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- 4 - • • • are of the Upper Cretaceous Age; their contact is at the elevation of approximately 6,875 feet. The rocks of the Mesa Verde Formation are sandstones, siltstones, shales, and coal. Sandstones and siltstones fre- quently form conspicuous cliffs and ledges outcropping at the valley sides. The most important of these sandstones is the Rollins Sandstone Member that form a distinct cliff at an elevation of approximately 7,000 feet. The Rollins Sand- stone Member overlies the Mancos Shale. The formations at the site dip some two to five degrees to the north-northeast. There are no known important faults outcropping within the area of the mine surface facilities; several minor faults can be observed in the rock cuts that have been excavated at the site. They do not have any import- ance for the stability since they are vertical. Bedrock formations are covered by~coll.uv.ial soils of various thickness. These soils are generally sandy and clayey soils with a large percentage of boulders of various sizes. Most of these boulders are formed by basaltic rocks. These rocks are apparently remnants of an old lava flow that covered the area, but was later eroded. The thickness of the soil cover varies widely: it reaches only several feet on steep slopes, but it reaches up to 50 or more feet at certain locations. It appears that the greatest thickness of the colluvial soils is in old erosional channels that have been filled during subsequent morphologi- cal development of the area. Channels of this type can be identified within the long and high diversion channel cut above the fan level. There are no perennial streams on the site and there cEw~roQO coKw~nwc. mc.