Did Pacific Southwest Airlines ever operate flights under VFR?
I was a controller at L.A. Center around that time, and it was extremely common for airlines on the short-haul routes to go VFR-on-top, which is VFR but on an IFR flight plan. There would have been a lot of downsides to flying VFR but every advantage to them to fly VFR on top: with on-top they didn't need clearance into class B (back then the TCA) or get refused or delayed because the controller was "too busy"; didn't have to fly airport patterns (basically guaranteed a straight-in since they would be on an instrument approach); and for flying into the metered airports like LAX or SFO they would have a guaranteed slot, unlike trying to call up as a VFR where they would go to the back of the line and might have to hold for an hour. Plus of course on-top has the benefits of not needing IFR separation, so ATC would almost always give them a direct routing and they could climb all the way up to 16500/17500 instead of being step-climbed under everyone else and capped at maybe 10,000. 

So while I don't remember specific routine flights from 25+ years ago, I do remember working a LOT of airlines flying VFR on top on the short routes like LAX to Bakersfield, Burbank to Fresno, etc.