Heads up if you are planning any mountain driving this weekend. Highway 20 remains closed at milepost 130 near Diablo Lake following a rockfall earlier this month. WSDOT says cleanup and stabilization will take an extensive amount of time, with no estimated reopening date. If you are heading east toward the Okanagan, plan to use alternate routes for now.
The closure affects one of the most scenic stretches of the North Cascades Highway. Spring rockfall events are common in this corridor as freeze-thaw cycles loosen rock above the roadway. WSDOT crews are assessing the slope above the closure point before declaring it safe to reopen.
Locally, the Ferndale area flooding that closed Slater Road and parts of Marine Drive in mid-March has largely cleared up. Slater Road reopened on March 23 as the Nooksack River levels dropped. Roads near the floodplain can still be soft, so use caution on unpaved sections.
For the most current road conditions in Whatcom County and across Washington state, check the WSDOT Traveler Information page or call 511.
Highway 20, officially known as the North Cascades Highway, is one of the most celebrated mountain routes in the Pacific Northwest. Stretching from Anacortes on the coast to Twisp and beyond into the Okanagan Highlands, it passes through the heart of the North Cascades National Park complex, offering some of the most dramatic mountain scenery accessible by road in Washington state. The highway typically closes for winter in mid-November and reopens in spring, usually in April, depending on avalanche clearing and road conditions. A rockfall closure on top of the winter shutdown adds additional weeks of uncertainty for anyone counting on the route.
Spring is the most hazardous season for rockfall along this corridor, and the reason comes down to freeze-thaw cycles. Through winter, water seeps into cracks and joints in the rock faces above the highway, then freezes and expands, slowly prying the rock apart. After many cycles, those cracks widen enough that a rise in temperature can cause loosened material to slide. The canyon walls above the Skagit River gorge near Diablo Lake are steep and geologically complex, making this one of the more rockfall-prone sections of the entire route.
When WSDOT responds to a rockfall closure, geotechnical engineers evaluate the extent of the slide, identify any remaining unstable rock above the roadway, and determine what stabilization work is needed. That process can involve rock bolting, installation of rockfall nets or catch fences, removal of loose material from the slope face, and debris cleanup from the road surface. When WSDOT declines to give an estimated reopening date, it usually means the slope assessment has revealed work complex enough that setting a timeline would be premature. Travelers should plan for weeks, not days.
Diablo Lake sits inside the Ross Lake National Recreation Area, part of the broader North Cascades National Park complex. The lake is known for its vivid turquoise color, produced by rock flour suspended in the water that scatters light in a distinctive way. The lake sits behind Diablo Dam, one of three dams operated by Seattle City Light along the Skagit River. The current closure cuts off highway access to this stretch of the park from the western approach.
Travelers who need to cross to eastern Washington have two main alternate routes. US Highway 2 over Stevens Pass connects the Everett and Monroe areas to Wenatchee. US Highway 97 via Oroville provides access to the Okanagan Highlands. If your destination is the Methow Valley, Winthrop, or Twisp, check WSDOT pass reports before heading out.
The Nooksack River flooding that closed Slater Road in mid-March was part of a late-winter wet pattern affecting low-lying areas in Ferndale and the floodplain west of Bellingham. The Nooksack has a well-documented history of flooding, particularly along its lower reaches between Everson and the delta near Lummi Bay. The March 23 reopening of Slater Road signals that river levels have dropped enough for safe travel, though soft shoulders and debris on nearby unpaved roads may persist for several more weeks. While the mountain pass is closed, the rest of Whatcom County is moving on: the Bellingham Farmers Market opens its 2026 season on April 4 at Depot Market Square.
