In humid regions, where the water table is near
the surface and where the rainfall is very abundant, no question has
been raised concerning the possibility of the descent of water
through the soil to the standing water. Considerable objection,
however, has been offered to the doctrine that the rainfall of arid
districts penetrates the soil to any great extent. Numerous writers
on the subject intimate that the rainfall under dry-farm conditions
reaches at the best the upper 3 or 4 feet of soil. This cannot be
true, for the deep rich soils of the arid region, which never have
been disturbed by the husbandman, are moist to very great depths. In
the deserts of the Great Basin, where vegetation is very scanty,
soil borings made almost anywhere will reveal the fact that moisture
exists in considerable quantities to the full depth of the ordinary
soil auger, usually 10 feet. The same is true for practically every
district of the arid region.
Such water has not come from below, for in the majority of cases the
standing water is 50 to 500 feet below the surface. Whitney made
this observation many years ago and reported it as a striking
feature of agriculture in arid regions, worthy of serious
consideration.
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