Some 960 pounds of marijuana was found hidden inside concrete pillars in the back of a tractor-trailer at the Mariposa Port of Entry in Nogales, authorities said.

U.S. Customs and Border Protection officers said they pulled the truck over Wednesday afternoon for secondary inspection due to the nervous behavior of the 32-year-old Mexican driver and suspicions about the cargo's destination in Colorado.

They pulled out one of the pillars, drilled a hole in it and found a bundle of marijuana. They unloaded 18 crates, 13 of which had concrete pillars.

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In all, officers found 51 bundles of marijuana inside the pillar sections. The bundles were surrounded by dirt inside the pillars to mask the odor, authorities said.

The unidentified driver was arrested and turned over to Immigration and Customs Enforcement, which will take over the investigation.