Authorities seized 8.5 tonnes of marijuana and 327 pounds of cocaine after discovering the tunnel, located 35 feet underground.
The tunnel connects warehouses in Tijuana, Mexico, with San Diego’s Otay Mesa industrial area – and zig-zags for around a third of a mile.
It includes ventilation systems, lighting, and an electrical rail system, and would have costs millions of dollars to complete, US officials said.
The passage is four feet high and three feet wide.
Arrests
“The discovery of today’s tunnel, which we call a super tunnel, is the fifth super tunnel that we’ve intercepted since 2010, and this tunnel, like those we found in November of 2011, were built by engineers and architects,” said US Attorney Laura Duffy.
Three men, said to be drivers, were also arrested following the discovery, and charged with possession of marijuana and cocaine with intent to distribute.
Federal agents had been watching the warehouse where the tunnel was located after receiving a tip-off that operators bought drills and other construction equipment in August and September.