Geologic-log data were used to construct thickness and surface-configuration maps of Jurassic deposits, and a map of general composition of Pleistocene glacial deposits, in the central Lower Peninsula of Michigan. These geologic units form the upper part of a regional system of aquifers and confining units in the Michigan Basin. In the peninsula, most bedrock is covered by glacial deposits that are primarily intercalated glaciofluvial sediments and till; in some areas, lacustrine clay and silt are surficial deposits. Areas of primarily glaciofluvial sediments (aquifer material) or till and lacustrine deposits (confining-unit material) were delineated.
Jurassic "red beds" underlie glacial deposits in the west-central part of the Michigan Basin. These confining deposits (primarily clay, shale, and gypsum) cover 4,000 square miles of salinewater-bearing Pennsylvanian rocks. Contour maps were generated to show general thickness and surface configuration of Jurassic "red beds." Contour maps of "red beds" and the map of general composition of glacial deposits were prepared to aid in assessing hydrogeologic and geochemical characteristics of the regional aquifer system.
