UCSD does not list GPA/SAT scores for enrolled students by major. The UC Website will give you general admissions information: https://admission.universityofcalifornia.edu/campuses-majors/freshman-admit-data.html
UCI’s Undeclared data for 2019 enrollees:
Acceptance rate: 35.1%
Average UC GPA capped weighted: 3.93
SAT: 1269
Just remember to research the difficulty of changing majors from Undeclared if you plan to apply to any of the UC campuses.