FORMATIONS AND PHYSICAL HISTORY 585 



division of the Tertiary were adopted, the earlier part of the Miocene 

 should <> with the early Tertiary, and the later part with the late 

 Ti-rliary. The marine part of the system has great thickness, the 

 Lower Miocene having a maximum thickness of some 8,000 feet, and 

 the I'pper hardly less. 



By the end of the period, the peneplanation of the Klamath and 

 Sierra Nevada Mountains seems to have approached completion. 



Fig. 491. Contorted beds of Monterey shale. Mouth of Vaquero Creek, Cal. 

 (Lippincott, U. S. Geol. Surv.) 



Much of the material eroded from them had been deposited in the 

 central valley of northern California, making the thick Miocene 

 beds of that valley. 



In western Oregon, Miocene (Empire) beds a few hundred feet 

 thick, containing volcanic ash, rest unconformably on the deformed 

 and eroded Eocene. In British Columbia, there are both clastic 

 and volcanic rocks referred to this period. 



The Miocene of the western coast has not the simple structure 

 of the corresponding beds along the Atlantic and Gulf coasts. 

 The strata have been deformed so as to stand at high angles (Fig. 

 491) in many places, and locally (Mount Diablo range) they have 



