And illegals' wages are at the bottom?
I believe SF also has a lot of legal immigrants who came to America at an age when it was hard for them to learn English (or they were surrounded by people speaking their language so could get by with it)...that would tend to exclude them from well-paid jobs. Look at how much lower the percentage of Asians getting 4-year degrees is than of whites--38% vs 63%. When young Asian-Americans are famous for studying harder than any other group, that discrepancy must be disproportionately among older people.