An episode of proglacial aggradation, here named the stage, is recorded in the Lewiston Basin region on the lower Snake River. Stream gravels accumulated to a depth of more than 400 feet in the Snake River canyon and in the lower portions of most tributary canyons. One or two tributary streams were ponded by the fill of the main canyon. The deposits are characterized by considerable cementation, weathering of basalt and granitic stones, and iron oxide stain. Two-story canyons were formed by cessation of erosion beneath the fill, prolonged lowering of slopes above, and later excavation of the fill. The Clarkston stage followed earlier Pleistocene deposition, deformation, and dissection but antedated the Wisconsin stage.