Modified from Regional Geologic Map Series, Indiana Geological Survey.' Includes insets of 'Thickness of unconsolidated materials' and 'Distribution of surface tills.' Scale approximately 1:1,900,000. Indiana Geological Survey; drafted by James R. Tolen.
Tolen, James R. (1979). Map of Indiana showing unconsolidated deposits. The Survey. https://purl.dlib.indiana.edu/iudl/images/VAC3073/VAC3073-M-00675 (map)