This is a 4x4 trail within the Great Sand Dunes National Park. (marked) Free dispersed camping sites located along this trail.
Wow what a place, there are some stunning campsites up and down this pass, I stayed closed to the dunes and absolutely loved it. Nothing but a fire pit and a bear box which was incredibly helpful! Road is tough so don’t try it unless you have something big and/or powerful. I did it in a ram 1500 4x4 (5.7 v8) and had no problems.
I drove into the National Park late, and all of the campgrounds were full. A helpful park employee pointed me & my Jeep to Medano Pass. Medano pass is just past the NTL Park campground. It is a fairly long 4x4 trail, first section is sand. I aired down to ~12 psi. Had to pull out a stuck 4 runner who didn't air down or engage 4wd... My Jeep is a stock JKU on 32" Duratracs. Also a few (shallow) creek crossings. Maybe 1 foot deep. Super fun trail!!
Campsites are clean, bear boxes included. Definitely use the bear boxes, I saw a lot of bear tracks & trees that were used as scratching posts. The sites are also marked, so make sure to only camp in designated spaces. Keep driving down Medano until you start to see marked spaces.