[Tijeras_Slim]

I'd add the Valles Caldera in New Mexico to that list. 11 miles by 11 miles that was privately owned and not developed, public got access in about 2005, and it's still closely controlled.

[Paladin2]

https://www.nps.gov/vall/index.htm

[Soul of the South]

Thanks for the suggestion. I’ll add to my to visit list.