The U.S. Forest Service says the chipmunk rolled up in a ball, shaking and struggling to breathe when it was discovered near the entrance to the Taylor Creek Visitor Center.
Warnings are now posted for Taylor Creek, Tallac Historic Site and Camp Richardson Resort. The public is being asked to report any sick or dead animals.
California Department of Public Health and El Dorado County officials are trapping and testing rodents in the areas.
Plague can be transmitted to humans through the bite of an infected flea, handling an infected rodent or exposure to an infected animal.