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• 3.4.3 Regional Ground Water Description <br />Ground water within bedrock aquifers is of limited quality and quan- <br />tity in this region. This is due to both the overall low porosity of <br />the various formations, lithologies which degrade quality, and struc- <br />tures (i,e., deep basins) which increase the cost of ground water pro- <br />duction. Also, relatively abundant surface water and shallow alluvial <br />ground water has limited the demand on deeper ground water aquifers, <br />thereby limiting knowledge of these systems. <br />The environment of deposition of rocks within the region has a direct <br />bearing on the hydrology of the area. During cretaceous time, an <br />east-to-Southeast prograding deltaic complex existed with a variety <br />of delta front and distributary mouth deposits (Rollins, Upper, and <br />Middle Standstones). The remaining rocks were deposited in a well- <br />drained swamp, channel and upper deltaic plain environments. Many of <br />the units are very lenticular and intertongued with each other and <br />• continuity of any of the units over large areas is rare, Most units <br />are poorly sorted, with considerable silt and clay, resulting in low <br />porosities and permeabilities. <br />In contrast, the glacial gravels along the Roaring Fork River are <br />generally well sorted and free of clays and silts, resulting in high <br />porosities and permeabilities, <br /> <br />3-16 <br />