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.
It is the law, and if you have a local officer after you it can be a problem. But they still have to prove it and this is pretty hard to do. It is especially a problem along the state border towns between Cali and Arizona, Nevada, and Oregon.
Then comes the State work/resident income tax situation....
Az honors dual Residency. 51% of the year is honored as a legal resident. But Cali does not honor it in return... If they want to get you, 15 days is it...
So... What RVers do is have family send them receipts from the other state so they can try to prove they were back in the other state and “just got back” to Cali...
If you do not have this proof you will pay...