FALLSTON, MD - An explosion at the Fallston post office is under investigation. Authorities found an explosive device had detonated inside a blue steel commercial mailbox in the 2400 block of Watervale Road.A passerby reported a mailbox had been destroyed at 7:35 a.m. on Sunday, prompting a response from the Office of the State Fire Marshal, Harford County Sheriff's Office, U.S. Postal Police and U.S. Postal Inspector.Officials said they gathered evidence at the scene and determined there was $1,000 in damage as a result of the explosion.Anyone with information is asked to contact the Office of the State Fire Marshal Bomb Squad at 410-859-7152.Photo courtesy of the Office of the State Fire Marshal.