SAN DIEGO -- Vehicle inspectors at Otay Mesa Port of Entry discovered a 1-ton haul of marijuana inside a big rig that entered the United States from Mexico over the weekend, a federal official said Monday.

U.S. Customs and Border Protection agents grew suspicious about the contents of the tractor-trailer while examining it with a gamma-ray device and a service dog about 1 p.m. Saturday, CBP information officer Vince Bond said.

Further inspection revealed a secret compartment containing 122 packages of cannabis with a combined weight of 2,017 pounds, Bond said.

Immigration and Customs Enforcement officers arrested the driver, a 34-year-old Tijuana man, and took him to Metropolitan Correctional Center in downtown San Diego for booking on drug-trafficking charges.