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nagy Younger alluvial gravels (late Plaistuccne): poorly surced, roundel <br />to subrounded, unconsvlidated pel,l,les and cobbles in :, matrix of <br />sand and sllt. These gravels v.rry greatly In composition because <br />of local soucce condi[iuus anJ they rap the first well-Jefiucd <br />terrace above modern stnvo,s. Shot t luuding, erosiuu, and Local <br />svelling culls a m lmpor[unt geJ!Jt;Lc hazarJs associated with <br />these gravels. <br />Qagm Middle alluvial gravels (middle Yluistoceue): poorly surced, rounded <br />Co subrounded, poorly consolidated gravels in a fine-grained matrix. <br />These gravels have a butter duvelupud soil profile and Iwve a greater <br />amount of veatttered ignevus-rock Cragments clean the younger alluvial <br />gravels. Middle gravels include alluvial-fan and river-terrace <br />materials, form neatly ylanar surfaces sicu:rced at tvu or more levels, <br />and are subject [o sheet flooding and erosion. <br />Qago Older alluvial ravels (middle Pleistocene): poorly sorted, rounded <br />[o subrounded, poorly consolidated gravels in a fine-granted matrix. <br />These older gravels have a slight increase Sn consolidation, slightly <br />greater weathering of igneous detritus, and a greater at:cumulativn <br />of calcium carbonate in the C horizon [Ilan the younger gravels. The <br />deposits are subject to sheet flooding and erosion. <br />Qpg Pediment gravels (earl Pleistocene): old, high-level alluvial gravels <br />that have an abundant accumulation in the C horizon and a higher <br />percentage of weathered igneous-rock Fragments than the younger gravels. <br />The gravels form nearly planar surCacus that are subject to shoe[ <br />flooding and erosion. <br />QTa Nigh-le_ eel alluvium (Quaternary/Terti~rY): bouldery alluvial deposits [hat <br />form nearly planar, gently sLupirrg surfaces high above modern streams. <br />The location and occurrence .,f the d~pusits above moduru streams and <br />similarity [o previously mapped Jbpusi[s (Tveto and others, 1y76) suggest <br />formation during the '1'er[iary ur c;rely tuaternary. 1'hcsu Japosits ate <br />subject to sheet flooding anJ eras iu u. <br />Colluvial Deposits <br />Qls Landslide deposlts (Holocene to I_rt~• Pleistocene): a heterogeneous <br />assemblage of unconsolidated soil and/ur ruck formed by sloe to rapid <br />dovn~acd and outward mass muvemeut in response to gravitational stress. <br />Those deposits, which include earthfluvs, usually Cocm an irregular, <br />hurmnocky topography and may have an associa[eJ main Scarp. Relative <br />age of the deposits is noted by subs,~ripts (1~is tt,e youngest). tllsl <br />deposlts most likely 4cre formcJ during the Holucune and Qls2 and <br />Qls3 deposits prububly ecru formed during the Wiscuusin glacial stage. <br />Qmf Mudflo~ deposits (Ilolorene): clay anJ Cine-grained debris that may <br />include larger rock fragments incurpurateJ into the Jebris during <br />dovnslope movunen[ uC the vot, ^.u.cuus uu~s of sail .ur~1 encl. n,a[erial. <br />The deposits have a youthful physiography charartcrir.cJ by a gently <br />undulating topography ~Lth .m inciseJ, braiJeJ Jrain.,l;c ne work. l:i[h <br />decreasing viscosity during movvnwnt the Jepusits 1;faJa• w fluvial <br />• sediments and with increasing viscosity I;raJe w sloe-wuvini; wrtlr <br />flues. <br />F.- 33 <br />Rev. 1:6-18-81 <br />