| Long Valley Caldera | |
|---|---|
 View from northeast rim of caldera | |
| Floor elevation | 6,500–8,500 ft (2,000–2,600 m) |
| Length | 20 mi (32 km) EW |
| Width | 11 mi (18 km) |
| Depth | up to 3,000 ft (900 m) |
| Geology | |
| Type | Caldera |
| Age | 760,000 yrs |
| Geography | |
| Location | Mono County, California United States |
| Coordinates | 37°43′00″N 118°53′03″W / 37.71667°N 118.88417°W [1] |
Long Valley Caldera is a depression in eastern California that is adjacent to Mammoth Mountain. The valley is one of the Earth's largest calderas, measuring about 20 mi (32 km) long (east-west), 11 mi (18 km) wide (north-south), and up to 3,000 ft (910 m) deep.
Long Valley was formed 760,000 years ago when a very large eruption released hot ash that later cooled to form the Bishop tuff that is common to the area. The eruption emptied the magma chamber under the area to the point of collapse. The second phase of the eruption released pyroclastic flows that burned and buried thousands of square miles. Ash from this eruption blanketed much of the western part of what is now the United States.