The Imperial Diversion Dam is a concrete slab and buttress, ogee weir structure across the California/Arizona border, 18 miles northeast of Yuma. Completed in 1938, the dam retains the waters of the Colorado River into the Imperial Reservoir before desilting and diversion into the All-American Canal, the Gila River, and the Yuma Project aqueduct. Between 1932 and 1940, the Imperial Irrigation District relied on the Inter-California Canal and the Imperial Canal and Alamo River.