Topography of the bedrock surface in Illinois. Bedrock topography is shown as 50-foot (15-meter) contours of bedrock elevation above mean sea level (msl). Several major bedrock valleys are found across the state. Attributes include contour values. ISGS, 1994.
Creator:
Chenoweth, Cheri, Herzog, B. L. (Beverly L.), J.B. Sievering, K.L. Warner, and Stiff, Barbara J.