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2.04.6 Geology Description <br />Geology <br />(1) General Requirements <br />The following discussion of geology is derived from the 1955 Grand <br />Junction Soil Survey and from the 1979 Geologic Map of Colorado. The <br />geologic formations of the Grand Junction Area are extraordinarily varied <br />and complex. Most of the valley is influenced by the Mancos shale <br />formation, which is extensive in western Colorado and ranges from 3,908 <br />to 4,150 feet in thickness. To the north and northeast, the Mancos shale is <br />capped by the Cretaceous Mount Garfield Formation and Sego <br />Sandstone, forming the Book Cliffs. The Book Cliffs stand out in bold <br />relief above the valley, rising in elevation from 5,500 feet at their base to a <br />crest of 6,500 to 7,000 feet. The total relief from the crest of the cliffs to <br />the lower base level of the Grand Valley is about 3,000 feet. <br />The Mount Garfield Formation and Sego Sandstone contain buff to <br />yellowish -brown sandstone bedded with soft gray shale that contains one <br />or more beds of bituminous coal and underlying thick beds of sandstone <br />that rest upon the marine Mancos shale. <br />The soils of the Persayo and Chipeta series have developed in place on <br />the Mancos shale, and the gray alluvium washed from this shale has <br />contributed to the Billings soils. The soils on the sloping and higher <br />benches north of the Colorado River have developed from brown sandy <br />alluvial materials largely derived from formations of the Mesaverde group <br />in the Book Cliffs. <br />Overlying the Mount Garfield and Sego Sandstone are the Hunter <br />Canyon, Wasatch, Green River and Uinta Formations, which successively <br />rise to the lava- capped deposits on Grand Mesa. The western <br />escarpment of Grand Mesa, elevation 10,000 feet, overlooks the Grand <br />Valley from the east. This lava- capped formation and others farther up the <br />Colorado River consist of igneous, sandstone, and shale formations and <br />are the source of the older alluvial deposits on Orchard Mesa and of the <br />younger alluvium on the Colorado River flood plain. <br />Permit Application 2.04 -9 04/11 <br />