Geologic Trip, Mammoth Area
The Owens Gorge is a steep-sided canyon that has been cut by the Owens River through thick deposits of the Bishop Tuff between Lake Crowley and Bishop, California. The pillars that line the walls of the gorge, as shown in this photo, are formed by columnar jointing within the Bishop Tuff.
The Bishop Tuff was deposited in this area during the eruption of the Long Valley volcano 760,000 years ago when 150 cubic miles of superheated ash was expelled from the volcano. Some of this eruptive material flowed down the flanks of the volcano as clouds of hot volcanic ash and some of these ash flows extended south down the Owens Valley as far as Big Pine. The Volcanic Tableland that covers much of the Owens Valley from Lake Crowley to Bishop is formed from these ash flows. The Bishop Tuff over the Volcanic Tableland was welded into an extremely hard rock while the ash flows were still hot.