Could Chinese submarines get through the Gulf of California to Rocky Point 65 miles from Arizona?
I would guess yes, since Mexico has a submarine base at Rocky Point.
Yes, as a general geographical and navigational matter. That would apply, of course, to any long-range submarines from any other country. Presumably their presence in the Gulf of Mexico would be detected by US satellites etc. Once detected it would be up to the USA what it would do about that discovery. In international waters (most of the Gulf of Mexico) any military action against any submarine of any nation would be an act of war.
not really ... the Gulf of California is shallow. And the US Navy has thought of that already