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Study area The Green River drains southward from the Wind River Range in west-central Wyoming, joining the Colorado River as its largest tributary in southeast Utah. Upon entering Utah from Wyoming, the river bends sharply eastward, exits into the northeast corner of Colorado (Figure 1) and, passing through Dinosaur National Monument, bends back westward, reentering northeast Utah near the City of Vernal. Flaming Gorge Dam is located 33 river miles downstream of the Utah-Wyoming state line. The study area is composed of the 29 mi (47.2 km) tailwater extending from Flaming Gorge Dam to the Colorado state line (Figure 1). The upper 15.5 mi (24.9 km) is bounded by the steep walls of Red Canyon. Consequently, access to this upper reach is limited to raft and foot trails between three vehicle access points -- Tailrace, Little Hole, and Indian Crossing. Little Hole and Indian Crossing are raft ramps located 7.2 and 15.7 mi (11.6 and 25.3 km), respectively, below Flaming Gorge Dam. Approaching Indian Crossing from upstream, the steep walls of Red Canyon are gradually replaced by the wide valley bottom known as Browns Park. Vehicle access to the river is relatively unrestricted in Browns Park, except where the bottom is briefly interrupted by Swallow Canyon, near the Utah-Colorado state line. The elevation of the tailwater ranges from 5,594 ft. (1,705 m) at Tailrace to 5,375 ft. (1,638 m) at the Utah-Colorado state line. Mean gradient of the study area is 7.6 ft/mi (1.4 m/km). Above Red Creek, the river's gradient is stairstepped at regular intervals by rapids and large pools. In contrast, below Red Creek Rapids (4.2 mi downstream of Little Hole) gradient is seemingly unbroken by distinct hydraulic controls. -12-