Five Marines have been confirmed dead after their helicopter crashed in the mountains of Southern California.

The Marines had initially been reported missing during a flight training Tuesday night.

Their tragic fate was confirmed Thursday by the Marine Corps, which added an effort to recover the remains is in progress.

“It is with a heavy heart and profound sadness that I share the loss of five outstanding Marines from 3d Marine Aircraft Wing and the ‘Flying Tigers,’” Maj. Gen. Michael J. Borgschulte, commander of the wing, said in a statement.

Marines killed in crash

The five Marines had left Tuesday night from Creech Air Force Base near Las Vegas, and they were headed for Marine Corps Air Station Miramar in San Diego.

Their helicopter was found in Pine Valley, located 30 miles east of San Diego in the Cuyamaca Mountains, on Wednesday morning. The cause of the crash is under investigation.

The Marines were reported missing Tuesday evening after their flight was found to be "overdue." The last "ping" was reported at around 11:30 p.m.

The helicopter went down during historic rains and flooding that slammed California this week.

Timothy Loranger, a former Marine Corps aircraft mechanic and current civilian pilot and lawyer, said extreme weather may have been a factor despite the capabilities of the CH-53E Super Stallion, which is designed to carry heavy loads through choppy weather.

"Here was a training mission with the crew flying back home to Miramar, so you have to ask, why fly in this weather now? Was this poor judgment or some pilot error issue? These are very important questions that have to be asked," Loranger said.

Biden sends condolences

President Biden and Defense Secretary Lloyd Austin sent their condolences.

“As the Department of Defense continues to assess what occurred, we extend our deepest condolences to their families, their squadron, and the U.S. Marine Corps as we grieve the loss of five of our nation’s finest warriors,” Biden said.

Austin said his prayers "are with these brave Marines and their families, loved ones, and teammates."

In 2016, two Super Stallions collided off the coast of Hawaii, killing 12 Marines.

The single biggest loss of American lives during the Iraq war was the result of a 2005 Super Stallion crash in a sandstorm that killed 31 U.S. soldiers.