the Great Unconformity

This post about the Great Unconformity is really well written:

http://written-in-stone-seen-through-my-lens.blogspot.com/2012/01/great-unconformity-of-grand-canyon-part.html

Blacktail Canyon is a very special spot on Earth. You can put your hand on a 1.2 Ga gap in time, ages and ages of rocks that are just... gone.