So CSU: CSUs are, on average, easier to get into than UCs. The CSU system concentrates on teaching whereas the UC system concentrates on research. In terms of undergraduate attendance (getting a bachelor's degree), they are very similar. Some like the prestige of the UC system (although some CSU's are 'better' than some UCs). However one point that I will address: It's very difficult to transfer from UC to CSU and vice versa. The community colleges are meant to feed into the UC's and CSU's...but that's it. (I'm not saying it's impossible...it's just difficult, especially when trying to get class credit to transfer between the systems). So if your life long desire is to attend a UC (and you don't get in), you are better off starting at a community college or other less 'prestigious' UC.
In terms of qualifications, CSUs mainly look at grades and SAT scores (actually, I don't remember putting extra curriculars on my applications for the CSUs). There is a chart online...here. Make sure to take a look at the site. The UC system also has a site here. Also look at that one. It'll give an idea of what the application process looks like.
Also, don't forget that private schools exist! I regret not applying to private schools when I was a Senior in high school. Many of them offer more financial aid than the state schools- UCs and CSUs, and with the way the budget crisis is in California...it may be a better option.
See if you can go talk to a college counselor at school. They should have a specific college counselor, or at least your guidance counselor should have some knowledge about everything. (Let me know if they discourage you....nobody should discourage you at this stage.) They may even give you some ideas about this summer and how to "beef up" your college application. :-D