Benjamin Kuzelka, 23, remained hospitalized and his mother and brother were arrested and jailed, Riverside County authorities said.
Authorities went to the home after a local hospital reported late Wednesday that Kuzelka had walked in and said he had shot himself in the hand, but the wound was inconsistent with that type of injury, sheriff's Sgt. Dennis Gutierrez said.
Investigators found explosives, a sophisticated marijuana growing facility and evidence that the home recently had been used as a state-licensed child care facility, Gutierrez said. The home is on a cul-de-sac in the small town 70 miles southeast of Los Angeles.
"We do believe that when all this illegal activity was going on, that children were present," he said. However, no children were home at the time of the explosion, authorities said.
Kuzelka's mother, Rebecca Kuzelka, 55, and brother Grey Kuzelka, 21, were arrested at the home for investigation of child endangerment, manufacture of explosives and cultivating marijuana, Deputy Melissa Nieburger said.
A hazardous device team responded to the scene, defused some explosives early Thursday and was still removing explosive materials Thursday afternoon. Authorities were investigating what type of explosives were being mixed.
"There's no immediate threat to public safety," said Laura Eimiller, a spokeswoman for the FBI, which also was investigating.
Eimiller had no information about the amount of drugs or explosives found at the home, or the type of explosives.
She said the investigation was in its preliminary stages but there was no immediate indication that the case was linked to any larger terrorist investigation.
Grey Kuzelka had been arrested on Saturday for investigation of possessing marijuana and concentrated cannabis, and was released the next day on $5,000 bail.