Apostrophe S->It was the epicenter of sanfrancisco arts movement
(It was the epicenter of sanfrancisco arts movement)
I heared the above sentence in a podcast, we can think that the text is like this:
It was the epicenter of sanfrancisco art's movement
Or
It was the epicenter of sanfrancisco arts' movement
But my questions is, why didnt he say "sanfrancisco('s) art's or arts'[this part is not important, my question is only about sanfrancisco's apostrophy S] movement?" and why did he chose the above question?