Discovered via the great Kottke.com:

No one is alive that can remember life before your day could be interrupted by a newsflash. The first event in this country to be experienced that way was when the transcontinental railroad was completed in the Utah desert in 1869. The entire nation was waiting for the moment a golden spike (wired to the telegraph) struck a silver hammer (also wired up to the telegraph), creating the first massive breaking news story.