MLA

Carson, Rachel, 1907-1964. Fan Mail for the Sea Trilogy from a High School Student in New Milford, Connecticut. Box 106, folder 2037. undated. https://collections.library.yale.edu/catalog/33433802.

APA, 6th edition

Carson, Rachel, 1907-1964. (["Box 106, folder 2037"])(undated)[Fan Mail for the Sea Trilogy from a High School Student in New Milford, Connecticut]. https://collections.library.yale.edu/catalog/33433802.