Till exposed at the Coal Creek site near the Moline, IL, airport has been previously interpreted as Illinoian in age, although clay mineralogy studies have not been done previously at this site. Rock Island County is near the western extent of Illinoian till, interpreted to have a Lake Michigan provenance, but older till with northwestern provenance conceivable exists locally.

The Coal Creek site is an active borrow pit, exposing till interpreted as the Kellerville Member of the Glasford Formation. This till is overlain by Sangamon soil, Roxana silt, and Peoria loess. In order to verify the identity of this till, samples were obtained during June, 2000, for x-ray analyses of clay minerals. Previous work by Hallberg (1980) in a nearby site revealed 34% illite, 20% chlorite and kaolinite, and 46% expandable clays. Unoxidized samples analyzed with an x-ray diffractometer will demonstrate similar clay mineral ratios at this site, reflecting a Lake Michigan Basin source area. In contrast, older till sourced from the northwest would reveal a high content of montmorillonite and calcite in the clay mineral ratios.