Devil’s Slide, Then and Now

It took 40 years, some committed individuals, a grass roots groundswell, and an act of Congress. In some ways it was a typical battle between conservationists and an entrenched bureaucracy. But in the end everyone is happy that there is a tunnel under San Pedro Mountain, bypassing Devil’s Slide in the most aesthetically pleasing and safest way.

Devil’s Slide is a notoriously unstable mountainside on the California Coast, where conglomerate, shale and sandstone sit unsteadily on steep sleek granite. For the over 70 years that the Coastal Highway has passed along this cliff, rockslides and mudslides have occurred again and again, due to seismic activity or rain. Residents of Pacifica and Montara, nearby towns, learned to live with this danger, and resigned to long detours when the road was closed. The worst landslide, in 1995, closed the road for 5 months and cost over $3mm to repair.

Caltrans had a solution. In 1958 they proposed building a 7-mile long, 6-lane highway over the mountain. They claimed it was the easiest, cheapest and most practical way to solve the landslide probabilities. But their plan would also assure heavy development along the coastline with the expectation of 200,000 new residents by 1990.

Fortunately the Committee for Green Foothills allied with other environmental groups to force Caltrans to look at other options. They started hesitantly, with lawsuits to delay Caltrans’ proposed ambitions. Then, in 1995, a panel of geologists and engineers recommended studying the feasibility of a tunnel.

Emboldened environmentalists collected 34,000 signatures in a petition to ask voters to force Caltrans to consider such a study.

Fast forward 10 years. In 2005 work began on the 4200 foot twin bore tunnel through San Pedro Mountain. Funds for the effort included Federal monies obtained through the efforts of Congressman Tom Lantos and Senator Barbara Boxer. The long construction project would result in a state-of-the-art, well-ventilated, well-lit passageway, now the longest tunnel in California.

Care was also taken to preserve habitat for the endangered California red-legged frog, the dusky-footed woodrat, and an endangered wildflower, the Hickman cinquefoil.

In 2013 the Tom Lantos Tunnels opened for the first time with a parade of antique cars. The first car was a Model T, with a license plate “THNK TNL”.

That problem stretch of highway called “Devil’s Slide” has now been turned into a nature trail 1.3 miles long, with spectacular views of the coastline. In March 2014 the trail opened to the public, dogs and bicycles welcome. 700 feet below, you can see San Pedro Rock, its distinctive sedimentary layers thrust above the surf. Look up and you can spot an abandoned concrete observation bunker used from 1943 to the 1980’s as part of the Harbor Defense System. Near the bunker you may even spot a peregrine falcon and his nest, oblivious to the commotion below.