SALIENT FEATURES OF THE GEOLOGY OF OREGON 8i 



Washburne, Arthur J. Collier, Graham John Mitchell, and others, 

 has contributed, if not voluminously, most substantially, to the 

 accumulated knowledge in this field. 



Besides those mentioned there are several other authors who 

 have contributed one or more papers in special fields, and these 

 are listed in the bibliography, which includes only the more impor- 

 tant contributions to the subject. 



PHYSIOGRAPHY 



The state of Oregon is only a part of the older and much larger 

 Oregon Territory. Its situation on the great western ocean is 

 greatly in its favor, though it is less fortunately placed than either 

 California or Washington. 



Oregon is divided by the great Cascade Mountains into two 

 very diverse regions, western and eastern Oregon, which differ 

 radically, at least in the later periods, in physiography (including 

 climate) , geology, economic greogaphy , and also politically, socially, 

 and in many other ways. Western Oregon is a marine province, 

 and its geology in part is, in common with California and Washing- 

 ton, similar to that of Eastern Asia, while eastern Oregon is conti- 

 nental and belongs to the Great Basin province. A great portion 

 of Oregon is covered by a part of the greatest lava flow in the world, 

 and this has had a profound influence upon its history, both geologic 

 and economic. 



Following the Committee of the Association of American Geog- 

 raphers' there have been recognized the following physiographic 

 divisions in Oregon: 



1. " The Oregon Coast Range is the section of the Pacific Border 

 Province west of the Puget Trough and consisting of Tertiary rocks," 

 sandstones, and shales cut by igneous intrusives. 



2. ^^The Puget Trough, the intermontane lowland west of the 

 Middle and Northern Cascade Mountains." In Orgeon this is 

 known as Willamette Valley and is filled largely with alluvium, but 

 many outliers of Tertiary sediments and buttes with Tertiary 

 igneous intrusives are found within this area. 



3. '^The Middle Cascade Mountains are that portion of the 

 Sierra-Cascade Province whose height is due in part to volcanic 



' Ann. Assoc. Am. Geographers, VI, 34. 



