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

Accurate geologic maps are a necessity for community planning. The Leland 7.5 minute Quadrangle is located in 88°52'30” and 88°45'00” west longitude and 41°37'30” and 41°30'30” north latitude. The goal of this research is to geologically map all of LaSalle County, Illinois. 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 Tonica Quadrangle. Loess which is greater than 5 feet in thickness was designated as Peoria Silt. The Peoria Silt consists of sandy silt to clayey silt. The Yorkville Member of the Lemont Formation is composed of calcareous silty clay to sandy loam diamicton 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. Along the Indian Creek small outcrops of the Equality and Henry Formations found among the Cahokia formation alluvium. These same patterns are found along the Little Indian Creek as well. This mapping project is necessary for updating geological records. It helps with construction and road planning.