Crystal Lake Recreation Area is a high-country destination in the San Gabriel Mountains of Southern California, centered on one of only two natural lakes in the range. The lake is a sag pond fed by snow and springs, with water levels that fluctuate sharply because a fissure drains it after wet seasons. Known earlier as Pine Flat and Sycamore Lake, it took the name Crystal Lake after Judge Benjamin Eaton praised its clear water in 1887. Developed across the early 20th century into a major campground and resort, it later suffered flooding, drought, fire, and closures, yet remains valued for camping, fishing, hiking, and its rare mountain setting.