California Attorney General Rob Bonta said the man, who was not named, was prohibited from possessing weapons at the time his home was searched in late January.
Agents of the US Bureau of Firearms inspected the subject's home on January 31.1. They found 11 military-grade machine guns, 133 handguns, 37 rifles, 60 assault rifles, 7 shotguns and 3.000 high-capacity magazines.
Authorities also discovered 1 million rounds of ammunition, dozens of rifle barrels and shotgun bodies, and 20 silencers.
The investigation team found several grenades in the suspect's house, but the local bomb disposal team determined that these grenades did not explode.
The attorney general's office released a video clip recording some areas inside the house, showing that the house is like a miniature armory, with many machine guns, long-range rifles and dozens of boxes of ammunition.
Attorney General Bonta did not mention the specific location or home address of this person.
Owning machine guns is generally prohibited in California, a state with one of the strictest gun control laws in the US.