MLA

Kilpatrick, Jack Frederick (1915-1967). Dotsuwa, Seli (Redbird, Seli). Letter, beginning "ayv tsotsuwa gowelvga unelanvhigwono wigisdela". Box 7, folder 589. undated. https://collections.library.yale.edu/catalog/15492888.

APA, 6th edition

Kilpatrick, Jack Frederick (1915-1967). (["Box 7, folder 589"])(undated)[Dotsuwa, Seli (Redbird, Seli). Letter, beginning "ayv tsotsuwa gowelvga unelanvhigwono wigisdela"]. https://collections.library.yale.edu/catalog/15492888.