MLA

Steinberg, Saul, 1914-1999. Wyoming. Box 452, folder 6239. 1968 Aug. https://collections.library.yale.edu/catalog/16851446.

APA, 6th edition

Steinberg, Saul, 1914-1999. (["Box 452, folder 6239"])(1968 Aug)[Wyoming]. https://collections.library.yale.edu/catalog/16851446.