Geologic units in Crawford county, Wisconsin

Prairie du Chien Group (Ordovician) at surface, covers 41 % of this area

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

Cambrian, undivided (Cambrian) at surface, covers 31 % of this area

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

Ancell Group (Ordovician) at surface, covers 21 % of this area

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

Sinnipee Group (Ordovician) at surface, covers 6 % of this area

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

Wonewoc Formation (Middle-Upper Cambrian, upper Marjuman-Steptoean (formerly upper Dresbachian-lower Franconian)) at surface, covers 0.4 % of this area

Surface exposures limited to northeastern Allamakee County; subcrops beneath Mississippi River alluvium in Allamakee County. Includes Ironton and Galesville members. Primary lithology: sandstone, fine to coarse grained, upper part fossiliferous (Ironton). Thicknesses: 125-155 ft (38-47 m).

Jordan Sandstone, St Lawrence and Lone Rock formations (Upper Cambrian, upper Steptoean-Sunwaptan-lower Skullrockian [formerly middle Franconian-Trempealeauan)) at surface, covers < 0.1 % of this area

Surface exposures limited to Allamakee and northeast Clayton counties; subcrops beneath Mississippi River alluvium in southern Allamakee and Clayton counties. Primary lithologies: sandstone, very fine to coarse grained, quartzose to feldspathic (Jordan); silty dolomite to dolomitic siltstone (St. Lawrence); sandstone, very fine to fine grained, glauconitic to very glauconitic, common greensands (Lone Rock). Secondary lithologies: siltstone, part argillaceous (St. Lawrence, Lone Rock). Minor: silty shale partings (St. Lawrence, Lone Rock); dolomite, part sandy; intraclastic dolomite, sandstone, and siltstone. Maximum thicknesses of total interval: 260-310 ft (79-95 m). Formation thicknesses: Lone Rock Fm, 110-140 ft (34-43 m); St. Lawrence Fm, 60-80 ft (18-24 m); Jordan Sandstone, 80-110 ft (244-34 m).

Eau Claire Formation (Middle Cambrian, upper Marjuman (formerly Dresbachian)) at surface, covers < 0.1 % of this area

Subcrops beneath Mississippi River alluvium in Allamakee County; surface exposures absent. Primary lithologies: sandstone, very fine to fine grained, part argillaceous; shale, silty, gray to green-gray, part glauconitic. Secondary lithology: siltstone, part argillaceous, part dolomitic. Minor: dolomite. Thicknesses: 120-145 ft (37-44 m).

Mt. Simon Sandstone (Middle Cambrian undifferentiated) at surface, covers < 0.1 % of this area

Subcrops beneath Mississippi River alluvium in northeastern Allamakee County; surface exposures absent. Overlies erosional surface on Precambrian granitic basement rocks. Primary lithology: sandstone, very fine to very coarse grained, part iron-stained. Minor: shale, silty to sandy, gray, red, green; quartz granules; granitic pebbles. Thicknesses: 365-405 ft (111-123 m).