Ioan Grillo | GlobalPost CULIACAN, Mexico -- The colossal water cistern set in a clearing in a hilly, heavily forested area can hold 25,000 liters of water -- enough to irrigate a major food farm. But follow the pipes down and there, beneath a corrugated iron roof and resting on hay bales, and its real, more sinister purpose is revealed. Here in the heat of northern Mexico, the factory churned out record amounts of methamphetamine -- known on the American streets as crystal meth, or ice -- a drug that has torn through the United States and become the biggest growth area for cartels south of the border. U.S. police have known for several years that the cartels were gaining strength in the meth trade, taking over a business that used to be run by American biker gangs that cooked up crystal in buckets and bath tubs. But a recent series of raids by the Mexican military revealed that the cartel meth factories have become even bigger and more sophisticated than previously thought. Busted in June, the factory in the clearing near this unwieldy Mexican city is estimated to have produced 40 metric tons of meth, worth some $1.4 billion on American streets, in just two months before it was shut down -- making it the largest operation of its kind to be exposed in the continent. Huge barrels with the precursor chemical pseudoephedrine also fill the factory, unleashing a foul smell throughout the clearing.