Originally Posted By OregonMouse
For use at high altitude in the Rockies, do take that down jacket! Even in midsummer, you can get snow and temps down to 15* or even 10* F, probably similar to what you get in NC in winter! In Yellowstone (lower altitude) you may be fine with just a lightweight fleece insulation layer.

I've been fortunate so far to not have temps that low where I needed to use my bag. I guess I should say my sleep clothes are Capilene 3 bottoms and Cap 4 top and my bag is 20F (likely 25 in reality). This is for Wind River Range and Maroon Bells (9000' and higher). I wouldn't say I'm an overly warm person. Though I will add that my first trip I did take down jacket and puffy pants. I decided after that it wasn't needed (for me) for July & Aug. I'd def take it Oct-May though if I happen to go then and likely June or Sep as well.