The lowest point in the U.S. is Death Valley, the highest is Mt. Mckinley, so I'd guess... level ground? The question sucks, by the way.
Edit:
Wait, specify America. The continents, USA, Canada (as much as Ron wouldn't like this, Canada
is part of America.
![Wink ;)](http://forum.x86labs.org/Smileys/default/wink.gif)
) etc etc