52 



p. B. KING 



deposited. Such stratigraphic evidence indicates a sideward shift on 

 the San Andreas and some of the other faults of 30 miles or more 

 since the mid-Tertiary (Crowell, 1952, pp. 2030-2035; Noble, 1954, 

 pp. 44-47). Even greater shifts are suggested when comparisons are 

 made between basement rocks on the opposite sides, but they are as 

 yet difficult to prove and require further detailed research (Fig. 11). 

 There is thus a suggestion that the San Andreas fault has been 

 moving progressively for a long period — at least since the close of the 



500 Miles 



Fig. 11. Maps of California during successive periods to illustrate an 

 hypothesis of extensive lateral displacement on the San Andreas and 

 related faults. A, In late Mesozoic time. B, In late Miocene time. C, 

 Present time. (Modified from M. L. Hill, 1954.) 1, Boundary between 

 Nevadan basement (to east) and Franciscan basement (to west). 2, 

 Boundary between Miocene continental sediments (to east) and marine 

 sediments (to west). 



Nevadan orogeny — so that rocks of each older age have been shifted 

 by greater amounts (Hill and Dibblee, 1953, pp. 445-451). This 

 picture, if valid, is greatly complicated by the fact that the San 

 Andreas, or master fault, is only one of many in the same region 

 with similar habit; attempts at reconstruction of the geography at 

 successive periods thus involve, not a single break, but many breaks 

 with diverse movements. 



Be that as it may, the possibility has thus suggested itself that 

 the anomalous strips of Nevadan basement are slivers that were 

 faulted off the orogenic belt on the east, and have been transported 

 scores or hundreds of miles northwestward, into an environment 

 foreign to them (Fig. 11). Such movements are strongly indicated in 



