Roche Percée, or Pierced Rock, is a natural arch in the Big Manitou Bluffs that once served as a landmark for travelers on the Missouri River. Unknown French voyageurs and engages gave it its name, and a nearby stream eventually came to be called Perche Creek, a corruption of Roche Percée. In the late 18th and early 19th centuries, Perche Creek emptied into the Missouri River here, but because the river frequently changed course before levees and wing dikes, the creek’s mouth is now three miles south. William Clark noted “Split Rock” in his journal on June 6, 1804, and that name had already appeared on a map drawn by James Mackay in 1797. Other early travelers and fur traders also observed the arch, including Henry Brackenridge, who noted “Roche percée” in 1811 while traveling with Manuel Lisa of the Missouri Fur Company, the Stephen Long expedition, which passed by in 1819 on only the second steamboat to go up the Missouri and mentioned both “Roche a Piercè” and a creek of the same name, and Duke Paul of Württemberg, who described it in 1823 and referred to a nearby island as “Ill du rocher Percé” or Pierced Rock Island. Roche Percée and the Manitou Bluffs are composed of Burlington limestone, formed when shallow seas covered Missouri. Slightly acidic rainwater seeping into the rock dissolved the limestone, and where the water found an outlet along the bluff face, it created a hole that erosion gradually widened into a split or pierced appearance; this process continues, and the arch will eventually collapse. Although the arch can be seen from Katy Trail State Park, it is located within Eagle Bluffs Conservation Area, whose wetlands support many thousands of migrating waterfowl and shorebirds and whose name reflects the bald eagles present in winter.