( CNN ) -- The discovery of a `` sophisticated '' tunnel between a Mexican eat-in kitchen and two Southern California warehouses led authorities on both sides of the U.S.-Mexico border to arrest at least nine suspects and seize between 20 and 30 tons of marijuana . The Thanksgiving Day find followed an eight-month investigation and came about three weeks after authorities discovered a similar drug tunnel in another warehouse in the Otay Mesa area of San Diego . Between the two incidents , agents in the United States and Mexico seized roughly the equivalent of one marijuana cigarette for each of California 's nearly 37 million residents , Drug Enforcement Administration special agent Ralph Partridge said Friday . `` This is obviously not a Mom and Pop operation , '' Miguel Unzueta , a San Diego-based agent with Immigration and Customs Enforcement , said Friday . `` This is a major , significant drug cartel working . '' Unzueta described the nearly half-mile-long and , in spots , 90-foot-deep passageway as `` very sophisticated , '' even more so than the one found earlier this month . Its southern entry was in the kitchen of a stucco Tijuana , Mexico , home , which had a garage attached big enough for tractor-trailer trucks . After removing a 2-foot by 4-foot piece of flooring in that house , smugglers could head 80 feet down a cinder-block-lined stretch into the tunnel . The passageway had lighting , ventilation , wood and cinder-block supports , wood floors and rail carts , U.S. law enforcement agents said . The tunnel split to lead into two separate warehouses in San Diego . `` Having been in several of these tunnels , this is one of the most sophisticated ... I 've ever seen , '' Partridge said . `` This is a tunnel where a lot of drugs were being pushed through . '' The discovery came after San Diego Tunnel Task Force agents , on Thursday morning , spotted a tractor-trailer arriving at one of the warehouses , said Unzueta . After getting its load , the truck headed to a border patrol checkpoint in Temecula , California , about 60 miles north of San Diego . There , authorities who had been tracking the shipment found the truck filled `` top to bottom , front to back '' with 27,000 600-pound packages of marijuana , Unzueta said . Authorities initially could not get through the tunnel from the California side because it was blocked by huge packages of marijuana . Much of the drug was in a 10- by 20-foot room about 60 feet below the surface . U.S. agents and Mexican military personnel formed a human chain to lug out what amounted to 3 to 4 tons of marijuana , according to Unzueta . In addition , U.S. law enforcement agencies tipped Mexican authorities about a ranch on that side of the border , where 3 to 4 more tons of the drug was captured . Unzueta estimated that all the marijuana seized Thursday could have sold wholesale for $ 17 million to $ 20 million or -- as Partridge estimated -- been equal to 16 million to 17 million individual 1-gram joints . The driver of the tractor-trailer truck was arrested and , if convicted on federal drug smuggling charges , could face between 10 years to life in prison , said Assistant U.S. Attorney Alana Robinson . The driver of a box truck who accompanied the tractor-trailer to the San Diego warehouse also was arrested , Unzueta said . Although that truck did n't carry any drugs , the residence it went to had $ 13,500 in cash . Both trucks ' drivers are U.S. citizens and are now in federal custody . Mexican authorities have arrested at least another seven people , Unzueta said . Earlier this month , agents made several arrests after seizing about 30 tons of marijuana related to the other San Diego tunnel discovery . John Morton , the head of the U.S. immigration and customs agency , said authorities `` caught them in the act . '' And in October , Mexican authorities seized 105 tons of marijuana in Tijuana . Law enforcement agents on both sides of the border have found at least 75 cross-border tunnels in the past four years , most of them in California and Arizona , according to Unzueta . `` Internal drug traffickers are using transborder tunnels to import tons of marijuana into the United States , '' Robinson said . `` Clearly , these transborder tunnels pose a significant threat to our national security as well . ''
USA : Agents describe a ` ` very sophisticated '' drug smuggling tunnel . NEW : The tunnel was between a Mexican eat - in restaurant and two San Diego warehouses . NEW : Two people have been arrested in the United States , and at least seven in Mexico . The tunnel is in the same area where agents found another this month .