State Route 504 (also known as the Spirit Lake Memorial Highway), is a highway that runs east from Castle Rock, Washington for 52 miles to its present terminus at Johnston Ridge Observatory at the northern base of Mount St. Helens. Other places of interest along this highway include the Mount St. Helens Visitor Center (which is part of the Washington State Park System), and the Coldwater Ridge Visitor Center .

Previous to the May 18, 1980 eruption of Mount St. Helens, S.R. 504 ran alongside the North Fork of the Toutle River to end at Spirit Lake, but this course was rendered impassable due to the lahars that followed the eruption. From the community of Toutle, the course of this highway was later relaid several hundred feet above the river valley. East of Toutle, where it enters the Gifford Pinchot National Forest, there is only one gas station, and no cell phone coverage.