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<br />Grams and Schmidt <br /> <br />10 <br /> <br />Deposits were divided into four broad classes based on textural differences that <br />could be clearly distinguished on aerial photographs. Figure 3 shows surficial geology of <br />a typical reach in Lodore Canyon that has numerous debris fans and abundant coarse- <br />grained alluvium. Fine-~ained alluvium includes all alluvial sands, silts, and clays. <br />Individual deposits may contain sedimentary structures or be massive. Thickness of fine- <br />grained deposits can range from a few centimeters to several meters. Coarse-~ained <br />alluvium, or 'gravel' includes all pebble- to cobble-sized material from 2 to 256 mID <br />median diameter. Deposits are moderately- to well-sorted and contain rounded to sub- <br />angular particles. A significant portion of the bank and bed material in the Green River <br />canyons consists partly or entirely of gravel. These include emergent mid- and side- <br />channel gravel bars and reworked talus or debris. Many gravel deposits are completely or <br />partially covered by a veneer of fme-grained alluvium. These deposits are mapped as <br />'mixed' fine- and coarse-grained alluvium (Fig. 3). Debris-fan material is poorly sorted, <br />angular to sub-rounded and includes particles ranging in size from clay to boulders. <br />Bedrock and talus includes rock outcrops and talus slopes. Talus is angular and <br />dominated by large cobble and boulder sizes of local lithology. Bedrock and talus are not <br />distinguished from one another because overlap of talus over bedrock is common. <br />6.1.2 Depositional Environment <br />Depositional environment describes the mechanism of fluvial deposition and is a <br />classification independent of deposit material. Depositional environments were identified <br />primarily upon location, morphology, and bar stratigraphy. Deposit location and <br />morphology were determined in the field and on aerial photographs. Stratigraphy was <br />examined in the field at selected locations by excavating shallow trenches and was used to <br />determine current direction during deposition. <br />Debris fans are accumulations of debris-flow deposited sediment located at the <br />mouths of tributary streams (Fig. 3). Debris fan size, form, and composition are the <br />products of tributary basin g~Qlogy, debris-flow frequency, and debris-fan reworking by <br />