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<br />~ <br />~ <br />~ <br />00 <br /> <br />The dissolved-solids concentration of Canyon Creek (site 1) was about <br />230 mg/L, of Elk Creek (site 2) was 721 mg/L, and of Rifle Creek (site 7) was <br />about 1,700 mg/L. Drainage areas of Canyon and Elk Creeks contain diverse <br />geologic formations that are predominantly Cambrian, Ordovician, Devonian, and <br />Mississippian rocks and other formations found in the Grand Hogback. The <br />rocks underlying Rifle Creek are similar in the upper and middle reaches to <br />those underlying Elk and Canyon Creeks. In the lower reaches, Rifle Creek is <br />underlain predominantly by the Wasatch Formation. These three streams <br />draining from the north into the Colorado River contributed a combined <br />discharge of 33.8 ft3/s and 18,500 ton/yr of base-flow salt load. <br /> <br />The dissolved-solids concentration of Garfield Creek (site 3) was <br />580 mg/L, of Divide Creek (site 4) 881 mg/L, and of Mamm Creek (site 5) about <br />2,000 mg/L. The drainages of these creeks are underlain predominantly by the <br />Wasatch Formation, and small deposits of gravel are adjacent to the streams. <br />The dissolved-solids concentration in Beaver Creek (site 6) was about 150 mg/L <br />and in Battlement Creek (site 8) about 300 mg/L. These creeks are underlain <br />primarily by the Wasatch Formation in the lower reaches and the Green River <br />Formation in the upper reaches. The combined discharge of these five <br />tributary streams draining from the south into the Colorado River was only 2.2 <br />ft'(s, and the base-flow salt-load contribution was only 2,570 ton(yr. <br /> <br />The dissolved-solids concentrations of Parachute Creek (site 9) was about <br />760 mg/L, and the dissolved-solids concentration of Roan Creek (site 10) was <br />2,340 mg(L. Parachute and Roan Creeks, in the lower reaches, drain the <br />Wasatch Formation; in the upper reaches they drain the oil-shale deposits in <br />the Green River Formation north of the Colorado River. The combined discharge <br />of these two creeks was 7.5 ft3Js, and the base-flow salt-load contribution <br />was 9,200 ton/yr. <br /> <br /> <br />The salt load entering the subregion at the site on the Colorado River <br />below Glenwood Springs (site 52, table 2) was measured to be 993,000 ton/yr. <br />The measured salt load of the Colorado River at Cameo, Colo., (site 11) was <br />1,274,000 ton/yr. Between these two sites, there was an increase in estimated <br />base-flow salt load of 281,000 ton/yr. Measured salt loads of tributaries <br />accounted for an estimated 30,300 ton/yr. The remaining estimated <br />249,700 ton/yr was produced by other sources, possibly direct ground-water <br />discharge to the river. Adjusting the discharge and salt load of the Colorado <br />River at Cameo (site 11) for reservoir effects upstream changes the values to <br />1,306 ft3/s and 1,255,000 ton/yr. <br /> <br />The largest tributary discharging into the Colorado lower headwaters <br />subregion is Plateau Creek. Plateau Creek (site 12) had a dissolved-solids <br />concentration of 511 mg/L at a measured discharge of 48 ft3Js. The main stem <br />of Plateau Creek is underlain predominantly by the Mesaverde Group in the <br />lower reacbes and the Wasatch Formation in the middle and upper reaches. Most <br />of the tributaries to Plateau Creek have their headwaters in,areas consisting <br />mostly of the Green River Formation. <br /> <br />Leach Creek (site 13), 'Adobe Creek (site 14), Reed Wash (site 17), and <br />Salt Creek (site 18) had dissolved-solids concentrations ranging from about <br />1,910 to about 4,220 mg/L at measured discharges ranging from 4.0 to 18 ft3/s. <br />These tributaries enter the Colorado River from the north through the Grand <br /> <br />50 <br />