What led to the limb falling, and its exact size, were not immediately revealed.

The last three cases of human plague in the state occurred in 2005 and 2006, the Health Department said. All three of those patients survived.

The deaths of two young campers killed when a tree branch fell on their tent and a campground closure because of plague cast a pall over California's Yosemite National Park at the height of the summer tourist season.

On Friday, park officials said they will temporarily close another popular campsite after two squirrels died of plague in the area.

Large fallen limbs are a common occurrence at Yosemite, and they have occasionally led to deaths. The most recent was in 2012, when a park concession employee died when his tent cabin was hit. When a 25-foot branch fell onto an open-air tram, two tourists were killed and nine were injured in 1985.

A child fell ill with the plague after camping with his family at Yosemite's Crane Flat Campground in mid-July. The park reopened Crane Flat on Friday after treating that campground for four days with an insecticide.

"Although this is a rare disease, and the current risk to humans is low, eliminating the fleas is the best way to protect the public from the disease," said Dr. Karen Smith, director of the state Health Department.

Tuolumne Meadows Campground will close from noon Monday through noon Friday so authorities can treat the area with a flea-killing insecticide. Campers had their reservations canceled at the 304-site campground so the insecticide can be sprayed into rodent "burrow holes," the California Department of Health said Friday.

Since 1970, 42 people in California have contracted plague, resulting in nine deaths. Health officials find plague-infected animals every year, mostly in the state's mountains and foothill regions.

Plague's symptoms can include fever, chills, weakness, abdominal pain, and sometimes shortness of breath and swollen lymph nodes. It can be treated and cured when antibiotics are given soon after infection, but it's deadly when treatment is delayed.

The child has been recovering in a hospital. No other family members became sick.

The large limb from a black oak fell on the tent of the two young campers as they slept in the heart of the park Friday, Yosemite spokesman Scott Gediman said. The campers, described only as under 18, were both dead when rangers arrived at the crowded Upper Pines Campground in response to 911 calls, he said.

Plague is carried by rodents and is spread by fleas, but transmission between people is rare.