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<br />SUMMARY (Continued) <br /> <br />..{~t~~~.1 <br /> <br />Uintah Countie8 are 10c8ted in the unit area. The major popu18tion cen- <br />ters in the 1980 cenSU8 were Vernal (6,600), Roosevelt (3,842), and <br />Duchesne (1,677). The smaller communities range in population from <br />fewer than 50 to 500. The combined population of the two counties was <br />38,071 in 1980 and was estimated at 38,800 in July 1984. The major com- <br />munities are located along U.S. Highway 40, a major east-west highway <br />which crosses the area. <br /> <br />The Uinta Mountain range and the Tavaputs Plateau are the northern <br />and southern rims of the basin, respectively. <br /> <br />Most of the Uinta Basin Unit area is semiarid, making irrigation <br />essential in cropped areas. An average total of 97,447 acres of land <br />was irrigated in the 17 subareas of the unit area during the study <br />period. Approximately 105,000 acres would be irrigated in the same area <br />under future conditions with full operation of both the Bonneville and <br />Upalco Units of the Central Utah Project. The irrigated acreages in the <br />Ashley Valley subarea (19,210 acres) and the Whiterocks-East Uinta sub- <br />area (18,400 acres) comprised about 39 percent of the total irrigated <br />acreage in the study area. During the study period, nine irrigation and <br />canal companies and the Bureau of Indian Affairs (operating the Uintah <br />Irrigation Project) diverted a historical average of about 350,670 acre- <br />feet of irrigation water annually to the Uinta Basin Unit lands from the <br />Duchesne River; from the Lake Fork, Yellowstone, Uinta, and Whiterocks <br />Rivers, which are tributaries of the Duchesne River; from Ashley Creek; <br />and from other smaller tributaries. Water is delivered from diversion <br />points to irrigated lands utilizing 22 canals and associated laterals <br />which were considered for potential lining, along with other associated <br />canals and laterals and three storage facilities (Steinaker, Big Sand <br />Wash, and Midview Reservoirs). The c8nals vary in capacity from 5 to <br />480 cubic feet per 8econd (cfs) and in length from 1.5 to 18 miles. The <br />laterals vary from 3 to 35 cfs in capacity and from 2.3 to 11.7 miles in <br />length. <br /> <br />Most of the farms, which produce mainly feed for livestock, are <br />irrigated by water from the Duchesne River and its major tributaries, <br />the Lake Fork and Uinta Rivers. These farms are situated along nearby <br />lower lying stream bottoms, benches, mesas, terraces, and bad land8. <br />A8hley Valley, in the eastern part of the basin, is irrigated by water <br />from Ashley Creek, which flows directly into the Green River. <br /> <br />Temperature and precipitation vary widely, with an average 8nnual <br />precipitation ranging from about 7 inches near the towns to about 40 <br />inches in the adjacent high mountains. Daily temperature extremes C8n <br />vary as much as 40 degrees. Annual extreme temperatures range from -30 <br />to 105 of. <br /> <br />The average frost-free period is 115 days at Duchesne, 120 days at <br />Vernal, and 125 days at Roosevelt. As elevation increases, the growing <br />season decreases. The peak precipitation months are April, May, and <br />June. Snowfall can occur as early as September 8nd as late as July, <br />but more commonly occurs from October to May. <br /> <br />S-3 <br /> <br />,--\ ,,r, r, (~Q <br />UUI.'.JvV <br />