MAP DETAIL from
"Map Showing the Thickness and Character of Quaternary Sediments in the Glaciated United States East of the Rocky Mountains"
U.S. Geological Survey Miscellaneous Investigations Series Map I-1970
1993-1998
by David R. Soller
Through western Indiana and east-central Illinois, a preglacial valley was deepened by glacial erosion and, during many glaciations, was filled with glacial and river sediment. Within these sediments (mostly glacial till) there are thick sand and gravel deposits that contain a valuable source of groundwater for the region. On the image at left, a large preglacial valley known as the Mahomet Bedrock Valley runs east-west through the central part of the map. The Mahomet Sand (shown on the second image as the area of yellow dots) supplies water for many of the major cities in east-central Illinois, including Champaign-Urbana.
