Bedforms and grain-size distributions in the middle and upper Tapeats Sandstone were analyzed to determine depositional conditions, including flow velocity, direction, and depth. I found that cut-andfill structures were formed by high-density turbulent flow. Alternating compound cross-beds and high-velocity flat beds are the products of changes in depth and competency, possibly caused by cycles of one large storm wave followed by a secondary wave train. Foreset azimuth readings from cross beds indicate a large, unidirectional depositional current, moving northeast to southwest, and composed of many parallel tongues of deposition. Its vast extent and lateral consistency are seen in the ubiquity of tangential toe contacts on both large and small internal cross beds of the compound cross bedding throughout the formation. Diplocraterium ichnofossils in these tangential toe contacts shows an unexpected association of trace fossils with high-energy environments. Flow velocities were determined from grain size corrected to show the total preserved load, recognizing that deposited sediments represent mixed and bed loads after removal of much of the suspended load. Calculated velocities of over 4 m/s show that the entire Tapeats was rapidly deposited. A rhythmic pattern of bedforms supports that depositional rate. Conditions during Tapeats deposition are better understood by this hydrodynamic approach rather than through the use of facies models.