In July and August 1806, Captain William Clark led part of the Corps of Discovery down the Yellowstone after the expedition divided at Traveler's Rest, crossing Bozeman Pass with 12 men, 49 horses, and a colt, then reaching the river near present-day Livingston and continuing to the Missouri confluence. Along the way, Clark recorded immense numbers of buffalo, elk, deer, antelope, wolves, beaver, birds, and bighorn sheep, showing both the abundance of wildlife that supplied meat, skins, and materials and the changes that later came to the river country, including the extinction of passenger pigeons and Audubon's race of prairie bighorn sheep. The party endured mosquitoes, lame horses whose feet were protected with buffalo-hide moccasins, delays in finding cottonwoods large enough for canoes, and the loss of their horses to the Crow, while also encountering signs of Native American life such as forts, ceremonial lodges, signal smoke, petroglyphs, and stone piles. Following Sacagawea's advice through familiar country, Clark split off another detachment under Ordway down the Missouri, named Pompey's Tower after Sacagawea's son, noted coal seams and red stone along the river, and finally used smaller cottonwoods lashed into canoes to continue down a fertile, navigable Yellowstone whose free-flowing waters shaped both the expedition's progress and the lives of wildlife and Native peoples.