The Farallon Plate was an ancient oceanic plate, which began subducting under the west coast of the North American Plate—then located in modern Utah—as Pangaea broke apart during the Jurassic Period. It is named for the Farallon Islands which are located just west of San Francisco, California.
Over time the central part of the Farallon Plate was completely subducted under the southwestern part of the North American Plate. The remains of the Farallon Plate are the Juan de Fuca, Explorer and Gorda Plates, subducting under the northern part of the North American Plate; the Cocos Plate subducting under Central America; and the Nazca Plate subducting under the South American Plate.
The Farallon Plate is also responsible for transporting old island arcs and various fragments of continental crustal material rifted off from other distant plates and accreting them to the North American Plate.
These fragments from elsewhere are called terranes (sometimes, "exotic" terranes). Much of western North America is composed of these accreted terranes.
Current state 
It is thought that much of the Farallon plate initially went under North America (particularly the western United States and southwest Canada) at a very shallow angle, creating much of the mountainous terrain in the area (particularly the southern Rocky Mountains).
A large fragment of the subducted Farallon plate is believed to presently be in the mantle under eastern North America. It is also speculated that the associated spreading center was also subducted and may be responsible for the rifting which has created the Basin and Range geologic province.
Geophysicists have discovered evidence indicating that large slabs of the Farallon Plate remain attached to the old subduction zone beneath portions of Washington State, Oregon, California, and Mexico.
See also 
- Schellart, W. P.; Stegman, D. R.; Farrington, R. J.; Freeman, J.; Moresi, L. (16 July 2010). "Cenozoic Tectonics of Western North America Controlled by Evolving Width of Farallon Slab". Science 329 (5989): 316–319. Bibcode:2010Sci...329..316S. doi:10.1126/science.1190366. PMID 20647465.
- Schmid, C.; Goes, S.; van der Lee, S.; Giardini, D (2002). "Fate of the Cenozoic Farallon slab from a comparison of kinematic thermal modeling with tomographic images". Earth Planet. Sci. Lett. 204: 17–32. Bibcode:2002E&PSL.204...17S. doi:10.1016/S0012-821X(02)00985-8.
- "Global plate reconstructions with velocity fields from 150 Ma to present in 10 Ma increments". Geological Survey of Norway.
- "Under California: An ancient tectonic plate". Brown University.
- Animation of the Farallon subduction, with special emphasis on the effects on the surface of western North America