Hkrshey.] 



Quaternary of Southern California . 



17 



The first or highest terrace I should refer to about the 

 Illinoian epoch. This reference is made not alone upon a con- 

 viction derived from the study of the Quaternary in other parts 

 of Southern California that a marked uplift of the entire south- 

 ern portion of the State began at the close of the Red Bluff 

 ( Illinoian f) epoch, but is also based upon a study of the erosion 

 of the upper terraces of San Pedro Hill. It is difficult to express 

 this in exact terms. However, to a student of geomorphology, 

 the impression is inevitable that had these upper terraces been 

 exposed to the action of subaerial forces as long as has been 

 occupied in the erosion of the deep Sierran canons of the Sierra 

 Nevada region, they should not remain in a recognizable form 

 to-day. It must be understood that these upper terraces even 

 when newly completed, were very subordinate features of the 

 topography and no considerable layer of the rocks of San Pedro 

 Hill could be removed without destroying all traces of them. 

 Erosion since the uplift of the terraces has etched the hill on all 

 sides, but only in a minor degree modified its general topography. 

 All the territory along the coast of Southern California which 

 was submerged during any part of the period of terracing has 

 compai-atively smooth contours. If we transfer our attention to 

 the Sierra Madre and other ranges of Southern California or to 

 the Pliocene basin of the Sauta Clara Valley, and study the char- 

 acter of demonstrably post-Pliocene erosion, we are forced to the 

 conclusion that the oldest terraces on San Pedro Hill are young, 

 quite young, in comparison with the whole of Quaternary time. 

 They certainly belong to its latter portion. The Sierran canons 

 were already approaching completion when San Pedro Hill last 

 emerged from the sea as a tiny wave-swept rock. The Ozarkian 

 valleys of the Eastern States were completed, the Kansan ice- 

 sheet had come and gone in the Central Mississippi region, and 

 it is only when we reach the Illinoian epoch, in our imaginary 

 flight through time, that we turn our eyes westward and look 

 expectantly for that new island in the Pacific Sea. 



At the time that Lawson first investigated the marine terraces 

 of the California coast, the length and complexity of the Quater- 

 nary era and the significance of the Sierran valleys were not fully 

 appreciated by students in general and he was not favored 



