Editing San Andreas Fault (section)

== Formation ==
[[File:San Andreas Fault Sequential Diagrams.jpg|thumb|upright=1.4|Tectonic evolution of the San Andreas Fault]]
The San Andreas began to form in the mid-[[Cenozoic]] about 30 [[Mya (unit)|Mya]] (million years ago).<ref>[[Tanya Atwater|Atwater, T.]], 1970, Implications of Plate Tectonics for the Cenozoic Tectonic Evolution of Western North America</ref> At this time, a [[Seafloor spreading|spreading center]] between the Pacific plate and the [[Farallon plate]] (which is now mostly subducted, with remnants including the [[Juan de Fuca plate]], [[Rivera plate]], [[Cocos plate]], and the [[Nazca plate]]) was beginning to reach the subduction zone off the western coast of North America. As the relative motion between the Pacific and North American plates was different from the relative motion between the Farallon and North American plates, the spreading ridge began to be "subducted", creating a new relative motion and a new style of deformation along the plate boundaries. These geological features are what are chiefly seen along San Andreas Fault. It also includes a possible driver for the deformation of the [[Basin and Range Province|Basin and Range]], separation of the [[Baja California peninsula]], and rotation of the [[Transverse Range]].

The main southern section of the San Andreas Fault proper has only existed for about 5 million years.<ref>{{cite journal |author1=Powell, R.E. |author2=Weldon, R.J. |year=1992 |title=Evolution of the San Andreas fault |journal=Annual Review of Earth and Planetary Sciences |volume=20 |pages=431–468|doi=10.1146/annurev.ea.20.050192.002243 |bibcode=1992AREPS..20..431P }}</ref> The first known incarnation of the southern part of the fault was Clemens Well-Fenner-[[San Francisquito Canyon|San Francisquito]] fault zone around 22–13 Ma. This system added the [[San Gabriel Fault]] as a primary focus of movement between 10–5 Ma. Currently, it is believed that the modern San Andreas will eventually transfer its motion toward a fault within the [[Eastern California Shear Zone|eastern California shear zone]]. This complicated evolution, especially along the southern segment, is mostly caused by either the "Big Bend" and/or a difference in the motion vector between the plates and the trend of the fault and its surrounding branches.