The temperature drops as you go higher in elevation due to lower air pressure and a thinner atmosphere.

As you ascend in elevation, such as in the Rocky Mountains, temperatures tend to drop because of lower air pressure and a thinner atmosphere. At higher altitudes, the air becomes less dense, meaning it can hold less heat. This leads to a natural cooling effect as you move upwards. The decrease in air pressure at higher elevations reduces the ability of the air to retain warmth, causing cooler temperatures. This phenomenon is why mountainous regions, like the Rockies, experience significant temperature differences between lower and higher elevations, especially in the winter months.