Updated at 4:05 p.m. ET
SAN DIEGO - Two Marine Corps helicopters collided over a remote section of the California desert during a nighttime exercise, killing seven Marines in one of the deadliest military training accidents in years.
There were no survivors in the latest in a series of crashes involving troops from Camp Pendleton, officials said Thursday.
Two Marines were aboard an AH-1W Cobra and the rest were in a UH-1 Huey utility helicopter when the crash occurred Wednesday night near the Chocolate Mountains along the California-Arizona border, said Lt. Maureen Dooley with Miramar Air Base in San Diego.
Six of the victims were from Camp Pendleton the largest base on the West Coast and one was from Marine Corps Air Station Yuma in Arizona. Their identities will not be released until their families have all been notified.
Officials were still scrambling after sunrise to gather evidence at the crash site in a remote section of the Yuma Training Range Complex.
The sprawling 1.2 million-acre range in Arizona and southeastern California is favored by the U.S. military and its allies for training because the hot, dusty conditions and craggy mountains replicate Afghanistan's harsh environment and the clear weather allows for constant flying.
The weather was mild on Wednesday when the helicopters were flying as part of a two-week standard training called "Scorpion Fire" that involved a squadron of about 450 troops from the 3rd Marine Aircraft Wing.
The wing has about 17,500 Marines and sailors, including six helicopter squadrons that fly both Cobras and Hueys. It's headquartered at Miramar Marine Corps Air Station and also has personnel stationed at Camp Pendleton and Yuma.
The helicopters collided at 8:45 p.m. near dunes at the edge of the Yuma range. Ground troops were in the area, but they were not affected, said Gunnery Sgt. Dustin Dunk, a spokesman at Marine Corp Air Station Yuma. The station is about an hour and a half drive from the accident site.
Part of the exercise involved having helicopters low on fuel descend to ground troops that have set up a refueling outpost, Dunk said.
He did not know if that's what the pilots were doing at the time of the crash, which occurred about an hour before the range was to shut down for the evening.
"Our training is always evolving, safety is paramount, and being prepared is paramount," he said. "It was a very standard exercise for what we do. Our thoughts and prayers go out to the family members ... Our investigation will look to see what went wrong and how to correct it."
The AH-1W 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, carries a crew of one or two pilots, a crew chief and other crew members, depending on the mission.
Hueys often are used to pick up and drop off ground crews, while Cobras hover by ready to fire if the Huey comes under attack.
Several accidents have happened in the past year involving Marine training in Southern California.
In September, a twin-engine, two-seat AH-1W Cobra helicopter went down during training in a remote area of Camp Pendleton, killing two Marine pilots and igniting a brush fire that burned about 120 acres at the base north of San Diego.
In August, two Marines were ejected from their F/A-18 Hornet fighter jet as it plunged toward the Pacific Ocean. The two Marines spent four hours in the dark, chilly ocean before they were rescued. Both suffered broken bones but survived.
In July, a decorated Marine from western New York was killed during a training exercise when his UH-1Y helicopter went down in a remote section of Camp Pendleton.
Another Hornet sustained at least $1 million damage when its engine caught fire on March 30 aboard the USS John C. Stennis during a training exercise about 100 miles off the San Diego coast. Eight sailors, a Marine and two civilians were injured.
A decade ago, in February 2002, a helicopter crash in the Chocolate Mountains California killed two Camp Pendleton Marines and injured two others. The UH-1N Huey was on a routine training mission in the Naval gunnery range.