San Luis belongs partly to the semi-arid pampa region, and partly to the mountainous region of the eastern Andes and Cordoba whose ranges terminate between the 33rd and 34th parallels.
The hay crop, 865,000 tons in 1909, is made quite largely from wild grasses and grains cut green; on the irrigated lands alfalfa is grown extensively for the cattle and sheep, which are otherwise almost wholly dependent for sustenance upon the bunch grass of the semi-arid plains.
In 1899 the irrigated area in the arid states and territories was more than, twice as great as in 1889, the acreage being as follows: - Total In addition to the area above given, in 18 99, 2 73, 11 7 acres were under irrigation in the semi-arid region, east of the states above mentioned and including portions of the states of North and South Dakota, Nebraska, Kansas, Texas and Oklahoma.
The general elevation is low, the surface sandy and covered with cactus and mesquite growth, and hot, semi-arid conditions prevail.
In the semi-arid districts on the south slope of the mountains the flora consists chiefly of dry grasses, acacias, yuccas and cactuses.
Or more, while other districts are semi-arid or subject to severe droughts.
Its semi-arid character is due to the mountain ranges on its northern frontier, which extract the moisture from the north-east trades and leave the Brazilian plateau behind them with a very limited rainfall, except near the Atlantic coast.
It is a stony, semi-arid region, thinly wooded, having good grazing campos in its extreme western section.
Sheep and cattle are raised extensively on ranches in the semi-arid regions, large herds of cattle are kept on lands too wet for cultivation in the western counties, and stock-raising and dairying have become important factors in the operation of many of the best farms. The acreage of wheat was 810,000 in 1909 and the crop was 16,377,000 bushels.
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.