On August 1, 1805, William Clark marked his thirty-fifth birthday by shooting a bighorn sheep while passing through the Jefferson River Canyon, and Sgt. Ordway recalled that Clark killed the mountain sheep from a flock on the south side of the river, after which the animal rolled down the steep cliffs and the party retrieved it and dined on it. When the Corps of Discovery traveled through this area, bighorn sheep were common, but later in the century hunting pressure and disease from domestic sheep wiped them out of the London Hills. Diseases transferred between domestic and wild animal populations, including lungworm, blue tongue, and especially pasteurella pneumonia, along with unchecked hunting, greatly reduced bighorn numbers in the western United States. The management plan for Lewis and Clark Caverns State Park calls for reintroducing bighorn sheep to the park, with the dry, rocky bunchgrass habitat seen as part of the setting for their return, and understanding these diseases and establishing wildlife management plans are presented as the means to help bring them back to this area.