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Show PART II PRESENT STATUS OF IRRIGATION As shown on the subregional maps, most irrigation development has taken place along the upper reaches of the major streams adjacent to high mountain ranges. Little development has taken place in the Lower Main Stem Areas where the streams are deeply entrenched in canyons 500 to 1,500 feet below and several miles distant from lands suitable for irrigation. Most of the 311,100 acres of irrigated land in the Wyoming portion of the Green River Subregion lie in the headwaters of the Green River and its tributaries at elevations ranging from 6,500 to 8,500 feet. Land re- ceiving sparse precipitation requires irrigation for successful crop pro- duction. The short growing season and cool summers combine to limit crops to forage and small grains. The frost-free period (32° F.) varies from about 20 days at Big Piney to 105 days at Green River, Wyo. For the pre- dominant crops grown, alfalfa and grass for hay and pasture, the growing season varies from about 70 days to 130 days at those stations. Irrigated soils in the headwaters of the Green River are composed pri- marily of alluvial materials derived from glacial deposits originating in the adjacent mountains. Some are derived from underlying shales, sand- stones, and mudstones of local geologic formations. The irrigated lands occur primarily along river and creek bottoms, with smaller acreages lying on benches or terraces 20 to 40 feet above streambeds. Soil textures vary from sandy loams on the benches to clays in some reaches of the river bot- toms. Most soils are underlain with several feet of sand and gravel, which provide natural drainage at elevated positions and allow little ac- cumulation of harmful salts. Low-lying lands along stream channels are irrigated by wild flooding, causing water table buildup during the early part of the irrigation season. About 90 percent of these higher eleva- tion lands in the Upper Green River Basin of Wyoming produces forage from meadow hay and pasture. Alfalfa is the principal crop raised on other lands such as in the Eden Project Area. A total of 332,600 acres of land is presently irrigated in the Utah portion of the region. These lands are located largely in the Uinta Basin but include scattered developments along the east slope of the Wasatch Range for a distance of about 100 miles. Small, widely scattered tracts also lie in southeastern Utah in Grand and San Juan Counties, served largely from intermittent streams. Crop production in the Utah segment of the region is almost entirely dependent on irrigation as the rainfall is sparse, ranging from about 6 to 12 inches over most of the area. Elevations of irrigated lands range from ^,000 to 8,000 feet, and the frost-free period (32° F.) ranges from about 90 to 190 days. Principal crops are alfalfa, small grains, native and improved pasture, and corn for silage. Only in the Monticello Area of southeastern Utah are winter wheat and dry beans grown in quantity without irrigation. 11 |