1z BOTANICAL FEATURES OF NORTH AMERICAN DESERTS. 
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. Recentinvestigations, however, have shown that 
the region traversed is in reality a basin, and that water is to be found, 
as in many other deserts, within a reasonable distance of the surface. 
The San Andreas Mountains form part of the eastern boundary of 
this basin, and beyond lies an equally remarkable desert, that of the Otero 
basin. This basin lies with its longer axis in a north and south direction, 
bounded on the east by the White and Sacramento Mountains and on 
the west by the San Andreas and Oscuro Mountains. Once the bed of 
an ancient lake, it has had a complicated geological history. A lava-flow 
extends without interruption for 50 miles east of the Oscuro Mountains, 
and this or other causes must have interrupted the great stream which 
may have flowed southward through the basin, expanding into a lake 
with varying dimensions as the conditions varied from humid to arid in 
the alternation of climate, which has finally brought it to a condition at 
the present time in which the rainfall is scarcely a dozen inches. The 
ancient Lake Otero probably began its existence in the Tertiary times and 
must have occupied an area of nearly 2,000 square miles, and a vertical 
section by means of well-bores shows a very heavy sedimentary deposit. 
The oscillation of this body of water carried its dissolved salts 
through various stages of concentration even to complete precipitation, 
and the beds of material thus laid down were covered by later deposits of 
sediment. The fact that different salts are precipitated at different 
degrees of saturation accounts for the deposition of the various saline 
compounds separately. More modern erosion cuts these deposits in 
places and lays them bare in others. Thus the intermittent streams 
which come down from the mountain canyons cut into and bring down 
in solution some of the ancient deposits, which are carried out toward the 
center of the basin and laid down again by evaporation in the level floor- 
like playas. In some places the drainage water percolates down through 
an inclined deposit and comes to the surface as a salt spring which builds 
up a cone-shaped deposit around its vent. (C. L. Herrick, Lake Otero, 
an ancient salt lake basin in southeastern New Mexico, Amer. Geol. 
vol. 34, p. 174, 1904). 
As a result of the interplay of a complex series of geological factors, 
the central portion of this basin to-day shows some highly characteristic 
desert features, among which are to be reckoned the great salt and soda 
flat in the western portion, the salt lake southwest from Alamogordo, 
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. 
