SH-75 Galena Summit Slide

This landslide at milepost 156.7 is 300 to 400 feet wide and just as long. It has damaged the highway many times in the past resulting in costly repairs, shifting of the roadway alignment and other impacts to travelers. The risk of not completing slope stabilization may result in a large slide that could block the highway indefinitely. With the use of federal funds, the Idaho Transportation Department will undertake a project to stabilize the landslide affecting SH-75. 

In addition to impacts on SH-75, if left uncorrected the slide would continue to impact the Sawtooth Park Highway/Old US-93, and various other trails within the slide zone. Project objectives include:

An active landslide exists on the southern slope of Galena Summit that does, and will continue to, impact State Highway 75 if left uncorrected.

This landslide at milepost 156.7 is 300 to 400 feet wide and just as long. It has damaged the highway many times in the past resulting in costly repairs, shifting of the roadway alignment and other impacts to travelers. The risk of not completing slope stabilization may result in a large slide that could block the highway indefinitely. With the use of federal funds, the Idaho Transportation Department will undertake a project to stabilize the landslide affecting SH-75. 

Project Objectives

In addition to impacts on SH-75, if left uncorrected the slide would continue to impact the Sawtooth Park Highway/Old US-93, and various other trails within the slide zone. Project objectives include:

• Ensure long-term stability and integrity of roadway
• Restore proper highway alignment to reduce curve around scarp (the area where material is shifting)
• Prevent movement of slide scarp into pavement
• Make repair compatible with environment and existing features

Selected Repair Option

ITD held a public meeting in 2018 to collect feedback on proposed solutions. The department has since selected an alternative that intends to lessen the impact of the landslide to SH-75 by constructing a hillside buttress support system. The project will place a rock/soil buttress at the toe of the slide area and reinforce the hillside supporting the highway. ITD will complete roadway improvements as needed and replace damaged sections of the existing Sawtooth National Forest Service trail system in the project area.

The “Toe Berm” will buttress the slide against the opposing hillside using 80,000-100,000 cubic yards of rock that can be obtained from local sources. This approach both meets project goals and is cost-effective.

Construction

Construction is planned for 2026 and 2027. Work in 2026 will include vegetation removal to the north of the proposed buttress location to harvest rock. Most roadway impacts won’t start until 2026 with the start of work on the buttress. 

All work is expected to take 12–18 months and be timed during the summer and fall to avoid times of heavier precipitation in the spring and winter.

Impacts during construction

Travelers should plan for delays from 30 to 60 minutes. Temporary signals, flaggers and pilot cars will be used to guide traffic. Nighttime closures to all travelers except emergency vehicles are possible. 

Additional full-width closures could take place during blasting. Turnouts and overlooks over Galena Summit could also be closed. Closures for recreational trails in the work area are also expected. 

Staging areas may include Horse Creek stockpile site at milepost 153.8. 

More information will be shared once the project is awarded to a contractor.

Contact Jake Turrittin for project questions: