A transform plate boundary is a margin between two lithospheric plates that constitutes a regional-scale transform fault. The best-known transform plate boundary is the San Andreas fault system, which accommodates the right-lateral displacement between the North American and Pacific plates. The northwards-moving Pacific plate is subducted at the Aleutian trench and at western Pacific island arcs. Western California, part of the Pacific Plate, comprises exotic terranes translated northwards and rotated through angles up to 90 degrees along the margin of the North American plate. In the north, the San Andreas fault system terminates at the Mendocino triple junction where it intersects the Mendocino Fracture Zone and Cascadia subduction. Here the North American and Pacific plates intersect the Gorda–Juan de Fuca plate. The easterly moving Gorda–Juan de Fuca plate is subducted beneath the American plate north of the San Andreas fault system termination forming...