Two deserts, two large ecosystems primarily determined by elevation, come together in the park. Adding interest to this arid land are small stands of spidery ocotillo and cholla cactus. The higher, slightly cooler, and wetter Mojave Desert is the special habitat of the undisciplined Joshua tree , extensive stands of which occur throughout the western half of the park. Standing like islands in a desolate sea, oases, a third ecosystem, provide dramatic contrast to their arid surroundings. Five fan palm oases dot the park, indicating those few areas where water occurs naturally at or near the surface, meeting the special life requirements of those stately trees.
Oases once serving earlier desert visitors now abound in wildlife.
The park encompasses some of the most interesting geologic displays found in California's deserts. Rugged mountains of twisted rock and exposed granite monoliths testify to the tremendous earth forces that shaped and formed this land. Arroyos, playas, alluvial fans, bajadas, pediments, desert varnish, granites, aplite, and gneiss interact to form a giant mosaic of immense beauty and complexity. As old as the desert may look, it is but a temporary phenomenon in the incomprehensible time-scale of geology. In more verdant times, one of the Southwest's earliest inhabitants, members of the Pinto Culture, lived here, hunting and gathering along a slow moving river that ran through the now dry Pinto Basin.