Mexican soldiers discovered the marijuana during a routine revision at a checkpoint on the highway from Mexicali to Tijuana.
More than five thousand bricks of marijuana wrapped in cellophane were hidden inside the trailer behind bags of onions.
Mexican army officials estimate the haul is worth more than four and a half million dollars.
Its impossible to know how many tons of marijuana drug cartels smuggle across the US Mexico border each year.
Federal officials say most marijuana available in the US comes from Mexico.
The marijuana soldiers found in the tractor trailer equals about a tenth of the amount of marijuana US customs agents seized all last year at California border crossings.