THE MIOCENE PERIOD 815 



and northern California, tilting and folding the Miocene and older 

 formations. The principal folding of the existing Coast Ranges 

 of both these states has been assigned to this time, 1 but it now ap- 

 pears that some of the deformations heretofore referred to the end 

 of the Miocene, took place after the Early Miocene (p. 808). The 

 Cascade Mountains of Washington were in process of growth at 

 this time. 2 



Similar movements appear to have been wide-spread east of 

 the coast, resulting, in some places, in the deformation of strata 

 heretofore horizontal, but more commonly affecting formations 

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

 northern California, the deformation was such as to emphasize the 

 central valley of the state though raising its northern part. De- 

 formation and faulting seem also to have been wide-spread and 

 pronounced in the Great Basin region, and elsewhere. 



The later part of the period was perhaps the time when the 

 greater relief features of the rugged west, as they now exist, were 

 initiated. The great relief features of earlier times appear to have 

 lost their greatness before the end of the Miocene (p. 810) . After the 

 movements of the late Miocene had been accomplished, it is prob- 

 able that the western part of the continent had a topography com- 

 parable, in its relief, to that of the present, though by no means in 

 correspondence with it. The details, and even many of the larger 

 features, of the present topography are of still later origin. Sub- 

 sequent changes have been the result of (1) deformation, largely 

 without notable folding, (2) faulting, (3) the extrusion of lava, and 

 (4) extensive degradation and aggradation, by running water, by 

 ice, and by wind. 



In the eastern part of the continent, the geographic changes 

 were less considerable, though the Atlantic and Gulf regions seem 

 to have emerged, transferring the coast-line to some such position 

 as it has to-day. 



Foreign 



Europe. The relations of sea and land remained much as in^the 

 early Tertiary, though the area of the sea was somewhat restricted 



1 Ashley, op. cit. 



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



