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<br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br /> <br />Oitch. It is not completely clear whether that loam is entirely alluvium or <br />whether it represents some weathered Oakota shale. <br /> <br />The Rocky Ford Ditch generally follows the contact of the Dakota anrl the <br />overlying Mancos Shale. Although sanrlstone of the Dakota does crop out in and <br />along the Oitch at several locations, most of the area has the surficial cover <br />of loam. Excavation class appears to be common along the route of the Rocky <br />Ford Di tch until Secti on 36, where a promi nent sanrlstone bed crops out. <br />Downstream of that area to Route 666, a considerable length of the line may be <br />in the rock. <br /> <br />Overlying the Dakota and underlying the pipeline route in the MontezuMa <br />Valley, the bedrock is Mancos Shale. The Mancos is a thick (2000 to 3000 <br />feet) sequence of marine clay shale. The !1ancos contains beds of calcareous <br />sandstone and sandy 1 imestone. One di sti ncti ve brown sandy 1 imestone, known <br />as the Juana Lopez Member, is found about 500 feet above the base of the <br />formation and forms cuestas, holding up flat-topped ridges around the <br />surl"ounding valley floor. The whole of the Montezuma Valley is underlain by <br />the Mancos Shale and is punctuated by low hills on the Aztec Oivide, held up <br />by a more resistant limestone member of the formation, perhaps the Juana Lopez <br />Member. Most of the route wi thi n the Montezuma Valley will be in weathered <br />Mancos Sha1 e that shoul d be easily excavated. The Mancos contai ns <br />considerable quantities of salts that will probably result in low electrical <br />resistivity and the resulting propensity for corrosion of ferrous materials. <br />The general limits of the Mancos and Oakota Formation are shown in Figure 3.~. <br /> <br />To the west of the !10ntezuma Valley some of the hill s are held up by the Juana <br />Lopez Member, but most are capped bY old gravels derived from the crystalline <br />mountains some five miles to the west. These gravels are composed of poorly <br />sorted sand through boul ders of di orite porphyry. Several pi ts have been <br />opened in the past as gravel operations. One is still in operation just east <br />of Towaoc. <br /> <br />Excavation within the Oakota Sandstone will probably require shooting, while <br />the r1ancos Shale should be sufficiently weathered to excavate without the use <br /> <br />3-25 <br /> <br />l060c <br />