U.S. law enforcement officials have discovered a 416-yard tunnel that runs from a home in the South California desert across the border of Mexico to a small business. They have deduced the passage was built for the express purpose of transporting drugs from one country to the other.

Authorities speculate the secret tunnel may be the first of its kind. One end of the tunnel was found in a 3-bedroom, 2-bath home in Calexico, California. A cement hole hides the entrance to the tunnel, which runs to an operating restaurant in Mexicali, Mexico.

U.S. Attorney Laura Duffy added the hole in the floor was covered by tile. It leads to a shaft that descends underground.

"We repeatedly see cartels trying to build these tunnels, they spend years doing it, they spend millions of dollars doing it, to create their own private underworld of secret passageways to move drugs unchecked into this country," Duffy said. "But for the builders, for the financiers, for the operators of these passageways, there's no light at the end of these tunnels."

Drugs Seized During Investigation

Over the course of their multi-agency investigation, authorities seized more than 1,350 pounds of marijuana with an estimated street value of more than $6 million.

Authorities also took note of just how careful smugglers were before settling on a location to set the entrance in the California home. The criminals scouted several properties beforehand, before selecting a contractor and instructing him to leave a space in the foundation when pouring concrete for what they said would be a safe.

After construction on the $86,000 home was completed sometime around Christmas, the smugglers are rumored to have rented a walk-behind saw and concrete blade from a local business, which they then presumably used to chisel the tunnel exit. Duffy added investigators suspect the crew began using the tunnel sometime in late February.

Four Arrested

So far, four people have been arrested in connection with the tunnel, including a mother and daughter in Arizona. The other two arrests were made in Calexico. All of the suspects were charged with drug trafficking, money laundering and charges relating to the border-crossing tunnel.

Several years ago, officials discovered a similar secret tunnel at a home not far from away. That residence is now empty.

However, authorities note this latest tunnel is the first to be discovered in the area in more than a decade, as the soil composition makes the land difficult to dig through. Duffy added the residential neighborhood also makes it more difficult to conceal smuggling activity.

Duffy also stressed this is the first time investigators have seen smugglers purchase land and build a home for the sole purpose of hiding the exit to a drug tunnel.

In recent years, more than 75 cross-border tunnels designed to smuggle drugs have been discovered along the U.S.-Mexico border. In California, most of the discoveries have come in the Otay Mesa region, where warehouses hide typical drug smuggling activities.

Mexico's Sinaloa cartel, the same crew tied to reputed Mexican drug kingpin Joaquin "El Chapo" Guzman, has long controlled drug trafficking along the border in California's Imperial Valley. The area offers quick and easy freeway access to Los Angeles and Phoenix.