My first thought was that it may be an ant hill, but the photographer says it was a rock. I would still think it to be a petrified something?
waht
Jan9-08, 08:11 PM
This area was certainly underwater. I suppose a vortex formed which grinded a funnel into the rock formation over eons. The river is pretty stagnant, but there were times when a rush of water from melted glacial dams flooded the area with intense surges of currents.
NoTime
Jan9-08, 08:58 PM
Kinda looks like limestone.
Perhaps a spring or possibly a steam vent.
hypatia
Jan9-08, 10:33 PM
Looks like a place where a mineral spring once flurished. I have even been to a city named Mineral Springs in ND, so its fairly common for that area.
waht
Jan10-08, 12:00 AM
A mineral spring or vent makes more sense.
matthyaouw
Jan11-08, 07:03 AM
Mineral precipitate around a spring was my first thought as well. Would be helpful to see a bit of it up close and know something about the area it was found in to say for sure.