LONG CREEK QUADRANGLE

The Long Creek 7.5’ Quadrangle is located in Macon County, and also contains the northwestern tip of Moultrie County, IL, and spans from 88°52'30" and 88°45' west longitude and 39°54' and 39°52'30" north latitude. Using soil maps from the Soil Survey of Macon and Moultrie Counties published by the University of Illinois Agricultural Experiment Station, a surficial geologic map was created. This map was constructed by sorting, mapping, and interpreting the soil parent materials and their descriptions designated by the aforementioned soil maps. Once the soils were identified and located, they were placed into different groups based on their relations to different formations. The area was then field checked, and the positions of contacts were refined. Water well records, engineering borings, and coal borings also were used to constrain the geologic soild data. The formations dealt with were: The Cahokia formation (QHc), the Equality formation (Qe), the Henry formation (Qh), the Peoria silt (Qps), the Lacon formation (Qla), the Yorkville member of member of the Lemont formation (Qly), the Batestown member of the Lemont formation (Qlb), and Bedrock.

Loess from the Equality formation (Qe) are found as the dominant deposits throughout the county, ranging in thickness from 0 to 80 inches. The Equality loess is absent from the river valley starting in the north eastern corner of the county and tapering off towards th south west. Here, the dominant deposit is alluvium from the Cahokia formation (QHc). This alluvium ranges from 24 inches to over 40 inches thick. Modern alluvium can be found in the riverbed in the western portion of the county ranging from 24 to 40 inches thick.