| Until approximately 30 million years ago (MYA),
the Pacific Spreading Center operated as a continuous north-south
zone, creating crust of the Pacific Plate (moving west)
and the Farallon Plate (moving east). The oceanic Farallon Plate
subducted under the western margin of the continental
North American Plate, creating a coastal volcanic/intrusive
belt similar to today's Andes or Cascades, wherein solidified
granites of the Sierra Nevada, Klamath, and Peninsular Ranges.
Where major oceanic
fracture zones intersected the North American
coast, they propagated into -- and weakened -- continental crust. |
