Sonoma County Caltrans Update

Landslide Repair Projects on State Route 116In Western Sonoma County

Three landslides have occurred between Monte Rio and Guerneville within the last year

^{An excavator builds an embankment between a temporary retaining wall and the Russian River on Route 116 between Duncans Mills and Monte Rio}

In a little over a year’s time, Caltrans has contended with three landslides on State Route 116 between Guerneville and Monte Rio, a distance of just four miles.

Fixing these slides required Caltrans to implement one–way traffic control. While, this may inconvenience motorists, the overwhelming majority of drivers understand the realities of living in a valley, squeezed between mountains and the river. It rains hard in winter, and saturated slopes give way to gravity. Yet nothing short of a massive widening project on Route 116 would stop the sliding, something that would be extraordinarily expensive and anathema to the area's woodsy, small-town character.

West Monte Rio Slide

Began January 5, 2026
Furthest west

^{View from across the river at the newest slide on Route 116 between Duncans Mills and Monte Rio}

Weeks of heavy rain and a swiftly flowing Russian River eroded the riverbank, causing the earth to give way along the eastbound shoulder of Route 116 between Duncan Road and Monte Cristo Avenue in western Monte Rio, taking out a span of guardrail, several trees, and undermining a 100-foot-long section of the eastbound shoulder.

As with the other slides, Caltrans put the road under one-way traffic control and built a temporary retaining wall to support the road while a larger, bulkier retaining wall is de-signed and built. Repairs have been swift, but upcoming rainy weather could stall progress.

East Monte Rio Slide

Began August 2025
Middle Slide

^{The slide between Monte Rio and Guerneville before crew went to work on it. This slide hasn’t become a catastrophic slide, meaning, most of it has stayed in place. Caltrans has a project to keep the slide in place before it gives way and slides onto the road.}

This slide hadn’t fully manifested it-self when Caltrans began work. In other words, it hadn’t tumbled onto the road yet. Geotech engineers had been watching a slope along the westbound lanes and noticed movement that portended a forth-coming downfall.

Recognizing the risks, Caltrans began proactive work to address the instability. Crews made substantial progress, but January downpours triggered further movement, exposing new slide planes. As a result, Caltrans paused construc-tion for several weeks to allow engineers revise the design plans. Work has since resumed, and Caltrans now estimates the project will be completed by Sep-tember 2026.

West Guerneville Slide

Began December 2025
Easternmost Slide

^{The West Guerneville Slide.
Day two of the west Monte Rio Slide.}

In addition to closing one lane, the slide threatened two sewer pipes located within the right-of-way. Caltrans hired a contractor to install a mini-pile retaining wall. Although the construction was substantial, great care was taken to avoid disrupting the sewer lines, one of which was a high-pressure line that, if damaged, could quickly contaminate the Russian River. Despite these chal-lenges, the project was successfully completed in August 2025.Top: The West Guerneville Slide. Middle: Day two of the west Monte Rio Slide. Bottom: Picturesque scene of fog lift-ing on the Russian River, showing why people love living in the Russian River valley.

Slide vs Slip-out

We have used the term ‘slide’ to de-scribe these landfalls. But in the par-lance of Caltrans, certain slides can be further defined as ‘slipouts.’A slide occurs above the highway, while a slipout (or washout) happens below the highway.The distinction is helpful for describing slides. All things being equal, a slipout is usually worse because it often washes away the earth supporting the road, leaving it unstable and necessitating extensive repairs.Slide vs Slip-out

^{Picturesque scene of fog lift-ing on the Russian River, showing why people love living in the Russian River valley.}

New HOV hours announced in Marin, Sonoma counties

Caltrans and its transportation partners, the Metropolitan Transportation Commission, the Transportation Authority of Marin and Sonoma County Transportation and Climate Authorities announced adjustments in January affecting High Occupancy Vehicle (HOV) hours on US-101 in Marin and Sonoma counties.

New HOV hours will take effect in late February (weather per-mitting) and operate between 6 a.m. to 9 a.m. in the mornings and 3 p.m. to 6:30 p.m. in the evenings, Monday through Friday. The hours are based on Caltrans traffic analysis along the corridor that was completed this month. The new hours will begin after work crews up-date freeway signs to reflect the new hours. Signs will be up-dated along the entire length of the HOV lanes, a 52-mile stretch from the Richardson Bay Bridge in Marin County to Windsor in Sonoma County.

For more info, see US-101 Marin-Sonoma Narrows Carpool Lanes Update | Caltrans

Bridge Railing Projects Need Your Understanding and Patience

Caltrans has completed six projects with three more scheduled
This Spring/Summer on Route 116

In the last six months, Caltrans has completed six bridge railing replacement projects in Sonoma County.

While some freeway overpasses sport new decorative fencing chosen by the local city—Santa Rosa for example—smaller projects, particularly those on two-lane highways, are typically refitted with new guardrails.

<sup>Lattice work adds architectural detail to the bridge railing on the Baker Street Overcrossing

The Jones Creek Bridge in western Sonoma County</sup>

These are important safety projects and much more difficult and time-consuming than one would imagine. The railings and guardrails can’t just be lifted from the bridge by un-screwing a few bolts. Their structural undercarriages are deeply embedded in the concrete and require demolishing most of a traffic lane to extract them.

Such construction needs adequate working room, so these projects require one-way traffic control, usually from start to finish.

Some of the railings, like those on the Arroyo Lindo Bridge and the Yellow Creek Bridge in Schellville are over a hundred years old, designed when autos were much lighter, and speeds were much lower. Wear and tear from minor collisions and wet weather has also taken its toll.

In August 2025, Caltrans finished replacing bridge railings on Highway 101 over-passes north of Santa Rosa, including Fulton Road, Mendocino Avenue, Shiloh Road, and Limerick Lane.

Shortly afterward, Caltrans replaced the bridge railings on a pair of bridges in Schellville (mentioned above) near the new Route 116/121 Roundabout. The Arroyo Seco Creek Bridge required a full closure of Route 121 for a month, while the Yellow Creek Bridge required three months of one-way traffic control.

Starting this summer, Caltrans will begin replacing the railings on bridges spanning small creeks on Route 116. You may not have heard of these creeks: Jones, Blucher, and Gossage creeks, but they carve a deep and wide enough channels in the winter to re-quire sturdy railings to protect motorists should they veer from the road.

Caltrans is still working on the construction sequence to determine which bridge will be worked on first, or if the bridges can be worked on simultaneously. Caltrans will implement one-way traffic control during construction.

Setting the PACE: Public Affairs Customer Engagement Site is Now Live!

District 4 is proud to announce the launch of our new Customer Service Request (CSR) platform. PACE, the Public Affairs Customer Engagement site, provides a regularly updated breakdown of services requested and rendered across the district.

• The CSR dashboard aims to provide an overview of the responsiveness to maintenance services requested across the nine Bay Area counties.
• The data represented as month-to-date falls within a rolling 30-day Service Level Agreement (SLA) and is updated weekly.
• We strive to close 60% (or more) of all monthly service requests received via the CSR website portal.
• For more information or to leave comments/suggestions, please contact D4CSLTEAM@dot.ca.gov.
• To report a highway issue/problem, please submit a CSR ticket through the Customer Service Request Form.

The Sonoma  County newsletter will be distributed on a regular schedule.

For 24/7 traffic updates, please visit 511.org: https://x.com/511SFBay
For real-time information, visit Caltrans QuickMap: https://quickmap.dot.ca.gov
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Or call 1-800-472-7623, 1-800-427-ROAD for state highway conditions statewide.

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