The mighty Columbia, which forms part of the border between Washington and Oregon, drains a huge inland area through the only waterway that crosses the Cascade Mountains. The area where it accomplishes this feat is now designated the Columbia River Gorge Nat'l Scenic Area. The river has been harnessed by a series of Dams for hydroelectric power, irrigation, and transportation. It empties into the Pacific Ocean at Astoria.
Major tributaries include the Snake River, which forms part of the Oregon/Idaho border and the Willamette River which empties into the Columbia just above Portland.