The marijuana garden, containing 1,305 plants, was 150 yards long and 30 yards wide and was watered by a lake on the property, Sgt. Chris Bertoli said.
It was discovered during aerial surveillance and was found during a search of a residence on state Highway 128, Bertoli said.
Narcotics agents also seized 14 pounds of processed marijuana, a loaded 9mm pistol, a loaded .38-caliber revolver, an unloaded .30- caliber carbine rifle and an unloaded 12-gauge shotgun, Bertoli said.
The search also uncovered pay and owe records, packaging material and $77,000 hidden in a false wall of a trailer, Bertoli said.
The FBI's Safe Street Task Force and the Mendocino County Major Crimes Task Force assisted the sheriff's department's narcotics unit in the operation.