I wouldn't be so sure. Does the employee visit California? Report to a California manager? Is the HR department calculating and applying some new, formulaic regional discount based in California?
It's also possible California & Ohio would have a shared worker-protection outlook. Many states, and some cities – among them Toledo & Cincinnati in Ohio - have matched California's ban of asking for salary histories. As public policy, they want employees judged for their current competitive skills, not some other non-germane circumstances of their life which doesn't affect work product.
Choice of residency could easily be treated the same. Even if California simply said, "you can't apply a salary-adjustment to residents of Fresno", it'd have a big effect. Ohio could then also add: "you can't pay Ohioans less simply because they live in Ohio".
Fresno has housing prices roughly "average" for the nation. It's one of the lower cost cities in California.
"Average" for the nation isn't exactly cheap. There's no place with a genuinely low cost of living anywhere in California that I can tell. Fresno and Victorville are some of the less insanely expensive places and they both more or less serve as retirement communities for the more expensive coastal cities.
Fresno is routinely listed as having some of the worst air quality in the nation. You rarely hear anything good about it. In the movie "Monsters vs Aliens" it is more or less the butt of the joke as a place no one would wish to live.
