The helicopter was en route from Nevada to California Tuesday night.
A military helicopter that had been missing as an historic storm continued drenching California was found Wednesday morning in a mountainous area outside San Diego, but a search and rescue operation continues for five missing Marines on board, the U.S. Marine Corps said.
The aircraft was located just after 9 a.m. by civil authorities near the mountain community of Pine Valley, about a 45-mile (72-kilometer) drive from San Diego but rescue crews said snowy conditions were making access challenging on the ground.
They were "using ground and aviation assets to locate the aircrew in coordination with the San Diego County Sheriff's Department and multiple federal state and local agencies," the Marine Corps said in a statement.
The Marines were flying a CH-53E Super Stallion helicopter from Creech Air Force Base, northwest of Las Vegas, where they had been doing unit-level training and were returning home to Marine Corps Air Station Miramar in San Diego, defense officials said.
It was not immediately known what time the helicopter left Creech nor what time they were due to arrive. Waves of heavy downpours hit the area throughout the night and snow was forecast for San Diego County mountains.
The five U.S. Marines were assigned to Marine Heavy Helicopter Squadron 361, Marine Aircraft Group 16, 3rd Marine Aircraft Wing at Miramar, the Marine Corps said in a statement.
The San Diego County Sheriff's Department was notified at 1 a.m. that the craft was overdue for arrival at Miramar and was last seen in the area of Pine Valley, a mountainous region near the Cleveland National Forest about 35 miles (56 kilometers) east of downtown San Diego, Lt. Matthew Carpenter said.
The military was coordinating search and rescue efforts with the San Diego County Sheriff's Department and the Civil Air Patrol, the Marine Corps said.
Heavy snow falling Wednesday in the sparsely populated mountains covered in pine trees and thick brush was making access to the area challenging, the California Department of Forestry and Fire Protection, known as Cal Fire, said in a statement on X, formerly known as Twitter. The agency said it requested additional resources and was coordinating with the military, the U.S. Forest Service, U.S. Border Patrol, San Diego sheriff's department and the state Civil Air Patrol.
The Cleveland National Forest covers 720 square miles (1,860 square kilometers) and many parts of its steep, rocky mountains have limited trails.
The National Weather Service in San Diego called for 6 to 10 inches (15 to 25 centimeters) of snow in the mountains above 5,000 feet (1,524 meters) and gusty winds late Wednesday. On Tuesday afternoon a tornado warning was issued but quickly canceled with the weather service saying the storm was not capable of forming a twister.
President Joe Biden was briefed on the missing Marines, said White House press secretary Karine Jean-Pierre, who answered questions as the president flew to New York City for campaign fundraisers.
"We're watching this closely and again our thoughts are for the best," National Security Council spokesperson John Kirby said.
About 99 feet (30 meters) long, the CH-53E Super Stallion is the largest and heaviest helicopter in the military. It can move troops and equipment over rugged terrain in bad weather, including at night, according to the Marine Corps website. It is also nicknamed the "hurricane maker" because of the amount of downwash generated from its three engines.
Two CH-53E helicopters were used in the civil war-torn capital of Mogadishu, Somalia, in January 1990 to rescue American and foreign allies from the U.S. embassy.