Observing the consequences of the Mexican drug trade on both sides of the U.S. border, Cartel Land toggles between Arizona and the state of Michoacan, about 1,000 miles to the south. Only the latter of the twinned storylines really pays off, but that one is riveting.

Up north, director Matthew Heineman and cinematographer Matt Porwoll follow Tim "Nailer" Foley, a military veteran who decided to secure the Arizona border. In part, this is a personal reclamation project. Nailer became a vigilante after kicking his addiction to booze and drugs and losing his construction job in the 2008 maxi-recession.

Nailer and his ad hoc troops are sincere, it seems, about wanting to protect their neighbors from Mexican thugs. But they're also instinctively anti-immigrant. (One Arizona vigilante considers any Mexican migrant who already speaks English a major villain, even after a hapless guy explains that he just picked up the lingo while working in a Cancun hotel.) If all illegal drugs stopped crossing the border, Nailer's men would not consider the battle won.

Further south, Michoacan's residents don't have to don night-vision goggles and patrol empty desert to locate narco-gangsters. They're everywhere in the impoverished state, which under more peaceful circumstances might be best known for its lime and avocado crops.

When the filmmakers arrive, the region is dominated by the Knights Templar, a murderous mob whose name alone indicates the muddled iconography of cartel-dominated territory. They have come to think of themselves as defenders of the faith, even as they expand from drugs to kidnapping and protection rackets.

Against the Knights, local pillars of the community organize the Autodefensas. The group is run by a committee, but one man emerges as its spokesperson: Jose Manuel Mireles Valverde, a white-haired, grandfatherly doctor who doesn't apply the Hippocratic oath to cartel members. Mireles is articulate and charismatic, but not without weaknesses that can be exploited by the Knights and the Mexican government — and those with a foot in each camp.

The movie, inevitably, focuses on Mireles and several dramatic events that involved him in 2014. But the larger story is the tendency of power to corrupt in a land where violence is the only controlling political authority. As the Autodefensas' influence grows, so do their transgressions. Michoacan may have traded one savage occupying army for another.

Heineman shot much of the footage himself, clearly at great risk. Impressively, he had the presence of mind to keep filming during tense standoffs and full-blown firefights. He also captured scenes with masked participants — such as a coven of Mexican cooks around a witches' cauldron of methamphetamine — and ones where the subjects probably thought the camera was off. Occasionally, he points the lens away from the action and settles just for audio of the events.

Although the musical score is sometimes intrusive, everything else in Cartel Land is skillfully balanced. The film is crisply photographed and tightly edited, both of which are essential to navigating so much narrative chaos and moral anarchy.

Heineman was lucky to come out of this project intact. After viewing Michoacan's mayhem from a more comfortable distance, Cartel Land viewers may feel similarly fortunate.

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