Tragedy struck in Yosemite National Park on Friday, as two young campers were killed by a falling tree trunk.

A limb from a black oak tree struck two minors dead around 5 a.m. on Friday as they lay sleeping in their tents at the Upper Pines Campground in Yosemite Valley, according to the National Park Service.

Park rangers arrived at the scene to find both campers dead. The incident remains under investigation, and no names have been released, USA Today reported.

"Our thoughts are with the families as they grieve this tragedy," said Don Neubacher, park superintendent. 

Large fallen limbs are actually a common occurrence in the park and have occasionally led to deaths.

One incident in 2012 involved a concession employee who was killed when a limb hit his cabin, and in 1985, a 25-foot branch fell onto an open-air tram, killing two and injuring nine, according to The Chicago Tribune.

Additionally, a campground in the park will be closed due to the presence of the plague. Tuolumne Meadows Campground, also in Yosemite, will be closing for five days after two squirrels were found dead from the plague, according to NBC News.

Though transmission to people is rare, the campground will be sprayed with insecticide, and campers won't be camping on the grounds until the treatment is finished.