This report presents a summary of the principal geologic and physiographic features of the upper part of the Snake River Canyon between Oregon and Idaho. The area discussed extends from Farewell Bend near Huntington, Oregon downriver to Granite Creek 6 miles below Hells Canyon Dam, a distance of 94 miles. Photographs and a series of geologic maps are included to illustrate the topography and geology. The information presented synthesizes the results of geologic mapping in progress by the writers and others.