By Tom Reopelle

CAMP PENDLETON (CBS) — U.S. Marine Corps officials on Thursday were working to determine what caused a mid-air collision between two helicopters that killed seven Marines, including six based in Southern California.

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“Getting in a helicopter crash without them even being at war is just sad,” Oceanside resident Patti Welton said.

KNX 1070’s Tom Reopelle reports the collision occurred during routine nighttime training in the desert three hours east of Camp Pendleton.

A Cobra helicopter carrying two people and a utility helicopter with five aboard were conducting training maneuvers in the Chocolate Mountains, east of the Salton Sea, when the crash occurred, said Lt. Chad Hill from the Marine Corps’ air station Miramar.

“The routine training operations that we do there when we go out to Yuma is for practice and to get realistic training as if they were overseas in, say, terrain such as Afghanistan,” said Hill.

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, carries a crew of one or two pilots, a crew chief and other crew members, depending on the mission, according to the Associated Press.

The names of those Marines killed will not be released until next of kin have been notified.

Welton said, “My husband is a Marine and we have friends who are Marines as well. A couple of their wives, I called them instantly, and asked them whether or not their husband on. So, it did affect me just because it’s so close to home.”

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An aerial view of the scene showed very little debris. An investigation into what may have caused the collision could take several months, Hill said.

(credit: CBS)

The weather Wednesday evening was described as mild. Marines flying in helicopters like the ones involved in the crash favor performing exercises in the desert because of the climate and because the terrain resembles that of Iraq and Afghanistan.

“It’s a Marine Corps motto, ‘Fight like you train, train like you fight.’ And, as dangerous as combat is, to be able to succeed in it the things we do back here, training-wise, do have a lot of inherent risk in them,” said U.S. Marine Corps spokesman Lt. Tyler Balzar.

The crash was the fifth training accident in nearly a year involving Marine Corps aircraft in California, including a helicopter crash at Camp Pendleton in September that killed two Marines.

Several Oceanside residents said they feel like those stationed at Camp Pendleton were part of their family and that the crash hit close to home.

“In fact, I’ve had them over at my place for Thanksgiving dinner and get to talk to their parents when they call home — so, yeah, we do feel like they’re family,” said an Oceanside resident.

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Resident Casey Chavez said, “I wish [the victims’ families] all the best. My heart and my prayers go out to them. It’s a sad day for us in San Diego.”