Seems I heard Oakland is a rather "ethnic" area.............
The North Bay and South Bay also don't have many blacks. (Santa Clara County is about 2% black while the rest are split evenly among Asians, Hispanics, and white nonHispanics)
The reason most black resident of the Bay Area live in the East Bay, is supposedly because the migration happened in World War II and after, to work in businesses owned by Henry J. Kaiser.