GEOLOGY OF CARRIZO MOUNTAIN, CALIFORNIA 353 



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sediments. As the sea withdrew, the destructive forces of weather- 

 ing and the erosive forces of wind and running water became active. 

 The clays which had accumulated were now dry and were cut away 

 again by these forces. The process was not long continued and the 

 plain was not completed, those clay 

 areas which were capped by protect- 

 ing sandstones remaining as monad- 

 nocks above the wide valley floor. 

 This valley, occupied by an earlier 

 vigorous ancestor of Carrizo Creek, 

 was strewn with rounded river cobbles 

 brought from the higher mountains to 

 the west. South and east of Carrizo 

 Mountain large areas seem to have 

 been reduced at this period well 

 toward the condition of a peneplain. 

 This plain lies perhaps two hundred 

 feet above the later Pleistocene lake- 

 level with which it seems to have no 

 connection. It is regarded as an 

 earlier independent feature, perhaps 

 Pliocene in age. . 



After the formation of this par- 

 tially planed surface, over the soft 

 rocks of Carrizo Valley, some change 

 either in the relations of land and 

 sea, or of climatic conditions, enabled 

 the streams to dissect it again. 

 The result of this dissection, which 

 may well have been contemporaneous 

 with the last occupancy of the 

 Colorado Desert by the Gulf of 

 California, is seen in the Carrizo Creek bad lands of today. 



The last important element in the development of the geography 

 of this part of the desert was the formation and the disappearance 

 of the desert lake. So late is it, that the calcium carbonate incrus- 

 tations which it left on its western shore (Fig. 8) show but little 



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Fig. 10. — Columnar section of 

 rocks exposed in Garnet Canyon. 



