The park is marking the occasion with some special events, including dinner in the desert, a Native American cultural performance and a night sky presentation.
Although admission is free, normal camping and user fees still apply.
President Franklin Roosevelt signed a proclamation making Joshua Tree National Monument part of the national park system on August 10, 1936. The area became a national park when the Desert Protection Act was passed by Congress and signed by President Bill Clinton on Oct. 31, 1994.
For a schedule of the day's special events, visit the park's official website at www.nps.gov/jotr.