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'.' ~~:'~,-.:: . -Ojl036 Description Colorado River. Below the Loma boat ramp, the Colorado swings south Into an uplift of pink stone, encasing itself up to 1000 feet in the red sandstone walls of Horsethief and Ruby Canyons. Often the walls wear a black and purple skin of desert varnish. High on the waifs are spires, towers, and curiously shaped monoliths reminiscent of those found in Colorado National Monument, whose backcountry overlooks the river. The Colorado cuts to the heart of the Uncompahgre Uplift, baring folds that resemble rainbows in stone. Placid canoeing water, a rarity in Colorado, attracts growing recreational use to the two canyons. The river itself has been proposed as critical habitat for the endangered Colorado River squawfish and humpback chub, large native fish (to 6 feet and 80 pounds) . Westwater Canyon, just below, is the river's deepest cut into the Uncompahgre Plateau. The river's course, determined recently (about 2-10 million years ago) when a small tributary captured it near Grand Junction, cleaves an 800-foot fault block directly in its way, creating a sinister and claustrophobic gorge within a spacious outer canyon. Westwater's rapids combine at high water, creating an 8-mile millrace where stopping is nearly impossible and the waves run continuously for miles. Below Westwater the red mesozoic sediments dip beneath the water, leaving the Colorado in a wide and placid valley. The stream is overlooked by arid buttes of the Morrison Formation (known for dinosaur fossils and uranium, some of which have been found nearby). The river is lined by tamarisk and overarched by cottonwoods. About 3 miles from the confluence with the Dolores River, Utah Highway 128 joins the stream and parallels it as the river again begins to entrench itself in a canyon that will carry it to Lake Powell. The segment ends just above Dewey Bridge, where the two rivers meet. Dolores River. The remains of the ancestral Colorado's course, from Gateway to Dewey Bridge, is now occupied by the Dolores alone. Since different rock was laid down south of the Uncompahgre Plateau, the rock sequence along this lower canyon of the Dolores contains three formations missing along the Colorado -- Navajo Sandstone, Moenkopi, and Cultler Formations. These rocks add russets, brick tones, purple, and tan to the pink colors found on the Colorado. The rivers' former power has opened a huge valley, miles wide and up to 2000 feet deep I below Gateway; thick stands of cottonwood line the shores. Near the Colorado border, the older, softer rocks dip under the stream; harder formations produce a narrow and intimate canyon. At the transition point, where the valley contricts into a' canyon I I i 6