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Show PART II DESCRIPTION Prior to about 1960 there were 33 storage reservoirs in the subregion, having usable capacities greater than 1,000 acre-feet, and total usable capacity of 831,600 acre-feet. The Blue Mesa Reservoir (capacity 941,000 acre-feet) was completed in 1965 and storage in Morrow Point Reservoir (121,300 acre-feet) began in 1968. In spite of the large exports of water from the subregion, the large areas of land under irrigation, and the fact that it contains the smaller area of the three subregions, the Upper Main Stem subregion is the largest contributor in total discharge, supplying about 46 per- cent of the total discharge at Lee Ferry from only 24 percent of the total area. See tabulation on page 5 for historic unit discharge. The San Juan - Colorado Subregion The San Juan-Colorado subregion includes all of the drainage area of the Colorado River downstream from the junction of the Colorado and Green Rivers, an area of about 38,644 square miles. The principal stream in this subregion is the San Juan River, which is the second largest tributary of the Colorado River, and drains parts of south- western Colorado, northwestern New Mexico, southeastern Utah, and northeastern Arizona. It rises on the west slope of the Continental Divide in the southeastern part of the Upper Colorado River basin, and flows westward to its junction with the Colorado River about 75 miles west of Bluff, Utah. The principal tributaries of the San Juan River are the Navajo, Los Pinos, Animas, and La Plata Rivers. The other main tributaries in the subregion are the Dirty Devil, Escalante, and Paria Rivers. Five transmountain diversions export an average of about 2,500 acre-feet per year from the San Juan-Colorado subregion. One diversion imports into the San Juan-Colorado subregion about 102,600 acre-feet per year from the Upper Main Stem subregion. Another diversion imports into the San Juan-Colorado subregion about 2,600 acre-feet per year from the Sevier River drainage of the Great Basin in Utah. Prior to about 1960 there were 18 storage reservoirs in the subregion having usable capacities greater than 1,000 acre-feet, and total usable capacity of 228,200 acre-feet. Navajo Reservoir on the San Juan R_iver near Archuleta, New Mexico, with a capacity of 1,696,000 acre-feet, was completed in June 1962. The Navajo Indian Irrigation. Project, the main contractor from Navajo Reservoir, with- draws water by gravity canal at an elevation which makes the usable capacity of Navajo Reservoir 1,036,100 acre-feet. Lake Powell on the Colorado R_iver was formed by Glen Canyon Dam at Page, Arizona. Storage began in March 1963, and the usable capacity is 25,002,000 acre-feet. These two reservoirs are part of the Upper Colorado River Storage Project. |