Rangers recently seized 3,500 marijuana plants in the Santa Monica Mountains, the National Park Service reported Tuesday.
Authorities found nine separate pot gardens in late June in Malibu's Zuma-Trancas Canyon area, said Lauren Newman, a spokeswoman for the park service. The street value of the seized drugs was estimated at $10.5 million, she said.
Officials also found herbicides, pesticides, rodent fencing and 2 miles of plastic hose over 9.6 acres of parkland, which was being irrigated with water from a nearby creek, officials said.
Authorities spent two weeks hauling pot and trash out of the area and working to restore it to its natural state. It costs about $12,000 an acre to clean up environmental damage caused by marijuana cultivation in pristine areas, according to the park service.
The marijuana-growing season typically lasts through November, and park rangers will patrol parklands regularly though the fall to combat the illegal farms, officials said.
Authorities encouraged hikers and bikers to stay on trails and report suspicious activity — such as drip irrigation lines near streams and supplies left along roadsides — to police.