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<br />Geologic structure In Dinosaur National Monument (Figure 1.2) is dominated by the main Uinta <br />Arch together with its accompanying steeply dipping synclinal and anticlinal flank folds, and fauJts with <br />considerable displacement (Untermann and Untermann, 1954). A geologic map of the lower Yampa <br />Canyon is shown on FlQure 1.3. The extremely sinuous reach of the lower canyon between Harding <br />Hole (RM 20) and about the Grand Overhang (AM 14.5) is probably located on the upstream dip slope <br />of an anticlinal fold (Gardner, 1975; Harden, 1990). The reduced channel gradient is the result of <br />downstream baselevel control due to the folding (Schumm and Kahn, 1973). Field evidence indicates <br />that the rocks dip upstream (east) through this reach. In contrast, downstream of the Grand Overhang <br />to about Mantle Ranch (AM 12) the rocks are relatively flat lying, or dip gently to the west which <br />suggests that they are located on the crest of the antiform or on the downstream dip slope. The low <br />sinuosity of the river downstream of the Grand Overhang tends to support the structural interpretation <br />(Gardner, 1975; Harden, 1990). Where the rocks are dipping east seeps and springs are located at the <br />contact between the Weber Sandstone and the underlying limestone units of the Morgan Formation. In <br />contrast, where the rocks are flat lying there are no seeps at the contact. <br /> <br />2.2 Resource Consultants & Engineers, Inc. <br />