Mexican drug growers have been seen walking through this famous national parkland, but they're not going camping.

In the newest battleground in the war on drugs, some of the cartels from across the border no longer bother to smuggle marijuana (search) into the United States. They simply grow it here, on public lands in California.

"They are going into national forests, national parks. And it's a huge problem," says Dave Dresson of the California Bureau of Narcotics (search).

In the past, most of the marijuana smoked in California was grown in Mexico. But that's no longer the case.

Police now seize twice as much pot growing in public forests throughout the state as they do at the Mexican border. And the seizures at the Sequoia National Forest (search) alone are up eight-fold.

The reason: It's just a lot easier to grow it here.

First of all, the land and water are free. There are no boats or planes to buy, and no officials to bribe. And if the drug dealers are unlucky enough to get caught, the penalties are relatively light compared to those faced by cross-border smugglers.

Anyone convicted of smuggling drugs from across the border faces a minimum 10-year federal sentence. But jail time isn't even mandated by California state law.

"It doesn't matter in California if you get caught growing two plants or 20,000 plants," said Eric Wyatt, depute district attorney of Madera County. "The punishment in California isn't very severe."

Officials say that people convicted of growing pot in California could be sentenced to 16 months in prison and would probably serve only eight months — even if they're growing large quantities, according to Dresson.

It's impossible to tell how much pot is actually being grown on parklands, but the estimates are that it comes to thousands of acres.

But even if California takes the issue of marijuana cultivation lightly, it's very serious business for the drug growers and dealers.

Officials say pot plants can sell for as much as $4,000 each on the street. And at those prices, the drug growers are taking precautions. They carry firearms into the parks, and have been known to plant booby traps to protect their investments.

Their activity has caused a number of problems with innocent passers-by who didn't know they were stumbling upon secret stashes. A number of hikers have been shot by the drug dealers, and the dealers have even traded gunfire with park rangers.

No one has been killed — yet. But the ongoing problem has left a number of officials worrying that there may be much more to fear in these woods than hungry bears.