KGS

Geology

  Thomas County Geohydrology

Prev Page--Quality of Water || Next Page--Tertiary System

Start

Table of Contents

Abstract

Introduction

Geography

Geology

Ground Water

Water Bearing Formations

Well Records

Well Logs

References

Plates

 

Water-bearing Formations

Cretaceous System

Pierre Shale

Rocks 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.

Pierre shale slopes from high in west to low in east

The Pierre shale of northwestern Kansas has been studied in detail by Elias (1931). It consists of gray, blue-gray, and black clayey shale containing zones of abundant concretions and thin beds of bentonite. Elias divided the Pierre shale into five named members and one unnamed unit. These are, in ascending order: Sharon Springs shale, Weskan shale, Lake Creek shale, Salt Grass shale, an unnamed shale interval, and the Beecher Island shale at the top. Probably all but the uppermost of the named members are present under Thomas County. The Pierre shale does not yield water to wells in Thomas County.

Prev Page--Quality of Water || Next Page--Tertiary System

  Kansas Geological Survey, Thomas County Geohydrology
Comments to webadmin@kgs.ku.edu
Web version Nov. 2001. Original publication date Dec. 1945.
URL=http://www.kgs.ku.edu/General/Geology/Thomas/06_form.html