Still less likely is it that they had been used as mining dams.
As soon as the plains of Northern Sonora were left behind, and the country became hilly and broken, these peculiar structures were conspicuous.

At first they appeared more like walls built simply along the slopes of the hills, and not crossing gulches.

They seem to be more numerous in the western and central part of the sierra, its spurs and foot-hills, than in the eastern part of the great range.

As regards their southern extent, they are not found further south than the middle part of the state of Chihuahua.

Captain Bourke, in his book, "An Apache Campaign," mentions that "in every sheltered spot could be discerned ruins, buildings, walls, and dams, erected by an extinct race once possessing these regions." Mr.A.F.