Celebrating America's birthday in the Bay Area?   Grab a sweater, pray that the fog doesn't roll in, and stake out a choice patch of grass in the Presidio or Golden Gate Park, or jostle with tourists on a rooftop with a prime view of the evening fireworks shows. Then after that, you can find yourself a late-night party where you can mingle, dance, and drink with the SF locals and tourists, whose wide-ranging diversity and eclectic party styles are truly what makes America great.