Two young people were killed early Friday after a limb from an oak tree fell on their tent as they slept at a popular campground in Yosemite National Park.
The names and ages of the minors were not released, and their deaths remain under investigation, according to park spokesman Scott Gediman. Tuolumne County sheriff's officials said they will not release the young people's identities.
"Our thoughts are with the families as they grieve this tragedy," park Supt. Don Neubacher said in a statement.
The youngsters were sleeping in their tent at the popular family Upper Pines Campground in Yosemite Valley. Then at about 5 a.m., a limb from a black oak collapsed on them, Gediman said.
The park's dispatchers received numerous 911 calls for medical assistance. When they arrived to the campground, the youngsters were dead.
It is unclear why the tree limb fell, but officials said it wasn't windy that morning, Gediman said.
"Fallen branches like this one are a common occurrence across the park," he said.
Situated at 4,000 feet in the Yosemite Valley near Curry Village, the campground with views of the park's most iconic rock formation Half Dome is the chosen destination for families site.
The youngsters' deaths add to what appears to be a long history of tree-related fatalities at the park.
Two tourists were killed and nine were injured in 1985 when a 25-foot oak branch fell 15 feet onto an open-air tram carrying 50 passengers.
The same series of events happened in 1992, when a branch from an oak tree fell onto another touring bus, injuring seven people. The visitors were stopped on a main road near the Merced River to observe Yosemite Falls. The large branch came crashing as the tour guide spoke.
Then in 2012, a concession worker was killed when a tree limb crashed onto his tent cabin during a windstorm. The employee, Ryan Hiller, 27, of Chapel Hill, N.C., was the last person to be killed by fallen tree limb at Yosemite.
In 2013, a counselor at the Jewish summer Camp Towango, a few miles away from Yosemite National Park, was crushed by a tree that crashed onto a campfire.
It is unclear why the tree's branch fell in Friday's deaths, but recently the U.S. Forest Service said more than 12 million trees have died off due to the drought.
Years of dry conditions have taken a toll on California forest lands. The weakened and dehydrated trees are susceptible to bark beetle infestations. The tiny brown beetles chew away at pines and make them brittle.
In Friday's incident, drought may have played a role but it's too early to say, Gediman said. Bark beetles steer away from oak, so he said that likely didn't cause the limb to fall.
Last month, an 85-foot pine toppled and injured children in a Pasadena park.
Officials said the prolonged drought, a lack of strong roots and a burst of heavy rain were factors.
The massive, city-owned Italian stone pine came crashing down on young day campers outside the Kidspace Museum at Brookside Park on July 28. Firefighters, police officers and bystanders worked feverishly to free the 33 children caught beneath its branches.
Two of the children were critically injured but were recovering, authorities said.
The thirsty tree may have absorbed too much water in a short period, concluded arborist Ted Lubeshkoff, hired by the city to investigate why the tree fell.
"California is currently in its fourth year of drought, where it is receiving abnormally low rainfall amounts. This probably resulted in the Italian stone pine not receiving adequate amounts of water," he wrote.
According to a Los Angeles parks department survey ending in April, as many as 14,000 trees in L.A. parks -- about 4% of the total -- may have died during the last year of drought. The year before that, officials said only about 1% of trees were found dead. In a normal year, the tally would be even less.
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Los Angeles Times staff writer Richard Winton contributed to this report.