Coasts 



Figure 4. Irregular cliflFed coast of Point Loma. Cretaceous sandstones and shales are overlain by Eocene shales and 

 then by terrace alluvium. Note complex profile controlled by varying lithology and the presence of small sea caves, 

 some with collapsed roofs. Narrow gravel beaches line indentations. The flat top of Point Loma is a marine terrace 

 raised to about 350 feet above sea level and surmounted by a beach ridge. In the distance is North Island, the end 

 of a long curved spit that encloses San Diego Bay. Photographed by R. E. Stevenson in 1952. 



beaches backed by rocky cliffs (Fig. 5) are 

 temporarily depositional because seasonal or 

 longer-term deposition has built a barrier of 

 wave- washed debris at the base of the chffs; 

 however, such shoreUnes must be considered 

 erosional on a long-time basis if only because 

 of the presence of the cliffs. Other sandy 

 beaches that are backed by mud flats, allu- 

 vial fans, and deltas (Fig. 6) are clearly of 

 depositional origin. Extending the classifi- 

 cation, we can say that the erosional shore- 

 lines are retreating ones, whereas deposi- 

 tional shorelines are prograding. A minor 

 rearrangement of the figures of Table 2 shows 

 that 87 per cent of the shoreline of southern 

 California (including islands) is erosional 

 and only 13 per cent is depositional. These 

 percentages are in agreement with what 

 might be expected of the region with its pre- 

 cipitous coastal areas and low stream runoff. 

 They lead to the obvious conclusion that the 

 supply of debris to the present shoreline is 



far less than the capacity of the ocean to 

 transport it seaward. 



Strict apphcation of Johnson's (1919) 

 emergent-submergent classification is beset 

 with difficulties. These arise because the 

 whole region has experienced great emer- 

 gence, both diastrophic and eustatic, as 

 shown by the widespread raised marine ter- 

 races; it has also undergone submergence 

 chiefly eustatic, as shown by submerged ter- 

 races and by numerous estuaries that are 

 filled with alluvium to depths now below sea 

 level. Only the larger streams were able to 

 cut vaUeys that later became drowned, owing 

 to rise of sea level at the end of glacial times; 

 smaller streams in this region of low rainfaU 

 could not cut deeply during the short time 

 of glacially lowered sea level, so they were 

 unable to add their evidence to the record of 

 submergence. During the Pleistocene Epoch, 

 as well as the present, most streams of south- 

 ern California were in stages of geomorphic 



