Unlike Seattle, whose big tunnel-boring machine is still stuck several stories beneath Pioneer Square downtown, the Mexicans don't need no steenkin' machines - as law enforcement in Arizona have noticed. Acting on a tip, they discovered two tons of marijuana and a tunnel connecting a home in Naco, AZ to Mexico.
This was described in the report as "an underground tunnel"; presumably in the belief that there is some other kind of tunnel as well.
Now, Mexican authorities are attempting to locate the other end of the tunnel.
You can see how difficult it might be to locate the other end of a tunnel. We have several tunnels in the Portland area, and few things are more frustrating than to go into one and then find yourself unable to locate the other end of the thing.