EVOLUTION OF xMODERN SURFACE FEATURES 53 



southern California, where shifts of as much as 30 miles on the San 

 Andreas fault since the mid-Tertiary have been proved, and where 

 even greater shifts are suggested in the carher rocks. Farther north, 

 however, total movements of less than a mile on the San Andreas 

 fault have been claimed (Taliaferro, 1943, pp. 159-161). Such claims 

 seem to be based merely on the latest of a series of breaks, and fail 

 to consider total offset in a broader San Andreas /aw// zone (Wallace, 

 1949, p. 803). Nevertheless, it is puzzling in this northern area that 

 there is so little offset of the coast where the San Andreas fault goes 

 out to sea south of San Francisco, and no detectable offset of the 

 edge of the continental shelf farther offshore to the northwest. An 

 offset of the continental shelf of more than 50 miles occurs west of 

 Cape Mendocino, but along an east-west fracture system, aligned 

 differently from the San i\ndreas trend (Menard and Dietz, 1952, 

 p. 273) (Fig. 10). 



Although we now appear to have acquired the rudiments of an 

 explanation for the anomalies of the Coast Ranges, this explanation 

 is still obscured by negations and contrary evidence. At this stage, 

 almost any explanation for a set of anomalies in the Coast Ranges 

 creates other, unexplainable anomalies. 



Tertiary Environments. Regardless of the anomalies in the base- 

 ment rocks and the possible shifts of large segments of the area along 

 through-going faults, the different types of basement have exerted a 

 profound influence on the structures of the Tertiary rocks. Areas 

 underlaid by Nevadan and Franciscan basement have been land or 

 sea at different times and, when compressive forces were exerted, 

 the areas underlaid by the weaker Franciscan basement have been 

 much more deformed than those underlaid by the stronger Nevadan 

 basement. 



Such compression was exerted at many different times during the 

 Tertiary. Some areas show a record of almost continuous deforma- 

 tion through long spans of Tertiary time, and the sedimentary 

 sequences frequently contain so many unconformities that it is 

 diflicult to generalize any orogenic climaxes (Gilluly, 1949, pp. 567- 

 569). Nevertheless, two principal climaxes seem to have occurred, 

 one near the middle of the Miocene, the other early in the Pleistocene 

 (Reed and Hollister, 1936, pp. 1551-1597). It is interesting to note 

 that these climaxes of deformation are of about the same age as 

 those which have been inferred in the Great Basin area. Effects of 



