Federal officials said the "fully operational" 775-foot tunnel linked a warehouse on the U.S. side of the border and a vacant ice manufacturing plant behind a strip club in Mexico, the Los Angeles Times reported Thursday.
The lighted, buttressed and ventilated passageway was high enough for a 6-foot person to stand and walk, officials said when announcing its discovery Thursday in Yuma, Ariz. It ran beneath the border fence, a park and a water canal.
"I would suspect that professional engineers were cooperating with the builders, if not working on-site," said Doug Coleman, special agent in charge of the Drug Enforcement Administration's Phoenix field office.
The people behind the tunnel haven't been identified but Coleman said "it's a good guess" it would be traced to the Sinaloa cartel and drug figure Joaquin "Chapo" Guzman.
Authorities said they discovered the tunnel following the seizure of 39 pounds of methamphetamine last week. Law enforcement officials found the drugs during a traffic stop on the highway between San Luis, Ariz., and Yuma and traced the cache back to the warehouse in San Luis.
DEA investigators who searched the warehouse found soil in dozens of 55-gallon drums, which "suggested there must be a tunnel," Coleman said during a news conference.
The tunnel's entry was found under a 2,000-gallon water tank.
In Mexico, the tunnel's entrance was found in the ice house, where investigators found 200-pound bags apparently filled with excavated sand and dirt, the Times said. Investigators had to drain a tank to access the entrance.
Coleman said the tunnel was an "extraordinary piece of engineering."