UCs use self-reported courses and grades on application, verified by transcripts if you matriculate.
For frosh admission to UCs, you must self-report all high school and college courses taken at all high schools and colleges when you apply. If you matriculate, you must send all high school and college transcripts from all high schools and colleges that you attended.
UCs recalculate GPA in a specific way, described at the following:
https://rogerhub.com/gpa-calculator-uc/
http://admission.universityofcalifornia.edu/freshman/requirements/gpa-requirement/index.html
http://admission.universityofcalifornia.edu/counselors/q-and-a/calculating-gpa/index.html
If you repeat courses, see http://admission.universityofcalifornia.edu/counselors/q-and-a/repeating/index.html .
Non-UC colleges may have different policies. But, in general, you must report and send transcripts for all high schools and colleges attended whenever such things are requested by a college that you apply to.