North American Plate
As the Pacific-Farallon Ridge began its subduction underneath the North American plate 30 million years ago, its southern segment, the East Pacific Rise continued spreading. The East Pacific Rise did not begin its subduction under the North American Plate until 20 million years ago, and the presently surviving portion of the East Pacific Rise is the Pacific-Nazca segment. The present-day spreading from the East Pacific Rise dominates the spreading regime in the Central and South Pacific.