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. load was forecasted to be 0.1 g, based on experience with other dams in the area. The abutments for the Webster Hill Dam will consist of rock on the north abutment and terrace gravel or rock on the south abutment. Strength test results of the Wasatch Formation shales and sandstones indicate that they have considerable strength and should provide adequate slope stability. Samples of the cemented gravel conglomerate material overlying the Wasatch Formation were not obtained. However, drilling conditions indicate that this material may be stronger than the underlying Wasatch Formation materials. Permeability testing done in the conglomerate zone indicated that this material is well cemented and essentially impermeable. . Should uncemented gravel form an abutment, it will be necessary to keep slopes in those deposits very flat to prevent instability during rapid drawdown of the reservoir. Since natural slopes in the area are the same as or flatter than the slopes required for stability (preliminary estimate, 4:1 to 6:1 horizontal:vertical), this requirement should present no problem should a gravel abutment be used. F. AVAILABILITY OF CONSTRUCTION MATERIALS One concern in the construction of a roller-compacted concrete (RCC) dam is the location of an aggregate source for the concrete. Aggregate quarries for the Webster Hill Dam can be established in the Colorado River gravel deposits within the reservoir area. This study did not evaluate potential aggregate sources. However, R.W. Beck and Associates, in their report on the proposed Una Dam Reservoir to the Colorado Water Conservation Board, indicated that the gravel deposits near "Rifle where the quantity of oi 1 shale fragments is too small to affect the qual ity" could be used for concrete aggregate. The . IV-8