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<br />. <br /> <br />GEOLOGY OF GREEN AND YAMPA RIVER CANYONS <br /> <br />. <br /> <br /> <br />685 <br /> <br />steepened by drag folding along faults, exbibiting the typical Uinta Mountain <br />structure. <br />Faults are numerous throughout the area and are chiefly of the normal type, <br />Some of them are distributive in character and are part of a larger system of <br />faulting, such as the Yampa fault zone, They commonly occur as strike faults, <br />but in some places they are diagonal in direction and rotational in habit, The <br />maximum displacement along these high-angle faults in the Monument area is <br />4,300 feet. Such a displacement occurs along the Yampa fault proper in the <br />Johnson Draw area near Tanks Peak, south rim of the Yampa Canyon, where <br />Lower Triassic beds are in fault contact with Algonkian, <br /> <br />STRATIGRAPHY <br /> <br />GENERAL STATEMENT <br /> <br />The formations within Dinosaur National Monument range in age from Al- <br />gonkian (Uinta Mountain group) to Pliocene (Browns Park formation), They are <br />sedimentary and largely of shallow marine deposition, Along much of the Green <br />and Yampa River Canyon country, Carboniferous formations with low south <br />dfps are well exposed on broad, gentle dip slopes, Along smaller anticlines, such <br />as in the Split Mountain area, formations range it, age from Mississippian (Madi, <br />son dolomite) to Upper Cretaceous (Mancos shale), The erosion of this arch and <br />the steep attitude of its flanking formations (with dips up to 670) produce a <br />spectacular and colorful geologic cross section, particularly well developed in the <br />headquarters area of the Monument. <br />With the exception of Pliocene (Browns Park formation) and Miocene <br />(Bishop conglomerate), no other Tertiary sediments are represented in the Monu- <br />ment~ However, outside the boundary, on the south and west, Eocene (Wasatch, <br />Green River, and Uinta formations) and Oligocene (Duchesne River formation) <br />are widespread and well exposed, <br />In the northeast corner of the Monument, the Browns Park formation (dip 30 <br />northwest) lies on the Uinta Mountain group (dip 80 southeast) with angular dis' <br />cordance, and brings the youngest and oldest formations in contact. In the Red <br />Creek and Jesse Ewing Canyon sections (Wheeler and Goslin mountains), near <br />the Browns Park settlement, Archean (Red Creek quartzite) with its hornblendic <br />and micaceous schists and pegmatitic dikes occurs north of the Monument <br />boundary, With the exception of these pegmatitic intrusives and a small amount <br />of lava (largely andesitic) on the west end of the range, the rocks of the Uintas <br />are sedimentary. <br />The only angular break noted, other tha.n that between Pliocene and Algon- <br />kian, is a possible slight discordance of 40 or 50 observed in one or two places <br />between the Lodore formation (Cambrian) and the Uinta Mountain group (AI-. <br />gonkian), and is probably only local. A pronounced erosional unconformity occurs <br />between these two formations in the upper end of Whirlpool Canyon of the Green <br />River, <br /> <br />