I got to go to Yellowstone National Park for the first time a few days ago. (I know, I live in Montana and I'd never been to Yellowstone. I'm as confused as you are.) These two sketches happened there.
This is a sketch from Artists Point of Lower Falls. I was kind of disappointed in this one when I first drew it, but looking at it now I actually kind of like it.
And here is a neat piece of geology that I saw.