MLA

Watkins, Carleton E., 1829-1916. Mt. Ophir. Folder 15. [ca. 1860-1861]. https://collections.library.yale.edu/catalog/2017933.

APA, 6th edition

Watkins, Carleton E., 1829-1916. (["Folder 15"])([ca. 1860-1861])[Mt. Ophir]. https://collections.library.yale.edu/catalog/2017933.