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Before the use of radar in war, soldiers and other military personnel made use of binoculars and compasses from posts built along the coast. They would relay coordinates to other posts, and this information would be triangulated to determine their exact locations. 

If you find yourself traveling Highway 1 through California, you may come across a stretch of road where you’ll see one of these old observation bunkers still standing atop a cliff that juts out into the Pacific Ocean, alongside a trail known as the Devil’s Slide Trail.

The structure, named appropriately the Devil’s Slide Bunker, was built during World War II atop what is known as both Devil’s Peak and Bunker Point. The bunker, one of six structures that made up Little Devil’s Slide Military Reservation, was to be used as a triangulation point and fire control station to defend the San Francisco harbor from incoming Japanese ships. 

Upon seeing incoming ships, coordinates would be triangulated and relayed to gun batteries located at Fort Funston. 
As radar technology advanced however, the need for these bunkers had become obsolete, and many of them, including the Devil’s Slide Bunker were abandoned without reuse. The bunker was abandoned in 1949, and was left to sit and crumble away into the ocean. In 1983, the land was purchased, and all other structures besides the bunker were removed.

Today, the structure remains looking out over the blue waters of the Pacific Ocean, though over the years it has seen some destruction by weather and vandals. Inside and out, the structure is covered in graffiti, and the hill has even become known far and wide as Graffiti Hill.