MLA

Dreier, Katherine S. (Katherine Sophie), 1877-1952. Walden, Herwarth. Box 116, folder 2768. n.d.. https://collections.library.yale.edu/catalog/16694462.

APA, 6th edition

Dreier, Katherine S. (Katherine Sophie), 1877-1952. (["Box 116, folder 2768"])(n.d.)[Walden, Herwarth]. https://collections.library.yale.edu/catalog/16694462.