Fraser, chief river of British Columbia, Canada, c.850 mi (1,370 km) long. It rises in the Rocky Mts., at Yellowhead Pass, near the British Columbia–Alta. line and flows northwest through the Rocky Mt. Trench to Prince George, thence south and west to the Strait of Georgia at Vancouver. Its chief tributaries are the Nechako, Quesnel, Chilcotin, and Thompson rivers. It is navigable to Yale, c.80 mi (130 km) upstream. The Fraser River canyon, which begins at Yale, is noted for its scenery; its mountain walls rise more than 3,000 ft (914 m). The river contains the chief spawning grounds in North America for the Pacific salmon. Logging is important along the upper course. The Fraser delta is the most fertile agricultural region of British Columbia; dairying and truck farming are important. The delta has the largest concentration of people in W Canada. Sections of the river are followed by oil and gas pipelines as well as transcontinental rail and highway routes. The Fraser River was visited by Sir Alexander Mackenzie, the Canadian explorer, who followed its upper course on his expedition (1793) to the Pacific Ocean and takes its name from Simon Fraser, the Canadian explorer and fur trader, who followed (1808) the river to its mouth, establishing fur-trading posts along the way. The river valley was the domain of the fur traders until the gold rush of 1858. After the discovery of gold (1859) in the Cariboo dist., on the river's upper reaches, the government built a road to serve the valley, and settlement of the region followed.