In the semi-arid regions of the United States, Argentina and other countries where the average annual rainfall lies between ioa to 20 in., irrigation is necessary to obtain full crops every year.
In the operation of ploughing the furrow slice is separated from the soil below, and although in humid soils this layer may be left to settle by degrees, in semi-arid regions this loosened layer becomes.
The state belongs to the elevated plateau region, with its semi-arid conditions.
the general elevation is low, the surface sandy and covered with cactus and mesquite growth, and hot, semi-arid conditions prevail.
The streams flowing from the central area have cut deep gorges and canons, and among the ridges the granitic rocks have assumed many strange forms. Though rising from a semi-arid plateau, these mountains have sufficient rainfall to support an abundant plant growth, and have derived their name from the fact that their slopes are dark with heavy forests.