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<br />~ <br />OJ <br />00 <br />C,il <br /> <br />Twenty-six sampling sites were selected in this subbasin (figs. 3 and 8; <br />table 2). The dissolved-solids concentration of the Colorado River below Lake <br />Granby (site 26), Willow Creek (site 27), Fraser River (site 28), Colorado <br />River at Hot Sulphur Springs (site 29), 'Williams Fork (sites 30 and 31), and <br />Corral Creek (site 32) in Colorado ranged from 72 to about 150 mg/L. These <br />relatively low concentrations are indicative of the insoluble igneous and <br />metamorphic rocks exposed in these areas. <br /> <br />The estimated base-flow salt load computed for the Colorado River at Hot <br />Sulphur Springs (site 29)'was 10,400 ton/yr with a measured discharge of <br />77 ftl/s. Comparisons with historical data for December, January, and <br />February of water years 1976-77 from a water-quality station at this site <br />indicate that the measured discharge was 26 percent greater than the average <br />of 61 ftl/s, and the measured dissolved-solids concentration was 54 percent <br />greater than the average of 89 mg/L; <br /> <br />Flow in the Williams Fork is regulated by the Williams Fork Reservoir. <br />Adjustments for the effects of Williams Fo'rk Reservoir resulted in a decrease <br />of 11 ftl/s discharge of the Williams Fork at its mouth (site 31) and a <br />corresponding decrease of 2,700 ton/yr in the estimated base-flow salt load. <br />This adjustment was applied to all affected downstream sites. The Williams <br />Fork contributed an adjusted base-flow salt load of 4,300 ton/yr and an <br />adjusted base-flow discharge of 60 ftl/s. <br /> <br />Troublesome Creek (site 33), which has a dissolved-solids concentration <br />of about 260 mg/L, reflects the slightly higher salinity of hydrogeologic <br />unit 3 (table 1) that it drains. The estimated base-flow salt load for <br />Troublesome Creek was 10,000 ton/yr. The large dissolved-solids concentration <br />of 984 mg/L in Muddy Creek (site 34) probably results from the large area of <br />Upper Cretaceous marine shales in hydrogeologic unit 7 (table 1) found in its <br />drainage. <br /> <br />Dissolved-solids concentrations of about 220 and 183 mg/L in Blacktail <br />(site 36) and Rock Creeks (site 40), respectively, are indicative of the <br />insolubility of igneous rocks underlying most of these drainages. Sheephorn <br />Creek (site 37) had a dissolved-solids concentration of about 730 mg/L. This <br />area is underlain by marine shales of hydrogeologic unit 7 (table 1), which <br />probably contribute to the relatively large dissolved-solids concentration. <br />The dissolved-solids concentration of the Piney River (site 38) was 209 mg/L. <br />The Piney River drains predominantly hydrogeologic unit 3 basalt (table 1) <br />and, in the upper reaches, Permian through Cretaceous rocks. Most of the base <br />flow in the Piney River is probably from the basalt and accounts for the <br />fairly low salinity concentrations. <br /> <br />27 <br />