Wildlife-vehicle collisions (WVC) are an important, under-recognized impact on driver safety and anthropogenic mortality for species of wildlife that attempt to cross roads. The California Roadkill Observation System (https://wildlifecrossing.net/California) includes >255,000 WVC observations from state agencies, California Highway Patrol, and expert volunteers. Between 2015 and 2024, there were 1,009 state highway 1-mile segments with annual rates of collision with large wild mammals of at least 1/mile. To estimate the equivalent cost of reported collisions, crash coefficients were applied to different crash types. Fencing these highways would cost at least $200,000,000 to build and save $46,654,000/year, or >$900,000,000 for the 20-year lifetime of the fencing. The rate and cost of reported large mammal WVC has declined 10% per year for the last 10 years. The highest annual rate of large WVC reported was for US 101 in Marin County (4.6/mile). Outside of the Bay Area, the highest rate was for US 50 in W El Dorado County (3.7/mile). Several hotspot highways are targets for wildlife crossing planning, but little attention has been devoted to wildlife fencing, which is the measure that can reduce WVC.