Because of its size and the distances between
its major sights Joshua Tree is best visitied by car. In fact
it's impossible to visit without a car. As far as I know there
is no public transportation oferred inside the park. The car
should be in good mechanical condition especially if you're
visiting in summer. Gas is not available inside the park. A few
roads (for example the Geology Tour Road) are only recommended for
vehicles with 4-wheel drive or with high clearance.