Expert: George Ardies - 6/13/2005

Question
When driving through Arizona and New Mexico, you can see large mountains with perfectly flat tops which are sporadically scattered throughout the landscape (I think they are called mesas).  I was wondering what causes this?  It can't be the same tectonic thrust that formed the rockies and the like, is it?  Wouldn't this thrust make it jagged and pointed at the peak.  It's almost as if the tops of these flat mountains used to be ground level until something eroded the ground away from around it leaving behind these large mountains.  Please, someone, explain what formed these mesas (as i think they are called)!

Answer
You are right, they are called mesas. These form by the process of erosion. At one time, the tops of the mesas were on large falt surface, with no valleys whatsoever. Then, as rivers continuously eroded the plateau, valleys were created. These valleys continued to erode. The remnant mesas are simply the areas of the initial plain that have not been eroded. You last suggestion is exactly right.

Cheers, and let me know if you have any other questions or need further explanation.
George