According to the Daily Mail:
Authorities in Arizona unearthed a sophisticated 240-yard drug-smuggling tunnel stretching into Mexico that included engineered support beams, lights and ventilation.
The six-foot-high corridor ran from a store in an abandoned strip mall near Yuma to an ice shop across the border in San Luis Rio Colorado. It provided a direct link to the US for Mexican drug cartels.
The Mexican Army also found a second, incomplete, tunnel under a bathroom sink in Tijuana that stretched more than 200 yards into San Diego, California. The diggers had not yet reached the surface when authorities shut it down.
More photos below.