SURFICIAL GEOLOGIC MAP OF THE PONTIAC NORTHWEST QUADRANGLE, LIVINGSTON COUNTY, IL

The Pontiac Northwest 7.5 Minute Quadrangle (Scale 1:24,000) is located in Livingston County, Illinois. This area reveals an interesting assemblage of Quaternary glacial deposits and Pennsylvanian strata that are exposed along the Vermilion River and its tributaries. Methods used in the preparation of this surficial geologic map were the analysis and conversion of soil survey data, the analysis of LiDAR data and the interpretation of well water logs, and traditional field observations. The surficial geology of the Quadrangle is comprised of Quaternary glacial sediment units that were deposited during the Wisconsin episode. Quaternary units include the Equality Formation, the Henry Formation, the Lemont Formation, and the Cahokia Alluvium. The Henry Formation and the Lemont Formation make up the majority of the surficial geology of the Quadrangle. The Lemont Formation (Wedron Group), is a gray, silty clay diamicton, which was deposited as a ground moraine locally. The Equality formation is a yellow-brown sandy silt that was deposited as loess. The Henry Formation, a sand and gravel unit of the Mason Group, is either an outwash plain or valley train deposit. The Cahokia Alluvium contains poorly sorted sand, silt and clay sized grains and can be found in abundance along the Panther Creek, a main tributary to the Vermilion River. The Pennsylvanian strata of the Bond Formation, which occur in quarries and along some of the lower order streams, consists of gray shale, siltstone, coal, limestone and sandstone.