A California ground squirrel tested positive for the plague, a disease for responsible for killing millions during the middle ages.
A section of national forest was evacuated after the infection was revealed, the BBC reported.
The squirrel's affliction was discovered after a routine check. No people are believed to have been infected.
In the middle ages the plague was responsible for the deaths of close to 25 million Europeans. Only four human cases have been reported in Los Angeles since 1984, none of which proved to be fatal.
The plague is also know as the "black death." It can be spread through flea bites. The infected fleas are most often found in the rat population, but can live on other domestic and wild animals as well, MedNet reported.
The illness is divided into three categories, the most notorious is the bubonic plague.
Symptoms of the bubonic strain include: swollen lymph nodes, fevers, chills, and weakness.
The Septicemic plague causes symptoms like abdominal pain, septic shock, and low blood pressure.
People suffering from the Pneumonic version may experience: coughing, bloody sputum, chest pains, fever, and headaches.
If the plague is not treated with antibiotics in a timely fashion it can be deadly, the BBC reported.
Further testing will be conducted in order to asses the scope of the infection. Camping grounds will only reopen to the public after the area has been deemed safe, but people will still be able to hike through.
Agricultural workers will dust squirrel burrows with anti-flea substances.
Jonathan Fielding, director of the Los Angeles County Department of Public Health, suggested using bug repellent if entering one of the possibly infected areas.
This is not the first time the plague has been discovered in California ground squirrels. The rodents have tested positive in 1996, 1996, 2007, and 2010, the Daily Mail reported.
"We want to advise everybody to make sure they don't bring their pets, and, if possible - I know it's important for the kids to be able to go camping - but to be sure to bring the proper insect repellent," Joe Kelso said, the Daily Mail reported via NBC.
WATCH: