GEOLOGY OF WEST COAST REGION OF UNITED STATES 

 important types of marine life were rare, but large 

 amounts of organic siliceous ooze were deposited. 

 The land mass from which the terrigenous sediments 

 were derived may have existed to the west of the 

 present coast line. 



THE CORDILLERAN REVOLUTION AND THE SlERRA 



NEVADA BATHOLITH. The intrusion of the Sierra 

 Nevada batholith and most of the outlying members 

 took place in late Jurassic times. The main batho- 

 lith occupies the eastern portion of California, ex- 

 tending northward in a direction a little west of 

 north. It disappears under the lava cover of north- 

 ern California and Oregon. In the northern part 

 of California and southern Oregon, small granitic 

 masses may be outlying members of the same great 

 intrusion. Towards the south the batholith ends 

 in a hook which curves around the southern rim of 

 the great valley of California. The irregular masses 

 of the Sierra Madre, ban Jacinto and San Bernar- 

 dino ranges of the southern part of California, as 

 well as the smaller granite areas of the Coast Ranges 

 south of San Francisco, may be closely related to 

 the main batholith. The intrusion was accompanied 

 by metamorphism so intense and widespread that 

 it resembles regional rather than contact action. 

 As a result much of the pre-Cretaceous rocks appear 

 as schists, slates and recrystallized limestones. The 

 small granitic masses of the desert region of south- 

 eastern California belong to the Great Basin pro- 

 vince, and a close relationship to the Sierra Nevada 

 batholith has not as yet been proved. In north- 

 eastern Washington, the granitic intrusives are re- 

 lated to the Idaho batholith rather than that of the 

 Sierra Nevada, while in central Washington a batho- 

 lith of proved Miocene age is reported. 



Sills and dikes of serpentine were intruded along 

 the axes of the present Coast Ranges. These may 

 have been contemporaneous in part with the later 

 phases of the batholithic intrusions of the Sierra 

 Nevada, which also include basic derivatives. The 

 intrusion of the Coast Range serpentines continued, 

 however, into early Cretaceous times. 



Prior to the intrusion of the last of the Sierra 

 Nevada granites, the earth movements which brought 

 about the Cordilleran revolution were well under 

 way. The pre-Cretaceous sediments west of the 

 batholith were closely appressed into isoclinal folds. 

 The axes of the folds are nearly vertical, occasion- 

 ally overturned, and trend northwestward well into 

 Oregon, where they swing to the northeast as if to 

 round the point of the main batholith, and dis- 

 appear under the cover of Tertiary lavas. 



46 



