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Tunnel to Marin Headlands Closed
The tunnel on Bunker Road from Alexander Avenue in Sausalito towards the Marin Headlands is closed for construction. Please follow the detour signs to Conzelman Road (just above the north end of the Golden Gate Bridge) to go up over the hill. More »
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Muir Beach (but not nearby Muir Woods) parking lot closed June-November 2013
Muir Beach parking lot will be closed from June-November 2013 due to construction. Restrooms or nearby parking will not be available at Muir Beach during this period. Pacific Way is closed except to residents. Check back for updates or call (415)561-3054 More »
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CAUTION: Post Storm Damage to Coastal Trail
The Presidio Coastal Trail segment just north of the Pacific Overlook and adjacent to Lincoln Blvd remains CLOSED indefinitely. We have posted signage to alert bicyclists and hikers and with information for safe trail alternatives. More »
Mines and Submarine Defenses
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If the big guns failed to stop an enemy vessel far offshore, the next line of defense was three minefields containing over 600 underwater mines outside the Golden Gate. An antisubmarine net located inside the Gate would prevent any submarine that penetrated the minefield from entering the bay. 
Four mineplanters, like the Spurgin shown here, placed mines outside the Golden Gate. They were supported by a flotilla of smaller craft, including many commandeered crab fishing boats.
PARC, Golden Gate National Recreation Area
A mine containing 3000 pounds of TNT is detonated during a test.
PARC, Golden Gate National Recreation Area
Early in the war, buoyant mines were anchored 15 feet below the surface and could be detonated from an onshore control station. "Ground" mines (above), which ships could not foul, later replaced the buoyant mines.
PARC, Golden Gate National Recreation Area
The antisubmarine net that protected the bay was made and serviced at the Tiburon Naval Net Depot and at Alcatraz prison (above). Navy ships would open and close the net for friendly vessels. Here, an Alcatraz prisoner is working on an antisubmarine buoy.
PARC, Golden Gate National Recreation Area
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Did You Know?
The tectonic forces that formed San Andreas Lake, in San Mateo County, are similar to those that formed Loch Ness in Scotland, the home of "Nessie," the rumored Loch Ness monster.