The higher the altitude, the lower the air pressure. While this is an excellent environment for training athletes, it is a difficult one for baking recipes. Baking depends on the specific interactions of several kinds of ingredients: flour, leavening, fats, liquid. To complicate things further, individual microclimates vary greatly in the mountains, so the adjustment that works for you may not work for your neighbor down (or up) the road.| King Arthur Baking