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ar <br />~. <br />alluvial-fan deposits. Debris-fan deposits may be prone to collapse when wetted or <br />loaded. <br />Qfi Alluvial-fan deposits, intermediate age (latest Pleistocene to Holocene) -Moderately <br />sorted sand- to boulder-size gravel in fan-shaped deposits from tributary streams, mainly <br />in intermittent tributary streams north of Trout Creek. Deposits typica]ly composed of <br />matrix-supported sandy alluvium locally derived from decomposed granite. Clasts aze <br />mostly angulaz to subangulaz. Deposit forms incised alluvial fans and small terraces 10 <br />to 16 ft above modem stream level. The maximum thickness is at least 10 ft. <br />~. <br />Qfo Alluvial-fan deposits, older (late Pleistocene) -Moderately sorted sand- to boulder-size <br />gravel in fan-shaped deposits from tributary streams on the eastern (unglaciated) side of <br />the upper Arkansas Valley. Deposits typically composed of both matrix-supported beds <br />3-5 ft thick (debris flow fades) and ceast-supported beds 1-2.6 ft thick (streamflow <br />fades), often interbedded. Clasts aze mostly angulaz to subround with vaned lithologies <br />dependant upon local source rock. Sediments aze deposited by the Arkansas River and <br />by tributary fans. Deposit forms erosional remnants 16-33 ft above Pinedale outwash <br />terraces on the eastern side of the upper Arkansas Valley. May correlate in part with map <br />unit Qbf mapped on the western (glaciated) side of the valley. The maximum thickness is <br />at least 16 ft. <br />Qbf Alluvial-fan deposits, Bull Lake outwash deposits, younger (late Pleistocene)-- - <br />Moderately sorted sand- to boulder-size gravel in terrace deposits from tributary streams <br />on the western side of the upper Arkansas Valley. Deposits typically composed of both <br />matrix-supported beds 3-5 ft thick (debris flow fades) and clast-supported beds 1-2.6 ft <br />thick (streamtlow fades), often interbedded. Clasts aze mostly angular to subround and <br />derived from crystalline rocks of the Sawatch Range, or recycled from erosion of the Dry <br />Union Formation. Sediments were deposited mainly by west-side tributaries to the <br />Arkansas River, although some main-stream gravel fades may be interbedded. Deposit <br />forms a large erosional remnant 16-33 ft above Pinedale outwash terraces (unit Qpoo) on <br />Buena Vista East quadrangle IS <br />