The Lewis and Clark Expedition: What They Were Actually Doing

Meriwether Lewis and William Clark entered what is now Montana on April twenty-seventh, eighteen oh five, moving up the Missouri River with thirty-three people, including Sacagawea and her husband Toussaint Charbonneau as interpreters. They spent a large share of their journey in what is now Montana, on the way west and again on the way home. Over the whole journey, the expedition described more than two hundred new species of plants and animals that American science had never formally recorded.

Thomas Jefferson had sent them for reasons that were simultaneously scientific, commercial, and imperial. He wanted to know what the Louisiana Purchase territory contained, whether there was a navigable water route to the Pacific, and what the existing political landscape looked like in terms of the Indigenous nations who controlled the land. The answer to the second question, a navigable water route, was no: the Rocky Mountains made that hope impossible. The answers to the other questions shaped American policy toward the West for the next century.

Montana is where the expedition encountered the Blackfeet for the only time, in a meeting that ended with Lewis's men killing two young Blackfeet men over stolen horses on the Marias River in July of eighteen oh six. It was the only lethal confrontation the Corps of Discovery had with any Indigenous people on the entire journey, and it set the tone for Blackfeet-American relations for decades afterward.

In Montana you are following a river system they described in precise detail. The scientific notes Lewis kept on this terrain, the plants he pressed and the animals he catalogued, arrived in Philadelphia as the basis for a new understanding of the continent. The journals themselves are held at the American Philosophical Society and have been published in full. They are worth reading. The country Lewis described is still recognizable from them.