The purpose of this map report is to provide a description of one of the principal geohydrologic systems in Upper Cambrian through Lower Cretaceous rocks in Kansas. The report is the result of an investigation made as part of the Central Midwest Regional Aquifer-System Analysis (CMRASA). The CMRASA is one of several major investigations by the U.S. Geological Survey of regional aquifer systems in the United States. These regional investigations are designed to increase knowledge of the flow regime and hydrologic properties of major aquifer systems and to provide quantitative information for the assessment, development, and management of water supplies. The CMRASA study area includes all or parts of 10 Central Midwestern States (Jorgensen and Signor, 1981), as shown on the envelope cover.

This Hydrologic Investigations Atlas, which consists of a series of nine chapters, presents a description of the physical framework and the geohydrology of principal aquifer and confining systems in Kansas. Chapter B describes the physical framework of the Great Plains aquifer system and presents maps and a geohydrologic cross section that show the thickness, the areal extent, and the altitude and configuration of the top of the Lower Cretaceous rocks that compose the Great Plains aquifer system. The maps are based on data from selected geophysical and lithologic logs and from published maps of stratigraphically equivalent units. Maps that show the thickness and the altitude and configuration of the top of the Great Plains aquifer system have been prepared as part of a series of interrelated maps that describe the stratigraphic interval from the Precambrian surface through Lower Cretaceous rocks. A concerted effort was made to ensure that maps of each geohydrologic system are consistent with maps of underlying and overlying systems; modifications were made where necessary.

Chapter A of this atlas series (Wolf and others, 1990) describes the relation of geohydrologic systems in Kansas and presents a more detailed discussion of the methods and data used to prepare and ensure consistency among the sets of maps in the series.