Mountains of the South 245 



Uplifted Sediments Worn Down, Submerged, 

 and Again Uplifted 



After the instrusion of the molten rock the region was up- 

 lifted and remained land during long geologic epochs. When- 

 ever any region is above sea level the rocks at the surface, how- 

 ever hard, are attacked by the weathering and eroding agencies 

 of heat and frost, wind and rain. The hardest rocks give way, 

 and slowly but ceaselessly the land surface is reduced back to- 

 ward sea level. The sediments which had been deposited on the 

 bottom of the Triassic sea and later intruded by molten rock, 

 uplifted, bulged upward into a vast anticlinal fold, now stood 

 as a land surface for long ages while streams eroded and the 

 lowering of the uplifted land went on. This continued for so 

 long that the once elevated land was worn down to a low plain 

 not much above sea level. 



Another epoch in the geologic history of the region was 

 ushered in. The land which had been reduced to a low essen- 

 tially flat plain sank so that it was covered by the sea. Gravels 

 and sands were deposited on the bottom of a shallow sea. These 

 deposits are now represented in the Topanga formation, which 

 is widespread in the Santa Monica Range, having a thickness of 

 approximately 5,000 feet. Basaltic lavas were poured out upon 

 the sea bottom or were forced into the consolidated rocks. The 

 disturbance involved in the volcanic activity resulted in the 

 outpouring of vast beds of lava, and upheaval occurred such 

 that the rocks were crumpled, folded, and faulted, and the 

 whole region involving the present mountain range was raised 

 in a dome-like ridge or arch (anticline) along the line of the 

 Santa Monica Range of today. 



The uplifting of this long dome or arch was followed by the 

 withdrawal of the sea, and the great arch became dry land. 

 The work of stream erosion started all over again. This all 

 involved a long time as measured in years, but it must be re- 

 membered that time is long in geologic history, and is marked 

 off in epochs or periods rather than in years. So let the imagina- 



