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<br />HYDROLOGY RESOURCES REVIEW <br /> <br />One of the most important resources of the Little Snake River to the habitat <br />and recovery of endangered fish is the highly variable water discharge and <br />sediment supply to the Green River system. Water and sediment yield in the Little <br />Snake River basin are influenced by a number of factors including geology, <br />topography, soils, vegetation, climate and land use. Soil conditions are related to <br />geology and climate. Clearly these factors are interrelated and combined with <br />man's activity can result in highly variable sediment yield. <br /> <br />Geology <br />The Little Snake River contains two different geological regions, the <br />headwaters region within the Southern Rocky Mountains and a lower watershed <br />region within the Wyoming Basin. The geology of the Little Snake River basin was <br />discussed by the Army Corps of Engineers (CaE) in the Draft Environmental <br />Impact Statement on the Sandstone Project (CaE, 1988) and by Resource <br />Consultants, Inc (RCI, 1991). The delineated geologic regions are: 1) the Tertiary <br />and Cretaceous age sedimentary formations of the lower and western Little Snake <br />River basin; and 2) the pre-Cambrian igneous and meta-sedimentary rock of the <br />Sierra Madre range on the eastern portion of the basin. Upstream of Dixon, <br />Wyoming the highest parts of the basin are underlain by Precambrian granites and <br />mafic intrusives. These bedrock units are relatively erosion resistant. The <br />sedimentary formations are dominated by Cretaceous age Steel Shale and <br />Mesaverde Group sandstones. The Steele Shale formation is an erosive older <br />formation consisting primarily of siltstones and claystone shales. The Mesaverde <br />Group is predominantly sandstones and shales. The Browns Park formation which <br />caps this sedimentary network consists of loosely cemented sandstones, siltstones <br />and mudstones. <br /> <br />9 <br />