Do you know what an endangered species is? It's a plant or animal that is in danger of extinction. The bison, or buffalo, was an endangered species in the United States. Before Europeans came to America, huge numbers of bison roamed free on the prairies -- about 30 million! European settlers hunted them eagerly, believing that there would always be a continual supply of wild bison. Unfortunately, they were wrong. So many bison were hunted that by 1890 there were only 750 animals left. A law was passed to protect them, and today most bison live in parks and wildlife reserves.
Custer State Park was the first state park created in South Dakota, in 1897. It's also South Dakota's largest state park, covering 73,000 acres. The park contains lakes, prairies, and pine forests. These settings are the perfect homes for many kinds of wildlife, such as elk and bighorn sheep, like the rams in the photo. Herds of bison also live in the park. Today, there are about 80,000 to 90,000 bison, thanks to efforts to preserve the species.