MLA

Warren, Gouverneur Kemble, 1830-1882. Map of the territory of the United States from the Mississippi River to the Pacific Ocean : ordered by Jeff'n Davis, Secretary of War to accompany the reports of the explorations for a railroad route. Sheet 1. 1858]. https://collections.library.yale.edu/catalog/15812946.

APA, 6th edition

Warren, Gouverneur Kemble, 1830-1882. (["Sheet 1"])(1858])[Map of the territory of the United States from the Mississippi River to the Pacific Ocean : ordered by Jeff'n Davis, Secretary of War to accompany the reports of the explorations for a railroad route]. https://collections.library.yale.edu/catalog/15812946.