The San Francisco Bay Area? That's where I live. Mono-cultural it is not. Maybe you meant another Bay Area (there are as many of those as there are bays.)
I meant relatively speaking. In London, there are many streets that all could be in different countries, right down to the script used for the shop signs. I never once saw someone in a niqab or a djellaba, for example.
Well, I'm honestly bewildered. Where did you go in San Francisco? You didn't hear Spanish, Mandarin, or Cantonese anywhere? How? I hear these languages and more, constantly, every day.