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The Lewis and Clark expedition, headed by Meriwether Lewis and William Clark, was the first organized expedition to cross Montana. This expedition followed the Missouri River across Montana to its source on the Beaverhead River. They crossed Lemhi Pass, descended the Bitterroot River and then crossed Lolo Pass. On the return trip, the expedition split into two groups near Lolo. Clark took a similar route back to the Three Forks of the Missouri and crossed the mountains to the Yellowstone drainage and then descended the Yellowstone River to its confluence with the Missouri River. Lewis ascended the Blackfoot River and crossed Lewis and Clark Pass down to the Missouri River. Lewis briefly explored the Marias River before descending the Missouri River to meet Clark on the Yellowstone River. This was a scientific expedition with the purpose of general exploration and discovery. The natural history notes recorded on this expedition are outstanding. Figure 1 shows the approximate route taken.

Bakeless, J.E.  1947.  Lewis and Clark: Partners in Discovery.  Morrow,  
     New York.

Burroughs, R.D.  1961.  The natural history of the Lewis and Clark
     expedition.  Michigan State Univ. Press.  East Lansing.  [Very good 
     for natural history information.]

Coues, E.  1883.  History of the expedition under the command of Lewis and 
     Clark.  Francis P. Harper, New York.       

Devoto, B. ed.  1953.  The journals of Lewis and Clark.  Houghton Mifflin, 
     Boston, MA.  

Eide, I.H.  1969.  American Odyssey: The journey of Lewis and Clark.  Rand 
     McNally, Chicago, IL. 

Gass, P.  1807.  Journal of the voyages and travels of the corps of 
     discovery under the command of Capt. Lewis and Capt. Clark of the 
     United States from the mouth of the River Missouri through the 
     interior parts of North America to the Pacific Ocean during the years 
     1804, 1805, 1806.  3rd ed. 1811. Philadelphia, PA.  [Sergeant Patrick 
     Gass accompanied Lewis and Clark on their travels across the 
     Louisiana Territory.]

Link, L.W.  1964.  The Lewis and Clark Expedition: From St. Louis, 
     Missouri to Pacific Ocean and return, with particular reference to 
     the Upper Missouri and Yellowstone Rivers.  Cardwell, MT.

Meehan, T.  1898.  The plants of the Lewis and Clark Expedition across the 
     continent, 1804-1806.  Proc. Acad. Sci. Phila. Jan 1898:12-49

Pursh, F.  1814.  Flora americae septentrionalis; or, A systematic 
     arrangement and description of the plants of North America; 
     containing, besides what have been described by preceding authors, 
     many new and rare species collected during twelve years of travels 
     and residence in that country. 2 vols. White, Cochrane & Co.

Thwaites, R.G., ed.  1904. Original journals of the Lewis and Clark 
     expedition, 1804-1806.  Dodd, Mead & Co., New York.  

Thompson, L.S.  1985.  Montana's Explorers: The pioneer naturalists.  The 
     Montana Magazine, Helena.

Walcheck, K.C.  1969.  Birds observed by Lewis and Clark in Montana, 
     1805-1806.  Proceedings of the Montana Acad. of Sci. 29:13-29.

Walcheck, K.C. 1976.  Montana wildlife 170 years ago.  Montana Outdoors 
     7(July-Aug.):15-30.