118 A. C. SPENCER — PACIFIC MOUNTAIN SYSTEM 



there is a wide belt of relative depression, marked in the extreme south 

 by the gulf of California ; within the United States by the faulted pla- 

 teaus of the Basin ranges, and the Columbia plateau ; in British Colum- 

 bia by the Interior plateau, and in Yukon territory and Alaska b}^ the 

 Yukon plateau. 



The portion of the Pacific Mountain system with which the present 

 paper is concerned lies between the northern boundary of the United 

 States and the mainland coast of Alaska in the vicinity of the Alaskan 

 peninsula. The generalizations which have been attempted are the 

 direct outgrowth of the principal conclusions concerning the physiog- 

 raphy of the Copper River district, already presented by Mr F. C. 

 Schrader and the writer in a report on that region.* The field-work of 

 the writer in Alaska has not extended be3^ond the drainage basin of the 

 Copper river ; but from the recorded observations of geologists who have 

 visited other portions of the coastal mountains, and from conversations 

 with some of them, he has been led to remark the similarity of certain 

 phj^siographic features throughout the whole of the region outlined, and 

 to seek certain correlations. In bringing together the available facts, lie 

 has been surprised to find so much alignment of evidence in the direc- 

 tion of a few wide-reaching conclusions regarding the topographic devel- 

 opment of the region at large. 



There are two notable resemblances between the physiographic features 

 of the Copper River region and the other portions of the coastal belt : 

 In the first place, the existing descriptions of the Coast range, both in 

 British Columbia and Alaska, suggest that their summits represent the 

 denuded remnants of former peneplains ; secondly, the Copper river, as 

 well as the large rivers which rise in the interior and flow across the Coast 

 range, are antecedent to the existence of the present mountain ranges. It 

 is the object of this communication to state the relations which are indi- 

 cated by a consideration of these two features of physiography. The 

 present statement of the conclusions which have been reached is neces- 

 sarily tentative and their discussion incomplete because of the frag- 

 mentary nature of the recorded evidence ; but it is hoped that the 

 suggestions which are made will prove of value to observers who may 

 have future opportunity to extend existing knowledge regarding the 

 physiograph}' of the Northern Pacific province. 



General Description 

 Be3'ond the state of Washington the component ranges of the Pacific 



* Department of the Interior, U. S. Geological Survey, Charles D. Waleott, Director, Washing- 

 ton, D. C, 1901, pp. 1-94. 



See also "A Reconnaissance of a Part of Prince William Sound and the Copper River District, 

 Alaska," in 1898, by F. C. Schrader. Twentieth Annual Report, U. S. Geol. Survey, part vii, 1900. 



