Title from title screen (viewed on July 29, 2008).
Supersedes U.S. Geological Survey fact sheet FS-50-98.
"May 2005, Revised 2007."
Mode of access: Internet from the USGS web site. Address as of 7/29/08: http://pubs.usgs.gov/fs/2005/3055/fs2005-3055.pdf; current access available via PURL.