10 



Physiography 



Figure 5. Straight cliifed coast north of La JoUa. Eocene shales are overlain by terrace alluvium. The broad flat 

 Linda Vista Terrace is for the most part between 300 and 400 feet above sea level. Note the straight cliffs, the wide 

 sand beach at their base, the talus, and the highly dissected upper slopes. Photographed by R. E. Stevenson in 1952. 



youth or early maturity and were able to cut 

 only narrow valleys. These contrast with the 

 wide valleys cut by the mature streams of the 

 eastern United States which produced broad 

 estuaries when they became drowned. Thus, 

 the evidence of submergence in southern 

 California is less obvious than that of emer- 

 gence, but still it is sufficient to show that all 

 the shorelines are compound, in the sense of 

 possessing characteristics of both emergence 

 and submergence. Even shorelines origi- 

 nally of neutral origin, such as the huge 

 alluvial fan or delta at Hueneme and the 

 fault scarp of San Clemente Island (Fig. 67, 

 p. 78), contain evidence of submergence 

 (small estuaries) and emergence (terraces), 

 respectively, that require them to be classed 

 as compound. In summary, if we consider 

 the coast in the broad sense (adjoining belts 

 of land and sea floor, and for lengths of 10 

 to 15 miles), we must classify it as nearly 100 

 per cent compound. The presence of both 

 estuaries and raised marine terraces on the 

 East and Gulf coasts of the United States 

 also require these shorelines to be classed as 

 compound in the broad sense. If, on the 



other hand, a restricted view is taken of the 

 shoreline (omitting terraces and classifying 

 short sections), it is often possible to deter- 

 mine whether the last major movement was 

 emergence or submergence. This is the way 

 in which Johnson's classification has gener- 

 ally been used on the East coast where the 

 terrace record of emergence is less obvious 

 than it is on the mountainous West coast. 

 By this restricted sense of the classification, 

 5.7 per cent of the southern California shore- 

 line is submergent in the youthful stage 

 (estuaries), 7.3 per cent is emergent in youth 

 (lagoons and offshore islands), 83.5 per cent 

 is emergent in maturity (cliffed shores), and 

 3.5 per cent is neutral (fault scarp). Per- 

 centagewise, this breakdown is only slightly 

 more divided than the 100 per cent com- 

 pound classification, and it is highly sub- 

 jective. 



The shoreline can also be classified using 

 Shepard's (1948, pp. 71-76) system, in which 

 the first breakdown is youthful or mature, 

 depending on whether the forming agent is 

 nonmarine or marine, respectively. Under 

 this classification only 3.5 per cent is non- 



