I'll never understand why so many poster are so enamored with Webb. Certainly if you have a Mt Runmore for HS runners, he's on it - along with Ryun, Lindgren. 4th is difficult.
However, other than 2-3 months in 2007, he is nowhere near America's best.
In any event, my Mt Runmore is Ryun, Shorter, Pre (he was Webb before Webb and actually backed up the hype with much better results). 4th is tough. Eventually, it might be Rupp or Jager. Right now:
Bill Rogers?
Meb?
Steve Scott?
Wottle?
Lagat - hard to consider him an American (sorry).
Khannouchi - ditto.
If you don't count Lagat or Khannouchi , then as much as it pisses many off, It's probably Rupp right now. Olympic Silver and Bronze. American record at 10k, and one of the few US born (or raised) Americans to win a major marathon in the past 20 years.