The Feather River is the principal tributary of the Sacramento River, in the Sacramento Valley of Northern California. The river's main stem is about 71 miles (114 km) long. Its length to its most distant headwater tributary is about 220 miles (350 km). Its drainage basin is about 6,000 square miles (16,000 km2). The main stem Feather River begins in Lake Oroville, where its four long tributary forks join together—the South Fork, Middle Fork, North Fork, and West Branch Feather Rivers. These and other tributaries drain part of the northern Sierra Nevada, and the extreme southern Cascades, as well as a small portion of the Sacramento Valley. The river's drainage basin above Lake Oroville is 3,222 square miles (8,340 km2), or about 53% of the whole.