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Qvf Vallev-fill deposits (Holocene to late <br />• Pleistocene): fine-grained materials usually <br />deposited by sheet-flow or mudflow processes. <br />The deposits, including alluvial fan <br />landforms, generally form gently sloping <br />surfaces which are incised by the modern <br />drainage system. Largely derived from the <br />Mancos Shale, these deposits may be subject <br />to expansion or hydrocompaction upon wetting, <br />may contain corrosive water, and are prone tc <br />sheetflood erosion and mudflow deposition. <br />Qas Slope-was debris (Holocene to late <br />Pleistocene): generally fine-grained soil and <br />rock detritus transported and deposited by <br />running water that is not confined to <br />channels. The deposits form a relatively <br />thin veneer over older surficial deposits or <br />bedrock, may include some wind-blown (eolian) <br />material, and may be easily eroded if <br />protective vegetation is removed. <br />Qaqy Younger alluvial gravels (late Pleistocene): <br />poorly sorted, rounded to subrounded, <br />unconsolidated pebbles and cobbles in a <br />matrix of sand and silt. These gravels vary <br />greatly in composition because of local <br />• source conditions and they cap the first <br />well-defined terrace above modern streams. <br />Sheet flooding, erosion, and local swelling <br />soils are important geologic hazards <br />associated with these gravels. <br />Qagm Middle alluvial gravels (middle Pleistocenel: <br />Poorly sorted, rounded to subrounded, poorly <br />consolidated gravels in a fine-grained <br />matrix. These gravels have a better <br />developed soil profile and have a greater <br />amount of weathered igneous-rock fragments <br />than the younger alluvial gravels. Middle <br />gravels include alluvial-fan and river- <br />terrace materials, form nearly planar <br />surfaces situated at two or more levels, and <br />are subject to sheet flooding and erosion. <br />u <br />P6PMIi 11PPGIC11SI011 EXH-12 - 10 - <br />