The light changes.
At Gaviota, at Santa Clarita, at San Bernardino. You come over the pass into a newer and more vibrant world, where shadows have edges, colors have vibrance, and the endemic NorCal drabness falls from memory.
The geology changes. SoCal was formed under ocean: the canyons are where the currents ran. The mountains are younger, they have sharp crests and irregular edges, where their northern cousins are smoothed and rounded by eons. The Lagunas are scattered with boulders, deposited there not by giants but by oceans. There's nothing like this in NorCal.
It's the colors that make the biggest difference. Driving west on 210 at sunset: spectacular subtleties of shading, vibrant and immediate. There are no colors like that in NorCal.
This. The light, the colors, the geology. Immediate visceral improvement in mood, tone, outlook. Overdetermined by gratitude: that with luck and perseverance this change may yet become permanent.