4 Marines were killed - "fatal incident"

They were killed 11/13/13 during a range maintenance operation at Camp Pendleton in Cali. 

The Marines were clearing the range of unexploded ordnance, and it was not a live firing range. No further details were released. 

The base said the cause of the accident is under investigation, and more information will be released as it becomes available.

The deaths come about eight months after a mortar explosion killed seven Marines during a live-fire training exercise in Nevada.

A military investigation determined human error was to blame for that accident. According to the probe's findings, a Marine operating a 60 mm mortar tube and ammunition did not follow correct procedures, resulting in the detonation of a high explosive round at the mortar position.