Thanks very much for the GMaps link, jk. The cited code would seem to be VC 21461 (disobeying traffic control device). That device is the "right lane must turn right" sign, which is
just before the intersection as jk observed.
But the sign
cannot be placed there when an existing lane turns into a right-turn only lane! It must be placed "150-300 feet" before the turn, usually at or near the point where the dashed white line turns solid.
Here's the illustration from the MUTCD, exemplifying strongly recommended practice:
On both sides, the rightmost lane becomes a mandatory right-turn lane (note the signs). On the left side though, you have an "additional" lane in the left turning lane, so no signs are required except pavement arrows (they assume that if a new lane appears and you change to it, you did so because you saw the arrows).
Edit: As jk asked me to clarify below, a "thru traffic" warning sign is posted along be way (its irrelevant though). Note also that the 50 ft notation in the figure above refers to the minimum length of the solid white line and NOT to the "must turn right".
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The sign was not posted correctly. You should FIGHT this via a trial by declaration. Attach a bunch of photographs and the MUTCD explanation. If the judge reads it, he should find you not guilty. If you are eligible for traffic school though, be aware that you
may not be if you fight and lose; it's up to the judge at that point whether to grant it.