The Corps of Discovery relied heavily upon the geographic knowledge of Native peoples. They had been told of a set of impassable waterfalls high up on the Missouri River and finding them would indicate they were on the correct. However, in the late Spring of 1805, they reached a confusing confluence of two large rivers. Their Native informants had not mentioned such a large tributary - the Marias. The existence of this river puzzled the captains, who were unsure which river was the Missouri since the Marias matched it in size. Knowing the optimal months for travel were quickly passing, the captains spent a week on the decision, carefully evaluating each option knowing that a wrong choice would be costly. Eventually, Lewis and some men traveled up the Missouri where, to Lewis’ delight, they came across the Great Falls in June 1805. Lewis sent a message to Clark labeled “from the Great falls of the Missouri,” and Clark and his men rejoined the group.
Confident of their path, the captains believed the next portion of their journey to be easy, but they would find their information from Natives again incorrect. Although they had told Lewis and Clark “that the portage around the falls was not more than a half mile, the actual portage proved to be a torturous, eighteen-mile traverse that consumed more than a month of travelling season already far gone.” The water route was almost impossible to travel, forcing the group to continuously go on shore and walk, carrying their belongings. They encountered grizzly bears, rattlesnakes, and mosquitos, which created various problems and hardships for them. Eventually, they made it through the Great Falls and crossed the Missouri River, traveling onward to the west coast of the continent.
Today, Great Falls has a Lewis and Clark National Historic Trail Interpretive Center where visitors can learn more about the expedition, participate in activities that the Corps would have done, and learn about the plants and animals Lewis and Clark documented during their journey through the Falls.