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| This view is looking downstream (south) along the Green River from the Split Mountain Overlook in Dinosaur National Monument.The modern river channel expands to cover the entire flood plain in times of high flow, particularly during the spring snow melt. The construction of the high dam in Flaming Gorge has significantly altered the natural discharge of the Green River, but the Yampa River and other regional streams still retain most of their uncontrolled natural flow. This view shows two stream terraces on the left bank of the river, and two higher terraces are visible on the flanks of Blue Mountain in the distance. The 1st Terrace is about 40 feet above river level, the 2nd Terrace is about 120 feet above stream level. The 3rd Terrace forms a flat bench above some low cliffs along the river in the distance and is about 350 feet above stream level, and a 4th Terrace is about 700 feet above stream level. The degree of erosional degradation of each of the terraces increase with each higher (and older) terrace. Early investigations of stream terraces in the American West recognized at least three, and usually four, major terraces along rivers in widely distributed areas ranging from the Sierra Nevada in California, the Wind River Mountains of northwestern Wyoming, the flanks of the Black Hills in South Dakota, to streams along the greater Colorado River drainages. These early investigations also demonstrated linkages between glacial deposits of major glaciation cycles and terraces, with glacial deposits resting on the surfaces of older terraces. Today these observations are still valid in many places. However, other complex factors may influence stream terrace development, including regional tectonics, stream capture, and even changes in sea level affecting the gradient of major river systems. In addition, many more glaciation cycles are now recognized in ocean sediments than on the land. This is because each successive glaciation cycle tends to destroy evidence of earlier glaciation periods on land's surface. As new geologic age-dating methods become available, and more data becomes available, the linkages between climate cycles and stream-terrace development may be better understood. |
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