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  Thomas County Geohydrology

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Table of Contents

Abstract

Introduction

Geography

Geology

Ground Water

Water Bearing Formations

Well Records

Well Logs

References

Plates

 

Geology

Summary of Stratigraphy

The surface geology of Thomas County is relatively simple. All the rocks that crop out at the surface are sedimentary in origin, are of Quaternary and Tertiary age, and for the most part are unconsolidated. The named formations are listed in table 2, and their areal distribution is shown on plate 1. Cross sections in figures 3 and 4 show the general relationship of the several formations. It will be noted by reference to the geologic map (pl. 1) that somewhat more than 90 percent of the surface area of the county is underlain by deposits of Quaternary age that are assigned to the Pleistocene Sanborn formation and the Recent slope deposits and alluvium. The oldest beds exposed are assigned to the Pliocene Ogallala formation.

Table 2--General section of the geologic formations of Thomas County, Kansas.

System Series Subdivisions Thickness
(feet)		 Character Water Supply
Quaternary Recent Alluvium 0-30 Silt, sand, and gravel along the major stream valleys. Mostly sandy silt but locally poorly sorted sand and gravel. Yields water to wells only at a few places along such valleys as South Sappa and Prairie Dog creeks.
Recent and Pleistocene Sanborn formation (Pleistocene) and slope deposits (Recent) 0-65 Silt, massive, with locally some sand and gravel at base. Slope deposits are silt, sand, and gravel. Generally above the water table and yields little or no water to wells.
Tertiary Pliocene Ogallala formation 60-275 Sand, gravel, silt, and clay, some zones cemented with calcium carbonate to form hard "mortar beds." Individual beds generally lenticular. Yields abundant supplies of water of good quality and is the source of water for nearly all the wells in the county.

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  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/04_geol.html