<P> The route of Lewis and Clark's expedition took them up the Missouri River to its headwaters, then on to the Pacific Ocean via the Columbia River, and may have been influenced by the purported transcontinental journey of Moncacht - Apé by the same route about a century before . Jefferson had a copy of Le Page's book detailing Moncacht - Apé's itinerary in his library, and Lewis carried a copy with him during the expedition . Le Page's description of Moncacht - Apé's route across the continent, which neglects to mention the need to cross the Rocky Mountains, may be the source of Lewis and Clark's mistaken belief that they could easily carry boats from the Missouri's headwaters to the westward - flowing Columbia . </P> <P> The historian John L. Loos of Louisiana State University wrote William Clark's Part in the Preparation of the Lewis and Clark Expedition, a 511 - page manuscript published in 1954 by the Missouri Historical Society . </P> <P> Thirty - three people, including 29 participants in training at the 1803--1804 Camp Dubois (Camp Wood) winter staging area, then in the Indiana Territory, were near present - day Wood River, Illinois, on the east bank of the Mississippi . In March 1804, the Spanish in New Mexico learned from U.S. General James Wilkinson, later discovered to be a paid agent of the Spanish crown, that the Americans were encroaching on territory claimed by Spain . </P> <P> On August 1, they sent four armed expeditions of 52 soldiers, mercenaries, and Indians from Santa Fe northward under Pedro Vial and José Jarvet, to intercept Lewis and Clark and imprison the entire expedition . When they reached the Pawnee settlement on the Platte River in central Nebraska, they learned that the expedition had been there many days before, but because the expedition at that point was covering 70 to 80 miles (110 to 130 km) a day, Vial's attempt to intercept them was unsuccessful . </P>

Where did lewis and clark's expedition begin
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