[No. 90: Photograph of pack horses grazing]
MLA
[No. 90: Photograph of Pack Horses Grazing]. 1915. https://collections.library.yale.edu/catalog/11680512.
APA, 6th edition
[No. 90: Photograph of pack horses grazing]. (1915). [Photographs, Slides (glass)]. https://collections.library.yale.edu/catalog/11680512.