A multi-agency operation led by the Campaign Against Marijuana Planting removed approximately 12,000 cannabis plants and more than four tons of irrigation equipment, pesticides, and camp infrastructure from an illegal grow site in the Six Rivers National Forest last week, the Humboldt County Sheriff’s Office announced Monday.

The operation, which ran over three days from March 26 to March 28, involved deputies from the Humboldt County Sheriff’s Office, agents from the California Department of Justice, U.S. Forest Service law enforcement, and the California National Guard’s Counterdrug Task Force. Helicopters were used to access the remote site and airlift seized materials.

No arrests were made. The site was unoccupied when officers arrived, though evidence indicated it had been active within the previous two weeks. The Sheriff’s Office said the investigation is ongoing and that suspects have been identified but not yet located.

The grow was situated across three separate clearings on a steep, south-facing hillside approximately seven miles from the nearest road, in a drainage that feeds into the Trinity River system. Deputies described the operation as “well-established,” with gravity-fed irrigation lines running more than a mile from a diverted creek, a propane-powered generator, multiple sleeping structures, and a cooking area with several months’ worth of stored food.

“This was not a weekend project,” said Humboldt County Sheriff William Honsal at a press briefing. “This was a large-scale, organized operation that was deliberately placed deep in federal land to avoid detection.”

CAMP teams also recovered approximately 30 pounds of processed cannabis flower, 85 pounds of commercial fertilizer, and containers of pesticides including carbofuran, a restricted-use insecticide that is illegal to apply to cannabis and has been linked to wildlife kills across the state. Carbofuran residue was found in the soil around the grow site and in the diverted creek downstream of the irrigation intake.

The environmental damage is significant. The Forest Service estimates that approximately two acres of forest were cleared for the grow, with trees felled and brush burned. Soil disturbance from terracing and irrigation trenching has created erosion channels that will require active remediation. The diverted creek, which the Forest Service has not named pending the investigation, showed reduced flow downstream of the intake point.

“Every one of these sites is a small environmental disaster,” said Six Rivers National Forest Supervisor Maria Gutierrez. “The pesticides get into the water, the erosion sends sediment into salmon habitat, and the cleanup costs come out of the public’s pocket.”

The Forest Service estimates cleanup and remediation costs for this site at between $200,000 and $350,000. The agency spent $1.2 million on trespass grow remediation across its Northern California forests in fiscal year 2025.

Trespass grows on federal land have been a persistent problem in the North Coast region for decades. While the total number of plants eradicated by CAMP statewide has declined from its peak in the early 2010s, law enforcement officials say the remaining operations are more sophisticated, better concealed, and increasingly associated with organized groups rather than individual growers.

The Hoopa Valley Tribe, whose reservation borders the area where the grow was found, issued a statement expressing concern about water quality impacts on the Trinity River, which is central to tribal fishing rights and cultural practices.

“Every illegal diversion in the Trinity watershed is a direct threat to our fishery and our way of life,” the statement read. “We call on federal agencies to increase patrols and dedicate resources to preventing these operations before they become established.”

Anyone with information about illegal cannabis cultivation on public lands is asked to contact the Humboldt County Sheriff’s Office tip line at (707) 268-2539 or the Forest Service law enforcement line at (707) 457-2500.