Editing Lewis and Clark Expedition (section)

== Prior discoveries ==
{{See also|Timeline of European exploration|Exploration of North America}}

In 1682, [[René-Robert Cavelier, Sieur de La Salle]] traveled down the Mississippi from the Great Lakes to the Gulf. The French then established a chain of posts along the Mississippi from New Orleans to the Great Lakes. There followed a number of French explorers including [[Pedro Vial]] and [[Pierre Antoine and Paul Mallet]], among others. Vial may have preceded Lewis and Clark to Montana. In 1787, he gave a map of the upper Missouri River and locations of "territories transited by Pedro Vial" to Spanish authorities.<ref>[[#Loomis|Loomis & Nasatir 1967]] pp. 382–386, map: p. 290</ref>

Early in 1792, the American explorer [[Robert Gray (sea captain)|Robert Gray]], sailing in the ''[[Columbia Rediviva]]'', discovered the yet to be named [[Columbia River]], named it after his ship and claimed it for the United States. Later in 1792, the [[Vancouver Expedition]] had learned of Gray's discovery and used his maps. Vancouver's expedition explored over {{convert|100|mi|km}} up the Columbia, into the [[Columbia River Gorge]]. Lewis and Clark used the maps produced by these expeditions when they descended the lower Columbia to the Pacific coast.<ref>[[#Ambrose|Ambrose, 1996]] p. 70, 91</ref><ref>[[#Woodger|Woodger, Toropov, 2009]] pp. 191, 351</ref>

From 1792 to 1793, [[Alexander Mackenzie (explorer)|Alexander Mackenzie]] had crossed North America from Quebec to the Pacific.<ref>{{Cite web|url=https://www.britannica.com/biography/Alexander-Mackenzie-Scottish-explorer|title=Sir Alexander Mackenzie &#124; Scottish explorer|website=Encyclopedia Britannica|access-date=June 23, 2020|archive-date=June 15, 2020|archive-url=https://web.archive.org/web/20200615031156/https://www.britannica.com/biography/Alexander-Mackenzie-Scottish-explorer|url-status=live}}</ref>