Top of bedrock elevation surface derived from airborne electromagnetic survey data for Illinois and the Illinois River Basin, 2025

In support of the U.S. Geological Survey (USGS) Illinois River Basin (IRB) Next Generation Water Observing System (NGWOS) program, a top of bedrock elevation surface was generated to improve understanding of the bedrock elevation, subsurface geologic structure, and unconsolidated materials thickness across IRB and the State of Illinois. The surface was derived primarily from models of electrical resistivity values collected along flight paths from a regional scale airborne electromagnetic (AEM) survey over IRB in 2023. The AEM derived estimate of the top of bedrock elevation was then interpolated with available bedrock elevation surfaces from the Illinois State Geological Survey (ISGS) and Indiana Geological and Water Survey (IGWS), where AEM data was absent.