Melissa and I went to Valley View Hot Springs during a western US vacation in 2002. I recommend it if you are in the San Luis Valley area of Colorado.
Their web site now says that they limit attendance to keep from overwhelming the facilities. If you plan to go make reservations per the instruction on this page:
Valley View is clothing optional, but the two times I’ve been there I don’t recall seeing any non-nude bathers. Our first visit was in 1977.
The photos on the web site look about the same as I remember it. rb
Me, photo by Melissa in 2002
One of Several Natural Setting Pools