A look at the illegal tunnels that have been dug under the Arizona-Mexico border by Mexican cartels to smuggle drugs, and how U.S. law enforcement teams are dealing with them:

“Crime has been coming up out of the ground in Nogales for a while now. Since 1995 more than 90 illicit underground passageways have been discovered in various states of completion in the two-mile stretch of urban frontier that separates Arizona’s Nogales from its far larger twin in Sonora. Twenty-two complete tunnels have been found in the past three years alone. Streets have opened up beneath unwary pedestrians and subsided under heavy vehicles; the city has become infamous as the Tunnel Capital of the Southwest.

“Although quantification is impossible, the underground shipment routes represent a significant economic investment, one that far exceeds the time and money spent on the homemade submarines, ultralight aircraft, and catapults used to move narcotics elsewhere. Some tunnels cost at least a million dollars to build and require architects, engineers, and teams of miners to work for months at a stretch. A few include spectacular feats of engineering, running as much as 100 feet deep, with electric rail systems, elevators, and hydraulic doors. But the economies of scale are extraordinary. Tunnels like these can be used to move several tons of narcotics in a single night.”