Arizona
Of course, the Grand Canyon, which really is one of Planet Earth's most conspicuous features.
That's looking across to Bright Angel, I think. And don't miss the ancient ruins on the south rim. And don't take chances on the rim. There's a marvelous book: Over the Edge: Death in the Grand Canyon, which indicates that, yes, that drop is real.
Another site that's suprisingly hard to find is the Meteor Crater near Winslow AZ. The trick is that it's privately owned, so that you can't find it on certain maps, and certainly it's not a national park. But it is truly remarkable, it's beautifully maintained, with visitor center, and people who visit this page should just go and stand in awe.
Down at the bottom---that's a rather substantial fenced area around one of the investigatory pits, from the days when they thought the meteor had bored straight down. It's hard to describe the scale of this place. But it's large. Go see it.