If your son is your dependent, then on your own tax return you can say he lived with you all year; living away at college is considered to be a "temporary absence." So he is a resident of CA for his own tax return. BUT---he earned income in the state of VA. So before he completes a CA tax return, he needs to prepare a NON-resident return for the state of VA. He did not earn any income in AZ (per what you say here) so there is nothing to file or prepare for AZ.
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