It is probable that at the time the mission was established, a mixture of three plant communities occupied the site: a narrow plant community consisting of dense tangled thickets of willows, cottonwoods, wild dogwoods, blackberries, elderberries, and other species common to riparian areas probably occurred in the floodplains along the Walla Walla River and nearby Mill Creek; an association of perennial grasses, shrubs, and native forbs occurred on the hillsides where soil depths and drainage were greater; perennial grasses common to the Palouse dominated the rest of the mission site.
Whitman Mission National Historic Site: General Management Plan, September 2000. U.S. Department of the Interior, National Park Service.
Marcus and Narcissa Whitman and the Opening of Old Oregon. Clifford M. Drury.1986. Northwest Interpretive Association, Seattle, Washington.