South California-Landscape description

 South California

The region called southern California slowly assembled over billion years recycled through lithosphere (Earth, Crust and Mantle) or accumulated from precipitation and biological activity in the oceans. Majority of the continental crust that is now considered to be of California was accumulated from the crust that formed beneath the Pacific Ocean region. The phase of deposition occurs in many geological time scales (Allen, C. R., Amand, P. S., Richter, C. F., & Nordquist, J, 1965).

Precambrian History

Archean - The oldest rocks in North America are of Late Archean age and are generally exist in the Canadian Shield region and also in the Rocky Mountain region. In California, none of these rocks of age is found.

Early to Middle Proterozoic - 

The oldest rocks exist in California region belongs to metamorphic rocks in the region of Mojave Desert ranging from 1600 to 1800 million years old.

Late Proterozoic – The region of Mojave Desert experiences much uplift and erosion that wore down the mountain to gentle regional plane. The proof of this region is the Great Unconformity between underlying crystalline basement and overlying sedimentary rocks of Late Proterozoic age. In present time these rocks are locally exposed in region belonging to Eastern Mojave and Death Valley region. Passive- margin style deposition continues along with California margin (Durham, J. Wyatt, and Edwin C. Allison, 1960).

Paleozoic History- 

 A large sequence of sedimentary formations is preserved in California’s mountain region especially in the region of Mojave Desert and Death Valley Region. It consists of limestone and dolomite, which show the evidence of evolution of marine forms. The oldest sedimentary rocks of the Cambrian Period contain an abundance of fossil algae (stromatolites) and the abundance of early invertebrate fauna, including trilobites (Crowell, John C, 1975).

Mesozoic History

Triassic-Jurassic-Cretaceous Periods: In California's geologic past the Mesozoic Era was a turmoltuous time. In starting triassic time, an extensive volcanic-arc system started to work along the western margin of the North American continent. In Southern California, this volcanic arc would develop in complete Mesozoic Era to become the geologic regions known as the Sierra Nevada Batholith, plutonic and volcanic centers throughout the greater Mojave region and the Southern California Batholith (in the Peninsular Ranges). About 100 to 80 million years ago the igneous activity in the region of Southern California region was ongoing throughout the Mesozoic Era, the peak of the plutonism in the southern Sierra Nevada region was in the Late Cretaceous. The region was covered with terrestrial and marine sedimentary deposit that interfingered volcanic deposit. Most of the material was later on stripped by the erosion following uplift that continues in following Cenozoic Era.

Cenozoic History (Tertiary and Quaternary Periods)

Paleocene-Eocene-Oligocene: Subduction continued along the western North American continental margin through the early Tertiary Period. Moreover the volcanic-arc style igneous activity that had started in the previous Mesozoic Era along the region of Sierra Nevada and Peninsular Ranges region had slowed down. The volcanic activity started in farther east region of the Rocky Mountains region. Majority of the region of modern Southern California experiences extensive uplift and erosion. In the time period landscape wore down and converted to extensive pediment that consist of rolling lowlands having  few mountains bordered on the west by a coastal plain, shallow embayments, and coastal uplands.

Miocene:  Subduction through the western margin of the North American Continent steadily shifted to transform faulting in early Miocene time. This gradually occurred as the ancient Farallon Plate cease into the subduction zone and the North American Plate start coming in the contact with the Pacific Plate. During the Late Miocene time the Baja Peninsula started to separate from mainland Mexico and started the gradual migration northward. The rift valley between the Mexican mainland and Baja California which was generally flooded with marine-water conditions stretches northward in the Salton Trough region. 

Pliocene: The Climate cycles related with ice ages started to disturb the region. The event which starts to shape the height and extent of mountain ranges visible today includes the Uplift in the Peninsular, Transverse, and the Sierra Nevada, and Coastal Ranges, and eastern Mojave region. The great lakes started to form in the interior basins of the Mojave, Death Valley, and Great Basin with the cooling’s of climate.

Pleistocene: Along with the Pleistocene Period, modern river systems of the region consisting of the Mojave and Colorado Rivers evolve at the expense of older drainage systems that were disturbed or diverted by faulting, tectonic uplift, volcanism, or as interior basins filled and spilled over into adjacent valleys. Climate fluctuation occurred in intermittent periods of ice ages and warm periods. Through the cool, wet periods, alpine glaciers shape the canyons in the Sierra Nevada and great lakes flooded intermontane valleys. During the Each glaciations cycle Sea level rose and fell dramatically. During high sea level periods coastal valley flooded and back-filled with sediments and during low sea level periods streams carved downward into their valleys. During high-standing seas, ocean embayments covered the coastal plains and lowland basins along the coast. 

Holocene: Starting making populations migrated into the California region starting about 10,000 years ago (possibly earlier). Sea level seems to rise the having the peak of continental glaciation during the last ice age also known as Wisconsin age, about 15,000 years ago. During this sea level was as much as 120 meters (350 to 400 feet) lower than present levels. Many large mammalian species that lived in the region became extinct at the beginning of the Holocene Epoch. The California Gold Rush beginning in 1849 initiated one of the greatest human migrations in modern history (Jones, David L., M. C. Blake Jr, and Claude Rangin, 1976)