There is AMR City and AMR County. City covers SD itself, County covers Coastal North County, the South Bay and the Heartland area(La Mesa, Lemon Grove, Spring Valley) and San Miguel. HQ for County is off the 15 and Balboa, City used to be off 15 and Aero. Pay is garbage. Shifts I believe are mostly 12's with some 24's. I haven't seen their pay structure since 08 but it was 10.40/hr for a medic then.
I'm not sure. My info may be outdated, I work for an FD in the boonies of the county and usually only see Mercy Amb if its not my dept's box. That pay is better but far from sufficient to live anywhere desirable in the county.