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SITE GEOLOGY <br /> Most of the undisturbed area of the property is underlain by 0 to 3 feet <br /> of colluvial material derived from the underlying bedrock and occuring pre- <br /> dominantly as a thin veneer, thickening locally in topographic lows. At the <br /> extreme western edge of the site alluvial material, deposited by Elk Creek, <br /> is in contact with the hillside colluvium. These surficial deposits are of <br /> Quaternary age, the alluvium being Pleistocene and the colluvium being <br /> Pleistocene to Holocene (recent). <br /> The bedrock underlying the surficial material is part of the Precambrian <br /> Idaho Springs Formation which makes up a large part of the uplifted crystalline <br /> rocks of the Front Range of the Central Rocky Mountains. At this particular <br /> locality,'the -Idaho Springs Formation is made up of migmatitic biotite gneiss <br /> and biotite schist interlayered with amphibolite and granitic gneiss. The gran- <br /> itic material occurs in numerous layers and lenses throughout the rock. The <br /> gneisses and schists are interlayered with the amphibolites and granitic <br /> materials to the extent that well developed compositional layering, usually <br /> parallel to sub-parallel with a less well developed foliation, is present <br /> striking variably from north-south to slightly northwest or slightly northeast. <br /> The dip of the compositional layering and the foliation is variable and in <br /> places undulating or erratic, but is predominantly 150 to 500 east (back into the <br /> hillside). The thickness of the compositional laminae varies from 1/2 inch <br /> to 12 inches or more where the granitic gneiss occurs in thick lenses. <br /> Near the surface biotitic gneisses and schists are weathered to the point <br /> where they can be scooped out by hand. At depth the degree of weathering <br /> decreases but the units are rippable. The amphibolite and granitic gneiss <br /> are less susceptible to weathering than the bietitic rocks and are more <br /> difficult to excavate. Blasting may be required in localities where amphibolitic <br /> -2- <br /> JC 00781 <br /> PetersoniElk Creek <br />