The fire started in a building near the San Francisco National Cemetery and spread to some grass.
There were some tense moments, as people gathered to watch a plume of smoke rise up from the hill that was visible for miles around. The flames spread quickly on a hill so steep firefighters struggled to keep their footing.
"These guys are heroic. I wouldn't get up there. It looks really hot and dangerous and slippery," said Alexis Perlmutter.
"I've never seen a fire here in all the years I've lived here and I've been here since 1974," said Chris Melanson.
As they battled the fire with water and foam, the thick smoke drew a crowd of onlookers. Firefighters believe the flames started in a concrete enclave full of graffiti at the top of the hill.
"It was an old gun battery from WWII," said San Francisco Fire Batt. Chief Steve Bokura. "It had some netting on top of it, and the netting caught fire, and then it caught the grass on fire."
It took city and federal firefighters half an hour to bring the flames under control -- in spite of the tough landscape, and a 1,000 foot hose run to the nearest hydrant.
Since the fire was on national park land, federal investigators -- unaffected by the government shutdown -- found clothes and bedding stashed away in the battery's nooks and crannies.
"Possibly a homeless encampment, but it's still under investigation at this time," said Bokura.
U.S. Park Police detained one homeless man for questioning. Neighbors say they're just happy all that smoke wasn't from something much bigger.
"You know it took me back to how many years ago when the East Bay hills were on fire. I haven't seen a plume of smoke like that since then," said Perlmutter.
Firefighters have turned the scene over to federal authorities and it'll be up to them to decide if they file criminal charges.