Whoever stole a pair of trailers plastered with company logos for Nvidia and PlusAI this week in Fremont probably thought they’d scored a fortune in high-tech hardware. What they actually got was a bunch of sand. About 40,000 pounds of it. Two trailers belonging to PlusAI — a self-driving trucking company headquartered in Santa Clara — were pilfered late Wednesday from the docks of its Fremont warehouse, police and a company official confirmed. The trailers held a combined 20 tons of sand, which the company uses to simulate real freight during research and development, according to Jocelyn Ren, a senior marketing manager. Warehouse workers discovered the theft early Thursday, reporting it to the Fremont Police Department just after 9:30 a.m. The locks on the trailers’ glad hands — the couplings that link the air brakes to the truck — appeared to have been forced off, the company said. The PlusAI cabs that normally pull the test trailers were parked elsewhere on the property and appeared untouched. Security footage shows two unidentified tractors driving around the warehouse, according to Lauren Kwan, the company’s vice president of marketing. “Those were not our tractors,” she said. “Those were from the thieves.” The company began filing police and insurance reports. Then, just hours after reporting the theft, a break came from an unlikely source. PlusAI’s vice president of legal got a text from a friend with a photo of the trailers parked outside an office in Newark — minutes from where they’d been stolen. “I have been proud of you for your adventure and success at Plus,” the friend wrote. “Just saw two of your trucks near my work place! :)” PlusAI sent its fleet operations team to confirm that the trailers were still in Newark and alerted the cops. Newark police officers recovered