Some 3.5-2 mya volcanoes began to form in this area, with a second round of volcanic eruptions 2.1 - 0.8 mya. However almost all of these were obliterated by the massive Long Valley Eruption 76000 years ago, when 600 km^3 of material erupted, sending debris as far as Kansas. This created the Long Valley Caldera in the Eastern Sierras, at 32km long and 18km wide one of the largest calderas on Earth.
Volcanic activity continued at the Long Valley Caldera, and a series of mountains were formed by volcanic activity: eruptions 400000-60000 years ago formed Mammoth Mountain, eruptions 40000-600 years ago formed the Mono Craters and eruptions 5000-500 years ago formed the Inyo Craters. As recently as 250 years ago, eruptions in Mono Lake created Paoha Island.
The Northernmost of the Mono-Inyo Craters and immediately South of Mono Lake, Panum was formed 600-700 years ago when magma rising from the Earth's crust came in contact with water underground, turning the water to steam and causing a violent explosion that ejected debris from the Earth, and creating a ring of cinders (cinder cone). Eventually, rising magma pushed up a dome, then broke as magma below continued pushing up, until the volcano finally ran out of source magma, leaving the crater seen today.
Mono Lake, Lee Vining, California
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