The Book of the National Parks

by Robert Sterling Yard

It is well to recall that these strata were laid in the sea, and that they hardened into stone when the earth's skin was pushed thousands of feet in air. Originally they were the washings of distant highlands brought down by rivers; the coloring of the shales and sandstones is that of the parent rock modified, no doubt, by chemical action in sea-water. The limestone, product of the sea, is gray.

As these differently colored strata were once continuous across the canyon, it follows that their sequence is practically identical on both sides of the canyon. That the colors seem confused is because, viewing the spectacle from an elevation, we see the enormous indentations of the opposite rim in broken and disorganized perspective. Few minds are patient and orderly enough to fully disentangle the kaleidoscopic disarray, but, if we can identify the strata by form as well as color, we can at least comprehend without trouble our principal outline; and comprehension is the broad highway to appreciation.

To identify these strata, it is necessary to call them by name. The names that geologists have assigned them have no scientific significance other than identity; they are Indian and local.

Beginning at the canyon rim we have a stalwart cliff of gray limestone known as the Kaibab Limestone, or, conversationally, the Kaibab; it is about seven hundred feet thick. Of this product of a million years of microscopic life and death on sea-bottoms is formed the splendid south-rim cliffs from which we view the chasm. Across the canyon it is always recognizable as the rim.

Below the talus of the Kaibab is the Coconino sandstone, light yellowish-gray, coarse of grain, the product of swift currents of untold thousands of centuries ago. This stratum makes a fine bright cliff usually about four hundred feet in thickness, an effective roofing for the glowing reds of the depths.

Immediately below the Coconino are the splendid red shales and sandstones known as the Supai formation. These lie in many strata of varying shades, qualities, and thicknesses, but all, seen across the canyon, merging into a single enormous horizontal body of gorgeous red. The Supai measures eleven hundred feet in perpendicular thickness, but as it is usually seen in slopes which sometimes are long and gentle, it presents to the eye a surface several times as broad. This is the most prominent single mass of color in the canyon, for not only does it form the broadest feature of the opposite wall and of the enormous promontories which jut therefrom, but the main bodies of Buddha, Zoroaster, and many others of the fantastic temples which rise from the floor.

Below the Supai, a perpendicular wall of intense red five hundred feet high forces its personality upon every foot of the canyon's vast length. This is the famous Redwall, a gray limestone stained crimson with the drip of Supai dye from above. Harder than the sloping sandstone above and the shale below, it pushes aggressively into the picture, squared, perpendicular, glowing. It winds in and out of every bay and gulf, and fronts precipitously every flaring promontory. It roofs with overhanging eaves many a noble palace and turns many a towering monument into a pagoda.

Next below in series is the Tonto, a deep, broad, shallow slant of dull-green and yellow shale, which, with the thin broad sandstone base on which it rests, forms the floor of the outer canyon, the tessellated pavement of the city of flame. Without the Tonto's green the spectacle of the Grand Canyon would have missed its contrast and its fulness.

Through this floor the Granite Gorge winds its serpentine way, two thousand feet deep, dark with shadows, shining in places where the river swings in view.

These are the series of form and color. They occur with great regularity except in several spots deep in the canyon where small patches of gleaming quartzites and brilliant red shales show against the dark granite; the largest of these lies in the depths directly opposite El Tovar. These rocks are all that one sees of ancient Algonkian strata which once overlay the granite to a depth of thirteen thousand feet—more than twice the present total depth of the canyon. The erosion of many thousands of centuries wore them away before the rocks that now compose the floor, the temples and the precipiced walls of the great canyon were even deposited in the sea as sand and limestone ooze, a fact that strikingly emphasizes the enormous age of this exhibit. Geologists speak of these splashes of Algonkian rocks as the Unkar group, another local Indian designation. There is also a similar Chuar group, which need not concern any except those who make a close study of the canyon.