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-7- <br /> <br />DESCRIPTION OF PALEONTOLOGICAL RESOURCES <br />For the pre- and post-Cretaceous geological history, I rely <br />upon Crowley (1955) and far the Cretaceous upon Haun (1959), Weimer <br />(1959), and Haun and Weimer (1960). <br />Because Paleozoic rocks are for the most part absent on the <br />• <br />surface, being deeply buried by post-Paleozoic deposits, little of <br />the structural history of this system is known in northwestern Colo- <br />rado. However, from the limited exposures around the Steamboat <br />Springs area it has been passible to determine that a pre-Pennsyl- <br />vanian, possibly Mississippian, uplift occured with an east west <br />axis as part of Siouxia. To the west the area received more or less <br />continuous deposition of marine sediments until [he close of the <br />Pennsylvanian when the area began to receive clastics. Throughout <br />the Permian and Triassic the land remained a more or less stable <br />platform except fora minor Triassic uplift as evidenced by the <br />Shinarump Conglomerate. Conditions during the Jurassic saw a <br />fluctuation between marine and continental, the latter being dominant. <br />The Cretaceous rocks are by far the best known rock units in <br />northwestern Colorado because of the immense fossil fuel reserves <br />locked within them. It has been determined that the Epicontinental <br />Sea that dominated North America during the Cretaceous, did not <br />occupy the study area until the Late Albian when the transitional <br />deposits of the Dakota appear. That this event, once started, was <br />rapid is seen by [he presence of the neritic Mowry•Formation before <br />• <br />