Coasts 



11 



marine, the fault scarp of San Clemente Is- 

 land. Of the remainder of the coast, 7.3 per 

 cent has been straightened by deposition of 

 sand beaches, 5.7 per cent has been straight- 

 ened by deposition of offshore sand islands, 

 37.5 per cent has been straightened by ma- 

 rine erosion, and 46.0 per cent has been made 

 irregular by marine erosion. Nearly five- 

 sixths of the latter category belongs to the 

 islands. For comparison, nearly the entire 

 southeastern and Gulf coasts of the United 

 States consist of shorelines straightened by 

 deposition of sand beaches or offshore sand 

 islands backed by mud flats. The difference 

 between the two coasts is a reflection of the 

 more mountainous nature of the California 

 coast and its much smaller supply of sand 

 relative to capacity of the ocean for redis- 

 tribution. 



In summary, it may be seen that Johnson's 

 genetic classification does not work well in 

 southern California because of the complex 

 history of the region and the imperfect rec- 

 ord of submergence left by smaller streams. 

 Shepard's classification as an extension of 

 pure description of the coast offers a break- 



down of the major type, erosional shorelines, 

 into two major subequal classes, those that 

 have been straightened and those that have 

 been made more irregular by marine erosion. 

 Of interest is the fact that the two largest 

 areas of depositional shorelines (Los Angeles 

 and Hueneme) are backed by the two low- 

 lands having the greatest agricultural pro- 

 duction. Only the former has developed as 

 the site of a large city, perhaps partly because 

 it is the only one having a deep-water harbor, 

 and this was built by sediments and man. 

 The third and fourth largest areas of depo- 

 sitional shores, San Diego and Santa Bar- 

 bara, are sites of less important agriculture 

 and of cities, the first and larger of which has 

 a deep-water port also buht by sediments. 



Erosional Coasts 



Erosional coasts everywhere consist chiefly 

 of sea cliffs. In southern California these 

 cliffs vary in height from a few feet to more 

 than 500 feet, with a mean of 75 feet for the 

 mainland and 175 feet for the islands. Slopes 

 range from overhanging to less than 45°, 



Figure 6. Seal Beach just west of breakwater. The wide offshore sand island provided quiet water for the accumu- 

 lation of fine marsh sediments. Highly meandering tidal channels are typical of such marshes. Note the shortening 

 of crest-to-crest spacing of waves as they approach the beach and enter progressively shallower water. Photographed 

 by R. E. Stevenson in 1952. 



