Firefighters stumbled upon 28 fully grown marijuana plants, which police later packed into evidence sacks. The street value is estimated at $75,000.
The whole thing was a shock to next-door neighbor Michael Williams, a local pastor.
"To me, when you say 'weed,' I think about weeds that are growing; I don't think about things that are growing inside of a house," Williams said.
The fire broke out on a grassy hillside around 3:30 p.m. near Charter Oak Avenue. Smoke from the fire could be seen from the nearby Highway 280/Highway 101 split.
The flames got as far as a back fence. Investigators are looking into whether the fire was started by people at a nearby homeless encampment.
Firefighters broke through the front door of an empty house to drag their hoses through; that's when they found the marijuana grow in two back bedrooms. There was an extensive wiring and lighting set-up and an air-filtration system.
Police say the wiring bypassed the electric meter, which is typical in illegal operations. More often police and firefighters are stumbling upon these types of pot farms.
"Certainly there is a lot of gray area about what is legal and what isn't, so we're going to have a lot of people who are going to stretch the boundaries," San Francisco Police Lt. Robert O'Sullivan said.
Police say there was no paperwork inside to indicate a legal growing operation. They have not tracked down the two people who rented the home. They could face charges of growing pot and stealing electricity.