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Deerfield Dam

Photo of Deerfield Dam and Reservoir
 
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Rapid Valley Project
 
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Schedule of Proposed NEPA Actions
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Deerfield Dam is located within the Precambrian core in the southeastern portion of the Black Hills Uplift.  It is situated between two bluffs composed primarily of steeply dipping phyllite and quartz mica schist.  The structural attitude of the bedding and scistosity indicate that the site is located near the plunging crest of an overturned major fold.  Change in foliation trends at the site indicate that Precambrian folding and faulting on a minor have also occurred.  The foliation or schistosity tends to parallel the hillside on the left abutment and dips obliquely upstream across the dam into the right abutment.  Because weathering tends to follow down the foliation planes, rock on the left abutment was found to be generally hard, moderately fractured and had shallow weathering, while rock through the stream channel and the right abutment was highly fractured and weathered to depths in excess of 30 feet.  The original valley floor consisted of an organic silt about 4 feet thick overlying 10 to 15 feet of water-bearing sand and gravel.

Last updated: Mar 29, 2013