"Largest Earthquake in Montana". Historic Earthquakes. United States Geological Survey. October 21, 2009. Archived from the original on January 5, 2010. Retrieved 2012-04-01.
web.archive.org
"Largest Earthquake in Montana". Historic Earthquakes. United States Geological Survey. October 21, 2009. Archived from the original on January 5, 2010. Retrieved 2012-04-01.