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<br /> <br />GEOLOGY <br />General Geology <br />The sands and graves deposited in the floodplain of the <br />South Platte River are Quaternary in ace. These aggregates <br />were deposited by the South Platte River and its t~~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 yeologic map of <br />the area, and Finur°e 3 is a geologic cross-section slro4:ing 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 Chin to thick bedded clayey, silty sand- <br />stone and sandy siltstone r:ith interbedded carbonaceous silty <br />si~ales and claystone. Thr_ carbonaceous shale is l~gitt to medium <br />darl: gray and locally contains plant fragments v:ith a fer•a poorly <br />preserved leaf imprints. This shale unit of the Denver-Arapahoe <br />Formation is the bedrock in the study at°e„ (6). <br />The Louviers Alluvium lies unconformably on the Denver-Arap- <br />altoe Formation and is a t:ell graded sand and gravel deposit. The <br />Louviers is composed of: 65% quartz, 15`/ feldspar, and 20% rock <br />fragments. The rock fragments are made up of graniie, argillite, <br />very weathered metamorphics, cirert end claystone. The Louviers <br />.s typically a valley-fill stream deposit. The material I~as been <br />