Geology and History

A spectacular display of a columnar-jointed basalt flow.

Geologic history of the Long Valley, Mono Basin region.

Possible eruption sequence for the Long Valley-Mono Lake area.

The area of eastern California that includes the Long Valley Caldera and the Mono-Inyo Craters volcanic chain has a long history of geologic activity that includes both earthquakes and volcanic eruptions. This activity is likely to continue long into the future.

The Bishop Tuff refers to the deposits of ash and pumice ejected during the enormous eruption that created Long Valley Caldera.

The broad depression of Long Valley Caldera that we see today is much shallower and a little larger in diameter than it was immediately after its formation about 760,000 years ago.

The resurgent dome is a broad area of the central caldera floor that was pushed upward within 100,000 years or less of the caldera-forming eruption 760,000 years ago.

Mammoth Mountain is a 3,369-m (11,053-ft) high volcano lies west of the structural rim of the caldera and is considered to represent a magmatic system distinct from Long Valley Caldera and the Mono-Inyo Craters.

Since the enormous explosive eruption formed the caldera about 760,000 years ago, hundreds of smaller eruptions have partially filled the initially deep depression.

Hot Creek is the lower reach of Mammoth Creek where several vigorous hot springs discharge hot water to the surface; the largest springs discharge subaqueously into the stream.

Several small cinder cones are located on the floor and rim of Long Valley caldera.

The area surrounding Long Valley caldera and the Mono-Inyo Craters volcanic chain is cut by a complicated mix of dozens of major north-northwest trending faults and down-faulted blocks called "grabens."