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unit consists of interbedded sandstones, shales, and coals. The <br />unit is thought to be of marine origin and, as a result, the <br />sandstones and the coals are highly lenticulaz, discontinuous, <br />of limited lateral extent in outcrop. The unit ranges up to <br />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 red <br />to gray conglomerates. The sediments of this formation are <br />weathered volcanic rocks. The Ohio Creek conglomerate is <br />the basal unit within the formation and is 100 to 200 feet <br />thick. <br />Igneous intrusive rock exists within the North Fork Drainage <br />Basin. A diorite plug about 1,000 feet in diameter outcrops <br />along Hubbazd Creek in the southeast quarter of Section 7. <br />This may represent the erosional remnants of a volcanic flow <br />feeder. Sills have injected the Lower Coal-Bearing member, <br />particularly the B and C seams. These sills consist of diorite <br />and appear to have their source to the northwest of Terror <br />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 unconforrnity which <br />indicates some channeling. The formation consists of <br />light-colored sandstone, locally containing abundant pebbles <br />of chert, jasperoid quartz, and several kinds of igneous rocks. <br />The sand of the matrix was lazgely derived from the <br />Mesaverde Group, from which it was eroded by eazly Tertiary <br />streams, and deposited chiefly in and around the cahnnels of <br />those streams. The Ohio Creek Conglomerate is erratic and <br />locally absent, though in places it is as much as 200 feet thick. <br />Where the pebbles are scattered or lacking the Ohio Creek <br />Conglomerate is difficult to separate from the underlying <br />Williams Fork Formation. <br />The Wasatch (Ruby) Formation lies unconformably on the <br />Ohio Creek Conglomernte or, where the Ohio Creek is absent, <br />on sandstone and shale of the Mesaverde Group. It is <br />composed principally of coazse red conglomeratic sandstone <br />and dazk red to maroon sandy shale. Locally, an abundance of <br />epidote and other ferrous silicates produces a greenish color. <br />20 <br />