Going across the border is very different that someone driving down Main street, USA.

The law in Arizona has nothing to do with getting across the border. You could be in Paige, AZ (on the Utah border) and still be required to show proof of citizenship.

If there is no probable cause, it is NOT legal for the police to stop you.

>Asking you what country your from is not detaining you. Ever cross the border from Mexico into the US? The Border Patrol agents
>ask that question all the time. It's perfectly legal. If after answering they suspect you're not legal, they can arrest you. How is
>that different in San Diego from AZ? It's not. It's perfectly legal for the authorities to stop you and ask where you're from.