California features a landscape in which real wilderness closely abuts the most densely populated suburbs. It does not rain typically from April to October, and watercourses become brushy arroyos instead of streams, and these serve as perfect mountain lion highways from the uninhabited mountains right into suburbia.

Smithsonian:

A nine-year study of cougars in the Yellowstone National Park has found that nearly half of the big cats they tracked were infected with the plague-carrying bacteria Yersinia pestis at some point, according to a paper published last month in Environmental Conservation.

The Y. pestis bacteria is behind the Black Death, the mid-1300s epidemic of bubonic plague that in five years killed over 20 million people in Europe. These days, only about seven people catch Y. pestis each year in the United States. The bacteria lives in the soil, gets picked up by fleas living on rodents, and infects other creatures on its way up the food chain. The new evidence in cougars, also known as pumas and mountain lions, shows how flexible and dangerous the pathogen is in different hosts.

The study was conducted on cougars in the southern Greater Yellowstone Ecosystem, specifically in Jackson Hole, the valley east of the Grand Teton mountain range and south of Yellowstone National Park. “You start to get a clear picture of how hard it is to be a mountain lion in Jackson Hole,” biologist and co-author Howard Quiqley tells Mike Koshmrl of Wyoming News. “If you get to be an adult mountain lion in Jackson Hole, you’re a survivor.”

RTWT

I guess it’s not really surprising. Black Plague is known to be endemic to rodent populations pretty much all over The West.