218 The National Geographic Magazine 



four distinct ranges — the Coast, St 

 Elias, Alaskan, and Aleutian. These 

 are often separated by broad valleys or 

 indentations of the coast line, and while 

 the topography of the system is mainly 

 rugged and mountainous, it includes 

 several large basins, like that of the 

 Copper River. 



East and north of the Pacific Moun- 

 tains is the Central Plateau region, 

 limited on the north and east by the 

 Rocky Mountains, corresponding with 

 the Great Basin region of the western 

 United States. The term plateau can 

 only be assigned to a part of this prov- 

 ince, and not even that by strictest 

 usage. Its dominating topography is 

 a gently rolling upland of low relief, 

 compared with the mountain systems, 

 in which the rivers have trenched broad 

 channels. The interstream areas mark 

 a former plateau surface, which the 

 erosive agents have dissected. This 

 plain slopes gently toward the axis of 

 the basin, and the axis is tilted to the 

 north and west. Its surface is inter- 

 rupted by a number of mountains and 

 mountain groups, which rise above the 

 general level. Within this belt are also 

 a number of lowland areas of consider- 

 able extent, which lie below the upland 

 surface. Among these the flat of the 

 middle Yukon is notable. The lowlands 

 which extend along Bering Sea adjacent 

 to the Knskokwim and Yukon rivers 

 are included in this province. 



To the east and north is a broad 

 mountain system, but little explored, 

 which forms the third of the geographic 

 provinces. It is, as has been shown, 

 the northern extension of the Rockies. 

 These, like the Pacific Mountains, also 

 undergo a marked change in direc- 

 tion. Trending northwestward from the 

 United States and Canada, they swing 

 to the southwest at the Arctic shore, 

 which they touch again north of Bering 

 Strait. The system is represented in 

 Alaska by the Endicott Mountains, and 

 probably by several other ranges as yet 

 unsurveyed. 



The fourth province is that of the 

 plains lying east of the Rockies, which 

 in Alaska is represented by the Arctic 

 Slope region, lying between the west- 

 ern extension of the Rockies and the 

 Arctic Ocean. This province, like that 

 of the western United States, is really a 

 slightly elevated plateau, dissected and 

 more or less rolling, which slopes to the 

 north from the foothills of the Rocky 

 Mountains. A featureless coastal plain , 

 of varying width, separates the north- 

 ern boundary of the plateau, which is 

 marked by a scarp, from the Arctic 

 Ocean. 



About one-fifth of the drainage of 

 Alaska is toward the Pacific Ocean, 

 nearly one-half toward the Bering Sea, 

 and the rest toward the Arctic Ocean. 



The map shows the Yukon to be the 

 master stream, and the outlines of its 

 basin correspond in a general way with 

 the boundaries of the Central Plateau 

 province. The headwaters of this 

 mighty river, the fifth in size of the 

 North American continent, lie in British 

 Columbia far to the southeast of Alaska, 

 where they fight for mastery on one 

 hand, with the water-courses flowing 

 into the Pacific, and on the other with 

 those belonging to the Mackenzie drain- 

 age basin, flowing into the Arctic Ocean. 

 The general course of the Upper Yukon 

 and its tributaries is northwest as far as 

 the Arctic Circle. It then makes a great 

 southwest bend and pours its great 

 volume of muddy waters into Bering 

 Sea nearly 3,000 miles from the source 

 of its longest tributaries. The valley 

 of the Yukon occupies the medial line of 

 the plateau province, and with it makes 

 the same great bend to the southwest 

 parallel to the swing of the two moun- 

 tain systems to the north and south. 

 The relief, which is measured by the 

 altitude of the remnants of the plateau 

 above the floor of the valley, is greatest 

 near the international boundary and 

 decreases both above and below. A 

 narrow valley characterizes the Upper 

 Yukon proper, which broadens out at 



