Surface and subsurface data determine the San Gabriel fault geometry and history of faulting in the Honor Rancho area. The northwest-trending, east-dipping San Gabriel fault consists of two strands: an older, concave-upward strand, which becomes low angle at depth, and a younger, high-angle, planar strand. The two strands merge to form one high-angle fault southeast of the Wayside Honor Rancho oil field. West of the San Gabriel fault zone the Modelo Formation (lower and upper Mohnian) overlies granitic basement. West of the fault, the Modelo and Towsley (Delmontian) Formations are in fault contact with the Castaic Formation present only east of the older San Gabriel fault strand. The marine Castaic Formation (lower and upper Mohnian) unconformably overlies the nonmarine M nt Canyon Formation of middle to late Miocene age. The Pico Formation (Pliocene) unconformably overlies older strata on both sides of the fault. Despite lithologic similarities of the Pico on both sides of the fault, markers within the formation cannot be correlated across the fault. The Saugus Formation (Pleistocene) unconformably overlies the Pico Formation and correlates well across and within the fault zone. Ease of correlation suggests that most of the right slip along the San Gabriel fault occurred prior to late Pliocene time. There appears to have been no lateral offset during Pleistocene and Holocene times, but primarily vertical displacement has occurred since the deposition of the Saugus Formation. However, seismic studies infer that right-slip activity is still present at dept along the San Gabriel fault.

End_of_Article - Last_Page 522------------