https://www.usgs.gov/publications/graphite-bishop-tuff-and-its-effect-postcaldera-oxygen-fugacity
Graphite in the Bishop Tuff and its effect on postcaldera oxygen fugacity | U.S. Geological Survey
Several cubic kilometers of Paleozoic graphite-bearing argillitic country rocks are present as lithic fragments in Bishop Tuff ignimbrite and fallout. The...