1919] Kew: Geology of a Part of the Santa Yncz River District 7 



The sedimentary strata- of the Franciscan series mainly consist of 

 sandstones and radiolarian cherts with a minor amount of shale. The 

 sandstones are massive, dark green in color, and arkosic. As a whole, 

 they show a marked similarity to those typically exposed around San 

 Francisco Bay. The cherts occur in relatively small patches, usually 

 as inclusions in the igneous rock, though they have been observed as 

 lenses in the sandstone. They show the characteristic banded struc- 

 ture and in some places are nodular. The shales occur mainly in a 

 small area at the head of the middle branch of Redrock Cafion and 

 are gray in color, rather soft, and contain numerous limestone nodules. 

 They resemble the Knoxville shales', but when traced to the east, are 

 seen to lie between beds of typical Franciscan rocks, such as the 

 radiolarian cherts. 



All the igneous rocks are of the basic type consisting mainly of 

 basalt and .serpentine with gradations into coarser grained diabase 

 and gabbro. The basalts have the characteristic pillow structure so 

 common in a similar rock of the San Francisco area. They are intrusive 

 in the sandstone, shale, and chert, as dikes, sills, and small laccoliths, 

 but have produced very little contact metamorphisra. All the in- 

 trusions follow the general strike of the Franciscan rocks, that is, a 

 northwesterly direction. On account of the great degree of ciisturb- 

 ance caused by the intrusion of the igneous rocks and later deforma- 

 tion, no attempt was made to separate the different rocks on the map. 

 The laccolithic structure is shown in the small area of ba.salt which 

 forms the red rock from which the canon of that name is taken. The 

 upper surface of this rock mass is rounded while the lower side or 

 bottom forms a steep almost overhanging cliif. Although on a very 

 small scale, this body of rock resembles closely a typical laccolith. 

 Serpentinization has not proceeded so far in some cases as in others, 

 the less altered rock containing numerous large bastite crystals and 

 some residual olivine. A serpentine, hydrometamorphosed to a silica- 

 carbonate rock,^ is exposed along the fault which parallels the Santa 

 Ynez River. This is usually a brown hard mass which shows very 

 little of the original serpentine. Cinnabar occurs in this and it has 

 been mined in a small way for many years. 



2 A more detailed account of the sandstones and cherts occurring in this area 

 may be found in two papers published by E. F. Davis, The Franciscan sandstone, 

 Univ. Calif. Publ. Bull. Dept. Geol., vol. 11, pp. 1-44, 1918, and The radiolarian 

 cherts of the Franciscan group, Univ. Calif. Publ. Bull. Dept. Geol., vol. 11, 

 pp. 2.3.5-432, 1918. 



3 Knopf, Adolph, An alteration of serpentine, Univ. Calif. Publ. Bull. Dept. 

 Geol., vol. 4, pp. 425-4.30, 1906. 



