http://www.outdoorresearch.com...e/advanced_bivy.html

I am thinking of using it on an extened scouting/huting trip in Colorado early October next year.
What rating of sleeping bag would I need to be warm at 10,000+feet?

It's a good bivy but as with all bivy's a tarp overhead in case os heavy rain will make a lot of sense.

I have found all of OR's stuff to be top notch.

However if you are hunting alone, or with a buddy, I would prefer a 4 season tent, big enough to at least cook a pot of soup in, just in case you get weathered in for a couple of days or so.

Also I consider a sleeping bag to be a survival and "battery" recharging system....

So above 10,000 feet I would want a 10 degree below zero bag, at least.

My "Mountain/winter" bag is a 30 below zero down bag.

I just came back from a solo elk hunt in the Oregon Coastal Mountain Range. Most of the roads were closed to vehicular traffic so I packed light but packed for comfort and hiked the rest of the way (as the crow flies, about 2 1/2 miles from my vehicle, but many more actual walking miles). There was snow in the higher elevation but I scouted and camped just below snowline.

An hour and a half before dark I found a good camping spot, protected from wind and from possible falling trees. First put up an 8x10 tarp between two small trees then pitched a one person 3-season tent beneath it (Coleman Exponent, I think). I'm not into brand names and endorsing any company in particular so I don't pay attention to who makes it - if it works for me that all that matters. My sleeping bag was a -30 deg F rated bag (Browning) with a closed-cell ensolite 1/4-inch pad. The sleeping bag was enclosed in a generic gore-tex bivy that an ex-wife sewed for me 25 years ago.

During one of the nights a storm blew in, bring high winds, much rain, and hail. My campfire was put out at the first soaking. For most of the nights I stayed hunkered in my small tent.

What all this comes down to is that safety, warmth, and comfort are my main concerns when I go solo. I was safe from the wind and possible falling trees. I was warm (slept in my sleeping bag with only my skivvies and a thermal shirt). I was not all the way comfortable since I had little room to move around during the storm. If I could carry more weight I would rather have taken a 2- or 3-person tent.

Sorry for the rambling. Have a good hunt. Keep safe, warm, and comfortable.

I'm sure that's a nice bivvy bag. OR stuff usually is. However I would recommend a tent. Even a if only a lightweight 3-season tent.

In Colorado, there USUALLY isn't a lot of heavy snow at 10,000 ft. in early October. But you can get freezing fog and light snow. Spending several days in a bivvy bag would be agony if the weather turned bad (especially in freezing fog)!