Thieves who stole two trailers bearing Nvidia logos in California were in for a disappointment: instead of valuable AI hardware, each container held 20,000 pounds of sand.

The trailers, parked outside the warehouse of PlusAI, an autonomous trucking startup working with Nvidia on self-driving technology, were taken from Fremont, California. The thieves broke the hand locks, hitched the trailers to their own cabs and drove off. When they stopped to inspect their haul, they found ballast.

PlusAI uses the sand as simulated cargo for research and development testing, spokesperson Lauren Kwan said, letting engineers test how heavy loads affect autonomous trucks without shipping real freight.

The theft was discovered when a friend of a PlusAI executive spotted the trailers near their workplace in Newark, California, and sent a congratulatory message. Both trailers were recovered with the full 40,000 pounds of sand intact. Police are investigating and no arrests have been made.