6 GITIDEBOOK OF THE WESTERN UNITED STATES, 



valley belt, there is a tract of generally mountainous country, 

 where, for 200 miles, the threefold longitudinal division of the Pacific 

 System into two ranges and an intervening belt of valleys is less evi- 

 dent than it is elsewhere. South of this interrupting mass of moun- 

 tains, wliich is dominated by Mount Shasta, the Great Valley of Cali- 

 fornia stretches for more than 400 miles, having a width in general of 



mile 



Sacramento 



drains southward, and its southern part, known as the San Joaquin 

 Vallev, drains northward, Sacramento and San Joaquin rivers 

 both flowing into San Francisco Bay. The south end of the San 

 Joaquin Valley is separated by the transverse Tehachapi Mountains 

 from the Mohave Desert. This in turn is separated by the San Ber- 

 nardino range from the Salton Basin, wliich is nothing more than the 

 former upper part of the Gulf of California, the sea having been 



ulf by 



Colorado River. 



GuK 



fornia are regarded as parts of the Pacific valley belt. By others, 

 however, notwithstanding the general alignment of these features 

 with the Great Valley of California, they are regarded as parts of the 

 plateau region that lies east of the Pacific System of mountains. 



As the Pacific valley belt separates in general two parallel ranges 

 of mountains, so those ranges in turn may be subdivided into moun- 

 tain groups that are sufficiently distinct in form or structure to have 



received individual names. 



At the north end of the western line, between Pugct Sound and the 

 ocean, stand the Ol^-mpic Mountains, which attain a height of 8,000 

 feet. Verv httle is known of their structure or of the rocks that 



compose 



01}Tupic 



Washinerton and Oregon for 350 miles, is a com 



simil 



maj 



chiefly 



mor 



rocks 



determined that the sands were deposited in the sea < 

 and middle Tertiary time. Lavas associated with these 

 that volcanoes were active in this region in early Te 

 These rocks are no longer in the original horizontal position in which 



)led bv nressure. Moreover, 



mi 



crum 



some 



rocks 



on the other side. The geologist would describe these effects briefly 

 by saying that the beds have been folded, fractured, and faulted. 



South of the Oregon Coast Range, partly m Oregon but chiefly in 

 California, are the Klamath Mountains. They are composed of rocks 

 that arc older and more comphcated in structure than those of the 



