That's when foie gras lovers descended on the restaurant to have their first taste of the delicacy since California imposed a ban on July 1.
Animal rights activists fought for the law because they detest the way foie gras is made: farmers force-feed ducks or geese to fatten their livers. Some fans of traditional French cuisine find the ban just as hard to swallow.
The restaurant owner, Ray Tang, and its general manager, Maureen Donegan, reasoned that the restaurant can legally ignore state law because the Presidio, now managed mostly as a national park, has remained federal property even after being decommissioned by the Army. Businesses on federal property must adhere to federal regulations, which trump state ones, they say.
Tang and Donegan timed their event for Bastille Day -- the French national day -- hired a publicist and sent out a press release.
"There are a lot of people who are upset about not being able to do something they have a right to do, so we just decided to go ahead and do it," Donegan told Reuters. "The next step was to celebrate independence."
By Saturday the drab clapboard building was on the map as never before, with diners claiming every one of its 117 seats, a dozen activists chanting outside and park service police -- some of them on horseback -- struggling to make sure the two groups didn't clash.
"Helpless ducks are force-fed," the protesters chanted. "Eat somewhere else instead."
Dana Portnoy, 32, a resident of nearby Oakland and member of the Animal Protection and Rescue League, organized the demonstrators, who held banners and placards displaying photographs of brutalized birds.
"We're here to educate consumers that they care more about serving a cruel delicacy than abiding by the law," she said.
Portnoy described horrific conditions in a foie gras facility she had visited: ducks too sick to stand up, asphyxiating on their own blood from feeding tube wounds, or choking on the corn they were forced to swallow.
The restaurant planned to continue serving foie gras, Donegan said.
QUESTION OF AUTHORITY
Portnoy rejects Tang's legal reasoning along with his ethics and has asked the federal agency managing the park, the Presidio Trust, to enforce the state ban.
The trust has yet to state its legal position. On Friday, Executive Director Craig Middleton issued a statement: "I met with Mr. Tang on Wednesday and encouraged him to reconsider his decision" but did not say what would happen if Tang kept serving foie gras.
Enforcement of the foie gras law in San Francisco falls to the Animal Care and Control Department, and its director, Rebecca Katz, was unsure what authority she had in the Presidio.
"It's not an unusual question to raise," Katz said, citing an ongoing dispute about dog leash laws in the Golden Gate National Recreation Area.
The state attorney general's office also withheld opinion. "We have not looked into it," spokeswoman Lynda Gledhill said.
Others have tried to work around the ban. Thirty miles (50 kilometres) away in Mountain View, California, Chez TJ restaurant was serving foie gras without listing it on the menu.
"It's given away by the chef as a complimentary gift at his discretion," said General Manager Jessamine McLellan, noting that the law bans the sale and production -- but not the possession or consumption -- of foie gras.
Back at the Presidio Social Club -- which, contrary to its name, is a public restaurant with no membership -- diners figured they would enjoy their loophole as long as it lasted. Tang ordered enough foie gras for 560 two-ounce (57-gram)servings.
"It's stunning," said Greg Pelling, 52, who was enjoying a $20 plate of foie gras sliders. "The pineapple adds a slight acidity, and paired with the sauterne (wine), it's amazing."
(Editing by Daniel Trotta and Eric Beech)