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Settron - 2.04.7 spruce/subalpine fu and Douglas Fir forest interspersed with mountain meadow at the higher • elevations, and mixed shrub and pinon-juniper dominating the steep lower slopes. The surface hydrologic environment N the immediate [rune area is a direct reflection of site topography, the locally semi-arid climate, and site geology. The North Fork of the Gunnison River is the major drainage in the azea flowing from northeast to southwest along the margins of the Grand Mesa monocline to the north and the Vi/est Elk Mountain uplift to the south. Tributary drainages on either side of the North Fork Valley are relatively steep and deeply incised. Topography in the mine permit and adjacent azeas is graphically illustrated by the Regional Geology/Hydrology Map, (Map 2.04M2). The semi-arid climate limits overall precipitation and there is significant variation in preupitation between the lowland valley areas to the west (approximately 5 inches per yeaz) and the high mountain peaks to the east (approxinately 20 inches per yeaz). Average annual precipitation in the immediate mine vicinity is approximately ]G.9 inches per yeaz. Because it is relatively dry, most of the precipitation which does occur infiltrates quickly into the relatively coarse, unconsolidated surface materials and is rapidly lost to evaporation and transpiration. Very little runoff occurs except during spring snowmelt and major thunderstorm events, and what little runoff does occur results in brief, high flow velocities in the smaller drainages due to the steep terrain. Downstream flows in the North Fork can also vary significantly during iaigation season due to sigrti6cant irrigation withdrawals. The only drainages which have a perennial Flow pattern aze those with relatively lazge watershed azeas and numerous tributaries, while many of the smaller ephemeral drainages flow razely, if at all. High flow velocities aze often accompanied by relatively high sediment loads. The intermittent high- velocity flows limit sediment deposition in the upper drainage reaches but result in significant sediment deposition in lower valley areas to the west where flow gradients flatten. The steep valley • sideslopes and extensive exposures of rocky cliffs, which dominate the azea, contribute to sigrtiLcant deposits of lazge, blocky colluvial material on the lower valley slopes and in most azea drainages. Potentially Affected Surface Water Drainages and Drainage Characteristics -Potentially affected surface drainages include the North Fork of the Gunnison River, as the primary receiving drainage, and the following small perennial, intermittent, and ephemeral tributaries, listed in sequence from east to west: • Thompson Creek (intermittent) • Bazdine Canyon (ephemeral) • Hoopla Gulch (ephemeral) • Hawk's Nest Creek (ephemeral) • C-Gulch (ephemeral) • B-Gulch (ephemeral) • A-Gulch (ephemeral) • Coal Gulch (ephemera]) • Unnamed Drainage (ephemeral] • Sanborn Creek (ephemeral) • Elk Creek (ephemeral) • West Valley Drainage (ephemeral) • West Valley 2 Drainage (ephemeral) • Beaz Creek (ephemeral) • 54dubazi~f,redRfperenniai~ • 'T'hese drainages aze shown on the Surface Water Hydrology Map, (Map 2.04MG), and described in the followi ng sections. PR04 2.04-53 Revised November 200]