Place Annual Precipitation Annual Evaporation Ratio (In Inches) (In Inches) El Paso, Texas 9.23 80 8.7 Fort Wingate, New Mexico 14.00 80 5.7 Fort Yuma, Arizona 2.84 100 35.2 Tucson, AZ 11.74 90 7.7 Mohave, CA 4.97 95 19.1 Hawthorne, Nevada 4.50 80 17.5 Winnemucca, Nevada 9.51 80 9.6 St. George, Utah 6.46 90 13.9 Fort Duchesne, Utah 6.49 75 11.6 Pineville, Oregon 9.01 70 7.8 Lost River, Idaho 8.47 70 8.3 Laramie, Wyoming 9.81 70 7.1 Torres, Mexico 16.97 100 6.0 To understand the methods employed for checking evaporation from the soil, it is necessary to review briefly the conditions that determine the evaporation of water into the air, and the manner in which water moves in the soil. The formation of water vapor Whenever water is left freely exposed to the air, it evaporates; that is, it passes into the gaseous state and mixes with the gases of the air. Even snow and ice give off water vapor, though in very small quantities. The quantity of water vapor which can enter a given volume of air is definitely limited. For instance, at the temperature of freezing water 2.126 grains of water vapor can enter one cubic foot of air, but no more. When air contains all the water possible, it is said to be saturated, and evaporation then ceases. The practical effect of this is the well-known experience that on the seashore, where the air is often very nearly fully saturated with water vapor, the drying of clothes goes on very slowly, whereas in the interior, like the dry-farming territory, away from the ocean, where the air is far from being saturated, drying goes on very rapidly.