recent posts about Glass Mountain, Siskiyou County, CA, I've put together a few links relating mostly to pumice:
Chesterman, C.W., 1956, Pumice, pumicite, and volcanic cinders in California and Technology of pumice, pumicite, and volcanic cinders [pdf; text]: CDMG Bulletin 174, 119 p.
Presley, G.C., 2006, Pumice, pumicite, and volcanic cinder, in Kogel, J.E., Trivedi, N.C., Barker, J.M., and Krukowski, S.T., eds., Industrial rocks and minerals (7th ed.): Littleton, CO, Society for Mining, Metallurgy, and Exploration, Inc., p. 743–754.
Pumice and Pumicite Statistics and Information - USGS links and reports.
What is the fate of the pumice rafts? (2012) - at Eruptions.
Pumice flows (down the page), a type of pyroclastic flow - at SDSU.
Pumice - at MEC.
Pumice - at Minerals Zone.
Pumice - at Sandatlas.
Pumice - at Volcano Discovery.