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' Mule Creek Gravel Pit ~ironmental Assessment • Page 25 <br />' plains. At the eastern edge of the Front Range, Pikes Peak and the Rampart Range, <br />composed of pink, coarse grained Precambrian granite, rise steeply above the plains to <br />' the 14,110-foot summit of Pikes Peak. Thick layers of sediments deposited in <br />intermountain basins before the mountains of the Front Range were formed aze evident in <br />the Florissant Fossil Beds, Manitou Pazk, and South Park to the west. <br />' The proposed project area is composed of Pikes Peak Granite. Pikes Peak Granite is a <br />coarse pink biotite ofpre-Cambrian age. The rock is coarse-grained, composed of alkalic <br />' feldspar, quartz and biotite. Its color is due to the abundance of feldspar. Quartz is less <br />abundant, and biotite is relatively rare. <br />' Pikes Peak Granite weathers in huge round masses, so characteristic that it may be <br />recognized from a distance. Boulders have broken away from dome-like outcrops, and <br />rocks up to 20 feet in diameter have fallen from the ledges. The mesh of coarse <br />' interlocking grains is easily ruptured by frost, and the rock-is broken into pieces by <br />disintegration, forming chazacteristic gravel. <br /> During the Pliocene epoch, the granite block that lies just west of the plains was uplifted <br />' to an elevation of about 9,500 feet, forming the Front Range of the Rocky Mountains. <br /> There was also movement within the granite block itself. The part of the Pikes Peak <br />' mass south of the Ute Pass Fault was uplifted to about 12,000 feet, thousands of feet <br /> above the granite adjoining it to the north. <br /> Areas of glacial drift are chiefly terminal moraines of local valley glaciers. They are <br />t made up almost wholly of Pikes Peak granite, and contain only small amounts of Cripple <br /> Creek and Windy Point granites. The material consists of angular fragments of many <br />' sizes, the largest being 8 to 10 feet in diameter. <br /> Glaciers were formed during the Pleistocene era in the valleys leading away from the <br /> summit of Pikes Peak at an altitude of 12,750 feet and lower, moving downstream a <br />t distance of four miles in some cases. The lower limit of ice work is at an elevation of <br /> about 9,500 feet. The ice reached a maximum thickness of nearly 350 Feet in some of the <br /> valleys. The higher slopes of Pikes Peak were covered with snow, but the summit was <br />' not glaciated. The ice sculpturing of the mountain did not proceed far enough to reduce <br /> its mass greatly. (USDA Forest Service, 1971) <br /> <br /> 3.1.1.2 Soils <br />' Soils within [he proposed project area aze derived from decomposed Pikes Peak Granite <br /> parent material. The parent rock is deeply weathered granite, composed of quartz and <br /> orthoclase, with biotite being an accessory mineral. The granite is composed of lazge <br />' crystals that are released as the biotite weathers. These large crystals then form a mass of <br /> coarse-grained material with little clay to serve as binding material and as exchange <br />' medium for soil nutrients. The complex thus formed is highly erosive under concentrated <br />water flows and may be relatively unproductive due to a lack of soil nutrients. Soils <br /> developed from Pikes Peak Granite aze pinkish in color due to the feldspars contained in <br />' the parent material (HRC, 1999). <br />' Hydrosphcre Resource Consuhartts, 1002 Walnut Suite 200, Bouldn, CO 80702 <br />