MLA

Williamson, R. S. (Robert Stockton), 1824-1882. Sketch of the route of Capt. Warner's exploring party in the Sacramento Valley and Sierra Nevada [Calif.] : during the months of August, September, and October 1849 / by R.S. Williamson, Lieut. Top. Engrs., assistant to Capt. Warner.. BRBL_00601. 1849 or 1850]. https://collections.library.yale.edu/catalog/15818626.

APA, 6th edition

Williamson, R. S. (Robert Stockton), 1824-1882. (["BRBL_00601"])(1849 or 1850])[Sketch of the route of Capt. Warner's exploring party in the Sacramento Valley and Sierra Nevada [Calif.] : during the months of August, September, and October 1849 / by R.S. Williamson, Lieut. Top. Engrs., assistant to Capt. Warner.]. https://collections.library.yale.edu/catalog/15818626.