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tamarisk and box elder (Ater negundo) stands which often overhang the river and form impenetrable barriers at river's-edge. Bed material is predominantly sand. The most upstream study reach is Cedar Ridge, which begins where the river-level bedrock changes to the sandstones of the Wasatch formation, and the valley changes from the low-gradient alluvial section to the high-gradient debris-fan affected-reach. The whitish-green color of the reducing lake bottom environment of the Green River formation gives way to the bright reds of the fluvial Wasatch formation. The Wasatch is predominantly a resistant sandstone deposited by streams than once flowed into the closed basin containing Lake Uinta. Small fluctuations in lake level caused the shallow lakes' shoreline to fluctuate over a wide area. As a result, the Wasatch and Green River formations are highly intertounged and almost indistinguishable from each other through much of the Cedar Ridge reach. Bedrock becomes progressively more resistant downstream, and the alluvial valley gradually-narrows from. a wide alluvial reach to a confined canyon, and the channel contains characteristics of both.. The alluvial valley is wide and filled with broad low angle debris fans which form small rapids. The river has a low gradient between rapids, and is lined by dense vegetation and fine-grained banks. The Surprise Canyon reach is approximately 8 km downstream from the Cedar Ridge reach; the Wasatch formation sandstones are the dominant bedrock in this reach. The alluvial valley is narrower, gradient is higher, and abundant debris fans create numerous riffles and small rapids. Vegetation is sporadic ranging from dense stands of tamarisk and willow on alluvial terraces to unvegetated debris.fan and talus deposits. The Joe Hutch study area begins near the downstream end of Desolation Canyon.. The canyon walls recede from the river, and the Wasatch formation erodes away in the stair-like escarpment of the Roan Cliffs. As the Wasatch formation erodes back, the alluvial valley widens and the siltstones and shales of the Flagstaff and North Horn formations appear at river level. Several large debris flows have occurred recently in this reach. Rapids are larger than those found upstream and reflect the increased debris flow activity. The two largest rapids in Desolation Canyon ,Wire Fence and Three Fords, occur about 1 km downstream from this reach. The Coal Creek study reach is the farthestdownstream and is within Gray Canyon. The river in this reach is narrowly confined by acliff-forming sandstone member of the Cretaceous Mesa Verde formation. The alluvial valley is almost completely constrained by bedrock cliffs which often rise vertically from the waters' edge. Debris flows entering the channel here do not enter a broad alluvial valley, and fans are often narrow and steep. Large recirculating eddies occur downstream from these fans. METHODS Flow patterns and the location of shorelines were mapped in the 4 study reaches in order to measure the areal extent and distribution of eddies and low-velocity zones at a wide range of discharges. These data were combined with data describing substrate and bank materials. Maps were made at discharges between 2,100 and 27,000 ft3/s. Surficial geology of the river corridor was mapped to determine the distribution. of alluvial deposits, and to compare and contrast the relationship between these deposits and available habitat in each of the study reaches.- Cross sections of the channel were measured to help characterize the geomorphic variability within and between reaches. Finally, historical oblique photos taken in Desolation and Gray Canyons were A-3