MLA

Dreier, Katherine S. (Katherine Sophie), 1877-1952. Black Mountain College (Black Mountain, N.C.). Box 59, folder 1616. 1934-40, n.d.. https://collections.library.yale.edu/catalog/32209443.

APA, 6th edition

Dreier, Katherine S. (Katherine Sophie), 1877-1952. (["Box 59, folder 1616"])(1934-40, n.d.)[Black Mountain College (Black Mountain, N.C.)]. https://collections.library.yale.edu/catalog/32209443.