1. Altitude, depth, and thickness of the Galena-Platteville bedrock unit in the subcrop area of Illinois and Wisconsin Author/Creator: Geological Survey (U.S.), cartographer Publication/Creation: Reston, Virginia : U.S. Department of the Interior, U.S. Geological Survey, 2000 Resource Type: Map Access & Availability: Loading
2. Bedrock-surface altitude in the midwestern basins and arches region of Indiana, Ohio, Michigan, and Illinois Author/Creator: Geological Survey (U.S.), cartographer Publication/Creation: Columbus, Ohio : U.S. Department of the Interior, U.S. Geological Survey, 1993 Resource Type: Map Access & Availability: Loading