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Geologic units in Sauk county, Wisconsin

Additional scientific data in this geographic area

Cambrian, undivided (Cambrian) at surface, covers 75 % of this area

Sandstone with some dolomite and shale, undivided; includes Trempealeau, Tunnel City, and Elk Mound Formations

Prairie du Chien Group (Ordovician) at surface, covers 16 % of this area

Dolomite with some sandstone and shale; includes Shakopee and Oneota Formations

Barron Quartzite (Early Proterozoic) at surface, covers 9 % of this area

Pink to maroon to light-gray, medium-grained, moderately sorted quartzite. Red argillite (pipestone) interbedded locally. At least 213 m thick

Rhyolite (Early Proterozoic) at surface, covers 0.1 % of this area

Ash-flow tuffs and interbedded volcaniclastic sedimentary rocks and cogenetic granite (unit Xga) exposed as inliers in southern Wisconsin. In central Wisconsin pink, flow-banded rhyolite and chert-cemented breccia inferred to be 1760 Ma.