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.
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