Coolidge and Laveen soils have less than 15 percent coarse fragments in the control section. Also, Laveen soils are of medium texture. Rillito soils are on fan terraces or stream terraces and have slopes of 0 to 40 percent. These soils formed in alluvium from mixed sources. Elevations range from 400 to 2200 feet.
Rillito soils are in a hot, arid and continental climate.
The mean annual precipitation ranges from 3 to 10 inches. Precipitation falls as summer thunderstorms and gentle winter rains. The frost-free period is about 240 to 350 days. These are the competing Coolidge and Laveen soils, and the Antho , Mohall , Pinamt , Tremant and Valencia soils. Antho soils do not have a calcic horizon and have less than 15 percent coarse fragments.