Quaternary geology and landscape evolution of eastern Grand Canyon, Arizona

Superimposed on overall downcutting in eastern Grand Canyon are dynamic responses of different landscape components to glacial-interglacial climate cycles. Five tributary stream terraces have been identified. Aggradation was occurring 50--34 ka, 12--7 ka, and 5--3.5 ka and appears to be driven by changes in sediment yield and hydrology of hillslopes. Seven Colorado River terraces have been identified. Aggradation was occurring 343--322 ka, 151--118 ka, and 71--64 ka and appears to be driven by increases in sediment yield associated with glacial conditions upstream in the Colorado River system.; Bedrock incision by the Colorado River has been occurring at a rate of 0.13 mm/yr over middle-late Quaternary time. The technique used to make this calculation involves tracing the elevation of the valley bottom through time. This method is advantageous it produces true bedrock incision and eliminates possible error associated with the use of short time intervals and thick fill deposits.