Geology and geological history of California
One of the most important events was the advent of the San Andreas Fault around 29 million years ago in the Oligocene, when the region subducted a spreading center in the East Pacific Rise.
Active subduction began in the Triassic during the Mesozoic, producing large granite intrusions and the beginning of the Nevadan Orogeny as well as more dryland conditions and the retreat of the ocean to the west.
Simultaneously island arcs and small sections of continental crust rafted onto the edge of North America, building out the continent.
The Franciscan subduction complex makes up the basement rock for part of the range, with a mélange dominated by graywacke first deposited in offshore deep ocean basins.
Sur Series schist, quartzite, marble, gneiss and granulite in the Salinian block were likely deposited in a marine shelf late in the Paleozoic.
The Coast Range is at even higher risk for damaging landslides than other parts of coastal California due to sheared serpentinite in Franciscan basement rocks.
It formed as a sandspit filled in to the north from sediment deposited by the Tijuana River and sheltered from wind and waves by the Cretaceous uplands of Point Loma.
[7] The Klamath Mountains formed as small island arc terranes accreted against the coast of North America before and during the Devonian and overlain by newer rocks, deposited from the Cretaceous to modern times.
The Josephine ophiolite forms the basement of the western Klamath Mountains, with extensive peridotite from the boundary between the oceanic crust and the mantle, as well as chromite and nickel deposits.
The thick Galice formation slate and metamorphosed greywacke overlie the Josephine ophiolite and likely deposited in a deep ocean environment offshore of the island arc.
The Western Paleozoic and Triassic Plate is the most common unit of the Klamath Mountains and is up to 50 miles (80 km) wide at the Oregon state line.
Geologists have struggled to define its structural geology with complex sequences of deep ocean crust, upper mantle rock and tectonic melanges.
Fast flowing rivers meant that the region has accumulated very little alluvium, except for a rare 400-foot (120 m) thick deposit in Scott Valley, southwest of Yreka, California.
The Warner Basalt is the most common rock in the plateau, bordered by the Surprise Valley fault zone that first became active in the Miocene 15 million years ago.
[9] The Mojave Desert extends into areas of Basin and Range terrain and includes some of the oldest rocks exposed at the surface in California.
[10] At the edge of the Los Angeles coastal plain and just west of the San Joaquin Hills, Newport Bay is a major hub of boating.
A thick sequence of mostly terrestrial sedimentary rocks including the Rosario, Ladd, Trabuco and Williams formations is exposed on the western slope of the Santa Ana Mountains and Santa Ana Canyon, stretching southward to Camp Pendleton, San Onofre, and smaller exposures in Encinitas, Leucadia, Point Loma and La Jolla.
Much more recent Pliocene terrestrial sedimentary rocks are also common in the northern Peninsular Ranges like the San Timoteo Canyon and Mount Eden conglomerate, sandstone and siltstone which are up to 7,000 feet (2,100 m) thick.
The bay system was the second place in the US to be mapped in 1826 by Edward Belcher and Alex Collie, a surveyor and surgeon respectively on the British vessel HMS Blossom.
Based on the presence of flat-topped guyot undersea volcanoes with geology similar to the bedded cherts and pillow lavas of the In the Shoo Fly complex, the Bullpen Lake sequence has bedded cherts and cooled pillow lava that closely resembles rocks found on flat-topped offshore volcanic guyots, suggesting a deep-sea origin for the base of the Sierras sometime before the Devonian.
The Foothill Metamorphic Belt likely came ashore as an island arc terrane, colliding with the edge of North America to the west of the current Melones fault zone.
twenty-five thousand feet (7,600 m) of Jurassic marine sediments in the Sacramento Valley do not necessarily correspond exactly to the height of the mountains, but fist-sized cobbles in conglomerates from the Cretaceous suggest steep conditions and potentially higher altitudes than today.
North of the San Joaquin River, the mountains have a tilted-block pattern caused the Sierra Nevada fault, which is interpreted as being similar to the more common Basin and Range terrain to the east.
Volcanic eruptions in the Miocene between 9.5 and 3.5 million years ago filled old eroded canyons in parts of the Sierras with lava flows.
[14] The Transverse Ranges extend from Point Arguello to Joshua Tree National Park, bounded by the San Andreas Fault to the north.
Up to 1,000 feet (300 m) of sandstone and red shale deposited during the Eocene, after which sea levels dropped in the Oligocene preserved the sand, gravel and silt of the Sespe Formation.
All of these rocks were uplifted in the Pleistocene at the same time as the Coast Range orogeny and formed an anticlinal arch or tilted block against the Santa Ynez fault in the north.
Initially, hydraulic mining was used to get at placer deposits, but it destroyed the landscape and choked rivers with sediments, ultimately being banned the California government in 1884.
These sulfide minerals derive from the Copley Greenstone and or sea floor vents when the region was far offshore and formed as hot water "invaded" the Balaklala rhyolite.
In the late 20th century, enough gold was found in association with mercury, arsenic, tungsten and thallium to open the McLaughlin mine in the Mayacmas Mountains around Knoxville.
