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0n1953 span of more than 1700 million years. Not all the geological periods in this time span are represented. However, many of the formations are exposed for easy study due to the deep down cutting of the rivers. The most concentrated deposit of dinosaur bones yet discovered anywhere in the world are found in the Morrison formation, within the monument. It is certainly possible that most deposits are yet to be found. Many interesting things can be learned from the study of the exposed formations. For instance, they show that the area was covered by seas at least 12 times in the past. Geologists have also determined that one of the sandstone beds was deposited by a great dune in a desert wind. The Mitten Park and Yampa faults, which may be seen along the river, are striking examples of rocks moving thousands of feet along fissures extending hundreds of miles. Split Mountain is also a unique geologic feature because the Green River cuts through the mountain rather than going around it. It is a phenomenon that has fascinated geologists since the time of John Wesley Powell, and continues to amaze people today. I I Wildlife, Fish The Yampa contains two species of fish that are on the endangered species list. Little is known about the humpback chub, Gila cypha, but it occurs in such small numbers in widely separated places in the Colorado and its tributaries, that it is considered in jeopardy. The Colorado squawfish, Ptychocheilos luciu~, was once widely distributed throughout the Colorado River' and its tributaries, but is now quite limited in its distribution. It is adapted to life in swift, warm rivers and will not reproduce in the cold tail waters of reservoirs behind high dams. Flaming Gorge dam was the cause of its demise in the Green River. The humpback sucker is currently listed as being "status undetermined". on\.. ~ _ __