The Pima tribe merits our special attention, because of the remarkable ruins and relics of a dense former population, sedentary and agricultural, in the region inhabited by it when the river basin was first explored. These are the large structures known as the Great Houses or Casas Grandes, and the remains of the numerous towns, extensive irrigating trenches, and ruined enclosures, brought to light by the Hemenway exploring expedition in the Salt river valley. Their walls were built of adobes or sun-dried bricks of large size, the clay probably placed in baskets upon the wall and allowed to dry there. The extent of these remains is surprising, and in the Salt river valley alone, in an area of half a million acres, it is estimated that two hundred thousand people may have found support. Making every allowance, there is no doubt that at some remote epoch the arable land in the valleys of the Gila and its affluents was under close cultivation. Who these busy planters were has supplied material for much speculation. As usual, the simplest explanation has been the last to be welcomed. In fact, there is no occasion for us to look elsewhere than to the ancestors of these Pimas, who lived in the valley when the whites first traveled it. There is nothing in the ruins and relics which demands a higher culture than the Pimas possessed. There is no sign of a knowledge of metals beyond hammered copper; the structures are such as the Pueblo Indians of the same stock live in now; and the Pimas have a historic tradition which claims these ruins and these old fields as the work of their ancestors, from which they were driven by the repeated attacks of the Apaches and other savage tribes of the north.[143] Some of them, a sub-tribe called the Sobaypuris (Sabaguis), and doubtless many others, took refuge in the deep cañons and constructed along their precipitous sides those “cliff houses,” which have been often described. About a hundred years ago the Apaches drove them out of these last resorts and forced them to flee to the main body of the Pimas in the south.[144] In conclusion, we may safely attribute most of the ruins in the Gila Basin, as well as most of the cliff houses in the various cañons, to these tribes of the Uto-Aztecan stock. When the early missionaries reached the Pimas they found them in precisely the condition of culture of which we see the remains in the Salt River valley. Their houses were built of large adobes, sometimes roofed with tiles; they were agricultural and industrious; their fields were irrigated by like extensive canals or trenches, and their weapons, utensils and clothing were just such as the Hemenway expedition showed were those of the early accolents of the Gila and the Salado.[145]