The ranger found the bat on La Paz Road in Laguna Niguel Regional Park. Authorities say it tested positive for rabies.
Last year, there were 11 rabid bats confirmed in Orange County.
Officials say if you find a bat, you should call for help instead of handling them yourself. Anyone who had recent contact with a bat is asked to call Orange County Health Care Agency Epidemiology at (714) 834-8180.