Fallen Leaf Lake is about one mile south of the much larger Lake Tahoe, near the California-Nevada state border. It is approximately aligned north-to-south and oval in shape, measuring approximately 2.9 miles (4.6 km) on the long axis and 0.9 miles (1.4 km) on the short axis. The lake was created by at least two glaciers which traveled northward down the Glen Alpine Valley. If the glacier had continued instead of stopping, Fallen Leaf Lake would be a bay similar to nearby Emerald Bay.