The Fifty-Year Slide: How Devil's Slide Beat the Engineers

The mountain started winning on the first day. Highway One opened to traffic at Devil's Slide in nineteen thirty-six, and within a few years it closed. A landslide took the road in nineteen forty. Engineers patched it and called it done. Then it slid again.

For fifty years, San Mateo County fought this cliff, and the cliff fought back on its own schedule. The roadbed here crosses Montara Mountain at a point where the geology is essentially a slow-motion collapse, a fractured face of rock and soil tilted toward the ocean, held by nothing permanent. When the rains came heavy, the mountain moved. Major slides closed the road for months in nineteen forty, nineteen fifty, nineteen sixty-one, and then dramatically in nineteen ninety-five, when a thirty-foot wall of hillside came down and sealed the highway entirely. The state kept patching. The cliff kept shrugging.

The numbers eventually made the argument. Each closure cost millions in emergency repairs. Traffic detoured inland through Half Moon Bay and down into Pacifica, adding time and miles for every vehicle that used this coast. Meanwhile, the patch jobs were lasting shorter intervals between each collapse. By the nineteen nineties, engineers were no longer arguing that they could hold the road. They were arguing about what to replace it with.

Voters answered that question in nineteen ninety-six. Seventy-six percent of San Mateo County approved a tunnel ballot measure, one of the highest margins on a public works project the county had seen. Ground broke in May of two thousand and five. Workers bored the twin tunnels through Montara Mountain, each thirty feet in diameter, for six years. On March twenty-sixth, two thousand and thirteen, they opened.

Congressman Tom Lantos, who grew up in Hungary and survived the Holocaust before coming to represent this district, secured the federal funding. The tunnels carry his name.

The old road became a hiking and cycling trail in two thousand and fourteen. You can walk it now. The cliff is still moving, at its own pace, in the direction it has always chosen. The engineers are no longer arguing with it.