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.
The understanding of the Farallon Plate is rapidly evolving as details from seismic tomography provide improved details of the submerged remnants. Since the North American west coast shows a convoluted structure, significant work has been required to resolve the complexity. In 2013 a new and more nuanced explanation emerged, proposing two additional now-subducted plates which would account for some of the complexity.
As data accumulated, a common view developed that one large oceanic plate, the Farallon plate, acted as a conveyor belt, conveying terranes to North America's west coast, where they accreted. As the continent overran the subducting Farallon plate, the denser plate became subducted into the mantle below the continent. When the plates converged, the dense oceanic plate sank into the mantle to form a slab below the lighter continent.