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On the West coast of North America, the coast ranges and the coastal plain form the margin. Most of the land is made of [[terrane]]s that have been [[Accretion (geology)|accreted]] onto the margin. In the north, the insular belt is an accreted terrane, forming the margin. This belt extends from the [[Wrangellia Terrane]] in Alaska to the Chilliwack group of Canada.<ref name = Townsend2002>{{cite web|title = Northwest Origins|last = Townsend|first = Catherine|last2 = Figge|first2 = John|publisher = The Burke Museum|date = 2002|url = http://www.burkemuseum.org/static/geo_history_wa/}}</ref>
A rupture in [[Rodinia]] 750 million years ago formed a passive margin in the eastern Pacific Northwest. The breakup of [[Pangea]] 200 million years ago began the westward movement of the North American plate, creating an active margin on the western continent. As the continent drifted West, terranes were accreted onto the west coast.<ref name = Townsend2002/> The timing of the accretion of the insular belt is uncertain, although the closure did not occur until at least 115 million years ago.<ref name = Townsend2002/> Other [[Mesozoic]] terranes that accreted onto the continent include the [[Klamath Mountains]], the [[Sierra Nevada (U.S.)|Sierra Nevada]], and the Guerrero super-terrane of western Mexico.<ref name=Dickinson2004>{{cite journal|title = Evolution of the North American Cordillera|last = Dickinson|first = William|journal = Annual Review of Earth and Planetary Sciences|date = 2004|volume = 32|pages = 13–45|url = http://www.geo.arizona.edu/tectonics/Ducea/teaching/Dickinson2004.pdf|accessdate = 9 April 2013|doi = 10.1146/annurev.earth.32.101802.120257|
Although many of the ranges do share a common geologic history, the Pacific Coast Ranges province is not defined by geology, but rather by geography. Many of the various ranges are composed of distinct forms of rock from many different periods of geological time from the [[Precambrian]] in parts of the [[Little San Bernardino Mountains]] to 10,000-year-old rock in the [[Cascade Range]]. For one example, the [[Peninsular Ranges]], composed of Mesozoic batholitic rock, are geologically extremely different from the [[San Bernardino Mountains]], composed of a mix of Precambrian metamorphic rock and Cenozoic sedimentary rock. However, both are considered part of the Pacific Coast Ranges due to their proximity and similar economic and social impact on surrounding communities.
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