Once hidden between rocks, the graffiti-covered remnants of a former military triangulation and observation station now rest atop a cliff at the Pacific Coast Highway. It was originally built during World War II as part of the harbor defense of San Francisco. The U.S. military began constructing a sprawling defensive system in the 1930s around the mouth of the Golden Gate. The San Francisco Bay was a potential strategic target. It was not only a vital transportation hub, but also home to Mare Island and Hunters Point naval shipyards, among other military installations.
Since radar was not invented yet, watchers used binoculars and compasses to search for Japanese ships at sea and relay their coordinates to the massive gun batteries in the Marin Headlands and at Fort Funston. By combining information from multiple observation posts, the enemy ship’s location could be precisely determined. In total, there were six military structures at Devil’s Slide. The facilities included three concrete and steel observation pill-boxes, two concrete and earth bunkers, and a reinforced steel observation tower. Today, only some of the structures remain.
After the Japanese bombed Pearl Harbor, the work took on new urgency and next-generation technology came to use. Just a few miles down the coast, the Army built a radar tower and anti-aircraft machine guns along Pillar Point Bluff (now the Pillar Point Air Force Station) and a mile-long airstrip (now Half Moon Bay Airport). The Army suspended hundreds of mines in the ocean outside the bay and strung a submarine net across the inside. They prepared the Bay Area for an enemy assault that would never come.
After the end of WWII, the station became obsolete and was abandoned in 1949. The earth at the top of the peak was removed for a construction project, but the plan to develop the property got never completed. The lonely, ghostly shell of the bunker is overhanging the edges and looks like a partially excavated fossil. The metal and concrete is exposed to the ocean air, but remaining strong in the decaying sand. The weather is causing erosion and mudslides, dragging away the dirt under the bunker base. The site was sold to a private owner in 1983 and is not open to the public. But this has not stopped graffiti artists from tagging most of the surfaces. The constantly changing graffiti provides a stunning contrast to the gorgeous seaside.