Gran Desierto de Altar

The Gran Desierto de Altar is one of the major portions of the Sonoran Desert of Mexico, including the only active erg dune region in North America. It extends across much of the northern border of the Gulf of California, reaching more than 100 kilometers east to west, and over 50 km north to south, and constitutes the largest continuous wilderness area within the Sonoran Desert. The eastern portion of the area is a biosphere reserve (the full title is Reserva de la Biosfera el Pinacate y Gran Desierto de Altar)

The Gran Desierto covers approximately 5,700 km2, most of it in the Mexican state of Sonora. The northernmost edges overlap the border into southwestern Arizona. The dominant sand sheets and dunes range in thickness from less than one meter to greater than 120 meters. The total volume of sand in the Gran Desierto is about 60 km3. Most of that volume was delivered by the Pleistocene Colorado River which flowed through the present-day Gran Desierto area ~120,000 years before present. This Pleistocene delta migrated westward concomitant with strike-slip faulting and rifting associated with the opening of the Salton Trough and the Gulf of California.