First Lt. Colleen McFadden said she had very few details to release, including what type of vehicle rolled over or the extent of the injuries involved.
She said the Marine who was killed was from the 1st Marine Division, and that person's name will not be released until 24 hours after relatives are notified.
"The command's priorities are to take care of the Marines, Sailors and families of the unit," McFadden said in a statement. "We want to ensure the Marines and their family members are being provided for during this difficult time."
Camp Pendleton, a vast seaside base north of San Diego, is the major West Coast outpost for the U.S. Marine Corps.
In November 2013, four Marines were killed there while clearing explosives in a Camp Pendleton training area.