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25 <br /> stratigraphic descriptions in this section are summarized from <br /> three graduate theses that contained detailed lithologic <br /> descriptions compiled during field mapping and section <br /> measurement activities (Hunter; 1947, Masters, 1957) . These <br /> documents provide the best available specific lithologic <br /> information on Dowe Flats. The most important stratigraphic unit <br /> in Dowe Flats are, from oldest to youngest, the Dakota Group, <br /> containing the Lytle and South Platte formations; the Ft. Benton <br /> Formation, the Niobrara Formation, containing the Fort Hays and <br /> Smokey Hill members, and the Pierre Shale. <br /> The Dakota Group contains the upper beds on the cuestas <br /> surrounding Dowe Flats. It has an average thickness in this area <br /> of 330 feet, and is subdivided into the lower Lytle and upper <br /> South. Platte formations. <br /> The Lytle Formation consists of nonmarine fluvial deposits. The <br /> lowest part is a fine to coarse-grained massive brown sandstone <br /> intercalated with a basal conglomerate containing quarter to half <br /> inch diameter chezt pebbles and granite fragments mixed with <br /> finer materials in a secondary silica cement. This bed is <br /> approximately 40 feet thick. The upper portion of the Lytle <br /> Formation consists of a series of variegated red and yellow <br /> claystones that, on exposure, weather to a reddish surface soil. <br /> This deposit varies in thickness from 30 to 60 feet. <br /> The South Platte Formation constitutes the upper part of the <br /> Dakota Group. Deposits in this interval are marine and near- <br /> marine in origin. The Plainview Member is a platy, fine-grained, <br /> hematite stained quartz and sandstone. It varies in thickness <br /> from 20 to 30 feet through differential incising of the <br /> underlying claystones. The middle part of the South Platte <br /> Formation is a 125 to 175 foot thick gray to black carbonaceous <br /> shale interbedded with thin, buff-colored siltstones and <br /> sandstones. The uppermost part of this formation is the Muddy <br /> member, a massive, ridge-forming tan quartzose sandstone 20 to 30 <br /> feet thick that is slightly cross-bedded and distinctly jointed. <br />