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Grams and Schmidt 12 These deposits were also identified in Grand Canyon by Schmidt and Graf (1990). Internal stratigraphy is typically horizontally bedded but may be ripples or drift cross- stratification indicating downstream flow during deposition. River-parallel levees occur locally. The material of channel-margin bars is commonly sand but may include silt and clay. Some channel-margin bars are located in the backwater immediately upstream from a channel constriction (Fig. 3 and Fig. 4). Point bars are channel-margin bars that are located on the inside of river bends in areas of decreased flow velocity but not in recirculating flow (Fig. 3). Mid-channel bars are distinguished from other alluvial bars based primarily on size, shape, and location. They are typically several channel widths in length, lenticular or irregular in shape, and may occur either mid-channel or on channel margins. They differ from expansion bars in that they do not typically occur in channel expansions below debris-fan-created constrictions. Figure 5 is an oblique photograph that shows the abundant mid-channel bars of Island Park. The bars that are currently located mid-stream are lower in elevation and are bare sand or covered by tamarisk or willow trees. High- elevation mid-channel bars contain stands of mature cottonwood. Mid-channel bars typically occur in reaches of restricted meanders rather than in the fan-dominated canyons._.. Although vertical accretion is still an important process of bar formation, lateral accretion .is evident by scroll-bar topography not displayed in the canyon deposits. 6.2 Distribution of Alluvium 6.2.1 Channel Bed and Bank Material Channel bed material and bank material are two fundamental geomorphic characteristics of any stream. It is especially important to distinguish between bed and bank material in a canyon-bound river that may flow between banks of bedrock on an alluvial bed. Surficial geologic maps show the bank material along 160 km of river bank length for 60 km of channel centerline distance. These data show that in canyon reaches bedrock and talus are the dominant bank materials, occurlng along about 42 percent of the