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<br />GOfJ078 <br /> <br />sandstone. In the eastern part of the monument, the Yampa River flows along <br />the approximate contact between the Morgan Formation and the Weber Sandstone, <br />Along this stream reach, the Morgan Formation can be seen as a series of <br />stepped cl iffs (fig. 2A). Downstream from this point, the Yampa River cuts <br />across the Weber Sandstone, which forms the spectacular sheer cl iffs of the <br />lower Yampa Canyon (fig. 2S). <br /> <br />Water temperature and specific conductance were measured at about 2-km <br />intervals within the study reach. At five sampling sites, ranging from 16 to <br />24 km apart (fig. 1), stream discharge, pH, and dissolved oxygen also were <br />measured. In addition, bottom-sediment samples were collected. After <br />extraction of the less than 2DB-micrometer fraction of the sediments in hot <br />hydrochloric acid, antimony, arsenic, chromium, copper, iron, lead, mercury, <br />and nickel were determined. <br /> <br />Dnly one tributary contributed inflow greater than 0.003 m3fs. This was <br />Warm Springs Draw (fig. 1), where surface flow coming from springs was <br />estimated to be about 0.1 m3fs. Several seeps were noticed along the canyon <br />walls throughout the study reach; however, the effects of these on the flow <br />and water qual ity of the Yampa River were considered to be minimal at the time <br />of the reconnaissance. <br /> <br />RESULTS AND DISCUSSION <br /> <br />Water temperature and specific-conductance profiles for the study reach <br />are shown on figure 3. The observed fluctuations in water temperature result <br />primarily from normal diel variations as measured by the time-series pattern <br />of sampling throughout a 10- to 12-hour period during each of the 3 days of <br />the reconnaissance. Maximum daily water temperatures increased from 190C <br />(Celsius) in the upstream part of the study reach (sites 4-7) to 220C in the <br />downstream part (sites 36-41) (fig. 1). Neither Warm Springs Draw (fig. 1) <br />nor other seeps in the monument had any pronounced effect on the water <br />temperature of the Yampa River. <br /> <br />Specific conductance, measured along the study reach, increased in a <br />downstream direction, although some degree of random fluctuation was noted <br />(fig. 3). Measurements ranged from 445 micromhos per centimeter at 250C at <br />site 1 and at site 17 to 495 to 500 micromhos at the last three downstream <br />sampling points (sites 41-43). This represents an 11- to 12-percent increase <br />in specific conductance within the study reach. Evaporation and ground-water <br />discharge probably accounted for much of this increase. <br /> <br />The data obtained at five selected sites within the study reach are <br />summarized in table 1. Dissolved oxygen was slightly supersaturated during <br />most of the daylight hours. Slight undersaturation was noted in early <br />morning, and the same situation probably occurred at night. Such a diel <br />pattern is common in mountain and hill-country streams (Reid and Wood, 1976, <br />p. 215). <br /> <br />5 <br />