This raster is a highly detailed map of geologic materials at the surface (delineations made from maps at 1:24,000 to 1:12,000 scale). The smaller extent maps were merged together by USDA-NRCS to produce the gSSURGO spatial database, covering the entire state of Illinois at a 10m resolution. The gSSURGO map was then interpreted by Iowa …Continue reading “Surficial Geology of Illinois”