A special subdivision to be known as an emergency medical service district may be established by the board of supervisors or boards of supervisors of any county or group of counties, and/or governing authority or authorities of a municipality or municipalities located in such counties, acting separately or jointly in any combination, to provide emergency hospital care and ambulance services for an area composed of all or part of the geographic areas under the jurisdiction of such boards of supervisors or municipal governing authorities, as may be agreed upon.