Named as a lower member of Coralville Formation (rank raised), 1 of 4 formations of Cedar Valley Group (revised). Type locality designated at Gizzard Creek Quarry, NW SW sec 23, T95N, R15W, Floyd Co, IA. Recognized in northern and central IA and adjacent southeast MN on the Iowa shelf, and northern MO on the Lincoln anticline. Reference sections designated at Tracey Quarry, N1/2 SW NE sec 29, T94N, R14W, Chickasaw Co, and in the FM-4 core, SW NW SE sec 31, T96N, R18W, Floyd Co. Mostly dolomite. Lower part is medium to thick-bedded. Upper part is medium to thin-bedded. Some dolomitic limestone. Slightly argillaceous. Calcite filled vugs common. Disconformably overlies Hinkle Member (named) of Little Cedar Formation (named) of Cedar Valley Group at all localities. Conformably overlain by Iowa City Member (named) of Coralville. Ranges between 3.7 to 7 m thick. Is 4.2 m thick at type. Fossils: conodonts of Upper SUBTERMINUS fauna, sparse to abundant crinoid debris and brachiopods, gastropods, bryozoans, stromatoporoids, favositids. Marine origin correlates with Cou Falls Member (named) of Coralville of eastern IA and adjacent areas. Of Middle Devonian, late Givetian age. Formerly was part of unit B, Cedar Valley Group or part of Coralville Member, Cedar Valley Formation.

Source: GNU records (USGS DDS-6; Denver GNULEX).