[pmoriarty]

That's a common misapprehension among people that don't live there.

For anyone in the Bay Area, Silicon Valley is some ways south of San Francisco.

That said, a lot of startups are in SF, because Silicon Valley is too expensive (though SF itself is catching up because of the second dot com boom/bubble), so it's not surprising that outsiders lump the two of them together as a hub of Bay Area tech activity (which they are.. but they're just two distinct geographical areas).