MLA

Clark, William, 1770-1838. June 6-9, 1804, small drawing of a painting seen on a rock: a Manitou, buffalo, and an Indian. Box 1, folder 18. 1803-1805. https://collections.library.yale.edu/catalog/2002960.

APA, 6th edition

Clark, William, 1770-1838. (["Box 1, folder 18"])(1803-1805)[June 6-9, 1804, small drawing of a painting seen on a rock: a Manitou, buffalo, and an Indian]. https://collections.library.yale.edu/catalog/2002960.