MEXICO CITY, Mexico (Reuters) - When architect Felipe de Jesus Corona built Mexico's most powerful drug lord a 200-foot-long tunnel under the U.S.-Mexican border with a hydraulic lift entrance opened by a fake water tap, the kingpin was impressed.

The architect "made me one f---ing cool tunnel" Joaquin "Shorty" Guzman said, according to court testimony that helped sentence Corona to 18 years in prison in 2006.

Built below a pool table in his lawyer's home, the tunnel was among the first of an increasingly sophisticated drug transport system used by Guzman's Sinaloa cartel. U.S. customs agents seized more than 2,000 pounds of cocaine which had allegedly been smuggled along the underground route.

In the past five years, a crackdown on drug smugglers in Mexico and tighter U.S. border security above ground has led to a dramatic increase in the use, and the sophistication, of tunnels under the border.

There have been more than 100 tunnels discovered during President Felipe Calderon's five years in office, double the number found over the previous 15 years.

Officials suspect most recently found tunnels belong to the Sinaloa cartel, which has been perfecting its technique for two decades using specialized technology and a cadre of trained builders.

Agents of U.S. Immigration and Customs Enforcement, or ICE, are trying to shut the tunnels down, working with the few companies that have the technology and equipment to dig deep and long horizontal shafts to prevent tunnel construction.

Two drug passageways were discovered along the California border in the past month, including one about 1,600 feet long in San Diego.

Authorities seized over 32 tonnes of marijuana, worth $65 million, there after busting drivers hauling drugs from the tunnel's end at a faux produce warehouse to an industrial suburb outside Los Angeles.

Graphic on tunnels:

"It's evident that those who constructed these tunnels are specialists, not only for the size but also because it requires study of the soil to prevent it from caving in," said General Gilberto Landeros, a Mexican army commander, during the recent discovery of a Tijuana tunnel. "The machinery they use for construction is really sophisticated."

That tunnel, replete with a hydraulically controlled steel door, elevator and electric rail tracks, was built by the Sinaloa cartel, which controls the California-Mexico border area where the bulk of subterranean passages are, he said.

To burrow deep and long - one tunnel stretched 2.5 miles - smugglers employ powerful machinery, some of which can bore a small hole deep in the soil and create a walled shaft without having to send anyone below ground.

"It's super fast, it's really actually scary," said Tim Durst, assistant special agent in charge of ICE's San Diego office. "You can have a tunnel done in a couple of weeks."


The drilling equipment costs between $50,000 and $75,000, and officials say they have no way to stop cartels from obtaining the high-powered gear.

"If it's the Sinaloa cartel, they have unlimited resources," Durst said. A well built tunnel could be used to move 25 tonnes of drugs in one or two days, he said.

Officials believe cartels are turning to smaller horizontal drills that dig the length of a tunnel fast and can easily be hidden in warehouses, a favored location among smugglers trying to blend into industrial areas along the border.

Only a handful of companies produce the specialized drills normally used for laying subterranean pipelines and other infrastructure projects. ICE officials are pushing to find the purchasers, but vendors say it is difficult to be sure of buyers' identities.

"If these guys have business cards that say (Mexico's state oil company) Pemex and they want to do a pipeline here, how am I to know exactly what they are going to do?" said Gregg Shelton, who sells large-scale drilling equipment for American Auger, an Ohio-based manufacturer.

Hauling tons of drugs is no easy task. Even with industrial-sized equipment, construction can take weeks and requires skilled workers.

"The profile is somebody who has engineering or mining experience," said Joe Garcia, deputy special agent in charge for homeland security investigations in ICE's San Diego office. "It has to be somebody who is going to use tried and true surveying techniques with a compass and line of sight."

Authorities are still searching for the architect of an Arizona tunnel discovered in 1999 and constructed by unemployed and striking miners. Operated by the Tijuana and Juarez cartel, smugglers slipped about 30 tonnes of cocaine through the tunnel.

"We all know that they have access to equipment such as hydraulic lifts, elevators, generators, water pumps," said Ramona F. Sanchez, a spokeswoman for the Drug Enforcement Agency in Phoenix. "It's not your pick and shovel operation."

(Additional reporting by Tim Gaynor in Phoenix; Editing by Kieran Murray)

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