Traffic cases such as this one are usually best handled by just telling the Judge the story of what happened. If it makes sense and you can show that there is some ambiguity in the law, then you might just prevail.
Reach California Vehicle Code 22562(c) and be very familiar with it. I also suggest various photographs of the scene so that the Judge can see what you saw. I also suggest that you don't talk about the officer making an "illegal U-Turn" or things like that. Judges tend to have a high view of police and you will just harm your credibility. The case is not about what the officer did, but it is 100% about whether or not you violated the express language of 22562(c).
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