Washington State Route 504

State Route 504
Spirit Lake Memorial Highway
Map of the Toutle River Valley in southwestern Washington with SR 504 highlighted in red
Route information
Auxiliary route of I-5
Maintained by WSDOT
Length	51.76 mi[1] (83.30 km)
Existed	1964–present
Tourist routes	Spirit Lake Memorial Highway
Major junctions
West end	I-5 / SR 411 in Castle Rock
Major intersections	SR 505 near Toutle
Eastern end	Johnston Ridge Observatory in Mount St. Helens NVM
Location
Country	United States
State	Washington
Counties	Cowlitz, Skamania
Highway system
State highways in Washington Interstate US State Scenic Pre-1964 1964 renumbering Former
← SR 503 → SR 505

State Route 504 (SR 504, designated as the Spirit Lake Memorial Highway) is a state highway in southwestern Washington state in the United States. It travels 52 miles (84 km) along the North Fork Toutle River to the Mount St. Helens area, serving as the main access to the Mount St. Helens National Volcanic Monument. The highway begins at an interchange with Interstate 5 (I-5) and SR 411 in Castle Rock and terminates at the Johnston Ridge Observatory near Spirit Lake.

The Cowlitz County government built the Spirit Lake Highway in 1903 and paved it in the early 1930s before it was transferred to state control, becoming Secondary State Highway 1R (SSH 1R) in 1937. SSH 1R initially ended at the boundary of Columbia National Forest (now Gifford Pinchot National Forest), but was extended in 1961 to the timberline of the mountain. It was renumbered to SR 504 in 1964 and remained popular with loggers and tourists, requiring bridges and sections to be rebuilt.

A major section of SR 504 was destroyed in the May 18, 1980, eruption of Mount St. Helens and its subsequent lahar on the North Fork Toutle River. The state government rebuilt most of the highway from 1988 to 1997, relocating it further north and connecting to new interpretive centers at Coldwater Ridge and Johnston Ridge. A part of the old alignment near the Toutle River Sediment Dam is signed as a spur route. Continued volcanic activity at Mount St. Helens, particularly in the mid-2000s, has resulted in closures and evacuations along the highway at various times.