Police in California say they have seized $2.2 billion worth of marijuana plants in the Sierra Nevada mountains.
They have also arrested 97 people over the past three weeks, most of them Mexican nationals believed to be connected to Mexican drug cartels.
The Director of the Office of National Drug Control Policy, Gil Kerlikowske, says "industrial-sized" plantations of marijuana have been found.
The BBC reports that 450 officers from local, state and federal agencies took part in the raids in the foothills of the Sierra Nevada.
They found more than a hundred locations where marijuana was being grown illegally.
Experts say Mexican cartels are increasingly growing marijuana in the US, rather than smuggling it there.
Mr Kerlikowske says the planting has caused "tremendous devastation": tonnes of toxic fertilizers and rubbish have had to be removed from the sites.
