Valles Caldera is a National Preserve — and the most recent (as of this writing). It includes a lovely 13 mile bowl circled by higher lands, courtesy of an eruption a very long time ago. It’s dormant, but there are signs of activity now and then.
I visited briefly while in the area. Alas, most of my visit was during a drenching rainstorm (seriously heavy rain, and this from someone who’s lived through some torrential downpours). There was a break long enough to stop by the visitors center and to walk around a bit.
Here’s a photo of part of the caldera, complete with the resurgent dome.
The image also captures the mistiness of the day, and the re-impending storm. Someday I’d like to go back during better weather to hike around!