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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 I <br />I <br /> <br />A. Geologic Mapping <br /> <br />Rock Creek, in the vicinity of Site B has carved a relatively symetri- <br />cal V-shaped valley into the Precambrian igneous/metamorphic bedrock. <br />The valley floor is about 100 feet wide where the creek meanders <br />through flat lying recent stream alluvium. The side slopes are about <br />1.5:1 and composed on the right abutment of weathered, in-place bedrock <br />and slope wash. The base of the left abutment is skirted by talus <br />debris originating from bedrock outcrops exposed above elevation 8580. <br />Small alluvial fans were mapped at the mouths of steep lateral drain- <br />ages both upstream and downstream of the axis. Geologic mapping in the <br />vicinity of Site B developed during these investigations is shown in <br />Exhibit 3-5. <br /> <br />Geologic mapping revealed that the Precambrian crystalline bedrock <br />represents three ages of granitization or intrusion. The oldest rock <br />is a medium grained, pink, granite containing about 10 to 20 percent <br />biotite mica, about 20 percent quartz, and 50 to 60 percent feldspar. <br />Petrographic analysis indicated much of the feldspar has been altered <br />hydrothermally to sericite and the biotite chlorite. The granite often <br />envelopes irregular shaped inclusions of amphibolite indicating the <br />complex may be a migmatite derived from granitization of metamorphic <br />rock. Jointing is regional and moderate with one set of sub vertical <br />joints striking E-W and another N450E. A third set of joints mapped on <br />the left abutment strikes north and dips to the west at about 300. The <br />joints exposed at the surface were generally open but fresh. Spacing <br />varied, with the subvertical joints occurring in swarms at a wide spac- <br />ing and the other joints spaced at about 1 to 2 feet. At the Site B <br />axis the medium grained granite is exposed over the entire left abut- <br />ment above approximately elevation 8580 and high on the right abutment <br />above 8740. <br /> <br />The second oldest unit mapped is an intrusive fine to coarse grained, <br />light pink granite composed primarily of feldspars with minor amounts <br />of mica and quartz. The intrusives are massive and irregular into the <br /> <br />3 - 8 <br /> <br />6819W/502OW <br />