[2][6] These domes formed in a long series of eruptions from 110,000 to 57,000 years ago, building a volcano that reaches 11,059 ft (3,371 m) in elevation.

[7] The Mono–Inyo Craters are a 25-mile (40 km)-long volcanic chain situated along a narrow, north–south-trending fissure system extending along the western rim of the caldera from Mammoth Mountain to the north shore of Mono Lake.

[8] The Mono-Inyo Craters erupted from 40,000 to 600 years ago, from a magma source separate from the Long Valley Caldera.

Long Valley is not above a hotspot, such as those which fuel Yellowstone Caldera or the volcanoes of Hawaii; nor is it the result of subduction such as that which produces the volcanism of the Cascades.

The known volcanic history of Long Valley Caldera area started a few million years ago when magma began to collect several miles below the surface.

About half of this material was ejected in a series of pyroclastic flows of a very hot (1,500 °F (820 °C)) mixture of noxious gas, pumice, and volcanic ash that covered the surrounding area hundreds of feet deep.

Subsequent eruptions from the Long Valley magma chamber were confined within the caldera with extrusions of relatively hot (crystal-free) rhyolite 700,000 to 600,000 years ago as the caldera floor was uplifted to form the resurgent dome followed by extrusions of cooler, crystal-rich moat rhyolite at 200,000-year intervals (500,000, 300,000, and 100,000 years ago) in clockwise succession around the dome.

[2] The declining volcanic activity and increasingly crystalline lava extruded over the last 650,000 years, as well as other trends, suggest that the magma reservoir under the caldera has now largely crystallized and is unlikely to produce large-scale eruptions in the future.

[17] The lake drained sometime in the last 100,000 years after it overtopped the southern rim of the caldera, eroded the sill, and created the Owens River Gorge.

[18] This ongoing unrest includes recurring earthquake swarms and continued dome-shaped uplift of the central section of the caldera accompanied by changes in thermal springs and gas emissions.

[18] The goal is to provide residents and civil authorities with reliable information on the nature of the potential hazards posed by this unrest and timely warning of an impending volcanic eruption, should it develop.

[18] Common precursory indicators of volcanic activity include increased seismicity, ground deformation, and variations in the nature and rate of gas emissions.

[18] The Long Valley Caldera hosts an active hydrothermal system that includes hot springs, fumaroles (steam vents), and mineral deposits.

The water from snow-melt and rainfall infiltrates to depths of a few kilometers (miles) where it is heated to at least 220 °C (428 °F) by hot rock near geologically young intrusions.

Upflow occurs in the west moat where the heated water with lower density rises along steeply inclined fractures to depths of 1–2 km (0.62–1.24 mi).

This hydrothermal fluid flows laterally, down the hydraulic gradient, from the west to the southeast around the resurgent dome and then eastward to discharge points along Hot Creek and around Crowley Lake.

Reservoir temperatures in the volcanic fill decline from 220 °C (428 °F) near the Inyo Craters to 50 °C (122 °F) near Crowley Lake due to a combination of heat loss and mixing with cold water.