SURFICIAL GEOLOGIC MAP OF THE GIBSON CITY WEST 7.5-MINUTE QUADRANGLE, CHAMPAIGN, FORD, AND MCLEAN COUNTIES, IL

This project was supported by a grant from the U.S. Geological Survey EDMAP program to construct a surficial (Quaternary) geologic map of the Gibson City West, 7.5-minute quadrangle (scale 1:24,000) in parts of Champaign, Ford, and McLean Counties, Illinois in order to better understand the spatial distribution of glacial deposits in this region of Illinois. Outcrop descriptions, field mapping, soil survey data, water well data, stratigraphic borehole data, LiDAR elevation data, and previous mapping efforts were used to construct the map. Computational methodologies included ESRI’s ArcGIS™, ACD Systems Canvas™, and Adobe Acrobat™ software. ESRI’s ArcMap 10.3.1 was used to construct geologic contacts. Canvas 11 was used to construct an explanation including descriptions of surficial geology materials. Adobe Acrobat Pro was used to assemble the map and explanation as a GeoPDF. The final map product is a compilation of geologic data, LiDAR elevation, and the 2015 USGS digital 7.5- minute topographic base map of the Gibson City West Quadrangle. The surficial geologic map includes four lithostratigraphic units. In stratigraphic order (from oldest to youngest) are the Wisconsin Episode Batestown Member of the Lemont Formation and the Batavia and Wasco Members of the Henry Formation, and the Holocene Cahokia Formation. Batestown Member diamicton comprise the Bloomington End Moraine in the northern part of the map and a ground moraine in the southern part of the map. The Batavia Member, which consists of stratified sand and silt occurs as outwash plain deposits along the moraine front. The sand and gravel deposits of Wasco Member occur as dissected kames and eskers on the till plane south of the moraine. The Cahokia Formation occurs as alluvium along the Sangamon River and Drummer Creek.