Well-rounded coarse gravel provides clues to the depositional process. The coarse gravel of the Mogollon Rim in central and northern Arizona, called Rim Gravel, was examined at two widely separated and representative locations. Further characteristics of the coarse gravel was obtained from the literature. The coarse gravel occupies the highest terrain in the region and is very coarse in east-central Arizona. It is deduced that this coarse gravel was deposited as a sheet and eroded into remnants during the Recessional Stage of the Genesis Flood. We conclude that the Rim Gravel provides evidence that the Flood/post-Flood (D/P) boundary corresponds to the stratigraphic location of rocks termed "late Cenozoic" in the uniformitarian geological column in this part of the western United States. This interpretation is relevant to theories for the formation of many notable geomorphic features, including the Grand Canyon of the Colorado River.