There are a bunch of these formations called hoodoos. A hoodoo is a rock formation that looks sort of like a chimney. The top of each hoodoo has a larger rock peak with a thin chimney underneath it , supporting it. This is because the top of each hoodoo is made of a harder, less easily eroded rock, while the sedimentary rock below is easier to wash away with time.
I highly recommend the hikes here. I'm really looking forward to going back so I can do the Rim Trail hikes.
