hershkv.] Quaternary of Southern California . 



15 



the marine Pleistocene material but the rather Light rainfall of 

 Los Angeles, I conclude that the sea retreated and sub-aerial 

 erosion began on this portion of the formation at about the time 

 of the uplift of the Red Bluff formation proper in the Great 

 Valley; in other words, they are probably chronologic equiva- 

 lents. The latter formation seems to have been the result of 

 a depression of the Great Valley, perhaps part of it below 

 sea-level. I imagine that there was temporarily formed a great 

 shallow geosyncline, having its axis approximately parallel to 

 that of the Great Valley. This axis prolonged southward 

 would intersect the plain of Los Angeles. Why may not the 

 marine Pleistocene of Southern California and the terraces on 

 the coast he due to this same depression? I believe that the 

 Red Bluff subsidence was rather general throughout the broad 

 valleys of the State and has given rise to most of our Quaternary 

 deposits. This period of subsidence constituted the Red Bluff 

 epoch, and all the deposits due to it are parts of the Red Bluff 

 formation. It seems proper to extend the term Red Bluff to the 

 marine Pleistocene in Los Angeles and to the alluvial material 

 of the 400-foot terrace of Soledad Canon. 



In going from the town of San Pedro directly up to the 

 summit of San Pedro Hill (altitude 1482 feet) I counted ten 

 terraces including the flattened summit, besides traces of several 

 other strands too indefinite to more than notice. These terraces 

 mark elevated marine shore-lines and were fully described years 

 ago by Prof. A. C. Lawson* and have since been discussed by 

 various writers. The three lower terraces are broad and not 

 much dissected. They consist of loose, stratified sand and 

 some fine gravel — a formation very easily eroded by running 

 water. Narrow canons have eaten hack from each sea-cliff 

 into the body of each terrace but their floors rapidly rise, and 

 in the case of the broader terraces the inner portions remain 

 nearly undissected. The attitude of these terraces with their 

 steeply- sloping outer margin, is identical with that of the 

 loess terrace following the margin of the Iowan drift sheet in 

 Northwestern Illinois and Northeastern Iowa. The Iowan 



*Bull. Dept. Geol., Univ. Calif., vol. 1, No. 4. pp. 122-128. 



