DESERTS OF THE UNITED STATES AND MEXICO 



693 



a portion of the route connecting the 

 earhest settlements along the Rio Grande, 

 and here the traveler was compelled to 

 leave the stream far to the westward, in 

 its deeply cut, inaccessible canyon, and 

 toil for two or three days in the burning 

 heat without water, except such as might 

 be carried. It was for three centuries one 

 of the most menacing and hazardous 

 overland journeys to be encountered in 

 the American Desert. Recent investiga- 

 tions, however, have shown that the re- 

 gion traversed is in realit}' a basin, and 

 that water is to be found, as in many 

 other deserts, within a reasonable dis- 

 tance of the surface. 



Beyond lies an equally remarkable des- 

 ert, the Otero basin, which is the bed of 

 an ancient lake, and is noted for a great 

 salt and soda flat, a salt lake, and, most 

 striking of all, the "White Sands," an 

 area of about 300 square miles covered 

 with dunes of gypsum sand rising to a 

 maximum height of 60 feet. 



The surface of the dunes is sparkling 

 white, due to the dry condition of the 

 gypsum powder, but a few inches be- 

 neath it is of a yellowish or buff color 

 and is distinctly moist and cool to the 

 touch, even when the air is extremely 

 hot. The smallest particles may be crum- 

 bled in the fingers, and as a consequence 

 the dunes are solidly packed. 



The most characteristic plant of the 

 dunes is the three-leaf sumac (Rhus 

 trilobata), which occurs in the form of 

 single hemispherical bushes 4 to 8 feet 

 high, the lower branches hugging the 

 sand. The plant grows vigorously, the 

 trunk at or beneath the surface often 

 reaching a diameter of 3 inches. The 

 binding and protecting effect of this bush 

 is often shown in a striking manner when 

 in the cutting down of an older dune by 

 the wind a column of sand may be left 

 protected above from the sun by the close 

 covering of the branches and leaves, and 

 the sand in the column itself bound to- 

 gether by the long penetrating roots. 

 One of these columns was about 15 feet 

 high from its base to the summit of the 

 protecting bush and about 8 feet in di- 

 ameter at the base (see page 692). 



A curious fact brought out in the ex- 

 posure of the underground trunks of this 

 plant by the shifting of the dunes is the 

 abundant exudation of a pale smber gum 

 with the characteristic aroma of the 

 crushed twigs. This, mixing with the 

 sand, forms hard, honeycombed masses 

 sometimes 3 inches in diameter. 



A marked peculiarity of the White 

 Sands is that a cottonwood is occasionally 

 found in the lower dunes, reaching a foot 

 in diameter, but seldom more than 15 feet 

 in height ; yet at the same time not a mes- 

 quite was seen. The mesquite is a tree 

 requiring less moisture than the cotton- 

 wood. Apparently the presence of an ex- 

 cess of gypsum is prejudicial to the 

 growth of the mesquite. 



The bottoms among the dunes have a 

 dense vegetation as compared with that 

 of the dunes themselves. It is character- 

 ized especially by the presence of a grama 

 grass (Bout cloua) forming almost a turf, 

 and by frequent clumps of Ephedra of a 

 grayish purple color at this season 

 and with 3-scaled nodes. These bot- 

 toms usually show no sign of moist- 

 ure, but in two places we found water- 

 holes, the water so alkaline that the 

 horses would not drink it at the end of 

 their first day's drive. 



The relation of Yucca radiosa to the 

 sand dunes is unusually interesting. A 

 group of four small yucca shoots stand- 

 ing about 3 feet high to the tip of the 

 highest leaf was found upon the summit 

 ridge of a 30-foot dune. We dug the 

 trunk out to a depth of 14 feet. All four 

 plants were from branches of the same 

 trunk, the lowest branch arising about 16 

 feet from the base of the dune ; the main 

 trunk and the branches bore marks of 

 rosettes of leaves at intervals all the way 

 to the lowest point reached. The trunk 

 sloped in the direction in which the dune 

 was moving. The yucca originally grew 

 on the plain, was engulfed by the sand, 

 and gradually grew through each suc- 

 cessive layer of sand that drifted over it 

 until the summit of the dune was 

 reached. In the vicinity, at the rear of 

 the dune, were other long trunks partly 

 denuded by the passing of the dune. '] 



