MLA

Lewis, Sinclair, 1885-1951. Sinclair, Upton. Box 72, folder 1050. 1953 March 23. https://collections.library.yale.edu/catalog/17116566.

APA, 6th edition

Lewis, Sinclair, 1885-1951. (["Box 72, folder 1050"])(1953 March 23)[Sinclair, Upton]. https://collections.library.yale.edu/catalog/17116566.