The Historic Columbia River Highway reopened in late September after repairs were completed to the section between Larch Mountain Road and Vista House.
The Oregon Department of Transportation closed the section of the historic highway, also known as U.S. 30, on July 7 to vehicles, bicyclists and pedestrians to repair damage from the ancient landslide there.
This section has required regular monitoring and maintenance since the highway was first built more than a century ago. In March 2025, geotechnical engineers noted that settling had accelerated and caused additional structural issues for guardrails and downslopes.
These safety concerns prompted the closure of the highway on March 12, 2025. After temporary repairs and dry weather, ODOT reopened the highway on March 25 while it designed a longer-term repair.
Summer 2025 Repair
The longer-term repair was challenging for many reasons.
The location of the work zone required getting crews, equipment and heavy metal materials down a steep slope for installation. The three pipe outfalls needed for improved soil drainage required a pully system to lower them about 100 ft. downslope to the site.
To improve stability, this project added geo-grid mesh in layers from the wall to the back of the cut into the slope to add stability to the wall. Crews also added soil anchor nails and wire mesh below the wall for additional stabilization.
Perhaps the biggest challenge was fitting the work into the narrow window of construction season.
"This was a quick-build project from design, bid, construction and finish before the rainy season," said Jason McNeil, an ODOT engineer. "Fortunately, we have not had any major issues with design and, with the help from the designers and the contractor, we worked through issues quickly to keep the project moving forward and on track."
After reopening the highway, final touches on the project required occasional lane closures and flagging traffic for a few more weeks to complete the work.
Background
The Larch Mountain landslide is a deep, massive landslide complex that occupies more than 100 acres of the Crown Point State Scenic Corridor. The historic highway skirts around the perimeter of this massive landslide, and approximately 800 ft. of the highway crosses an active section of the landslide just east of the intersection with Larch Mountain Road, approximately half a mile west of Crown Point.
When the highway was built between 1913 and 1922, the ancient Larch Mountain Slide was a challenge. The original design for the highway at this location was a viaduct, or a bridge over land, though the structure could not accommodate the continuous movement of the landslide. This viaduct was removed in the 1960s when ODOT built the current alignment.
In 1983, and then again in 2007, ODOT constructed a retaining wall to support the historic highway. Continued ground movement, sometimes up to 12 in. in a year, has required annual repaving and reassessment.
