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rado River near Cisco, Utah) indicated a decrease in dissolved-solids load associated with initiation of the Alva B. Adams Tunnel/Lake Granby exports, and annual mono- tonic trends indicated a recent decrease in median annual flow-adjusted dissolved-solids concentration, which may be related to the trends in the Eagle and Gunnison Rivers. Green Region Most of the flow of the Green River in the Green region originates on the western slope of the Rocky Mountains in Colorado and Wyoming. The drainage area of the Green region is about 45,000 mil and occupies parts of Colorado, Wyoming, and Utah (pl. 1). The Green region contains about 41 percent of the total drainage area of the Upper Colorado River Basin and contributes 39 percent of the streamflow and 34 percent of the dissolved-solids load. Compared to the streamflow at Lees Ferry, Ariz., water of the Green region has relatively high concentrations of dissolved magnesium and bicarbonate and low concentrations of dissolved chloride, resulting from the predominance of Tertiary rocks. The major tributaries in the Green region are the New Fork, Big Sandy, Yampa, Duchesne, White, Price, and San Rafael Rivers, and the Blacks Fork and Henrys Fork. Data for 36 sites were evaluated in the Green region (pl. 1). Long-term mean annual runoff, streamflow, dissolved-solids concentrations and loads, and major- constituent loads were determined at each of these sites (table 7). The chemical composition of streamflow at selected sites in the Green region is shown in figure 14. Selected annual monotonic-trend-analysis results for the Green region are listed in table 8. For purposes of discussion, the Green region was divided into four subregions: the upper Green, the middle Green, the White, and the lower Green (pl. 1). Upper Green Subregion The upper Green subregion includes all of the drainage area upstream from the streamflow-gaging station on the Green River near Greendale, Utah, exclusive of the Great Divide basin. The major drainages in the upper Green subregion include the New Fork and Big Sandy Rivers, and Blacks Fork, Hams Fork, and Henrys Fork and tributaries. About 200,000 acres is irrigated upstream from La Barge, Wyo., including large tracts along the Green River in the vicinity of Pinedale, Wyo., along the New Fork River (62,000 acres), and in the Piney Creek basin. A number of small reservoirs store water in the New Fork River basin. The Big Sandy River begins in the southern Wind River Range, in central Wyoming, but most of its drainage basin is very arid. The Eden Valley Project to supply irrigation water was begun in 1950 and completed in 1960. Some 20,000 acres is irrigated in the basin, and water is stored in Big Sandy and Eden Valley Reservoirs. The average grow- ing season lasts only 90 days. The agricultural area is underlain by the Laney Member of the Green River Forma- tion. Shallow aquifers annually discharge an estimated 116,000 tons of dissolved solids from saline seeps into the Big Sandy River (U.S. Department of the Interior, 1985). About 76,000 acres is irrigated in the Blacks Fork basin. The basin contains numerous reservoirs. The largest is Viva Naughton Reservoir on Hams Fork, with a capacity of about 42,000 acre-ft. Most of the irrigated land is on the Blacks Fork and Smiths Fork, upstream from site 31. About 9,000 acres is irrigated in the Henrys Fork basin, which con- tains numerous small lakes and reservoirs. In the Blacks Fork and Henrys Fork basins, irrigation is on alluvium underlain by the Tertiary Bridger Formation. Fontenelle Reservoir, on the Green River between the towns of La Barge and Fontenelle, Wyo., was built to pro- vide storage for irrigation water; however, the purpose of the reservoir was changed to supply water for the anticipated energy development in the area. The reservoir has inundated outcrops of the Laney Member and the Wilkins Peak Member of the Green River Formation. In 1960, substantial deposits of trona (sodium carbonate and sodium bicarbonate) were found in the area later inundated by the reservoir. In 1983, the reservoir was drained because of concern caused by observations of unstable conditions, including seepage around the left abutment caused by cavernous dissolution. Flaming Gorge Reservoir was completed in 1964 and has a capacity of 3.8 million acre-ft. It is the second largest reservoir in the Upper Colorado River Basin and is located on the Green River between Green River, Wyo., and Green- dale, Utah. Filling began in November 1962, and very little water was released from the reservoir during the 1963 water year. The reservoir was two-thirds full by the end of 1965, but it did not reach 90 percent of capacity until 1972. Flam- ing Gorge Reservoir also has inundated outcrops of the Laney Member of the Green River Formation. A chemocline developed during the first few years of operation, produc- ing a stable saline layer in the bottom of the reservoir. The chemocline began to diminish following the conversion to a selective withdrawal operation in 1978 (Miller and others, 1983). During the high-flow year of 1983, the low gates were opened, and the saline water was flushed out of the reservoir. Green River at Warren Bridge, near Daniel, Wyo. (site 22) The streamflow hydrograph for site 22 (table 3, pl. 1) shows a well-defined snowmelt-runoff peak during June and a period of steady base flow (fig. 15A). The predominant ions are calcium and bicarbonate during the snowmelt-runoff season and calcium and sulfate during the base-flow season. Mean annual runoff averages 15.3 in., and the mean annual flow-weighted dissolved-solids concentration is 147 mg/L (table 7). During 1962-82, annual monotonic-trend analyses indicated a significant decrease in median annual dissolved- solids load of 615 tons/yr (table 8), mostly as a result of decreases in dissolved calcium and bicarbonate. During the Upper Green Subregion 33