A three-mile stretch of California’s Highway 101 known as Last Chance Grade is undergoing plans for a major engineering project aimed at addressing its ongoing geological instability. Located in Del Norte County in the state’s remote northwest corner, this section of highway runs along cliffs between the redwood forest and the Pacific Ocean and has been steadily eroding for decades.

The California Department of Transportation (Caltrans) is proposing the construction of a 1.1-mile tunnel to bypass the most unstable portions of the roadway. The estimated cost of the project is $2.5 billion. In late May, state officials released the final environmental impact report, a comprehensive 712-page document compiled after more than ten years of public engagement and coordination with government agencies, Indigenous tribes, businesses, and environmental groups.

Last Chance Grade, first built as a wagon trail in 1894 and then realigned in the 1930s, is perched atop four active landslides. The stretch has experienced significant movement, including horizontal shifts of up to 40 feet and vertical changes of 30 feet since its construction. These movements have accelerated in recent years, with some sections sliding several feet annually toward the ocean. The highway had to be reduced to one-way traffic for nearly a decade and was only fully reopened in October 2023, though restrictions have continued to be implemented as new shifts occur.

Repeated efforts to stabilize the highway, such as building more than two dozen retaining walls, have been largely unsuccessful, with many structures also suffering damage. The instability has had fatal consequences in the past; in 1972, a roadway collapse resulted in the death of two people when their car plunged over the cliff before dawn.

Highway 101 is the primary transportation link connecting Crescent City, a tsunami-prone community of about 6,000 residents, with Humboldt County and the broader state. When Last Chance Grade is closed, the only alternative routes are either steep, unpaved logging roads or a circuitous 449-mile detour that can take up to eight hours through Redding and southern Oregon. This detour poses significant challenges for local residents, including families whose children regularly commute to schools in Crescent City.

The proposed tunnel would be the longest highway tunnel in California at 6,000 feet, exceeding the length of Yosemite’s Wawona Tunnel. It would be situated east of the existing highway to avoid the most geologically unstable areas. Tunnel construction, however, would impact the environment, including the removal of 16 old-growth redwood trees wider than four feet, in addition to other tree losses within the Redwood National and State Parks, a UNESCO World Heritage Site.

Caltrans plans to request $225 million from the California Transportation Commission during the summer to fund the design phase, which will involve collaboration with international experts experienced in tunnel construction in seismically active regions. Project manager Jaime Matteoli indicated that construction could begin by around 2031, with the tunnel potentially opening by 2038.

While some local residents have expressed frustration about the lengthy timeline, there is general consensus that the project addresses a critical safety and connectivity issue. The tunnel represents a long-term solution to an ongoing hazard posed by the deteriorating roadway and its precarious position above the Pacific Coast.