The Sol Duc River is a river in the U.S. state of Washington. About 78 miles (126 km) long, it flows west through the northwest part of the Olympic Peninsula, from the Olympic Mountains of Olympic National Park and Olympic National Forest, then through the broad Sol Duc Valley. Near the Pacific Ocean the Sol Duc River joins the Bogachiel River, forming the Quillayute River, which flows about 4 miles (6.4 km) to the Pacific Ocean at La Push. Although the Quillayute River is short, its large tributary rivers—the Sol Duc, Bogachiel, Calawah, and Dickey Rivers—drain the largest watershed of the northern Olympic Peninsula, 629 square miles (1,630 km2). The Sol Duc's watershed is the largest of the Quillayute's tributaries, at 219 square miles (570 km2).