22 



Physiography 



Figure 23. Distribution of some 

 low rock platforms ("storm 

 terraces") and of some sea 



caves. 



During storms, waves wash across the low 

 platforms removing weathered material and 

 eroding fresh rock. In opposition, it should 

 be pointed out that the stronghold of the 

 concept of storm terraces is New Zealand, 

 where at least two low terraces (at Welling- 

 ton and Napier) are known to have been pro- 

 duced by earth movements associated with 

 historical earthquakes. Moreover, it is diffi- 

 cult to see why storm waves, being larger 

 than ordinary ones, should not erode deeper 

 rather than shallower than usual. Certainly 

 all storms do not have waves of the same 

 height, nor do they occur at tides of the same 

 height, so at best we would expect storm ter- 

 races to have profiles with outer edges that 

 are convex upward. However, most low 

 rock platforms in southern California and 

 elsewhere have abrupt outer edges. In ad- 

 dition, in this area there are small off'shore 

 islands surrounded on all sides by low plat- 

 forms having no difference in height on sea- 

 ward and leeward sides. The height of these 

 island platforms and of off'shore platforms 

 having no central island is about the same as 

 the platforms fringing the nearby mainland 

 sea cliffs. An alternate explanation, favored 

 by the writer, is that the low rock platforms 



indicate a recent eustatic lowering of sea 

 level, supporting the evidence of the talus 

 slopes. The low platform left by a drop in 

 sea level can, of course be reached by storm 

 waves and by spray, and so it is the site of 

 solution basins and other forms of water- 

 level weathering described by Wentworth 

 (1938-1939) for the Hawaiian Islands. The 

 fact that most of the low platforms and their 

 adjacent sea cliffs of southern California con- 

 sist of the hardest kinds of rock in the area, 

 such as basalt, is more in line with inheri- 

 tance from a time of higher sea level than 

 with erosion by present-day storms. 



An interesting feature associated with sea 

 cliffs is the sea cave. More than 350 are 

 present in southern California. All that have 

 been inspected are localized along zones of 

 structural weakness, faults or joints (Moore, 

 19546). Waves have succeeded in abrading 

 and prying away the rocks on both sides of 

 the fault zones, widening the zones to form 

 caves that are elongate into the sea cliffs. 

 The comminuted rock debris is carried in 

 suspension and solution out of the cave. 

 Most of these caves are less than 20 feet long, 

 but one extends nearly 600 feet into Santa 

 Cruz Island (Fig. 24) (Emery, 1954«). The 



