Authorities are probing a second case of the plague at Yosemite National Park.
A child from Los Angeles and a woman from Georgia have fallen ill over the past few months after visiting two different campgrounds at the national park.
Both visitors are being treated with antibiotics and are expected to recover.
Humans usually contract the plague through infected fleas. Rodents also carry the plague; two infected squirrels have been found at Yosemite so far.
Officials urge the public not to touch or handle rodents. They also ask people to alert authorities if they see a dead rodent at the park.
Symptoms of the plague include fevers, headaches, and swollen lymph nodes.