You can get a free brochure at the visitor centre, but it is pretty sparse on details. There is no cell service in most of the park, so it's hard to look things up on the go. I was really glad I bought a map and guidebook. I used them to plan before the trip and also to choose where to go each day in the park. The best guidebook is The Complete Guide: Joshua Tree National Park by James Kaiser. It has a great overview on things to do in Joshua Tree, history of the area, geology, and animals as well as good descriptions of the main hikes. The map I used was the National Geographic Trails Illustrated Map for Joshua Tree National Park. Its an easy to read map with all the roads and trails marked, plus distance markers and points of interest. Plus it's waterproof and tear resistant so you can't wreck it. (I've wrecked so many maps! )