YOSEMITE NATIONAL PARK, Calif. » An oak tree limb fell on a tent in the heart of Yosemite National Park, killing two young campers, officials said.

Park spokesman Scott Gediman on Friday morning declined to release the ages or any details about the two, describing them only as under age 18. He also declined to describe the size of the limb, citing a pending investigation.

The limb fell from a black oak tree about 5 a.m. Friday in the popular Upper Pines Campground in Yosemite Valley, striking the tent where two minors were sleeping, Gediman said. The campground is one of the parks most popular with a view of Half Dome, he said. It was either near capacity or full when the tree limb fell.

Park Rangers were alerted to the fall by 911 calls from the park. They responded to the campground to provide medical assistance.

When rangers arrived, both were dead.

California is parched as the state enters the fourth year of drought, and temperatures in the park have been hovering in the 80s and 90s during the last month, causing dry conditions. The temperature was 97 degrees in the park Thursday, the National Weather Service reported.

But what led to the limb toppling remains under investigation, Gediman said.

Last month, an 85-foot-tall tree fell in a Pasadena, California, park, injuring eight children. The tree had root problems, was leaning and may have absorbed a heavy load of water from a recent storm, according to an arborist’s report released Thursday. Some roots were girdled, meaning they were twisted around the main stem of the tree instead of spreading out.

In 2012, a Yosemite concession employee died when his tent cabin was hit by a falling limb.