Mojave Block

Mojave Block
Name	Mojave Block
Settlement type	Geological terrane
Coordinates	35°N 117°W
Subdivision type	Country
Subdivision name	United States
Subdivision type1	State
Subdivision name1	California
Area km2	60000

Mojave Block The Mojave Block is a crustal terrane in the southern California region characterized by distinctive fault-bounded geometry, lithologic assemblages, and tectonic behavior within the western North American Plate. It occupies a key position between the San Andreas Fault system, the Basin and Range Province, and the Transverse Ranges, and influences patterns of deformation, seismicity, and mineralization across Kern County, San Bernardino County, Los Angeles County, and Clark County, Nevada. Studies by the United States Geological Survey, California Geological Survey, and numerous universities have integrated paleomagnetic, geochronologic, and structural data to delineate its limits and evolution.

Geology and Tectonic Setting

The block is composed of crystalline basement, Proterozoic to Mesozoic metamorphic and igneous complexes, and Mesozoic to Cenozoic sedimentary cover exposed across the Mojave Desert, Kern River, Antelope Valley, and Victorville areas. Its tectonic context links the relative motions accommodated by the San Andreas Fault, the northwest-striking Garlock Fault, and the northeast-tilted extensional domains of the Walker Lane. Regional studies reference correlations to the Sierra Nevada Batholith, the Peninsular Ranges Batholith, and the Great Basin metamorphic framework. Paleomagnetic rotations and GPS geodesy from the Plate Boundary Observatory and UNAVCO indicate block-scale rotation and translation relative to the Pacific Plate and the North American Plate.

Boundaries and Structural Features

Boundaries are defined by the dextral San Andreas Fault system to the southwest, the left-lateral Garlock Fault to the northwest, and a complex transition to the Basin and Range Province to the northeast near Death Valley National Park and Mojave National Preserve. Internal structures include high-angle reverse faults, low-angle detachment systems associated with the Lone Pine Fault and Owens Valley Fault Zone in the broader region, and strike-slip splays such as the Landers Fault and Hector Mine Fault. Major basins—Antelope Valley Basin, Victor Basin, and Lucerne Basin—are filled with Neogene and Quaternary alluvium recording uplift and subsidence. Boundaries and thrust imbrications have been mapped by the USGS Southern California Mapping Project and researchers from Caltech, UCLA, and the University of California, Riverside.

Geologic History and Evolution

The terrane records a Paleozoic to Mesozoic history of passive margin deposition followed by Mesozoic arc magmatism tied to subduction beneath the North American Plate and emplacement of the Sierra Nevada Batholith. Cretaceous plutonism and associated metamorphism produced the crystalline core studied near Tehachapi Mountains and San Gabriel Mountains. Cenozoic strike-slip reorganization associated with the initiation of the San Andreas system during the Miocene produced crustal partitioning, transtensional basins, and late Neogene uplift of the Transverse Ranges. Quaternary volcanism in the region is expressed by Pleistocene basaltic fields near Amboy Crater and younger basalt flows in Mojave National Preserve. Thermochronology, including apatite fission-track and (U–Th)/He studies by teams at Stanford University and University of Southern California, constrains exhumation and cooling histories linked to Neogene deformation.

Mineral Resources and Economic Geology

The block hosts significant mineral occurrences including gold and silver veins in metamorphic terranes near Randsburg, barite and borates in evaporite basins such as around Searles Lake, and tungsten and rare earth element anomalies in alkaline complexes investigated near Cima Dome and Ivanpah Valley. Historic mining districts—Calico Mountains, Bridal Chamber Mine, and Goldstone exploration areas—reflect Laramide and subsequent hydrothermal episodes. Sedimentary basins yield aggregate, dimension stone, and groundwater resources exploited by municipalities like Lancaster, Palmdale, and Barstow. Resource assessments by the USGS Mineral Resources Program and the Bureau of Land Management inform land-use planning and federal leasing decisions.

Seismicity and Geohazards

Seismic behavior includes strain accumulation and episodic rupture on regional faults such as the San Andreas Fault, Garlock Fault, and splays like the Garlock–San Andreas junction where interaction has produced historic seismic events recorded in the Southern California Seismic Network. Notable earthquakes affecting the region include the 1857 Fort Tejon earthquake rupture footprint and the 1992 Landers earthquake sequence, which produced well-documented aftershock patterns across block boundaries. Hazards include fault rupture, ground shaking, surface faulting, liquefaction in basin deposits near Victorville and Barstow, and debris flows in upland drainages affecting Interstate 15 and State Route 58. Seismic hazard models by the Southern California Earthquake Center and USGS National Seismic Hazard Model incorporate block behavior for probabilistic forecasts.

Research History and Mapping

Early geological reconnaissance by the California Division of Mines and Geology and map compilations by Charles W. Jennings and R. F. Marvin established foundational mapping. Modern contributions include structural analyses and paleomagnetic studies by investigators at Caltech and UCLA, geochronology from USGS laboratories, and remote sensing studies using Landsat and LiDAR datasets. Key datasets and maps—compiled in cooperative projects with the California Geological Survey and the National Park Service—have refined fault traces, lithologic contacts, and Quaternary deposits. Ongoing academic theses at University of California, Santa Barbara, University of Nevada, Reno, and Arizona State University continue to test models of block rotation, slip partitioning, and crustal rheology.

Ecology and Human Land Use

The physiography influences ecosystems managed by the National Park Service and the Bureau of Land Management within Mojave National Preserve and Joshua Tree National Park buffer zones, supporting creosote scrub, Joshua tree woodlands, and desert tortoise habitat monitored by the U.S. Fish and Wildlife Service. Human land use includes military reservations like Edwards Air Force Base and Fort Irwin National Training Center, transportation corridors such as Interstate 15 and Interstate 40, and renewable energy projects sited near Ivanpah Solar Power Facility and Mojave Solar Project. Water resource management involves agencies like the Metropolitan Water District of Southern California and local water districts in Victor Valley coping with groundwater withdrawal and recharge issues.

Category:Geology of California Category:Structural geology Category:Mojave Desert