Straddling the San Bernardino County and Riverside County border the park includes the higher Mojave Desert and lower Colorado Desert.
The higher and cooler Mojave Desert is the special habitat of Yucca brevifolia, the Joshua tree for which the park is named. It occurs in patterns from dense forests to distantly spaced specimens. In addition to Joshua tree forests, the western part of the park includes some of the most interesting geologic displays found in California's deserts.
The dominant geologic features of this landscape are hills of bare rock, usually broken up into loose boulders.
The flatland between these hills is sparsely forested with Joshua trees. Together with the boulder piles and Skull Rock, the trees make the landscape otherworldly.