US 101 - S of Cosmopolis - Stabilize Slope

Project news

  • US 101 at milepost 78.3 just south of Cosmopolis has a history of reoccurring landslides which occur beneath the highway due to a chronic, unstable slope. WSDOT has invested millions of dollars in correcting the area to keep the highway open to travelers. This particular site was first discovered on Jan. 24, 2020 and resulted in nearly 12 inches of roadway settlement. WSDOT corrected the first unstable slope roughly 1,000 feet away in the summer of 2020.
  • One-way alternating traffic is in place following several feet of recent roadway settlement. WSDOT will continue to monitor the roadway for further settlement issues. Loads are restricted to no wider than 14 feet to provide clearance.

Needs & benefits

Why is WSDOT stabilizing a slope on US 101 north of the SR 107 interchange in Cosmopolis?

Since January of 2020, this stretch of highway which locals refer to as “Cosi Hill,” has been reduced to single lane with a temporary traffic signal due to chronic roadway settlement. The roadway sits on a pre-historic landslide, resulting in repeated lane closures and delays for travelers between Aberdeen and Raymond.

WSDOT geotechnical engineers have evaluated the site and are actively designing a repair. Previous lower-cost repairs have proven to only last a season and have not addressed underlying causes. This solution will save money year over year, while addressing the chronic settlement issues.  

The End Result
A stabilized roadway will help secure the hillside, reducing the potential for roadway settlement and repeated lane closures.  


  • Spring 2021: Contract advertised
  • Summer 2021: Construction begins
  • Fall 2022: Most work complete


Financial Data for PIN 310178F
Funding Source Amount ($ in thousands)
2003 Gas Tax (Nickel Funding) $0
2005 Gas Tax (TPA) $0
Pre-Existing Funds (PEF) $5,345
CWA $0
Total $5,345


Karen Boone
Aberdeen Project Engineer 

Tina Werner
Media Relations