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LEGEND FOR DWG. N0. 8 <br /> <br />u <br /> <br />Qagy Youn er alluvial ravels (late Pleistocene?): poorly <br />sorted, rounded to subrounded, unconsolidated pebbles <br />and cobbles in a matrix of sand and silt. These <br />gravels vary greatly in composition because of local <br />conditions and they cap the first well-defined terrace <br />above modern streams. Sheet flooding, erosion, and local <br />swelling soils are important geologic conditions <br />associated with these gravels. <br />Qago Older alluvial ravels (middle Pleistocene?): poorly <br />sorted, rounded to subrounded, poorly consolidated <br />gravels in a fine-grained matrix. These older gravels <br />have a slight increase in consolidation, slightly <br />greater weathering of igneous detritus, and a greater <br />accumulation of calcium carbonate in the C horizon <br />than the younger gravels. The deposits are subject to <br />sheet flooding and erosion. <br />K m Mancos Shale (U er Cretaceous): dark brown to gray, <br />laminated silty shale which is susceptible to erosion <br />and mass-wasting. The shale locally contains swelling <br />clays (montmorillonite) and water corrosive to con- <br />crete. Drainages that traverse the Mancos Shale are <br />prone to flash floods and mudflows. <br />Qv} Va_ 1leY-fill^de~ sits (Holocene to late Pleistocene): , <br /> <br />or mudflow processes. These deposits, including <br />alluvial fan landforms, generally form gently sloping <br />surfaces which are incised by the modern streams. <br />Largely derived from Mancos Shale, these deposits may <br />be subject to expansion or hydrocompaction upon <br />wetting, may contain corrosive water, and are prone <br />to sheetflood erosion and mudflow deposition. <br />41 <br />