On clear nights the colder air accumulates, by drainage, on the valley bottoms, while the foothills and bench areas remain relatively warm. For this reason, the higher lands at the edges of the valleys are devoted ordinarily to the more valuable and delicate fruits, berries, and vegetables, while the hardier grains and vegetables are planted in the bottom lands.
Owing to the varied topography of the State, there are no orderly nor extensive zones of equal length of growing season between the last freeze in spring and the first in fall. There are, however, from 4 ½ to 5 months of freeze-free growing weather in the State’s principal agricultural areas. A difference of two weeks in the growing season is often noted in the same valley between the bottomlands and the adjacent farming lands at the foot of the mountains.
PRECIPITATION – Precipitation varies greatly, from an average of less than five inches annually over the Great Salt Lake Desert (west of Great Salt Lake), to more than 40 inches in some parts of the Wasatch Mountains. The average annual precipitation in the leading agricultural areas is between 10 to 15 inches, necessitating irrigation for the economic production of most crops. However, the mountains, where winter snows form the chief reservoirs of moisture, are conveniently adjacent to practically all farming areas, and there is usually sufficient water for most land under irrigation. The areas of the State below an elevation of 4,000 feet, all in the southern part, generally receive less than 10 inches of moisture annually.