Most areas have a classic nature writer. For example Colorado Plateau:Edward Abbey, Sierras: John Muir, or Alaska: Jack London/Robert Service.
Colorado doesn't really have one though. A few options I've come across are Anne Zmigger (Beyond the Aspen Grove) or Enos Mills (he seems a little dry though).
Another option would be Arthur H. Carhartt although I haven't been able to get ahold of any of his books and am confined to the short excerpt on the flat tops page (if anyone knows what book that is from please tell me)
Also Albert Ellingwoods account of the ascent of lizard head is good climbing literature though it isn't really nature writing.
Anyone?