Deserts form in general from the high atmospheric pressure and cold air that comes from the upper altitudes nearby. The heat from the sun causes high ground temperatures with low humidity.
The fact that glaciers have been retreating during the past 8,000 to 10,000 years is a major contributing factor to the formation of deserts. The land that previously had been covered with a great deal of water for thousands of years has since dried out. Leaving the area arid and dry. Deserts are formed in several ways. One type is formed by a "rain shadow," which occurs to land is between two mountain ranges. The precipitation falls on the other side of the mountains, leaving the land in-between dry. Deserts have been around for approximately 125 million years, according to evidence that has been found.