Eric Gay, AP
FILE - In this June 8, 2011, file photo U.S. Customs and Border Patrol and Texas Department of Public Safety seize 57 bundles of marijuana weighing more than 1,200 pound at the Texas border along the Rio Grande in Abram, Texas. Most illegal border crossers are apprehended along the 2,000-mile long Mexican border in California, Arizona, New Mexico, and Texas. In the budget year that ended in September, 18,506 agents on that border made a combined 327,577 apprehensions, an average of nearly 18 apprehensions per agent, and spent about $283 million on overtime an according to Associated Press analysis of agency records. (AP Photo/Eric Gay, File)

SALT LAKE CITY — Federal agents are waging a war against Mexican drug cartels that are hiding large-scale marijuana grows on Utah's public lands, especially in the southern part of the state.

"(It's) the greatest threat to public safety," said Frank Smith, DEA assistant special agent in charge of Utah. He warned Utahns to be cautious in the backcountry this spring and summer.

"The traffickers made no money in Utah last year, and this is about greed," he said. "If we can stop them from making a profit, they're going to go away."

But that won't happen right away. "Dateline NBC's" Chris Hansen and Smith talked about just how dangerous these farms are to the people of Utah. Smith said what keeps him up at night is the fear that innocent people will stumble into a confrontation.

"They steal the land, they steal the water, and then they decimate the environment," Smith said.

He's passionate about busting marijuana farms on public lands. He said they couldn't do it without the help of local and state resources in Utah's southern counties. They've been fighting pot farms for years, but the enemy has changed.

The drug team spent many hours gathering intelligence, hiking to remote pot farms and setting up surveillance to gather even more evidence. They raided one growing operation with the "Dateline" crew, as the cartel's farmers and armed guards fled. Hansen said he was amazed by what he witnessed.

"It was massive, and it looked like it had been professionally grown in a greenhouse someplace," he said. "It's a sophisticated operation with irrigation. These were very mature plants, and in some cases these were worth $20 (million) to $40 million on the street."    

Each of the last two summers, Mexican drug cartels took over large tracts of Utah wilderness and set up dozens of these sophisticated, irrigated operations. Smith estimates they know where 25 percent to 35 percent of the grows are located.

"Last year we eradicated over 78,000 plants," he said, "so it's a half a billion to a billion-dollar industry, here in Utah alone."

The cartels sell the marijuana in the U.S. and send the money back to Mexico to help continue to run their criminal enterprises. The crews are armed and dangerous.

"What's going to happen when a family of hikers stumbles across one of these grows?" Hansen asked. "With $20 (million) to $40 million on the line, do you think these growers are just going to let these people go? No."    

That is Smith's greatest fear. Two years ago, he said, a cartel gunman held several teen girls at gunpoint in Garfield County before the DEA hunted him down.

"They don't care about the well-being of American citizens or the well-being of our environment," he said.

According to Smith, the cartel crews dump illegal fertilizers into the ground, along with human waste, and other trash. The agents even discover multiple car batteries used for charging their cellphones, to keep in touch with their bosses.

Last summer, the DEA worked with Utah law enforcement to arrest nearly 40 drug growers. Smith said the number of farms dropped last year, too.    

"So, we're having success," he said. "We just have to be diligent. We have to be strong and not yield to these traffickers."

Agents have some safety tips if people find a marijuana grow. Agents say those people should leave immediately, go back the way they came and call law enforcement. Those who have a GPS device should take down the coordinates. Otherwise, they should make note of substantial landmarks so they can help law enforcement find it later.

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