A national forest outside of Los Angeles has been evacuated and shut down after a squirrel was found infected with the plague.
The squirrel tested positive for plague after it was trapped in the Angeles National Forest during routine surveillance activities.
Health officials said that as a precaution, visitors were ordered to leave three camp grounds and a recreation area of the Angeles National Forest.
The forest encompasses 655,000 acres in the San Gabriel Mountains just north of metropolitan Los Angeles.
The plague, known as the "Black Death" was blamed for killing 25m Europeans during the Middle Ages.
It is a bacterial infection that can be transmitted to humans through the bites of infected fleas.
A health department spokesman said no people were believed to have been infected.
An average of seven cases of plague are reported each year in the US.
The disease is typically not fatal if treated with antibiotics.
Officials said further testing of squirrels would be conducted in the Angeles National Forest before the Broken Blade, Twisted Arrow and Pima Loops camp grounds were re-opened to the public.
According to the health department, plague has been known to reside in the San Gabriel Mountains ground squirrel population.
Previous surveillance efforts have identified five other squirrels carrying the disease since 1996.
The most recent squirrel found to be infected was trapped on 16 July during routine checks in the park and confirmed to carry the disease on 23 July, according to the health advisory.
Last year, an Oregon man survived a bout with plague, one of three reported in that state since the mid-1990s, none of which was fatal.