Bishop Tuff is a welded tuff that formed 767,100 ± 900 years ago as a rhyolitic pyroclastic flow during the eruption that created the Long Valley Caldera. Large outcrops of the tuff are located in Inyo and Mono Counties, California, United States.

The Bishop Tuff caps a volcanic plateau in the northern Owens Valley. The tableland formation is located east of U.S. Route 395 and west of the Nevada state line, sitting northwest of Bishop and southeast of Crowley Lake and Mammoth Lakes. Another part of the flow is south of Mono Lake, and surrounding the Mono-Inyo Craters.

Deposits of Bishop Tuff in this area cover nearly 2,200-square-kilometer (850 sq mi), and range in thickness from 490-660 ft.

The Owens River cuts through the Volcanic Tableland, an ignimbrite plateau that is a principal sector of the Bishop Tuff outflow sheet. Erosion of the plateau by the Owens River has created the Owens River Gorge.

Source
Wikipedia