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. .~...r ...,,. <br />.- -. During January, 1984 FII~C made field imrestigations of the Refuse'" "°`. <br />Disposal Area (RDA) to evaluate the geologic c~anpetence of the RDA founding ' <br />material. Characteristic lithologies were described at thirteen locations <br />throughout the RDA. In addition, a backhoe trench was dug near the-toe~of ~'• <br />~ .. <br />the RDA, see Map 6, Surface and Bedrock Geology (Refuse Area). This _~.. <br />investigation described jointing, bedding, structure and lithology of the <br />R!]A. General geologic descriptions are presented in EXhibit 8, Hydrology <br />and Geology Information. .Five geologic mapping units were identified <br />within the RI]A as described below. <br />Colluvium and Soil Cover (Qsc). This mapping unit consists of thick <br />soil and colluvial cover which obscures bedrock Raton Formation and <br />Poison Canyon Formation lithologies, cartmn on north facing forested <br />slopes. <br />Surficial Fan Terrace Deposit (Qt). This mapping unit is aflat-topped <br />terrace located at the drainage confluence. It is believed to be <br />colluvial, but may be a fan deposit fran the eastern drainage system; <br />an arroyo cut through the deposit reveals unsorted angular boulder to <br />cobble sized sandstone clasts in calcareous sandy soil; the top of <br />terrace is 10 to 15 feet above stream bed. <br />Surficial Undifferentiated (Qsu). This mapping unit consists of <br />Surficial deposits of unknown nature; three localities revealed weakly <br />stratified and sorted subangular pebble-cobble sized sandstone clasts <br />in a sandy soil to sand matrix with very poorly sorted and non- <br />stratified colluviwn. <br />Poison Canyon Formation (Tpc). This mapping unit consists of <br />sandstone, siltstone and mudstone. The sandstone is light reddish- <br />brown to Iight tan, fine to very coarse grained with local granule <br />conglomerates, subangular, feldspathic to arkosic, poor to moderately <br />well-sorted; frequently in very lenticular beds 3 to 10 feet thick with <br />abrupt scour bases, occasional massice cross-bedded beds to 25 feet • <br />2.04-12 <br />