A reader, who sent in the above photo, tells us, "Most of Fort Funston is closed due to the discovery of an old, possibly active bomb." Twitter user fiercekitten reports: "Half of [Fort Funston] is closed because they found a live shell from the old fort."
We're also getting word that a bomb squad just detonated the old bomb.
SFist talked to someone at the Parks & Rec Department who explained that from time to time they "still do turn up WWII pieces and bombs" at Fort Funston, old explosives "covered with sand that nobody noticed."
We'll update as soon as we know more.
Update: According to the police, the area has reopened.