Last year, a wildfire in Santa Barbara's Los Padres National Park consumed more than 136 square miles. That fire was sparked by a cooking fire started by the employees of a Mexican drug cartel tending to some 30,000 marijuana plants in the remote and rather inaccessible canyons of central California. It was far from an isolated incident according to US law enforcement agents and the fire highlighted an alarming trend: the unseen invasion of California wilderness and public lands by Mexico's ruthless drug cartels that has taken place underneath our very noses over the past two decades.

Today, the Associated Press takes a look at the invasion of public lands by Mexican drug cartels.

Pot has been grown on public lands for decades, but Mexican traffickers have taken it to a whole new level: using armed guards and trip wires to safeguard sprawling plots that in some cases contain tens of thousands of plants offering a potential yield of more than 30 tons of pot a year. "Just like the Mexicans took over the methamphetamine trade, they've gone to mega, monster gardens," said Brent Wood, a supervisor for the California Department of Justice's Bureau of Narcotics Enforcement. He said Mexican traffickers have "supersized" the marijuana trade.

Interviews conducted by The Associated Press with law enforcement officials across the country showed that Mexican gangs are largely responsible for a spike in large-scale marijuana farms over the last several years.

Local, state and federal agents found about a million more pot plants each year between 2004 and 2008, and authorities say an estimated 75 percent to 90 percent of the new marijuana farms can be linked to Mexican gangs.

In 2008 alone, according to the Drug Enforcement Administration, police across the country confiscated or destroyed 7.6 million plants from about 20,000 outdoor plots. Growing marijuana in the U.S. saves traffickers the risk and expense of smuggling their product across the border and allows gangs to produce their crops closer to local markets.

Distribution also becomes less risky. Once the marijuana is harvested and dried on the hidden farms, drug gangs can drive it to major cities, where it is distributed to street dealers and sold along with pot that was grown in Mexico.

About the only risk to the Mexican growers, experts say, is that a stray hiker or hunter could stumble onto a hidden field.

The remote plots are nestled under the cover of thick forest canopies in places such as Sequoia National Park, or hidden high in the rugged-yet-fertile Sierra Nevada Mountains. Others are secretly planted on remote stretches of Texas ranch land.

All of the sites are far from the eyes of law enforcement, where growers can take the time needed to grow far more potent marijuana. Farmers of these fields use illegal fertilizers to help the plants along, and use cloned female plants to reduce the amount of seed in the bud that is dried and eventually sold.

Mexican gang plots can often be distinguished from those of domestic-based growers, who usually cultivate much smaller fields with perhaps 100 plants and no security measures. Some of the fields tied to the drug gangs have as many as 75,000 plants, each of which can yield at least a pound of pot annually, according to federal data reviewed by the AP.

I've noted this before but the war on drugs is a forty year failure. Prohibitionist policies based on eradication, interdiction and criminalization of consumption simply haven't worked. The war on drugs is an enormous waste of resources. The United States now incarcerates people at a rate nearly five times the world average. In large part, that’s because the number of people in prison for drug offenses has risen from under 50,000 in 1980 to over half million today. Until the war on drugs with their draconian drug laws came along, our incarceration rate was roughly the same as that of other countries. Jeffrey Miron, a Harvard economist, has found that federal, state and local governments spend $44.1 billion annually enforcing drug prohibitions. We spend seven times as much on drug interdiction, policing and imprisonment as we do on treatment. It's time to treat drug addiction as healthcare problem and not a law enforcement problem. It is also high time to consider legalization, not as a panacea but as the least worst option.