The Department of Public Safety says 743 pounds of marijuana was found inside the tank of a septic truck.
The bust occurred when a DPS officer pulled over the truck Wednesday on Interstate 19 near Tubac for an invalid license plate.
Authorities say the truck had suspicious markings and the driver — 24-year-old Leonard Salcido of Tucson — gave permission for a search.
When the officer opened the holding tank, authorities say he discovered the marijuana wrapped up in bales.
The DPS says the street value of the marijuana is estimated to be about $409,000.
Salcido was booked into the Santa Cruz County Jail on suspicion of possession and transportation of marijuana.