I do know that the UC system’s first priority is kids from California community colleges (over 90% of transfer admittances).
Breakdown of transfer students at USC:
49% - California community colleges
28% - colleges outside of California
8% - California private colleges/universities
8% - Cal State/University of Cal
7% - international
Privates in general tend to have more flexibility in their policies for transfers (they don’t have a mandate to educate mostly California students, for instance).