SURFICIAL GEOLOGIC MAP OF THE BENSON 7.5 MINUTE QUADRANGLE,WOODFORD COUNTY, IL

The Benson 7.5 Minute Quadrangle (Scale 1:24,000) is located in Woodford County, Illinois. Methods used in generating this surficial geologic map were analysis and conversion of soil data, analysis of LiDAR data and interpretation of well water logs. Formations were interpreted and mapped based on lithological and thickness descriptions of well data from the Woodford County Soil Survey. The surficial geology of the Quadrangle is comprised of Quaternary glacial sediment units that were deposited during the Wisconsin episode. Quaternary units include the Wedron Group, the Henry Formation, the Peoria Silt, and the Cahokia Alluvium. Units present with less than five feet in thickness were not considered as mappable. The Wedron Group makes up the majority of the surficial geology of the Quadrangle. The Wedron Group contains the Lemont Formation, a grey, silty clay diamicton, which has been deposited on a ground moraine. The Peoria Silt is a yellow-brown sandy silt interpreted as loess. The Henry Formation, a sand and gravel unit of the Mason Group, can be found where outwash deposits are thick enough to map. The Cahokia Alluvium contains poorly sorted sand, silt and clay sized grains and can be found in abundance along the Panther Creek, a modern stream system which flows through the Quadrangle.