Re: WHERE IS THE DEEPEST SINK HOLE IN THE U.S.?

I'm not sure where the deepest sink hole in the U.S. is, but it is probably 
in a area of limestone or dolomite (carbonate rocks).   Carbonate rocks 
dissolve when water percolates through fractures in them to form caverns.  
To assist you in locate various sinkholes...   and possibly some candidates 
for deepest in the U.S. and other places in the world, I found some 
internet links that you can explore:

WILD CAVE TOURS http://www.utexas.edu/depts/tnhc/.www/tss/wildtours.htm

The deepest cenote or sinkhole in the Maya World  http://www.mayanstar.com.mx/priadven.html
   
Deep Sinkhole in Turkey http://www.naturekey.com/articles/intros/professionalcaves.html

Harwood's Hole, Takaka NZ http://www-svr.eng.cam.ac.uk/~jccc/Egallery/cave/harwood3.html

Speleological Potential Of Turkey http://www.turkey.org/groupe/e

Good luck in exploring the internet in your quest for sink holes!