I asked, "did the slums exist before the highways and freeways that divide them from the wealthy whites?" The best I've come up with is "Sort of."
Apparently, in the 50's and 60s, city officials throughout the US thought of urban freeways as "a good opportunity to get rid of the local 'niggertown.'"[1] But that attempt at clearing the local slums ended up further disrupting and distressing them, deepening the problem.
[1] Google Books: Downtown, Inc: How America Rebuilds Cities https://goo.gl/mdgYXE
That was before the Cypress freeway tore West Oakland in two, or 980 sheared it away from downtown Oakland, or the trans-bay BART tracks, or before the USPS distribution center was built. The last, for those not familiar, is a 6 story concrete windowless menace that I've started calling the "Ministry of Truth."
Slums exist because the privileged spent a century paving over neighborhoods filled with people that they wished would just stop existing.
You mean Oakland and Vallejo? Yeah that stuff has been there before the start of SV. See MC Hammer and Too Short for references to past gang activity in Oakland.
But, yeah, in general Silicon Valley is pretty much a sprawl. There are some nice small downtowns scattered around but you mostly need a car to get from place to place and most big companies are on their own disconnected campuses and others are scattered around industrial parks.