i live a couple of hours away from Lassen Natl Park Volcanic Area.
which erupted in 1914 Lassen National Park Volcano..northern California and on the other side of me is a plateau which was formed by a lava flow....Table Mountain.
http://www.calphoto.com/clpc/table.pdf
http://www.dfg.ca.gov/lands/articles/notablemt00.html
In Oregon there is a huge lave flow -- an Obsidian deposit. which the natives used for arrow heads...
http://www.fs.fed.us/r6/centraloregon/newberrynvm/index.shtml
http://vulcan.wr.usgs.gov/Volcanoes/Newberry/Locale/framework.html