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University of California Publications in Geology [Vol. ll 



number could be obtained. Some of the larger boulders are over a 

 foot in diameter and usually consist of a hard, calcareous, gray sand- 

 stone. Some are quite angular and apparently could not have been 

 transported far. It seems probable that they were derived from a 

 cliff in the vicinity of the beach during Monterey time. 



Summary of Section of San Ramon Formation, Including the Upper Part of 

 the Tejon and the Lower Part of the Monterey, Measured 

 About Two Miles to the South of Walnut Creek 



<- Claremont shale. 

 Sobrante sandstone. 



85 feet — Coarse sands and thin layers of shale ; shallow- 

 water deposits, 

 k. 15 feet — Coarse basal conglomerates. 



Discpnformity 

 San Ramon formation. 



210 feet — Fine, light gray sandstone; not very hard; out- 

 crops very poor. 

 20 feet — Fairly hard, siliceous gray shale ; laminations not 

 distinct. 



290 feet — Fine gray sandstone which, for the most part, 

 is not well indurated; part of this sandstone has a 

 bluish cast and is tuff aceous ; thin lentals of harder, 

 calcareous, fossiliferous gray sandstone are quite com- 

 mon. 



3 feet — Coarse gray tuffaceous sandstone. 

 Unconformity 



25 feet — Fine yellowish brown sandstone ; not very hard ; 

 exposures few. 



About 6 feet — Hard, massive, calcareous gray sandstone. 

 About 50 feet — Shaly sandstone and soft, argillaceous shale ; 

 exposures few. 



Fault 



San Ramon Formation on East Side of San Ramon Syncline 



Occurrence and Lithology. — Beds of the San Ramon formation are 

 found about three miles to the east of the section just described and 

 on the east limb of the same syncline. These outcrops occur on the 

 first ridge to the north of Shell Ridge near the east edge of the Con- 

 cord Quadrangle, where they have a thickness of only between fifty 

 and seventy-five feet. They consist mostly of a fine gray sandstone 

 similar to the basal Agasoma gravidum beds south of Walnut Creek, 

 and are overlain by coarse, cross-bedded sandstones and conglomerates 



Basal beds of 

 Monterey Group 

 (Area montereyana 

 zone) 



San Lorenzo 

 series 



Tejon 



