MLA

Luhan, Mabel Dodge, 1879-1962. Young, Ella. Box 73, folder 2057. n.d.. https://collections.library.yale.edu/catalog/2032266.

APA, 6th edition

Luhan, Mabel Dodge, 1879-1962. (["Box 73, folder 2057"])(n.d.)[Young, Ella]. https://collections.library.yale.edu/catalog/2032266.