Water of good quality from mountain streams is degraded as it moves through urban areas to the Jordan River in Salt Lake County, Utah. The impact of urban runoff and atmospheric deposition on the quality of water in those streams and in storm conduits and canals functioning as storm drains was evaluated using data collected during 1980-81. Atmospheric-wetfall loads for an average storm were as much as 10 pounds per acre for total solids, but the dissolved trace metals were generally present in insignificant quantities. Wetfall-deposition loads generally were greater than storm-runoff loads, indicating that a large quantity of the wetfall load remained as soil deposits. Acid rain fell in more than one-half of the storms sampled, most commonly in September and October. Dustfall concentrations reflected the composition of local soils, particularly with regard to iron, manganese, and chromium; but concentrations of cadmium, copper, lead, zinc, and chloride were considerably enriched. Monthly loads of dryfall solids reached a maximum of 62 pounds per acre in the Little Cottonwood Creek urban basin, but were of the same magnitude as total storm loads for a heavy rainfall. Urban runoff represented about 38 percent of the discharge in three canals. The water in the canals was poorer in quality than the water in the mountain streams. The impact of the canal discharges to the streams is slight, however, owing to their ' relatively small amounts. ' Concentrations of sediment, suspended solids, suspended trace metals, phosphorus, and oxygen-demanding substances were much greater during storm runoff than under base-flow conditions. This report contains data for basin and storm characteristics and water-quality information for atmospheric deposition and urban runoff. (USGS)