The Map That Guided Lewis and Clark Up the Missouri

In 1803 most of the settlers around St. Louis spoke French. John Hay, the postmaster at Cahokia Courthouse, spoke both French and English, and he became an important link for Meriwether Lewis and William Clark. Hay had spent nearly twenty years in the fur trade, and he introduced the two captains to James Mackay — whose map of the Upper Missouri River became one of the expedition's key resources.

The map of the Missouri River that Lewis and Clark used on their 1804 expedition. Library of Congress, Geography and Map Division.

James Mackay

Mackay left Scotland for Canada in the 1770s and went to work for a British fur trading company. In 1787 it sent him overland to trade with the Mandan and Hidatsa villages on the Upper Missouri. By the early 1790s he was running his own trading company out of Cahokia.

The Evans expedition

In 1795 the Missouri Company, a Spanish trading firm, hired Mackay to lead an expedition up the Missouri; its investors wanted to trade with the Mandan villages he had visited years before. Mackay sent his assistant, John Evans, in his place. Evans kept detailed field notes, recording what he learned from Indigenous people who had traveled that stretch of river many times. Back in Cahokia, Evans and Mackay turned the information into a map covering the country from St. Charles, Missouri, to Mandan territory in what is now North Dakota.

Passed to Clark

Mackay shared the map with Clark, and it became an important tool as the expedition navigated the Missouri. Clark later drew his own map of the same territory — and, like Mackay, relied on Indigenous knowledge of its rivers, mountains, streams and trails.

Sources

• National Park Service, Lewis and Clark National Historic Trail: "Maps of the Missouri River," part of the series Pivotal Places: Stories from the Lewis and Clark National Historic Trail.