Brown Rocks 

 and White Sands 



The Hot Deserts of the Tularosa and 

 Chihuahua, and the Deserts and Scrublands 

 of the Central Mexican Plateau 



Between the great deserts and scrublands of Sonora and the East 

 Chaparral Province where these two belts reach the east side of 

 our continent, there lies a land that is customarily referred to as 

 the Chihuahua Deserts after the Mexican state of that name. 

 Much of this is a desert indeed — in many parts even more des- 

 olate than any we have so far visited. It is a vast upland country 

 of most odd construction, so that, unless you travel with an al- 

 timeter or a map showing the elevations, you would never know 

 that the whole of it starts at some three thousand feet above sea 

 level and rises southward to over six thousand feet. Many atlases 

 show the whole province as just a great upland plain; but it is 

 quite otherwise, being covered with mountain ranges. Apart 

 from the small part that lies within the boundaries of the United 

 States, detailed information about much of this province is 

 difficult to obtain. The northern part of it, in Mexican territory, 

 is a wilderness, with only one or two roads crossing it, and con- 

 taining several huge areas that are completely uninhabited. 

 Apart from the difficulty of travel in this area, information is 

 hard to come by because of the practice of printing maps, in- 

 cluding even road maps and atlases, in such a way that every- 

 thing ends abruptly on the publisher's side of any international 

 political boundary. This is particularly misleading here since 

 there is no true boundary or change of any kind at this point. 

 The net result is that practically nobody on one side has any 

 idea what the country looks like on the other. On all readily 

 available maps, the country immediately south of the Rio Grande 

 is shown as a smooth blank, just as are lowland plains elsewhere. 

 However, that entire region stands at a considerably higher 

 general level than on the United States side. Moreover, the whole 

 of it, from the region of the Big Bend all the way to Monterrey 

 and the grand Sierras, is covered with strings of mountains and 

 small ranges, rising some four to six thousand feet above the 

 already elevated plain. 



Coming from the Sonoran region, we enter this province via 

 the dry, cactus-covered plains of southern Arizona, which run up 

 into the foothills and gorges of the southern block of the South 

 Montane Province. This narrow neck of territory represents the 

 northernmost bulge of the South Scrub Belt, and it winds its way 

 between little mountain ranges that litter its otherwise more or 

 less level surface. These are outliers of the great Sierra Madre 



Occidental. Were the whole area some three thousand feet lower, 

 they would form a galaxy of islands like stepping stones between 

 that range and the southwestern edge of the Rockies. These 

 mountain ranges are, in any case, very much like islands, each 

 having its own crown of special vegetation, often containing a 

 fauna that may be unique, including the only parrot (a Conure) 

 native to the United States. The taller these mountains are, the 

 more forest they have on their upper slopes; the farther south 

 one goes, the more these forests come to resemble those of the 

 Sierra Occidental, while the northern-type conifers, of course, 

 rise ever higher on them. This narrow neck of scrubland thus 

 completely separates the Sonoran Deserts to the west from the 

 Chihuahuan to the east, for the deserts pass north under the 

 mountains of Arizona and New Mexico to appear on the Colo- 

 rado Platea. 



The most northerly extension of the Chihuahua Province 

 comprises the Tularosa plain or basin. This is a fascinating area, 

 containing some of the most remarkable sights. It is enclosed 

 between two great mountain blocks — the San Andreas and 

 Oscura on the west, beyond which lies the upper Rio Grande 

 valley containing the Jornada del Muerto desert; and the very 

 high Sacramentos and Guadalupe Mountains to the east. This 

 basin is a long, wedge-shaped depression pointing north and 

 continues on into the Estancia Valley beyond some low hills. If 

 you get up from this plain a short distance, you see two un- 

 expected phenomena. To one side, it looks as if there had been 

 a tremendous snowstorm over a limited area, for a well-defined 

 portion of it glistens so that, in bright sunlight, one can hardly 

 look at it. Somewhat beyond and to the northwest of this appari- 

 tion, another area looks as if tar had been poured upon it in 

 even greater quantity. This is a large lava flow, jet-black in color, 

 and of comparatively recent date, geologically speaking. The first 

 phenomenon is now very appropriately named "White Sands" 

 and is a national monument. 



WHITE LAND 



White sands occur rarely in various parts of the world. There 

 are a number in our Southwest that form an arc following the 

 curve of the Northern Scrub Zone and center on a point about 

 the middle Colorado River valley. White sands, per se, originate 

 from a rather special kind of rock laid down around the edges of 

 warm ancient seas that became landlocked and eventually dried 

 out. This rock is composed of gypsum, a hydrous calcium sul- 

 phate which, when dehydrated or baked, forms the basis of 

 plaster of Paris. The origin of the white sands in the Tularosa 

 Valley is interesting and serves to explain how most of these 

 oddities come about. 



What is now the Tularosa Valley was once the exact oppo- 

 site — i.e., a long ridge formed by an upfold of the earth's surface 

 that took place some time after the ancient sea had disappeared. 

 This raised the gypsum stratum into a sort of immense elongated 

 shield. Then two vast parallel faults or "cracks" developed along 

 either side of this shield, and the whole strip of territory between 

 them collapsed and sank downward to form a valley or basin, 

 while the blocks of land on either side rose up to form moun- 

 tains. Then erosion got to work, and the gypsum stratum, which 

 was near the surface of the shield, was quickly washed away. 



Great areas of this province, north of Bolson de Mapimi, 

 are covered with massive lava flows. These are scoured and 

 cracked but support a tough flora. 



268 



