You can get it "expunged" in California, however, its not a true expungement. The conviction will remain on your record. All the "expungement" will do is add a note that indicates the charge has been dismissed pursuant to Cal. Penal code 1203.4. In California, what is commonly known as an "expungement" is more accurately described as a dismissal. The conviction is never removed, so it is unlikely that it will help with the Illinois case.
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Expungement doesn't mean it is not priorable, at least according to CA law. See CA Penal Code 1203.4.
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