William Clark and Meriwether Lewis set out on a historic expedition in 1804. The Hidatsa Indians had informed the two men that they would come across a large waterfall in Missouri once they approach the Rocky Mountains. The Hidatsa – who lived near present-day North Dakota- had traveled farther to the West and were an important source of information for the expedition. The Hidatsa had also informed the explorers that the portage around the falls would not exceed half a mile.
Accompanied by a group of 33, Lewis and Clark resumed their quest up the Missouri in April 1805. They kept time, and by early June, they were approaching the Rocky Mountains. They then encountered a puzzle that required careful thought: a fork where two large rivers converged.
The members were not sure which of the two rivers Missouri was. Most of the men believed that the river coming from the north was Missouri since it resembled River Missouri with its muddy turbulence. However, Lewis deviated from that idea. According to him, water from the Missouri would have been clear and fast running because it would only need to travel a short distance. His description tallied with the south fork.
The explorers had been looking forward to meeting the Shoshone Indians, from whom they were to obtain horses for their transportation over the Rockies. Therefore, choosing the wrong river meant they would never find these Indians, and their journey would be jeopardized.
Both Lewis and Clark agreed that they should proceed towards the direction of the south fork. All of their fellow explorers opposed their decision; however, as a precautionary measure, the captains made a decision that Lewis and a group of four would lead the way by foot. Their mission was to return and backtrack to the other river in case Lewis failed to come across the big waterfall that the Hidatsa had informed them about.
On June 13, 1805, four days after hurrying ahead of the expedition, Lewis, and four other men were overjoyed after arriving at the Great Falls of River Missouri. They had confirmed that the team was heading in the right direction. Lewis was happy to hear “the agreeable sound of a fall of water.” Lewis and his group had witnessed “the grandest sight” after they became the first white men to reach the Great Falls of River Missouri.
The discovery confirmed that the south fork was River Missouri while the northern fork was River Marias. If the explorers had chosen to follow Marias River, they would not have found the Shoshone Indians, yet they needed their horses to cross the Rocky Mountains.
Lewis rejoined with Clark after finding the falls and informed him about the good news. Their joy was, however, short-lived when they discovered that transportation around the Great Falls was a rigorous 18-mile trek over a harsh terrain. It was far from the easy half-mile journey that had been reported by the Hidatsa. The mission was later called The Great Portage and took the men almost one month to complete. The Great Falls Portage presented a challenging experience to both captains.
The expedition was moving ahead by mid-July before finding the Shoshone Indians a month later. The Shoshone Indians handed them the horses that were crucial in the success of their expedition.