MLA

Dellenbaugh, Frederick Samuel, 1853-1935. Colorado River. Box 3, folder 100. n.d.. https://collections.library.yale.edu/catalog/2018302.

APA, 6th edition

Dellenbaugh, Frederick Samuel, 1853-1935. (["Box 3, folder 100"])(n.d.)[Colorado River]. https://collections.library.yale.edu/catalog/2018302.