Four Marines died on Wednesday at Camp Pendleton while performing maintenance. Their identities have not yet been released, and the cause of the accident is under investigation. 

There are just a few details available on the accident, which occurred at the Zulu Impact Area near the center of the base at about 11 in the morning. The Zulu Impact Area, Fox 5 San Diego explained, is "used for artillery and bombing practice." The Marines were conducting "a range maintenance operation" there, an exercise that reportedly involved clearing the range of unexploded ordnance. Brig. Gen. John W. Bullard, Commanding General, Marine Corps Installations West, released a statement on the incident: 

We offer our heartfelt prayers and condolences to the families of the Marines lost today in this tragic accident. Our first priority is to provide the families with the support they need during this difficult time.

The U.S. Marine Corps. will release the names of the deceased 24 hours after their families are notified.

Camp Pendleton, located about 40 miles from San Diego, is the main West Coast base for amphibious training. Sadly, this isn't the first deadly accident for the Marine Corps. this year. In February, a Camp Pendleton-based Marine died during a skydiving training exercise. And in March, seven Marines died in a live fire exercise when a mortar round exploded. Investigators later ruled that the deadly accident was due to "human error."