State Route 131 (SR 131) begins at the northern end of Forest Route 25 (FR 25) located at the Gifford Pinchot National Forest boundary, which continues south (via FR 90), east of Mount St. Helens and Spirit Lake, to SR 503 Spur in Cougar. From FR 25, the roadway travels northbound as Woods Creek Road to an intersection with Cispus Road, where it is renamed to the aforementioned street. The highway then crosses the Cowlitz River and ends at U.S. Route 12 (US 12) in Randle. Before the US 12 intersection in Randle, the road was used by a daily average of 1,700 motorists in 2007, making this segment the busiest along the route. The same intersection was also the busiest on SR 131 in 1992, only with a daily average of 3,100 motorists.