"The prairie dog colonies are being monitored and the caves are being treated with insecticides, but there is still evidence of fleas in the walking and camping areas that could endanger humans and pets, leaving these areas closed," said John M. Douglas, Jr., the executive director of the Tri-County Health Department.
No human infections were reported, he said.
Despite its name and fateful history in the Middle Ages, the plague, at least in the United States, is rare and generally treatable.
In general, small mammals and rodents carrying infected fleas carry the disease, which can spread through flea bites or contact with pets or humans with an infected mammal.
More than 80% of US cases were bumps. Untreated bubonic plague can turn into a more severe lung infection that causes rapid pneumonia after bacteria spread to the lungs.