A drug cartel took a big hit when Nogales port of entry officials seized a marijuana cargo this month worth up to $12 million, the biggest pot seizure on the Arizona border and possibly the Southwest, Customs and Border Protection officials said.

"There was a lot of profit lost," Guadalupe Ramirez, the Nogales port director, said at a news conference Tuesday.

Last week's shipment from Mexico through the commercial truck crossing in Nogales was supposed to be metal parts for fans. Instead officers found about 600 bundles of pot inside cardboard boxes, each weighing between 25 to 30 pounds, a total of about 15,000 pounds.

A 26-year-old man from Nogales, Sonora, who was driving the tractor-trailer was turned over to Homeland Security Investigations, part of Immigration and Customs Enforcement.

Mexican drug-trafficking organizations, mainly those associated with the Sinaloa Cartel, have increased their use of the region as a primary entry point for marijuana and heroin into the United States as well as shipping bulk currency and weapons into Mexico, a 2011 report by the Arizona High Intensity Drug Trafficking Area said. Congress created the program in 1988 to provide assistance to local law enforcement agencies in heavy drug-trafficking regions of the country.

Ramirez wouldn't say if anyone had been arrested in connection with the marijuana seizure, saying it's an ongoing investigation. He also would not say what led the officers to send the tractor-trailer to the X-ray machine.

Not all truck shipments get a second inspection because that would cause major delays at the commercial border crossing. Instead officials use a wide range of factors to determine which shipments are deemed suspicious and should get a closer examination.

When a seizure this size happens, the drug cartels change their operations, Ramirez said, perhaps to shipping smaller cargos.

As to what might have prompted someone to risk sending more than 7 tons of marijuana, "maybe they thought it was a sure thing, that we would be focus on produce and not metal," he said.

The high season for shipping produce is on its way.

The port of entry on Mariposa Road sees about 1,200 trucks daily, which increases to 2,000 in the peak of the produce season.

"This is one of the busiest ports," Ramirez said.

About 15 percent of the produce imported to the United States comes through Mariposa.

Drug traffickers often look at what's being shipped and try to blend in, officials said.

"They use this time to play the numbers game," said Ramirez.

For instance, when there are a lot of tomato shipments, traffickers might hide drugs in between the produce, he said.

"They also use this high-traffic time to study us and figure out what cargo is being examined the most," he added.

The last seizure that comes even close to this one was about two years ago when agents intercepted 12,000 pounds of marijuana in three different shipments, officials said.

In fiscal year 2011, Customs and Border Protection seized almost 4.6 million pounds of marijuana.

Once the investigation is completed, the bundles of marijuana will be incinerated.

2 Arizona pot busts worth $2.25M

Tucson Sector Border Patrol agents seized nearly 4,500 pounds of marijuana worth about $2.25 million in two separate incidents Friday, officials said.

A Mexican man was arrested Friday after a canine team alerted agents from the Willcox Station working at the Arizona 90 checkpoint.

During a secondary inspection, agents said they found found nearly 2,900 pounds of marijuana hidden in a tractor-trailer he was driving. The drug load had an estimated street value of $1.45 million. It will be turned over to the Drug Enforcement Administration, while the driver faces possible prosecution, a news release said.

Also Friday, Ajo Station agents working near Pia Oik Village north of Menegers Dam found a GMC Yukon hidden in dense brush.

Inside, agents said they found 86 bundles of marijuana weighing almost 1,600 pounds worth about $800,000.

The Yukon and the pot were taken to Ajo Station to be turned over to the DEA.

Contact reporter Perla Trevizo at ptrevizo@azstarnet.com or at 573-4213. On Twitter: @Perla_Trevizo.