UC Riverside is less selective than many of the University of California schools. In 2010, over 80% of applicants were accepted. In the scattergram above, the green and blue dots represent accepted students. The majority of students who got into UCR had GPAs of 3.0 or higher, SAT scores (CR+M+W) of 1400 or higher, and ACT scores of 19 or higher. Note that there is some red hidden behind the blue and green, so some students with grades and test scores on target for UC Riverside still get rejected. The reasons for a rejection could come down to many factors -- a high school curriculum that wasn't challenging, lack of extracurrucular involvement, or a poorly crafted essay.
UC Riverside has holistic admissions, so the admissions officers are evaluating students based on more than numerical data. Students who show some kind of special talent or have a compelling story to tell will often get a close look even if grades and test scores are a little below the ideal. You can improve your chances of admission by taking challenging courses, participating in meaningful extracurricular activities, and writing strong essays.
To learn more about UC Riverside, high school GPAs, SAT scores and ACT scores, these articles can help: