DOES THE MUDDY CREEK FORMATION SUPPORT AN ALTERNATIVE EXPLANATION FOR THE EVOLUTION OF A PRE-COLORADO RIVER CANYON?

The geomorphology of the western Colorado Plateau and the origin of a through-flowing Colorado River have long been considered to be restricted by the location and sedimentary character of the Muddy Creek Formation, an interior basin fill. An analysis of inherited Laramide landscape elements and the structural controls on late Tertiary drainage development suggest a resolution of the central dilemma. Development of scarp-controlled (subsequent) drainage on the western plateau must have begun in Miocene time, following Basin and Range extension. The existence of a headward eroding canyon on the Hualapai Plateau can explain both the upward transition to carbonate facies in the Muddy Creek Formation (Hualapai Limestone) and the lack of massive deltaic facies from an early “Colorado River” in the Grand Wash Trough. This scenario is compatible with the prevailing evidence that indicates an integrated Colorado River did not emerge until Pliocene time.