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unsorted, clast-supported, pebble to boulder gravel in a sandy silt matrix to matrix- <br />supported, gravelly, clayey, sandy silt. Clast lithologies vary and aze dependent upon the <br />bedrock or surticial unit from which the deposit was derived. Maximum thickness of the <br />unit is approximately 20 ft. <br />Qf Alluvial-fan deposits, undifferentiated (Holocene and late Pleistocene) -Moderately <br />sorted sand- to boulder-size gravel infan-shaped deposits from tributary streams of Trout <br />Creek, and from smaller side streams in those tributaries. Deposits typically composed of <br />both matrix-supported beds 3-5 ft thick (debris flow facies) and clast-supported beds 1- <br />2.6 ftthick (streamflow facies), often interbedded. Clasts are mostly angular to subround <br />with varied lithologies dependant upon local source rock. Sediments aze deposited by <br />debris flows, hyperconcentrated flows, streams, and sheetwash. Fan-shaped deposits <br />form where tributary drainages with steep gradients join lower gradient streams. Debris- <br />fan deposits commonly grade from boulder- and cobble-size fragments at the head of the <br />fan to silty sand near the fan terminus. The maximum estimated thickness for debris fans <br />C along Trout Creek may exceed 30 ft. Elsewhere, the deposit is typically less than 10 ft <br />thick. Extraordinary precipitation events may trigger future deposition in areas mapped as <br />debris-fan deposits. Debris-fan deposits may be prone to collapse when wetted or <br />loaded. <br />Qfy Alluvial-fan deposits, younger (Holocene) -Moderately sorted, sand- to boulder-size <br />gravel in fan-shaped deposits from tributary streams. Deposits typically composed of <br />both matrix-supported beds 3-5 ft thick (debris flow facies) and clast-supported beds 1- <br />2.6 ftthick (streamflow facies), often interbedded. Clasts aze mostly angular to subround <br />with varied lithologies dependant upon local source rock. Sediments are deposited by <br />debris flows, hyperconcentrated flows, streams, and sheetwash. Fan-shaped deposits <br />form where tributary drainages with steep gradients join lower gradient streams. Deposit <br />overlies and thus post-dates Pinedale outwash deposits in many places. The maximum <br />estimated thickness for fan deposits along lower Trout Creek may exceed 16 ft. <br />Extraordinary precipitation events may trigger future deposition in azeas mapped as <br />Buena Vista East quadrangle 14 <br />