This varies greatly from campus to campus. The minimum GPA for the CSU system is 2.0, and the minimum GPA for the UC system is 2.4 for California residents and 2.8 for non-residents.
However, obtaining the minimum GPA does not necessarily mean that you will be able to transfer into the major and/or campus of your choice.
Several campuses are considered impacted, meaning the student application pool far exceeds the number of admission slots available. Therefore, the impacted universities/majors will accept only highly-qualified students into their campus and major.
In these cases, students who only meet the minimum GPA may not be selected for admission. The higher the GPA the more options you will have when considering transfer institutions.