A child contracted the plague while visiting the Stanislaus National Forest and the Crane Flat Campground in Yosemite National Park in mid-July, state public health officials said.
The child, who's from L.A. County, is recovering, but officials are concerned others may contract the disease, according to the California Department of Public Health.
The plague is an infectious bacterial disease carried by squirrels, chipmunks, other rodents and their fleas. Fleas feeding on sick or dead infected rodents can carry the infection to other animals or humans.
In California, infected animals will likely be found in the mountains, foothills and sometimes the coast.