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<br /> <br />GEO1.0GY <br />General Geology <br />The sands and graves deposited in the fl oodplain of the <br />South Platte River are Quaternary in acre. These aggregates <br />were deposited by the South Platte River and its tr;butaries. <br />The Post-Piney Creek Alluvium forms a surface cover on the <br />Louviers Alluvium which overlies the sandstones and shales of <br />the Denver-Arapahoe Formation. Figure 2 is a geologic map of <br />the area, and Figure 3 is a geologic cross-section showing the <br />relationships of the units mapped. <br />Formations <br />The oldest rock unit to be considered in the study area is <br />the Cretaceous Denver,-Arapahoe Formation. This bedrock forma- <br />tion is composed of very thin to thick bedded clayey, silty sand- <br />stone and sandy siltstone with interbedded carbonaceous silty <br />shales and claystone. The carbonaceous shale is light to medium <br />dark gray and locally contains plant fragments with a fern poorly <br />preserved leaf imprints. This shale unit of the Denver-Arapahoe <br />Formation is the bedrock in the study are, (6). <br />The Louviers Alluvium lies unconformably on the Denver-Arap- <br />ahoe Formation and is a vrell graded sand and gravel deposit. The <br />Louviers is composed of: 6510' quartz, 15% feldspar, and 20% rock <br />fragments. The rock fragments are made up of granite, argillite, <br />very weathered metamorphics, chert and claystone. The Louviers <br />:s typically a valley-fill stream deposit. The material has been