Because it is such a young school that is still building its reputation, UC Merced is the least selective of the University of California schools. In 2010, about 90% of applicants were accepted. In the graph above, the green and blue dots represent accepted students. The majority of students who got into UC Merced had GPAs of 3.0 or higher, SAT scores (CR+M+W) of 1400 or higher, and ACT scores of 18 or higher. Keep in mind that there are a few red dots hidden behind the blue and green, so some students with grades and test scores on target for UC Merced 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 Merced, like all the UC schools, has holistic admissions, so the admissions officers are evaluating students based on more than numerical data. You can improve your chances of admission by taking challenging courses, participating in meaningful extracurricular activities, and writing winning essays.
To learn more about UC Merced, high school GPAs, SAT scores and ACT scores, these articles can help: