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The Bishop Tuff is a welded tuff which formed 764,800 ± 600 years ago as a rhyolite pyroclastic flow during the approximately six-day eruption that formed the Long Valley Caldera. Large outcrops of the tuff are located in Inyo and Mono Counties, California, United States. Approximately 200 cubic kilometers of ash and tuff erupted outside the caldera.
Deposits of Bishop Tuff in this area cover nearly , and are as thick as .
The Owens River cuts through the Volcanic Tableland, an ignimbrite plateau which is a principal sector of the Bishop Tuff outflow sheet. Erosion of the plateau by the Owens River has carved the Owens River Gorge.
The Bishop Tuff is compositionally zoned. The lower section, formed from ash fall, is notated by pyroxene-free high-silica rhyolite pumice. The upper section, formed by pyroclastic flow, is notated by pyroxene-bearing high-silica rhyolite pumice. The magma that formed the Bishop Tuff is suggested to be a "residual magma derived from some parental magma and not itself a primary or parental partial melt of common crustal rocks".
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