The Algodones Dunes in southeastern California form the largest sand-dune ecosystem in the United States, extending about 45 miles and shaped by persistent winds. Often linked to the former shores of Lake Cahuilla, the dunes continue to migrate slowly southeastward. They long hindered travel, influencing routes from footpaths and the Southern Pacific Railroad to Colonel Ed Fletcher’s 1915 plank road, later incorporated into Interstate 8, and they also served as a World War II desert training ground. Today they are both a major recreation area and a globally distinctive ecological site, supporting unusual plants and more than 1,100 insect species despite the harsh desert environment.