Gran Desierto de Altar - Physiography

Physiography

The eastern margin of the Gran Desierto abuts the Cenozoic volcanic complex of the Sierra Pinacate, a composite volcanic field covering more than 1,800 km2 with a summit elevation of 1,206 m. Aeolian sands have climbed onto many of the western slopes of the Sierras 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.

The southernmost extension of the San Andreas Fault cuts across the area and lies beneath several prominent granite inselbergs, most notably the Sierra del Rosario mountains which are surrounded by the erg on all sides. The Sierra Enternada is a smaller inselberg almost completely buried by the sand near the boundary of the Gran Desierto and the Pinacate volcanic complex.