The person is believed to have been bitten by an infected flea while camping, officials said.
In a separate incident last month, a person in Arizona died from plague.
Plague is a disease caused by a type of bacteria that usually results in about seven cases nationally each year, according to the Centers for Disease Control and Prevention.
It occurs naturally in areas of the western U.S., where it circulates among wild rodents and other animals. Humans usually get infected through the bite of an infected rodent flea or by handling an infected animal. Symptoms, including fever, nausea, weakness and swollen lymph nodes, usually show up within two weeks of exposure, according to health officials.
“Plague is naturally present in many parts of California, including higher elevation areas of El Dorado County,” Kyle Fliflet, El Dorado County’s acting director of public health, said in a statement. “It’s important that individuals take precautions for themselves and their pets when outdoors, especially while walking, hiking and or camping in areas where wild rodents are present.”