southeastern sides, trincheras were encountered in every gulch as high
up as six thousand feet, though steep crests and the mountain tops
bear no traces of them. In one arroyo, which was about a thousand feet
in length and of comparatively gentle slope, twenty-nine trincheras
were counted from the bed of the main drainage to the summit of the
mountain. Some of them were quite close together, three being within
eighteen feet of one another.

These trincheras somewhat resemble the small terrace gardens of
the Moqui Indians, and have undoubtedly been used for agricultural
purposes, just as they are used by the Tarahumares to this day (page
152). It is true that they are built in great numbers, sometimes
in localities that would appear unsuitable for farming; but, on the
other hand, they are seldom, if ever, found far from the remains of
habitations, a fact from which it may also reasonably be inferred
that the ruined houses, as well as the trincheras, were originally
built by the same race. Some of the terraces were, no doubt, erected
as a protection of the crop against enemies and wild animals; but
it is impossible to think that they were intended for irrigation
dams, though we did see water running through some, coming out of a
marsh. 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,