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EXPLANATLON OF' llAt• UNLTS <br />l <br />~ Glacial Deposits <br />• Qgdy Younger glacial drift (late Nl.:istocene): unsorted to poorly sorted, <br />subangulat, unconsolidated, pebble to boulder-size detritus in a <br />fine-grained matrix. These deposits generally form a hummocky <br />topography above 7500 ft, may be ioodified by mass-wasting processes, <br />and are potentially unstable especially vl~,:n underlain by the <br />Wasatch Formation. <br />Qgdm Middle glacial drift (middle Pleistocene): unsorted, subangulat, <br />poorly consolidated, bouldery detritus. These deposits usually <br />have a greater amount of veatltered igneous-rock fragments and <br />form a more subdued topography than the younger glacial deposits. <br />Qgdo Older glacial drift (middle Pleistocene): unsorted, subangulat, <br />poorly consolidated, pebble to boulder-size detritus. These <br />deposits, exposed in the northern part of the Bowie Quadrangle, <br />are separated from Qgdm by a partially eroded paleosol. <br />Alluvial Deposits <br />Qal Flood- lp sin alluvium (Holocene): mixtures of silt, sand, pebbles, <br />and cobbles that have been recently deposited and/or reworked by <br />fluvial processes. 'f he alluvium forms the physiographic flood <br />plains of the modern drainage system and is a potential source of <br />sand, gravel, and crushed-ruck aggregate. <br />Qat Stream-terrace alluvium (Holuct•ne): poorly sorted deposits ti~at are <br />similar to Qal in composition and form small terraces r.car [he <br />present drainages. Generally the deposits are Less than 10 ft <br />(3 m) above modern screams. <br />Qvf Valley-fill del~osi[s (Holocene to late Pleistocene): fine-grained <br />materials usually deposited by sheet-floe ur mudflov processes. <br />The deposits, incluJlnE, alluvial Can Landforms, generally form <br />gently sloping surfaces vhic•h are incised by the modern drainage <br />system. Largely derived from the Manaus tilrale, these deposits may <br />be subject [u expansion or hydrocompaction upon vetting, may con- <br />tain corrosive eater, and are prone to sheetflood erosion and mud- <br />flov deposition. <br />Qas Slope-vas debris (Holocene to late Pleistocene): generally Eine- <br />gralned soil and rock detritus transported and deposited by <br />running eater that is not confined to channels. The deposits <br />form a relatively thin veneer over older ::urficial deposits or <br />bedrock, may include some wind-blown (enlian) material, and may <br />be easily eroded if protective vegetation is removed. <br />• F- 32 <br />Rev. 1: 6-18-81 <br />