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lenticular, discontinuous, of limited lateral extent in <br />outcrop. The unit ranges up to 1,500 feet in thickness. <br />The Mesaverde Formation is unconformably overlain by the <br />Tertiary aged Ruby or Wasatch Formation. This formation <br />consists of red to buff-colored shales, red sandstones, and <br />red to gray conglomerates. The sediments of this formation <br />are weathered volcanic rocks. The Ohio Creek conglomerate <br />is the basal unit within the formation and is 100 to 200 <br />feet thick. <br />Igneous intrusive rock exists within the North Fork <br />Drainage Basin. A diorite plug about 1,000 feet in <br />diameter outcrops along Hubbard Creek in the southeast <br />quarter of Section 7. This may represent the erosional <br />remnants of a volcanic flow feeder. Sills have injected <br />the Lower Coal-Bearing member, particularly the B and C <br />seams. These sills consist of diorite and appear to have <br />their source to the northwest of Terror Creek. <br />The Ohio Creek Conglomerate of very late Cretaceous and <br />early Tertiary age rests on the Mesaverde Group and is <br />separated from it by an irregular unconformity which <br />indicates some channeling. The formation consists of <br />light-colored sandstone, locally containing abundant <br />pebbles of chert, jasperoid quartz, and several kinds of <br />igneous rocks. The sand of the matrix was largely derived <br />from the Mesaverde Group, from which it was eroded by early <br />Tertiary streams, and deposited chiefly in and around the <br />cahnnels of those streams. The Ohio Creek Conglomerate is <br />erratic and locally absent, though in places it is as much <br />as 200 feet thick. Where the pebbles are scattered or <br />lacking the Ohio Creek Conglomerate is difficult to <br />separate from the underlying Williams Fork Formation. <br />The Wasatch (Ruby) Formation lies unconformably on the Ohio <br />Creek Conglomerate or, where the Ohio Creek is absent, on <br />sandstone and shale of the Mesaverde Group. It is composed <br />principally of coarse red conglomeratic sandstone and dark <br />red to maroon sandy shale. Locally, an abundance of <br />epidote and other ferrous silicates produces a greenish <br />color. The strong coloring of the Wasatch (Ruby) Formation <br />contrasts sharply with that of the light-colored Ohio Creek <br />Conglomerate and with the sandstone of the Mesaverde <br />Group. Conglomerate and sandstone predominate in the lower <br />100 feet of the Wasatch (Ruby) Formation. Several boulders <br />of scoriaceuos basalt as much as 2-1/2 feet in diameter are <br />present, and smaller pebbles of chert, jasperoid quartz, <br />and a variety of igneous and metamorphic rocks are widely <br />distributed. Above the conglomerate and sandstone zone, <br />red and green shale and silt predominate. <br />The local geology around the Blue Ribbon Mine consists of <br />Tertiary and Cretacious sediments that strike north 77 <br />-20- <br />