Why a mummy bag you may ask?  If you have never used one of these bags, you may be skeptical at first by its design.  Why so narrow?  Why a hood?  Both of these features will help trap the warm air you create inside the bag and fill the space between you and the bag.  This results in a much warmer sleep and minimizes cold spots in your bag.    You will come to appreciate this on  those nights when the temperature dips below freezing.  

Mummy bags with down or synthetic fill are both appropriate for the climate you will be living in Yosemite.  Just remember, a down bag will not insulate when wet, a synthetic one will.  Down is usually lighter in weight, more compressible and has a higher price tag than synthetic. You will also need to take extra precaution from tearing a down bag, it only takes a small hole before the feathers begin to fall out.  

Synthetic fill bags will get the job done.  Heavier in weight and larger in compression size are the trade offs to  a lower price tag and more durable material.  These make great first-time mummy bag owners!