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Northern Wisconsin's Chequamegon-Nicolet National Forest is a vast, verdant getaway for hundreds of thousands of campers, hikers and anglers every year. But hidden within was a marijuana megafarm.

Investigators say a band of Hispanic men turned the forest's southeastern tip into a giant pot farm, growing thousands of plants on remote plots, moving supplies along forgotten logging roads and buying supplies and ammunition at local stores.

Nobody in law enforcement has said it publicly, but the style matches that of Mexican cartels that have been using public land in the United States to grow vast amounts of marijuana and avoid the risk and expense of smuggling the drugs across the border.

"There certainly is an element to this that leads one to believe there is a Hispanic connection here," Wisconsin Attorney General J.B. Van Hollen said. He declined to elaborate.

According to court documents, investigators discovered nine plots of plants in the southeastern tip of the Nicolet section after a person noticed two Hispanic men preparing a grow site in the forest.

Federal, state and local police spent June and July tailing suspected growers, following pickup trucks down abandoned logging roads and watching Hispanic men appear in the trees and toss nylon sacks resembling grain feed bags into the beds.

They followed one suspect to a Fleet Farm in Green Bay, where he purchased six pairs of pruning shears. They watched another man purchase 9 mm ammunition at a nearby Wal-Mart, documents said.

The suspected growers eventually led investigators to a house in Seymour, about 15 miles southwest of Green Bay. According to court documents, the house was a marijuana processing factory.

According to the U.S. Drug Enforcement Administration, drug agents around the country seized about a million plants a year between 2004 and 2008. In 2008 alone, agents seized or destroyed 7.6 million marijuana plants from about 20,000 illicit plots.

In Wisconsin, the number of seized plants in grew six-fold between 2003 and 2008, a year when more than 32,000 plants were seized. Authorities eradicated $2.5 million worth of marijuana plants in the national forest system alone, said Richard Glodowski, special agent in charge of the U.S. Forest Service's investigations in the eastern half of the U.S.

Drug investigators believe Mexican cartels are largely responsible for the spike. Growing the drug here helps them get it to major American markets more quickly. They often import unskilled laborers from Mexico to help find the best land and tend their crops.

The Chequamegon-Nicolet National Forest covers about 1.5 million acres across northern Wisconsin and is divided into two sections — the 860,000-acre Chequamegon in far northwestern Wisconsin and the 660,000-acre Nicolet portion in northeastern Wisconsin.

The southeastern edge of the Nicolet portion lies about 50 miles from Green Bay and hosts about three-quarters of the 700,000 visitors who travel to both sections each year, said Tony Erba, the forest's deputy supervisor. Featuring dense woods, streams and lakes, the forest is a veritable playground for campers, hikers, ATV enthusiasts and hunters — and a perfect haven for growing marijuana.

About 163,000 people use the southeastern tip of the Nicolet where the farms were established each year. Most of the plots were in secluded areas, forest supervisor Paul Strong said. But investigators realized bear hunting season and fall leaves would soon bring more people into the woods and decided to take down the operation on Tuesday.

Investigators discovered at least nine different plots in the forest as well as at least 1,000 plants on the adjacent Menominee Indian Reservation.

Oconto County Sheriff Mike Jansen estimated they seized about 50,000 plants, but Van Hollen cautioned that authorities were still counting and the number currently stood closer to 10,000. The attorney general estimated that each plant might yield a pound of marijuana worth about $1,000.

"This amount of marijuana in northern Wisconsin is a big, big deal," Van Hollen said.

A search of the Seymour house found marijuana drying throughout it and a stash of firearms, including an AK-47 assault rifle. Officers said the smell of pot permeated the entire house. They also raided a storage unit, where they discovered a wire transfer of $2,500 to a man in Modesto, Calif., about $6,000 in cash and 72 pounds worth of processed marijuana in cardboard boxes and garbage bags — yet another cartel grow operation standby.

Eight men were arrested and arraigned Wednesday in federal court on charges of conspiring to manufacture and distribute more than 1,000 marijuana plants and possession with intent to deliver more than 100 marijuana plants. Four more men were arraigned on Thursday. Three were charged with the same counts. The fourth, Bernabe J. Nunez-Guzman, was charged only with conspiracy, but court documents indicate he was the ring leader.

An unnamed informant arrested at the Seymour house told detectives on Wednesday he was in San Jose, Calif., several months ago when he was approached by a man who asked him if he wanted to work at a ranch. This person arranged for the man to travel to Green Bay, where he met Nunez-Guzman.

The informant said he helped dry marijuana at the house and Nunez-Guzman, also known as "Green Bay," was the boss. He came to the house every 15 days to check on the operation and sent a runner into the woods every three days to check the crop.

Federal defender Krista Halla-Valdes, who represents the four men charged Thursday, said she hasn't seen any evidence in the case and it's too early to comment.

Cartel grow recruiters often look for people with family in Mexico so they can use them as leverage to keep the farmers working and quiet. If anyone betrays the farm, they go after the worker's family, intelligence experts say.

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Associated Press Writer Alicia A. Caldwell contributed to this story from El Paso, Texas.