Boy this is making a lot of noise. Simplified breakdown from a 20+ year southern-kalifornificating resident:
1) It was a slow news day. This has happened before, I guess it's been a while and nobody has remembered recently, it's that time of year (fall, the jet stream slips further south over California, and the cold Alaskan air and storms begin influencing the weather in our region) and flights from the far East and Hawaii make contrails like this fairly often.
2) I guess an advantage of living further north than most the metropolitan area... The "contrail" originated way too Westerly for it to have anything to do something originating out of Vandenburg. I can see how living south and/or east of LAX would give it a Vandenburg-originating apearance.
3) It could of been "something" going on in the very southern region of the Pt. Magu Naval Weapons and Evaluation Test Range offshore to the NW of LA, and which is a prety substantial chunk of ocean and airspace, including a couple of the Catalina Islands. The Navy (and Air Force out of Edwards, China Lake, March, and/or Vandenberg) does a lot of training and testing on that range too, much of which is never publicly mentioned or verified with exception to air space restriction advisories... one of which was indeed made and which someone on this board posted a link to... so if it was the Navy, they've already said as much on these type of things that they usualy will.