U.S. Customs and Border Protection agents seized 1,619 pounds of marijuana concealed in a shipment of fake landscaping stones at the Otay Mesa port of entry on Saturday.

A flatbed semi-truck carrying several pallets of large red stones attempted to cross into the United States around noon on June 11. After a CBP agent performed an initial inspection, the truck and its cargo, manifested as “red stone,” were referred for an x-ray examination.

According to the CBP, an “anomaly” was discovered during the examination and the truck was sent for further investigation.

Agents then screened the truck and cargo with the help of a narcotics-detecting canine unit which tipped the officers to the trailer.

A hole was drilled into the side of one of the red boulders and CBP agents discovered a “leafy-green substance”.

“My officers not only need to enforce typical import and export laws, but also need to be vigilant for smuggling attempts like this,” Otay Mesa Cargo Port Director Rosa Hernandez said. “Officers used their skill and tools at their disposal to find and seize this large shipment, and then used sledge hammers and jack hammers to remove the packages from the stone shaped objects made from a cement type material.”

The stones concealed 577 individually-wrapped packages of marijuana carrying an estimated street value of $810,000, according to the CBP.