“Dual State Citizenship” is illegal in Ca. Has been for decades. If you overstay your welcome while you are on a 14 day “vacation” in Ca it is mandatory you become a resident and Citizen on the 15th day... License and ID, Vehicles, State tax payer... Everything...
Ironically if you don’t you are hit with Illegal immigration penalties and fines...
There are loopholes for “Temporary” workers from out of state, but only for 90 days at a time and then you have to prove you went back into your home State for a substantial length of time in a row. And you CANNOT hold a “full time position” on the books.
That’s interesting since when my folks vacationed down there, they would spend several consecutive weeks in Cali, then AZ, then NV, then back to Cali.
They never got any sort of harassment from the authorities over residency.