“My boyfriend and I were recently traveling through Eastern Montana in August 2006 and noticed the occasional lone pyramidal-looking mountain. These look like they could be ancient pyramids from the times of antiquity, as discussed by Steve Quayle and other popular Coast guests.
They obviously show signs of wear, but that would be expected of structures that old. (If you add some reddish tint to the photos, they actually look they could be Martian landscape!)
Source: Coast to Coast