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I I I I I I I I I I I I I I I I I I I I 002S')(} any additional water entering the ground water system beneath the reservoir will not "daylight" (1), The upper layers of the Mesa Verde Group are exposed at the upper end of the reservoir basin. There are coal seams in this part of the Mesa Verde Group and mining occurs in the area, No seams, however, are exposed in the reservoir basin nor will any be inundated by the reservoir (1). The dam site lies on the northeast flank of the east-west trending Rangely anticline, The crest of this anticline has eroded to a topographic basin with a floor of Mancos Shale. The surrounding highlands are ridges and ledges formed in the sandstones and shales of the Mesa Verde Group, The right abutment is very steep and covered with slope wash and residual soils above and below the thick sandstone outcrop ledges, The left abutment is mantled by terrace deposits exposed on a low sandstone ledge, overlain by alluvial fan and slope wash deposits, These are poorly consolidated and dry so that settle- ment would occur under the weight of the proposed dam embankment. To provide a solid foundation these alluvial fan materials will be stripped off and the embankment constructed on the more stable terrace deposits and bedrock underneath. An upstream impervious blanket is necessary to reduce seepage through the unconsolidated soils and terrace deposits on this abutment (1). The alluvium in the valley floor is comprised of silty-clayey fine sand near the surface and grades downward into sand and gravel. The upper portion of this soil is nearly impervious but becomes very porous in the deeper sand and gravel portions. To prevent large amounts of ~nderseepage through these porous soils a cutoff trench will be excavated to bedrock with a shallow grout curtain and cap rHO