MLA

Luhan, Mabel Dodge, 1879-1962. Blue Lake. Box 78, folder 2156. n.d.. https://collections.library.yale.edu/catalog/10268304.

APA, 6th edition

Luhan, Mabel Dodge, 1879-1962. (["Box 78, folder 2156"])(n.d.)[Blue Lake]. https://collections.library.yale.edu/catalog/10268304.