HISTORY AND PROBLEMS 21 
Human Extension of Desert Lands 
Man, prehistoric, ancient, and modern, has been responsible 
for greatly increasing the desert lands. His herds have removed 
much of the scanty cover of nutritious grasses and shrubs, and 
thereby favored the non-palatable ones. His path has been marked 
by ruins of human settlements. It is doubtful if desiccation has 
been the cause. The cause seems to have been over-use. Within 
the life span of many of us beautiful areas of desert grassland have 
been reduced to bare soil and useless weeds by over-grazing, the 
short grass of our high plains have been replaced by wheat and 
summer fallow, followed by the dust bowl, and the brushlands of 
the Mediterranean type have been reduced to non-palatable brush 
by fire followed by grazing of the young sprouts, a practice gen- 
erally employed and one very detrimental to palatable plants. It 
is almost impossible to reverse these destructive trends under 
increasing population pressure, but it must be done if future 
generations are to find the resource in as good condition as we 
found it. 
Great areas of our most productive soils are being occupied by 
cities, highways, landing fields, reservoirs, recreational areas, and 
factories, in which the crop production capacity of the land is 
lost. It is possible that some of this unproductive occupancy can 
be halted by shifting some of these uses to more arid land. The 
arid zone is a delightful place in which to live during at least a 
part of the year, and it affords a retreat to many who can choose 
their place of abode and to some who find health only on the 
arid lands. 
Future Lines of Development 
In general the ancients used flood waters by using naturally 
flooded areas and by building deflectors and large stone terraces 
to retain flood water in selected places. It was, in fact, a type of 
irrigation agriculture. The Indians of our Southwest did the same, 
but they took every advantage of the natural drainage areas, 
allowing nature to concentrate water in channels, fans, and 
temporary pools. Dry farming is based on a very different prin- 
ciple: to catch the water where it falls, hold it in the soil, and 
