High Quality Content by WIKIPEDIA articles! 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)