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Government of Canada (8 April 2016). "National Topographic System Maps". Earth Sciences – Geography. Natural Resources Canada. Archived from the original on 15 May 2016. Retrieved 16 May 2016. yes
"Organizing the U.S. Geological Survey". The United States Geological Survey: 1879–1989. U.S. Geological Survey, U.S. Department of the Interior. 10 April 2000. Archived from the original on 2 July 2007. Retrieved 19 June 2007.
"The Four Great Surveys of the West". The United States Geological Survey: 1879–1989. U.S. Geological Survey, U.S. Department of the Interior. 10 April 2000. Archived from the original on 10 June 2007. Retrieved 19 June 2007.
Government of Canada (8 April 2016). "National Topographic System Maps". Earth Sciences – Geography. Natural Resources Canada. Archived from the original on 15 May 2016. Retrieved 16 May 2016. yes
"Organizing the U.S. Geological Survey". The United States Geological Survey: 1879–1989. U.S. Geological Survey, U.S. Department of the Interior. 10 April 2000. Archived from the original on 2 July 2007. Retrieved 19 June 2007.
"The Four Great Surveys of the West". The United States Geological Survey: 1879–1989. U.S. Geological Survey, U.S. Department of the Interior. 10 April 2000. Archived from the original on 10 June 2007. Retrieved 19 June 2007.