9521 - Laserfiche WebLink

Home Browse Search

1982). Sedimentary formations also contain deposits of oil, oil shale, coal, and natural gas. Structural features, including anticlines, domes, and faults, expose large sequences of strata in the Upper Colorado River Basin. More than 200 forma- tions have been identified (Ioms and others, 1965; Warner and others, 1985). Several geologic units are major contributors of dis- solved solids to streams in the Upper Colorado River Basin. Most important is the Upper Cretaceous Mancos Shale and equivalent formations such as the Tropic Shale. The upper members of the Mancos Shale consist of thick beds of marine shale that commonly form flat benches that underlie irrigated lands. The Mancos Shale contains gypsum, calcite (calcium carbonate), dolomite (calcium magnesium carbonate), and sodium-rich clay. Weathering of the Mancos Shale includes dissolution of gypsum, followed by cation exchange on the clay, resulting in water containing high concentrations of dissolved sulfate, sodium, and calcium (Rittmaster and Mueller, 1985). Mancos Shale is most widely exposed in the Roaring Fork, Gunnison, Uncompahgre, San Juan, Yampa, White, Price, San Rafael, Dirty Devil, and Dolores River basins (fig. 3). The Paradox Member of the Pennsylvanian Hermosa Formation has formed a series of salt anticlines near the Colorado-Utah border, which contain large deposits of halite. Water interacting with these salt domes contains very high concentrations of dissolved sodium and chloride. The Eagle Valley Evaporite, of Pennsylvanian age, contains soluble salts and gypsum and is exposed in the Eagle River and Roaring Fork River basins. The Jurassic Carmel Formation contains deposits of halite. It is exposed in a narrow band across the Price, San Rafael, and Dirty Devil River basins. Several coal-bearing formations occur in the Upper Colorado River Basin. These are mined in the Gunnison, Upper Green, Yampa, White, Price, San Rafael, Dirty Devil, and San Juan River basins. Water in these formations con- tains high concentrations of magnesium, sodium, and sulfate. The Green River Formation is extensively exposed in southern Wyoming, northeastern Utah, and northwestern Colorado. This formation consists of Tertiary lacustrine deposits containing nahcolite (sodium bicarbonate), dolomite, and calcite, as well as the world's largest deposits of oil shale. The Parachute Creek Member of the Green River Forma- tion crops out in the Piceance, Yellow, Parachute, and Roan Creek basins. Water in the Parachute Creek Member contains high concentrations of sodium, bicarbonate, and chloride. The Laney Member of the Green River Formation underlies irrigated agricultural land in the Big Sandy River basin. The Tertiary Uinta Formation and its equivalent, the Bridger Formation, are exposed north and south of the Uinta Mountains near the Utah-Wyoming border. These formations contain gypsum and a thick, saline layer deposited during the final phase of the ancestral Lake Uinta. A large area overlying the Uinta Formation is irrigated in the Duchesne River basin. Climate Climate in the Upper Colorado River Basin is diverse because of physiographic features, prevailing wind patterns, and wide variations in elevation and latitude. Extremes of temperature may range from -50 to 115 °F. The basin generally is arid; annual precipitation averages 15.9 in. (Ioms and others, 1965), ranging from 60 in. in the higher moun- tains to less than 5 in. in the southern part of the basin. The northern and high-mountain parts of the Upper Colorado River Basin are characterized by long, cold winters and short, warm summers. Many areas are covered by snow all winter, and 10-ft snowpacks are not unusual. Plateau and high-basin areas may have cold winters and hot summers; the southern end of the basin has mild winters and very hot summers. Mountainous areas generally receive most of their precipitation as snow; the lower areas have dry winters and receive most of their precipitation from summer thunder- storms. DEVELOPMENT OF WATER RESOURCES The Upper Colorado River Basin is sparsely populated; the average density is about six persons per square mile. Population has increased from 288,000 in 1930 to 664,000 in 1982 (U.S. Bureau of Census, 1982). The largest increase occurred from 1970 to 1980, when the population increased by 55 percent (fig. 4). The basin is primarily rural; only five towns had populations greater than 10,000 in 1982, and only 40 percent of the population lived in towns with more than 1,000 people. Farmington, N. Mex., with a population of 36,000, was the basin's largest town in 1982. Several metropolitan areas outside the Upper Colorado River Basin have a marked effect on water and land use in the basin. They increase the demand for water, energy, and food produced in the basin. The cities of Denver and Colo- rado Springs, Colo., Albuquerque, N. Mex., and Salt Lake City, Utah, are dependent on water diverted from the Upper Colorado River Basin. Irrigation Most of the water used in the Upper Colorado River Basin is for irrigated agriculture. Crops that are irrigated in- clude livestock feed, fruit, and vegetables. The practice of irrigation in the basin began with the first settlements. After the passage of the Reclamation Act in 1902 (Follansbee, 1929), the irrigated area increased substantially to a total of 1.3 million acres by 1910. Since then the total irrigated acreage has not increased appreciably, but usually has fluc- tuated between about 1.4 and 1.6 million acres (U.S. Bureau of Census, 1984). Most of the irrigated lands (fig. 5) are in river valleys or on plateaus and are supplied by extensive 6 Characteristics and Trends of Streamflow and Dissolved Solids in the Upper Colorado River Basin