An hour away from Las Cruces on the way back to Wisconsin is White Sands National Monument. Known for its very rare almost pure white sand dunes, it seems almost out of place compared to the other local landscape. Interesting fact: at 275 square miles, it is the largest gypsum dune field in the world.
When I visited here in 2011 with my family we spent time sledding down the hills on saucers just like sledding snow in winter. No sledding for me this time but many other visitors were. I hiked about 1/2 mile in barefoot and surveyed the landscape. Today was almost windless and the silence was peaceful. Most of the trails were closed due to being off-season so no longer walks without a backcountry permit (or so I was told).
Heading to Amarillo, TX for the night to rest for the next section of driving. Likely passing through Kansas City, MO next.
EDIT 2017-12-21: Added a new page for tracking visits to all National Monuments – see the list here!