Then the river is joined by Chinook Creek from the north. The Ohanapecosh turns south and flows through a broad glacial U-shaped valley, which it shares with Washington State Route 123, east of the river, and the Eastside Trail on the west side of the river. Many tributary streams joins the river, including Panther Creek from the east and Olallie Creek from the west. Shortly below Panther Creek the Ohanapecosh exits Pierce County and enters Lewis County. Below Olallie Creek the Ohanapecosh River flows through a broad flat bottomland called Cedar Flats. The river splits into two channels which join at the south end of Cedar Flats. The Grove of the Patriarchs trail crosses the river and loops through the island created by the Ohanapecosh's channels. Just downstream from the rejoining of the two channels the Ohanapecosh flows by the east end of Stevens Canyon Road, which joins State Route 123 near the river. The high ridge west of the Ohanapecosh River north of the Stevens Canyon entrance road is called the Cowlitz Divide. South of the Stevens Canyon entrance the ridge is called Backbone Ridge. Both form a continuous ridgeline separating the watershed of the Ohanapecosh from the Muddy Fork Cowlitz River. The river plunges over Silver Falls near river mile 6, between Stevens Canyon Road and Laughingwater Creek. Just below that the river is joined by Laughingwater Creek from the east. At approximately river mile 5, less than a mile below Laughingwater Creek, the Ohanapecosh flows by Ohanapecosh Hot Springs and the Ohanapecosh Campground, Visitor Center, and Ranger Station. This southeastern part of Mount Rainier National Park is known as the Ohanapecosh area. After flowing through it the river exits the national park and enters Gifford Pinchot National Forest. Continuing south the Ohanapecosh is joined by Carlton Creek and Summit Creek from the east. Near La Wis Wis Campground the Ohanapecosh River joins the Clear Fork Cowlitz River. Below the confluence the stream is called the Cowlitz River. State Route 123 ends near La Wis Wis, joining U.S. Route 12. Route 12 continues to follow the Cowlitz River downstream.