About the Golf course and SF: You clearly see the LS skyline near the golf course, so this one is in LS.
I was checking the old GTA SA trailers, and in the first one (correct me if I'm wrong) they were only showing pieces of Los Santos. Even the airplane scene on that trailer is situated in Los Santos. Then with the 2nd trailer they showed the Golden gate bridge, Las venturas, etc...
In fact this first GTA5 trailer has given away much more information than the first GTA SA trailer did, namely countryside, this mountain, etc...
Then I see most people think that mountain is Mt. Chilliad? Perfect, because that would mean San Fierro should be in this game. Mt. Chilliad being based on Mt. Diablo in the SF bay area. Why would they use a natural landmark of SF area and not have SF?
Another clue is the sheer size of the game Red Dead Redemption. When Rockstar is saying they are working on one of their biggest games with GTA5, would they compare it to GTA SA, or another game they have produced? GTA5 *could* become 3 or 4x the size of GTA SA, if with biggest they are referring to the size of the map.
I can't wait for the next trailer, or teaser, with more clues