The Long Valley Caldera cranked out a massive pyroclastic flow about 3/4 million years ago. Just east of the caldera the flow is 200 meters (700 feet) deep and was so hot the bottom compacted into glass.
The caldera is shown below in yellow. Contour interval is 100 meters, and the floor of the caldera is below 2500 meters. The caldera is still underlain by magma, as shown by hot springs in the caldera and post caldera volcanism. The brown area is a resurgent dome. In the 1980's an episode of rapid uplift, not long after the Mount Saint Helens eruption alerted Americans to the fact that we have volcanoes, caused the U.S. Geological Survey to issue a volcanic hazard alert.
|Left and below: the road to Crowley Reservoir reveals a complete cross-section of the Bishop Tuff.|
|The tuff is porous and light near the top but here, about midway down the section, it is flattened, compacted and foliated. Near the base it is completely vitrified.|
|Left and below: Looking north from the south end of the caldera. The lake is Crowley Reservoir.|
Panorama from the south entrance to the caldera. The mountain spur is the Sierra Nevada front. The Sierra Nevada front fault is truncated by the caldera ring fault at the end of the spur.
|Left and below: looking south from the north end of the caldera near Crestview.|
There are places where mountains are higher and steeper but for sheer esthetic perfection I don't know anything to equal the view from the north rim of the caldera. The hilly terrain on the valley floor is the resurgent dome.
Created 14 July 2003, Last Update 01 July 2012
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