Largest illegal marijuana bust in years

PHOENIX (CNN, KYMA/KECY) - Months of undercover work by local law enforcement have led to the discovery of the largest illegal homegrown marijuana operation Maricopa County has seen in ten years.

Investigators say the sophisticated grow operation was hidden in an unassuming facility in central Phoenix.

The marijuana grown there was allegedly being shipped across the country.

"A marijuana grow is not rare. A marijuana grow this large is very rare. We’re talking millions of dollars," said the Maricopa County Sheriff's Office (MCSO), which worked with the Department of Corrections and Tempe and Phoenix Police on the investigation.

Neighbor Jonathan Trevino wasn’t surprised to learn about the bust, saying, "This is probably another bust, you know, bust of drugs or illegal activity."

So far, three people have been detained, and the state Attorney General’s Office is working to file charges. Lt. Ryan Nivelle with MCSO says they’re confident their investigation will "bear fruit."

MCSO also says evidence of butane extraction was found on-site, a process that can pose a serious explosion risk if not properly managed.

"This isn't what I would characterize as a scientific environment," an assistant sheriff said. "So there is absolutely a danger to the community with having something like this."

Officials estimate the operation had been running for years but does not appear to be connected to any cartels. One bag of marijuana alone could retail for as much as $2,700.

"There is a process to do this legally. There is nothing legal about this operation," the sheriff said.

It will take crews two days to collect and impound all the evidence.