The Devil’s Corkscrews I've excavated groundhog burrows that spiraled down as deep as five or six feet, but the spiral-burrowing land beavers named the Palaeocastor take the cake. The web site of the National Parks and Conservation Association tell the remarkable story of "the beaver that did not give a dam" -- the remnant of a kind of ancient Groundhog or Nutria from 22 million years ago.