There is a SoCal feed that handles Ontario and Los Angeles (the STADIUM and some low banning sectors I think) but no, there is no dedicated SoCal feed for LAX arrivals and departures - which is a bummer.
Set distance? Yes, it is the boundry of KZLA/KZAK - Los Angeles Center and Oakland Oceanic
Frequencies? No idea, but most of the communication is done via ACARS and SELCAL, there is very rarely a need to go through ARINC or voice these days