Look on the side of a cake mix box and you might find special directions for baking the cake at high altitudes.

Why Do Bakers Have To Adjust Their Cake Ingredients When They Live At Higher Elevations?

Because atmospheric pressure decreases the higher up you go, and atmospheric pressure has everything to do with effective baking.

The level of atmospheric pressure measures how many air molecules exist within a given space.  As altitude increases, the number of air molecules per square inch decreases.

Baking In The Rocky Mountains

To picture the impact this bit of physics has on cooking, think of air as a weight that rests on top of a pan of water about to boil.  If that pan of water is in the Rocky Mountains, it would boil at a lower temperature than at sea level because the weight of air on top of it is less, and therefore the water molecules have a bit more freedom to move from liquid to gas.

In fact, every thousand feet in altitude, the boiling point of water drops two degrees Fahrenheit.  And since the boiling point of water is lower the higher up you go, the evaporation point of water is also lower.

Liquid Evaporation

How fast liquid evaporates makes a big difference in how well a cake turns out.  The liquid that turns the cake mix into batter will evaporate out of the cake earlier in the baking process at a higher altitude than at a lower one.

Unless you follow the special directions on the side of the cake mix box, by decreasing the amount of cake mix or increasing the amount of liquid, the cake you bake in the Rocky Mountains will probably end up very dry and perhaps even burnt.