The southern Great Plains and the Southwest often are called "Big Country." (See Fig. 11.1.) This not only refers to the size of individual holdings but to the sparseness of urban centers. Annual precipitation averages less than 250 mm in the lower elevations of Arizona, New Mexico, and western Texas. It ranges up to 750 mm in the eastern portions of the southern Great Plains. Precipitation not only varies greatly within and among seasons and years but also among locations separated by only a few kilometers. (See Fig. 41.2.) About 70% of the average annual precipitation occurs during the spring-summer period in the Great Plains. In western New Mexico and southern Arizona the growing season precipitation occurs during summer, and spring normally is very dry. The entire region frequently is plagued by drought. During a prolonged drought, the Great Plains may take on a desertlike appearance.