The eastern margin of the Gran Desierto abuts the Cenozoic volcanic complex of the Sierra Pinacate, a composite volcanic field covering more than with a summit elevation of . Aeolian sands have climbed onto many of the western slopes of the Sierra Pinacate, defining the eastern limit of the dune field. To the north, the sands thin out against the distal margins of alluvial fans from the Tinajas Altas and Tule Mountains along the Arizona–Sonora border. The southern border of the sand sea is the northern shore of the Gulf of California.