Coasts 



Emery (1941) to distinguish it from ordinary 

 continental shelves. Even casual examina- 

 tion of Chart I shows that the continental 

 borderland is a checkerboard-like arrange- 

 ment of high and low areas having a general 

 elongation that ranges from southeast-north- 

 west to east-west, more or less parallel to 

 the topographic trends of the nearby land 

 areas. Some of the topographic highs ex- 

 tend above sea level to form islands, whereas 

 others rise almost to sea level, constituting 

 banks, most of which are flat-topped. Still 

 other highs are deeply submerged. Border- 

 ing the high areas are slopes that lead down 

 into the adjacent deep areas formed by 

 thirteen closed basins and several open but 

 flat-floored troughs. Measurement of the 

 total areas covered by the major kinds of 

 sea floor features of Chart I shows (Table 1) 

 that the flat basin and trough floors, the 

 chief areas of sediment accumulation, com- 

 prise about 17 per cent of the total 30,370 

 square statute mile (78,580 sq km) area of the 

 continental borderland. The remaining 70 

 per cent of the area consists of slopes, bank 

 tops, and shelves, on all of which the accu- 

 mulation of sediments is relatively minor. 

 In the basin range physiographic province 

 of eastern California and Nevada the per- 

 centages are reversed, with 30 per cent of 

 the area being mountains and 70 per cent 

 depositional areas. This reversal is the re- 



sult of the abundance (30 per cent) of sloping 

 fans and bajadas on the land area and their 

 tendency to bury the lower parts of mountains. 



Coasts 



Raised Marine Terraces 



Perhaps the best-known physiographic 

 feature of the southern California coast is its 

 series of raised marine terraces (Fig. 2) 

 which rise in steps from the shores up the 

 slopes of the nearby mountains. Widths 

 range from barely perceptible to more than 

 5 miles. Slopes of the wider terraces are a 

 fraction of a degree, but those of the nar- 

 rower ones are only sHghtly gentler than the 

 slopes of the steps that separate them from 

 the next terraces. 



The terraces were recognized by Blake 

 (1856) and J. G. Cooper in 1863 (Lawson, 

 1893/?) as raised shorelines, but later David- 

 son (1875) unaccountably ascribed them to 

 erosion by glaciers moving parallel to the 

 coast. Lawson, after a reconnaissance of 

 the coast, vigorously defended the concept 

 of ancient marine erosion. He and later 

 Smith (1898, 1900) made aneroid measure- 

 ments of terrace elevations on several islands 

 and on the mainland and concluded that ele- 

 vations of most terraces were too great for 

 them to have been left exposed by with- 



Table 1 



Total Areas of Major Topographic Features of Chart I 



