82 Adventures in Scenery 



Coast Ranges and in the Great Valley of California which lies 

 between. 



Region of Coast Ranges Sinks 

 and Rises 



In a basin on the Peninsula on which the city of San Fran- 

 cisco is built sediments had accumulated during Pliocene time 

 to a thickness of more than a mile. The valley bottom sank 

 as sediments accumulated till this (Merced) formation reached 

 this astounding thickness. At the close of Tertiary time this 

 area was upheaved so that the basement on which these sedi- 

 ments were deposited stood far above sea level. The extent of 

 this upheaval shows the magnitude of the mountain-building 

 (orogenic) earth movements that closed the Tertiary period. 



At the end of the period of uplift, which extended well into 

 the Quaternary period, a general subsidence took place. At the 

 end of this subsidence a great uplift again occurred, the land 

 being raised probably higher than at present. The uplift took 

 places by stages, as is attested by terraces that mark the Pacific 

 Coast. A wave-cut terrace is the mark made by the waters 

 where land and sea meet. Submerged cliffs or banks off-shore 

 show that what had been shore has subsided now below sea level. 



North of the Golden Gate a striking wave-cut terrace at Bo- 

 linas is 2 5 feet above the cliff that is now being cut by the waves. 

 South of this the Marin Peninsula between Bolinas and San Fran- 

 cisco Bay has undergone depression. This depression or sinking is 

 associated with the complex crustal movements which enabled 

 the sea to enter San Francisco Bay by way of the Golden Gate. 

 The recent subsidence of San Francisco Bay has been estimated 

 at 300 to 400 feet. The earth movements about San Francisco 

 Bay are complex and will be considered in another chapter. 



Terraces showing uplift of the land are conspicuous at many 

 points along the coast. Near Santa Cruz terraces occur at 100, 

 250, 500, and 800 feet above the present waves, showing suc- 

 cessive uplifts of the shore. At Half Moon Bay a terrace that 



