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<br />1 <br /> <br /> <br />1 <br /> <br /> <br /> <br />1 <br /> <br /> <br /> <br /> <br /> <br /> <br /> <br /> <br />1 <br /> <br />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 (Figure 2j. <br />Currently, the.floor of the. main pit is at elevation 6,340 feet; the middle..leuel is at <br />an elevation of 6,480 feet; and the third and fourth benches of the southern <br />quarry expansion have been excavated, and the fifth bench is currently being <br />advanced to below the 6,975 foot elevation. <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, 1968j. During this <br />time, the bedrock material was intruded by several distinct igneous bodies and <br />dikes. The gneisses are mapped as a series of folds, which are oriented roughly <br />east-west and have been broken and displaced by faults believed to range in <br />age from Precambrian to Tertiary. The two regional fault orientations that have <br />been mapped are approximately east-west and north-south (Figure 3j. <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 />occasional banding visible along the foliation of the rock. The term foliation <br />refers to the realignment of minerals into a parallel orientation as a result of the <br />intense heat and/or pressure of metamorphism. The rock mass tends to be <br />weakest along the foliation planes, which ultimately results in a discontinuity set <br />that is parallel to the orientation of the foliation. The foliation orientation is the <br />-4- <br />