A federal drug investigation has led to the discovery of an elaborate cross-border tunnel between the U.S. and Mexico.

Justice department officials say the passageway is about a third of a mile long, four feet wide, and is outfitted with reinforced walls, a rail system, electricity and a ventilation system.

The tunnel, which stretches from Tijuana, Mexico to a San Diego warehouse, was discovered early Saturday morning as law enforcement was conducting surveillance of the warehouse during a cocaine smuggling investigation.

Six people are now facing charges for conspiring to distribute over 1,700 pounds of cocaine.