In early
Triassic
The Triassic ( ; sometimes symbolized 🝈) is a geologic period and system which spans 50.5 million years from the end of the Permian Period 251.902 million years ago ( Mya), to the beginning of the Jurassic Period 201.4 Mya. The Triassic is t ...
time, an extensive
volcanic arc
A volcanic arc (also known as a magmatic arc) is a belt of volcanoes formed above a subducting oceanic tectonic plate, with the belt arranged in an arc shape as seen from above. Volcanic arcs typically parallel an oceanic trench, with the arc ...
system called the Sierran Arc began to develop along the western margin of the
North America
North America is a continent in the Northern Hemisphere, Northern and Western Hemisphere, Western hemispheres. North America is bordered to the north by the Arctic Ocean, to the east by the Atlantic Ocean, to the southeast by South Ameri ...
n continent. In
Southern California
Southern California (commonly shortened to SoCal) is a geographic and Cultural area, cultural List of regions of California, region that generally comprises the southern portion of the U.S. state of California. Its densely populated coastal reg ...
, this volcanic arc would develop throughout the
Mesozoic Era
The Mesozoic Era is the era of Earth's geological history, lasting from about , comprising the Triassic, Jurassic and Cretaceous Periods. It is characterized by the dominance of archosaurian reptiles such as the dinosaurs, and of gymnosperms s ...
to become the geologic regions known as the
Sierra Nevada Batholith
The Sierra Nevada Batholith is a large batholith that is approximately 400 miles long and 60-80 miles wide which forms the core of the Sierra Nevada mountain range in California, exposed at the surface as granite.
The batholith is composed of ...
, the
Peninsular Ranges Batholith, (in the
Peninsular Ranges
The Peninsular Ranges (also called the Lower California province) are a group of mountain ranges that stretch from Southern California to the southern tip of the Baja California peninsula; they are part of the North American Pacific Coast Range ...
), and other
plutonic and volcanic centers throughout the greater
Mojave Desert
The Mojave Desert (; ; ) is a desert in the rain shadow of the southern Sierra Nevada mountains and Transverse Ranges in the Southwestern United States. Named for the Indigenous peoples of the Americas, indigenous Mohave people, it is located pr ...
region.
[ Douglas M. Morton, Fred K. Miller, Peninsular Ranges Batholith, Baja and Southern California, Geological Society of America, 2014]
/ref>
Geology
These massive belts of plutonic (intrusive) and volcanic (extrusive) regional belts and isolated centers developed as plate convergence and subduction
Subduction is a geological process in which the oceanic lithosphere and some continental lithosphere is recycled into the Earth's mantle at the convergent boundaries between tectonic plates. Where one tectonic plate converges with a second p ...
took place farther west along the western continental margin
A continental margin is the outer edge of continental crust abutting oceanic crust under coastal waters. It is one of the three major zones of the ocean floor, the other two being deep-ocean basins and mid-ocean ridges.
The continental marg ...
. These igneous provinces shed vast quantities of sediment both eastward into the Western Interior Seaway
The Western Interior Seaway (also called the Cretaceous Seaway, the Niobraran Sea, the North American Inland Sea, or the Western Interior Sea) was a large inland sea (geology), inland sea that existed roughly over the present-day Great Plains of ...
and westward into Pacific margin basin. At the same time, older sedimentary materials and rocks were subjected to regional metamorphism
Metamorphism is the transformation of existing Rock (geology), rock (the protolith) to rock with a different mineral composition or Texture (geology), texture. Metamorphism takes place at temperatures in excess of , and often also at elevated ...
throughout much of Baja and Southern California
Southern California (commonly shortened to SoCal) is a geographic and Cultural area, cultural List of regions of California, region that generally comprises the southern portion of the U.S. state of California. Its densely populated coastal reg ...
. In the region today, granitic rocks of Mesozoic age dominate the bedrock exposed in the Peninsular Ranges, western Transverse Range, the southern Sierra Nevada, and the greater Mojave region.[
Although igneous activity in the 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 Cretaceous ( ) is a geological period that lasted from about 143.1 to 66 mya (unit), million years ago (Mya). It is the third and final period of the Mesozoic Era (geology), Era, as well as the longest. At around 77.1 million years, it is the ...
, about 100 to 80 million years ago. In addition, thick sequences (accumulations) of Mesozoic-age sedimentary rocks, mostly marine shale
Shale is a fine-grained, clastic sedimentary rock formed from mud that is a mix of flakes of Clay mineral, clay minerals (hydrous aluminium phyllosilicates, e.g., Kaolinite, kaolin, aluminium, Al2Silicon, Si2Oxygen, O5(hydroxide, OH)4) and tiny f ...
s and sandstone
Sandstone is a Clastic rock#Sedimentary clastic rocks, clastic sedimentary rock composed mainly of grain size, sand-sized (0.0625 to 2 mm) silicate mineral, silicate grains, Cementation (geology), cemented together by another mineral. Sand ...
of Jurassic
The Jurassic ( ) is a Geological period, geologic period and System (stratigraphy), stratigraphic system that spanned from the end of the Triassic Period million years ago (Mya) to the beginning of the Cretaceous Period, approximately 143.1 Mya. ...
and Cretaceous age, are locally preserved along the western side of the Peninsular Ranges and throughout the western Transverse Ranges
The Transverse Ranges are a group of mountain ranges of Southern California, in the Pacific Coast Ranges physiographic region in North America. The Transverse Ranges begin at the southern end of the California Coast Ranges and lie within Santa Ba ...
in parts of the Santa Monica Mountains
The Santa Monica Mountains are a coastal mountain range in Southern California, next to the Pacific Ocean. It is part of the Transverse Ranges. The Santa Monica Mountains National Recreation Area encompasses this mountain range. Because of its p ...
and mountainous Los Padres National Forest
Los Padres National Forest is a United States national forest in Southern California, southern and central California. Administered by the United States Forest Service, Los Padres includes most of the mountainous land along the California coast ...
region north of Santa Barbara, California
Santa Barbara (, meaning ) is a coastal city in Santa Barbara County, California, of which it is also the county seat. Situated on a south-facing section of coastline, the longest such section on the West Coast of the United States excepting A ...
. A thick sequence of terrestrial sedimentary rocks are also preserved in the McCoy Mountains region near Blythe, California
Blythe () is a city in eastern Riverside County, California, United States. It is in the Palo Verde Valley of the Lower Colorado River Valley region, an agricultural area and part of the Colorado Desert along the Colorado River, approximatel ...
. Except for the sedimentary rocks mentioned above, most of the Mesozoic-age rocks in preserved in Southern California display intermediate to high grades of metamorphism, typical of material that may have been buried to mid-crustal depths (probably in a range of 10 to 20 kilometers). Although the region was no doubt extensively covered with terrestrial and marine sedimentary deposits that interfingered volcanic deposits from the volcanic centers, most of this material was stripped away by erosion following regional uplift that continued into the following Cenozoic Era
The Cenozoic Era ( ; ) is Earth's current geological Era (geology), era, representing the last 66million years of Earth's history. It is characterized by the dominance of mammals, Insect, insects, birds and flowering plant, angiosperms (floweri ...
.
See also
* Nevadan orogeny
The Nevadan orogeny occurred along the western margin of North America during the Late Jurassic to Early Cretaceous approximately 155 Ma to 145 Ma. Throughout the duration of this orogeny there were at least two different kinds of orogenic process ...
References
{{reflist
Geologic provinces of California
Sierra Nevada (United States)
Transverse Ranges
Peninsular Ranges
Santa Monica Mountains
Mesozoic volcanism
Volcanic arcs