The Algodones Dunes is a large Erg (landform) (sand Dune field) located in southeastern portion of the U.S. state of California, near the border with Arizona and the Mexican state of Baja California. The field is approximately 72 kilometers long by 10 kilometers wide (45 miles by 6 miles) and extends along a northwest-southeast line that correlates to the prevailing northerly and westerly wind directions. The name "Algodones Dunes" refers to the entire geographic feature, while the administrative designation for that portion managed by the Bureau of Land Management is the Imperial Sand Dunes Recreation Area (sometimes called the Glamis Dunes). The Algodones Dunes are split into many different sections. These sections include Glamis, Gordon's Well, Buttercup, Midway, and Patton's Valley. The Spanish word algodones translates to the English word cotton.
The dunes are located west of the Chocolate Mountains in Imperial County, and are crossed by California, which passes through the old train stop of Glamis at the eastern edge of the dune field. The northwestern end is located at about 18 km (11 miles) east of Calipatria, California, and the southeastern end is located at near Los Algodones in Mexico about 10 km (six miles) west of Yuma, Arizona. The dunes are also now separated at the southern end by agricultural land (see accompanying photo) from the much more extensive Gran Desierto de Altar, to which they once were linked as an extreme peripheral "finger". The only significant human-made structures in the area are the All-American Canal that cuts across the southern portion from west to east and the Coachella Canal on the western edge.
Because the Colorado River flowed through very flat terrain, the course of the river varied over a wide area, being periodically diverted in one direction or another by silt deposits remaining after floods. Sometimes the river flowed into the Gulf of California, as it does today; other times it turned westward toward the Salton Sink. Each time the Salton Sink received the river flow, a large freshwater lake called Lake Cahuilla formed. The last Lake Cahuilla covered much of the Imperial Valley (California), Coachella and Mexicali Valleys as late as 1450. The most popular theory holds that the Algodones Dunes were formed from windblown beach sands of Lake Cahuilla. The prevailing westerly and northwesterly winds carried the sand eastward from the old lake shore to their present location which continues to migrate southeast by approximately one foot per year.
The dunes have frequently been a barrier to human movement in the area. Foot travelers frequently diverted south into Mexico, and in 1877 the Southern Pacific Railroad was diverted north to avoid the dunes, but in 1915 Colonel Ed Fletcher built a wooden plank road across the dunes to prove that cars could cross the dunes and to connect San Diego with Yuma, Arizona. This trail eventually became part of Interstate 8 (California). During World War II, the U.S. military conducted desert warfare training on the dunes, which were part of the California-Arizona Maneuver Area. People have been driving on the dunes for recreation almost since vehicles first reached the area, which may have been the proving ground for the first Dune, a modified Ford Model A. Off-road driving surged following World War II when surplus Jeeps became available to the public.) and off-highway vehicle advocacy groups (notably the American Sand Association) have filed numerous petitions and lawsuits to either restrict or open vehicular access to the dunes. Most of the dunes located north of California are off-limits to vehicular traffic due to designation as the North Algodones Dunes Wilderness. The federal government protected these 25,818 acres (104 km²) in the early 1980s and closed them to vehicles as part of the 1994 California (Public Law 103-433). Much of the area south of this road remains open for off-highway vehicle use, though a lawsuit in 2000 closed over 49,000 acres (200 km²) to vehicular access, leaving about 40% of the recreation area open to vehicles. The site's large sand dunes are a preferred terrain for many Off-road vehicle owners. Motorcycles, Sandrails, ATVs, and 4-wheel-drive vehicles are commonly Dune. Open camping is permitted, and on major winter holidays, as many as 150,000 people can visit in a single weekend. These recreationalists bring an economic boom during the cooler months to the nearby towns of Brawley, California, Yuma, Arizona and El Centro, California.
As they are the largest dune ecosystem in the United States, there are many species which are Endemic (ecology) to the Algodones system, so the region overall is biologically unique on a global scale. The Algodones were once part of an even greater dune system that now resides primarily in the Mexican state of Sonora, with a few extensions also in southwestern Arizona, especially in the vicinity of Yuma, Arizona. Accordingly, it is likely that many of the species presently known only from the Algodones also occur in the Gran Desierto de Altar in Mexico, but this is difficult to ascertain without biological surveys of the latter area.
- The Perennial plant Peirson's Milkvetch (Astragalus magdalenae var. peirsonii) is found in the Algodones and is listed as a Threatened species under the U.S. Endangered Species Act and as an Endangered species under the California Endangered Species Act. The plant germinates only during years of sufficient rainfall. During one such year, over 71,000 plants were found in the open areas of the dunes, and it is suspected at least that many more in the closed areas.
The dunes were used to film parts of Road to Zanzibar, Stargate (film), Resident Evil: Extinction and the Tatooine scenes in the Star Wars series.