I think SJ vs SF distinction is not very material to this thread. The OG Silicon Valley of HP and Fairchild Semiconductor fame liked to build corporate campuses around Stanford on cheap (at the time) land. 90's Yahoo, Doubleclick, Google followed suit. In the late 2000's, a new wave of startups like Twitter figured they don't have to stick to corporate code and just move up to a more fun city up north, combined with some tax breaks from SF specifically. How does it matter? It's the same area (i drive up and down every day) with much the same problems.