50 THE CLIMATIC FACTOR AS ILLUSTRATED IN ARID AMERICA. 

 THE FORMER POPULATION OF THE SANTA CRUZ VALLEY. 



Turning now to the discussion of specific areas, it is e\ddent that the solution of our 

 problem depends upon the relative density of population and the amount of water available 

 for agriculture in the past as compared with the present. We must exclude regions now 

 well populated, for they prove nothing either one way or the other. We must also exclude 

 regions now depopulated and full of ruins, but capable of being reoccupied. These also 

 prove nothing : the driving out of the former inhabitants may have been due to pestilence, 

 or to the incursion of warhke tribes, such as the Apaches; but the pestilence and the raids, 

 in their turn, may have been the result of adverse cUmatic changes. Accordingly we shall 

 pay little attention to such regions and shall confine ourselves for the present to the almost 

 uninhabited lower part of the Santa Cruz Valley below Tucson, and to certain tributary 

 valleys with an equally sparse population. Then, for the sake of comparison, we shall 

 consider the Altar and Magdalena valleys in northern Sonora. These, like the Santa Cruz 

 and its tributaries, rise near the border between Mexico and Arizona, but instead of flowdng 

 northwest for 150 miles to the Gila, they flow a similar distance to the southwest, where 

 they unite and empty into the Gulf of Cahfornia. As a matter of fact, neither the Altar- 

 Magdalena nor the Santa Cruz sends any water to the sea except in occasional years of 

 phenomenal floods. The permanent stream of the Santa Cruz ends near Tucson, more 

 than 70 miles from the Gila, while the permanent stream of the Altar terminates near 

 Caborca, about 50 miles from the Gulf. (See map, frontispiece.) 



Before investigating the ruins, let us see how many people the Santa Cruz \'alley is 

 capable of supporting by agriculture at the present time. According to Professor R. H. 

 Forbes, the records of the Arizona Experiment Station, of which he is the Director, show 

 that the entire drainage area of the Santa Cruz, including all its tributaries, contains 

 approximately 6,000 acres under cultivation of some sort. This includes not only areas 

 regularly irrigated in the ordinary fashion by surface water, but also some that depend 

 upon underground water raised by steam or gasoline pumps, and other considerable tracts 

 which are watered merely by temporary floods and hence produce only a single crop of 

 alfalfa per year instead of four or five, as is the case in the lands receiving more abundant 

 water. Under the best system of irrigation available at the present time. Professor Forbes 

 estimates that for every 2 acres brought under full cultivation one person is added to the 

 population of Arizona. This includes merchants, artisans, and all the varieties of people 

 needed to carry on the business of life. In other words, if the Santa Cruz Valley were 

 cut off from the rest of the world and left to its own resources, as it was in the days of the 

 Hohokam, the population would be hmited to the number of persons who could be sup- 

 ported on the 6,000 acres of irrigated or partly irrigated land. To this number nothing 

 could be added by dry farming without irrigation, for Professor Forbes expressly states 

 that at the present time, in spite of various attempts, no such thing as genuine diy farming 

 is carried on in the lower parts of Arizona. Experiments are in progress which may soon 

 render it possible, but any such process was certainly far beyond the capacity of primitive 

 people hke the Hohokam. A certain number of persons might be added by the possibiUties 

 of hunting and of sustenance from wild products, such as the fruit of the cacti, the mesquite 

 beans, and so forth. The number would be hmited, however, for it is well known that 

 a hunting population of one person to the square mile is dense even in a nioist region 

 furnishing abundant forage for herbivores and rodents. In a dry region hke Arizona 

 the number would be less. Nor could wild fruits and seeds add greatly to the density of 

 population, for they are abundant in the years of good rainfaU when the cultivated crops 

 are also abundant, while they fail in dry years, "especiaUy in hard times," as a Pima 

 Indian naively remarked to Russell. In times of poor crops the Hohokam doubtless 

 made extensive use of wild products; but this means that there could not have been any 



