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an average boundary shear stress that is about 20% higher than the critical shear stress for bed load transport. Pitlick et al. (1999) provided support for Parker's theory by showing that the bankfull hydraulic geometry of the Colorado River and the Gunnison River were adjusted to a flow that produces an average shear stress that is about 1.5 times the critical shear stress. This result, coupled with findings from other sediment transport analyses, formed the basis for their conclusion that flows greater than about 1/2 the bankfull discharge play a primary role in maintaining habitats used by native fishes. The work described in the present report was undertaken to assess how lengthwise variations in the physical characteristics of the Colorado River influence micro- and meso-scale habitats used by benthic invertebrates and native fishes. As discussed above, the upper and lower reaches of the Colorado River appear to provide different types of habitats for adult and juvenile fishes, and presumably these differences affect the food base upon which they rely. Recent studies of channel change and geomorphic processes in the reach near Grand Junction (Pitlick et al., 1999) have clarified certain questions regarding the impacts of flow regulation, rates of channel change, and processes of habitat formation and maintenance, but large parts of the Colorado River that could serve as potential habitat for native fishes were left unstudied. The present study extends this earlier work by examining fluvial processes and geomorphic characteristics of the reaches upstream and downstream of the area near Grand Junction, from approximately Rifle, CO to Moab, UT. The specific objectives of the study are as follows: 1) To determine from separate sets of aerial photographs whether there have been significant changes in the geomorphology of the Colorado River in the reach between Rifle and DeBeque Canyon. Historical accounts indicate that Colorado pikeminnow occupied this reach prior to the construction of three diversion dams in DeBeque Canyon (Quarterone, 1993). One of these structures has been modified to allow fish passage, and the other two are under consideration, thus information on the suitability of habitats within this reach is desirable. 2) To evaluate long-term trends in sediment loads at points both upstream and downstream of Grand Junction. Annual sediment loads were estimated using discharge and sediment data from existing US Geological Survey (USGS) gauging stations below Glenwood Springs, CO, near Cameo, CO, near Colorado-Utah State Line, and near Cisco, UT. When combined with information from the previous study (Pitlick et al., 1999), these data show how sediment loads and turbidity levels change moving downstream through the Colorado River system. 3) To characterize the existing geomorphology of the river. Additional cross sections of the river were surveyed at 1.6-km intervals from Rulison, CO to Potash, UT. These cross sections provide a semi-continuous view of the hydraulic geometry of the Colorado River, and allow testing of ecologically based models of food web dynamics. 4) To provide estimates of discharges that transport coarse sediment (gravels and cobbles) in specific reaches of the Colorado River. Periodic movement of the gravel substrate is required to prevent fine sediment from accumulating in the bed (Kondolf and Wilcock, 1996), which, if allowed to persist, limits primary productivity and reduces the amount of interstitial void space available to benthic invertebrates (Waters, 1995). Assessment of the frequency of coarse- sediment transport provides one indication of the suitability of potential habitats in individual reaches. 2