A cataclysmic eruption of 600 km3 of rhyolite magma (Bishop Tuff) about 760,000 years ago resulted in the collapse of the partially evacuated magma chamber to form the present 17 by 32 km (10 by 20 mi) Long Valley Caldera.
Published overview of low-level unrest in the Long Valley Caldera, eastern California
Although the most recent eruptions within the caldera occurred about 50,000 years ago, Long Valley Caldera remains thermally active and has had significant seismicity and deformation since at least 1978. USGS scientists have monitored geologic unrest in Long Valley Caldera since 1980, when they detected dome-like swelling in the middle of the caldera after a swarm of strong earthquakes. The new U.S. Geological Survey Open-File Report 2014–1222 by CalVO geologist Stuart Wilkinson and colleagues documents the seismicity and deformation in the Long Valley Caldera over the past decade.