The Salton Sea, 35 miles long and between nine and 15 miles wide, is the largest lake by surface area in California. Its history is complex—and an anomaly in the natural world. Today’s Salton Sea lies 228 feet below sea level, on the site of the much-larger ancient Lake Cahuilla. Peaking at 40 feet above sea level, Lake Cahuilla encompassed much of the Imperial, Mexicali and Coachella valleys, most recently between 500 and 1,000 years ago. With evaporation and no outlet, over the years, Lake Cahuilla dried up, leaving a huge 2,000-square-mile desert sink—from the Gulf of California to the Banning Pass. A horizontal dark band from the earlier shoreline is easily spotted along the cliffs near today’s Salton Sea.