The central Ventura basin, containing at least 20,000 ft (6,000 m) of Pliocene and Pleistocene sedimentary rocks, has been long recognized as bounded by thrust faults--the north-dipping San Cayetano fault (SCF) on the north and the south-dipping Oak Ridge fault (ORF) on the south. Field investigations and synthesis of available surface and subsurface data show that the three strands of the SCF, here named the Main, Goodenough, and Piru, join at depth to form a single fault plane. The SCF shows a 30,000-ft (9,000 m) maximum separation in the Fillmore area where a possible structural downstep is stepped to the left along the Goodenough strand. The SCF loses the separation progressively eastward and within about 14 mi (22 km) the fault apparently disappears in the north flan of the Santa Clara Valley syncline. The ORF, exposed within the southeastern part of the study area, also loses its separation eastward and disappears along the axis of the syncline. The Main strand of the SCF was initiated during the deposition of the "Pico." West of Hopper Canyon, the fault involves movement during and after the deposition of the Pleistocene Saugus Formation. The SCF cuts late Quaternary deposits and should be considered as potentially active. Most of the folds in the upper (north) block, and all the folds in the lower (south) block of the SCF, were contemporaneous with fault movement.

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