They say after the stop, driver Anselmo Diaz-Perez, 19, acted suspiciously so they used a drug dog to check out the truck.
Hidden inside an electric transformer on the back of the vehicle, officers found 21 wrapped packages of marijuana weighing 251 pounds. The drugs have a street value estimated at $1.1 million.
Diaz-Perez now faces trafficking charges.
"I'm proud of the personnel involved in this seizure. They went with their training and followed up on their suspicions, which led to 251 pounds of marijuana being seized instead of being sold to someone's child," Sheriff Jimmy Thornton stated.