INCREASING PRODUCTION WITHOUT ACCELERATING EROSION 235 
ous farming and livestock enterprise as shown by ruins of once 
substantial ranches and homes. Now the valley is gashed by enor- 
mous straight-walled channels 20 to 40 feet deep. 
Lower down on the Rio Grande, the river has not been able to 
carry the enormous load of sediment dumped into it by its muddy 
tributaries. As a result, adjacent valley lands have become water- 
logged and are no longer cultivated. The raising river bed also 
brings an increased flood threat to bordering cities and farms. 
Sand and mud bars furnish a foothold for salt cedar (Tamarix 
spp.) and other water-wasting vegetation. 
Improvement of the land and water situation of the Rio Grande 
Valley and other similar arid land is not impossible. Restoration 
of plant cover on the watersheds is a necessary step in this im- 
provement. Unfortunately, many are puzzled when the need for 
cover improvement and erosion control is emphasized. Often dete- 
riorated conditions are accepted as normal. The great difference 
between present day vegetation and that of an earlier day is not 
fully realized. Demonstrations provided by some ranch lands, 
national forests, and other well-managed areas show what can be 
and has been accomplished. Research and experience have shown 
many ways to maintain and improve production on grass and 
forest lands. 
Management of Forage Resources Adjusted to Rainfall Deficiency 
A perpetual problem in range land management is how to bal- 
ance animal numbers with forage supplies. This is troublesome 
enough anywhere but particularly difficult in dry lands, which are 
almost universally characterized by large fluctuations in precipi- 
tation between seasons and from year to year. Man, misled by 
optimism or driven by short-range necessity, has all too often 
overused the ranges. Recovery proceeds more slowly and less cer- 
tainly than in humid lands. If deterioration is severe, unfavorable 
conditions may persist in the absence of any use unless the natural 
forces tending toward recovery are given assistance. 
Average annual rainfall in arid lands is of little value in land 
management. Extremes of rainfall occur more frequently than do 
mean conditions. In southeastern Arizona and southwestern New 
Mexico of the United States, rainfall varies exceedingly from one 
