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3.0 Location and Geologic Setting <br />The Spec-Agg Quarry is located to the north of Interstate 70 near Jackson Gulch <br />on the east flank of the Rocky Mountain Front Range, approximately 3 miles <br />south of downtown Golden (Figure 1). The natural topography of the property <br />increases significantly in elevation to the west, with elevations varying from <br />approximately 6,250 feet along the eastern boundary to 7,110 feet on the <br />western boundary. The quarry currently consists of three distinct mining areas: <br />the main pit, the middle level that is adjacent to but above and south of the main <br />pit, and the upper level of excavation in the southern expansion area with <br />elevations ranging from approximately 6,900 to 6,950 feet (Figure 2). Currently, <br />the floor of the main pit is at elevation 6,340 feet with an upper temporary bench <br />at an approximate elevation of 6,370 feet; the middle level is at an elevation of <br />6,400 feet; and the fifth bench of the southern expansion area has been <br />excavated to approximately an elevation of 6,950 feet, and the sixth and seventh <br />benches are currently being advanced to approximately the 6,900 foot elevation <br />(Figure 2). <br />This region of the Rocky Mountain Front Range was formed structurally during <br />the Laramide orogeny in the Late Cretaceous and early Tertiary period. The <br />gneissic bedrock within the quarry is believed to have undergone two to three <br />episodes of deformation during Precambrian time (Gable, 1968). During this <br />time, the bedrock material was intruded by several distinct igneous bodies and <br />dikes that have been mapped up to 2 feet wide and can be fairly continuous over <br />long distances. The gneisses are mapped as a series of folds, which are <br />oriented roughly east-west and have been broken and displaced by faults <br />believed to range in age from Precambrian to Tertiary. The two regional fault <br />orientations that have been mapped are approximately east-west and north- <br />south (Figure 3). <br />The granitic gneiss found in the quarry is generally hard and relatively <br />competent. The gneiss varies in color from grayish orange to dark gray, with <br />-4- <br />