"Annual Estimates of the Resident Population for the United States, Regions, States, and Puerto Rico: April 1, 2000 to July 1, 2008". United States Census Bureau. Retrieved 2009-02-01.  "Elevations and Distances in the United States". U.S Geological Survey. 29 April 2005. Retrieved November 3 2006.  Unknown parameter |dateformat= ignored (help); Check date values in: |access-date= (help)