The federal Drug Enforcement Administration estimates the plants' street value at $5.4 million, Lt. Barry Heying said.
The grow sites, which were spread out over a quarter-mile area, were discovered after a California Department of Fish and Game warden encountered a man dressed in camouflage clothing walking in the 1400 block of Marshall-Petaluma Road around 11 a.m. Monday, Heying said.
It was determined that the unidentified man, who was carrying pruning clippers, was associated with the illegal marijuana grows, Heying said.
The suspect, an undocumented immigrant, was detained by the Department of Fish and Game and was taken into custody by U.S. Immigration and Customs Enforcement agents, Heying said.
The initial estimate on the growing operation's size was 4,500 plants with an average height of 5 feet, but that was updated to 5,400 plants this morning, Heying said.
An elaborate irrigation system involving pipes fed by a natural spring connected the grow sites, and many of the plants were hidden in thick clusters of manzanita, Heying said.
Narcotics agents also found rat traps, rodent poison and fertilizer at the site, Heying said. Additionally, there was erosion damage, chemical and pesticide pollution and discarded trash in the area, Heying said.
"Those responsible for caring for and guarding marijuana grow sites also pose a danger to hikers, bicyclists, ranchers and water district rangers who patrol the lands," Heying said.
The California Highway Patrol and Marin Municipal Water District also participated in the raid.
Anyone with information about the growing operation is asked to call the Marin County Sheriff's Office at (415) 473-7233 or Bay Area Crime Stoppers at (800) 222-TIPS.
