(Southern) California. End of story. Period.
You have to go with history. Where would bodybuilding be today if Pumping Iron had never existed (set in So. Cal), Muscle Beach, and the birthplace of Gold's or World's, not to mention the film industry that started exposing bodybuilders to the public at large and historic photos of bodybuilders at Muscle Rock shot on Malibu Canyon.
I can't believe this question was even asked, it's not even open to debate.