The Lewis and Clark Expedition passed beneath this bluff early on June 9, 1804, after camping the night before on Island of Mills near Arrow Rock Island. William Clark recorded the nearby “Prairie of the Arrows,” or Arrow Rock, an old geographic name among many lower Missouri River landmarks named by Europeans who had explored and traded there for a century before the expedition passed. On June 8 the party had met three fur traders returning from the Big Sioux River, about 850 miles above the Missouri’s mouth, the fifth trading party encountered since leaving St. Charles, and they also found a cache of canteens, axes, pumice stone, and furs hidden and buried on the island. After passing the prairie on June 9, the keelboat’s stern struck a submerged log, the current swung the bow around, and the boat became caught in snags clogged with driftwood while large trees drifted downriver in its path. Crewmen quickly jumped into the river, swam ashore with a rope, and freed the boat within minutes, prompting Clark to praise the party’s skill. The accident was one of many dangers the expedition faced on the Missouri, where logs, moving sand, collapsing banks, and a strong spring current repeatedly threatened the keelboat and two pirogues. Heavy May and June rains had raised the river, and the Corps of Discovery had not yet reached the most difficult stretch between the Grand and Kansas rivers. Earlier at Retrograde Bend the boat had nearly been lost, but by June 9 the crew had shown that they could handle the fifty-five-foot deep-drafted keelboat with a level of ability Clark considered equal to the best French boatmen in St. Louis.