Those who have been to the rocky shores of the Colorado River in Grand Canyon, who have heard its wild roar, and seen its mad waves rush along their course, need no further introduction to the power of this stream. It is a mighty river! In the open stretch above the mouth of Bright Angel Creek its speed varies between two and a half and ten miles an hour. Its width at the same place is over one hundred yards and its depth between twelve and forty-five feet. But the Colorado River alone would have made but little progress were it not for the many rocks—boulders, pebbles, and sand grains—all of which act as tools and are constantly gouging and cutting as they move. Just as sandpaper rubbing over the same place continuously leaves its groove, so this combination of power and tools is ever carving its course. The Colorado River during a vast period has cut almost a mile vertically through all of the great rock layers now exposed in the walls of Grand Canyon.

The width of the Grand Canyon, an average of about ten miles, has been brought about by the wearing and washing-in of its sides by natural processes of erosion. Rain, wind, frost, temperature changes and plant action have all combined to break down the Canyon walls. The soft rocks on the slopes are continually being broken and removed; the more resistant ones in the cliffs are undermined so in time fall down. While the river has been cutting deeper, the Canyon’s sides have been steadily receding. The Grand Canyon itself is the valley of the Colorado, and its narrowness rather than its width is the remarkable feature when compared with the valleys of other rivers. This present canyon profile has been brought about as the combined effects of an arid climate and a rapidly downward cutting river.

Even a distant view of the Colorado River in the Grand Canyon bottom is sufficient to convince one of the tremendous transporting power of this stream. Thus it not only does the work of cutting downward, but also carries off the vast load of sand and silt which is continually emptied into its waters. It has been aptly described as being “too thick to drink but too thin to plow.” In this region the river known at its headwaters as the “Silvery Colorado” bears even a higher percentage of sediment than does the muddy Mississippi-Missouri. It has been found from carefully made tests by the United States Geological Survey that the Colorado River carries past any given point in the Grand Canyon an average of nearly a million tons of sand and silt every day. Thus has the Grand Canyon been excavated!

THE FORMING OF ZION CANYON
(PLIOCENE AND PLEISTOCENE EPOCHS)

“A Yosemite Valley in colors” is a very apt description which has often been applied to Zion Canyon in southern Utah. Sheer-walled with a beautiful flat valley floor, this canyon is not unlike California’s glacier-carved fairyland in general size and shape, but in formation it has a very different history.

The brilliant Vermilion Cliffs which form the bottom two thousand feet of Zion’s walls and the contrasting White Cliffs which rise an additional thousand feet are hard, resistant sandstones. Wherever these rocks are found, they form conspicuous perpendicular cliffs because of their hardness, yet even they show the results of the constant attacks of weather and erosion over long periods. From once continuous layers, they have in many places gradually been cut and dissected by running water until now numerous canyons expose their secrets.

It was relatively late in the last chapter of the earth’s history (Cenozoic Era) that the cutting of Zion and associated canyons was made possible by gradual though tremendous crustal movements in the region. The then broad, low-lying country was raised several thousand feet to about its present altitude. This was the means of giving power to the streams, including the masterstream—the Virgin River. Steadily and relentlessly these active agents of erosion, heavy-laden with their tools, the muds, sands, and pebbles, have been cutting notches and then canyons. Zion Creek itself, which is one of the largest tributaries of the Virgin River, has cut downward through all of the layers now exposed in the walls of its canyon, and the rock fragments derived from these have been the means of grinding and gouging. As the stream has struggled in its course, these sides have slowly but surely receded through the combined efforts of rain, wind, frost and plants. They have been undermined and otherwise attacked, but as yet represent comparatively little progress in widening. Beautiful Zion Canyon, therefore, has been created as the result of crustal movements bringing into action the effective cutting power of running water, assisted by all the ever-working forces of disintegration and decay.

GLACIERS
(PLEISTOCENE EPOCH)

“What part did glaciers play in cutting the Grand Canyon?” This is a question asked almost daily on the rim of that great chasm. Everyone has heard of the mighty ice sheets which somewhere back in geologic history covered a large part of eastern and midwestern United States. Many people have seen beautiful Yosemite Valley in the far west, and have been told how it was carved by the action of glaciers. It is not altogether strange, therefore, that visitors to the Grand Canyon should associate the cutting power of ice with that tremendous gash in the earth’s surface. But geologists agree that the glaciers of the Ice Ages had no direct part in the story of Grand Canyon. No scratches or gouges made by ice are to be found on the canyon walls, no great rock piles formed at a glacier’s front are in evidence, and lastly, the very V-shape of the canyon itself is vastly different from the usual flat-bottomed valley scooped out by moving ice.

During the last epoch of geologic history, climatic conditions the world over altered very materially. Upon five different occasions snow accumulated in the north to form extensive ice sheets which advanced steadily toward the equator and then retreated with a later change in conditions. These were not the only ice ages in history, but they were of such a comparatively recent date that their influence is strongly felt today in many parts of the world. At the time of greatest expansion the glaciers reached New York in the east, Missouri in the mid west, and Washington in the far west. Contemporaneous with these main ice sheets, furthermore, were large glaciers throughout the Rocky Mountains and the Sierra Nevadas. In the mountains of Utah and even in the San Francisco Peaks, just south of the Grand Canyon, are found evidences of glaciers of this period. Evidently then, climatic conditions in the Southwest as elsewhere were greatly different from those of today. It is believed that there was much more rainfall and less evaporation, as shown by the extensive lakes which existed in this region at that time. Furthermore, the later melting of the glaciers must have supplied a vast quantity of water to the Colorado River causing it to be far larger and more powerful than today.

SAN FRANCISCO MOUNTAIN VOLCANIC FIELD
(PLIOCENE AND PLEISTOCENE EPOCHS)

Over a large part of the great plateau of northern Arizona are found sheets of hard lava and cone-shaped craters. The center of this volcanic activity is located in the San Francisco Peaks just north of the town of Flagstaff, but lavas and cones are found westward beyond Williams and to a considerable extent in every other direction. Looking south from Grand Canyon these peaks may be seen to rise high above the plateau and are a very beautiful sight. From Flagstaff and Williams not only the mountains but also great sheets of lava resting on the limestone surface are conspicuous.

It was during the last great era in geological history, and for the most part after the Colorado River had already started to cut the Grand Canyon, that molten masses broke through and flowed out on the northern Arizona plateau. Three great periods of such volcanic activity are represented by the rocks of this region and they range in age from probably at least a million to relatively recent years.

The first general period of eruption in the San Francisco Volcanic Field was characterized by a predominance of lava flows which formed a black rock known as basalt. These flows had an average thickness of about 50 feet and covered an area of 3,000 square miles. Accompanying them was the formation of about a hundred small cinder cones.

It was during the second period of volcanism that six isolated cones of large size and a somewhat greater number of small cones were formed by the eruption of lavas widely ranging in composition. San Francisco Peak, the largest of these cones and a dominant feature of the region reaches an elevation of 12,611 feet above sea level, or about 5,000 feet above the plateau surface. It is composed of five different types, of lava—mostly red or light colored—which represent a corresponding number of distinct stages in eruption. Since the termination of its building-up, the crest of this cone has been eroded and worn away to the extent of 3,000 feet as estimated from restored cross-sections. Other large volcanic craters of this period are Bill Williams (9,090 feet), Kendrick (10,418 feet), O’Leary (8,925 feet) and Sitgreaves (9,240 feet).

Two hundred small cones and about twenty cubic miles of lava were produced in this same general region during a third and relatively recent period of volcanic activity. Much of this material overlies that of the two preceding periods. Probably the most interesting feature of these cones and flows is their age, at least one cone being so recent that ash from it buried numerous pithouses built by Pueblo Indians during the eleventh century, A. D.

ELEPHANTS AND CAMELS
(PLEISTOCENE EPOCH)

It was during the fifth and last great era in the earth’s history that mammals developed and that man made his appearance on earth. In many places in the world the remains of animals that lived during various parts of this age have been preserved. In the famous asphalt pits of California literally hundreds of the bones of large mammals—tigers, mastodons, wolves and many others—have been brought to light. In the receding ice of northern Siberia, large mammoths—elephant-like animals representative of the last era, but unknown today—have come to the surface with even their skin and flesh preserved. But in the Grand Canyon region few fossils of the more recent times remain to tell the story of the life that then roamed over this surface. For long ages this region has been above the level of the sea, erosion has been continuous, so sediments have not accumulated and consequently few records of life have been made.

Recently near the western Navajo Indian agency at Tuba City, Arizona, however, the remains of several extinct animals were discovered. In a spring, hidden in a sandstone crevice, were found the tusks of a mammoth and some teeth which belonged to camels and bison. These were creatures native to this country not far back in history. They give but a very fragmentary insight into the more recent geologic history of the region, but they open up a field for interesting speculation to the imaginative person.

ADVENT OF MAN IN THE SOUTHWEST
(PLEISTOCENE HISTORIC)

After reviewing the chapters of the earth’s history and witnessing the procession and the slow but steady development of life through the ages, it is very natural that one should wonder when man came upon the scene. Compared with the hundreds of millions of years which have elapsed since the time of the first plants, or the millions of years following the first appearance of vertebrate animals, the age of man is as nothing. In the Old World there is evidence that humans existed before the last great Ice Ages, more than a million years ago, but in the Americas human occupation is measured in terms of thousands of years only.

Numerous recent discoveries in widely scattered parts of the Southwest indicate that man first occupied this region at a time when it was still inhabited by such animals as the ground sloth, the mammoth and the camel. Artifacts of stone and bone have been found associated with the remains of these animals. Early man’s camp sites are located along the margins of former extensive water bodies that existed throughout this region at a time when the climate was far more humid than now. Little is known about the nature or habits of these men, but it is supposed that they were hunters with no knowledge of agriculture.

In the Grand Canyon region, the earliest human history with a clear, detailed record goes back only to about 300 A. D. From that time up to the present, however, the story of a flourishing and rapidly changing civilization is well recorded. Although no written documents have been left, abundant reliable information is available as a result of archeological excavations. Even the dates of many important events have been accurately determined through an ingenious method of calculating years on the basis of growth rings in the trees used for house construction.

Two distinct cultures are represented in the people who have inhabited the Grand Canyon region for the past 1,600 years. The earlier and more primitive was that of a long-headed type of man known as the Basketmaker. This culture was replaced at about 700 A. D. by another, probably the result of new people entering the area, mixing with the older inhabitants and introducing new ideas. A broad-headed type of man who lived in pueblos and made pottery was the result. In the earliest stages he built only small one-roomed houses and made relatively crude pottery, but by 1,200 A. D. his architecture and crafts had developed to a very high stage as witnessed in the largest cliff-dwellings and pueblos of the region. Since then the culture has declined. The Hopi Indians of today who live near the Painted Desert Country to the east of Grand Canyon are considered to be modern representatives of this group.

In numerous localities throughout southern Utah burials of the early Farmer Basketmaker period and also pithouses of the later Potter Basketmaker period have been found. One of the latter has also been discovered near Clear Creek in Grand Canyon. The remains of cliff-dwellings and surface houses built by the later Pueblo Indians are common everywhere throughout the region and show all stages of development. Those at and in the Grand Canyon are typical of the intermediate periods and, judging from pottery fragments in them, were made by the ancestors of the modern Hopi.