Officials seized $1 billion worth of marijuana in what they call thee largest illegal marijuana bust in Los Angeles County history.

373,000 plants were seized by authorities after multiple law enforcement agencies carried out a 10-day operation in the Antelope Valley last month that resulted in 131 arrests and the seizure of more than 33,000 pounds (14,969 kilograms) of harvested marijuana plants.

California broadly legalized recreational marijuana sales in January 2018. But the black market is thriving, in part because hefty legal marijuana taxes send consumers looking for better deals.

Officials sought to differentiate between the Antelope Valley operation and the legal market.

“This is not a war on the legal cannabis business in California,” said U.S. Rep. Mike Garcia, who represents the area.