tranfer from UC/CSU to another UC

I was wondering how hard and/or how much harder it is to transfer from a UC like say riverside or Cal state like say san diego to a mid tier UC such as Irvine or santa barba compared to a community college

It depends on your GPA.

of course, but obviously getting a 3.5 at uc riverside is harder tan getting a 3.5 at CC, so what GPA would i need to transfer from riverside to another UC