if not maybe in the bay area (pleasanton, etc.)

There is nothing in Tracy as far as I can tell. Sacramento or Oakland might be the closest places.
Here is a list of studios in CA:

http://ballroomdancers.com/Directory/Studios/search_results.asp?PageNum=1&Region=1&Subregion=California&Dance_Style=All&Sex=&Status=&Relocate=

You can search by ZIP code: http://ballroomdancers.com/Directory/Studios/zip.asp
Also check http://www.accessdance.com/dance_lessons/state/CA/

I know there are lot of good studios in San Francisco. Metronome (SF) and Allegro (Emeryville) are definitely good places. DanceSpectrum at Campbell is good. But they are all too far away from Tracy as far as I remember. There is also something in Sacramento, but those I'm not familiar with.