But granted the quantity and the quality of local colors in the desert, and the fact still remains that the air is the medium that influences if it does not radically change them all. The local hue of a sierra may be gray, dark red, iron-hued, or lead-colored; but at a distance, seen through dust-laden air, it may appear topaz-yellow, sapphire-blue, bright lilac, rose-red—yes, fire-red. During the heated months of summer such colors are not exceptional. They appear almost every evening. I have seen at sunset, looking north from Sonora some twenty miles, the whole tower-like shaft of Baboquivari change from blue to topaz and from topaz to glowing red in the course of half an hour. I do not mean edgings or rims or spots of these colors upon the peak, but the whole upper half of the mountain completely changed by them. The red color gave the peak the appearance of hot iron, and when it finally died out the dark dull hue that came after was like that of a clouded garnet.
Buttes and spires.
Sun-shafts through canyons.
The high ranges along the western side of Arizona, and the buttes and tall spires in the Upper Basin region, all show these warm fire-colors under heat and sunset light, and often in the full of noon. The colored air in conjunction with light is always responsible for the hues. Even when you are close up to the mountains you can see the effect of the air in small ways. There are edgings of bright color to the hill-ridges and the peaks; and in the canyons, where perhaps a sunshaft streams across the shadow, you can see the gold or fire-color of the air most distinctly. Very beautiful are these golden sun-shafts shot through the canyons. And the red shafts are often startling. It would seem as though the canyons were packed thick with yellow or red haze. And so in reality they are.
Complementary hues in shadow.
There is one marked departure from the uniform warm colors of the desert that should be mentioned just here. It is the clear blue seen in the shadows of western-lying mountains at sunset. This colored shadow shows only when there is a yellow or orange hued sunset, and it is produced by the yellow of the sky casting its complementary hue (blue) in the shadow. At sea a ship crossing a yellow sunset will show a marvellous blue in her sails just as she crosses the line of the sun, and the desert mountains repeat the same complementary color with equal facility and greater variety. It is not of long duration. It changes as the sky changes, but maintains always the complementary hue.
Colored shadows.
Blue shadows upon salt-beds.
The presence of the complementary color in the shadow is exceptional, however. The shadows cast by such objects as the sahuaro and the palo verde are apparently quite colorless; and so, too, are the shadows of passing clouds. The colored shadow is produced by reflection from the sky, mixed with something of local color in the background, and also complementary color. It is usually blue or lilac-blue, on snow for example, when there is a blue sky overhead; and lilac when shown upon sand or a blue stone road. Perhaps it does not appear often on the Mojave-Colorado because the surfaces are too rough and broken with coarse gravel to make good reflectors of the sky. The fault is not in the light or in the sky, for upon the fine sands of the dunes, and upon beds of fine gypsum and salt, you can see your own shadow colored an absolute indigo; and often upon bowlders of white quartz the shadows of cholla and grease wood are cast in almost cobalt hues.
How light makes color.