MLA

Marsh, Othniel Charles, 1831-1899. Red Cloud Correspondence. Box 52, folder 20. 1875 August 1-15. https://collections.library.yale.edu/catalog/32510285.

APA, 6th edition

Marsh, Othniel Charles, 1831-1899. (["Box 52, folder 20"])(1875 August 1-15)[Red Cloud Correspondence]. https://collections.library.yale.edu/catalog/32510285.