Northern Prairie Wildlife Research Center
Douglas was a Scottish explorer and botanist who traveled in the Pacific northwest from 1824-1833 but didn't enter Montana during this period. His closest approach to Montana was the present site of Spokane, Washington and Lewiston, Idaho. Douglas kept excellent journals detailing his explorations and botanical discoveries. We recommend reading McKelvey's book for a detailed summary and bibliography of Douglas' work.
McKelvey, S.D. 1955. Botanical explorations of the trans-Mississippi west, 1790-1850. Arnold Arboretum of Harvard Univ., Jamaica Plain, MA.