Tough analysis to do: the best club teams tend to have much wider geographic distribution but the best HS teams have a much wider age-based distribution [i.e., freshmen to seniors]. Given maturation averages, the latter is probably typically more a factor for girls than boys.
Anecdotally, it's hard to disagree with Soccerdog6 and Hurst66 on this one. Taking the CSC's U17G team which is currently leading the U17G challenge league, you have players from high schools in Chapin, Dutch Fork, Irmo, Lexington, and probably elsewhere.
