Now let me add some other obscure NM's and NP's:
Effigy Mounds in Iowa. For those of us used to the ruins in the west, Effigy Mounds are much more subtle.
Dinosaur NM is well know for its, well, dinosaur fossils. But there are other, far more obscure NMs highlighting fossils: Florissant Fossil Beds, Fossil Butte, Agate Fossil Beds, John Day Fossil Beds, Hagerman Fossil Beds, Prehistoric Trackways, Waco Mammoth. Many of these fossils may be insects, fish, and mammals instead of dinosaurs. Even though I'm a geologist, there's a good many of these I have yet to visit.
El Morro NM. If you're travelling I-40 through western NM, if you have some extra time it is certainly worth detouring on NM 53 just to stop at El Morro. We went there a few years ago and I was very impressed with all there is to see there considering how small it is (less than 1/2 square mile!). We may head back there again next summer.
Lava Beds NM in northern California. One can explore the lava tubes without guides. Really interesting way to spend a whole day. There's also a historic side where the Modoc wars were fought and the caves were used strategically. The CG is also quite nice. I love waking to the smell of sagebrush in the morning. Quite different than the usual smell of pine or spruce we're used to. There are also lava tubes at El Malpais in NM and at Craters of the Moon but access is often blocked due to bat habiation. Lava River Cave at Newberry Crater NM is usually open and is 1 1/2 mile long.
The further east one travels, the more historic military parks there are. One can spend many days once one is in Virginia and surrounding areas. But further afield, places like Pea Ridge in Arkansas are obscure but important nonetheless.
Many might not realize that many NM's aren't shown on the NPS website as they are on BLM or NFS lands.
