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<br />GEOLOGY OF GREEN AND YAMPA RIVER CANYONS
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<br />693
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<br />area famous, The dinosaur quarry is outstanding for four reasons: (,) quantity of
<br />fossil material, (2) variety, (3) excellent state of preservation, and (4) most nearly
<br />complete articulated skeleton, Camarasaurus lentus (Marsh), Twenty-three nearly
<br />complete and 300 partial skeletons are said to have been excavated from '909 to
<br />'924, largely by the Carnegie Museum of Pittsburgh, Pennsylvania, Some quar-
<br />rying was also done by the United States National Museum of Washington,
<br />D, C, and the University of Utah during the last 2 years of this period, Of the
<br />number of specimens removed, II genera and 12 species have been described.
<br />They included herbivorous (sauropod and the low-armored Stegosaurus), om-
<br />nivorous (duckbill), and carnivorous (theropod) forms, Crocodiles, turtles, and
<br />one aetosaurian form were also found. Small fresh-water unios and gastropods
<br />occur, as well as an abundance of silicified wood.
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<br />GEOLOGIC HISTORY
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<br />The depositional history of the formations in and adjacent to the Dinosaur
<br />National Monument is one of great stratigraphic regularity, For the most part,
<br />breaks are faunal and lithologic rather than stratigraphic, and a transitional se,
<br />quence in sedimentation is the rule rather than the exception, Noticeable un-
<br />conformities are rare, This is particularly true of the the formations representing
<br />both Paleozoic and Mesozoic eras, Even the absence of Ordovician, Silurian, and
<br />Devonian strata does not reveal a pronounced erosional unconformity, The most
<br />conspicuous erosional breaks are between Algonkian (Uinta Mountain group) and
<br />Cambrian (Lodore formation), between Mississippian (Madison dolomite) and
<br />Pennsylvanian (Morgan formation), and between Moenkopi and Shinarump for-
<br />mations of the Triassic,
<br />Within this area are exposed eighteen major formations (excluding the Browns
<br />Park beds, Pliocene) ranging in age from Algonkian (Uinta Mountain group) to
<br />Cretaceous (Mancos shale), representing eight geological systems and three eras,
<br />and totalil).g more than 20,000 feet of sediments, all of which were involved in the
<br />depositional and diastrophic history of the Uinta Mountains, Ten of these forma-
<br />tions are in part of marine origin, indicating the frequency with which the area
<br />was submerged beneath the sea,
<br />The major diastrophic and erosional events since the inception of the Uinta
<br />Mountains at the close of the Cretaceous are also clearly revealed in the geologic
<br />history of Dinosaur National Monument, The total uplift in the central part of
<br />the range as a result of folding and faulting may have been as much as 45,000
<br />feet. This figure represents the total thickness of sediments exposed to erosion,
<br />Uplift within the Monument area appears to have been 25,000 to 30,000 feet.
<br />The geologic history of this section may be summarized as follows, " Deposition
<br />of shallow marine and continental (lake, flood'plain, and eolian) sediments be-
<br />tween Algonkian and Upper Cretaceous time in the more shallow eastern part of
<br />the Uinta geosyncline, 2, Folding of this geosyncline during the Laramide revolu-
<br />tion elevated the range and formed minor folds along its flanks, This deformation
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