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00l:j Elevations of the area studied range from 3048 m at the most upstream station to 2743 m at the station just below Lake Creek. Vegetation along the river in the study area con- sists mainly of grass and shrubs. with very few trees. The shrubs include willow, sagebrush. billerbrush. and common shadbush. Common forbs are silver lupine, fairy trumpet, sulfur flower. cranesbill. and a shrub squaw currant. along with numerous wheat grasses, fescues. foxtails, and sedges ILaBounty et al.. 1975 1941 }. Sampling Stations Thirteen stations were selected. approximately equidistant from one another, along a 30-km reach of the upper Arkansas River (fig. 3). The stations were chosen by accessibility, and also by locations used in previous studies for pur- poses of comparison. These stations are desig- nated from upstream to downstream as: EF-1, leadville Drain, EF-2, AR-1. AR-2, California Gulch. AR-3, AR-4. AR-5. AR-6. AR-7. AR-8. and AR-9. In a previous report IlaBounty et al.. 1975 1941 1 these stations were designated EF-1. leadville Drain, EF-7. AR-1, AR-3. Cali- fornia Gulch. AR-4. AR-5. AR-6. AR-9. AR-10. AR-7, and AR-B. respectively. Figure 3 shows the approximate locations of these sampling sta- tions. Most sampling stations consisted of a gravel-rubble substrate according to a modifica- tion of the Wentworth 119221 11641 classifica- tion. Station EF-1 is located on the west side of Colo- rado Highway 91 about 1.3 km upstream of the inflow from the leadville Drainage Tunnel. This station was the control for this study. The sub- strate consists primarily of sand, with gravel and rubble from 1 7 to 1 67 mm in diameter. Many pools and undercut banks are present in this sec- tion of the river. The leadville Drainage Tunnel is near the city of Leadville and the Molly Brown Trailer Park. It was constructed during the periods of 1943-45 and 1950-52 to drain operating mines. Although in a state of disrepair, it continues to drain abandoned mines and a portion of the local aquifer IBureau of Reclamation, 1976 [18]) and Turk and Taylor. 1979 [15111. The sub- strate at the leadville Drain sampling station is composed mostly of gravel and rubble from 43 to 214 mm in diameter. Station EF-2 is approximately 6.1 km down- stream of the Leadville Drain inflow and up- stream of the confluence with Tennessee Creek. The substrate is comprised primarily of stones from 40 to 196 mm in diameter. Station AR-1 is located about 1.4 km below the confluence with Tennessee Creek and down- stream of he USGS Leadville gaging station. The predominately cobble substrate is composed of gravel and rubble from 37 to 206 mm in diameter. Station AR-2 is located below the bridge over the Arkansas River on Colorado Highway 300, about 1 50 m above the California Gulch inflow. Much of the substrate is composed of 23- to 248-mm-diameter rocks, with some sand also present. California Gulch is the drainage for a large, pre- viously mined area above the city of Leadville. It drains many abandoned and some active mines by way of the Yak Tunnel and collects runoff and seepage from surface mine tailing piles. The Leadville sewage treatment plant also dis- charges into California Gulch. The substrate at this station consists primarily of 56- to 225-mm stones. with some gravel and a fine layer of precipitated iron. Station AR-3 is located about 0.4 km below the confluence of California Gulch and 1.6 km above the confluence with Lake Fork. At this point. the discharge from California Gulch is thoroughly mixed into the riverflow. The area adjacent to this stretch of the Arkansas River is heavily grazed. The substrate contains some sand, but is with predominantly gravel and rub- ble 26 to 256 mm in diameter. Station AR-4 is located on the Smith ranch, about 0.8 km downstream of the confluence of Lake Fork. The substrate at this point consists primarily of 44- to 137-mm-diameter smooth river rock. Flows at this station are irregular and at times quite high due to the releases of water from Turquoise Lake. Station AR-5 is immediately upstream of the Snowden Overpass on U.S. Highway 24. The substrate consists of coarse sand. with some 33- to 186-mm-diameter gravel and rubble. lit- tle bank vegetation is present in this section of river. 15