Long Valley Caldera is a depression in eastern California that is adjacent to Mammoth Mountain. The valley is one of the largest calderas on earth, measuring about 32 km long (east-west) and 18 km wide (north-south). The Long Valley volcano is unique in that it has produced eruptions of both basaltic and silicic lava in the same geological place. The Mono-Inyo Craters volcanic field developed along a 50 km fissure system that extends northward from Mammoth Mountain on the southwestern rim of the caldera to Mono Lake. In May 1980, a strong earthquake swarm that included four Richter magnitude 6 earthquakes struck the southern margin of Long Valley Caldera associated with a 25-cm, dome-shaped uplift of the caldera floor. These events marked the onset of the latest period of caldera unrest that continues to this day. Read more