Here are just two threads from a quick search. Every year people successfully transfer in from a CSU. I also think the admit rate is about 7-10%, depending on uc campus. The CRUCIAL KEY is getting major courses done, most of gen ed, and have a strong gpa.
So if you’re hoping to transfer from a CSU, do not be disheartened at all.
http://talk.collegeconfidential.com/uc-transfers/1469916-advice-on-csu-to-uc-transfer-strategy.html
http://talk.collegeconfidential.com/uc-transfers/1581178-csu-to-uc-transfer.html