UH-1Y Huey Helicopters depart Camp Bastion Airfield for a battlefield site survey. (U.S. Army Photo/Sgt. April Campbell, Creative Commons)

Authorities are investigating the collision and have not yet released the names of the Marines.

"We won’t know exactly what happened until the investigation is complete, and we can’t make any assumptions right now," said 1st Lt. Maureen Dooley, a Marine Corps spokeswoman, in a statement to CNN.

According to Dooley, the Marines were preparing for deployment to Afghanistan.

"We have aircraft going out to Yuma training ranges on a weekly basis, and they go out there primarily because the aircraft mimics what they will see in Afghanistan," Dooley said.

A report from the Los Angeles Times said six of the seven Marines killed in the collision were from Camp Pendleton. The seventh was from the base at Yuma.

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