SCIENTIFIC BACKGROUND 135 



sion of the Northwest trends into two groups is not 

 entirely satisfactory to me, and that the classification 

 used is probably more geographic than genetic. I have 

 placed the northwesterly faults of the Coast Range and 

 Submerged Continent Shelf in the older group and 

 these of mainland Southern California in the later. In 

 fact, many of the northwest fault lines shown on Plate 

 III are of the later age. 



FIRST GROUP OF NORTHWEST TRENDING 



STRUCTURES 

 It has been my opinion, based on the researches of 

 others in this field, that the Coast Ranges of North- 

 ern California present two aspects of structure, one 

 of which consists of more or less closely compacted 

 folds and faults of a North 40= west trend, and the 

 other of a later series of north-westerly faults which 

 may have paralleled them or cut slightly diagonally 

 across them. Others consider that both movements 

 are of similar age. The first group of structures was 

 supposedly produced by the Coast Range revolution of 

 late Miocene or Pliocene age. The second group of 

 movements was supposedly of Pleistocene age. The 

 structure of the Coast Range is now being thoroughly 

 described by Prcfessor Clarke of the University of 

 California in a paper to be presented soon. I defer any 

 opinions of my own on this subject to his. 



Conspicuous physiographic units occur in which the 

 older north-west structures are apparently outlined by 

 the master fault lines of later epoch. The San Ra- 

 fael Highland Block of the Coast Ranges, for ex- 

 ample, is bordered on either side by the Cuyama and 

 Sisquoc master rifts which may be of the later north- 

 west systems. It is not within my province or ability, 



