84 



University of California Publications. 



[Geology 



of conglomerate were observed between the two, as seen on Yulen 

 Creek in Shasta County, and at Berkeley. 



Very little Eoeene strata were recognized in this field, 

 although they may exist in the lower foothills along the west 

 side of the Sacramento Valley beneath the late Tertiary sedi- 

 mentaries. The greater part of the territory to the west was 

 probably nnderoing erosion during this period. 



The present almost entire absence of Monterey in this large 

 field, when it is known to be developed so extensively farther 

 south, does not necessarily mean that the Monterey sea was con- 

 fined to Point Reyes Peninsula, but the occurrence of San Pablo 

 strata so near by, resting upon a very uneven Franciscan sur- 

 face free from Monterey, points to the region having been dry 

 land during Monterey times. 



In spite of the enormous length of this erosion interval, from 

 Eocene to the end of the San Pablo, the Franciscan does not ap- 

 pear to have reached the stage of a peneplain, and it is not until 

 the end of the Pliocene that we find it reduced to that form. 



The San Pablo strata are nowhere in contact with the known 

 Monterey, so that the relations between the two are not clear 

 in this field, it being impossible to tell whether there was an ele- 

 vation of the region during the time between their depositon 

 and that of the Monterey, or whether continuous sedimentation 

 went on. 



The blue San Pablo sandstone (tuff) at Cameros Creek indi- 

 cates that the andesitic detritus reached at least as far north 

 as the southern portion of this area. The sandstones and gravels 

 of supposed Orindan age in Petaluma Valley, containing lignite 

 beds and horse-teeth, indicate that lakes existed here during late 

 Miocene or early Pliocene times. 



Between the supposed Orindan and the Mark West Andesite 

 there is a glaring unconformity. Hence it is probable that be- 

 tween the Orindan and the Merced there was an erosion interval 

 followed by a gradual sidjsidence of the land, the sea encroach- 

 ing from the west toward the east on the area now roughly repre- 

 sented by Santa Rosa and Petaluma Valleys. Seemingly part 

 of the San Pablo beds to the west remained under water during 

 the elevation of those farther east, for along the Estero San Anto- 



