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glacials provided the sireamflow to entrench the alluvium. The Qt4 terraces are <br />• likely to be Pre-Wisconsin, Buffalo and Bull Lake in age. This interpretation is <br />consistent with work in nearby areas of The Colorado River drainage and else where <br />in the Rocky Mountains. <br />The (lt3 terraces probably represent the Bull Lake glaciation and possibly the <br />earliest Pinedale events. The extensive Qt2 terraces, like similar terraces in the <br />Rocky Mountain region, are thought to be of Pinedale age. <br />The small, Qtl, terraces are, in part, attributed to neoglacial events, and in <br />part, to the complex response of the fluvial system to Holocene climatic changes <br />and/or changes in land use (viz. the Arroyo Cutting Cycle). Both Trout Creek and <br />Oak Creek contain several low knickpoints that indicate degradation. These <br />knickpoints were identified from longitudinal profiles prepared from maps with <br />contour interval of 5 feet. After field confirmation, benchmarks were established <br />and detailed longitudinal profiles of the knickpoints surveyed along with mapping of <br />the thalweg of the stream (Exhibits 2.5-19 and 2.5-20). These stream reaches can <br />be resurveyed in the future to monitor equilibrium. Locations are shown on Exhibits <br />2.5-2 and 2.5-10. <br />A stability analysis, following the procedure specified in OSM's alluvial valley <br />• floor guidelines, has been conducted for Trout and Oak Creeks. The purpose of such <br />an analysis is to identify relatively stable and unstable stream reaches. <br />The procedure used is as follows. Three representative transects of each <br />stream were identified and streambed and bank samples collected. These transects <br />correspond to locations identified for representative cross-sections (Exhibits 2.5-15, <br />2.5-16, 2.5-17 and 2.5-18). The 30 bed and bank samples were subjected to <br />mechanical analysis, the results of which are shown in Section 2.5.5. Using these <br />data, the M-factor for each transect was computed using the following equation: <br />M = SbdW + Sbk2d <br />W+2d <br />Where Sbd = % silt-cloy (i.e. < .074 mm) of streambed samples, Sbk = % of <br />silt-clay (i.e. < .074 mm) of streambank samples, W = stream width (in feet) and <br />d = stream depth (in feet). For each sample, I/2 The weight retained on the 170 <br />mesh (.088 mm) sieve was added to all sieve and pan weights smaller than 170 mesh <br />to determine the silt-clay content. This technique is in accordance with Schumm, <br />• 1960, U.S.G.S. Professional Paper 424-B. <br />Revised 7-81 2.5-64 <br />