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<br />tm.IELD HOU~,E: OJ: NATURAL HIS ORY
<br />
<br />BULLETIN OF THE;";AMERICAN ASSOCIATION OF PETROLEUM GEOLOGISTS
<br />VOL. 38, NO.5 (MAY. 1949), PP. 683-694, t FIG.
<br />
<br />GEOLOGY OF GREEN AND YAMPA RIVER CANYONS
<br />
<br />AND VICINITY, DINOSAUR NATIONAL MONUMENT,
<br />
<br />UTAH AND COLORADO'
<br />
<br />G, E. UNTERMANN' AND B, R, UNTERMANN'
<br />
<br />Vernal, Utah
<br />
<br />ABSTRACT
<br />
<br />The Green and Yampa River Canyon country within the boundaries of Dinosaur National
<br />Monument represents the deeply dissected eastern end of an east-west anticlinal fold, the Uinta
<br />Mountains, and its accompanying smaller flank folds. Oldest formatiol:1 exposed in this area is the
<br />Uinta Mountain group (Algonkian) and the youngest, Browns Park fOI'lnation (Pliocene). Along the
<br />crest of the main arch, in th~ deeper canyons, and at some places along the upthrown sides of faults
<br />are exposed massive dark red blocky~weathering quartzitic sandstone, shale, and conglomerate beds of
<br />the Uinta Mountain group, and the shale and quartzitic sandstone beds of the Lodore formation
<br />(Cambrian). In much of the 'area, Mississippian, Pennsylvanian, and Permian rocks form long .dip~
<br />slopes toward the south. _ -
<br />Typical of Uinta Mountain structure and representative of the smaller folds that flank the main
<br />arch of the Uinta Mountainsois the Split Mountain~Yampa Plateau area. Formations along the crest
<br />of tbis anticlinorium have lo~ attitudes in contrast to the sharply :flex~d, steeply dipping, younger
<br />flanking formations. These strata with their well developed flat-iron aIld race~track patterns of ex.
<br />posure exhibit a striking, colorful geological cross section ranging in ag~ from Lower Pennsylvanian
<br />(Morga.n) to Upper Cretaceous (Mancos). Lower Pennsylvanian and Lower Mississippian are ex~
<br />posed in the deeper part of Split Mountain Canyon.
<br />High-angle normal faults occur in the Monument area. The Split Mountain-YampaPlateau
<br />section is traversed by the Yampa fault which seems to die out in the Western part of the fold. Split
<br />Mountain Canyon has been carved by the Green River along the western end of this zone.
<br />Stl:eam piracy and deep entrenching of the meandering stream courses during Pleistocene have
<br />produced a spectacular scenic area.
<br />
<br />INTRODUCTION
<br />
<br />The work discussed was begun in the spring of r943 as an aid to basic plan,
<br />ning and interpretation relative to the future development of Dinosaur National
<br />Monument. Proposed dams to be constructed within the Monument, namely,
<br />those at Echo Park and Split Mountain Canyon, resulting in the submergence of
<br />more than 100 miles of canyon country along the Green and Yampa rivers, were
<br />an additional incentive for making this investigation,
<br />Shortly after this work was initiated, major exploration of the Rangely oil
<br />field and contiguous areas south of the Monument, in Colorado, was begun, Be-
<br />cause the same formations being drilled in this field are so well exposed in the
<br />Dinosaur National Monument, the writers' preliminary studies at that time
<br />served to orient many 'of the newly arrived geologists,
<br />
<br />,
<br />
<br />DISCOVERY OF ])INOSAUR QUARRY AND CREATION OF MONUMENT
<br />
<br />On August 19, 1909, Professor .Earl Douglass' (Carnegie Museum) discovery
<br />of dinosaur remains near Split Mountain Canyon, Green River, formed the basis
<br />
<br />1 Preliminary report on this region. Manuscript received, November IS, 1948.
<br />
<br />2 Utah Field House of Natural History. The writers wish to express appreciation to chief natural-
<br />ist John E. Doerr and C. Max Bauer of the National Park Service, Lloyd G. Henbest, John B. Ree-
<br />side, Jr., and J. Steele Williams of the United States Geological Survey, G. Arthur Cooper of the
<br />United States National-Mus~um, and Christina LQchman, paleontologist, for helpful suggestions and
<br />for assistance in fossil deterni.inations.
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