The areas closed, since 1 p.m. Wednesday, include the Twisted Arrow, Broken Blade and Pima Loops of the Table Mountain campgrounds.
The areas will be closed for at least a week, according to a health advisory from the county Department of Public Health.
"Plague is a bacterial infection that can be transmitted to humans through the bites of infected fleas, which is why we close affected campgrounds and recreational areas as a precaution while preventive measures are taken to control the flea population," Jonathan E. Fielding, head of the health department, said in the advisory.
"It is important for the public to know that there have only been four cases of human plague in Los Angeles County residents since 1984, none of which were fatal," he said.
The ground squirrel population in the San Gabriel Mountains has been known to have the plague, and officials said squirrel burrows in the affected area will be dusted for fleas.
Officials also advised those visiting areas nearby the Broken Blade, Twisted Arrow and Pima Loops to take precautions, such as not feeding wild animals and preventing pets from getting fleas.
"Protection with an insect repellent containing DEET is also recommended for persons visiting the Angeles National Forest and engaging in outside recreational activities in other areas of L.A. County," Fielding said, adding that products containing DEET are not safe for pets.
In the advisory, officials said “transmission of plague through flea bites causes bubonic plague, with symptoms including enlargement of lymph glands (buboes) near the flea bite and rapid onset of fever and chills.”
“Untreated bubonic plague can progress to infection of the blood, or rarely, the lungs, causing pneumonic plague,” the advisory said, adding that all types of the plague can be fatal if not treated, though patients generally respond well to antibiotic therapy.