Secret Tunnels from Mexico to the US for Smuggling Drugs, Guns, People Mexican soldiers hold a ladder for journalists to climb out of tunnel between San Diego and Tijuana, Mexico, Nov. 16, 2011. Approximately 17 tons of marijuana were discovered in a cross-border tunnel that appears to be one of the most significant drug smuggling passages found between the U.S.and Mexico. David Maung/Bloomberg/ Getty Images