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West Elk Mine • by a thin veneer of clluvial deposits composed chiefly of debris from sheet erosion, deposits by unconcentrated runoff or slope wash, together with talus, other mass movement accumulation and wind-blown deposits. 30 CFR, Chapter VII, Subchapter A, Part 701.5 states that "Alluvial Valley Floors" means the unconsolidated stream-laid deposits holding streams with water availability sufficient for subirrigation or flood irrigation agricultural activities but does not include upland areas which are generally overlain by a thin veneer of colluvial deposits composed chiefly of debris from sheet erosion, deposits formed by unconcentrated runoff or slope wash, together with talus, or other mass movement accumulations, and wind-blown deposits; and "Upland Areas" means, with respect to Alluvial Valley Floors, those geomorphic features located outside the flood plain and the terrace complex, such as isolated higher terraces, alluvial fans, pediment surfaces, landslide deposits, and surfaces covered with residuum, mud flows or debris flows, as well as highland azeas underlain by bedrock and covered by residual weathered material or debris deposited by sheet wash, rillwash, or wind-blown material. On the basis of the statutes and regulations, the primary consideration in the AVF investigation is the identification of unconsolidated stream-laid deposits (alluvial deposits). Furthermore, these deposits should be located within the valley floor and should not include isolated high terraces, alluvial fans, or landslide deposits. Once alluvial valley floor deposits aze identified, then the capability to support flood irrigated or subirrigated agricultural activities must be assessed. . Identification of locations where unconsolidated stream-laid deposits might occur was performed by analyzing aerial photographs of the mine permit azea and adjacent azeas. A break in valley sides slope and an identifiable valley floor served as the primary criteria for selecting possible alluvial deposits. These potential alluvial deposits locations have been mapped and the surface azea calculated (Table 65). From a geomorphic standpoint, the rugged mountainous terrain of the mine permit site has resulted in drainages still in a youthful stage of development. The streams are confined in narrow, steep- sided, V-shaped valleys with generally steep channel gradients. This is in duect contrast to the broader flood plain type valleys found at lower elevations. Meanders, normally associated with AVF development, aze absent. Generally, the streams are actively downcutting with the exception of the reaches above the Minnesota and Beaver Reservoirs. For these stream reaches, erosional downcutting has been curtailed by the change in base level these reservoirs represem;. One of the locations for possible alluvial deposits within the mine permit azea is irmnediately above the Minnesota Reservoir. The valley floor widens at this location and there is a d.efurite break in slope from the steep sides confining the valley floor. Numerous beaver ponds and willow thickets occupy the valley floor in this location, and grazing is limited to isolated locations along the margins of the valley. • 2.06-3