SURFICIAL GEOLOGIC MAP OF THE 7.5 MINUTE NORMAL EAST QUADRANGLE IN MCLEAN COUNTY, ILLINOIS

This study involved the construction of a surficial geologic map of the 7.5 minute Normal East Quadrangle in McLean County, Illinois which covers 40°30’ to 40°37’30” latitude and 89°00’ to 88°52’30” longitude. This area includes part of the Bloomington moraine, which is a recessional moraine of the Wisconsin glacial stage. Methods used in the construction included water well data, conversion of soil survey, and field outcrop descriptions. There are four major sediment units exposed in the Normal East Quadrangle, all Quaternary in age. These formations are 30 to 90 meter in thickness and; include the Peoria Silt, Wedron Group, the Cahokia Alluvium, and the Henry Formation. Pennsylvanian bedrock rests beneath these sediments. The Peoria Silt is yellow clay which is interpreted to be loess that is 0-6 meters in thickness. The Peoria Silt is exposed over much of the Quadrangle. The Wedron Group consists of the Lemont and Tiskilwa Formations. In the Normal East Quadrangle, only the Lemont Formation is exposed. Lemont is diamict consisting of gray, black, blue, brown, and green clay which is interpreted to be silty loess combined with loamy till. This till is as much as 60 meters thick, found in both the surface and subsurface, and is typically found in ground moraines which make up most of the Normal East Quadrangle. The Cahokia Formation consists of gravel, sand, and yellow, blue, black, green, and gray clay which is interpreted to be clayey colluvium and silty alluvium that has variable thickness. Alluvium is primarily found along the major creeks, including Sugar Creek, Six Mile Creek, and Money Creek. The Henry Formation is sand and gravel which is interpreted to be valley train outwash. Outwash gravel is primarily found in both the surface and subsurface, along Sugar Creek and in other stream terraces or outwash plains.