MLA

Kilpatrick, Jack Frederick (1915-1967). Letter from American Indian Defense Association to Mr. James Foster (Tsuwanosgi Atsila).. Box 17, folder 1433. undated. https://collections.library.yale.edu/catalog/15532137.

APA, 6th edition

Kilpatrick, Jack Frederick (1915-1967). (["Box 17, folder 1433"])(undated)[Letter from American Indian Defense Association to Mr. James Foster (Tsuwanosgi Atsila).]. https://collections.library.yale.edu/catalog/15532137.