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silts of light-colored sandstones interbedded with dark shales. <br />This formation often forms steep outcrops in upland areas. The <br />Mancos Shale, also of Upper Cretaceous age, and stratigraphi- <br />cally below the Mesaverde, is a thick sequence of marine- <br />deposited shales. These shales often form deeply incised, rol- <br />ling topography. <br />Much of the subject area is covered with more recent sur- <br />face deposits of Quaternary age. These younger deposits con- <br />sist of hillslope colluviums, upland outwashes, river-terraces <br />and flood-plain alluvium. Surface deposits northwest of the <br />North Fork river contain much basaltic material derived from <br />the Tertiary intrusives. <br />3.2 MORPHOLOGY <br />Erosional processes during the late Tertiary and `1,uater- <br />nary periods resulted in the present mesa and mountain land- <br />forms . <br />The North Fork Valley is dominated by the deeply in- <br />cised, east-west trending valley of the North Fork Gunnison <br />River. Numerous intermittent streams flow into the North <br />Fork from both the north and south. Mountainous ranges on <br />both the south and north sides of the North Fork valley are <br />formed by Mesaverde sandstones and shales and by flatter <br />slopes underlain by Mancos Shale. It is very probable that <br />some of the northern ranges contain intrusions of basaltic <br />rocks, or that the frequent basalt blocks originated in the <br />eroded flow of the Grand Mesa basalt. <br />The intermediate slopes between the higher eleva*_ions <br />and both the North Fork and Stevens Gulch are covered either <br />- 6 - <br />oeaHroao coNSU~n~, we. <br />