Willamette, river, 294 mi (473 km) long, rising in several headstreams in the Cascade Range, W Oregon. It flows N past Eugene, Salem, and Portland to the Columbia River just NW of Portland. The river is navigable for most of its course. Its wide, fertile valley is a major fruit-growing and dairying region. There is also diversified agriculture, manufacturing, and an important lumber industry. A federal project begun in 1938 harnesses the river and its tributaries for flood control, navigation, and power production with numerous dams and reservoirs in the Willamette basin. First settled in the 1830s, the valley was the goal of many pioneers traveling west to the Oregon Country on the Oregon Trail. The region quickly became the chief source of food products on the West coast, especially with the California gold rush in the mid-1800s. Rapidly settled after 1846, the valley has long been the most densely populated part of Oregon.