During 1978, the U.S. Geological Survey began a 5-year study of the High Plains regional aquifer system to provide hydrologic information for evaluation of the effects of long-term development of the aquifer and to develop computer models for prediction of aquifer response to alternative changes in ground-water management (Weeks, 1978). This report is one of a series presenting hydrologic information of the High Plains aquifer in Oklahoma.
This report consists of two maps showing the altitude and configuration of the eroded pre-Ogallala bedrock surface (sheets 1 and 2) that forms the base of the aquifer. Bedrock slopes generally from west to east and is composed of rocks of Permian, Triassic-Jurassic, and Cretaceous age. The subcrop extent of these rocks is shown by Morton (1973) for Oklahoma and by Weeks and Gutentag (1981) for the entire High Plains study area. Altitudes of the aquifer base were determined from drillers' logs provided by the Oklahoma Water Resources Board and from published and unpublished information in the files of the U.S. Geological Survey. Where data were sparse, the total well depth was used as the aquifer base under the assumption that wells generally are not drilled very deep into non-water yielding bedrock.