1913] 



Louderback: The Monterey Series 



221 



is conjectural." The beds are said to be 1700-1800 feet thick 

 around the Vallecitos and to consist of sandstone and conglom- 

 erate interbedded with thick layers of siliceous diatomaceous 

 shale. 



McKittrick-Sunset Region. Arnold and Johnson, 1910. — A 

 discussion of the territory to the south of the Coalinga district 

 is contained in the "Preliminary report on the McKittrick- 

 Sunset Oil Region" (1910) by Arnold and Johnson. 00 The 

 "Vaqueros sandstone (lower Miocene)" is described as for the 

 most part uniformly arenaceous, but near Annette and upon 

 the southwest side of the Carrizo Plain the sands evidently in 

 part grade into light colored shales closely resembling the Mon- 

 terey 10 (p. 43). It is given as from (30 to 2400 feet thick. These 

 are of course F. M. Anderson's "Temblor beds." 



The "Monterey shale (lower middle Miocene)" in which 

 F. M. Anderson and others had included "the whole of the 

 prominent series of white shale extending uninterruptedly from 

 just east of Polonio Pass southeastward along the flank of the 

 Temblor Range nearly to Temblor ranch, and to the great area 

 of shale embracing practically all of the range from the head 

 of Salt Creek southeast to the limits of the region studied," was 

 separated into two formations, "one of which is thought to be 

 the equivalent of the Santa Margarita (?) formation (upper 

 middle Miocene) in the Coalinga region, while the earlier more 

 closely resembles the Monterey (lower middle Miocene) as it 

 has been described in other parts of the state. Definite palaeon- 

 tologic evidence for the separation in the McKittrick-Sunset 

 region has been scant. . . . The main consideration involved in 

 the present separation of the rocks, however, is one of convenience 

 to the prospector. Since there is a marked difference in the 

 physical appearance of the rocks, it simplifies an understanding 

 of the geologic and structural conditions" . . . (pp. 55-50). 



"The lowest portion of the series is usually made up of 

 calcareous and arenaceous shales which represent a transition 

 into the sandstones and fossiliferous beds of the Vaqueros. These 

 grade upward into typical siliceous and argillaceous shales that 



««U. S. Geol. Surv. Bull. 40(3 (1910). 

 7,1 Italics not in original. 



