Crews work along Last Chance Grade, where ongoing landslide repairs fight to keep Highway 101 open-California's only coastal link to Crescent City. (Caltrans)

A long-awaited fix is finally taking shape for one of the most hazardous and landslide-prone stretches of California's Highway 101: a massive tunnel project that would become the longest in the state's history.

The trouble spot lies deep in the so-called Redwood Curtain - the remote, forested region of California's far North Coast, where Highway 101 clings to steep cliffs above the Pacific. It's a rugged, isolated stretch of road, more than five hours north of San Francisco and nearly as far from Portland. When it fails, entire communities like Crescent City and the hamlet of Klamath are cut off.

This 3-mile stretch of highway sits on a tangled web of overlapping landslides, Caltrans spokesperson Myles Cochrane told SFGATE in an email. Caltrans faces a daunting task, Cochrane explained: keeping the road open and safe while also working toward a permanent fix. That has meant years of slope monitoring, field studies and emergency repairs - all while planning a massive tunnel to bypass the unstable zone entirely.

The California Transportation Commission recently allocated $40 million to support what Cochrane described as "part of the design phase of the Last Chance Grade Project along U.S. Highway 101 south of Crescent City in Del Norte County." The funding will go toward designing a 6,000-foot tunnel that would avoid the notoriously unstable cliffs at Last Chance Grade - a section so prone to landslides it's become infamous among travelers and engineers alike.

Currently, California's longest highway tunnel is the Wawona Tunnel in Yosemite - a 4,233-foot passage blasted through granite in 1933. It's still a vital route into the valley and delivers one of the park's most iconic views just beyond its eastern end.

A conceptual rendering of the proposed tunnel's north portal, which would emerge just south of Crescent City to bypass the unstable cliffs of Last Chance Grade. (Caltrans)

According to the Environmental Impact Report, the proposed tunnel would "avoid the most intense area of known landslides and geologic instability, thereby avoiding the portion of U.S. 101 most prone to closure" by replacing it altogether.

The stakes are especially high in this remote corner of the state. The Environmental Impact Report notes that "U.S. 101 is the only north/south state highway in the county, and the only viable route between Klamath and Crescent City; a closure of the highway between the two communities would result in a 449-mile detour."

Cindy Vosburg, director of the Crescent City Chamber of Commerce, told SFGATE in an email that a landslide in February 2021 closed the road for months, "forcing the Klamath community, including schoolchildren, to take an eight-hour detour."

A February 2021 landslide dropped 40,000 cubic yards of debris onto Highway 101 at Last Chance Grade, severing access for months. (California Highway Patrol)

That slide was major. Cochrane said roughly 40,000 cubic yards of rock and debris crashed down onto the highway on Feb. 15, 2021, following a major storm. The road was fully closed for a time, and lane restrictions dragged on for months as crews cleared debris and stabilized the slope, with repairs stretching into late August.

Landslides at Last Chance Grade typically occur one to three times per decade, Cochrane said, but they've been happening more often in recent years. The 2021 closure was just the latest in a string of costly emergencies. According to Cochrane, between 2015 and 2018, Caltrans spent $49 million on storm damage repairs - replacing three damaged retaining walls, building three more and restoring a southbound lane lost in 2017.

Cochrane said that despite these efforts, the hillside hasn't stopped moving. In October 2023, crews completed yet another series of retaining walls, finally restoring two-way traffic for the first time in nearly a decade. The following winter, Caltrans remained on high alert, clearing debris from several smaller slides and patching pavement along the narrow, weather-beaten corridor between Wilson Creek and the northern end of Last Chance Grade.

A mock-up of the tunnel's south portal, designed to divert traffic away from one of California's most landslide-prone stretches of Highway 101. (Caltrans)

For those who live and work here, the impacts go far beyond roadwork.

"Such closures not only cut off tourists who are essential to our local economy and the survival of many businesses," Vosburg said, "but they also prevent community members from reaching critical doctor appointments or grocery stores."

Cochrane called the recent $40 million allocation "a significant milestone toward securing a lasting solution to one of the state's most geologically vulnerable stretches of highway." He said it marks the first year of funding for the project's next stage - the Plans, Specifications, and Estimates phase - which involves detailed engineering and design. That phase is expected to cost $225 million in total, with the remaining $185 million anticipated in 2026. In total, the project is expected to cost $2.1 billion.

Vosburg believes the region's future depends on it. She wrote that the project "is a vital undertaking that will significantly impact the future of businesses and the community in Del Norte County."

"Without a lasting solution to the constant landslides on Highway 101, we face an uncertain future regarding the accessibility of this main road into Crescent City and onward to Oregon," she added.

Cochrane told SFGATE that Caltrans is exploring "options to accelerate the timeline," but as it stands, "construction could begin as early as 2030, with the tunnel projected to open in 2038."

Valerie Stuckey, a Del Norte County supervisor, told SFGATE via email, "Last Chance Grade has been a long standing concern for the residents of Del Norte County. We are very isolated, with only three real routes out of the region, and HWY 101 is our only direct connection to the south."

"When the road is closed, our Klamath neighbors cannot access services in Crescent City. Likewise, emergency services cannot reach Klamath when slides shut down LCG," she wrote."We look forward to a secure and safe passage into one of the most beautiful areas of California."

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