GEOLOGIC MAP OF THE TROY GROVE 7.5 MINUTE QUADRANGLE, LASALLE COUNTY, ILLINOIS

The Troy Grove 7.5’ quadrangle is located in LaSalle County, Illinois. It occupies the area between 89º 00’ and 89 º 07’ 30” west longitudes, and 41º 22’ 30” and 41º 30’ north latitude. Work was supported by grants from the U.S. Geological Survey EDMAP, the Illinois State Geological Survey, and NICOR, Inc. A surficial geologic map of the Troy Grove Quadrangle was constructed using soils maps and traditional field methods for the purpose of developing a better understanding of shallow subsurface geology over the NICOR Inc. gas storage field. Soils were classified by content and formation. Parent materials were interpreted based on these parameters and elevation. Prominent formations include Cahokia Alluvium, bedded silts and clays from lake sediment of the Equality Formation, and bedded sands and gravels from river sediment of the Henry Formation. Peoria silt was grouped and mapped as soils forming in loess greater than 1.5 meters. The Yorkville (silty clay loam) and Batestown (coarser loam) Members of the Lemont Formation were grouped together as till units. Bedrock units such as shale, sandstone, and limestone from the Pennsylvanian Carbondale and Ordovician St. Peter Formations were defined by field methods. The compiled soils map was digitized in Canvas 9.0.2. Once the surface map is digitized, it can be geo-rectified and brought into GlobalMapper and layered with a DEM, DRG, aerial photo, or other representation of the quadrangle for comparison or enhancement.