The staff bus from the Phantom Regiment was involved in an accident early Monday morning near the Arizona-California border. Here's a statement from Phantom: 

"A bus carrying volunteers and staff for the Phantom Regiment Drum and Bugle Corps was involved in a rollover incident early Monday morning near the Arizona-California border. None of the performing members were involved. Police and emergency responders were called to the scene and are investigating.

We will release more details when possible."

UPDATE: 

(10:10 AM CST) According to 12 News KPNX and AZFamily.com, the accident occurred on Interstate 10 near Quartzsite, AZ, early Monday. Arizona Department of Public Safety officials have said that the bus driver was killed. Four passengers have been taken to local hospitals, with two of them having to be airlifted. Their conditions have not been released at this time.

There were a total of 14 people on board the bus at the time of the incident including the driver.