Marine Corps identifies four killed in Camp Pendleton explosion

Vehicles file through the main gate of Camp Pendleton Marine Base on Wednesday, Nov. 13, 2013. Lenny Ignelzi / AP

The four U.S. Marines killed when unexploded ordnance blew up in a training accident at what is known as the Zulu impact area of Camp Pendleton, Calif., were all experienced in their field, and three had more than a decade of service.

The deadly accident occurred Wednesday during a “range maintenance operation” to dispose of the weapons at the Zulu site, military officials said. The area is used for firing grenades, mortars, artillery and rockets and for dropping weapons from aircraft, but no live firing was going on when the incident happened, according to the Marine Corps.

On Thursday, Camp Pendleton released the names of the four fallen Marines:

Staff Sgt. Mathew R. Marsh, 28, of Long Beach, Calif., an explosive ordnance disposal technician, who joined the Marine Corps in July 2003. He served in Iraq in 2005 and 2008 and Afghanistan in 2010 and 2012.

Gunnery Sgt. Gregory J. Mullins, 31, of Bayou L'Ourse, La., an explosive ordnance disposal staff noncommissioned officer who joined the Marine Corps in March 2002 and deployed to Afghanistan in 2011 and 2012.

Sgt. Miguel Ortiz, 27, of Vista, Calif., an explosive ordnance disposal technician who joined the Marine Corps in March 2006 and was deployed to Iraq in 2007, to the Western Pacific in 2008 and to Afghanistan in 2012.

Staff Sgt. Eric W. Summers, 32, of Poplar Bluff, Mo., an explosive ordnance disposal technician who joined the Marine Corps in July 2000 and was deployed to Kuwait in 2003, Iraq in 2004 and Afghanistan in 2009, 2011 and 2012.

In addition to the Marines killed, one Navy hospital corpsman and two other Marines nearby were treated at the scene of the accident and released.

The cause of the explosion is under investigation.

"Today, our thoughts and prayers are with the families of the Marines we lost yesterday," Brig. Gen. John W. Bullard, commanding general at Camp Pendleton, said in a statement. “Explosive ordnance disposal is a small and tight-knit community, not just in the Marine Corps, but in the entire U.S. military. Our focus now is on ensuring these families receive the help and support they need." 

Camp Pendleton, in Southern California about 40 miles north of San Diego, is the Marine Corps' main amphibious training base on the West Coast and is home to the I Marine Expeditionary Force.

Jim Miklaszewski, Courtney Kube and Alex Johnson of NBC News contributed to this report.