MLA

Dellenbaugh, Frederick Samuel, 1853-1935. Colorado. Box 4, folder 133. n.d.. https://collections.library.yale.edu/catalog/2025207.

APA, 6th edition

Dellenbaugh, Frederick Samuel, 1853-1935. (["Box 4, folder 133"])(n.d.)[Colorado]. https://collections.library.yale.edu/catalog/2025207.