SURFICIAL GEOLOGIC MAP OF THE SHERIDAN 7.5 MINUTE QUADRANGLE, LASALLE COUNTY ILLINOIS

The Sheridan 7.5 minute Quadrangle is located in 88°45'00” and 88°37'30” west longitude and 41°37'30” and 41°30'00” north latitude. The goal of this research is to GEOLOGICALLY map all of LaSalle County, IL. Funding for the project was provided by the Illinois State Geologic Survey. This geologic map was constructed using soils maps and traditional field methods. The University of Illinois Agricultural Experiment Station published the soils maps used during the construction of this map. Soil descriptions from Illinois were separated into groups with similar qualities. Soil groups were then assigned to Stratigraphic units. The Cahokia, Peoria, Henry, Equality and Lemont Formations are all present in the Sheridan Quadrangle. Loess that is greater than 5 feet in thickness was designated as Peoria Silt. The Yorkville member of the Lemont Formation is composed of calcareous silty clay to sandy loam diamicton unit with lenses of gravel, sand, silt and clay. The Equality formation is a bedded silt and clay diamicton with lenses of gravel, sand and organic debris. The Cahokia Formation is composed of alluvium that accumulates in the flood planes. There are a few areas where bedrock exposures of the Carbondale formation are present along the Fox River, and many areas where the Equality formation is present along the Fox River, Little Indian Creek, and the Somonauk Creek.