For all the talk about a wall between the United States and Mexico, the problem with border security continues to be as much below ground as above. On Wednesday, officials in San Diego announced the discovery of another cross-border tunnel built by drug smugglers — the longest one found yet, at about half a mile.

The tunnel had rails, lighting, ventilation and even a large elevator leading to a closet in a modest house in Tijuana, United States Attorney Laura E. Duffy said. On the San Diego side, where the tunnel emerged in an industrial park in the Otay Mesa neighborhood, the authorities arrested and charged six people last week and confiscated more than a ton of cocaine and seven tons of marijuana that they said had been smuggled through the passage — the largest drug seizure associated with a tunnel.

Despite the superlatives cited by officials, the cat-and-mole game between law enforcement and drug cartels shows no sign of abating. In the last five years, the authorities said, they have found more than 75 cross-border tunnels, mostly in areas of California and Arizona where there are enough buildings to disguise illicit activity, and the soil is conducive to digging. In Tijuana, in particular, the tunnels are considered an intractable fact of life.

Specialists on border control say no one has a clear idea how many tunnels are operating, or how much of a role they play in the drug trade, but they will be a factor for the foreseeable future. In just the last month, another long tunnel was found linking Calexico to Mexicali, and a shorter one near Calexico.