MLA

Dellenbaugh, Frederick Samuel, 1853-1935. Colorado River. Box 2, folder 72. n.d.. https://collections.library.yale.edu/catalog/2017924.

APA, 6th edition

Dellenbaugh, Frederick Samuel, 1853-1935. (["Box 2, folder 72"])(n.d.)[Colorado River]. https://collections.library.yale.edu/catalog/2017924.