A massive tunnel that officials believe was a heavily traveled route for bringing illegal drugs into the United States has been discovered at the U.S.-Mexican border in California.

The tunnel, about a third of a mile long, connects a warehouse in San Diego with Tijuana, Mexico, according to Fox News.

"It’s estimated to be about 1,744 feet long, 61 feet deep, with a diameter of about 4 feet at its widest point," Randy Grossman, U.S. attorney for the Southern District of California, said.

"It has reinforced walls, a rail system, and electricity for ventilation," he said.

“I’m very happy to report there’s no light at the end of this narco tunnel," Grossman said, according to KNSD-TV.

"We and our agency partners will continue to work zealously to take down every subterranean smuggling route and other means that drug traffickers use to bring illicit drugs into our community,” he said.

Officials said about $25 million worth of drugs were seized from the tunnel, which they described as containing a "sophisticated" structural system.

The haul included 1,762 pounds of cocaine, 165 pounds of methamphetamine and 3.5 pounds of heroin.

Six California residents were arrested and charged with conspiring to distribute cocaine, officials said.

6 charged, drugs seized after big cross-border tunnel found linking Tijuana, San Diego https://t.co/sQBoDL0MWD

— ABC7 Eyewitness News (@ABC7) May 17, 2022

The tunnel connected to a warehouse named Amistad Park on a street filled with tractor-trailer traffic all day, according to The San Diego Union-Tribune.

On Monday, armed guards watched over a small shaft with a ladder that descended into the tunnel, the report said.

After staking out a home that had been used to store drugs, officials made multiple traffic stops of trucks leaving that site or the warehouse, according to a federal criminal complaint.

The tunnel was discovered when the warehouse was raided.

Authorities have found multiple sophisticated tunnels along California’s border with Mexico -- many in the same Otay Mesa industrial area around San Diego.

“It’s really the ideal place for a tunnel,” said Pat Abbott, a geology professor at San Diego State University, according to the Los Angeles Times. “It’s quite easy to dig through. You could do it with a pickax.”

Since 1993, 90 tunnels have been discovered in the Southern California region. The last time it happened was in 2020. https://t.co/fZkyvw3tLQ

— CBS 8 San Diego (@CBS8) May 17, 2022

Dave Shaw, the special agent in charge for Immigration Customs Enforcement Homeland Security Investigations in San Diego, said truck traffic would not be noticed in the area.

“It’s not uncommon to see that kind of commercial traffic, so it’s so easy to hide,” he said.

Federal law requires that drug tunnels that are discovered be filled in with concrete on the American side.

This article appeared originally on The Western Journal.