If I am interested in undergraduate research/internships and strong programs in ecology and evolutionary biology and/or environmental science (I’m interested in a career in conservation!) which UC should I go to?
I would put UCD or UCSB as your top picks for Environmental Science and Ecology/Evolutionary Biology since both are top rated in these fields.
Older son is a current 3rd year ESM major at UCD and constantly gets emails for jobs/internships/volunteer opportunities from his Department. He is currently interviewing for 2 paid internships and has unpaid internship as a backup for this summer. He is also doing a course credit internship on campus at the UCD arboretum which you can apply to several times during your tenure at UCD.
I suggest you check out the career center website to see job/internship listings to give you an idea of what is available. At UCD most of the research positions are posted by the professors in the student email or at the career center but not on the career website. Also part of the major requirements for ES majors is Capstone, where you are paired with a professor to do research.
Oh, wow! That sounds fantastic! Thank you so much for your input. I’m really leaning towards UCD now 
@annielee0134: If your focus is more on Marine Env. Sci, then UCSB/UCSD might give you more opportunities although UCD does have a joint program with Bodega Bay Marine Research Insititute. All schools are good choices but make sure you visit the campuses since all three are different in campus social life and overall feel.