i5o 



University of California. 



[Vol. 2. 



The regular and normal succession of these strata indicate a 

 gradual subsidence and retreat of the shore line, which probably 

 extended considerably eastward of the Olema Valley, as shown by 

 the character of the later Miocene sediments, which could hardly 

 have been deposited near shore, and by the fact also that farther 

 eastward the Miocene is known to occur upon the mainland. 

 Following the Miocene depression was an uplift and period of 

 erosion, during which the strata just deposited were subjected to 

 erosion, the extent of which cannot here be seen. There are 

 reasons, however, for believing it was considerable. Perhaps, also, 

 a portion of the folding of the series took place with this uplift, 

 though it may have been subsequently very much increased. 



As to the faulting that forms so conspicuous a feature of the 

 topography, it is not known to have had even its inception prior to 

 the close of this post-Miocene land period, but apparently it was 

 connected with the next succeeding movements of the land, the 

 records of which are best known outside of this field. The Plio- 

 cene of the Coast Ranges is known to contain at least two series of 

 deposits, the San Pablo 1 and the Merced," which are unconform- 

 ably related to each other. Both appear to be represented in the 

 near vicinity, though neither of them within the boundaries of the 

 peninsula. Near the town of Tomales are beds supposed to be of 

 San Pablo age, while near Baulinas are others that are probably to 

 be classed with the Merced. If these suppositions are correct, the 

 development of the fault seems to have been progressive from the 

 beginning of the Pliocene. The San Pablo formation is not known 

 to the west of this fault-line, either here or elsewhere, while the 

 Merced seems to be confined in its distribution to the immediate 

 vicinity of the coast. The evidence afforded by this peculiar 

 circumstance seems to indicate that the oscillations of the two 

 contiguous blocks have been independent throughout the Pliocene, 

 and that the faulting began with a subsidence which covered at least 

 a large portion of the mainland with San Pablo marine deposits. 



The re -elevation of this block was perhaps accompanied by a 



1 Bull. Dept. Geol. Univ. Cal., Vol. 2, No. 4; Jour. Geol., Vol. 6, No. 6. 

 2 15th An. Rept. U. S. Geol. Sur., pp. 409-476. 



