Prairie du Chien Group includes Oneota Fm (Coon Valley, Hager City members) and Shakopee Fm (New Richmond Sandstone, Willow River members); St. Peter Sandstone includes Readstown and Tonti members. Sub-St. Peter erosional surface bevels and locally truncates Prairie du Chien strata. Primary lithologies: dolomite, part cherty, part sandy, mostly unfossiliferous, common voids and vugs (Prairie du Chien); sandstone, quartzose, very fine to medium grained (St. Peter, Shakopee). Secondary lithologies: dolomite, laminated to stromatolitic, part intraclastic; dolomite, fossil molds (primarily mollusks); interbedded very fine to fine sandstone and dolomite (Coon Valley, Shakopee); conglomerate, dolomite and chert clasts in sandy matrix (Readstown). Minor: oolitic dolomite and oolitic chert (Shakopee); shale, green, part sandy (Shakopee); shale, green-brown to gray, part laminated, silty to sandy, part fossiliferous (locally in St. Peter of Winneshiek Co.); coarse sand grains (St. Peter, Shakopee); breccia, dolomite-chert clasts; chalcedony/quartz nodules. Maximum thicknesses total interval: generally 300-400 ft (90-120 m), may reach thicknesses to 700 ft (210 m) (locally thick St. Peter in Winneshiek Co.). Unit thicknesses: Prairie du Chien Group, 225-335 ft (69-102 m), locally thinner where overlain by thick St. Peter; Oneota Fm, 130-225 ft (40-69 m), locally thinned beneath thick St. Peter; Shakopee Fm, 55-100 ft (17-30 m), locally thinned to absent beneath thick St. Peter; St. Peter Sandstone, generally 40-75 ft (12-23 m), varies 25-225 ft (8-69 m), may locally reach thicknesses to 700 ft (210 m) in Winneshiek Co.