Route 116 Retaining Wall Project near Monte Rio
State Route 116 Retaining Wall Project on the east side of Monte Rio
Please note that Caltrans is working on two retaining wall projects - one on the east side of Monte Rio, and another on the west side of town. If you'd like to view the page for the western slide, click here.
Update April 2, 2026
Using heavy machinery, work crews are drilling holes deep into the hillside above Route 116. Workers then insert gigantic soil nails that are grouted into placed and post-tensioned to grip the surrounding earth. The heads of the nails will act as anchors for a wall of shotcrete that will be spayed onto the surface of the slope and left to harden.
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Caltrans began a year-long retaining wall project on Monday, August 18, on State Route 116 in Sonoma County just east of Cnopius Road in Monte Rio, Sonoma County. Ghilotti Brothers is the contractor on the $14 million project to replace a culvert beneath the highway and build a retaining wall to shore up a steep and imminently failing slope on the north side of the road.
Flaggers will direct one-way traffic control during work hours, Monday – Friday.
Caltrans will install concrete barriers on September 3 that will cordon off one of the two lanes for the rest of the project. At that time, Caltrans will operate an electronic traffic signal, implementing one-way traffic control 24 hours a day until project completion.
With steep hills, and heavy winter rains, this area of SR-116 is especially prone to landslide. Indeed, Caltrans will be lifting one-way traffic control on the landslide repair just two miles to the east of this project in mid-August.
While anther slide project in the vicinity has been undertaken as emergencies, the upcoming project has been planned for several years, as Caltrans geologists and hydrologist have long-noted the tenuous soil conditions along the north side of the road. A damaged, and outdated culvert that carries water beneath the road adds to the urgency of the project.
