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

The Ransom 7.5 minute Quadrangle is located in LaSalle County, IL. It occupies the area between 88º 37' 30" and 88º 45' 00" west longitude, and 41º 07' 3" and 41º 15' 00" north latitude. The Ransom Quadrangle includes the towns of Kernan and Ransom. A surficial geologic map of the Quadrangle was constructed as part of Illinois State University?s ongoing mapping effort in LaSalle County. The Illinois State Geologic Survey, United States Geological Survey, and Nicor Gas funded this research. Soil maps were used to determine the surficial geology by interpreting soils into their parent materials, which were then converted to stratigraphic units. The Ransom Quadrangle displays Holocene aged alluvium, gravel, sand, and loess, as well as Quaternary and Wisconsin aged tills. The geologic units of the area are: the Equality Formation, including the Cahokia Member; the Henry Formation; the Lemont Formation; and the Peoria Silt of the Woodfordian Sub-stage. Erosion caused by Otter Creek has exposed bedded sands and gravels of the Henry Formation, the bedded silt and clay of the Equality Formation, and the alluvium of the Cahokia Formation. No bedrock is exposed at the surface within the quadrangle. The Ransom Quadrangle also contains isolated accumulations of the Peoria Silt. Loess accumulations less than 5 feet thick were not mapped.