Found on www.funtrivia.com--
The name comes from a type of hole made by a stone in a river bed. The stone is trapped in a spinning current and wears away the rock beneath to form a hole shaped like a pot. As this enlarges, the pebble wears away but other stones drop in. The end result is a deep hole which can even extend down to other holes lower down in limestone country. The name pothole is applied to other holes as well, most of which are really caves (except for the ones in the road!).
It's amazing what you can find with Google!
at 9:15 PM on Apr. 7, 2009