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At the time of Lewis & Clark’s expedition, this map represented the best information available about the western United States.
Aaron Arrowsmith was considered the finest mapmaker of his day. He produced his first map of North America in 1795 from data collected from the archives of the Hudson’s Bay Company. Arrowsmith’s 1795 map shows a vestige of the "Great River of the West" and the Missouri River appears as a river fragment unconnected to either the single ridge of the "Stony Mountains" or the Mississippi River. Arrowsmith notes that the "Stony Mountains" are "3250 Feet High Above the Level of their Base and according to the Indian account is five Ridges in some parts."
The 1802 revision of the map of North America delineates the complete length of the Missouri River. Although the revised map still shows a single ridge of mountains in the west, a note placed near the southern sources of the Missouri states: "Hereabout the Mountains divide into several low Ridges." This note, which was based on the reports of Fidler, Mackenzie, and Thompson, was more encouraging to Jefferson and Lewis than the note about the Stony Mountains on the 1795 map, which, unfortunately, turned out to be more accurate. Arrowsmith’s map situates the Great Lake River on the western slopes of the mountain range and connects this river to the Columbia River with a dotted line. Since another note claims that this river can be descended to the sea in eight days, the Arrowsmith map supported the erroneous belief in a convenient route to the Pacific Ocean.
Arrowsmith’s map was probably the most important map used in planning the Lewis and Clark Expedition. Nicholas King consulted both the 1795 and 1802 versions as he prepared his map for the expedition. Lewis and Clark, in fact, carried the 1802 Arrowsmith map along on their journey. Thomas Jefferson owned the 1802 map of North America, which was the most comprehensive map of the West available at the time.
Map courtesy of The Library of Congress, Washington, D.C.
Text courtesy of Lewis & Clark: The Maps of Exploration 150718 14, Special Collections, University of Virginia Library. www.lib.virginia.edu/speccol/exhibits/lewis_clark/planning3.html
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A 365Kb PDF of this article as it appeared in the magazine—complete with the map—is available by clicking HERE