One of the main roads from Mexico into this part of the US is route 54, via El Paso and Las Cruces, so there was a Customs station checking every vehicle passing through.
"American citizen?"
"Yup!"
"Thank you, have a nice day."
That was right after White Sands National Monument. (I'm not sure what the difference is between all the classifications - Park, Monument, Forest, Refuge.) Only a few miles of the Dunes Drive are open, and there's not much to see, just a lot of white sand.
That whole area is part of the huge White Sands Missile Range. Every so often along the road you can see some kind of military installation. There's also an Air Force base nearby.
I camped in Oliver Lee State Park, outside of Alamogordo. My first stop today is the Space Museum in Alamogordo.