Route of a recently discovered tunnel used to smuggle drugs from Mexicali to Calexico, with a little help from storm drains on the U.S. side of the border.
Federal officials say they've uncovered something disturbing along the U.S.-Mexico border: more underground tunnels, used by drug traffickers and immigrant smugglers to evade tighter border enforcement.
One tunnel a year used to be the average, but since a border crackdown after the attacks on Sept. 11, 2001, more than 10 passageways have been discovered. NPR's Carrie Kahn reports on two "hot spots" for tunnels -- the border at San Diego and Tijuana, and between the California border town of Calexico and Mexicali.
Armed with drills and ground-penetrating radar, U.S. border authorities are busy looking for tunnels running under the fences that separate the two countries. Officials say that if drugs and illegal aliens can come across, terrorists or even "dirty bomb" components could get smuggled across just as easily.