Ventura County sheriff's deputies arrested Christopher Oleksik on Thursday after serving a search warrant at his home.
The weapons found include 20,000 rounds of ammunition, four AR-15 assault rifles and a functioning flamethrower, according to the authorities.
"We're talking about a device that is probably firing from 15 to 25 feet, it has a fuel port on top, but it looks very dangerous."
Investigators say they found heroin and drug paraphernalia in a room in the house, and say some of the guns were allegedly illegal.
Oleksik must appear in court in two weeks.
