Coasts 



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Figure 8. Palos Verdes Hills viewed toward southsoutheast across Palos Verdes Point. Six raised terraces are easily 

 visible, the lowest one clearly beveling deformed Middle Miocene siliceous shales at an elevation of 125 to 150 feet. 

 Note the presence along most of the cliff of talus largely covered by vegetation. The ship is the Gratia stranded 

 during a storm in 1932. Photographed by Fairchild Aerial Surveys in 1933. 



the ocean can reach the sea cliffs, one of the 

 most important processes by which it erodes 

 is abrasion and impact by the stones that 

 the water moves. The well-known rattle of 

 a gravel beach is probably intensified to a 

 roar when the ocean waves are large enough 

 to move boulders against the base of a sea 

 cliff. Such waves are infrequent enough in 

 southern California to allow sharp-edged 

 solution basins and pits to develop on 

 boulders at the base of sea cliffs, yet move- 

 ment of large boulders is noted on photo- 

 graphs taken several years apart (Fig. 9). 

 Occasionally we can also find gravel and 

 pebbles driven tightly into cracks of sea 

 cliffs in such a way that it is clear that the 

 driving force was upward. The ability of 

 the ocean to throw stones is attested to by 

 many records of broken lighthouse windows 

 cited by Johnson (1919, p. 68) and Cornish 

 (1912) and by the windows and siding of 

 houses at Redondo, California, broken by 

 stones thrown by storm waves (Fig. 10). 



Stones up to 5 cm in diameter were seen to 

 be thrown more than 100 feet through the 

 air and over the Redondo sea wall in Jan- 

 uary 1953. Similar observations at the base 

 of sea cliffs during storms are virtually im- 

 possible to make, so the role of abrasion 

 must be based on indirect evidence. Such 

 evidence as the presence at the base of cliffs 

 of smoothly concave surfaces of hard un- 

 weathered rock and of deep potholes con- 

 taining one or more tool stones are evidence 

 of abrasion. Impact by rocks thrown against 

 the cliff is more likely to be indicated by 

 broken-off former projections. 



Hydraulic action developed by sudden 

 pressure of water against a sea cliff and by 

 its rapid retreat is an erosional process that 

 is very difficult to evaluate. However, it 

 would seem to be the chief process that is 

 capable of dislodging large blocks of rock 

 near sea level. Certainly, it can be important 

 only where rocks are jointed and are thus 

 able to be removed in blocks. Even less 



