Long Valley Caldera - Geography

Geography

Near the center of the caldera there is a mound called the "resurgent dome" that was formed by magmatic uplift. Though the area is still volcanically active, the caldera itself is extinct: seismic mapping has shown the magma body deep underground is mostly crystallized and not molten anymore. There is a hydrothermal power plant near the resurgent dome. The Bishop tuff is the oldest normally magnetized tuff (that is, it was formed when the Earth's magnetic north was near the north pole – as it is today). In the geologic past, water gathered in the Long Valley caldera and overtopped its rim, forming the Owens River Gorge.

Notable geothermal areas in Long Valley include Casa Diablo Hot Springs at the base of the resurgent dome; and Hot Creek, which is about 5 mi (8.0 km) from Casa Diablo and cuts into part of the resurgent dome. Hydrothermal activity has altered many rocks in the caldera, transforming them into travertine and clay. At the Huntley clay mine white chalky clay called kaolinite is mined; the kaolinite is exposed on the resurgent dome and appears as a brilliant white band.

Mammoth Mountain (11,050 ft (3,370 m)), is a composite volcano made up of about 12 rhyodacite and quartz latite domes extruded along the southwest rim of Long Valley Caldera from 200,000 to 50,000 years ago. Mammoth Mountain is one of the eruptive centers that developed late in the evolutionary cycle of the Long Valley Caldera complex.

The history and deposits of the Mono and Inyo Craters overlap with Long Valley Caldera in time and space. The Mono-Inyo Craters volcanic field developed along a 30 mi (48 km) fissure system that extends northward from Mammoth Mountain on the southwestern rim of the caldera to Mono Lake.

Hot Creek has cut into the floor of the caldera and passes through hot springs. The warm water of Hot Creek supports many trout, and is used at the Hot Creek Fish Hatchery. Hot Creek is part of a stream that follows part of a fault line and is well known for its hydrothermal pools and for the contrast swimmers experience between the cold stream water and either the occasional plume of very hot water (which can scald swimmers' feet and can on rare occasions cause more serious injury) or even long and very strong upwellings of hot water when enough water is in the hydrothermal system. The creek was closed to swimming in 2006 after geothermal activity in the area increased, and was still closed as of August 2010. There are a number of other hot springs in the area, some of which are open to bathers.