Arches National Park contains the greatest density of natural arches in the world. As you can see from the pictures though, it is not all arches. The 3rd and 4th pictures show Delicate Arch which is probably the most famous arch at the park.
We learned an interesting fact on our travels. The Colorado Plateau (everything we went to is on this) has the cleanest air in America. The visibility is about 145 miles due to the lack of pollution. The mountains in the second picture are over 80 miles away. One sign gave the contrast of the visibility in the Ohio Valley as 9 miles. This area does not have any large cities so that helps. Hopefully it will stay that way.