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entirely controlled by Glen Canyon Dam and differ substantially from the unregulated conditions of the Green River. Thus, studies of habitat requirements conducted in Grand Canyon may not necessarily apply to the warmer, more turbid, and more wide-ranging flows of the Green River. The purpose of this study is to describe the spatial and temporal variability in habitat availability in Desolation and Gray Canyons. Because the specific habitat requirements of humpback chub in these canyons are unknown to us, we report the availability of a wide range of habitats and defer to the biologists of the Utah Division of Wildlife Resources (UDWR) and the U.S. Fish and Wildlife Service as to the identification of which habitats are most important to humpback chub. Spatial variation in habitat availability was determined by mapping in four 5-mi reaches of the canyons; these reaches were also sampled by UDWR. In each of these reaches, we mapped (1) the surficial geology of the river corridor so that bank and shallow bed material at all discharges is known, (2) the distribution of vegetation along the modern channel, and (3) the distribution of eddies and low-velocity zones at discharges between 2,100 and 27,000 ft3/s. These data are being entered into a geographic information system, and we report the results for the most upstream of these reaches in this report. In an effort to determine if habitat availability has changed with time, we conducted archival searches of available historical photography of the river corridor and matched these photographs in 1995 and 1996. We have matched approximately 20 photos. STUDY AREA Four study reaches were established during the 1995 and 1996 field seasons within Desolation and Gray Canyons. Each study area is approximately 5 mi in length. The study reaches are located between river miles 23 and 28, 38 and 43, 52.5 and 58, and 62 and 70 upstream from the town of Green River, Utah (Fig. 1). In this report, we refer to these reaches as the Coal Creek, Joe Hutch, Surprise Canyon and Cedar Ridge study reaches, respectively. The three upstream reaches -- Cedar Ridge, Surprise Canyon and Joe Hutch - 3