274 GEOLOGY. 



faulting, vulcanism, and gradation all produced changes in the physi- 

 ography of the west. Locally, as in the Santa Cruz mountains of Cali- 

 fornia, there were pronounced orogenic movements l in the course 

 of the period, but toward its close crustal movements seem to have 

 been general. At this time pronounced deformative movements took 

 place in the coastal regions of Oregon 2 and California, tilting and 

 folding the Miocene and older formations. The principal growth 

 of the existing Coast ranges of both these States, and of the San Fer- 

 nando mountains of California are usually assigned to this time. 3 The 

 orogenic movements in the Mount Diablo region have already been 

 referred to. The Cascade mountains of Washington also had notable 

 growth at this time. 4 



Similar movements appear to have been wide-spread throughout 

 the Cordilleran system, sometimes resulting in the deformation of 

 strata heretofore horizontal, but more commonly affecting formations 

 and areas which had suffered deformation at some earlier time. In 

 California, the Sierra peneplain, developed during the Cretaceous, 

 Eocene, and early Miocene periods, was deformed by being tilted up 

 on the east, increasing the grade of the westward flowing streams. 

 This deformation appears to have begun before the close of the Mio- 

 cene, and to have furnished the conditions necessary for the depo- 

 sition of the late Miocene auriferous gravels. 5 Remnants of this old 

 plain are now 600 to 1900 feet above sea-level at the head of Sacra- 

 mento valley, and several thousand feet high in the main range. In 

 northern California, the deformation was such as to emphasize the 

 central valley of the State. Since that time, too, there has been fault- 

 ing to the extent of 3000 feet on the east side of the northern Sierras. 6 

 Deformation and faulting at the close of the Miocene seem also to 

 have been wide-spread and pronounced in the Great Basin region, 7 

 and to have affected some parts of Colorado. 8 



1 Ashley, Jour. Geol., Vol. Ill, p. 434; Whitney, Geol. of California, I. 



2 Diller, 17th Ann. Rept. U. S. Geol. Surv. 



3 Ashley, op. cit. 



4 Willis, Professional Paper 19, U. S. Geol. Surv. 



5 Diller, Jour. Geol., Vol. II, p. 30, and Lindgren, Jour, of Geol., Vol. IV, p. 881 

 et seq. 



6 Diller, 14th Ann. Rept., U. S. Geol. Surv. 



7 King, op. cit., p. 414, and Dutton, op. cit., p. 226. 



8 Walsenburg folio, U. S. Geol. Surv. 



