p. B. KING 



creasingly larger entitles, but even these surface forms are diversely 

 interpreted. 



Finally, in so large a subject as western North America, I cannot 

 hope to do justice to all items and problems in a single paper. The 

 best one can do is to make a sampling and to hope that the samples 

 will be sufficiently representative of the whole. In this paper, the 

 samples will be chosen mainly from the segment in the United 

 States, partly because this is the region I know best, partly because 

 it is the region best known to geologists in general. 



PRESENT GEOGRAPHY 



Western North America is the region of the Cordilleran system of 

 mountain ranges, which extend unbroken along the Pacific Coast 

 from Alaska to Central America, and beyond, and inland 400 to 1,000 

 miles (Fig. 1). In Canada and the western United States they front 

 eastward on the Great Plains of the continental interior, but in 

 Alaska they front northward on a coastal plain at the edge of the 

 Arctic Ocean, and in Mexico they front northeastward on a coastal 

 plain at the edge of the Gulf of Mexico. 



Geographically, the Cordillera north of Mexico is commonly 

 divided into two chains of ranges, one along the coast on the west, 

 another fronting the Great Plains on the east, with lower, more 

 broken ranges and plateaus intervening. Highest summits in North 

 America and in the United States are in the chain nearest the coast, 

 Mount McKinley in Alaska at 20,300 feet and Mount Whitney in 

 California at 14,495 feet. The summit of the interior chain. Mount 

 Elbert in Colorado at 14,431 feet, is somewhat lower. Many other 

 peaks in both chains project to heights nearly as great as the ab- 

 solute summits, and some of these have greater relief relative to 

 their immediate surroundings. 



The western mountain chain includes the Alaska Range of Alaska, 

 and the Coast Mountains of British Columbia. In the United States 

 the chain is double, with low Coast Ranges on the west separated 

 by the Puget Trough, Willamette Valley, and Great Valley of 

 California from the higher Cascade Range and Sierra Nevada on the 

 east. A comparable pattern is expressed to the north, in Canada and 

 southeastern Alaska, by the offshore islands and Inland Passage, 

 and to the south, in Mexico, by the peninsula of Baja California 

 and the Gulf of California. 



