12 



Physiography 



with higher cliffs being generally less steep 

 than lower ones. The profiles are commonly 

 broken into steps of varying steepness that 

 are controlled by differences in lithology and 

 structure. Other departures from simple 

 slopes are common at the base where low 

 rock platforms may extend as much as 100 

 yards seaward (Fig. 7) or where talus slopes 

 cover the foot of the sea cliffs (Fig. 8). Boul- 

 der and gravel beaches locally skirt the base 

 of the sea chffs or of their talus slopes. It is 

 estimated that talus covers the base of about 

 20 per cent of the coast having sea cliffs. 

 Even where the base of a cliff is covered by 

 talus, it is evident that shoreline erosion was 

 active during the past and was responsible 

 for the steepening of the cliff which even- 



tually resulted in landsliding and deposition 

 of talus. 



The ocean washes continually against the 

 base of some sea cliffs but is separated from 

 others most of the time by the talus or by 

 sand beaches. During single exceptionally 

 large storms, or as the cumulative effect of a 

 winter season of smaller storms, beaches are 

 commonly narrowed by seaward transporta- 

 tion of sand. While the beach is absent 

 or narrow, the ocean can do more erosion 

 of the cliff than during the whole remaining 

 bulk of the year. Thus, marine erosion is 

 similar to stream erosion in that by far the 

 greatest effect comes during short periods 

 separated by much longer intervals of very 

 slight erosion or even of deposition. When 



Figure 7. Laguna Beach. Cliffs consist of Miocene schist breccia and basalt. The marine terrace is between 80 and 

 120 feet above sea level. At the base of the cliffs is a low rock terrace of the type sometimes known as a storm ter- 

 race. Note the pocket beaches, only one of which is at the mouth of a stream. Photographed by R. E. Stevenson in 

 1952. 



