Aerial shot of illegal marijuana plot in Death Valley National Park/NPS

Editor's note: This updates to include the arrest of a North Carolina man in connection with marijuana cultivation at Cape Hatteras National Seashore.

Illegal cultivation of marijuana has cropped up in at least two units of the National Park System, with more than 4,000 plants found in Death Valley National Park and an undisclosed number at Cape Hatteras National Seashore in North Carolina.

In Death Valley, rangers last week raided a pot growing operation with thousands of plants that were irrigated with an extensive hose system pulling water from a spring in Hanaupah Canyon. The operation was stumbled upon by some hikers who thought three men installing the watering system were working on a park project.

"They asked them what they were doing. One of the men responded, 'Growing marijuana. You won’t tell the cops, will you?'," park officials said.

They didn't tell the cops, but they did tell the park. And on July 3 National Park Service and Bureau of Land Management rangers raided the site. They found more than 4,000 marijuana plants in four garden plots. No workers were on location at the time of the raid.

“Even though California and Nevada have passed laws legalizing marijuana sale, it remains illegal at the federal level," said Death Valley Superintendent Mike Reynolds. "Our biggest concerns in Death Valley are that grow sites decimate vegetation around springs, poison wildlife, and are dangerous for the public.”

No arrests had been made in the case.

Closeup of marijuana garden in Death Valley National Park/NPS

Native plants in lush areas near desert springs provide critical habitat and food for bighorn sheep, birds, and other wildlife. The workers had cleared away vegetation to make room for their crops. Each marijuana plant can use up to 6 gallons of water per day, which was delivered by a network of irrigation tubing from the springs. The rangers’ greatest concern was finding carbofuran, a pesticide that is highly toxic to humans and wildlife.

People hiking to infrequently-visited regions of Death Valley National Park should be aware of the risk of finding a marijuana grow site, which could be defended by the growers. Hikers should be on the alert for irrigation hose, fertilizer, signs of digging, unusual litter, and anything or anyone that seems out of place. If a hiker finds a grow site, he or she should leave the site as quickly as possible and notify the NPS at 760-786-2330.

Hiking to popular destinations, such as Golden Canyon, Mosaic Canyon, and Telescope Peak, is safe, according to park staff.

At Cape Hatteras, federal authorities said only that an Ocracoke, N.C., man had been arrested and charged with cultivation of marijuana at the national seashore. James Daniel Garrish III, who was arrested Tuesday, also was charged with "introducing plants into the park ecosystem, littering, trespassing, and defacing and damaging real property. Each of these charges carries up to six months’ imprisonment, a $5,000 fine, up to one year supervised release, and/or up to five years’ probation," a press release from the U.S. Attorney's Office for the Eastern District of North Carolina said.

The release about the arrest, which was initially reported by the Raleigh (N.C.) News and Observer, did not provide details on the operation. Cape Hatteras staff were not releasing details on the case, and Department of Justice officials did not immediately return a phone call Thursday. The press release said Garrish was indicted back in May.

"Criminal acts which blemish the beauty of our public seashore and the safety of its visitors will not be ignored,” said Robert J. Higdon, Jr., the U.S. Attorney for the Eastern District of North Carolina in the release.

If convicted of the cultivation charge, Garrish would face a maximum term of 5 years' imprisonment, a $250,000 fine, and a term of up to three years supervised release following any term of imprisonment, according to the U.S. Attorney's Office.