Concrete structure from Fort Funston in San Francisco tumbles onto beach

SAN FRANCISCO -- A portion of the ruins at Fort Funston in San Francisco slid down a rain-soaked bluff onto the beach below, authorities said Monday.

A concrete structure, which had been jutting out and partially buried in the sand dunes, tumbled onto Funston Beach, according to a social media post by the Golden Gate National Recreation Area. The post said the structure had been undermined by the saturated soil.

No injuries were reported, but visitors were urged to follow posted trail signs and be attentive to their surroundings. 

The concrete structure, possibly an old lookout post or base end station, was part of a series of buildings and installations at Fort Funston, which was established as a military base in 1900, with the first structures built there beginning in 1917. 

The structure was about 1,000 feet north of the Battery Davis gun emplacement at the former army post. Built in 1936, Battery Davis was one of a series of harbor defenses built north and south of the strategic Golden Gate. The two 16" guns could fire a one-ton shell some 25 miles out into the Pacific Ocean, although the San Francisco harbor defense guns were only fired in training and never in combat. 

By the end of the war, the gun emplacements were deemed obsolete because of advances in air power and nuclear power. Metal from the batteries was turned into scrap, with the hulking concrete structures and support buildings left behind as visible reminders of the era.

During the Cold War, Fort Funston was also one of the Bay Area's 12 missile defense installations. The fort was deactivated in the 60s and turned over to the National Park Service.