The Long Valley caldera region, located between the Sierra Nevada and the Basin and Range Province in eastern California, encompasses a large volcanic complex whose eruptive history began nearly 4 m.y.a. and continues to the present, with eruptions occurring, on average, every few hundred years. Eruptive activity in the area occurred as recently as 250 years ago with small eruptions from vents on Paoha Island in the middle of Mono Lake and 550–600 years ago from three vents at the southern end of the Inyo volcanic chain in the west moat of Long Valley caldera. The current unrest in the caldera began in 1980 and has included recurring earthquake swarms and uplift of the resurgent dome in the center of the caldera by over 70 cm [Bailey and Hill, 1990]. Long Valley caldera is one of several large calderas around the world that have shown similar signs of magmatic unrest in the last few decades.