"Largest Earthquake in Montana". Historic Earthquakes. United States Geological Survey. October 21, 2009. Archived from the original on January 5, 2010. Retrieved April 1, 2012.
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"Largest Earthquake in Montana". Historic Earthquakes. United States Geological Survey. October 21, 2009. Archived from the original on January 5, 2010. Retrieved April 1, 2012.