In this photo provided by Immigration and Customs Enforcement, 20 tons of marijuana were seized by ICE agents in Otay Mesa, California, on November 3, 2010.

Credit: Immigration and Customs Enforcement

In this photo released by Immigration and Customs Enforcement, an agent with ICE Homeland Security Investigations tests the safety of the air in the drug-smuggling tunnel discovered in Otay Mesa, California on November 3, 2010.

Credit: Immigration and Customs Enforcement

Warehouse in Otay Mesa, California, where a drug-smuggling tunnel and 20 tons of marijuana were discovered.

In this photo provided by Immigration and Customs Enforcement, 20 tons of marijuana were seized by ICE agents in Otay Mesa, California, on November 3, 2010.