elevation for me, not so much impact on bg, climbing mountains however, can be a major impact on bg. if it’s way above your normal exercise then you may want to reduce basal insulin, and reduce meal shots while you are active. check with your endo if you are uncomfortable making insulin changes. Glucose is great for a fast lift, but sustained vigorous activity needs long acting carbs and fat and protein. cliff bars and granola are compact and can provide slow released carbs, but they tend to be salty and you’ll need a lot of water.
vigorous exercise in thin dry air can make you a little dehydrated. hypoxia can make you crazy. neither are fun. I hiked galena summit and “mount baldy” Id, one summer a long time ago and I was completely unprepared, nothing bad happened but I was just lucky. if 13er means above 13k feet, it’s something to be aware of. 12k feet is about the limit, under which a person in great health will not have trouble breathing. I hope you are going to be in a group and not by yourself.
your insulin will bubble a little bit because dissolved gasses will bubble and come out of solution at high elevation, but nothing bad should happen to it that an extra “air shot” can’t take care of.
have fun and take lots of pictures.