Boundary of fortress (referring to South Bay) changes slightly now and then, at this moment, should be:
Cupertino
Los Altos
Los Altos Hills
Mountain View
Palo Alto
Saratoga
West San Jose (95129, 95130)
West Sunnyvale (94087)
Los Gatos used to be part of the fortress, recent years lose favor, prices there appreciate by less than 50% from bottom, whereas those in Fortress appreciates nearly 100%.