I second the Hudson Valley, it’s hard to imagine there’s a more gorgeous and horse-friendly part of the country. So many barns have stunning indoors, too. It makes winter even more bearable than in the south, where it’s cold and dark enough to be miserable, but not enough to justify building an indoor. The only drawback is the HCOL, but coming from the Bay Area, you wouldn’t have much in the way of sticker shock.
I also would second the Willamette Valley. I only knew of it for the wine . But I drove through Corvallis and was struck by what gorgeous horse country it was. Bend was too dry for my tastes, but Corvallis was just lovely. Idk if it’s actually in the Willamette Valley, so I apologize if my geography is off. I’ve lived my whole life a long way away from the west coast!