Among the accomplishments of the Lewis & Clark expedition, the “discovery” of more than 100 species of birds and mammals previously unknown to early scientists represented a fascinating trove of information for biologists. Trained to describe and sketch such species in preparation for their intrepid trek to the Pacific, the captains nonetheless encountered animals that scrambled their sensibilities. While camped with friendly natives in autumn after the expedition departed St. Louis, Clark observed a ladle made from the horn of an animal he estimated would hold two quarts. Some weeks later, Jean Valle, a trader, told them of an animal with “large circular horns nearly the size of an argali or small elk.”
On May 25, 1805, William Clark and two other hunters each killed what French explorers dubbed the “rock mountain sheep.” Members of the expedition had never seen animals like these. In their camp in the rugged breaks of the Missouri River in north-central Montana, Lewis painstakingly portrayed the creatures in one of the most complete descriptions he penned of any animal on the expedition. On the return trip down the Missouri and Yellowstone Rivers the following year, each of the captains took great pains to secure specimens of this creature, returning to civilization with the heads and hides of a half-dozen animals.
Some two centuries after Clark killed his first “rock mountain sheep,” the inquisitive eyes of