The original trailer for San Andreas only showed Los Santos, so it's possible that this game will feature San Fierro and Los Venturas too but they're holding them back for future trailers. IGN are saying
that Rockstar confirmed the game is in San Andreas, but I wouldn't be too surprised if there were mixed wires there.
Either way, the game looks amazing, particularly that mountain range. Here's hoping that we're able to climb that and it's not just scenery, like the cliffs that surrounded the world in RDR.
Speaking of RDR, there was a dog on the beach in the trailer, so hopefully they'll be taking some more animal models and AI from RDR and putting them into the game. Gunning down bears with an attack helicopter is the revenge I'm looking for after all the times they snuck up on me up in Tall Trees.