As marijuana prices have plummeted in the last five years, in part because of decriminalization in some states of the U.S., Mexican drug farmers in the remote valleys of the northern Sierra Madre have began to harvest opium poppies instead and distribute cheap $4 heroin to many rural areas in America.

The Washington Post reported that U.S. law enforcement agencies have been cracking down on prescription painkiller abuse including hydrocodone and OxyContin, which have created a new market for Mexican trafficking organizations to sell heroin.

The flow of the heroin into cities such as Winchester, Va. and Brattleboro, Vt. have been traced to the "Golden Triangle" region in the Mexico's Sinaloa state. Sinaloa is known for its infamous drug cartels and production of the biggest marijuana harvest.

However, farmers don't want to sell marijuana anymore because of the steep decline in wholesale price, which has dropped from $100 per kilogram to less than $25, lifelong cannabis farmer Rodrigo Silla told the Post.

"It's not worth it anymore," Silla said. "I wish the American would stop with the legalization."

He also said that he couldn't recall a time when his family or members of his small community stopped growing marijuana.

The Post also reported that authorities have begun to find areas not known previously for growing heroin and that growers as far south as Central America have begun to grow plant the opium poppies instead of marijuana.

Honduras police in late January found the nation's first poppy farm in a sophisticated mountain greenhouse that was roughly the size of a soccer field. The same week, Guatemala police and military personnel attempted to raid and destroy 160 acres of poppy but were met with farmers armed with clubs and gas bombs.

Last year, U.S. authorities confiscated 2,162 kilos of heroin along the U.S.-Mexico border, which was a record find and up from 367 kilos in 2007.