MLA

Dellenbaugh, Frederick Samuel, 1853-1935. Colorado. Box 1, folder 6. 1871. https://collections.library.yale.edu/catalog/2015537.

APA, 6th edition

Dellenbaugh, Frederick Samuel, 1853-1935. (["Box 1, folder 6"])(1871)[Colorado]. https://collections.library.yale.edu/catalog/2015537.