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Bank-full flow and over-bank events have occurred on the main trunk drainages <br />since Kaycee equivalent alluvium deposition. These deposits overlie the Kaycee equivalent <br />alluvium, but have markedly different chemical modification, and instead of braided stream <br />deposits, are represented by natural levee, crevasse splay and back water deposits which are <br />fine grained deposits (usually silt) and lack evidence of numerous interbedded and stacked <br />channels that compose the Kaycee braided stream deposits. The most recent deposition on <br />the valley floors away from the arroyos consists of sheet flow alluvium from the valley <br />flanks and renewed loess deposition. <br />One unique aspect of the overbank deposition is the total organic content. The <br />organics derive from the petroliferous shale more than decaying vegetation. Much of the <br />fine sediment contributed to the alluvial system is weathered shale and the organic content <br />of the shale is sufficient to color the alluvial sediment dark gray to black. Of course, C14 <br />ages obtained from these deposits, should that become desired in the future, will be <br />problematic because of the admixture of old carbon with new. <br />Ephemeral drainages feeding the major trunk streams display sequences equivalent <br />to the sequence originally described in Leopold and Miller (1954), essentially consisting of <br />Kaycee and Lightning equivalent alluvium upstream. Most of the fill in the upstream <br />reaches of these tributaries is again Kaycee equivalent, overlain by more recent sheet flow <br />alluvium and loess. While something like the Moorecroft cut terrace is occasionally <br />present, it is usually absent. Lightning equivalent alluvium again occupies the depth of the <br />middle Holocene incisions. The underlying dissections on ephemeral drainages relic of the <br />Late Glacial are also shallower, and it is not uncommon to have the equivalent of the Late <br />Glacial gravel or bedrock exposed less than a hundred meters upstream from the point that <br />the various tributaries enter the valleys of the main trunks. <br />Once the ephemeral tributaries enter the valley floor of the main trunks, distribution <br />of flow during more arid intervals builds alluvial fans from the tributary mouths and into the <br />valley proper. Fan alluvium is roughly correlatable to the alluvial sequences in the trunk <br />streams and interbed with braided stream and other deposits being deposited by the main <br />trunks, but sediment and rock delivered by the ephemeral tributaries sometimes overwhelms <br />the capacity of the main trunks, so fan alluvium forces a realignment of the main trunks <br />through avulsion. As noted, sediment production from the ephemeral tributaries draining <br />the highlands north of the main trunk drainages is more significant and kept forcing the <br />main trunks to the south sides of the valleys along many reaches. <br />The final component of the alluvial system is sheet flow alluviation. Sheet flow <br />alluviation is unchannelized flow affecting slopes and contributes sediment to other <br />deposits, and is perhaps the most important process on the pinyon-juniper forest floors. <br />Sheet flow deposits on the forest floor are heavily affected by growth and death in the forest, <br />and the biologic factors considerably confuse the stratigraphy, limit the lateral extent of <br />contiguous deposits, and displace artifacts. The effect of tree growth churns the deposits, <br />and when a tree dies and falls, it churns the deposits more. Dead fall dams establish rills, <br />creating pockets of new deposition that force the realignment of the original rills, and create <br />11