Erosion caused by surface and subterranean water during the Jan. 10-11 storms has weakened part of Highway 84 in the hills above Woodside. A 75-to-100-foot section located a few minutes north of Skylonda and just past Grandview Drive dropped by about 9 inches, according to a foreman directing a clean-up crew on Jan. 14.

Traffic is one lane for several hundred feet and will likely remain one lane while the California Department of Transportation designs and builds a retaining wall to shore up a new section of road, said Granite Construction Foreman Joel Duckworth, on the scene under contract to Caltrans.

The Almanac sought a comment from Caltrans, but the offices were closed for the holiday.

It could be a few months before normal two-way traffic resumes, Mr. Duckworth said. At both ends of the damaged section, flag crews will be on hand around the clock to direct traffic until temporary autonomous traffic lights go in, he said.

Drivers are advised to consider alternate routes, including Kings Mountain Road in Woodside and, further north, Highway 92 across the Crystal Springs Reservoir.

What happened

Residents near the damaged area have been complaining to Caltrans for months about erosion along the downhill edges of the road, particularly a spot a half-mile to the east at the intersection of Highway 84 and Friars Lane.

As for the current subsidence, Grandview Drive resident William Fender said he recalled seeing a "big crack" in the road as he drove down the hill. The road surface dropped 6 inches when crossing the crack, he said, adding that at one point, his entire vehicle was within the borders of the subsidence area.

"That's mountain living," he said at one point, and complimented crews who restored electrical power after a couple of outages during the storm. "That was great! They did a good job," he said.

Town Manager Kevin Bryant said that staff "constantly remind Caltrans that (erosion) is an issue" on Highway 84, and that Caltrans typically responds with a plan on how they're going to address it. "I was always under the impression that (Friars Lane) was an urgent repair project," he said.

The roadbed of Highway 84 is subject to erosion because much of it happens to lie directly in the path of storm-water runoff descending steep slopes. In the recent storm, enough water flowed on the surface to cause mudslides onto the road surface and the toppling of two major trees located on the uphill side of the road, Mr. Duckworth said.

But water also ran below the surface, undermining support for the road, sending semi-liquid soil to the bottom of the slope, and triggering the subsidence, Mr. Duckworth said, adding: "The road is failing."

To create a workable surface for a new road, a crew with an excavator has already built a temporary soil roadbed with a 3-foot berm between the road's edge and the downhill slope. The retaining wall -- now in the design phase, Mr. Duckworth said -- will come after bore holes and soil testing indicate the most appropriate wall for the situation.

Design will take a couple of weeks, and in a few months, "they'll have a retaining wall," he said.

"They'll have to dig way down. We're talking big time," Woodside Town Engineer Sean Rose said, taking care to note that he was speculating about the repair.

Asked about Town Hall's working relationship with Caltrans, Mr. Rose said that staff members contact Caltrans in response to residents' calls about state roads. "We did that (for the Friars Lane spot) and that's all we can do because they make the decisions," he said. The staff did not receive calls about the current problem area, he said.

Friars Lane "looks to me like it could go at any time," he added.

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