WSP01683 - Laserfiche WebLink

Home Browse Search

CCC;" ;':"i" -,' -':.". "'-'~'- .~...'.' ;:(~ lower the salinity of the Colorado River by approximately 16 milligrams per liter (mg/l) at Imperial Dam near Yuma, Arizona. INTRODUCTION TO THE PROBLEM Paradox Valley Trending northwest-southeast, Paradox Valley is 3 to 5 miles wide and about 24 miles long, and is crossed near its midpoint by the Dolores River. The surrounding wa11s of sandstone and shale layers are quite steep and rugged, while the floor itself is relatively flat and featureless. With the exception of about 3,600 acres of irrigated crop- land in the northwestern half, the area is generally undeveloped. The major source of income is livestock, although some malting barley is grown as a cash crop. The climate of the valley is generally arid; typically hot and dry during the summer and cold and dry during the winter. .Geophysicat. studies including deep. drilling by oil companies haveestab- Ii shed the presence of a series of five major salt anticlines in south- western Colorado and southeastern Utah. As shown in Figure I, the anti- clinal region is about 100 miles long along its northwest-southeast axis and is marked by the extrusive mass of the La Sal Mountains prominently perched over its center. Paradox Valley, lying along the axis of one of the largest al,ticlines, has been formed by the erosion of faulted and up- lifted sandstone and shale formations, exposing a residual gypsum cap which covers about 14,000 feet of pure salt and salt-rich shale. Paradox Valley has been identified as a major natural contributor of salinity in the upper basin. The Dolores River, in crossing the valley, picks up an'estimated 200,000 tons of salt each year and carries this load to its confluence with the Colorado River. Geology Figures 2 and 3 illustrate the development of the valley. Briefly stated, the emergence of mountainous uplifts on each side of the area has placed intense lateral pressures on the intervening sedimentary formations, resulting in faulting and fracturing along weak zones. Under these pressures 3 oor584