chimneys, all natural

Somewhere I haven't been before; Natural Chimney park. The drive is absolutely beautiful and definitely worth it. There is also a great trail which takes you to the top of the chimneys. Of course you aren't supposed to climb on them, but not much is stopping you either. The park is a little run down; but the chimneys are still beautiful. I wonder what it would be like to be hiking along in the wilderness and just come across something like that?

The only other thing I can't figure out; why isn't it "chimnies" when it's plural?