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<br />. <br /> <br />. <br /> <br />t.t.) <br />l;,() <br />N <br />~ <br /> <br />. <br /> <br />. <br /> <br />. <br /> <br />. <br /> <br />. <br /> <br />. <br /> <br />. <br /> <br />. <br /> <br />. <br /> <br />barriers. In the Colorado Plateau province, the river runs for much of <br /> <br />its 300 mile cour se in canyons cut in colorful rock formations. Grand <br /> <br />Canyon cuts across the high southwest rim of the plateau. Broad valleys, <br /> <br />such as those of the Wyoming Basin, also are found on the Colorado Pla- <br /> <br />teau, for example, in the Uintah Basin and adjacent to the San Juan and <br /> <br />Little Colorado Rivers. In the Basin and Range provinces the flood plains <br /> <br />of the <br /> <br />Colorado are extensive, particularly be. the Bill Williams River. <br /> <br />The boundaries of the Upper Colorado River Basin consist of up- <br /> <br />lifted earth masses heavily dissected by erosion, glaciation weathering. <br /> <br />In the interior of the basin are plateaus, mesas, and basins all considera- <br /> <br />bly affected by erosion. <br /> <br />Before the creation of the existing mountains, the Upper Basin was <br /> <br />subjected to a series of inundations and retreats of great land-locked seas. <br /> <br />The sedimentary materials that accumulated and were not removed by <br /> <br />erosion when the lands stood above the ancient seas is : manifested by <br /> <br />sedimentary formations that reach thicknes ses of several thousand feet. <br /> <br />These events occurred in the Paleozoic and Mesozoic Eras. <br /> <br />The earth movement that formed the Rocky Mountains began in the <br /> <br />Mesozoic and continued into the Cenezoic Eras. The emergence of the <br /> <br />Rocky Mountains and the uplifting of the Colorado Plateau from the ancient <br /> <br />sea started the history of the Colorado River (ca. 65 million years ago). <br /> <br />These earth movements formed huge lakes, in the northern Colorado <br /> <br />Plateau, which received sediments from the newly formed highlands. <br /> <br />5 <br />