I don't know the boundary of the SF Bay Area region. It is based on some US designation. Once you leave the region around an office you become a part of some general state-wide designation.

This has some failure cases, with some weird places being included in regions like NYC while some other places where people really do commute to NYC (though it is extremely far) are excluded. I don't actually know anybody who has been impacted by this, but clever Googlers made a pretty compete map of all of counties in the US and their pay region once the tool for getting salary information for proposed moves was available.