Border Patrol Special Operations Supervisor Cesar Sotelo looks on next to the entrance of a tunnel leading to Mexico from a lot along the border, Wednesday, April 20, 2016, in San Diego. Officials announced the recent discovery of the nearly half-mile-long tunnel Wednesday, along with the seizure of more than a ton of cocaine and seven tons of marijuana. Six people were also arrested. (AP Photo/Gregory Bull)
The bust resulted in seizures of 2,240 pounds of cocaine and more than seven tons of marijuana.
The tunnel - 46 feet below ground and believed to be the longest tunnel ever found on the California-Mexico border - was unusual because it was used for cocaine, not just marijuana, said Laura Duffy, US attorney for the Southern District of California.
Tunnels are often built for marijuana because its bulk and odor make it more difficult to escape border inspectors' scrutiny than cocaine and other drugs.
The elevator, which was big enough for eight to 10 people, was located in the closet of a Tijuana house whose floors were strewn with mattresses, Duffy said. The tunnel zig-zagged for 874 yards to the fenced commercial lot in San Diego, where the exit - a 3-foot diameter hole - was covered by a large dumpster.
"It's a rabbit hole," Duffy told reporters, according to the Associated Press. "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."
The tunnel was only about three feet wide, making it one of the narrowest found so far, and it was equipped with a rail system, lighting and ventilation.
Thomson Reuters An air vent helps authorities with their investigation after the discovery of a cross-border tunnel from Tijuana, Mexico to Otay Mesa, California 
Federal agents who patrol the Otay Mesa area immediately north of the border began watching the pallet company, its yard stacked with grimy, wood-frame racks, in October, Duffy said, according to Reuters. "The investigation began with an astute border patrol agent who identified this business as suspicious," Duffy added. "They began monitoring this location and saw the people here conducting dry runs."
The heavy traffic raised suspicious among investigators, who began daily monitoring of the lot, according to the AP. Duffy said she was "fairly confident" that the first drug load was sent earlier this month but didn't rule out the possibility that some got through undetected. Investigators didn't know when the tunnel was completed.
"On the surface, few would ever suspect that traffickers were moving multi-ton quantities of cocaine and marijuana worth tens of millions of dollars in such an unassuming way ... in full view of the world around it," Duffy said.
Margarita Ontiveros, who works at a
Authorities saw a trash bin forklifted on to a truck at the San Diego lot on April 13 and followed it to a parking lot 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 parking lot, seizing 2,240 pounds of cocaine and 11,030 pounds of marijuana. More than 3,000 pounds of marijuana found in the tunnel and trash bin brought the total pot haul to more than seven tons.
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.
Other tunnels that have ended in California were inside houses and warehouses.
Six people were arrested in the San Diego area Friday on drug- and tunnel-related crimes, including one U.S. citizen, two Cubans who were granted asylum and three Mexicans who were legally entitled to be in the country, Duffy said.
The discovery demonstrates the enduring appeal of tunnels to smugglers, despite the significant time and money required to build one. Dozens have been found along the U.S.-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.
(Elliot Spagat of the Associated Press contributed to this report.)