As the arroyo rises and narrows, the walls, each placed a little higher up the slope than the preceding one, are necessarily smaller.
In the mountains near Nacori, especially on their eastern and 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.