COAST RANGES OF THE PACIFIC AND THE SAN ANDREAS FAULT SYSTEM 



455 



that the Coast Ranges of southern California have probably shifted some 

 300 miles northwestward to their present position, and therefore the 

 paleotectonic maps of Fig. 29.3 are probably not correct. They show, how- 

 ever, the principal tectonic elements, and are reproduced because they 

 help in understanding the make-up of the region. 



The evolution of the central Coast Ranges in Early Tertiary time is 

 idealized in Fig. 29.4, and the deposits under that part of the San Joaquin 

 embayment that were not deformed appreciably and later became the 

 San Joaquin Valley are shown in Fig. 29.5. 



Early Tertiary Phase 



In Chapter 17 it was pointed out that the Santa Lucian orogeny was the 

 last disturbance in the Cretaceous, and that following it, the widespread, 

 thick Asuncion group was deposited in Senonian, Maestrichtian, and 

 Danian time. The deposition of the Asuncion was brought to a close in the 

 Central Coast Ranges by uplift, tilting, and probably folding; but so little 

 of the Paleocene is preserved that its original extent and thickness and the 

 degree and extent of the post-Cretaceous disturbance are not known. 

 However, it is believed that the disturbance was not as severe as previous 

 ones, because the uppermost Cretaceous and Paleocene, where observed, 

 are only slightly discordant, and very little change in the character of the 

 sediments is noted ( Taliaferro, 1943b ) . 



Taliaferro (1943a) suggests that the Paleocene represents a final stage 

 in the history of the late Mesozoic geosyncline, the California trough of 

 this book, in which the Franciscan, Knoxville, Shasta, and Chico sedi- 

 ments were deposited. See Fig. 29.6. The part of the trough in the site of 

 [ the present central Coast Ranges and along the western border of the 

 present San Joaquin Valley received sediments throughout the late Upper 

 Cretaceous, and then weak uplift, folding, and erosion occurred to the 

 west, while the central part of the trough was little affected. Probably 

 general uplift occurred, and the seas retreated; but the uplift appears to 

 have been quickly succeeded by downsinking, and the Paleocene sea 

 flooded at least parts of the Cretaceous deposits. This was the last time 

 that deposition took place over rather large areas of the trough. The 

 changes that had taken place previously were of lesser magnitude than 



PACIFIC 



DIABLO 



5AN JOAQUIN 



MOMAVIA 



OCEAN 



UPLIFT 



ELMBAYMENT 



Rosomond Basins 







™ TV , , 



/ 



------.----------; ; -.V_-_-£££=, 







■■■/:>:-:--,^r- 





1 



i 



Beginning of Miocene (Monterey) Time 

 Tov ? ^- 



In late Olioocene (close of Vaqueros) time 



Close of Eocene time 



Close of Cretaceous (Chico) time 



Fig. 29.4. Evolution of Coast Ranges and Great Valley in Early Tertiary time. Kc, Chico 

 formation; Te, Eocene formations; Tov, Oligocene and Vaqueros formation; Tt, Temblor forma- 

 toin. After Reed, 1933. Section E-E', Fig. 29.1. 



those that took place after the Paleocene. The available evidence indicates 

 that the final fragmentation of the California trough took place in the 

 Eocene. Great thicknesses of Tertiarv sediments accumulated, but they 

 formed in comparatively narrow basins, some of which were at a marked 

 angle to the more extensive and enduring late Mesozoic trough. 



Eocene and Oligocene strata have limited distribution in the central 

 Coast Ranges, and their nomenclature and correlation have been the ob- 

 jects of considerable discussion. Typical Tertiarv formations are listed in 

 the chart on page 458. Although thick lower Eocene sections occur, 

 they are in small, isolated localities; and more of the California Coast 

 Ranges were emergent than at any time during the Cretaceous and Juras- 



