<P> The San Andreas began to form in the mid Cenozoic about 30 Mya (million years ago). At this time, a 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, separation of the Baja California Peninsula, and rotation of the Transverse Range . </P> <P> The main southern section of the San Andreas Fault proper has only existed for about 5 million years . The first known incarnation of the southern part of the fault was Clemens Well - Fenner - 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 . 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 . </P> <P> The fault was first identified in Northern California by UC Berkeley geology professor Andrew Lawson in 1895 and named by him after the Laguna de San Andreas, a small lake which lies in a linear valley formed by the fault just south of San Francisco . Eleven years later, Lawson discovered that the San Andreas Fault stretched southward into southern California after reviewing the effects of the 1906 San Francisco earthquake . Large - scale (hundreds of miles) lateral movement along the fault was first proposed in a 1953 paper by geologists Mason Hill and Thomas Dibblee . This idea, which was considered radical at the time, has since been vindicated by modern plate tectonics . </P> <P> Seismologists discovered that the San Andreas Fault near Parkfield in central California consistently produces a magnitude 6.0 earthquake approximately once every 22 years . Following recorded seismic events in 1857, 1881, 1901, 1922, 1934, and 1966, scientists predicted that another earthquake should occur in Parkfield in 1993 . It eventually occurred in 2004 . Due to the frequency of predictable activity, Parkfield has become one of the most important areas in the world for large earthquake research . </P>

Which type of plate boundary is in the southern coastal california region