Bishop Tuff is a vast welded volcanic deposit in eastern California, formed about 764,800 years ago during the roughly six-day eruption that created the Long Valley Caldera. Rhyolitic pyroclastic flows spread ash and pumice widely beyond the caldera, producing about 200 cubic kilometers of erupted material and leaving deposits that cover nearly 2,200 square kilometers. Especially prominent on the Volcanic Tableland in northern Owens Valley, the formation also appears in other nearby areas of Inyo and Mono Counties. Its layered, compositionally zoned ash and pumice record different eruptive phases, while later erosion by the Owens River carved the Owens River Gorge through one of its main outflow sheets.