Eau Claire Formation

The Eau Claire Formation consists mostly of a silty, argillaceous dolomitic sandstone that ranges in thickness from 320 to 473 feet. Compared to shallower units, few wells penetrated the entire Eau Claire. Those that do are concentrated in specific areas and fail to give good indication of the countywide thickness trends. The Eau Claire is an important aquitard that separates the underlying Mt. Simon from the Ironton-Galesville. The shales of the Eau Claire Formation protect the groundwater in the Ironton-Galesville from intrusion from the more mineralized water of the underlying Mt. Simon aquifer.