wide valley bounded, on the west, by the Mackenzie Mountains and to the east by low hills of the Canadian Shield. This mostly uninhabited area is called the Mackenzie Lowlands; although partly forested, it is mostly covered by large areas of muskeg, swamps and many small lakes. A number of major tributaries join from the west, including the Root River, Redstone River and Keele River. Below the Keele River, the Mackenzie River flows north along the western base of the Franklin Mountains before turning northwest, and receives the Great Bear River, the outflow of Great Bear Lake at Tulita. The Mackenzie widens considerably to about at Norman Wells, a major center of oil production. There is a narrows at the Mountain River confluence called the Sans Sault Rapids, where the Mackenzie falls about . Below the Mountain River the Mackenzie flows due north until reaching The Ramparts, a limestone gorge barely wide and up to deep. Below The Ramparts is the village of Fort Good Hope, where the Mackenzie turns northwest again, soon crossing the Arctic Circle. The Mackenzie here flows slightly lower in elevation than the surrounding tundra, as a braided river between low bluffs about apart. It receives the Arctic Red River from the southwest at Tsiigehtchic, where traffic on the Dempster Highway crosses via ferry/ice bridge. About northwest of Tsiigehtchic is Point Separation, the head of the vast Mackenzie River Delta, whose branching channels, ponds and wetlands spread across more than of the coastal plain. The delta is nearly from north to south, and ranges in width from . It is the second biggest Arctic delta in the world, after the Lena River delta in Russia. Most land in the Mackenzie delta consists of permafrost, with great depths to bedrock. A characteristic feature of the delta is its numerous pingos, or hills of earth-covered-ice – some 1,400 of them. The Peel River, carrying much of the runoff from the northern Yukon, joins in the delta at a point northeast of Fort McPherson. Below there, the Mackenzie diverges into several large channels with the largest heading north-northeast, emptying into the Beaufort Sea west of Tuktoyaktuk. Drainage basin At , the Mackenzie River drainage basin encompasses nearly 20 percent of Canada. About , or 54 percent of the basin, lies above Great Slave Lake. Permafrost underlies about three-quarters of the watershed, reaching up to deep in the Mackenzie Delta.