Post route map of the state of Montana.
MLA
Department, United States. Post Office. Post Route Map of the State of Montana. 1891. https://collections.library.yale.edu/catalog/16364740.
APA, 6th edition
Department, U. S. P. O. (1891). Post route map of the state of Montana. [Maps]. https://collections.library.yale.edu/catalog/16364740.