Coasts 



terraces were estimated from contours of the 

 new 7V2-minute U. S. Geological Survey 

 topographic quadrangles, on most of which 

 topography was compiled from aerial photo- 

 graphs. Contour intervals range from 5 to 

 50 feet, with 20 and 25 feet the most com- 

 mon. The results were grouped for eight 

 sections of mainland coast and for seven is- 

 lands (Fig. 3), at all of which many terraces 

 are present, some to elevations of more than 

 1 500 feet above sea level. Some terraces are 

 very certain; others that are narrow or highly 

 eroded (such as those on Santa Catalina 

 Island) may have been overlooked. Cer- 

 tainly, small terraces have been missed be- 

 cause of not being shown by the contours; 

 for example, altimeter readings on Santa 

 Barbara Island showed four small terraces 



between 87 and 112 feet where contours in- 

 dicate only one. Other terraces are buried 

 under alluvial material, which itself is shown 

 as a terrace. Considering the various uncer- 

 tainties in the compilation, it is doubtful 

 whether more than half the existing number 

 of terraces were recognized, although prob- 

 ably all wide ones are included. 



Among the most interesting physiographic 

 problems of southern California is the ques- 

 tion of the presence of raised terraces on 

 Santa Catalina Island. Lawson (1893^) be- 

 lieved the island to be free of terraces and, 

 therefore, to be an area of submergence, in 

 contrast to San Clemente Island and Palos 

 Verdes Hills where great emergence is shown 

 by the high terraces. Some support to this 

 belief is given by the drowned character of 



Figure 3. Elevations of raised 

 marine terraces as estimated 

 from recently published con- 

 tour maps of the U. S. Geo- 

 logical Survey. Numbers refer 

 to the sections of mainland 

 coast and islands in which all 

 coastal quadrangles were ex- 

 amined. Thin vertical lines 

 show the range of elevations 

 that is included by contours in 

 each section of coast; wide ver- 

 tical lines indicate the eleva- 

 tions of individual terraces 

 from the low seaward edge to 

 the high alluvium-covered edge 

 against the raised sea cliffs. 



