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.