Six of the seven Marines were based out of Camp Pendleton. The seventh was based out of Yuma, Ariz.
One of the Marines killed in the crash has been identified by his family as Justin Everett, originally from Fresno but lived in the San Diego area. His family says he was expected to be deployed in about two weeks.
Everett, in his early 30s, leaves behind his wife Holly and two young children. Everett's mother Patsy recalled the painful conversation she had with her son's wife.
"She said, 'I'm really sad. I hurt,' she said, 'But I can't be mad. I can't be angry about it because he was doing what he loved to do.' And it was, he loved to fly, he loved to be on that helicopter," she said.
The names of the other Marines were expected to be released on Friday.
The accident happened at about 8 p.m. Wednesday during routine training operations and involved an AH-1W Cobra and an UH-1Y Huey. The aircraft went down in a remote area above the Yuma, Ariz. training range complex, on the California side of the Chocolate Mountains.
"It's devastating. My husband was a Marine, and when you hear things like that, your heart goes out to the family," said Alexx Summers of Vista.
The Cobra carries a crew of two, a pilot and gunner, and is considered the Marine Corps' main attack helicopter. The UH-1Y, which is replacing the aging version of the Huey utility helicopter first used during the Vietnam War, was carrying the other five servicemembers who were killed.
The cause of the crash remains under investigation. U.S. military officials say these helicopters are often used for routine training, and that weather does not appear to be a factor in the crash.
"They were conducting routine training operations. It was nothing really out of the ordinary. We have aircraft going out to Yuma training ranges on a weekly basis. They go out there primarily because the aircraft mimics what they will see in Afghanistan so they get familiarization with training on that terrain," said Lt. Maureen Dooley with Miramar Air Base in San Diego.
No one on the ground was injured.
There have been two other crashes involving these two types of helicopters just in the last few months. In September, a Cobra helicopter went down during training in a remote area of Camp Pendleton, killing two Marines. In July, a Marine was killed during a training exercise when his Huey helicopter crashed, also in a remote area of Camp Pendleton.
"These pilots have been flying for at least three or four years before they got to that unit, so they're prepared, but things happen. Anything we do in the Marine Corps has an inherent risk," Dooley said.
The Associated Press contributed to this report.