I'm coming in on UA 451 from DEN into terminal 1. The UA TT then says I depart from terminal R (??) for LAX on UX. Is this the commuter terminal?

I looked up all the LAX flights on UX on the SAN website and they say "gate 4". But the terminal map shows a gate 4 both in terminal 1 and in the commuter terminal. So which is it?

Also, is 45 mins enough time to get between gates comfortably?

Thanks, SAN flyers!