Horse Thief Lake is a lake in Pennington County, South Dakota. It is approximately two miles northwest of Mount Rushmore, the closest lake to the monument. It appears to be the lake seen north of Mount Rushmore in the 2007 Disney movie National Treasure 2: Book of Secrets when the entrance to the secret golden city of Cibola is found. However, the lake that is actually in the film is nearby Sylvan Lake, which is just five miles southwest of Mount Rushmore.
The lake's name is derived from the fact a gang of horse thieves operated there.