On June 6, 1804, Lewis and Clark's Corps of Discovery passed this section of Missouri River bluffs and, five miles into the day, stopped at Roche Percée Natural Arch, which Capt. William Clark called Split Rock in his journal. At that time, the Missouri River ran past the natural arch, and Perche Creek entered the river here. The arch and the lower Missouri River were already well known to French explorers and traders long before Lewis and Clark, and later travelers also recorded descriptions of it. Clark took the name Split Rock from a map by Scotsman James Mackay, a trader and surveyor who had visited the expedition's winter camp to advise the captains about Missouri River geography; on his map, Mackay called Perchee Creek Split Rock Creek. Early river travelers called the arch roche percée, or pierced rock, and the modern name Perche Creek developed over time from the arch's name through forms including Roche a Piercè, Roche Percée, and Percee. Just above Split Rock Creek, Capt. Meriwether Lewis took a meridian altitude reading with his octant. The expedition then traveled another nine miles upriver and camped on the east side of the river. Earlier that morning, the party had repaired the keelboat's mast, which had broken two days before when the boat passed too close to shore and struck a sycamore branch. They were on the river by 7, while Clark was suffering from a sore throat and headache. That day the expedition saw signs of bison for the first time, though the nature of those signs was not specified; more signs appeared the next day at Big Monetou Creek near present-day Rocheport, but the animals themselves were not seen until June 28 near the confluence with the Kansas River. The expedition traveled with a large keelboat and two pirogues that could have carried as much as 30 tons of cargo, including gunpowder, Indian trade goods, a medical kit, non-perishable food, scientific instruments, reference books, tobacco, whiskey, and camping and cooking gear. The men likely reserved Army uniforms for important meetings with Indian tribes and wore military-issue fatigue clothing for everyday use until it was replaced by leather clothing, while at least one tailor, Pvt. Joseph Whitehouse, accompanied the party. After acquiring its first moccasins from a trading party on June 1, 1804, each member went through many pairs during the long journey across the continent.