Smugglers of Drugs Burrow on Border

But there is another route across the border, one in which smugglers slither north. As enforcement efforts have increased and border barriers have been built, tunneling has gained in popularity, with Nogales becoming the capital.

Over the last four years, at least 51 unauthorized tunnels, or more than one a month, have been found in the two border cities. Some are short, narrow passageways that require those navigating them to slither. Others are long, sophisticated underground thoroughfares strung with electric cables and ventilation hoses.

Last year, a resident tipped off the authorities to a tunnel that extended 48 feet into Mexico and 35 feet into the United States, making it one of the longest ever found in Nogales.