Tectonism near Cape Mendocino is ascribed to the north-northwestward migration of the Mendocino triple junction; it is characterized as a process in which the wedge of continental plate left in the wake of the retreating subducted extension of the Juan de Fuca plate is pushed and folded back by the advancing corner of the Pacific plate. Between Late Jurassic and Paleocene time, a different type of triple junction in which the oceanic plate and its obliquely subducting continuation advanced rather than retreated, herein named the Humboldt type, transited the western side of the continental plate. The laterally advancing subducted extension of the oceanic plate uplifted and snowplowed aside the continental plate, resulting in up-heaval, disruption, and gravity sliding of deep elements of the crust, including blueschist. The melange of the Franciscan Complex is a product of successive transits of Humboldt- and Mendocino-type triple junctions along the western edge of the continental plate.

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