Altar Desert

The Gran Desierto de Altar is one of the major sub-ecoregions of the Sonoran Desert, located in the State of Sonora, Northwest Mexico. It includes the only active erg dune region in North America. The desert extends across much of the northern border of the Gulf of California, reaching more than 100 kilometres (62 mi) east to west, and over 50 kilometres (31 mi) north to south. It constitutes the largest continuous wilderness area within the Sonoran Desert.

The eastern portion of the area contains the volcanic Pinacate Peaks region, and with the western Gran Desierto de Altar area, together they form the El Pinacate y Gran Desierto de Altar Biosphere Reserve and a UNESCO World Heritage Site.

The Gran Desierto covers approximately 5700 square km, most of it in the Mexican state of Sonora. The northernmost edges overlap the border into Organ Pipe Cactus National Monument and Cabeza Prieta National Wildlife Refuge in southwestern Arizona. The dominant sand sheets and dunes range in thickness from less than 1 kilometre (0.62 mi) to greater than 12 kilometres (7.5 mi). The total volume of sand in the Gran Desierto is about 60 cubic km. Most of that volume was delivered by the 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.

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