Long Valley Observatory

It is easy to forget that North America hosts two major caldera volcanoes - the Yellowstone and Long Valley in California. The Long Valley area, in fact, has seen more recent volcanism that Yellowstone, with the eruptions from the Mono-Inyo chain of rhyolite domes coming as recently as 600 years ago. However, the reason for the close watch on Long Valley comes from activity at Mammoth Mountain, where carbon dioxide seeps out of the ground enough to kill trees, and the colossal caldera itself that produced the Bishop Tuff over 740,000 years ago. The Long Valley Observatory watches over the caldera and the younger domes and is operated out of the USGS offices at Menlo Park, CA and you can access monitoring data for the caldera as well.

Image: The Bishop Tuff seen near Bishop, California. LVO/USGS