Originally posted by gerzald:

mayhaps stumps underneath?

It is rocky soil underneath. If you can look around and see big rocks on top of the ground, you can bet there are some rocks under it. A rock does no smooth out from a hoe. When I use the hoe on a large hum and it doesn;t go down I use the pick 1 or 2 times to flatten it and smooth again with hoe.

YES, it is time-consuming but it works, When I get a low spot/ground sink that won't rise with hoe, I add some rocks and try to smooth over.

BTW, this is a very good idea when in the swamp as you never know if you are walking into a puddle or a deep pool. Raise the ground around the portal and make trails.