MLA

Mellen, George Egbert. Pikes Peak 15 Miles Distant. 0AD. https://collections.library.yale.edu/catalog/2014640.

APA, 6th edition

Mellen, G. E. (0 C.E.). Pikes Peak 15 miles distant [Card photographs, Photographic prints, Photographs]. https://collections.library.yale.edu/catalog/2014640.