Lance Cpl. Marco Barranco was among six Marines, two others who were also from Southern California and one Navy sailor who went missing July 30 when their landing craft sank during a training exercise near San Clemente Island.
Fifteen Marines and one sailor were inside the AAV at the time. Eight Marines were rescued.
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All of the Marines involved were assigned to the 15th Marine Expeditionary Unit, based out of Camp Pendleton.
The I Marine Expeditionary Force is a Marine Air Ground Task Force whose mission is "generating, deploying, and employing ready forces and formations for crisis response, forward presence, major combat operations, and campaigns."
The amphibious assault vehicle involved has been recovered since the training accident.
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Officials said the cause of the incident is under investigation.
Barranco's body will now be sent to Dover Air Force Base in Delaware to be prepared for burial before being released to his family.
The 21-year-old was a rifleman with Bravo Company, BLT 1/4.
City News Service contributed to this report.