78 



University of California Publications in Geology [Vol. ll 



sented in this record may be open to donbt. On the north side of 

 Mount Diablo there is a marked disconformity between the Kirker 

 tuffs and sands and the Oligocene beds below, described a little fur- 

 ther on in this paper. If there was an erosion period between the 

 San Ramon formation and the Kirker sands of Sobrante Ridge sec- 

 tion, this might easily account for the former beds in that section 

 being so much thinner than to the south of the town of Walnut Creek, 

 where no tuff beds are present. More will be said about the correla- 

 tion of the different sections in a later part of this paper. 



San Ramon Formation on West Side of Syncline 

 Lithology. — On the west side of the San Ramon syncline, to the 

 southwest of the town of Walnut Creek, the beds of the San Ramon 

 formation have a thickness of about 525 feet, consisting for the most 

 part of a fine gray sandstone which in some localities has a bluish 



A ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 



Fig. 2. A northeast-southwest section through the San Ramon syncline (AA 

 on pi. 4). Ttj, Tejon; To, San Ramon; Tin, Monterey; Tb, Briones; Tsp, San 

 Pablo ; Tp, Pinole tuff ; Tor, Orinda ; Qtc, Quaternary. 



cast and is tuffaceous. A little above the middle of the section there 

 is a thin bed of a siliceous gray shale. This shale, as is suggested 

 later, is very possibly in part equivalent to the diatomaceous shales 

 of the Markley formation of the section on the north side of the moun- 

 tain. 



Relation to Tejon 



Relation to Tejon. — The San Ramon formation, as found on the 

 west side of the San Ramon syncline, shows an unconformable rela- 

 tionship to the Tejon (Upper Eocene). At one locality in the creek 

 bed about one-half mile south of the town of Walnut Creek, University 

 of California locality 1131. this contact may be seen separating the 

 beds of these two horizons. 



The uppermost beds of the Tejon, as exposed on the north bank 

 of the creek, consist of a soft bluish clay-shale which butts into the 

 basal sandstone of the San Ramon along an irregular contact with a 

 difference in strike of more than fifteen degrees. Only a few feet 

 distant on the south bank of the creek, a sandstone member, which, 

 on the north side of the creek, is below the shale, comes in contact 



