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I'm sure there will be people around. It won't be as crowded as during the semester, but there should be more than enough girls. On the other hand, there are far more tourists (usually Europeans, but not only) in the Market Street area, and around the city in general, which can be fun to meet, but less exciting for you since you're coming from there. Also, don't hesitate to catch BART across the bay to visit Berkeley. The weather is a little warmer there, and there are still a decent number of students around for summer.