This is Devil's Tower! It's in Wyoming. This was our last stop for the day. We spent about an hour and a half here.
It is all rock, but looks like a huge tree stump.
They have prayer cloths hanging in the trees that you are not allowed to disturb. They are left by the indigenous people in the area.
(To be honest, when I was walking on the trail by myself it was kinda creepy)
I found it so interesting because they made the movie "Close encounters of the third kind" here.