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<br />Received <br /> <br />JOHN GENGBINEERRF'•c•~~a~ ~'•~,~~~~•~{~°~' DEC 262000 <br />~~;,; ~t iv ~ ~Ia.~~ v <br />~~~/ ~, Durango Field Office <br />~, I ~~;:~,~'~?°°~0"rvision of Minerals & Geology <br />~ '~N l~ <br />i~ <br />~'E'~ <br />iii iiiiiiiiiiiii iii <br />310 LOOKOUT VIEW COURT <br />GOLDEN, CO 80401 <br />3osz764901 <br />FAX 27&8183 <br />JFAb~Q01bnM.aom <br />`~ ~ A ~ ~ R@~ober 31, 2000 <br />Mr. Warren 0. Wilcox <br />Gunnison Gravel <br />P.O. Box 42 <br />Gunnison, CO 81230 <br />pEp 2~~VFd <br />~/r/~oa oI <br />Mr"e~e/a sod ~Bn/pBY <br />Reference: Dickerson Quarry slope stability evaluation <br />Dear Warren: <br />The strength of the fresh granite and fracture set <br />orientations present in the Dickerson Quarry and the quarry <br />expansion geometry are generally favorable for the long term <br />stability of the planned overall 63° slope angles (2 vertical to 1 <br />horizontal) for the planned expansion. Figure 1 presents the <br />planned quarry expansion. The only potentially adverse fracture <br />set strikes from N33°W to N38°W and dips from 20° to 38°NE. This <br />joint set is more westerly striking and steeper dipping where <br />exposed in the existing quarry and more northerly striking and <br />flatter dipping where exposed in outcrops on the west side of the <br />property. It is recommended that the ultimate slope in the <br />southwest corner of the quarry be flattened to 95° in order to <br />assure the long term stability of the northeast facing section of <br />the ultimate quarry wall. <br />GEOLOGIC INPUT <br />Fresh granite is exposed on the west wall the existing <br />quarry. The existing quarry and the Dickerson property are shown <br />on Figure 2. The fresh granite forms an over 30-foot high <br />overhanging face at the base of the west highwall. The fresh <br />granite is overlain by 40 to 60 feet of weak decomposed granite <br />and capped with up to 10 feet of the West Elk volcanic breccia. <br />The breccia thins and disappears to the south and west across the <br />property. Figure 3a shows the decomposed granite siting on the <br />overhanging fresh granite face, with a detached block of the <br />massive West Elk breccia in the foreground. Figure 3a also shows <br />the northeast dip of the contact between the decomposed and fresh <br />granite. Figure 3b shows the slot bulldozed back approximately <br />100 feet westward into the decomposed granite and thin breccia <br />capping in the center of the present west quarry wall. Figure 3b <br />also indicates the thinning of the decomposed granite and West Elk <br />1 <br />