A traffic stop near Ashland sparked an investigation that led authorities to a massive marijuana growing operation in Grants Pass that was apparently producing hundreds of pounds more than is allowed under the site's medical marijuana permits.

Police on Oct. 29 seized 200 pounds of marijuana at the Wilderville Avenue operation and arrested three Grants Pass residents on related drug charges.

The investigation began when an Oregon State Police trooper stopped a southbound 2000 Honda Civic with Nevada license plates on Interstate 5 near milepost 12 for a traffic violation at about 5:50 a.m. on Oct. 29. A subsequent investigation with the help of a drug detection dog found a pound of marijuana in the car.

The 46-year-old man driving and his 49-year-old woman passenger, both from Las Vegas, said they had got the pot from what they believed was a medical-marijuana production site, police reported. They had traded cash and work pruning marijuana plants for the drug, they told police.

OSP said charges are still pending against the two, who weren't identified in the press release issued today.

With the information from the stop, the Rogue Area Drug Enforcement team, which includes Grants Pass Department of Public Safety, Oregon State Police, Josephine County Sheriff's Office, Josephine County District Attorney's Office, and the Josephine County Community Corrections, got a search warrant for the growing site, OSP said.

Detectives found evidence of a large scale marijuana growing operation capable of producing hundreds of pounds of marijuana.

Two registered growers there were producing medical marijuana for 13 patients. The legal amount of usable marijuana that can be possessed for 13 patients is 19 1/2 pounds. The roughly 180 pounds of marijuana in excess of that legal amount likely would have been worth $450,000 on the open market, where conservative estimates by law enforcement authorities indicated it could fetch about $2,500 per pound.

The growers and another person were all arrested on charges of manufacture and possession of marijuana. They are Brenda Thomas, 43; Susan Bryant, 48; and, Thomas Bletko, 50.

— Anita Burke