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• <br />GEOLOGY <br />General Geology <br />The sands and gravels deposited in the floodplain of the South Platte River are Quaternary in <br />age. These aggregates were deposited by the South Platte River and its tributaries. The Post- <br />Piney Creek Alluvium forms a surface cover on the Louviers All which overlies the sandstones <br />and shales of the Denver-Arapahoe Formation. Figure 2 is a geologic map of <br />the area, and Figure 3 is a geologic cross-section showing the relationships of the units mapped. <br />Formations <br />The oldest rock unit to be considered in the study area is the Cretaceous Denver-Arapahoe <br />Formation. This bedrock formation is composed of very thin to thick bedded clayey, silty <br />sandstone and sandy siltstone with interbedded carbonaceous silty shales and claystone. The <br />carbonaceous shale is light to medium dark gray and locally contains plant fragments with a few <br />poorly reserved leaf imprints. This shale unit of the Denver-Arapahoe Formation is the bedrock <br />in the study area (6). The Louviers Alluvium lies unconformably on the Denver-Arapahoe <br />Formation and is a well graded sand and gravel deposit. The Louviers is composed of. 65% <br />quartz, 15% feldspar, and 20% rock fragments. The rock fragments are made up of granite, <br />argillite, very weathered metamorphics, chert and claystone. The Louviers is typically a valley- <br />fill stream deposit. The material has been <br />• <br />excerpt from 1977 report AFS Walstrum Pit <br />•