I would just keep in mind that the difference in housing cost between newcomers and those who have lived here for a long time can be very significant because of prop 13, rent control, and a local housing market that has inflated rapidly over the past 30 years.
I bet if you limited the range to households with college-age children, the median would be much higher. Those are peak earnings years for most people.
For San Mateo it's 87,633.
For Santa Clara it's 89,064.
http://en.wikipedia.org/wiki/California_locations_by_income