250 Adventures in Scenery 



cessive Tertiary epochs occur. These do not lie regularly one 

 above another in order of age or time of deposition, but with 

 intervening gaps or skips (unconformities) , showing that the 

 sea withdrew and re-advanced over different parts during the 

 successive epochs of Tertiary time. 



Upheaval at Close of Tertiary Period 



The end of Tertiary and the beginning of Quaternary time 

 was marked by very profound disturbances affecting a large 

 area. During late stages of Tertiary time a great region of 

 southern California had been depressed and covered by the sea. 

 An upheaval of tremendous proportions followed, and the for- 

 mations that had been laid down during the successive epochs 

 since Cretaceous time were not only uplifted but were bent, 

 folded, and crumpled by earth contortions due to stresses in the 

 crust of the earth. Sediments which had been deposited in hori- 

 zontal layers were wrinkled, warped, and upturned so that they 

 now appear, where exposed in canyons or other outcroppings, 

 tilted at various angles and even in vertical position. Slipping 

 movement along old fault lines, and the forming of new faults 

 contributed to the mountain-building activities. The Santa 

 Ana Mountains were uplifted to approximately their present 

 height at about this time. 



This great disturbance which marked the close of Tertiary 

 time and the beginning of Quaternary was followed in early 

 Quaternary time by a widespread subsidence of the land. 

 Quaternary sediments were carried to the sea, or deposited in 

 valleys before reaching the sea. Deposits that now make up 

 large areas of the Coastal Plain were laid down during this time. 

 Later in Quaternary time upheaval brought these deposits high 

 above sea level. Terraces of great extent that now make up 

 parts of the Coastal Plain are these deposits which were thrown 

 down in horizontal layers over the bent, broken, crumpled and 

 deformed rocks and eroded edges of the Cretaceous and Tertiary 

 formations. In many valleys these have been cut in recent time 



