I don't know anything about UCSD in particular, but in general the portfolio is by far the most important aspect of your application. Most schools will look only at the portfolios in the first round of review, and eliminate a whole bunch of people based on portfolio alone. Then they might look at the written statements, and eliminate another batch. Once they've narrowed the pool down to a group with strong portfolios and strong statements, they'll start looking at references and maybe transcripts.
Basically, I wouldn't worry at all about a 3.0 gpa, since the transcript is at the bottom of the priority list and 3.0 isn't notably bad. Focus on your portfolio and your statement. And then again on your portfolio.