The California Highway Patrol (CHP) received a call from another CHP dispatcher in a neighboring County. The dispatcher relayed a tip from a 911 caller, which the Mendocino County team recorded as follows: “‘Showing southbound Highway 1 at mile marker 88, Silver Ford 150 pickup. Plate of 8-David-94925. Ran the reporting party off the roadway and was last seen approximately five [minutes] ago.’” The Mendocino County team then broadcast that information to CHP officers at 3:47 p.m. A CHP officer responded to the broadcast. At 4:00 p.m., the officer passed the truck near mile marker 69. After making a U-turn, he pulled the truck over. A second officer, who had separately responded to the broadcast, also arrived on the scene. They smelled marijuana. A search of the truck bed revealed 30 pounds of marijuana. The officers arrested Ds. Ds moved to suppress the evidence, arguing that the traffic stop violated the Fourth Amendment because the officer lacked reasonable suspicion of criminal activity. Their motion was denied. The California Court of Appeal affirmed, concluding that the officer had reasonable suspicion to conduct an investigative stop. The California Supreme Court denied review. The Supreme Court granted certiorari.