chilis are the principal garden crops, and flowers (poppies, asters, roses, etc.) in pots or beds in the patios or dooryards of nearly all dwellings, however humble. Fields of corn and barley, with calabasas (squashes), are scattered about the plain not far away, where crops are matured in the short season of the summer rains. Their corn planted in July is harvested in October, its growth hastened by irrigation of a primitive sort; running a ditch along the face of the slope, the ranchero collects the run-off from the rains and directs it on to his field. On some of these fields corn grows to the height of ten feet with a degree of luxuriance that would gladden the heart of a northern farmer.
Although no permanent streams of any consequence exist, yet the rapid drainage of the land makes feasible a mode of existence otherwise impossible. The herdsman pushes out away from walls and springs and establishes himself in the midst of the desert. Choosing a place where the land lies to form a basin or wide valley, he throws a dam across the mouth and collects the run-off from a large area. For this purpose a gently sloping drainage basin is preferred, else the labor of building the dam will come to naught in a few years by the reservoir's becoming filled with silt and drift; moreover, the rushing torrent may cut through the embankment and drain the tank dry. I have seen old tanks which had been filled to a depth of fifteen feet or more, and as the earthen dam was finally cut through, the later floods had sluiced down an arroyo through the flat sedimentary plain above. So the tanks in such situations are short lived, but where fed by the gentle drainage of a gravelly plain they may last indefinitely and supply water the year round to large herds. Frequently these tanks hold water covering several acres at the height of the dry season, and when at its deepest it may assume the proportions of a small lake. Some of the dams are strong and well-built structures of stone masonry a half mile or more in length and ten to twenty feet in height. To the "tanques" come the horses, the mules, the burros, the sheep, the goats and every other animal of the desert; they drink the turbid liquid, they wade in it, they bathe in it, they discharge into it, and all around the margin is a fringe of greenish drift and scum, but it is water in a thirsty land and man is grateful for it. It is the objective camping point in the day's travels and at noonday the cool shade on its banks is the favorite resting-place for man and beast.
From one to two and a half feet of rain falls on this land in a year, depending partly on the altitude and local conditions. Records of rainfall at Chihuahua and San Luis Potosi show 10.86 and 10.41 inches, respectively, for one year (1901), and at the city of Zacatecas the average for ten years (1897-1907) was thirty-one and a half inches. The precipitation at Cedros for one year (1907-8) was about eighteen inches.