BAKERSFIELD, Calif. (AP) – Authorities in Central California have seized and destroyed about 10 million plants they said were being grown as legal hemp but contained higher-than-allowed levels THC, the chemical compound that gives marijuana its high.

The Kern County Sheriff’s office said it served search warrants at several fields totaling 459 acres in the Arvin area on Oct. 25 as part of a joint investigation with the FBI and California Department of Fish and Wildlife, The Bakersfield Californian reported.

Hemp and marijuana are cannabis plants but only pot has enough THC to get users high. Authorities said samples of the seized plants tested “well above” the federal limit of 0.3 percent of THC for “industrial” hemp.

They classified the plants as marijuana worth about $1 billion on the black market. Authorities wouldn’t name the grower, citing the ongoing probe.

Hemp cultivation is allowed throughout Kern County but pot production, sale and processing is largely illegal.