The Long Valley Caldera
The Long Valley Caldera was born more than 760,000
years ago. A cataclysmic explosion of such magnitude,
ash was found as far away as Nebraska! Bordered by Mammoth
Mountain, the Mono Basin, the Glass Mountains and Crowley
Dam, a mountaintop of nearly 12,500 feet was literally
Remnants of the explosion are visible today on the
Sherwin grade in the pinkish-white ash deposits known
as "Bishop Tuff". Highway 395 has been chiseled
through much of this ancient formation.
The caldera and its perimeters may be best viewed
from the McGee Creek road, above Crowley Lake, as it
ascends toward the McGee Creek Pack Station.