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Geologic units in Blue Earth county, Minnesota

Upper Cambrian (Upper Cambrian) at surface, covers 56 % of this area

Sandstone, siltstone, shale, and dolostone; includes the Jordan Sandstone and St. Lawrence Formation, and the Mazomanie, Lone Rock, and Davis Formations of the Tunnel City Group.

Lower Ordovician (Lower Ordovician) at surface, covers 39 % of this area

Dolostone, sandy to silty dolostone, and sandstone; includes the Shakopee Formation and Oneota Dolomite of the Prairie du Chien Group.

Middle and Upper Ordovician (Middle and Upper Ordovician) at surface, covers 4 % of this area

Shale, dolomitic limestone, and sandstone; includes the Decorah Shale of the Galena Group, the Platteville and Glenwood Formations, and the St. Peter Sandstone.

Middle and Upper Cambrian (Middle and Upper Cambrian) at surface, covers 0.2 % of this area

Sandstone, siltstone, and shale; includes the Wonewoc Sandstone, Eau Claire Formation, and Mt. Simon Sandstone.