Altar Desert

The Altar Desert is a sandy region in the north of Sonora; it is part of the Sonoran Desert. The desert extends across much of the northern reach 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.

Understand
The Altar desert lies above the northeast corner of the Sea of Cortez (Gulf of California). The region is part of the 2 million-acre El Pinacate/Gran Desierto del Altar Biosphere Reserve, a Mexican National Preserve. The fishing village of El Golfo lies at the southwestern corner of the desert.

The Gran Desierto covers approximately 5,700 km² (2,200 sq mi), most of it in the Mexican state of Sonora. The northernmost edges reach across the international border into Organ Pipe Cactus National Monument and Cabeza Prieta National Wildlife Refuge in southwestern Arizona, United States. The region is dominated by sand sheets and dunes ranging in thickness from less than 1 km (0.62 mi) to greater than 12 km (7.5 mi). Most of the sand of the desert was delivered by the Colorado River during the Pleistocene, which flowed through the present-day Gran Desierto area approximately 120,000 years ago.

Flora
Large areas of the southern and eastern sand sea, especially near the margins, have a moderately dense (up to 20%) cover of perennial low shrubs and herbs such as bursage and longleaf jointfir with creosote bush in areas of thin sand cover. Palo verde, acacia, and ocotillo communities occur on alluvial slopes on the northern side of the sand sea, particularly in arroyos and washes.

Climate
The Gran Desierto has a warm to hot arid climate. Mean annual rainfall, most of which occurs between September and December, is 73 mm (2.9 in) at Puerto Peñasco, Sonora (located at the southeastern margin of the sand sea on the Gulf of California) and decreases northward toward Yuma, Arizona (on the northwestern edge) to 62 mm (2.4 in) per year. Mid-summer highs in excess of 45 °C (113 °F) are common in the central sand sea. Mid-winter lows of less than 10 °C (50 °F) are rare.

Get in
The Altar may be reached from San Luis Rio Colorado, south of Yuma Arizona.

Most of the area is protected; there are a few routes through the desert (next to the railway tracks) to El Golfo. Offroad cross-country travel is prohibited, though locals and American off-road groups still traverse the desert illegally on a regular basis.

See
The Gran Desierto is best known for its magnificent star dunes, many in excess of 100 metres (330 ft) high. More than two-thirds of the Gran Desierto is covered by sand sheets and sand streaks. The remaining area is split equally between a western population of star dunes and an eastern set of transverse or crescentic dunes. Some of the larger crescentic dunes in the northeastern sand sea exhibit reversing crests, a transitional morphological feature associated with star dunes.