Just to add to the forum, Sierra also combined the Monterey TRACON into their facility, which is located at the Mather AFB. In addition, portions of Oakland Center's airspace are going to be given to Sierra to control the areas surrounding Napa, Santa Rosa, etc., but Travis RAPCON is going to stay. There are even talks of forming a Central California TRACON, basically combining Fresno, Bakersfield, Santa Barbara, etc. TRACONS into one facility.
The way the combined TRACONS work is like this: The TRACON is split up into different areas, each area handling a different section of airspace (e.g. In Sierra, Area A controls mostly Monterey airspace, as well as SJC final and SJC departure, Area B handles mostly SFO arrivals, Area C is mostly the Stockton Area, as well as Oakland final, Area D is Oakland and SFO departures, and will be given the sections of Oakland Center airspace, Area E is Sacramento airspace, and Area F is the ETG or "training lab"). Each area is then broken down into numerous sectors, with one controller at each sector (this is how it works in the Centers as well). In a nutshell, each sector makes up an area, and each area makes up the total airspace of the TRACON. Hope this helps!