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California Geology Key concept: Major features of California Geography can be explained in terms of plate tectonics. Building California by Plate Tectonics • Many Years Ago California did not exist as it does today. • Nevada was thought by some scientists to be the continent’s west coast. • When Pangaea began to break up, the North American plate moved west. • The western part of the continent began a subduction era. • This Built California Ancient Plate Boundaries • Three major plates influenced California’s geological history -North American Plate -Farallon Plate -Pacific Plate • The Farallon Plate had convergent boundaries on both east and west sides. • As the Farallon plate subducted between the Pacific and North American plates, it disappeared. • Eventually the Pacific and North American Plates came together, the boundary became a transform boundary. Subduction and Volcanism • The subduction of the Farallon plate had two major results. - It caused rock to melt. - It caused chunks of rock to collide with North American Continent. Sierra Nevada Batholith • Because of Subduction, a large amount of magma formed in the lithosphere. • The magmas solidified and formed a batholith. • A batholith is a large mass of igneous rock that forms below the surface. The Cascadia Subduction Zone • Today the subduction zone extends from Northern California to Canada. • The result is a chain of volcanoes that extend the entire distance. • It is called the Cascadia Subduction Zone • During subduction, pieces of rock are scraped off the bottom plate, called accretion. • They accumulate and eventually form mountain chains called accreted terranes. • California’s coastal mountains where formed by accreted terranes. • California’s gold was collected in its rocks this way. San Andreas Fault System • California is home to the most famous transform boundary in the world. • On land the fault extends about 1000km, from U.S. /Mexican border to Northern California. • The San Andreas is thought to be a system of faults. Offset of San Andreas Fault • The Pacific and N. American Plate have been sliding past each other for many years. • Scientist study offset by matching unusual rocks separated by the fault • By measuring offset, geologists estimate the amount and rate of movement along the fault. Compression in Southern California • The San Andreas Fault bends around the Los Angeles area. • Because the fault is not a straight line, It is not 100% transform. • There are parts of it that are convergent. • The compression created the San Bernardino and San Gabriel Mountains, Plate Tectonics and California Landscape • Most of California's landscape has been formed by plate tectonics. • Even though most of the motion along the San Andreas is transform motion, compression has caused uplift along the plate boundary. Plate Tectonics and California Landscape continued • Major rivers and mountain valleys run northwesterly, because they run parallel to the plate boundary. • The Transverse Mountain ranges are only mountains that run East-West.