Spectrum colors.
Bands of yellow.
The orange sky.
Ordinarily the sky at evening over the desert, when seen without clouds, shows the colors of the spectrum beginning with red at the bottom and running through the yellows, greens, and blues up to the purple of the zenith. In cool weather, however, this spectrum arrangement seems swept out of existence by a broad band of yellow-green that stretches half way around the circle. It is a pale yellow fading into a pale green, which in turn melts into a pale blue. In hot weather this pallor is changed to something much richer and deeper. A band of orange takes its place. It is a flame-colored orange, and its hue is felt in reflection upon valley, plain, and mountain peak. This indeed is the orange light that converts the air in the mountain canyons into golden mist, and is measurably responsible for the yellow sun-shafts that, streaming through the pinnacles of the western mountains, reach far across the upper sky in ever-widening bands. This great orange belt is lacking in that variety and vividness of coloring that comes with clouds, but it is not wanting in a splendor of its own. It is the broadest, the simplest, and in many respects the sublimest sunset imaginable—a golden dream with the sky enthroned in glory and the earth at its feet reflecting its lustre.
Desert clouds.
Rainfall.
But the more brilliant sunsets are only seen when there are broken translucent clouds in the west. There are cloudy days even on the desert. After many nights of heat, long skeins of white stratus will gather along the horizons, and out of them will slowly be woven forms of the cumulus and the nimbus. And it will rain in short squalls of great violence on the lomas, mesas, and bordering mountains. But usually the cloud that drenches a mountain top eight thousand feet up will pass over an intervening valley, pouring down the same flood of rain, and yet not a drop of it reaching the ground. The air is always dry and the rain-drop that has to fall through eight thousand feet of it before reaching the earth, never gets there. It is evaporated and carried up to its parent cloud again. During the so-called “rainy season” you may frequently see clouds all about the horizon and overhead that are “raining”—letting down long tails and sheets of rain that are plainly visible; but they never touch the earth. The sheet lightens, breaks, and dissipates two thousand feet up. It rains, true enough, but there is no water, just as there are desert rivers, but they have no visible stream. That is the desert of it both above and below.
Effect of the nimbus.
With the rain come trooping almost all the cloud-forms known to the sky. And the thick ones like the nimbus carry with them a chilling, deadening effect. The rolls and sheets of rain-clouds that cover the heavens at times rob the desert of light, air, and color at one fell swoop. Its beauty vanishes as by magic. Instead of colored haze there is gray gloom settling along the hills and about the mesas. The sands lose their lustre and become dull and formless, the vegetation darkens to a dead gray, and the mountains turn slate-colored, mouldy, unwholesome looking. A mantle of drab envelops the scene, and the glory of the desert has departed.
Cumuli.