Image of subduction of Farallon plate removed for copyright reasons.
Though the arc has rolled back and reestablished itself in along the western edge of NA, complications we about to begin regarding the subducting oceanic crust. Around 38ma, the Farallon plate (the eastern side of the north pacific spreading ridge) was about to be subducted into the trench. At 29ma the spreading ridge has begun to be subducted beneath the edge of NA, establishing a transform fault at the boundary between the Pacific plate and North America. Through time, more of the oceanic spreading ridge is pulled into the subduction zone and the right lateral transform fault extends over a greater and greater extent of the western edge of NA. The oblique convergence of the two plates drives the right-lateral motion along this transform fault, now known as the San Andreas fault system. (Owner unknown.)