Cars kill about 780 mountain lions a year in California, and I-280 is among the worst stretches, UC Davis report finds

Vehicles kill at least 780 mountain lions in California each year, about 18% of the state's estimated population, according to the 2026 California Roadkill Hotspots Report released Tuesday by the Road Ecology Center at the University of California, Davis.

The report names portions of Interstate 280 among the stretches with the highest rates of mountain lion collisions. The others it lists are parts of Interstate 15, state routes 62 and 118, and U.S. Highway 101. The UC Davis announcement does not say which segments of each road are worst.

The population estimate the researchers used comes from the California Department of Fish and Wildlife's 2025 count.

Smaller coastal populations hit harder

More lions are being killed in Northern California, said Fraser Shilling, who directs the center, but the effect on the population is greater in southern and central coastal California, where there are fewer of the animals. The state recently listed mountain lions in those regions as threatened under the California Endangered Species Act, the university noted.

The report also estimates that cars and trucks on major paved roads kill about 44,000 mule deer a year, close to 10% of the state's herd and two to four times the number taken by hunters. The worst deer hotspot is U.S. 50 in western El Dorado County.

Shilling said the real tolls are probably higher, because the data cover only about half of California's roads.

Fences over crossings

The report's central argument is that wildlife crossings by themselves do not reduce roadkill. Apart from removing roads or cutting traffic volume and speed, it says, the only proven fix is fencing that keeps animals off the pavement.

"But just building a crossing doesn't mean wildlife will use it," Shilling said in the university's announcement. "Fencing is the answer to reducing roadkill, not crossings alone."

California has paid for the world's largest wildlife bridge, the Wallis Annenberg crossing over U.S. 101 in Southern California, and for smaller projects such as a recently finished overpass on State Route 97 in Siskiyou County. Those help animals move between habitats, the report says, but they leave roadkill rates unchanged because so little fencing is built alongside them.

Shilling said fencing is most needed at hotspots and next to existing creek and minor-road undercrossings that animals already use.

The findings draw on the California Roadkill Observation System, which holds about 235,000 records submitted by state agencies, biologists and other trained observers, covering 770 species of amphibians, birds, reptiles and mammals.

Sources

ucdavis.edu