One firefighter was injured putting out the fire, which was reported at 4:47 p.m. Wednesday at 568 Warwick Ave.
A beam fell on the firefighter's head, knocking him to the ground. He was conscious and able to stand on his own but he was transported to Eden Medical Center for observation. He was released later that night.
Firefighters spotted what they suspected were marijuana plants in the detached garage, and once the fire was out, police investigated their suspicions.
Police found that there was marijuana growing in the garage, and that the power to the garage had been rewired so the PG&E service panel would not report power usage data to PG&E.
The garage was deemed unsafe and red-tagged by a building inspector. No other structures were damaged.
The resident of the home, Edward Davis, 37, was arrested and booked into jail on suspicion of marijuana cultivation and possession of marijuana for sale.