Geologic map of the Sawmill Mountain quadrangle, Kern and Ventura Counties, California

The Sawmill Mountain quadrangle is located in the western Transverse Ranges of California, about 10 km west of Frazier Park. It includes Mt. Pinos, Mt. Abel (Cerro Noroeste), a part of the southern San Emigdio Mountains, and straddles an eleven-kilometer reach of the nearly east-west striking "Big Bend" section of the San Andreas Fault.
South of the San Andreas Fault, the oldest rocks include undated amphibolite-grade biotite and hornblende-biotite gneiss that is probably early or middle Proterozoic in age. The older gneiss is intruded by strongly deformed and foliated biotite orthogneiss that has an age on biotite of 67.2+0.5 Ma (Late Cretaceous). Several other weakly foliated to massive Late Cretaceous granitic plutons intrude the orthogneiss, one of which has a 40Ar/39Ar on biotite of 65.9+0.2 Ma. The youngest granitic pluton, the coarse-grained, locally porphyritic granite of Mt. Pinos, is undated, but assumed to be Late Cretaceous in age. These granitic and gneissic rocks were thrust northward over Pelona Schist, which has a 40Ar/39Ar age on muscovite of 63.24+0.26 Ma. All crystalline rocks were subsequently thrust westward on the Abel Mountain thrust over rocks of the Miocene Caliente Formation.
A thick section of Eocene to Pliocene sedimentary and igneous rocks is exposed in the quadrangle. In the south part of the quadrangle, lacustrine and fluvial sediments and basaltic volcanic rocks of the Plush Range Formation are in fault contact with Eocene marine shales and, across the Big Pine fault, are mostly in fault contact with rocks of the Miocene Caliente Formation; locally, the Caliente unconformably overlies the rocks of the Plush Ranch Formation. The Caliente is unconformably overlain by the distinctive Lockwood Clay, which is successively overlain by the Pliocene Quatal and Morales Formations.
Rocks north of the San Andreas Fault are mostly Early Cretaceous tonalite and granodiorite containing strongly hornfelsed roof pendants of marble, metasandstone, and metapelite. Some of these rocks have been thrust over a mid-Tertiary marine section of sandstones and silicic shales.
The San Andreas Fault zone is as wide as 0.7 km and occupies a valley across most of the quadrangle. It is characterized by linear scarps, grabens, sag ponds and contains several enigmatic fault-bounded phacoids of exotic rocks apparently derived from many kilometers east of the quadrangle. Many of the prominent scarps probably resulted from the giant Ft. Tejon earthquake of 1859.