Elemental warfare.
Yet this conflict is not so obvious on the face of things. You hear no clash or crash or snarl. The desert is overwhelmingly silent. There is not a sound to be heard; and not a thing moves save the wind and the sands. But you look up at the worn peaks and the jagged barrancas, you look down at the wash-outs and piled bowlders, you look about at the wind-tossed, half-starved bushes; and, for all the silence, you know that there is a struggle for life, a war for place, going on day by day.
Desert vegetation.
Protruding edges.
How is it possible under such conditions for much vegetation to flourish? The grasses are scanty, the grease wood and cactus grow in patches, the mesquite crops out only along the dry river-beds. All told there is hardly enough covering to hide the anatomy of the earth. And the winds are always blowing it aside. You have noticed how bare and bony the hills of New England are in winter when the trees are leafless and the grasses are dead? You have seen the rocks loom up harsh and sharp, the ledges assume angles, and the backbone and ribs of the open field crop out of the soil? The desert is not unlike that all the year round. To be sure there are snow-like driftings of sand that muffle certain edges. Valleys, hills, and even mountains are turned into rounded lines by it at times. But the drift rolled high in one place was cut out from some other place; and always there are vertebræ showing—elbows and shoulders protruding through the yellow byssus of sand.
Shifting sands.
The shifting sands! Slowly they move, wave upon wave, drift upon drift; but by day and by night they gather, gather, gather. They overwhelm, they bury, they destroy, and then a spirit of restlessness seizes them and they move off elsewhere, swirl upon swirl, line upon line, in serpentine windings that enfold some new growth or fill in some new valley in the waste. So it happens that the surface of the desert is far from being a permanent affair. There is hardly enough vegetation to hold the sands in place. With little or no restraint upon them they are transported hither and yon at the mercy of the winds.
Desert winds.
Radiation of heat.
Yet the desert winds hardly blow where they list. They follow certain channels or “draws” through the mountain ranges; and the reason for their doing so is plain enough. During the day the intense heat of the desert, meeting with only a thin dry air above it, rises rapidly skyward leaving a vast vacuum below that must be filled with a colder air from without. This colder air on the southern portion of the Colorado Desert comes in from the Gulf region. One can feel it in the passes of the mountains about Baboquivari, rushing up toward the heated portions of Arizona around Tucson. And the hotter the day the stronger the inward rush of the wind. Some days it will blow at the rate of fifty miles an hour until sunset, and then with a cessation of radiation the wind stops and the night is still.