Sounds like my adventure last year at Crested Butte CO.
My sister has a "home" above the ski area. I mountain bike alot in the winter and ride the roadie in the summer so I am in decent shape.
Get there, wait 2 days to get aclimated to the 10,000 feet and go out and hit it.
On a long grinding climb, just about to die, get pasted by a 12 year old girl and she asked me if I am ok,,,,
Sums up the trip.
Lots of great single track though and beautiful scenery.