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<br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br /> <br />001112 <br /> <br />The borehole also revealed a thickness of only about 25 feet of sound <br />sandstone of the Maroon Fonnation overlying poorer quality bedrock of the top <br />of the Eag1 e 'Ia11y-Mi nturn sequence. Although no gypsum or anhydrite was <br />recovered as core, surficial mapping indicates these rocks to be associated <br />with this fonnation, making it a very unfavorable foundation for a large water <br />storage facility. <br /> <br />No boreholes were drilled on the right abutment, but the seismic refraction <br />study showed the weathered rock zone to extend over the enti re 1 ength of the <br />abutment to depths up to 100 feet. The amount of excavati on requi red to <br />provi de a sui tab1 e foundati on for an RCC gravi ty dam e1 imi nated the <br />feasibility of that type of design. <br /> <br />Adequate construction materials for an embankment dam are located within close <br />proximity to the site. Alluvial sand and gravel for use in the shell zones is <br />abundant in the river valley both upstream and downstream of the dam. <br />Impervious core material is available from the same borrow source as for <br />Warner Point, less than one mile north of the site. <br /> <br />The slopes of the reservoir that would be fonned by the construction of Choke <br />Cherry dam are potentially unstable in the area of the surficial landslides <br />along the left side of the reservoir between Choke Cherry and Warner Point. <br /> <br />'Ieatch Gulch Dam <br />The alluvial gravel in the valley floor at Veatch Gulch is only about 40 feet <br />thick as compared to 50 to 70 feet upstream at Choke Cherry and Warner Point. <br />The reduced depth of excavati on necessary for the gravity dam is favorabl e for <br />the RCC dam design, but is offset by the width of the canyon. <br /> <br />The massi ve sil tstone bedrock of the Chi nl e Fonnati on whi ch underl i es the <br />all uvi urn wou1 d be an excell ent foundati on for the RCC dam. No grouti ng or <br />speci a1 foundati on treatment wou1 d be necessary. The qual ity of the over1yi ng <br />sandstone of the Entrada Fonnation that fonns the vertical c1 iffs on either <br />abutment was not investigated at depth. Judging from the outcrops, it appears <br />that the rock wou1 d provi de an adequate foundati on but wou1 d probably requi re <br />grouti ng. <br /> <br />E-9 <br />