FIGURE 3.13.-Western margin of North America, showing tectonic capture of part of the North American plate by the Pacific plate (plate-tectonic base modified from Moore, 1981). Captured part of the North American plate is now moving northwesterly with the Pacific plate and is commonly considered to be part of the Pacific plate. West boundary of captured part of the North American plate is inactive early transform fault with component of subduction (open sawteeth; see text); interfaces of the North American plate with remnants of the Farallon plate are active subduction zones (solid sawteeth).