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2.06.8(9) ALLUL'IAL VALLEY FLOOR DETERMINATION Black Hawk Canyon and Santa Clara Creek border the southeastern edges of the Pryor Mine Lease Area. Both have wide valley floors within or adjacent to the permit area. The valley floor of the Pryor Canyon within the permit area had been mined and reclaimed. Immediately downstream of the permit area the valley floor of the Pryor Canyon has badland topography and is partly occupied by ol~' mine dumps, Most of the surface drainage from the permit area flows into Pi•yor Canyon. The remainder goes to Black Hawk Canyon which joins Santa Clara Creek just outside the southeastern margin of the permit area. Pryor Canyon drainage area is highly disturbed from past underground mining and present strip mining. Past subsurface workings also exist in parts of the Dlack Hawk Carryon within the permit area (see Figure 2.04.6-1). At least three future surface workings will lie within the area draining into Black Hawk Canyon. If future mining activiiy in the Pryor Mine is to effect changes in the quality and quantity of surface water and ground water, these changes would affect the Black Hawk Canyon more directly than Santa Clara Creek, Black Hawk Canyon lies in the down dip direction of the projected mine workings in 1982(2) and would catch some of the surface discharges from these workings and the 1983 (3A) partial permit area. The stretch of the Black Hawk Canyon that was considered for the reconnaissance alluvial valley floor investigation is over a mile long, upstream from the junction with Santa Clara Creek (Figure~,06.8-1). The valley narrows very rapidly and rock is exposed along the floor and the sides above the crossing of Rouse Road within this stretch. Black Hawk Canyon enters Santa Clara Creek about 900 feet northeast of the southern edge of the 1982 partial permit area. Santa Clara Creek is a major drainage system and is the dominant influence on the characteristics of the valley downstream from the confluence with Black Hawk Canyon, Black Hawk Canyon valley floor is open rangeland. Over-grazing and disturbances from past mining activity may account for the poor vegetation cover. There are no signs of past or present irrigation practices of any form and definitely no potential for subirrigation as the creek is dry most of the year and the groundwater table has to be at least 20 feet below the surface. Black Hawk Canyon is dry and no signs of seepage were observed anywhere along the stretch under consideration. The Creek has incised a flat bottomed, U-shaped channel as deep as 20 feet in the alluvial fill (Figure "$,.06.8-2). On either side of the cF~annel, the valley floor is flat with a total width of ,..~, , 3~ a SSA-64 J. F 5AT0 & ASSOCIATES, tNC.