Significantly more challenging to install solar onto already developed land.

California is also largely desert itself. Such farming is only possible through unsustainable levels of irrigation.

SoCal (not just SD) really need to get to work on industrial-scale desal, storage, and aqueduct infrastructure to potentially augment ordinarily and sustain the Southwest in times of drought. It's going to happen, they won't be prepared, and it's going to be really, really bad. (This is partially why I moved to around the 100th meridian west.)