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Dicke, Robert J. (ed.) / Transactions of the Wisconsin Academy of Sciences, Arts and Letters
volume XLIV (1955)

McCabe, Robert A.
The prehistoric engineer-farmers of Chihuahua,   pp. 75-90 PDF (6.1 MB)

Page 85

 1955] McCabe—Engineer-Farmers of Chihuahua 85 
the periphery. ' These stones were about the size of loaves of bread, partly
buried and grown over in places with grass. This wagon wheel design was not
easily discernible when walking near it, for I must have passed by or over
it 25 times before seeing it in this fresh perspective. 
 Studying and hunting game animals of ' this rugged back country left me
little time for reflection on the archaic masonry that was seldom out of
sight. This much, however, seems obvious: 
The dams were in some way associated with the pursuit of agriculture. ' The
presence of pottery fragments in the ruins implies that the culture was archeologically
recent and probably a cornbean-squash agriculture. 
 Were these dams the precursor of mo'dern soil conservation practices and
built to check soil erosion? Perhaps, but only as a secondary measure. The
real reason, as stated earlier and also as expressed by others, was to catch
and hold silt. Most of the country, including fairly level mesa tops, is
extremely rocky and unsuited generally even to hand agriculture; the formation
of soil from the flaky volcanic rock is reasonably fast and a check-dam along
a run-off course would soon collect enough soil to support vegetation. Thus
behind each trinchera arose a potential field. As the silt accumulated, a
new tier of stones could be added to the dam. ' The water basin, or more
properly soil basin, thus formed would mean additional land for the enlarging
 Seemingly in opposition :to this hypothesis is the fact that many of the
dams were in places where there was little chance to catch or hold enough
soil to make dam-building a worthwhile operation. Likewise there now exist
slopes that would make very good fields if dammed, located near these almost
negligible fields behind well-built dams. Those areas behind dams built on
steep slopes and in narrow canyons are subject to periodic washing or side
cutting during the rainy season. Thus it seems unlikely these were meant
to be fields. It is difficult ' to guess what other function this type of
dam may have served. 
 If the deductions made thus far are correct, then the preconquest farmer
of Chihuahua probably practiced soil conservation before he farmed much of
his land. This has an ironic twist, since we came from a rich and "enlightened"
land to the north where a small group of soil conservationists are trying
to help an unwilling country prevent its soil, and indirectly its wealth,
from flowing seaward. 

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