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Long Valley was formed 760,000 years ago when a huge volcanic eruption released very hot ash that later cooled to form the Bishop tuff[?] that is common to the area. The eruption was so colossal that the magma chamber[?] under the now completely destroyed volcano was significantly emptied to the point of collapse. The collapse itself caused an even larger secondary eruption of pyroclastic[?] ash that burned and buried thousands of square miles. Ash from this eruption blanketed much of the western part of what is now the United States. Geologists call topographic depressions formed in this manner calderas.
Near the center of the caldera there is a mound called the "resurgent dome" that was formed by magmatic uplift. The area is still volcanically active and has periodic rhyolitic lava flows. There is a hydrothermal[?] power plant near the resurgent dome. The Bishop tuff is the oldest normally magnetized tuff (that is, it was formed when the earth's magnetic north[?] was near the north pole - as it is today). In the geologic past, water gathered in the Long Valley caldera and overtopped its rim forming the Owens River[?] Gorge.
Hot Creek[?] (shown in the image to the right) has cut into the floor of the caldera and passes through hot springs. The warm water of Hot Creek supports many trout, and is used at the Hot Creek Fish Hatchery[?].
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