Video: Mexican drug tunnel found under sink The tunnel entrance was located inside a factory in the Garita de Otay area of Tijuana in Mexico, and extended 200 yards towards San Diego, California but did not breach the US side of the border. Mexican Army General Gilberto Landeros Briseno said that the tunnel was discovered after a man fled and soldiers became suspicious of the large quantities of rubbish found at the location. Under pressure from tightened security along the nearly 2,000-mile southern border in recent years, Mexican cartels have increasingly resorted to boring tunnels, particularly to Arizona and California, where geological conditions are favourable. In the past 10 years, 89 cross-border tunnels have been discovered in Arizona and 50 in California, according to DEA figures.