One of the missions of the California public universities is to extend opportunity widely. Hence the aristocratic legacy preference is not used. Also, the large community college transfer pathway (target of 1/3 of graduates) is another way to extend opportunity widely, by offering another route for late bloomers and those who take non-traditional paths to college (note that private USC has a relatively high rate of community college transfers among private universities). In-state financial aid is better than in many other states, and uses FAFSA only (i.e. students with divorced parents still fighting their divorce are not locked out).
However, the UCs did lazily use check-box URM preference that resulted in the Proposition 209 backlash in the late 1990s. Current policies in UC holistic admissions do consider overcoming obstacles and adversity (commonly encountered by those from lower SES families) rather significantly, both to extend opportunity and probably under the idea that achievement despite obstacles is more meritous than achievement starting from advantage. Based on its own research, UCs do emphasize HS GPA more than test scores, which sometimes unpleasantly surprises those who are “test score heavy”.
But the recession funding squeeze resulting in fewer in-state (subsidized) seats and increased enrollment of international students paying list price resulted in another backlash a few years ago.
Not everything in frosh admissions is as transparent as it should be. For example, some divisions or majors can be significantly more selective than others on the same campus, but public information about frosh admissions does not show such differences. Transparency in this respect is actually better for transfer students (unlike the usual case where there is very little information available for transfer students to know reach/match/likely/safety), as shown at https://www.universityofcalifornia.edu/infocenter/transfers-major .
The UCs may be somewhat unusual even among public universities. Some other public flagships have policies more similar to private universities, like considering legacy, requiring both divorced parents’ financials for financial aid, having poor in-state financial aid, and/or not having good articulation agreements with in-state community colleges.