RANGE MANAGEMENT IN NEW MEXICO. 7 



region and accepted as the natural order of things ; but it is of vastly- 

 more importance in regions of scanty rainfall. Here any kind of 

 management that permits or assists in the waste of water in any 

 way tends in the long run to the desiccation of the region. Hence, 

 any practice that increases the rapidity or amount of superficial run- 

 off or increases the evaporation of water (other than that which passes 

 through the bodies of growing plants) makes for the gradual drying 

 out and increased sterility of the region. These processes are cumu- 

 lative, and regions that are easily habitable under one kind of treat- 

 ment may be gradually changed to desert wastes by another pro- 

 cedure which, to the careless observer, does not seem materially 

 different from the first. 



SOILS. 



Speaking very generally, the soils of most localities in the State 

 have been formed almost in situ by the disintegration of the under- 

 lying or near-by rocks and necessarily have the chemical composi- 

 tion arishig from the breaking up of these rocks, mechanical or chem- 

 ical, or both. The soils of the river valleys have been transported 

 considerable distances and the particles assorted to size by the action 

 of the water. They consist mostly of sand or adobe and are uniform 

 in character and depth only for very short distances, because of the 

 great variations in the volume and velocity of the waters of the 

 streams that have deposited them. 



The soils of the larger and higher mountains, wherever they occur, 

 are mostly a rather rich loam, due to the nearly complete chemical 

 decomposition of the rocks, and contain considerable humus derived 

 from the vegetation of such regions. The foothills of the mountams 

 are mostly flanked by talus slopes and outwash plains composed of 

 partially disintegrated rock particles of various sizes, forming grav- 

 elly ridges and slopes in which proper soil particles constitute only a 

 small part of the volume. 



The soils of the plains and bolsons are largely wind-blown sand or 

 loess. In the bottoms of the basins such soils are sometimes deep, 

 but mostly they form only a thin layer. 



Wherever the water collects, evaporation goes on rapidly, with a 

 consequent accumulation of the soluble salts of sodium and calcium 

 known as alkali. Alkali often occurs in the river valleys in the soil 

 of terraces whose surfaces are but 2 or 3 feet above the water table, 

 as a result of the concentration of these salts at the surface by evapo- 

 ration. 



The lava-covered areas are in places but bare black rock, with scat- 

 tered patches of loess or sand in depressions and behind projecting 

 angles. In other places, where the lava is older, the basalt has de- 

 composed to a rich reddish loam, a soil that is recognizedly one of 

 the best. 



