I think that rockstar has only mentioned about los satos because thats gonna be the only city returning from gta sa.There can be some other cities such as san diego which is in southern california, but they couldn't introduce them in their real life names at the official announcement so rockstar did not give any info about them.And also if rockstar has introduced them in their fictional(in game) names,that would be like giving too much information at the official announcement.so they did not mention about them.
