Cite

(MONTANA) Bischoff, A. Map of North- West part of Montana...Great Northern Line St. Paul, Minneapolis & Manitoba Ry. Pacific Extension. Elbridge H. Beckler, Chief Engineer. Helena, Mont. Scale 1 in.= 2 miles.

MLA

Beckler, Eldridge H., and A. Bischoff. (MONTANA) Bischoff, A. Map of North- West Part of Montana...Great Northern Line St. Paul, Minneapolis & Manitoba Ry. Pacific Extension. Elbridge H. Beckler, Chief Engineer. Helena, Mont. Scale 1 in.= 2 Miles. 1891. https://collections.library.yale.edu/catalog/2016954.

APA, 6th edition

Beckler, E. H., & Bischoff, A. (1891). (MONTANA) Bischoff, A. Map of North- West part of Montana...Great Northern Line St. Paul, Minneapolis & Manitoba Ry. Pacific Extension. Elbridge H. Beckler, Chief Engineer. Helena, Mont. Scale 1 in.= 2 miles. [Maps]. https://collections.library.yale.edu/catalog/2016954.