Agents with the federal San Diego Tunnel Task Force recorded what's believed to be one of the largest marijuana seizures in U.S. history, when they uncovered one of the most elaborate smuggling tunnels in years.

The passageway, found Tuesday after a six-month investigation, connects a warehouse in Otay Mesa with one in Tijuana, Mexico. The 612-yard long passageway is equipped with electric rail cars, lighting, reinforced walls and wooden floors.

More than 32 tons of marijuana worth an estimated $65 million at various locations. Federal officials believe the tunnel had only recently become operational.

"From the conditions inside the passageway and our ongoing investigation, we're confident we've been able to shut this operation down before the perpetrators were able to use it for smuggling narcotics," said Derek Benner, special agent in charge for ICE HSI in San Diego. "It's clear though, from the level of sophistication involved, that the criminal organization responsible for constructing this tunnel had very ambitious plans."

On the Mexican side, the tunnel's entrance is accessed through a hydraulically-controlled steel door and an elevator concealed beneath the warehouse floor. At the bottom of the tunnel shaft is a large storage room where agents recovered approximately three tons of marijuana. Another ton of marijuana was piled in bundles near the tunnel's entrance.

Investigators also searched the Otay Mesa building that housed the tunnel's U.S. entry point, where they found nearly 17 tons of marijuana wrapped in plastic and stacked neatly on pallets.

The enforcement actions leading to the tunnel's discovery began unfolding Monday evening when investigators observed a tractor trailer truck leaving the Otay Mesa warehouse.

The truck was parked overnight in the Miramar area. Early Tuesday, a man picked up the rig early and headed toward Los Angeles. Canines at the U.S. Customs and Border Protection-Border Patrol checkpoint in San Clemente alerted officers to the presence of drugs in the vehicle.

Agents, who were aware of the ongoing investigation, waived the truck through the checkpoint and the driver proceeded to the city of Industry, Calif. After arriving, he pulled into the parking lot of a warehouse located at 14837 Proctor Ave. and began unloading the trailer with three other individuals.

Agents with U.S. Immigration and Customs Enforcement's (ICE) Homeland Security Investigations (HSI) moved in, arresting four suspects and seizing more than 11 tons of marijuana packed inside the truck's trailer.

Two other suspects linked to the scheme were arrested overnight in Baldwin Park, Calif. The six defendants are all Latino males.

"The tunnel task force, working with the government of Mexico, is putting a stranglehold on the cartels' ability to smuggle drugs into the United States," said William R. Sherman, the DEA's acting special agent in San Diego. "Seizing close to 50 tons of marijuana in one month denies the cartels the financial means to continue their operations."

The tunnel is the second major cross-border smuggling passageway detected in the San Diego area in the last two weeks. The Tunnel Task Force uncovered another tunnel on Nov. 15 that came up inside a warehouse near the Otay Mesa border crossing. More than 14 tons of marijuana were seized. In the last four years, federal authorities have detected more than 75 cross-border smuggling tunnels, most of them in California and Arizona.

The tunnel task force is made up of representatives from ICE HSI, U.S. Customs and Border Protection (CBP) Border Patrol, the Drug Enforcement Administration (DEA), and the California Bureau of Narcotics Enforcement.