SF Bay Area is not really representative of California as a whole. Most people outside of the dense cores have a place for a small garden. State is large and diverse. Los Angeles is a lot less dense and most people have at least a balcony on which you can grow stuff in pots. Won’t sustain you as the only source, but will provide greens and some variety. Yards are pretty common and usually green. Water shortages have led to some converting to hardscape, but that can be reversed.

Prop 13 is an issue, but the level of development opposition in Bay Area is another matter all together compared to the rest of the state. Where little you can build developers end up cramming every last inch with profit-producing structures. Couple with crappy commuting infrastructure and you have what we are living.