Enlarge Handout Thousands of marijuana plants were seized last month in the Dixie National Forest in Utah, pictured here. Ignacio Rodriguez has been charged with drug and immigration offenses in connection with that bust, according to the DEA. CHICAGO  Mexican drug cartels are stepping up marijuana cultivation in national parks and on other public land, endangering visitors and damaging the environment, law enforcement and National Park Service officials say. John Walters, director of the Office of National Drug Control Policy, says 75%-80% of marijuana grown outdoors is on state or federal land. The Drug Enforcement Administration (DEA) says there were more than 4.8 million marijuana-plant seizures at outdoor sites in 2006. Tighter border controls make it harder to smuggle marijuana into the USA, so more Mexican drug networks are growing crops here, Walters says. "We are finding more marijuana gardens in the park year after year," says Jim Milestone, superintendent of Whiskeytown National Recreation Area in Northern California. "We're dealing with some bad characters," Milestone says. "We are arresting people … who have criminal records in Mexico, and almost all of them are here illegally with false papers." The number of marijuana plants confiscated on public land in California grew from 40% to 75% of total seizures between 2001-2007, says the state's Campaign Against Marijuana Planting task force. Hunting and cleaning up after pot growers diverts resources at a time when parks face chronic funding shortfalls, says Laine Hendricks of the non-profit National Parks Conservation Association. Recent busts: • A site with 16,742 marijuana plants was raided last month in North Cascades National Park in Washington state. It was operated by a Mexican organization, says park Superintendent Chip Jenkins. People living at the site downed trees, dammed creeks and left 1,000 pounds of trash, he says. • Thousands of marijuana plants were seized last month in Utah's Dixie National Forest. Ignacio Rodriguez was charged with drug and immigration offenses, says Michael Root, a DEA special agent. The problem is worst on the West Coast, but law-enforcement pressure on growers, Root says, "has pushed them out this way." • Last month, officials burned thousands of marijuana plants seized in Cook County, Ill., forest preserves. Drug organizations use the Chicago area as a base for distributing marijuana across the Midwest, says DEA special agent Joanna Zoltay. • In July and August, officials seized more than 340,000 plants, some from Sequoia National Forest and Kings Canyon and Sequoia national parks. Ranger Alexandra Picavet says Mexican cartels are responsible for many sites in those parks. They leave behind car batteries and propane tanks and poach deer and birds, she says. Visitors to wilderness areas are at risk, says Shasta County, Calif., Sheriff Tom Bosenko. "We have found marijuana within a half-mile of public beaches and very short distances from campgrounds and highways," he says. "It's a shame." Guidelines: You share in the USA TODAY community, so please keep your comments smart and civil. Don't attack other readers personally, and keep your language decent. Use the "Report Abuse" button to make a difference. You share in the USA TODAY community, so please keep your comments smart and civil. Don't attack other readers personally, and keep your language decent. Use the "Report Abuse" button to make a difference. Read more