Joshua Tree National Park Geologic Formations

Joshua Tree National Park is located in southern California on the eastern end of the broad mountainous belt called the Transverse Ranges, which stretch from Point Arguello, 50 miles west of Santa Barbara, eastward for nearly 300 miles to the Eagle Mountains in the Mojave Desert. Unlike most mountain ranges in North America that run north-south, the Transverse Ranges lie on an east-west axis.

Within the park there are six distinct mountain ranges: the Little San Bernardino Mountains in the southwestern part; the Cottonwood, Hexie, and Pinto Mountains in the center; and the Eagle and Coxcomb Mountains in the eastern part. Both the southern and northern margins of the park are marked by steep escarpments that rise abruptly from the lower desert areas. Much of the park lies at elevations above 4,000 feet. Between the park's numerous mountain ranges, there are valleys, which are classified according to their method of formation.

Queen Valley and Lost Horse Valley were formed by a difference in the rate of erosion between the rock underlying the valley itself and the rock composing the surrounding mountains. The mountainous rock is more resistant to erosion and therefore rises above the valleys. Pleasant Valley, on the other hand, was formed by down-dropped motion along faults that formed basins (called grabens). Some valleys have playas: lakes that may contain water a few weeks a year during the rainy season.