Cedar City Police Sgt. J.R. Robinson said 30-year-old Brandon Mark Gillman of South Jordan was one of three drivers working for Utah Trailways, contracted to transport the kids from Canyon View High School on their senior trip.
Prior to leaving, police say a K-9 unit performed a sweep of the bus and the dog detected a controlled substance in a backpack belonging to Gillman.
Robinson said Gillman was questioned, and the drug turned out to be a prescription.
Robinson said the officers investigated further and found other prescription drugs in Gillman's pockets, some of which did not appear to be his own.
Robinson said the officers performed a field sobriety test on Gillman.
Robinson said Gillman failed the tests which resulted in his arrest, because the officers deemed him unsafe to drive the vehicle.
Robinson said officers took urine and blood samples from Gillman as well, and that preliminary tests showed he had some cocaine in his system.
Another driver was dispatched to drive the bus to California.