MLA

Dreier, Katherine S. (Katherine Sophie), 1877-1952. Gray, Cleve. Box 15, folder 427. n.d.. https://collections.library.yale.edu/catalog/2030243.

APA, 6th edition

Dreier, Katherine S. (Katherine Sophie), 1877-1952. (["Box 15, folder 427"])(n.d.)[Gray, Cleve]. https://collections.library.yale.edu/catalog/2030243.