It could be trending away from that, but historically https://www.ycombinator.com/ is the center of bay area startup culture, and then those startups grew into bay area tech culture as a whole.
Ycombinator comes from Stanford which centers around creating CEOs, creating most of the companies in the bay area. Most non-yc bay area companies still have Stanford at its roots. I don't have a direct data point, but almost every company I've interviewed for in the last 10 years and have worked with, their CEO or CTO or some other c-suite "club" is strongly tied to Stanford and from that directly or indirectly tied to YC.
Ycombinator comes from Stanford which centers around creating CEOs, creating most of the companies in the bay area. Most non-yc bay area companies still have Stanford at its roots. I don't have a direct data point, but almost every company I've interviewed for in the last 10 years and have worked with, their CEO or CTO or some other c-suite "club" is strongly tied to Stanford and from that directly or indirectly tied to YC.