BULLETIN OF THE GEOLOGICAL SOCIETY OF AMERICA 

 Vol. 14, pp. 117-132, PLS. 8-13 APRIL 18, 1903 



PACIFIC MOUNTAIN SYSTEM IN BRITISH COLUMBIA AND 



ALASKA* 



BY ARTHUR C. SPENCER 



{Presented before the Society July i, 1902) 

 CONTENTS 



Page 



Introduction 117 



General description 118 



Copper River district 120 



Peneplains in the Pacific mountains 1 21 



Interior and Yukon plateaus 122 



Correlation of peneplains 123 



Antecedent rivers 125 



Origin of the Pacific mountains 128 



Geologic dates 131 



Summary 1 32 



Introduction 



The Pacific mountains of the United States, as defined by Powell, t 

 occupy a belt between the Pacific ocean and that region of lower relief 

 which, lying west of the Rocky mountains, comprises the Basin ranges 

 on the south and the Columbia plateau on the north. Had the discus- 

 sion presented by Powell been extended to the physiographic features 

 of the whole of the North American continent, it would doubtless have 

 been recognized that the Pacific mountains are continued toward the 

 south into Lower California and toward the north, northwest, and west 

 through British Columbia, the mainland of Alaska, and the Aleutian 

 islands. The colligation of the features of high physiographic relief 

 throughout this belt under the designation of the Pacific Mountain sys- 

 tem is here proposed at the suggestion of Mr Alfred H. Brooks. 



Throughout its extent, the Pacific system has a general parallelism 

 with the Rocky Mountain system, but between the two in all latitudes 



♦Published with the permission of the Director of the U. S. Geological Survey, 

 t Physiographic regions of the United States, Geographic Monograph, New York, 1896. Pp. 

 65-100. 



XVII— Buu.. GEOt. Soc. Am.. Vol. 14, 1902 (117) 



