My take on the this is that tremendous amount of access politics in the Bay Area seem to revolve around where you went to school and what your pedigree is, and that since those are very highly correlated with the class you were born into, it ends up being emergently classist.
Poor people mostly don't go to the schools that matriculate the players who participate in the traditional valley power scene. I don't buy that this scene is any more racist than the rest of the US, and probably would argue that it is less so. But in terms of class bias, I think considerably greater. And the low incidence of black and latino folks can be attributed significantly to their statistically-lower class distribution.
As an anecdotal data point, I haven't met a lot of white people from lower-class backgrounds who are players in the Bay Area technology scene. Actually haven't met a lot of technology workers that are.
This is in contrast to the environment when I worked in finance in NYC and London. I found that scene to be transparently racist and sexist, but there are very many powerful white dudes who started off poor and lower-class.