Description
Item Description:Title from title screen (viewed on Feb. 11, 2008).
Electronic resource.
Physical Description:v, 19 pages : digital, PDF file.
Format:Mode of access: Internet from the USGS web site. Address as of 02/11/08: http://pubs.usgs.gov/sir/2007/5256/pdf/SIR2007-5256.pdf ; current access available via PURL.
Bibliography:Includes bibliographical references (page 19).