ROBBm"s^°'^] CLIMATE AND EVIDENCE OF CLIMATIC CHANGES 51 



tively dense population once lived there. What, then, were the causes which led 

 to the extinction of these people? So far as may be inferred from present conditions, 

 the environment was favorable for the maintenance of Indian tribes, and it is prob- 

 able, therefore, that there is no geographic or climatic condition adequate to explain 

 the depopulation of the whole region. In some sections disease may have checked 

 the growth of population and finally exterminated the inhabitants, for even in the 

 elevated localities fevers of a certain class bear heavily at times upon the present 

 settlers. In some of the river valleys malaria also at times is prevalent. On the 

 whole, however, the climate is salubrious. Exploration of the ancient ruins, so far 

 as this has been accomplished, invariably shows, moreover, that the abandonment 

 of the pueblos was not due to internal warfare or to attacks by outside enemies. In 

 reference to the failure of the food supply, due to prolonged drought or other circum- 

 stances, there is reason to believe that such failures were less prevalent in former 

 times than in the years since the occupancy by white men. However, starvation 

 may have been a factor in the decline of population in certain localities. It may be 

 that the most potent cause existed in the social organization of the people, coupled 

 with the isolation enforced by the environment. It is known that the social organi- 

 zation of the existing Pueblo tribes among which marriage is prohibited within the 

 clan tends to self-extinction, and it is possible that the tribes of'the Gila suffered 

 from the same cause. . . . The evidence invariably shows that no sudden cata- 

 clysm overwhelmed the pueblos; no hasty, disorganized abandonment took place, 

 no wars decimated them, but rather that, like a tree, they passed through successive 

 stages of growth, decline, and decay to final extinction. 



Fewkes^ takes another view of the cause of abandonment. He 

 says: 



The prehistoric population of the Gila Valley may have risen into the thousands, 

 and it is not too much to say that the number of Indians in the valley at the advent of 

 the Spaniards could not have been more than a tithe of what it was in prehistoric 

 times [p. 406]. 



It appears that the valley of the Salt River in the neighborhood of Phoenix, Tempe, 

 and Mesa was the most densely populated region of this whole drainage area and ap- 

 parently contained the oldest settlements. These facts may be ascribed to the ease 

 with which the plains in this region could be irrigated as compared with other parts 

 of the valley, or may have been due to the presence of more fertile land in those locali- 

 ties [p. 407]. 



The extent of the aboriginal ditches that can be traced for miles shows that the pre- 

 historic inhabitants Jjjxd discovered and applied a more extensive system of irrigation 

 than any of their contemporaries who dwelt in other sections of what is now the United 

 States. ... It is probable that certain clans were driven away from their 

 homes and forced into other regions by the changed conditions, as the inroads of hos- 

 tiles. This theory is in fact supported by legends still told by the Hopi and other 

 Pueblo people. . . . The author would state in conclusion that he believes the 

 abandonment of the Casas Grandes was brought about by an invasion of nomads from 

 farther down the river in prehistoric times [pp. 434-36] . 



JVImdeleff " suggests that the many droughts and constant varia- 

 tions and local changes in water supj^ly compelled frequent re- 

 movals and rebuilding, so that the number of ruins by no means 

 indicates the number of former inhabitants. 



> Fewkes, J. AValter, Prehistoric Ruins of the Gila Valley, in Smithson. Misc. Coll., lu, 400, 407, 432, 

 4.34, 436, 1909. 



- Mindeleff, Victor, A Study of Pueblo Architecture in Tusayan and Cibola, in Stii Ann. Rep. But. 

 Amer. Ethn., for 1886-87, pp. 23, 227, 1891. 



