EnglishAl,
Just read about that horrible accident. There is little doubt that had they had a traffic info system - which would have worked there - it is less likely that this accident would have happened.
I suspect they were in a radar blind spot, so TIS would have dropped out. It's quite hilly around there and SOCAL cannot see you when close to the ground (used this once when I bust miramar Class B, suddenly decided to land at Ramona, this was before it had a tower - filed the NASA form of course
)