YUKON, the largest river in Alaska, and the fifth largest in North America. With its longest tributaries not in Alaska, the Lewes and the Teslin (or Hootalinqua), its length is about 2,300 m., in the form of a great arc, beginning in the Yukon district of British Columbia, near the Pacific ocean, and ending at the Bering sea coast. Its catchment area is about 330,00o sq.m., more than one-half of which lies in Canada. The Lewes river rises in Lake Bennet, or, more accurately speaking, Lake Lindeman, on the northern slope of the coast range just over the Dyea pass up from Lynn canal (at the head of Chatham strait). It flows north through a chain of lakes with connecting streams until it is joined by the Hootalinqua about 3o m. below the last of these lakes (Lebarge). Its confluence with the Pelly river, at Selkirk, Yukon district, about 120 m. due east of the Alaskan-Canadian boundary, forms the headwaters of the Yukon proper. Flowing thence north west, the Yukon turns abruptly to the south-west near Ft. Yukon, Alaska, on the Arctic Circle, and continues nearly at right angles to its former course to a point south of the head of Norton sound, where it turns again and flows in a north-west direction, emptying into the sound from its south shore.
The Yukon valley comprises four sub-provinces, or physio graphic divisions, called the "Upper Yukon," "Yukon flats," "Rampart region" and "Lower Yukon." The "Upper Yukon" valley is about 450 m. long and from r to 3 m. broad, and is flanked by walls rising to the plateau level from 1,5oo to 3,00o ft. above the stream. In this part of its course the Yukon receives from the south the Selwyn river (about 4o m. below the junction of the Lewes and Pelly rivers) ; from the west the White river (about 6o m. below the Selwyn) ; from the north the Stewart river (about 10 m. below the White), one of the largest tributaries of the Yukon ; from the east the Klondike river (near 64° N. lat.) ; from the west Forty-mile creek (about 4o m. above the Alaskan-Canadian boundary line), and many other smaller streams. The "Yukon flats" flank the river for about zoo m. and are from 4o to loo m. wide. Here the stream varies in width from 10 to nearly 20 m., and involves a confused network of constantly changing channels. Here, too, the river makes its
great bend to the south-west, and its channels are constantly changing. The "flats" are monotonous areas of sand bars and low islands, thickly wooded with spruce. The principal tributaries here are the Porcupine river (an important affluent, which enters the main stream at the great bend about 3 m. N. of the Arctic Circle) ; the Chandlar river, also confluent at the great bend, from the north, and, near the west edge of the flats, the Dall river, also from the north. The "Rampart region" begins near 66° N. lat., where the "flats" end abruptly, and includes about i io m. of the valley, from I to 3 m. wide, and extending to the mouth of the Tanana. No large tributaries are received in this part of the river. At the west edge of the Ramparts the Yukon receives the Tanana river, its largest tributary lying wholly within Alaska. The Tanana valley is about 450 m. long, nearly parallel to the Yukon from about due west of its headquarters to the great bend, and drains about 25,00o square miles. Its sources lie in the glaciers on the north slopes of the coast, or St. Elias range, and it receives many tributaries. The Lower Yukon includes that portion between the ramparts and the sea, a stretch of about Boo m. At the mouth of the Tanana (which enters the main stream from the south) the gorge opens into a lowland from 15 to 20 m. wide. Along the north-west boundary of the valley are low mountains whose base the Yukon skirts, and it continues to press upon its north bank until the delta is reached. The valley is never less than 2 or 3 m., and the river has many channels and numerous islands; it has walls nearly to the head of the delta, though about 1 oo m. above the delta the south wall merges into the lowland coastal plain ; the relief is about i,000 feet. The Yukon delta begins near 63° N. lat. Here the main stream branches into several channels which follow north or north-west courses to Norton sound. The north ernmost of these channels is the Aphoon pass, and the most southerly is Kwikpak pass; their outlets are about 75 m. apart on the coast, and from 4o to 5o m. from the head of the delta. Between them is a labyrinth of waterways, most of the interven ing land being not more than 1 o ft. above low tide.