The Bighorn River is a tributary of the Yellowstone, approximately 461 miles (742 km) long, in the states of Wyoming and Montana in the western United States. The river was named in 1805 by fur trader François Larocque for the bighorn sheep he saw along its banks as he explored the Yellowstone.The upper reaches of the Bighorn, south of the Owl Creek Mountains in Wyoming, are known as the Wind River. The two rivers are sometimes referred to as the Wind/Bighorn. The Wind River officially becomes the Bighorn River at the Wedding of the Waters, on the north side of ... Source: Wikipedia