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the Mesaverde include the more popularly known genera Edozontosaurus and Albertosaurus, as <br />well as champsosaurs, mosasaurs, plesiosaurs, pterosaurs, ornithischian and saurischian <br />dinosaurs (DeMar and Breithaupt 2006; Deklar and Breithaupt 2008). The marine units in the <br />Mesaverde have also produced abundant remains of invertebrates including ammonite, <br />baculites. bivalves. and planktonic formanitera (Young 1955). <br />Rollins Sandstone <br />During most of Late Cretaceous time, northwestern Colorado was part of the interior <br />seaway. <br />The marine Mancos Shale was deposited in this seaway. About 77 million dears ago <br />(mya). the next to last regression of the seaway began. As the shoreline prograded erratically to <br />the southeast across northwestern Colorado. it left behind the shallow- marine to shoreface <br />blanket deposits presently known as the Castlegate, Sego. Corcoran, Cozzette, and Rollins <br />(also called Trout Creek) Sandstones. Behind these sandstones, the coals, mudstones. and <br />sandstones of the paludal (lower) part of the Mesaverde Formation were deposited in swamp. <br />lacustrine. and fluvial distributary channels. <br />The Rollins Sandstone is the lowest formation of the Mesaverde Group in the Yaonia <br />area and sedimentation occurred in a shallow! sea. near -shore environment. It is characterized <br />as a huff and light -grey tine- grained Sandstone and grey shalt. It is the thickest of the shoreline <br />blanket sandstones and varies from about tarty to three hundred feet, with eastward thinning <br />(Cashion 1973). Contact with the underlying Mancos Shale is conformable. <br />Fresh water and marine fossils have been found in the formation. but it is unspecified as <br />to whether they are vertebrates or invertebrates (Fisher et al. 1959). Outcrops tend to weather <br />as white to tan massive sandstones:. steep talus slopes of Mancos Shale often occur below <br />exposures. Because vertebrate fossils have not been directly reported from the formation, and <br />because of the steepness of its outcrops. the Rollins Sandstone holds little potential for the <br />occurrence of vertebrate fossil remains in the general area. <br />LoNvcr Mesaverdc (Coal Bearing Members) <br />The coal bearing members (upper and lower) of the Mesaverde formation are <br />stratigraphically between the Rollins sandstone and the barren member, with an approximate <br />700 ft. thickness completely present, except near the outcrop area. These members consist of <br />buff and grey fine- to medium - grained sandstone and grey shale. Coal occurs in minor <br />amounts in the upper part. but is considerably more abundant in the lower part. Thickness of <br />the formation varies in the area from 50 to 300 feet (Cashion 1973). Contact with the <br />underlying Rollins Sandstone is completely conformable. The sediments of the lower <br />Mesaverde member were deposited in the Late Cretaceous (77 mya) and represent regression of <br />the Cretaceous seas. <br />The environment of deposition was extremely variable, being marine, brackish. and <br />fresh water at various times. Although somewhat similar to the Dakota Sandstone. the lower <br />20 <br />