GEOLOGIC DATABASES CONTRIBUTE TO RESOURCE MANAGEMENT AND NATURAL HISTORY INTERPRETATION IN JOSHUA TREE NATIONAL PARK, SOUTHERN CALIFORNIA

Joshua Tree National Park (JOTR) lies within the eastern part of California’s Transverse Ranges province and straddles the transition between the Mojave and Sonoran deserts. Mountain ranges and basins in the Park exhibit an E-W physiographic grain controlled by left-lateral fault zones that form a sinistral domain within the broad zone of dextral shear along the transform boundary between the North American and Pacific plates.

The geologically diverse terrain that underlies JOTR reveals a rich and varied geologic evolution, one that spans nearly two billion years of Earth history. The Park’s treasured landscape is a culmination of this evolution, its landforms expressions of narrative threads woven through the pages of its geologic history. Crystalline basement in the Park consists of Proterozoic plutonic and metamorphic rocks intruded by a composite Mesozoic batholith of Triassic through Late Cretaceous plutons arrayed in NW-trending lithodemic belts. The basement was exhumed during the Cenozoic and underwent differential deep weathering beneath a low-relief erosion surface, with the deepest weathering profiles forming on quartz-rich, biotite-bearing granitoid rocks. Disruption of the basement terrain by faults of the San Andreas system began ca 20 Ma and the JOTR sinistral domain, preceded by basalt eruptions, began perhaps as early as ca 7 Ma, but no later than 5 Ma. Uplift of the mountain blocks during this interval led to erosional stripping of the thick zones of weathered quartz-rich granitoid rocks to form etchplains dotted by bouldery tors—the iconic landscape of the Park. The stripped debris filled basins along the fault zones.

Crystalline rocks in and around the Park are host to gold and iron deposits and the extraction of these mineral resources is now part of the Park’s cultural history. Water, a key resource in the desert setting of the Park, emerges as springs at oases along faults and is present in the fault-controlled basins. Faults in the Park form a tectonic link between the San Andreas Fault Zone just west of the Park and the Eastern California Shear Zone to the north and east, both source zones for major earthquakes.

U.S. Geological Survey geoscience investigations in JOTR have yielded an array of geological, geophysical, and geochronological data. We are assembling these datasets into a layered database.