Geologic units in Columbia county, Wisconsin

Cambrian, undivided (Cambrian) at surface, covers 70 % 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 22 % of this area

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

Ancell Group (Ordovician) at surface, covers 5 % of this area

Orthoquartzitic sandstone with minor limestone, shale and conglomerate; includes Glenwood and St. Peter Formations

Barron Quartzite (Early Proterozoic) at surface, covers 2 % of this area

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

Sinnipee Group (Ordovician) at surface, covers 1 % of this area

Dolomite with some limestone and shale; includes Galena, Decorah, and Platteville Formations

Rhyolite (Early Proterozoic) at surface, covers 0.2 % 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.