The US is so full of amazing geological wonders that making the top twenty is a tough call
Everyone thinks of the grand canyon, the rockies, and yellowstone but few will have heard of Kasha katuwe tent rocks in New Mexico. Situated about 40 miles south of Santa Fe which is a great stop for original jewellery, artifacts, and of course the summer opera season. Known as a magnet for artists from the US and beyond, be warned – the credit card may be red hot! Anyway back to the natural wonders, the trails are very accessible but remember the summers are hot. Get out early if you are there in the summer.
I hope I've given you a reason to give tent rock a day or two of your time if you find yourself near Santa Fe, before or after giving your credit card a beating there or in nearby Taos!