The movement of water in the American Falls Reservoir has eroded some fossil sites, making them much more accessible. One example of that was the discovery of two gigantic longhorn bison--Bison latifrons, to use the scientific name. The first skull was uncovered by Wayne Whitlow, a zoology teacher at Pocatello High School. He and a student, Woodrow Benson, excavated the fossil in 1933. The tip of one horn gave it away, sticking out from the side of a cliff that had been exposed by the lapping waters of the reservoir.
An even better specimen, an adult female bison nicknamed Mary Lou by Merle Hopkins who discovered it, was found along the shores of the reservoir in 1947. The replica of that skull—the original is too fragile to display—can be seen at the Orma J. Smith Museum of Natural History at the College of Idaho.
Long-horned bison have been extinct for a while. The Idaho specimens probably lived between 72,000 and 75,000 years ago. They would have been about 8 feet tall at the shoulder, weighing more than two tons, making them the largest and heaviest bison known.
For a fascinating story about long-horned bison and the digitizing of fossils at ISU, check this story by Jennifer Huang from Idaho Magazine.