If that's the case, O'Neill has free camping in the town park, (
http://www.rvparkreviews.com/regions/nebraska/oneill) as do a fair number of small towns on the Great Plains. If you head north from the Alibates Flint Quarry on 287(?) you can camp just outside of Picture Canyon which is west off 287 on a dirt road. It's one of the strangest places on the plains.
https://en.wikipedia.org/wiki/Picture_Canyon_%28Colorado%29
Just north of that is the Sand Creek Massacre Historic Site.
http://www.nps.gov/sand/index.htm
You could also hit Ft. Union National Monument which is east of Santa Fe
Fort Union National Monument (U.S. National Park Service)
And just east of the Capulin Volcano is the site of discovery of Folsom Points although I don't think there's any visitor information there.
https://en.wikipedia.org/wiki/Folsom_point