<P> The timing of the accretion of the insular belt is uncertain, although the closure did not occur until at least 115 million years ago . Other Mesozoic terranes that accreted onto the continent include the Klamath Mountains, the Sierra Nevada, and the Guerrero super-terrane of western Mexico . 80 to 90 million years ago the subducting Farallon plate split and formed the Kula Plate to the North . Many of the major batholiths date from the late Cretaceous . As the Laramide Orogeny ended around 48 million years ago, the accretion of the Siletzia terrane began in the Pacific Northwest . This began the volcanic activity in the Cascadia subduction zone, forming the modern Cascade Range, and lasted into the Miocene . As extension in the Basin and Range Province slowed by a change in North American Plate movement circa 7 to 8 Million years ago, rifting began on the Gulf of California . </P> <P> The Sierra Madre mountain ranges of Mexico are separated by the Mexican Plateau, and transected by the Trans - Mexican Volcanic Belt . The Southern extent of the American Cordillera makes up Western Mexico and northern Central America . This includes the Sierra Madre Occidental, the Sierra Madre del Sur, and the Trans - Mexican Volcanic Belt . </P> <P> The Cordillera ends in the south in a belt of miogeoclines, including the Sierra Madre Oriental fold and thrust belt, the Mesa Central, and parts of the Sierra Madre del Sur . This belt also extends into Guatemala and Honduras in Central America . </P>

Much of the western north american continent was formed by