In California, highly pathogenic avian influenza (HPAI) H5N1 virus infections resulted in the deaths of a free-ranging bobcat (Lynx rufus), six mountain lions (Puma concolor), two fishers (Pekania pennanti) and two raccoons (Procyon lotor) between October 2022 and April 2023. Three of the animals, a fisher and two raccoons, were reported to have had neurological signs and were either euthanized or died in care. The cadavers of the other eight animals were recovered after mortality sensors from their radio collars were activated. Necropsies were conducted, and tissues were submitted for histopathological analysis. HPAI H5N1 virus was detected in the brains with associated encephalitis. Genotyping showed that the virus belonged to the HPAI GsGd H5 clade 2.3.4.4b of viruses found in wild birds. Further analysis demonstrated that the viruses were not closely related in eight of the 11 cases, suggesting that the virus was not transmitted between these individuals. However, viral sequences were identical in three mountain lions indicating potential for mammal-to-mammal transmission. While mammals primarily become infected through consumption of infected birds, these results indicate infections in mammals should be monitored to detect the emergence of mutations that may increase species spillover and zoonotic potential of HPAI H5N1 viruses.