 drill holes, only 168 are public data points and are primarily located in the areas that have been permitted for surface mining (fig. 2; Appendix 1). The remaining 1632 drill holes, which are distributed throughout the assessment area, were provided to the U.S. Geological Survey (USGS) on a confidential basis by various coal companies for use in regional studies. Nine coal zones were identified and assessed in the central Texas assessment area. Several other coal zones (as many as 9 unassessed zones) were identified but were not assessed due to the thinness of the coal beds or the lack of deep stratigraphic data (fig. 3). A total of 7.7 billion short tons of coal was identified in this assessment that excluded the resources within current coal mine lease areas (fig. 2).
Corresponding maps were constructed to show the overburden, structure contour of the top of the coal zone, and cumulative coal-zone thickness for each of the nine coal zones. Warwick and Crowley (1995) offer a discussion of the general geologic setting and stratigraphy of the central Texas study area, and Tewalt (1986) presents a discussion of the coal quality aspects of the central Texas study area.