Named as upper member (of 3) of the Lithograph City Formation (new) of Cedar Valley Group (rank raised) in north-central and central IA, Iowa shelf; named for Idlewild State Park in north-central Floyd Co. Type section designated at Floyd Quarry in SW SW SE sec 9, T96N, R16W, Floyd Co. Occurs in Floyd, Mitchell, and Butler Cos. Consists dominantly of unfossiliferous laminated to intraclastic limestone and dolomite. Dense lithographic and sublithographic limestones are locally prominent, but over relatively short distances, are replaced laterally by dolomites and dolomitic limestones. Mudcracked horizons. Thin shales. Burrowed beds. Where capped by Shell Rock Formation, ranges in thickness from 52 to 79 feet. Overlies Thunder Woman Shale (new) of Lithograph City Formation of Cedar Valley Group; at places, underlies Shell Rock Formation of Cedar Valley Group. Brachiopods (listed); crinoids; stromatoporoid biostromes. Graphic sections; cross section; measured sections. Of Devonian age. Middle Devonian-Upper Devonian boundary lies somewhere in Lithograph City.

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

Named as upper member of Lithograph City Formation (named), 1 of 4 formations Cedar Valley Group (revised). Present in northern, central IA and adjacent MN on Iowa shelf. Type locality at Floyd Quarry 2.3 km downstream on Cedar River from Idlewild State Park, SW SW SE sec 9, T96N, R16W, Floyd Co, IA. Is 13+ m thick at type; here overlies Osage Springs Member (new) of Lithograph City. May overlie Thunder Woman Shale Member (new) of Lithograph City at other localities. Where underlies Shell Rock Formation (formation rank assigned), Cedar Valley Group, is 16-24 ft thick. Consists of 1) interbedded laminated, pelleted lithographic and sublithographic limestones and their dolomitized equivalents, with mudcracks, birdseye, evaporite molds; 2) non-laminated dolomite, limestone, partly sublithographic, pelleted, oncolitic, intraclastic, brecciated, sandy, mudcracked; 3) calcareous shale, partly brecciated to intraclastic; 4) fossiliferous dolomite, limestone with abundant brachiopods, stromatoporoids. Gypsum, anhydrite in subsurface central IA (map). Replaced in southeast IA by Andalusia Member (new), Lithograph City. Fossils: conodonts suggest member may span Lowermost and Lower ASYMMETRICUS Zone. Biostromes formed locally. Supratidal, intertidal flat, shallow marine embayment deposit. Late Devonian, Frasnian age. Formerly part of unit C, Cedar Valley Group or of Coralville Member, Cedar Valley Formation. Nomenclature charts; graphic sections.

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