Water Bearing Formations
Pierre ShaleRocks of Cretaceous age do not crop out in Thomas County. However, the Pierre shale of Cretaceous age crops out along valleys immediately adjacent to the county on the southwest, along Beaver Creek valley in Rawlins County to the north, and in large areas of central Wallace and Logan counties. The Pierre shale underlies all of Thomas County at relatively shallow depths and serves as an impervious floor below the water-bearing sediments. It retards the downward percolation of water in much the same manner as the floor of a tank. Although the thickness of the Pierre shale below all parts of the county is not known, it is probably nowhere less than 100 feet thick and may be as much as 1,000 feet thick under the northwestern part of the county. Contours that show the topography of the Pierre shale surface have been plotted from test-hole data and are shown in figure 13.
Figure 13--Contour map showing the topography of the Pierre shale surface. Figures denote altitude of the Pierre shale surface in test holes, and figures in parentheses are the test-hole numbers which correspond to the numbers of the logs included in this report. A large version of this figure is available.
Kansas Geological Survey, Thomas County Geohydrology|
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Web version Nov. 2001. Original publication date Dec. 1945.