Glacial geologic layers in east-central Illinois

Three-dimensional stack of glacial geologic layers in east-central Illinois. Layer 1 (top) is land surface; layer 8 (bottom) is the underlying bedrock. The light-colored unit in layer 7 is a sand and gravel aquifer filling a bedrock valley, and buried by low-permeability glacial till. After Soller, D.R., et al., 1999, Three-dimensional geologic maps of Quaternary sediments in East-Central Illinois, U.S. Geological Survey Geologic Investigation Series Map I-2669, 1:500,000-scale.