An Orange County sheriff's bomb squad was summoned to the scene. At least six grenades were in the backpack, which was found in a drainage channel. Blasting caps, fuses and explosive powders were found in and around the backpack, according to the department.
The grenades were safely exploded in a bomb-disposal vessel. The O.C. sheriff's bomb squad then detonated powder and plastic blasting caps, rocking the Placentia neighborhood with explosions.
The explosives were found with six live grenades and two canisters in and around a backpack under a bridge on Lakeview Ave. The bomb squad was called in after workers found the backpack in a drainage ditch around 9 a.m.
"An ordinary person would not have access to some of the items found," said sheriff's spokesman Jim Amormino.
Authorities say whoever left the backpack had knowledge of explosives.
Officials believe the backpack had been there for months. The contents of the backpack were extremely volatile with age.
"It would have caused major structural damage to the bridge, and needless to say, any traffic that was driving on this busy thoroughfare would have been in danger," said Amormino.
Bomb experts were forced to bring special equipment in to detonate the explosives.
The street was shut down for hours and nearby businesses were evacuated as a precaution.
The sheriff's department and the FBI are investigating who left the explosives and for what reason.
After the explosives were safely detonated, Lakeview Ave. was reopened to traffic by 4 p.m.
There were no injuries and there was no property damage from the incident.