304 University of California Publications in Geology [Vol. 10 



SALINAS VALLEY 



The Santa Margarita is extensively exposed along the Nacimiento 

 and San Antonio Rivers several miles west of San Miguel, San Luis 

 Obispo County. The formation here consists of a grayish-white sand- 

 stone several hundred feet in thickness, resting on banded siliceous 

 Monterey shale. The unconformity between these formations in this 

 vicinity is very marked, so that while the Monterey has been intensely 

 folded and faulted, the overlying Santa Margarita usually has rela- 

 tively gentle dips. The lithology and included fauna indicate that 

 this formation was here deposited near the ocean shore. Prom the 

 distribution of these sandstones it is evident that the Santa Lucia 

 Mountains were at this time above water and that the sediments must 

 have been derived from this range. Also it is evident that following 

 the folding of the Monterey, prior to or during Lower San Pablo time, 

 this range was subjected to extensive erosion and probable mountain- 

 making movements, while during the Upper San Pablo, or Santa Mar- 

 garita time, an extensive transgression occurred. From the sand- 

 stones near the base on the north side of the Nacimiento River, about 

 eight miles west of San Miguel, the following fauna was obtained : 



The Santa Margarita also has a large areal extent in the eastern 

 part of Monterey County along tributaries entering the Salinas River 

 from the east. Among these may be mentioned Cholame Creek, Vine- 

 yard Creek and Indian Valley. This formation at some localities 

 shows exposures estimated at 1200-2000 feet, consisting essentially of 

 shale in many respects lithologically similar to the Monterey. On 

 Vineyard Creek in the lower portion of the formation, are found 

 highly fossiliferous beds of sandstone and conglomerate with a typical 

 Santa Margarita fauna. Above the Santa Margarita in this region 



Santa Margarita Fauna from Nacimiento Eiver 



Bryozoa, sp. 

 Brachiopod, sp. A. 

 Astrodapsis antiselli Conrad 

 Astrodapsis margaritanus Kew 



(Gray) 

 Pecten raymondi Clark 

 Pecten sancti-ludovici Anderson 



Ostrea, sp. (small) 

 Pecten estrellanus Conrad 

 Pecten (Hinnites) giganteus 



(MS) 

 Calyptraea, sp. 

 Crepidula, sp. 

 Lima, sp. 



Metis alta (Conrad) 

 Mytilus kewi Nomland 

 Ostrea titan Conrad 

 Ostrea titan corrugata, n. var. 



and Martin 

 Pecten, sp. A. 



Sehizothaerus, cf. nuttalli Conrad 

 Trophon perelegans, n. sp. 

 Turritella, sp. 

 Balanus coneavus Bronn 



