MLA

Gilbert, Grove Karl, 1843-1918, OSullivan, Timothy H., 1840-1882, United States. War Dep, Wheeler, George M. (George Montague), 1842-1905. No. 88. Rock carved by drifting sand below Fortification Rock.. https://collections.library.yale.edu/catalog/2020040.

APA, 6th edition

Gilbert, Grove Karl, 1843-1918, & OSullivan, Timothy H., 1840-1882, & United States. War Dep, & Wheeler, George M. (George Montague), 1842-1905. [No. 88. Rock carved by drifting sand below Fortification Rock.]. https://collections.library.yale.edu/catalog/2020040.