1 919] Keto : Geology of a Fart of th e San ta Yiicz Rivrr District 17 



deformation of the San Rafael ]\Iountain.s. Although only a small part 

 of the San Rafael Mountains was examined, the Little Pine Mountain 

 vicinity indicates a northeastward dipping series of rocks ranging in 

 age from Jurassic (?) to the end of the Miocene. These are faulted 

 on the south side by the Little Pine fault which is of pre-Fernando 

 age. In the area between these two faults is a belt of acutely folded 

 rocks, in greater part of Miocene age, though Franciscan and Tejon 

 strata appear between Oso and Redrock creeks. These three areas 

 constitute separate structural belts which will be described more in 

 detail. 



Three large faults cut this district in an east-west direction, tlie 

 longest being the Santa Ynez fault, which follows the north side of 

 the Santa Ynez Range and has evidently controlled the corrasion of 

 the river. The Redrock fault is comparatively short, but has brought 

 the Franciscan rocks up against the beds of the jMonterey group. North 

 of this fault, the Little Pine fault extends along the foot of Little Pine 

 Mountain and continues to the east, following the Santa Ynez River 

 Canon to Blue Canon. The age of the first is post-Pliocene, while 

 the latter two are pre-Pliocene. Several cross faults are present in 

 this region, which will be discussed in the section on detailed structure. 



DETAILED STRUCTUEE 

 Little Pine Mountain Area 

 This area includes all the territory lying north of the Little Pine 

 fault and extending east to Agua Caliente Creek. Little Pine Moun- 

 tain is composed of a block of northward dipping Franciscan and 

 Cretaceous strata overlain by beds belonging to the Monterey group. 

 The structure of the Franciscan series is complex and obscure, due 

 to the great amount of deformation chiefly caused by the large in- 

 trusions of igneous rocks. In general the sandstones and cherts strike 

 in a northwesterly direction, and the igneous rocks are intruded along 

 their bedding planes. The Cretaceous dips on the average about forty 

 degrees to the north, except in the ea.stern part of the area, where the 

 strata have been so acutely folded that the structure is obscure. Lying 

 upon the Cretaceous are two relatively small synclinal areas of 

 Miocene rocks. The eastern one lies directly north of the Santa Ynez 

 River and crosses Mono Creek at the ranger's cabin. The Monterey 

 group is here considerably less folded than the underlying Cretaceous 

 sand.stones and shales, and the syncline pitches east about five degrees 

 and gradually broadens. Near the junction of Blue Canon with the 



