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<br />Ttte area south of the Virgin River and north of the~Colorado <br />River is known as the "Arizona Strip." It is composed of a series <br />of five plateaus-which are from west to east:- Shivwits, Unikaret, <br />Kanab and Kaibab plateaus and the P1arble Platform. They are <br />- delineated by faults and flexures and, together comprise the North <br />Rim of the Grand Canyon (Crampton 1972). <br />- The western portion of the Virgin River basin belongs to the <br />Basin and Range province which is characterized by elongate, isolated <br />northward-trending mountain ranges (usually fault blocks) separated <br />by broad alluvium filled valleys or topographic 'basins. The valley <br />fill deposits are deep and generally unconsolidated; consolidated <br />~~ strata comprising the mountains are locally folded and faulted <br />(Longwell et a1.-1965, Dolan 1943): - <br />The St. George basin lying west of the Hurricane fault and <br />approximately in the center of the Virgin -River basin, is the lowered <br />northern end of the Shivwits Plateau block somewhat more deformed. <br />The structural features are not as complex as those typical of the <br />Great Basin. The St. George basin resembles the plateau region in <br />that it lacks the Tertiary and Quaternary deposits characteristic of <br />-the Basin and Range province. These facts and the fact that-the <br />St. George basin is lower than the Great Basin to the north and west <br />. - indicate that it did not drop below the level of the plateaus until <br />the-Great Basin had accumulated thick alluvial deposits (Gardner 1941). <br />Differential uplift along the Hurricane fault raised the plateau <br />region some 1,500 to 1,800 m higher than basin areas to the west <br />(Cook 1960). - . <br />