County of San Diego Emergency Medical Services (EMS) is a part of the Health and Human Services Agency's (HHSA's) Medical Care Services Division.  HHSA is the 'local EMS agency', or LEMSA, as defined in California law. 

State of California Emergency Medical Services Law Health & Safety Code Section 1797.200

California's EMS Act authorizes each county to develop an EMS program and to designate a local EMS agency (LEMSA) that oversees the delivery of EMS within that geographic area:

http://emsaac.org/about/lemsas