The entire home was full of pot plants and investigators estimate that it brought in $1.5 million to $2 million a year.
The fire was so big that firefighters were forced to fight it defensively at first, but once they got inside they discovered the plants.
"With grow house fires, a lot of times it is related to the electrical use, so our investigators are looking at that in this particular case. It is unfortunately becoming relatively common," said Contra Costa County Fire Dept. Capt. Robert Marshall.
No one was inside the house at the time. There were no injuries and no arrests have been made.