An estimated 17 tons of marijuana were seized in the discovery of a cross-border tunnel that authorities said Wednesday was one of the most significant secret drug smuggling passages ever found on the U.S.-Mexico border.

The tunnel discovered Tuesday stretched about 400 yards and linked warehouses in San Diego and Tijuana, authorities said.

U.S. authorities seized about nine tons of marijuana inside a truck and at the warehouse in San Diego's Otay Mesa area, said Derek Benner, U.S. Immigration and Customs Enforcement special agent in charge of investigations in San Diego. Mexican authorities recovered about eight tons south of the border.Authorities spoke at a news conference near packages of seized dope festooned with labels of Captain America, Sprite and Bud Light. The markings are codes to identify the owners.

Photos taken by Mexican authorities show an entry blocked by bundles that were likely stuffed with marijuana, said Paul Beeson, chief of the Border Patrol's San Diego sector. Tunnel walls were lined with wood supports. The passage was equipped with lighting and ventilation systems.

The tunnel was about four feet high and three feet wide. It dropped about 20 feet on the U.S. side.

Two men allegedly seen leaving the warehouse in a truck packed with about three tons of pot were pulled over Tuesday on a highway in suburban La Mesa and arrested. A California Highway Patrol officer was overwhelmed by the smell, according to a federal complaint.

Cesar Beltran and Ruben Gomez each face a maximum penalty of life in prison if convicted of conspiracy to distribute marijuana, said Alana Robinson, chief of the U.S. attorney's narcotics enforcement section in San Diego. They were scheduled to be arraigned Thursday.

Cross-border tunnels have proliferated in recent years, but the latest find is one of the more significant, based on the amount of drugs seized.

Raids last November on two tunnels linking San Diego and Tijuana netted a combined 50 tons of marijuana on both sides of the border, two of the largest pot busts in U.S. history. Those secret passages were lined with rail tracks, lighting and ventilation.

As U.S. authorities tighten their noose on land, tunnels have emerged as a major tack to smuggle marijuana. Smugglers also use single-engine wooden boats to ferry bales of marijuana up the Pacific Coast and pilot low-flying aircraft that look like motorized hang gliders to make lightning-quick drops across the border.

More than 70 tunnels have been found on the border since October 2008, surpassing the number of discoveries in the previous six years. Many are clustered around San Diego, California's Imperial Valley and Nogales, Ariz.

California is popular because its clay-like soil is easy to dig with shovels. In Nogales, smugglers tap into vast underground drainage canals. Authorities said they found a drug tunnel Tuesday in Nogales, running from a drain in Mexico to a rented house on the U.S. side.

San Diego's Otay Mesa area has the added draw that there are plenty of warehouses on both sides of the border to conceal trucks getting loaded with drugs. Its streets hum with semitrailers by day and fall silent on nights and weekends.

After last November's twin finds, U.S. authorities launched a campaign to alert Otay Mesa warehouse landlords to warning signs. Landlords were told to look for construction equipment, piles of dirt, sounds of jackhammers and the scent of unburned marijuana.

U.S. authorities linked the November finds to Mexico's Sinaloa cartel, headed by that country's most-wanted drug lord, Joaquin "El Chapo" Guzman. The cartel has expanded its sphere of influence to Tijuana in recent years.

U.S. authorities said the sophistication of the latest tunnel suggests that a major Mexican drug cartel was involved, but no link has been established.