Colorado River Aqueduct in Vidal Junction, California

In the 1920s, Los Angeles needed an outside source of water to sustain its growth, and engineer William Mulholland looked to the Colorado River as a solution. The Metropolitan Water District of Southern California was formed in 1928 to implement plans for the Colorado River Aqueduct. The aqueduct was designed by Chief Engineer Frank E. Weymouth and included 62 miles of canals, 92 miles of tunnels, and several intermediate reservoirs. The reservoirs would supply five pumping stations, which would raise the water in stages using hydroelectricity from the Hoover Dam. The initial stage would raise water from Lake Havasu behind Parker Dam, and the last link to be finished was the 13-mile-long San Jacinto Tunnel, completed in 1939. The system ends at Lake Mathews, and a distribution network extends to Santa Monica and the Palo Verde Hills. Water first flowed to Lake Mathews on January 7, 1939. Only about a quarter of the total length of the aqueduct is above ground, with the rest being underground tunnels and pipes. The aqueduct uses siphons to allow drainages to cross its course, with subterranean pipes connecting the two ends of the aqueduct. The siphoning action is never broken, allowing water to flow continuously.