Getting Oriented
The western terminus is at I-5 exit 49 (Castle Rock), an hour and a half south of Seattle. The route runs east through the rural North Fork Toutle valley, climbs into Mount St. Helens National Volcanic Monument on Gifford Pinchot National Forest land, and (when open) ends at Johnston Ridge Observatory at 4,200 feet, five miles north of the crater. The Forest Service operates the Mount St. Helens National Volcanic Monument; WSDOT maintains the highway itself.
Trail Overview
Fifty-two miles, out-and-back. The first 30 miles are flat valley road through small communities and tree farms. Past the Sediment Retention Structure dam, the highway climbs into the blast zone, with progressively more visible eruption damage at each pull-out. Coldwater Lake (at milepost 45) is the practical end of the open highway as of 2026 because of the closure beyond. Five interpretive viewing centers line the route at varying elevations, each focused on a different aspect of the 1980 eruption and the recovery since.
Points of Interest
- Mount St. Helens Visitor Center, Silver Lake. State Parks-operated visitor center near milepost 5.
- Sediment Retention Structure dam. Engineering response to the lahar; a viewpoint sits above the dam.
- Forest Learning Center. Weyerhaeuser-operated interpretive site (free admission).
- Hoffstadt Bluffs Visitor Center. County-operated viewpoint with helicopter tours.
- Coldwater Lake. Lake formed when the lahar dammed Coldwater Creek. Boat ramp and short walking loops.
- Johnston Ridge Observatory. End of the highway when open; closed since December 2023, slated to reopen spring 2027.
- South Coldwater Trail. Walk-in trail near Coldwater Lake with views into the blast zone.
- Boundary Trail. Pacific Northwest Trail crossing.
Where to Camp
There are no campgrounds directly on SR-504 inside Mount St. Helens National Volcanic Monument. Seaquest State Park, near the highway's western end at Silver Lake, has reservable developed sites and is the standard base. Toutle River RV Resort and Cougar Camp on the south side of the volcano (separate access via SR-503) offer alternatives. Dispersed camping is generally not permitted within the monument's interpretive corridor.
Tips for a Safe and Enjoyable Trip
- Confirm current closure status with WSDOT before driving. The upper highway has been closed since December 2023.
- A Northwest Forest Pass or Monument Pass is required at the higher visitor sites when they are open. Federal interagency passes do not cover all of them; check the Forest Service site.
- The interpretive centers each charge separate admission; budget for entry fees if visiting multiple.
- Carry layers. Coldwater Lake and Johnston Ridge sit 4,000+ feet higher than the I-5 valley.
- The blast zone has limited shade. Carry sun protection.
- Cell coverage drops past Coldwater Lake.
- Wildlife (elk in particular) is abundant in the recovering blast zone.
- The highway closes seasonally past Coldwater Lake even when the slide closure is lifted; full upper access is May through October most years.
