Two-Headed Calf, Sacrifice Cliff
The Yellowstone County Museum, on the access loop in front of Logan International Airport claims their stuffed 2-headed calf is "the most famous in the country." It looks in photos like your standard county museum mutant, but who are we to disagree?
The museum also exhibits a detailed miniature diorama depicting the Legend of Sacrifice Cliff. Sacrifice Cliff (or was it Skeleton Cliff?) is the place where in 1833 (or was it 1837?) a group of 16 (or was it 40?) Crow Indians rode their blindfolded horses over the side to satisfy the spirits and stop the smallpox epidemic killing most of the tribe.
No one knows exactly which cliff it is -- there are several candidates in Billings.