Much of the displacement between the Pacific and North American plates can be explained by movements on California faults other than the presently conspicuous segments of the San Andreas fault system. The faults are hypothesized to comprise three fault systems, in addition to the San Andreas fault system itself, along which there may have been a total of 400 km of pre-Eocene right slip. These three fault systems are (A) the Huasna, Suey, Little Pine, and Palos Verdes faults; (B) the Sur-Nacimiento, Pine Mountain, Newport-Inglewood, and Rose Canyon (?) faults; and (C) the Healdsburg, Jackson, Hayward, Calaveras, Reliz, Espinosa, San Antonio, Marcos, and Rinconada faults.

The San Andreas fault system formed in late Miocene time and developed sub-parallel to the three older fault systems. The San Andreas fault system obliquely transected fault system C, giving to the northern San Andreas fault an appearance of having the pre-Eocene right-lateral displacement of fault system C.

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