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-20- The alluvia of the tributaries to the roaring Fork River (e.g., Fourmile Creek, Thompson Creek, and Coal Creek) are generally thin, intermittent and, for the most part, restricted to the immediate stream channels. The most extensive alluvium occurs at the confluence of two or more tributaries. The alluvium of the Roaring Fork River consist of young stream, terrace, and outwash gravels. The thickness of these gravels ranges up to 100 feet. Unconsolidated colluvial and landslide deposits exist along the slopes of the ridges formed by the more resistant sandstones. The east-facing dip slopes along the Grand Hogback are naturally unstable slopes. Numerous landslides have developed on the unstable slopes, which has led to the characteristic hummocky topography. Ground Water The general area around the three mines contain four Types of aquifers; alluvial, continuous bedrock, laminar to lenticular discontinuous bedrock, and fracture aquifers. The regional movement of ground water is controlled by the geologic structures along the Grand Hogback (i.e., the folds and faults). Local ground water movement is controlled by the vertical and lateral extent of the aquifer, and also by the type and magnitude of localized secondary porosity related to fault, fracture and joint systems. The overall regional ground wafer movement in the general area of the Coal Basin Mines, North Thompson Creek Mines and the Sunlight Mine would be towards the axis of the Piceance Basin, were it not for the folds and faults which occur along the Grand Hogback. There is a high displacement fault north of the Coal Basin Mines. This fault restricts the migration of ground water from the Hunter's Point Syncline adjacent to the Coal Basin Mines and the unnamed syncline adjacent to the North Thompson Creek Mines, thus forming two separate ground water basins along the Grand Hogback. Alluvial ground water aquifers exist along the Roaring Fork River and the tributaries to the Roaring Fork. These alluvial aquifers are the most significant source of ground water put to beneficial use in the general area. The alluvial ground water also serves as the primary source of recharge water to the underlying bedrock aquifer. The aTluviurn is rapidly recharged by the stream and serves as a reservoir for surface water available for the recharge of bedrock aquifers and fracture aquifers. The most significant alluvial aquifers in the general area are the Roaring Fork and Crystal River alluvia. Many water supply wells are completed in these aquifers. This is due to their high-storage capacities and rapid recharge from their associated streams. Two water supply wells are completed in the Roaring fork alluvium at the North