MLA

Lindbergh, Charles A. (Charles Augustus), 1902-1974. In North Haven, Maine, with relatives. Box 15, folder 20-22. 1935 August. https://collections.library.yale.edu/catalog/10013277.

APA, 6th edition

Lindbergh, Charles A. (Charles Augustus), 1902-1974. (["Box 15, folder 20-22"])(1935 August)[In North Haven, Maine, with relatives]. https://collections.library.yale.edu/catalog/10013277.