Transfer admission at the UCs is primarily focused on students from California Community colleges. Well over 90% of transfers come from a CCC.
From Cal’s website:
“The Haas Undergraduate Program rarely admits transfer students from 4-year institutions. Transfer admissions priority is given to students who are US citizens, California residents, and are transferring from a California community college. This is according to California’s Master Plan for Higher Education, the University of California Office of the President and the UC Berkeley faculty. Transfer applicants from 4-year colleges should follow the transfer admission requirements and application procedures outlined on our website.”
https://haas.berkeley.edu/Undergrad/admissionsfaq.html#4yearcolleges