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BASIC STUDIES o w ~ The study reported here defines water-quality conditions in the Green w::. River when the river flowed unhindered through the area now inundated by the waf; ers of Flaming Gorge Reservoir (Fig. A). Subsequent reports will include studies of postreservoir conditions and comparisons to appraise the effects of impoundment on water quality. Most inflow of water to the reservoir is from the Green River, Blacks Fork, Henrys Fork; Sheep and Carter Creeks are smaller sources of inflow. Bitter Creek, which drains an area of about 2,400 square miles northeast of the reservoir, and other much smaller drainage areas are minor sources of inflow. Prereservoir Increases in Dissolved Constituents Continuous records of streamflow and water quality have been obtained during a six-year period prior to closure of Flaming Gorge Dam at sites listed in Table D and shown on Figure A. Although Chemical quality of the major tributaries to the reservoir area has been determined since 1951, the chemical quality of water in the Green River near Greendale, the out- flow from the reservoir, has been measured only since October 1956. Flam- ing Gorge Dam was closed in November 1962; therefore, the preclosure pe- riod, during which both inflow and outflow data were obtained, was October 1956 through October 1962. Suf'ficient data are not available on the chem~ ical quality and runoff of Bitter, Sheep, and Carter Creeks at their mouths to include them in this analysis. During the six-year period of common record, once-daily chemical- quality data were obtained concurrently at all four sites only for 19 months. Reasonably accUrate dissolved solids and dissolved-constituent loads can be computed for these months. During winter months ice condi- tions at one or more of the four data-collection sites often precluded daily sampling; thus, common records for November through March are not suf'ficiently complete to compute dissolved solids and dissolved-. constituent loads for the purposes of this study. At times during the April through October periods daily data were not suf'ficiently complete at all four sites to permit accurate computation of loads. Even for the 19 selected months the relation between inflow and out- flow is not precise. Some of the discrepancies can be attributed to in- flow from intermittent intense storms in the Bitter Creek basin, lower Blacks Fork Basin, and other drainage basins downstream from the data col- lection sites on Blacks Fork and on Green River near Green River, Wyoming. Part of the discrepancy can be attributed to errors introduced by assum- ing that water-discharge data obtained at a site several miles downstream or upstream from the site where chemical-quality data are obtained can be applied to the chemical data to compute loads. The measured monthly runoff and dissolved-solids loads entering the Flaming Gorge Reservoir area are compared in Table D to those leaving the 35