MLA

American Publishing Co. (Milwaukee, Wis.). Perspective map of the city of Helena, Mont. : capital of state, county seat of Lewis & Clarke Co. / compliments of Kessler's Brewery.. BRBL_00580. 1890. https://collections.library.yale.edu/catalog/15814923.

APA, 6th edition

American Publishing Co. (Milwaukee, Wis.). (["BRBL_00580"])(1890)[Perspective map of the city of Helena, Mont. : capital of state, county seat of Lewis & Clarke Co. / compliments of Kessler's Brewery.]. https://collections.library.yale.edu/catalog/15814923.