Please explain what you mean by optimal. Thanks.
It includes, but is not limited to, the following unique combination of factors:
1)The massive talent pool (mostly Asian) at the Engineering and CS departments of Stanford and Univ. Of California at Berkeley. These schools have a very high standard of post-graduate and undergraduate education in the Sciences and Engineering, which is vastly and demonstrably superior to anywhere else on the West Coast or surrounding states.
2) The historic and unparalleled presence of Venture Capital on Sand Hill Rd. in Palo Alto that has served as the incubator and nurturer of Silicon Valley businesses. See this link for more information: https://en.wikipedia.org/wiki/Sand_Hill_Road#Venture_capital_firms
3) Great weather and low crime rates in Cupertino, Sunnyvale, Mountain View, Los Gatos, Santa Clara, etc. make it easy to attract and retain the best talent.
4) The large Asian communities (Cupertino is majority Asian) complete the "virtuous cycle" of circumstances by keeping the talent firmly rooted in the Bay Area.