On the afternoon of June 13, 1805, the expedition arrived at the first of the five falls. Lewis described the falls and made careful notes of the heights of each. The first and highest stood at almost 90 feet. From start to finish, the falls brought the level of the Missouri down almost 400 feet. Lewis' journal called the falls a "truly magnificent and sublimely grand object which has from the commencement of time been concealed from the view of civilized man."
The route around the series of falls presented one of the greatest obstacles faced by the expedition. Lewis and Clark had believed the portage around the falls would take a week at most. It took them a month to emerge from this ordeal.
The portage meant passing through 18 miles of mosquitoes, gnats, rattlesnakes, and grizzlies. Men in moccasins, harnessed to primitive wagons with wheels cut from tree-trunks, hauled six canoes and all their baggage over rutted buffalo trail covered in cactus. Eight trips each way were required to finish the job.
Rough weather assaulted them on the way. Hailstones that were "7 inches in circumference and waied 3 ounces, fortunately for us it was not so large (on the whole route) if it had we should most certainly have fallen victims to its rage as the men were mostly naked, and but a few with hats or any covering on their heads." Wind gales proved useful as "the men informed me that they hoisted a sail in the canoe and it had driven her along on the truck wheels." For a time it seemed they were actually sailing on land.
A flash flood nearly washed Sacagawea, her son, and Clark away on June 29, while the Corps moved through a ravine. Several pieces of equipment were lost in the torrent. On July 4, a celebration consumed the last of the company's alcohol. Mosquitoes and illness took a toll on many, including Sacagawea, but the portage that had begun June 21 was completed on July 15, 1805. The Corps of Discovery moved on to Three Forks and the Missouri Headwaters.