From the 459 acres of land, authorities destroyed about 10 million marijuana plants --- a value of approximately $1 billion on the black market, the sheriff's office said.

"These illicit marijuana gardens were grown under the guise of legitimate hemp production," the sheriff's office said. The Food and Agricultural Code and Health and Safety Code define industrial hemp as containing less than 0.3% THC content.

Tests showed THC levels in those fields were much higher than the legal limit, the sheriff's office said. THC is the psychoactive substance within cannabis.

An investigation is ongoing, authorities said.