Each state has its own definition of a resident, so it's possible to be considered a resident of more than one state at the same time. If Arizona is your home (your "domicile") I don't think that renting an apartment in California would make you a California resident. But you should review the rules for California residency to make sure. The California Franchise Tax Board has a publication that explains how to determine whether you are a California resident for income tax purposes, FTB Publication 1031, "Guidelines for Determining Resident Status." The publication also explains the concept of domicile, which is not the same as residence.
