The Gran Desierto de Altar is one of the major sub-ecoregions of the Sonoran Desert, located in the State of Sonora, in 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, spanning 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; together with the western portion, the area forms the El Pinacate y Gran Desierto de Altar Biosphere Reserve and a UNESCO World Heritage Site.