Lawson. ] 



Post-Pliocene Diastrophism. 



of demarkation between the Pliocene and the Mesozoic rocks, which 

 extends from Mussel Rock southeastward, is in part, also, the trace 

 of a post-Pliocene fault. The great slide on the north side of Mussel 

 Rock is near the land terminus of this fault zone, where it intersects 

 the shore line. Movement on this fault zone is still in progress. 

 A series of depressions or sinks, occupied by ponds, marks its 

 course. Modern fault scarps in the Pliocene terrane are features of 

 the country traversed by it. 



Thus we have at our doors, at the University of California, a 

 most wonderful chapter of geological history spread out for our 

 perusal, so that he who runs may read; all the more wonderful 

 because the events recorded are occurrences of but yesterday, and 

 are still in progress. To geologists this brief note on the Merced 

 series is but an announcement of some of the salient facts of a sub- 

 ject which the writer hopes to be able to discuss more fully in a 

 future paper. 



THE EVIDENCE FROM THE RIVER VALLEYS. 



The conception of the general uplift of the coast from the Golden 

 Gate to San Diego, which is forced upon us by a study of the coastal 

 topography , is fully confirmed by what is known of the topography 

 and geological character of the chief river valleys of the coast. The 

 more important of these are the (l) Santa Clara-San Benito, (2) 

 Salinas, (3) Santa Maria, and (4) Santa Clara of the South. Only 

 the first two of these have been examined by the writer; fortu- 

 nately, however, we have, also, useful information respecting the 

 other two. The evidence from these four valleys will be briefly 

 considered in the order named. 



The Santa Clara-San Benito Valley. — The Santa Clara Valley 

 is the continuation to the southeastward, between the Mount Ham- 

 ilton and the Santa Cruz Ranges, of the depression which contains 

 the Bay of San Francisco. It in turn passes without essential 

 change of character or of direction into the valley of the San 

 Benito River, which lies between the Mount Hamilton and Gavilan 

 Ranges. The three valleys, thus differently named the Bay of 

 San Francisco, the Santa Clara, and the San Benito, form a single 

 topographic feature. For this combined valley, whose essential 



