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<br />G, E. UNTERMANN AND B, R, UNTERMANN
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<br />for the famous Dinosaur Quarry, which, in r9'5, was included in the original 80
<br />acres proclaimed as Dinosaur National Monument, Uintah County, Utah, Be-
<br />cause of the scenic and recreationat'values of the adjoining Green and Yampa
<br />river canyons, the monument was extended in '938 to its present size of slightly
<br />mOle than 200,000 acres, As now constituted, it is located in northeastern Utah
<br />and northwestern Colora<jo; the larger part in Colorado,
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<br />STRUCTURE
<br />The eastern end of the Uinta Mountain arch and its minor flank folds com,
<br />prise the main structural features of Dinosaur National Monument, These folds
<br />represent part of an original geosynclinal trough into which were deposited sedi-
<br />ments from possibly Algopkian to late Cretaceous time, That the Uinta depo-
<br />sitional basin was an east-",est arm of the Wasatch trough is shown by the merg-
<br />ing of the two folded are~s, similarity in some of the lithologic character and
<br />stratigraphic breaks in the western part of the range, and by thickening of many
<br />of the sediments in a westerly direction, Both trough areas were part of the great
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<br />Rocky Mountain geosyncline, Elevation and folding of these depositional basins
<br />at the close of the Cretaceous period produced, among other ranges, the Uinta
<br />Mountains, the principaleast-west-trending range in the western hemisphere,
<br />The average height is between 8,000 and 9,000 feet, The western half has many
<br />peaks more than '3,000 feet in elevation, highest of which is Kings Peak, '3,498
<br />feet, located west of the center of the range. Maximum elevation within tbe
<br />Monument area, Zenobial Peak, Douglas Mountain, on the east end of the
<br />Uintas, is 9,006 feet, Thel axis of the range is slightly north of the center, It
<br />pitches downward at bothi ends and is somewhat convex northward and asym,
<br />metrical. A broadening OGcurs on the east end where there are more parallel
<br />flank folds, This structural broadening, together with thinning of many of the
<br />formations eastward and a generally lower elevation of the range in the east, is
<br />indicative of a shallowing of the Uinta trough in that direction,
<br />The northwald convexity of the Uintas suggests a greater stress from a
<br />southerly'direction, High land areas on the south may have supplied the Uinta
<br />trough with some of its se~iments, Heaton' has shown that the presence of the
<br />"Nevada Mountains" on tp.e west and southwest and "Cascadia" on the north-
<br />west, both positive areas during much of the time the Rocky Mountain geosyn,
<br />cline was receiving sediments, probably contributed much of this material. This
<br />conclusion is substantiated by the westward thickening of many of the forma-
<br />tions.
<br />Some of the smaller structures, such as the Split Mountain,Blue MOuntain
<br />anticline (Yampa Plateau), withi\, the Monument boundary, pitch at moderate
<br />angles in a westerly directipn, The formations are relatively flat on the crests of
<br />the anticlines and are veryisharply flexed on the flanks of these folds, commonly
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<br />8 Ross L." Heaton, HAncestra'l Rockies and Mesozoic and Late Paleozoic Stratigraphy of the
<br />Rocky Mountain Region," Bull. 4mer. Assoc. Petrol. Geol., Vol. 17, No.:3 (February, 1933), pp. 1-68.
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