The tunnel scheme, which links warehouses in San Diego and Tijuana, even has a hydraulic lift to take people and contraband underground.
It is the latest in a spate of secret passages found smuggling drugs from Mexico into the U.S.
Mexican soldiers found the entrance on the south side of the border at a Tijuana warehouse, near the airport, after the U.S. opening was discovered.
'It is clearly the most sophisticated tunnel we have ever found,' said Lauren Mack, a spokesman for U.S. Immigration and Customs Enforcement in San Diego.
As U.S. authorities heighten enforcement on land, tunnels have emerged as a major tack to smuggle marijuana.
More than 70 have been found on the border since October 2008, surpassing the number of discoveries in the previous six years.