Hi guys,
I took this a little over eight years ago when I still lived in (served in?) Gunnison County. I have always assumed these pens were constructed by the South Park and later maintained by the Rio Grande after this part of the mainline became the Grande's Baldwin branch. Anyway, I am guessing these are the last remaining South Park stock pens.
Like so many other pretty places in Colorado, they are bordered by trophy homes these days.
Cheers,
Matt