US authorities have discovered a cross-border tunnel that ran half a mile from Mexico, seizing more than a tonne of cocaine and seven tonnes of marijuana.
The tunnel ran from a Tijuana house equipped with a large lift to an industrial site in San Diego that was advertised as a wooden pallet business.
It was the 13th sophisticated secret passage found along California's border with Mexico since 2006, including three on the same short street in San Diego that runs parallel to a border fence with a densely populated residential area on the Mexican side.
The unusually narrow tunnel was only about 3ft wide, equipped with a rail system, lighting and ventilation.
The tunnel was unusual because it was used for cocaine, not just marijuana, Southern California District Attorney Laura Duffy said.
Tunnels are often built for marijuana because its bulk and odour make it more difficult to escape border inspectors' scrutiny than cocaine and other drugs.
The lift, which was big enough for eight to 10 people, was located in the cupboard of a Tijuana house whose floors were strewn with mattresses, Ms Duffy said.
The tunnel zig-zagged for 874 yards to the fenced commercial site in San Diego, where the exit was covered by a large rubbish bin.
Other tunnels that have ended in California were inside houses and warehouses.
"It's a rabbit hole," Ms Duffy told reporters.
"Just the whole way that it comes up and that it comes up out right into the open, it is a bit ingenious, I think, and it's something completely different than what we've seen."
Investigators do not know when the tunnel was completed.
Margarita Ontiveros, who works at a law office next to the San Diego site, said the tenants arrived about a year ago and often bought and sold wooden pallets.
"They loaded and unloaded a lot of pallets," Ms Ontiveros said. "They sold very cheap."
Investigators began to monitor the site daily last autumn after Border Patrol agents assigned to the area saw heavy traffic and grew suspicious, Ms Duffy said.
The prosecutor said she was "fairly confident" that the first drug-load was sent earlier this month but did not rule out the possibility that some got through undetected.
Six people were arrested in the San Diego area on drug and tunnel-related crimes, including one US citizen, two Cubans who were granted asylum and three Mexicans who were legally entitled to be in the country, Ms Duffy said.
Authorities saw a rubbish bin forklifted on to a truck at the San Diego site on April 13 and followed it to a car park in San Diego, a US Immigration and Customs Enforcement Homeland Security Investigations investigator said in a criminal complaint.
Two days later, San Diego County sheriff's deputies stopped a truck after it left the car park, seizing 2,240lb of cocaine and 11,030lb of marijuana.
Marijuana found in the tunnel and rubbish bin brought the total pot haul to more than seven tonnes, authorities said.
The discovery demonstrated the enduring appeal of tunnels to smugglers, despite the significant time and money required to build one.
Dozens have been found along the US-Mexico border in recent years, mostly in California and Arizona. Many are found incomplete.
The San Diego-Tijuana region is popular because its clay-like soil is relatively easy to dig with shovels and pneumatic tools, and both sides of the border have warehouses that provide cover for trucks and heavy equipment.
