I think you should focus on South Dakota, Colorado, and New Mexico because it gives you a wide variety.
In South Dakota you could choose a base like rapid city or a cabin in Custer State Park. You can drive Pinnacles Highway, see the Badlands, Wind Cave, Jewel Cave, Minuteman Missile, and Mount Rushmore. There is a lot of wildlife in the area and natural attractions. The NPS sites will have guided tours and ranger talks you can attend.
Then go to Colorado. Denver is not terribly interesting for tourists, but you could check out the usual big city stuff. Head west through Glenwood Canyon on I-70 and spend a bit of time in Glenwood Springs at the largest natural hot springs pool. Black Canyon of the Gunnison is worth a visit. Head south into Telluride or Ouray. Go river rafting and hike the mountains. Spend some time at Mesa Verde.
Last will be New Mexico. Make Santa Fe your base. Enjoy the rich food tradition, explore the museums, go on a hike. There are several nice resorts in the Santa Fe area.
https://www.hotspringspool.com/
https://aubergeresorts.com/bishopslodge/itineraries/santa-fe-family-adventure/